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IETF RFC 3010
NFS version 4 Protocol
Last modified on Tuesday, December 5th, 2000
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Network Working Group S. Shepler
Request for Comments: 3010 B. Callaghan
Obsoletes: 1813, 1094 D. Robinson
Category: Standards Track R. Thurlow
Sun Microsystems Inc.
C. Beame
Hummingbird Ltd.
M. Eisler
Zambeel, Inc.
D. Noveck
Network Appliance, Inc.
December 2000
NFS version 4 Protocol
 Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright © The Internet Society (2000). All Rights Reserved.
Abstract
NFS (Network File System) version 4 is a distributed file system
protocol which owes heritage to NFS protocol versions 2 [RFC 1094] and
3 [RFC 1813]. Unlike earlier versions, the NFS version 4 protocol
supports traditional file access while integrating support for file
locking and the mount protocol. In addition, support for strong
security (and its negotiation), compound operations, client caching,
and internationalization have been added. Of course, attention has
been applied to making NFS version 4 operate well in an Internet
environment.
Key Words
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
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RFC 3010 NFS version 4 Protocol December 2000
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Overview of NFS Version 4 Features . . . . . . . . . . . . 6
1.1.1. RPC and Security . . . . . . . . . . . . . . . . . . . . 6
1.1.2. Procedure and Operation Structure . . . . . . . . . . . 7
1.1.3. File System Model . . . . . . . . . . . . . . . . . . . 8
1.1.3.1. Filehandle Types . . . . . . . . . . . . . . . . . . . 8
1.1.3.2. Attribute Types . . . . . . . . . . . . . . . . . . . 8
1.1.3.3. File System Replication and Migration . . . . . . . . 9
1.1.4. OPEN and CLOSE . . . . . . . . . . . . . . . . . . . . . 9
1.1.5. File locking . . . . . . . . . . . . . . . . . . . . . . 9
1.1.6. Client Caching and Delegation . . . . . . . . . . . . . 10
1.2. General Definitions . . . . . . . . . . . . . . . . . . . 11
2. Protocol Data Types . . . . . . . . . . . . . . . . . . . . 12
2.1. Basic Data Types . . . . . . . . . . . . . . . . . . . . . 12
2.2. Structured Data Types . . . . . . . . . . . . . . . . . . 14
3. RPC and Security Flavor . . . . . . . . . . . . . . . . . . 18
3.1. Ports and Transports . . . . . . . . . . . . . . . . . . . 18
3.2. Security Flavors . . . . . . . . . . . . . . . . . . . . . 18
3.2.1. Security mechanisms for NFS version 4 . . . . . . . . . 19
3.2.1.1. Kerberos V5 as security triple . . . . . . . . . . . . 19
3.2.1.2. LIPKEY as a security triple . . . . . . . . . . . . . 19
3.2.1.3. SPKM-3 as a security triple . . . . . . . . . . . . . 20
3.3. Security Negotiation . . . . . . . . . . . . . . . . . . . 21
3.3.1. Security Error . . . . . . . . . . . . . . . . . . . . . 21
3.3.2. SECINFO . . . . . . . . . . . . . . . . . . . . . . . . 21
3.4. Callback RPC Authentication . . . . . . . . . . . . . . . 22
4. Filehandles . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1. Obtaining the First Filehandle . . . . . . . . . . . . . . 24
4.1.1. Root Filehandle . . . . . . . . . . . . . . . . . . . . 24
4.1.2. Public Filehandle . . . . . . . . . . . . . . . . . . . 24
4.2. Filehandle Types . . . . . . . . . . . . . . . . . . . . . 25
4.2.1. General Properties of a Filehandle . . . . . . . . . . . 25
4.2.2. Persistent Filehandle . . . . . . . . . . . . . . . . . 26
4.2.3. Volatile Filehandle . . . . . . . . . . . . . . . . . . 26
4.2.4. One Method of Constructing a Volatile Filehandle . . . . 28
4.3. Client Recovery from Filehandle Expiration . . . . . . . . 28
5. File Attributes . . . . . . . . . . . . . . . . . . . . . . 29
5.1. Mandatory Attributes . . . . . . . . . . . . . . . . . . . 30
5.2. Recommended Attributes . . . . . . . . . . . . . . . . . . 30
5.3. Named Attributes . . . . . . . . . . . . . . . . . . . . . 31
5.4. Mandatory Attributes - Definitions . . . . . . . . . . . . 31
5.5. Recommended Attributes - Definitions . . . . . . . . . . . 33
5.6. Interpreting owner and owner_group . . . . . . . . . . . . 38
5.7. Character Case Attributes . . . . . . . . . . . . . . . . 39
5.8. Quota Attributes . . . . . . . . . . . . . . . . . . . . . 39
5.9. Access Control Lists . . . . . . . . . . . . . . . . . . . 40
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5.9.1. ACE type . . . . . . . . . . . . . . . . . . . . . . . . 41
5.9.2. ACE flag . . . . . . . . . . . . . . . . . . . . . . . . 41
5.9.3. ACE Access Mask . . . . . . . . . . . . . . . . . . . . 43
5.9.4. ACE who . . . . . . . . . . . . . . . . . . . . . . . . 44
6. File System Migration and Replication . . . . . . . . . . . 44
6.1. Replication . . . . . . . . . . . . . . . . . . . . . . . 45
6.2. Migration . . . . . . . . . . . . . . . . . . . . . . . . 45
6.3. Interpretation of the fs_locations Attribute . . . . . . . 46
6.4. Filehandle Recovery for Migration or Replication . . . . . 47
7. NFS Server Name Space . . . . . . . . . . . . . . . . . . . 47
7.1. Server Exports . . . . . . . . . . . . . . . . . . . . . . 47
7.2. Browsing Exports . . . . . . . . . . . . . . . . . . . . . 48
7.3. Server Pseudo File System . . . . . . . . . . . . . . . . 48
7.4. Multiple Roots . . . . . . . . . . . . . . . . . . . . . . 49
7.5. Filehandle Volatility . . . . . . . . . . . . . . . . . . 49
7.6. Exported Root . . . . . . . . . . . . . . . . . . . . . . 49
7.7. Mount Point Crossing . . . . . . . . . . . . . . . . . . . 49
7.8. Security Policy and Name Space Presentation . . . . . . . 50
8. File Locking and Share Reservations . . . . . . . . . . . . 50
8.1. Locking . . . . . . . . . . . . . . . . . . . . . . . . . 51
8.1.1. Client ID . . . . . . . . . . . . . . . . . . . . . . . 51
8.1.2. Server Release of Clientid . . . . . . . . . . . . . . . 53
8.1.3. nfs_lockowner and stateid Definition . . . . . . . . . . 54
8.1.4. Use of the stateid . . . . . . . . . . . . . . . . . . . 55
8.1.5. Sequencing of Lock Requests . . . . . . . . . . . . . . 56
8.1.6. Recovery from Replayed Requests . . . . . . . . . . . . 56
8.1.7. Releasing nfs_lockowner State . . . . . . . . . . . . . 57
8.2. Lock Ranges . . . . . . . . . . . . . . . . . . . . . . . 57
8.3. Blocking Locks . . . . . . . . . . . . . . . . . . . . . . 58
8.4. Lease Renewal . . . . . . . . . . . . . . . . . . . . . . 58
8.5. Crash Recovery . . . . . . . . . . . . . . . . . . . . . . 59
8.5.1. Client Failure and Recovery . . . . . . . . . . . . . . 59
8.5.2. Server Failure and Recovery . . . . . . . . . . . . . . 60
8.5.3. Network Partitions and Recovery . . . . . . . . . . . . 62
8.6. Recovery from a Lock Request Timeout or Abort . . . . . . 63
8.7. Server Revocation of Locks . . . . . . . . . . . . . . . . 63
8.8. Share Reservations . . . . . . . . . . . . . . . . . . . . 65
8.9. OPEN/CLOSE Operations . . . . . . . . . . . . . . . . . . 65
8.10. Open Upgrade and Downgrade . . . . . . . . . . . . . . . 66
8.11. Short and Long Leases . . . . . . . . . . . . . . . . . . 66
8.12. Clocks and Calculating Lease Expiration . . . . . . . . . 67
8.13. Migration, Replication and State . . . . . . . . . . . . 67
8.13.1. Migration and State . . . . . . . . . . . . . . . . . . 67
8.13.2. Replication and State . . . . . . . . . . . . . . . . . 68
8.13.3. Notification of Migrated Lease . . . . . . . . . . . . 69
9. Client-Side Caching . . . . . . . . . . . . . . . . . . . . 69
9.1. Performance Challenges for Client-Side Caching . . . . . . 70
9.2. Delegation and Callbacks . . . . . . . . . . . . . . . . . 71
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9.2.1. Delegation Recovery . . . . . . . . . . . . . . . . . . 72
9.3. Data Caching . . . . . . . . . . . . . . . . . . . . . . . 74
9.3.1. Data Caching and OPENs . . . . . . . . . . . . . . . . . 74
9.3.2. Data Caching and File Locking . . . . . . . . . . . . . 75
9.3.3. Data Caching and Mandatory File Locking . . . . . . . . 77
9.3.4. Data Caching and File Identity . . . . . . . . . . . . . 77
9.4. Open Delegation . . . . . . . . . . . . . . . . . . . . . 78
9.4.1. Open Delegation and Data Caching . . . . . . . . . . . . 80
9.4.2. Open Delegation and File Locks . . . . . . . . . . . . . 82
9.4.3. Recall of Open Delegation . . . . . . . . . . . . . . . 82
9.4.4. Delegation Revocation . . . . . . . . . . . . . . . . . 84
9.5. Data Caching and Revocation . . . . . . . . . . . . . . . 84
9.5.1. Revocation Recovery for Write Open Delegation . . . . . 85
9.6. Attribute Caching . . . . . . . . . . . . . . . . . . . . 85
9.7. Name Caching . . . . . . . . . . . . . . . . . . . . . . . 86
9.8. Directory Caching . . . . . . . . . . . . . . . . . . . . 87
10. Minor Versioning . . . . . . . . . . . . . . . . . . . . . 88
11. Internationalization . . . . . . . . . . . . . . . . . . . 91
11.1. Universal Versus Local Character Sets . . . . . . . . . . 91
11.2. Overview of Universal Character Set Standards . . . . . . 92
11.3. Difficulties with UCS-4, UCS-2, Unicode . . . . . . . . . 93
11.4. UTF-8 and its solutions . . . . . . . . . . . . . . . . . 94
11.5. Normalization . . . . . . . . . . . . . . . . . . . . . . 94
12. Error Definitions . . . . . . . . . . . . . . . . . . . . . 95
13. NFS Version 4 Requests . . . . . . . . . . . . . . . . . . 99
13.1. Compound Procedure . . . . . . . . . . . . . . . . . . . 100
13.2. Evaluation of a Compound Request . . . . . . . . . . . . 100
13.3. Synchronous Modifying Operations . . . . . . . . . . . . 101
13.4. Operation Values . . . . . . . . . . . . . . . . . . . . 102
14. NFS Version 4 Procedures . . . . . . . . . . . . . . . . . 102
14.1. Procedure 0: NULL - No Operation . . . . . . . . . . . . 102
14.2. Procedure 1: COMPOUND - Compound Operations . . . . . . . 102
14.2.1. Operation 3: ACCESS - Check Access Rights . . . . . . . 105
14.2.2. Operation 4: CLOSE - Close File . . . . . . . . . . . . 108
14.2.3. Operation 5: COMMIT - Commit Cached Data . . . . . . . 109
14.2.4. Operation 6: CREATE - Create a Non-Regular File Object. 112
14.2.5. Operation 7: DELEGPURGE - Purge Delegations Awaiting
Recovery . . . . . . . . . . . . . . . . . . . . . . . 114
14.2.6. Operation 8: DELEGRETURN - Return Delegation . . . . . 115
14.2.7. Operation 9: GETATTR - Get Attributes . . . . . . . . . 115
14.2.8. Operation 10: GETFH - Get Current Filehandle . . . . . 117
14.2.9. Operation 11: LINK - Create Link to a File . . . . . . 118
14.2.10. Operation 12: LOCK - Create Lock . . . . . . . . . . . 119
14.2.11. Operation 13: LOCKT - Test For Lock . . . . . . . . . 121
14.2.12. Operation 14: LOCKU - Unlock File . . . . . . . . . . 122
14.2.13. Operation 15: LOOKUP - Lookup Filename . . . . . . . . 123
14.2.14. Operation 16: LOOKUPP - Lookup Parent Directory . . . 126
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RFC 3010 NFS version 4 Protocol December 2000
14.2.15. Operation 17: NVERIFY - Verify Difference in
Attributes . . . . . . . . . . . . . . . . . . . . . . 127
14.2.16. Operation 18: OPEN - Open a Regular File . . . . . . . 128
14.2.17. Operation 19: OPENATTR - Open Named Attribute
Directory . . . . . . . . . . . . . . . . . . . . . . 137
14.2.18. Operation 20: OPEN_CONFIRM - Confirm Open . . . . . . 138
14.2.19. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access 140
14.2.20. Operation 22: PUTFH - Set Current Filehandle . . . . . 141
14.2.21. Operation 23: PUTPUBFH - Set Public Filehandle . . . . 142
14.2.22. Operation 24: PUTROOTFH - Set Root Filehandle . . . . 143
14.2.23. Operation 25: READ - Read from File . . . . . . . . . 144
14.2.24. Operation 26: READDIR - Read Directory . . . . . . . . 146
14.2.25. Operation 27: READLINK - Read Symbolic Link . . . . . 150
14.2.26. Operation 28: REMOVE - Remove Filesystem Object . . . 151
14.2.27. Operation 29: RENAME - Rename Directory Entry . . . . 153
14.2.28. Operation 30: RENEW - Renew a Lease . . . . . . . . . 155
14.2.29. Operation 31: RESTOREFH - Restore Saved Filehandle . . 156
14.2.30. Operation 32: SAVEFH - Save Current Filehandle . . . . 157
14.2.31. Operation 33: SECINFO - Obtain Available Security . . 158
14.2.32. Operation 34: SETATTR - Set Attributes . . . . . . . . 160
14.2.33. Operation 35: SETCLIENTID - Negotiate Clientid . . . . 162
14.2.34. Operation 36: SETCLIENTID_CONFIRM - Confirm Clientid . 163
14.2.35. Operation 37: VERIFY - Verify Same Attributes . . . . 164
14.2.36. Operation 38: WRITE - Write to File . . . . . . . . . 166
15. NFS Version 4 Callback Procedures . . . . . . . . . . . . . 170
15.1. Procedure 0: CB_NULL - No Operation . . . . . . . . . . . 170
15.2. Procedure 1: CB_COMPOUND - Compound Operations . . . . . 171
15.2.1. Operation 3: CB_GETATTR - Get Attributes . . . . . . . 172
15.2.2. Operation 4: CB_RECALL - Recall an Open Delegation . . 173
16. Security Considerations . . . . . . . . . . . . . . . . . . 174
17. IANA Considerations . . . . . . . . . . . . . . . . . . . . 174
17.1. Named Attribute Definition . . . . . . . . . . . . . . . 174
18. RPC definition file . . . . . . . . . . . . . . . . . . . . 175
19. Bibliography . . . . . . . . . . . . . . . . . . . . . . . 206
20. Authors . . . . . . . . . . . . . . . . . . . . . . . . . . 210
20.1. Editor's Address . . . . . . . . . . . . . . . . . . . . 210
20.2. Authors' Addresses . . . . . . . . . . . . . . . . . . . 210
20.3. Acknowledgements . . . . . . . . . . . . . . . . . . . . 211
21. Full Copyright Statement . . . . . . . . . . . . . . . . . 212
1. Introduction
The NFS version 4 protocol is a further revision of the NFS protocol
defined already by versions 2 [RFC 1094] and 3 [RFC 1813]. It retains
the essential characteristics of previous versions: design for easy
recovery, independent of transport protocols, operating systems and
filesystems, simplicity, and good performance. The NFS version 4
revision has the following goals:
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RFC 3010 NFS version 4 Protocol December 2000
o Improved access and good performance on the Internet.
The protocol is designed to transit firewalls easily, perform well
where latency is high and bandwidth is low, and scale to very
large numbers of clients per server.
o Strong security with negotiation built into the protocol.
The protocol builds on the work of the ONCRPC working group in
supporting the RPCSEC_GSS protocol. Additionally, the NFS version
4 protocol provides a mechanism to allow clients and servers the
ability to negotiate security and require clients and servers to
support a minimal set of security schemes.
o Good cross-platform interoperability.
The protocol features a file system model that provides a useful,
common set of features that does not unduly favor one file system
or operating system over another.
o Designed for protocol extensions.
The protocol is designed to accept standard extensions that do not
compromise backward compatibility.
1.1. Overview of NFS Version 4 Features
To provide a reasonable context for the reader, the major features of
NFS version 4 protocol will be reviewed in brief. This will be done
to provide an appropriate context for both the reader who is familiar
with the previous versions of the NFS protocol and the reader that is
new to the NFS protocols. For the reader new to the NFS protocols,
there is still a fundamental knowledge that is expected. The reader
should be familiar with the XDR and RPC protocols as described in
[RFC 1831] and [RFC 1832]. A basic knowledge of file systems and
distributed file systems is expected as well.
1.1.1. RPC and Security
As with previous versions of NFS, the External Data Representation
(XDR) and Remote Procedure Call (RPC) mechanisms used for the NFS
version 4 protocol are those defined in [RFC 1831] and [RFC 1832]. To
meet end to end security requirements, the RPCSEC_GSS framework
[RFC 2203] will be used to extend the basic RPC security. With the
use of RPCSEC_GSS, various mechanisms can be provided to offer
authentication, integrity, and privacy to the NFS version 4 protocol.
Kerberos V5 will be used as described in [RFC 1964] to provide one
security framework. The LIPKEY GSS-API mechanism described in
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RFC 3010 NFS version 4 Protocol December 2000
[RFC 2847] will be used to provide for the use of user password and
server public key by the NFS version 4 protocol. With the use of
RPCSEC_GSS, other mechanisms may also be specified and used for NFS
version 4 security.
To enable in-band security negotiation, the NFS version 4 protocol
has added a new operation which provides the client a method of
querying the server about its policies regarding which security
mechanisms must be used for access to the server's file system
resources. With this, the client can securely match the security
mechanism that meets the policies specified at both the client and
server.
1.1.2. Procedure and Operation Structure
A significant departure from the previous versions of the NFS
protocol is the introduction of the COMPOUND procedure. For the NFS
version 4 protocol, there are two RPC procedures, NULL and COMPOUND.
The COMPOUND procedure is defined in terms of operations and these
operations correspond more closely to the traditional NFS procedures.
With the use of the COMPOUND procedure, the client is able to build
simple or complex requests. These COMPOUND requests allow for a
reduction in the number of RPCs needed for logical file system
operations. For example, without previous contact with a server a
client will be able to read data from a file in one request by
combining LOOKUP, OPEN, and READ operations in a single COMPOUND RPC.
With previous versions of the NFS protocol, this type of single
request was not possible.
The model used for COMPOUND is very simple. There is no logical OR
or ANDing of operations. The operations combined within a COMPOUND
request are evaluated in order by the server. Once an operation
returns a failing result, the evaluation ends and the results of all
evaluated operations are returned to the client.
The NFS version 4 protocol continues to have the client refer to a
file or directory at the server by a "filehandle". The COMPOUND
procedure has a method of passing a filehandle from one operation to
another within the sequence of operations. There is a concept of a
"current filehandle" and "saved filehandle". Most operations use the
"current filehandle" as the file system object to operate upon. The
"saved filehandle" is used as temporary filehandle storage within a
COMPOUND procedure as well as an additional operand for certain
operations.
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RFC 3010 NFS version 4 Protocol December 2000
1.1.3. File System Model
The general file system model used for the NFS version 4 protocol is
the same as previous versions. The server file system is
hierarchical with the regular files contained within being treated as
opaque byte streams. In a slight departure, file and directory names
are encoded with UTF-8 to deal with the basics of
internationalization.
The NFS version 4 protocol does not require a separate protocol to
provide for the initial mapping between path name and filehandle.
Instead of using the older MOUNT protocol for this mapping, the
server provides a ROOT filehandle that represents the logical root or
top of the file system tree provided by the server. The server
provides multiple file systems by gluing them together with pseudo
file systems. These pseudo file systems provide for potential gaps
in the path names between real file systems.
1.1.3.1. Filehandle Types
In previous versions of the NFS protocol, the filehandle provided by
the server was guaranteed to be valid or persistent for the lifetime
of the file system object to which it referred. For some server
implementations, this persistence requirement has been difficult to
meet. For the NFS version 4 protocol, this requirement has been
relaxed by introducing another type of filehandle, volatile. With
persistent and volatile filehandle types, the server implementation
can match the abilities of the file system at the server along with
the operating environment. The client will have knowledge of the
type of filehandle being provided by the server and can be prepared
to deal with the semantics of each.
1.1.3.2. Attribute Types
The NFS version 4 protocol introduces three classes of file system or
file attributes. Like the additional filehandle type, the
classification of file attributes has been done to ease server
implementations along with extending the overall functionality of the
NFS protocol. This attribute model is structured to be extensible
such that new attributes can be introduced in minor revisions of the
protocol without requiring significant rework.
The three classifications are: mandatory, recommended and named
attributes. This is a significant departure from the previous
attribute model used in the NFS protocol. Previously, the attributes
for the file system and file objects were a fixed set of mainly Unix
attributes. If the server or client did not support a particular
attribute, it would have to simulate the attribute the best it could.
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Mandatory attributes are the minimal set of file or file system
attributes that must be provided by the server and must be properly
represented by the server. Recommended attributes represent
different file system types and operating environments. The
recommended attributes will allow for better interoperability and the
inclusion of more operating environments. The mandatory and
recommended attribute sets are traditional file or file system
attributes. The third type of attribute is the named attribute. A
named attribute is an opaque byte stream that is associated with a
directory or file and referred to by a string name. Named attributes
are meant to be used by client applications as a method to associate
application specific data with a regular file or directory.
One significant addition to the recommended set of file attributes is
the Access Control List (ACL) attribute. This attribute provides for
directory and file access control beyond the model used in previous
versions of the NFS protocol. The ACL definition allows for
specification of user and group level access control.
1.1.3.3. File System Replication and Migration
With the use of a special file attribute, the ability to migrate or
replicate server file systems is enabled within the protocol. The
file system locations attribute provides a method for the client to
probe the server about the location of a file system. In the event
of a migration of a file system, the client will receive an error
when operating on the file system and it can then query as to the new
file system location. Similar steps are used for replication, the
client is able to query the server for the multiple available
locations of a particular file system. From this information, the
client can use its own policies to access the appropriate file system
location.
1.1.4. OPEN and CLOSE
The NFS version 4 protocol introduces OPEN and CLOSE operations. The
OPEN operation provides a single point where file lookup, creation,
and share semantics can be combined. The CLOSE operation also
provides for the release of state accumulated by OPEN.
1.1.5. File locking
With the NFS version 4 protocol, the support for byte range file
locking is part of the NFS protocol. The file locking support is
structured so that an RPC callback mechanism is not required. This
is a departure from the previous versions of the NFS file locking
protocol, Network Lock Manager (NLM). The state associated with file
locks is maintained at the server under a lease-based model. The
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RFC 3010 NFS version 4 Protocol December 2000
server defines a single lease period for all state held by a NFS
client. If the client does not renew its lease within the defined
period, all state associated with the client's lease may be released
by the server. The client may renew its lease with use of the RENEW
operation or implicitly by use of other operations (primarily READ).
1.1.6. Client Caching and Delegation
The file, attribute, and directory caching for the NFS version 4
protocol is similar to previous versions. Attributes and directory
information are cached for a duration determined by the client. At
the end of a predefined timeout, the client will query the server to
see if the related file system object has been updated.
For file data, the client checks its cache validity when the file is
opened. A query is sent to the server to determine if the file has
been changed. Based on this information, the client determines if
the data cache for the file should kept or released. Also, when the
file is closed, any modified data is written to the server.
If an application wants to serialize access to file data, file
locking of the file data ranges in question should be used.
The major addition to NFS version 4 in the area of caching is the
ability of the server to delegate certain responsibilities to the
client. When the server grants a delegation for a file to a client,
the client is guaranteed certain semantics with respect to the
sharing of that file with other clients. At OPEN, the server may
provide the client either a read or write delegation for the file.
If the client is granted a read delegation, it is assured that no
other client has the ability to write to the file for the duration of
the delegation. If the client is granted a write delegation, the
client is assured that no other client has read or write access to
the file.
Delegations can be recalled by the server. If another client
requests access to the file in such a way that the access conflicts
with the granted delegation, the server is able to notify the initial
client and recall the delegation. This requires that a callback path
exist between the server and client. If this callback path does not
exist, then delegations can not be granted. The essence of a
delegation is that it allows the client to locally service operations
such as OPEN, CLOSE, LOCK, LOCKU, READ, WRITE without immediate
interaction with the server.
Shepler, et al. Standards Track PAGE 10
RFC 3010 NFS version 4 Protocol December 2000
1.2. General Definitions
The following definitions are provided for the purpose of providing
an appropriate context for the reader.
Client The "client" is the entity that accesses the NFS server's
resources. The client may be an application which contains
the logic to access the NFS server directly. The client
may also be the traditional operating system client remote
file system services for a set of applications.
In the case of file locking the client is the entity that
maintains a set of locks on behalf of one or more
applications. This client is responsible for crash or
failure recovery for those locks it manages.
Note that multiple clients may share the same transport and
multiple clients may exist on the same network node.
Clientid A 64-bit quantity used as a unique, short-hand reference to
a client supplied Verifier and ID. The server is
responsible for supplying the Clientid.
Lease An interval of time defined by the server for which the
client is irrevocably granted a lock. At the end of a
lease period the lock may be revoked if the lease has not
been extended. The lock must be revoked if a conflicting
lock has been granted after the lease interval.
All leases granted by a server have the same fixed
interval. Note that the fixed interval was chosen to
alleviate the expense a server would have in maintaining
state about variable length leases across server failures.
Lock The term "lock" is used to refer to both record (byte-
range) locks as well as file (share) locks unless
specifically stated otherwise.
Server The "Server" is the entity responsible for coordinating
client access to a set of file systems.
Stable Storage
NFS version 4 servers must be able to recover without data
loss from multiple power failures (including cascading
power failures, that is, several power failures in quick
succession), operating system failures, and hardware
failure of components other than the storage medium itself
(for example, disk, nonvolatile RAM).
Shepler, et al. Standards Track PAGE 11
RFC 3010 NFS version 4 Protocol December 2000
Some examples of stable storage that are allowable for an
NFS server include:
1. Media commit of data, that is, the modified data has
been successfully written to the disk media, for
example, the disk platter.
2. An immediate reply disk drive with battery-backed on-
drive intermediate storage or uninterruptible power
system (UPS).
3. Server commit of data with battery-backed intermediate
storage and recovery software.
4. Cache commit with uninterruptible power system (UPS) and
recovery software.
Stateid A 64-bit quantity returned by a server that uniquely
defines the locking state granted by the server for a
specific lock owner for a specific file.
Stateids composed of all bits 0 or all bits 1 have special
meaning and are reserved values.
Verifier A 64-bit quantity generated by the client that the server
can use to determine if the client has restarted and lost
all previous lock state.
2. Protocol Data Types
The syntax and semantics to describe the data types of the NFS
version 4 protocol are defined in the XDR [RFC 1832] and RPC [RFC 1831]
documents. The next sections build upon the XDR data types to define
types and structures specific to this protocol.
2.1. Basic Data Types
Data Type Definition
_____________________________________________________________________
int32_t typedef int int32_t;
uint32_t typedef unsigned int uint32_t;
int64_t typedef hyper int64_t;
uint64_t typedef unsigned hyper uint64_t;
Shepler, et al. Standards Track PAGE 12
RFC 3010 NFS version 4 Protocol December 2000
attrlist4 typedef opaque attrlist4<>;
Used for file/directory attributes
bitmap4 typedef uint32_t bitmap4<>;
Used in attribute array encoding.
changeid4 typedef uint64_t changeid4;
Used in definition of change_info
clientid4 typedef uint64_t clientid4;
Shorthand reference to client identification
component4 typedef utf8string component4;
Represents path name components
count4 typedef uint32_t count4;
Various count parameters (READ, WRITE, COMMIT)
length4 typedef uint64_t length4;
Describes LOCK lengths
linktext4 typedef utf8string linktext4;
Symbolic link contents
mode4 typedef uint32_t mode4;
Mode attribute data type
nfs_cookie4 typedef uint64_t nfs_cookie4;
Opaque cookie value for READDIR
nfs_fh4 typedef opaque nfs_fh4<NFS4_FHSIZE>;
Filehandle definition; NFS4_FHSIZE is defined as 128
nfs_ftype4 enum nfs_ftype4;
Various defined file types
nfsstat4 enum nfsstat4;
Return value for operations
offset4 typedef uint64_t offset4;
Various offset designations (READ, WRITE, LOCK, COMMIT)
pathname4 typedef component4 pathname4<>;
Represents path name for LOOKUP, OPEN and others
qop4 typedef uint32_t qop4;
Quality of protection designation in SECINFO
Shepler, et al. Standards Track PAGE 13
RFC 3010 NFS version 4 Protocol December 2000
sec_oid4 typedef opaque sec_oid4<>;
Security Object Identifier
The sec_oid4 data type is not really opaque.
Instead contains an ASN.1 OBJECT IDENTIFIER as used
by GSS-API in the mech_type argument to
GSS_Init_sec_context. See [RFC 2078] for details.
seqid4 typedef uint32_t seqid4;
Sequence identifier used for file locking
stateid4 typedef uint64_t stateid4;
State identifier used for file locking and delegation
utf8string typedef opaque utf8string<>;
UTF-8 encoding for strings
verifier4 typedef opaque verifier4[NFS4_VERIFIER_SIZE];
Verifier used for various operations (COMMIT, CREATE,
OPEN, READDIR, SETCLIENTID, WRITE)
NFS4_VERIFIER_SIZE is defined as 8
2.2. Structured Data Types
nfstime4
struct nfstime4 {
int64_t seconds;
uint32_t nseconds;
}
The nfstime4 structure gives the number of seconds and nanoseconds
since midnight or 0 hour January 1, 1970 Coordinated Universal
Time (UTC). Values greater than zero for the seconds field denote
dates after the 0 hour January 1, 1970. Values less than zero for
the seconds field denote dates before the 0 hour January 1, 1970.
In both cases, the nseconds field is to be added to the seconds
field for the final time representation. For example, if the time
to be represented is one-half second before 0 hour January 1,
1970, the seconds field would have a value of negative one (-1)
and the nseconds fields would have a value of one-half second
(500000000). Values greater than 999,999,999 for nseconds are
considered invalid.
This data type is used to pass time and date information. A
server converts to and from its local representation of time when
processing time values, preserving as much accuracy as possible.
If the precision of timestamps stored for a file system object is
Shepler, et al. Standards Track PAGE 14
RFC 3010 NFS version 4 Protocol December 2000
less than defined, loss of precision can occur. An adjunct time
maintenance protocol is recommended to reduce client and server
time skew.
time_how4
enum time_how4 {
SET_TO_SERVER_TIME4 = 0,
SET_TO_CLIENT_TIME4 = 1
};
settime4
union settime4 switch (time_how4 set_it) {
case SET_TO_CLIENT_TIME4:
nfstime4 time;
default:
void;
};
The above definitions are used as the attribute definitions to
set time values. If set_it is SET_TO_SERVER_TIME4, then the
server uses its local representation of time for the time value.
specdata4
struct specdata4 {
uint32_t specdata1;
uint32_t specdata2;
};
This data type represents additional information for the device
file types NF4CHR and NF4BLK.
fsid4
struct fsid4 {
uint64_t major;
uint64_t minor;
};
This type is the file system identifier that is used as a
mandatory attribute.
Shepler, et al. Standards Track PAGE 15
RFC 3010 NFS version 4 Protocol December 2000
fs_location4
struct fs_location4 {
utf8string server<>;
pathname4 rootpath;
};
fs_locations4
struct fs_locations4 {
pathname4 fs_root;
fs_location4 locations<>;
};
The fs_location4 and fs_locations4 data types are used for the
fs_locations recommended attribute which is used for migration
and replication support.
fattr4
struct fattr4 {
bitmap4 attrmask;
attrlist4 attr_vals;
};
The fattr4 structure is used to represent file and directory
attributes.
The bitmap is a counted array of 32 bit integers used to contain
bit values. The position of the integer in the array that
contains bit n can be computed from the expression (n / 32) and
its bit within that integer is (n mod 32).
0 1
+-----------+-----------+-----------+--
| count | 31 .. 0 | 63 .. 32 |
+-----------+-----------+-----------+--
change_info4
struct change_info4 {
bool atomic;
changeid4 before;
changeid4 after;
};
Shepler, et al. Standards Track PAGE 16
RFC 3010 NFS version 4 Protocol December 2000
This structure is used with the CREATE, LINK, REMOVE, RENAME
operations to let the client the know value of the change
attribute for the directory in which the target file system
object resides.
clientaddr4
struct clientaddr4 {
/* see struct rpcb in RFC 1833 */
string r_netid<>; /* network id */
string r_addr<>; /* universal address */
};
The clientaddr4 structure is used as part of the SETCLIENT
operation to either specify the address of the client that is
using a clientid or as part of the call back registration.
cb_client4
struct cb_client4 {
unsigned int cb_program;
clientaddr4 cb_location;
};
This structure is used by the client to inform the server of its
call back address; includes the program number and client
address.
nfs_client_id4
struct nfs_client_id4 {
verifier4 verifier;
opaque id<>;
};
This structure is part of the arguments to the SETCLIENTID
operation.
nfs_lockowner4
struct nfs_lockowner4 {
clientid4 clientid;
opaque owner<>;
};
Shepler, et al. Standards Track PAGE 17
RFC 3010 NFS version 4 Protocol December 2000
This structure is used to identify the owner of a OPEN share or
file lock.
3. RPC and Security Flavor
The NFS version 4 protocol is a Remote Procedure Call (RPC)
application that uses RPC version 2 and the corresponding eXternal
Data Representation (XDR) as defined in [RFC 1831] and [RFC 1832]. The
RPCSEC_GSS security flavor as defined in [RFC 2203] MUST be used as
the mechanism to deliver stronger security for the NFS version 4
protocol.
3.1. Ports and Transports
Historically, NFS version 2 and version 3 servers have resided on
port 2049. The registered port 2049 [RFC 1700] for the NFS protocol
should be the default configuration. Using the registered port for
NFS services means the NFS client will not need to use the RPC
binding protocols as described in [RFC 1833]; this will allow NFS to
transit firewalls.
The transport used by the RPC service for the NFS version 4 protocol
MUST provide congestion control comparable to that defined for TCP in
[RFC 2581]. If the operating environment implements TCP, the NFS
version 4 protocol SHOULD be supported over TCP. The NFS client and
server may use other transports if they support congestion control as
defined above and in those cases a mechanism may be provided to
override TCP usage in favor of another transport.
If TCP is used as the transport, the client and server SHOULD use
persistent connections. This will prevent the weakening of TCP's
congestion control via short lived connections and will improve
performance for the WAN environment by eliminating the need for SYN
handshakes.
Note that for various timers, the client and server should avoid
inadvertent synchronization of those timers. For further discussion
of the general issue refer to [Floyd].
3.2. Security Flavors
Traditional RPC implementations have included AUTH_NONE, AUTH_SYS,
AUTH_DH, and AUTH_KRB4 as security flavors. With [RFC 2203] an
additional security flavor of RPCSEC_GSS has been introduced which
uses the functionality of GSS-API [RFC 2078]. This allows for the use
of varying security mechanisms by the RPC layer without the
additional implementation overhead of adding RPC security flavors.
For NFS version 4, the RPCSEC_GSS security flavor MUST be used to
Shepler, et al. Standards Track PAGE 18
RFC 3010 NFS version 4 Protocol December 2000
enable the mandatory security mechanism. Other flavors, such as,
AUTH_NONE, AUTH_SYS, and AUTH_DH MAY be implemented as well.
3.2.1. Security mechanisms for NFS version 4
The use of RPCSEC_GSS requires selection of: mechanism, quality of
protection, and service (authentication, integrity, privacy). The
remainder of this document will refer to these three parameters of
the RPCSEC_GSS security as the security triple.
3.2.1.1. Kerberos V5 as security triple
The Kerberos V5 GSS-API mechanism as described in [RFC 1964] MUST be
implemented and provide the following security triples.
column descriptions:
1 == number of pseudo flavor
2 == name of pseudo flavor
3 == mechanism's OID
4 == mechanism's algorithm(s)
5 == RPCSEC_GSS service
1 2 3 4 5
-----------------------------------------------------------------------
390003 krb5 1.2.840.113554.1.2.2 DES MAC MD5 rpc_gss_svc_none
390004 krb5i 1.2.840.113554.1.2.2 DES MAC MD5 rpc_gss_svc_integrity
390005 krb5p 1.2.840.113554.1.2.2 DES MAC MD5 rpc_gss_svc_privacy
for integrity,
and 56 bit DES
for privacy.
Note that the pseudo flavor is presented here as a mapping aid to the
implementor. Because this NFS protocol includes a method to
negotiate security and it understands the GSS-API mechanism, the
pseudo flavor is not needed. The pseudo flavor is needed for NFS
version 3 since the security negotiation is done via the MOUNT
protocol.
For a discussion of NFS' use of RPCSEC_GSS and Kerberos V5, please
see [RFC 2623].
3.2.1.2. LIPKEY as a security triple
The LIPKEY GSS-API mechanism as described in [RFC 2847] MUST be
implemented and provide the following security triples. The
definition of the columns matches the previous subsection "Kerberos
V5 as security triple"
Shepler, et al. Standards Track PAGE 19
RFC 3010 NFS version 4 Protocol December 2000
1 2 3 4 5
-----------------------------------------------------------------------
390006 lipkey 1.3.6.1.5.5.9 negotiated rpc_gss_svc_none
390007 lipkey-i 1.3.6.1.5.5.9 negotiated rpc_gss_svc_integrity
390008 lipkey-p 1.3.6.1.5.5.9 negotiated rpc_gss_svc_privacy
The mechanism algorithm is listed as "negotiated". This is because
LIPKEY is layered on SPKM-3 and in SPKM-3 [RFC 2847] the
confidentiality and integrity algorithms are negotiated. Since
SPKM-3 specifies HMAC-MD5 for integrity as MANDATORY, 128 bit
cast5CBC for confidentiality for privacy as MANDATORY, and further
specifies that HMAC-MD5 and cast5CBC MUST be listed first before
weaker algorithms, specifying "negotiated" in column 4 does not
impair interoperability. In the event an SPKM-3 peer does not
support the mandatory algorithms, the other peer is free to accept or
reject the GSS-API context creation.
Because SPKM-3 negotiates the algorithms, subsequent calls to
LIPKEY's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality
of protection value of 0 (zero). See section 5.2 of [RFC 2025] for an
explanation.
LIPKEY uses SPKM-3 to create a secure channel in which to pass a user
name and password from the client to the user. Once the user name
and password have been accepted by the server, calls to the LIPKEY
context are redirected to the SPKM-3 context. See [RFC 2847] for more
details.
3.2.1.3. SPKM-3 as a security triple
The SPKM-3 GSS-API mechanism as described in [RFC 2847] MUST be
implemented and provide the following security triples. The
definition of the columns matches the previous subsection "Kerberos
V5 as security triple".
1 2 3 4 5
-----------------------------------------------------------------------
390009 spkm3 1.3.6.1.5.5.1.3 negotiated rpc_gss_svc_none
390010 spkm3i 1.3.6.1.5.5.1.3 negotiated rpc_gss_svc_integrity
390011 spkm3p 1.3.6.1.5.5.1.3 negotiated rpc_gss_svc_privacy
For a discussion as to why the mechanism algorithm is listed as
"negotiated", see the previous section "LIPKEY as a security triple."
Because SPKM-3 negotiates the algorithms, subsequent calls to SPKM-
3's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality of
protection value of 0 (zero). See section 5.2 of [RFC 2025] for an
explanation.
Shepler, et al. Standards Track PAGE 20
RFC 3010 NFS version 4 Protocol December 2000
Even though LIPKEY is layered over SPKM-3, SPKM-3 is specified as a
mandatory set of triples to handle the situations where the initiator
(the client) is anonymous or where the initiator has its own
certificate. If the initiator is anonymous, there will not be a user
name and password to send to the target (the server). If the
initiator has its own certificate, then using passwords is
superfluous.
3.3. Security Negotiation
With the NFS version 4 server potentially offering multiple security
mechanisms, the client needs a method to determine or negotiate which
mechanism is to be used for its communication with the server. The
NFS server may have multiple points within its file system name space
that are available for use by NFS clients. In turn the NFS server
may be configured such that each of these entry points may have
different or multiple security mechanisms in use.
The security negotiation between client and server must be done with
a secure channel to eliminate the possibility of a third party
intercepting the negotiation sequence and forcing the client and
server to choose a lower level of security than required or desired.
3.3.1. Security Error
Based on the assumption that each NFS version 4 client and server
must support a minimum set of security (i.e. LIPKEY, SPKM-3, and
Kerberos-V5 all under RPCSEC_GSS), the NFS client will start its
communication with the server with one of the minimal security
triples. During communication with the server, the client may
receive an NFS error of NFS4ERR_WRONGSEC. This error allows the
server to notify the client that the security triple currently being
used is not appropriate for access to the server's file system
resources. The client is then responsible for determining what
security triples are available at the server and choose one which is
appropriate for the client.
3.3.2. SECINFO
The new SECINFO operation will allow the client to determine, on a
per filehandle basis, what security triple is to be used for server
access. In general, the client will not have to use the SECINFO
procedure except during initial communication with the server or when
the client crosses policy boundaries at the server. It is possible
that the server's policies change during the client's interaction
therefore forcing the client to negotiate a new security triple.
Shepler, et al. Standards Track PAGE 21
RFC 3010 NFS version 4 Protocol December 2000
3.4. Callback RPC Authentication
The callback RPC (described later) must mutually authenticate the NFS
server to the principal that acquired the clientid (also described
later), using the same security flavor the original SETCLIENTID
operation used. Because LIPKEY is layered over SPKM-3, it is
permissible for the server to use SPKM-3 and not LIPKEY for the
callback even if the client used LIPKEY for SETCLIENTID.
For AUTH_NONE, there are no principals, so this is a non-issue.
For AUTH_SYS, the server simply uses the AUTH_SYS credential that the
user used when it set up the delegation.
For AUTH_DH, one commonly used convention is that the server uses the
credential corresponding to this AUTH_DH principal:
unix.host@domain
where host and domain are variables corresponding to the name of
server host and directory services domain in which it lives such as a
Network Information System domain or a DNS domain.
Regardless of what security mechanism under RPCSEC_GSS is being used,
the NFS server, MUST identify itself in GSS-API via a
GSS_C_NT_HOSTBASED_SERVICE name type. GSS_C_NT_HOSTBASED_SERVICE
names are of the form:
service@hostname
For NFS, the "service" element is
nfs
Implementations of security mechanisms will convert nfs@hostname to
various different forms. For Kerberos V5 and LIPKEY, the following
form is RECOMMENDED:
nfs/hostname
For Kerberos V5, nfs/hostname would be a server principal in the
Kerberos Key Distribution Center database. For LIPKEY, this would be
the username passed to the target (the NFS version 4 client that
receives the callback).
It should be noted that LIPKEY may not work for callbacks, since the
LIPKEY client uses a user id/password. If the NFS client receiving
the callback can authenticate the NFS server's user name/password
Shepler, et al. Standards Track PAGE 22
RFC 3010 NFS version 4 Protocol December 2000
pair, and if the user that the NFS server is authenticating to has a
public key certificate, then it works.
In situations where NFS client uses LIPKEY and uses a per-host
principal for the SETCLIENTID operation, instead of using LIPKEY for
SETCLIENTID, it is RECOMMENDED that SPKM-3 with mutual authentication
be used. This effectively means that the client will use a
certificate to authenticate and identify the initiator to the target
on the NFS server. Using SPKM-3 and not LIPKEY has the following
advantages:
o When the server does a callback, it must authenticate to the
principal used in the SETCLIENTID. Even if LIPKEY is used,
because LIPKEY is layered over SPKM-3, the NFS client will need to
have a certificate that corresponds to the principal used in the
SETCLIENTID operation. From an administrative perspective, having
a user name, password, and certificate for both the client and
server is redundant.
o LIPKEY was intended to minimize additional infrastructure
requirements beyond a certificate for the target, and the
expectation is that existing password infrastructure can be
leveraged for the initiator. In some environments, a per-host
password does not exist yet. If certificates are used for any
per-host principals, then additional password infrastructure is
not needed.
o In cases when a host is both an NFS client and server, it can
share the same per-host certificate.
4. Filehandles
The filehandle in the NFS protocol is a per server unique identifier
for a file system object. The contents of the filehandle are opaque
to the client. Therefore, the server is responsible for translating
the filehandle to an internal representation of the file system
object. Since the filehandle is the client's reference to an object
and the client may cache this reference, the server SHOULD not reuse
a filehandle for another file system object. If the server needs to
reuse a filehandle value, the time elapsed before reuse SHOULD be
large enough such that it is unlikely the client has a cached copy of
the reused filehandle value. Note that a client may cache a
filehandle for a very long time. For example, a client may cache NFS
data to local storage as a method to expand its effective cache size
and as a means to survive client restarts. Therefore, the lifetime
of a cached filehandle may be extended.
Shepler, et al. Standards Track PAGE 23
RFC 3010 NFS version 4 Protocol December 2000
4.1. Obtaining the First Filehandle
The operations of the NFS protocol are defined in terms of one or
more filehandles. Therefore, the client needs a filehandle to
initiate communication with the server. With the NFS version 2
protocol [RFC 1094] and the NFS version 3 protocol [RFC 1813], there
exists an ancillary protocol to obtain this first filehandle. The
MOUNT protocol, RPC program number 100005, provides the mechanism of
translating a string based file system path name to a filehandle
which can then be used by the NFS protocols.
The MOUNT protocol has deficiencies in the area of security and use
via firewalls. This is one reason that the use of the public
filehandle was introduced in [RFC 2054] and [RFC 2055]. With the use
of the public filehandle in combination with the LOOKUP procedure in
the NFS version 2 and 3 protocols, it has been demonstrated that the
MOUNT protocol is unnecessary for viable interaction between NFS
client and server.
Therefore, the NFS version 4 protocol will not use an ancillary
protocol for translation from string based path names to a
filehandle. Two special filehandles will be used as starting points
for the NFS client.
4.1.1. Root Filehandle
The first of the special filehandles is the ROOT filehandle. The
ROOT filehandle is the "conceptual" root of the file system name
space at the NFS server. The client uses or starts with the ROOT
filehandle by employing the PUTROOTFH operation. The PUTROOTFH
operation instructs the server to set the "current" filehandle to the
ROOT of the server's file tree. Once this PUTROOTFH operation is
used, the client can then traverse the entirety of the server's file
tree with the LOOKUP procedure. A complete discussion of the server
name space is in the section "NFS Server Name Space".
4.1.2. Public Filehandle
The second special filehandle is the PUBLIC filehandle. Unlike the
ROOT filehandle, the PUBLIC filehandle may be bound or represent an
arbitrary file system object at the server. The server is
responsible for this binding. It may be that the PUBLIC filehandle
and the ROOT filehandle refer to the same file system object.
However, it is up to the administrative software at the server and
the policies of the server administrator to define the binding of the
PUBLIC filehandle and server file system object. The client may not
make any assumptions about this binding.
Shepler, et al. Standards Track PAGE 24
RFC 3010 NFS version 4 Protocol December 2000
4.2. Filehandle Types
In the NFS version 2 and 3 protocols, there was one type of
filehandle with a single set of semantics. The NFS version 4
protocol introduces a new type of filehandle in an attempt to
accommodate certain server environments. The first type of
filehandle is 'persistent'. The semantics of a persistent filehandle
are the same as the filehandles of the NFS version 2 and 3 protocols.
The second or new type of filehandle is the "volatile" filehandle.
The volatile filehandle type is being introduced to address server
functionality or implementation issues which make correct
implementation of a persistent filehandle infeasible. Some server
environments do not provide a file system level invariant that can be
used to construct a persistent filehandle. The underlying server
file system may not provide the invariant or the server's file system
programming interfaces may not provide access to the needed
invariant. Volatile filehandles may ease the implementation of
server functionality such as hierarchical storage management or file
system reorganization or migration. However, the volatile filehandle
increases the implementation burden for the client. However this
increased burden is deemed acceptable based on the overall gains
achieved by the protocol.
Since the client will need to handle persistent and volatile
filehandle differently, a file attribute is defined which may be used
by the client to determine the filehandle types being returned by the
server.
4.2.1. General Properties of a Filehandle
The filehandle contains all the information the server needs to
distinguish an individual file. To the client, the filehandle is
opaque. The client stores filehandles for use in a later request and
can compare two filehandles from the same server for equality by
doing a byte-by-byte comparison. However, the client MUST NOT
otherwise interpret the contents of filehandles. If two filehandles
from the same server are equal, they MUST refer to the same file. If
they are not equal, the client may use information provided by the
server, in the form of file attributes, to determine whether they
denote the same files or different files. The client would do this
as necessary for client side caching. Servers SHOULD try to maintain
a one-to-one correspondence between filehandles and files but this is
not required. Clients MUST use filehandle comparisons only to
improve performance, not for correct behavior. All clients need to
be prepared for situations in which it cannot be determined whether
two filehandles denote the same object and in such cases, avoid
making invalid assumptions which might cause incorrect behavior.
Shepler, et al. Standards Track PAGE 25
RFC 3010 NFS version 4 Protocol December 2000
Further discussion of filehandle and attribute comparison in the
context of data caching is presented in the section "Data Caching and
File Identity".
As an example, in the case that two different path names when
traversed at the server terminate at the same file system object, the
server SHOULD return the same filehandle for each path. This can
occur if a hard link is used to create two file names which refer to
the same underlying file object and associated data. For example, if
paths /a/b/c and /a/d/c refer to the same file, the server SHOULD
return the same filehandle for both path names traversals.
4.2.2. Persistent Filehandle
A persistent filehandle is defined as having a fixed value for the
lifetime of the file system object to which it refers. Once the
server creates the filehandle for a file system object, the server
MUST accept the same filehandle for the object for the lifetime of
the object. If the server restarts or reboots the NFS server must
honor the same filehandle value as it did in the server's previous
instantiation. Similarly, if the file system is migrated, the new
NFS server must honor the same file handle as the old NFS server.
The persistent filehandle will be become stale or invalid when the
file system object is removed. When the server is presented with a
persistent filehandle that refers to a deleted object, it MUST return
an error of NFS4ERR_STALE. A filehandle may become stale when the
file system containing the object is no longer available. The file
system may become unavailable if it exists on removable media and the
media is no longer available at the server or the file system in
whole has been destroyed or the file system has simply been removed
from the server's name space (i.e. unmounted in a Unix environment).
4.2.3. Volatile Filehandle
A volatile filehandle does not share the same longevity
characteristics of a persistent filehandle. The server may determine
that a volatile filehandle is no longer valid at many different
points in time. If the server can definitively determine that a
volatile filehandle refers to an object that has been removed, the
server should return NFS4ERR_STALE to the client (as is the case for
persistent filehandles). In all other cases where the server
determines that a volatile filehandle can no longer be used, it
should return an error of NFS4ERR_FHEXPIRED.
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RFC 3010 NFS version 4 Protocol December 2000
The mandatory attribute "fh_expire_type" is used by the client to
determine what type of filehandle the server is providing for a
particular file system. This attribute is a bitmask with the
following values:
FH4_PERSISTENT
The value of FH4_PERSISTENT is used to indicate a persistent
filehandle, which is valid until the object is removed from the
file system. The server will not return NFS4ERR_FHEXPIRED for
this filehandle. FH4_PERSISTENT is defined as a value in which
none of the bits specified below are set.
FH4_NOEXPIRE_WITH_OPEN
The filehandle will not expire while client has the file open.
If this bit is set, then the values FH4_VOLATILE_ANY or
FH4_VOL_RENAME do not impact expiration while the file is open.
Once the file is closed or if the FH4_NOEXPIRE_WITH_OPEN bit is
false, the rest of the volatile related bits apply.
FH4_VOLATILE_ANY
The filehandle may expire at any time and will expire during
system migration and rename.
FH4_VOL_MIGRATION
The filehandle will expire during file system migration. May
only be set if FH4_VOLATILE_ANY is not set.
FH4_VOL_RENAME
The filehandle may expire due to a rename. This includes a
rename by the requesting client or a rename by another client.
May only be set if FH4_VOLATILE_ANY is not set.
Servers which provide volatile filehandles should deny a RENAME or
REMOVE that would affect an OPEN file or any of the components
leading to the OPEN file. In addition, the server should deny all
RENAME or REMOVE requests during the grace or lease period upon
server restart.
The reader may be wondering why there are three FH4_VOL* bits and why
FH4_VOLATILE_ANY is exclusive of FH4_VOL_MIGRATION and
FH4_VOL_RENAME. If the a filehandle is normally persistent but
cannot persist across a file set migration, then the presence of the
FH4_VOL_MIGRATION or FH4_VOL_RENAME tells the client that it can
treat the file handle as persistent for purposes of maintaining a
file name to file handle cache, except for the specific event
described by the bit. However, FH4_VOLATILE_ANY tells the client
that it should not maintain such a cache for unopened files. A
server MUST not present FH4_VOLATILE_ANY with FH4_VOL_MIGRATION or
Shepler, et al. Standards Track PAGE 27
RFC 3010 NFS version 4 Protocol December 2000
FH4_VOL_RENAME as this will lead to confusion. FH4_VOLATILE_ANY
implies that the file handle will expire upon migration or rename, in
addition to other events.
4.2.4. One Method of Constructing a Volatile Filehandle
As mentioned, in some instances a filehandle is stale (no longer
valid; perhaps because the file was removed from the server) or it is
expired (the underlying file is valid but since the filehandle is
volatile, it may have expired). Thus the server needs to be able to
return NFS4ERR_STALE in the former case and NFS4ERR_FHEXPIRED in the
latter case. This can be done by careful construction of the volatile
filehandle. One possible implementation follows.
A volatile filehandle, while opaque to the client could contain:
[volatile bit = 1 | server boot time | slot | generation number]
o slot is an index in the server volatile filehandle table
o generation number is the generation number for the table
entry/slot
If the server boot time is less than the current server boot time,
return NFS4ERR_FHEXPIRED. If slot is out of range, return
NFS4ERR_BADHANDLE. If the generation number does not match, return
NFS4ERR_FHEXPIRED.
When the server reboots, the table is gone (it is volatile).
If volatile bit is 0, then it is a persistent filehandle with a
different structure following it.
4.3. Client Recovery from Filehandle Expiration
If possible, the client SHOULD recover from the receipt of an
NFS4ERR_FHEXPIRED error. The client must take on additional
responsibility so that it may prepare itself to recover from the
expiration of a volatile filehandle. If the server returns
persistent filehandles, the client does not need these additional
steps.
For volatile filehandles, most commonly the client will need to store
the component names leading up to and including the file system
object in question. With these names, the client should be able to
recover by finding a filehandle in the name space that is still
available or by starting at the root of the server's file system name
space.
Shepler, et al. Standards Track PAGE 28
RFC 3010 NFS version 4 Protocol December 2000
If the expired filehandle refers to an object that has been removed
from the file system, obviously the client will not be able to
recover from the expired filehandle.
It is also possible that the expired filehandle refers to a file that
has been renamed. If the file was renamed by another client, again
it is possible that the original client will not be able to recover.
However, in the case that the client itself is renaming the file and
the file is open, it is possible that the client may be able to
recover. The client can determine the new path name based on the
processing of the rename request. The client can then regenerate the
new filehandle based on the new path name. The client could also use
the compound operation mechanism to construct a set of operations
like:
RENAME A B
LOOKUP B
GETFH
5. File Attributes
To meet the requirements of extensibility and increased
interoperability with non-Unix platforms, attributes must be handled
in a flexible manner. The NFS Version 3 fattr3 structure contains a
fixed list of attributes that not all clients and servers are able to
support or care about. The fattr3 structure can not be extended as
new needs arise and it provides no way to indicate non-support. With
the NFS Version 4 protocol, the client will be able to ask what
attributes the server supports and will be able to request only those
attributes in which it is interested.
To this end, attributes will be divided into three groups: mandatory,
recommended, and named. Both mandatory and recommended attributes
are supported in the NFS version 4 protocol by a specific and well-
defined encoding and are identified by number. They are requested by
setting a bit in the bit vector sent in the GETATTR request; the
server response includes a bit vector to list what attributes were
returned in the response. New mandatory or recommended attributes
may be added to the NFS protocol between major revisions by
publishing a standards-track RFC which allocates a new attribute
number value and defines the encoding for the attribute. See the
section "Minor Versioning" for further discussion.
Named attributes are accessed by the new OPENATTR operation, which
accesses a hidden directory of attributes associated with a file
system object. OPENATTR takes a filehandle for the object and
returns the filehandle for the attribute hierarchy. The filehandle
for the named attributes is a directory object accessible by LOOKUP
Shepler, et al. Standards Track PAGE 29
RFC 3010 NFS version 4 Protocol December 2000
or READDIR and contains files whose names represent the named
attributes and whose data bytes are the value of the attribute. For
example:
LOOKUP "foo" ; look up file
GETATTR attrbits
OPENATTR ; access foo's named attributes
LOOKUP "x11icon" ; look up specific attribute
READ 0,4096 ; read stream of bytes
Named attributes are intended for data needed by applications rather
than by an NFS client implementation. NFS implementors are strongly
encouraged to define their new attributes as recommended attributes
by bringing them to the IETF standards-track process.
The set of attributes which are classified as mandatory is
deliberately small since servers must do whatever it takes to support
them. The recommended attributes may be unsupported; though a server
should support as many as it can. Attributes are deemed mandatory if
the data is both needed by a large number of clients and is not
otherwise reasonably computable by the client when support is not
provided on the server.
5.1. Mandatory Attributes
These MUST be supported by every NFS Version 4 client and server in
order to ensure a minimum level of interoperability. The server must
store and return these attributes and the client must be able to
function with an attribute set limited to these attributes. With
just the mandatory attributes some client functionality may be
impaired or limited in some ways. A client may ask for any of these
attributes to be returned by setting a bit in the GETATTR request and
the server must return their value.
5.2. Recommended Attributes
These attributes are understood well enough to warrant support in the
NFS Version 4 protocol. However, they may not be supported on all
clients and servers. A client may ask for any of these attributes to
be returned by setting a bit in the GETATTR request but must handle
the case where the server does not return them. A client may ask for
the set of attributes the server supports and should not request
attributes the server does not support. A server should be tolerant
of requests for unsupported attributes and simply not return them
rather than considering the request an error. It is expected that
servers will support all attributes they comfortably can and only
fail to support attributes which are difficult to support in their
operating environments. A server should provide attributes whenever
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RFC 3010 NFS version 4 Protocol December 2000
they don't have to "tell lies" to the client. For example, a file
modification time should be either an accurate time or should not be
supported by the server. This will not always be comfortable to
clients but it seems that the client has a better ability to
fabricate or construct an attribute or do without the attribute.
5.3. Named Attributes
These attributes are not supported by direct encoding in the NFS
Version 4 protocol but are accessed by string names rather than
numbers and correspond to an uninterpreted stream of bytes which are
stored with the file system object. The name space for these
attributes may be accessed by using the OPENATTR operation. The
OPENATTR operation returns a filehandle for a virtual "attribute
directory" and further perusal of the name space may be done using
READDIR and LOOKUP operations on this filehandle. Named attributes
may then be examined or changed by normal READ and WRITE and CREATE
operations on the filehandles returned from READDIR and LOOKUP.
Named attributes may have attributes.
It is recommended that servers support arbitrary named attributes. A
client should not depend on the ability to store any named attributes
in the server's file system. If a server does support named
attributes, a client which is also able to handle them should be able
to copy a file's data and meta-data with complete transparency from
one location to another; this would imply that names allowed for
regular directory entries are valid for named attribute names as
well.
Names of attributes will not be controlled by this document or other
IETF standards track documents. See the section "IANA
Considerations" for further discussion.
5.4. Mandatory Attributes - Definitions
Name # DataType Access Description
___________________________________________________________________
supp_attr 0 bitmap READ The bit vector which
would retrieve all
mandatory and
recommended attributes
that are supported for
this object.
type 1 nfs4_ftype READ The type of the object
(file, directory,
symlink)
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RFC 3010 NFS version 4 Protocol December 2000
fh_expire_type 2 uint32 READ Server uses this to
specify filehandle
expiration behavior to
the client. See the
section "Filehandles"
for additional
description.
change 3 uint64 READ A value created by the
server that the client
can use to determine
if file data,
directory contents or
attributes of the
object have been
modified. The server
may return the
object's time_modify
attribute for this
attribute's value but
only if the file
system object can not
be updated more
frequently than the
resolution of
time_modify.
size 4 uint64 R/W The size of the object
in bytes.
link_support 5 boolean READ Does the object's file
system supports hard
links?
symlink_support 6 boolean READ Does the object's file
system supports
symbolic links?
named_attr 7 boolean READ Does this object have
named attributes?
fsid 8 fsid4 READ Unique file system
identifier for the
file system holding
this object. fsid
contains major and
minor components each
of which are uint64.
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RFC 3010 NFS version 4 Protocol December 2000
unique_handles 9 boolean READ Are two distinct
filehandles guaranteed
to refer to two
different file system
objects?
lease_time 10 nfs_lease4 READ Duration of leases at
server in seconds.
rdattr_error 11 enum READ Error returned from
getattr during
readdir.
5.5. Recommended Attributes - Definitions
Name # Data Type Access Description
_____________________________________________________________________
ACL 12 nfsace4<> R/W The access control
list for the object.
aclsupport 13 uint32 READ Indicates what types
of ACLs are supported
on the current file
system.
archive 14 boolean R/W Whether or not this
file has been
archived since the
time of last
modification
(deprecated in favor
of time_backup).
cansettime 15 boolean READ Is the server able to
change the times for
a file system object
as specified in a
SETATTR operation?
case_insensitive 16 boolean READ Are filename
comparisons on this
file system case
insensitive?
case_preserving 17 boolean READ Is filename case on
this file system
preserved?
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RFC 3010 NFS version 4 Protocol December 2000
chown_restricted 18 boolean READ If TRUE, the server
will reject any
request to change
either the owner or
the group associated
with a file if the
caller is not a
privileged user (for
example, "root" in
Unix operating
environments or in NT
the "Take Ownership"
privilege)
filehandle 19 nfs4_fh READ The filehandle of
this object
(primarily for
readdir requests).
fileid 20 uint64 READ A number uniquely
identifying the file
within the file
system.
files_avail 21 uint64 READ File slots available
to this user on the
file system
containing this
object - this should
be the smallest
relevant limit.
files_free 22 uint64 READ Free file slots on
the file system
containing this
object - this should
be the smallest
relevant limit.
files_total 23 uint64 READ Total file slots on
the file system
containing this
object.
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RFC 3010 NFS version 4 Protocol December 2000
fs_locations 24 fs_locations READ Locations where this
file system may be
found. If the server
returns NFS4ERR_MOVED
as an error, this
attribute must be
supported.
hidden 25 boolean R/W Is file considered
hidden with respect
to the WIN32 API?
homogeneous 26 boolean READ Whether or not this
object's file system
is homogeneous, i.e.
are per file system
attributes the same
for all file system's
objects.
maxfilesize 27 uint64 READ Maximum supported
file size for the
file system of this
object.
maxlink 28 uint32 READ Maximum number of
links for this
object.
maxname 29 uint32 READ Maximum filename size
supported for this
object.
maxread 30 uint64 READ Maximum read size
supported for this
object.
maxwrite 31 uint64 READ Maximum write size
supported for this
object. This
attribute SHOULD be
supported if the file
is writable. Lack of
this attribute can
lead to the client
either wasting
Shepler, et al. Standards Track PAGE 35
RFC 3010 NFS version 4 Protocol December 2000
bandwidth or not
receiving the best
performance.
mimetype 32 utf8<> R/W MIME body
type/subtype of this
object.
mode 33 mode4 R/W Unix-style permission
bits for this object
(deprecated in favor
of ACLs)
no_trunc 34 boolean READ If a name longer than
name_max is used,
will an error be
returned or will the
name be truncated?
numlinks 35 uint32 READ Number of hard links
to this object.
owner 36 utf8<> R/W The string name of
the owner of this
object.
owner_group 37 utf8<> R/W The string name of
the group ownership
of this object.
quota_avail_hard 38 uint64 READ For definition see
"Quota Attributes"
section below.
quota_avail_soft 39 uint64 READ For definition see
"Quota Attributes"
section below.
quota_used 40 uint64 READ For definition see
"Quota Attributes"
section below.
rawdev 41 specdata4 READ Raw device
identifier. Unix
device major/minor
node information.
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RFC 3010 NFS version 4 Protocol December 2000
space_avail 42 uint64 READ Disk space in bytes
available to this
user on the file
system containing
this object - this
should be the
smallest relevant
limit.
space_free 43 uint64 READ Free disk space in
bytes on the file
system containing
this object - this
should be the
smallest relevant
limit.
space_total 44 uint64 READ Total disk space in
bytes on the file
system containing
this object.
space_used 45 uint64 READ Number of file system
bytes allocated to
this object.
system 46 boolean R/W Is this file a system
file with respect to
the WIN32 API?
time_access 47 nfstime4 READ The time of last
access to the object.
time_access_set 48 settime4 WRITE Set the time of last
access to the object.
SETATTR use only.
time_backup 49 nfstime4 R/W The time of last
backup of the object.
time_create 50 nfstime4 R/W The time of creation
of the object. This
attribute does not
have any relation to
the traditional Unix
file attribute
"ctime" or "change
time".
Shepler, et al. Standards Track PAGE 37
RFC 3010 NFS version 4 Protocol December 2000
time_delta 51 nfstime4 READ Smallest useful
server time
granularity.
time_metadata 52 nfstime4 R/W The time of last
meta-data
modification of the
object.
time_modify 53 nfstime4 READ The time of last
modification to the
object.
time_modify_set 54 settime4 WRITE Set the time of last
modification to the
object. SETATTR use
only.
5.6. Interpreting owner and owner_group
The recommended attributes "owner" and "owner_group" are represented
in terms of a UTF-8 string. To avoid a representation that is tied
to a particular underlying implementation at the client or server,
the use of the UTF-8 string has been chosen. Note that section 6.1
of [RFC 2624] provides additional rationale. It is expected that the
client and server will have their own local representation of owner
and owner_group that is used for local storage or presentation to the
end user. Therefore, it is expected that when these attributes are
transferred between the client and server that the local
representation is translated to a syntax of the form
"user@dns_domain". This will allow for a client and server that do
not use the same local representation the ability to translate to a
common syntax that can be interpreted by both.
The translation is not specified as part of the protocol. This
allows various solutions to be employed. For example, a local
translation table may be consulted that maps between a numeric id to
the user@dns_domain syntax. A name service may also be used to
accomplish the translation. The "dns_domain" portion of the owner
string is meant to be a DNS domain name. For example, user@ietf.org.
In the case where there is no translation available to the client or
server, the attribute value must be constructed without the "@".
Therefore, the absence of the @ from the owner or owner_group
attribute signifies that no translation was available and the
receiver of the attribute should not place any special meaning with
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RFC 3010 NFS version 4 Protocol December 2000
the attribute value. Even though the attribute value can not be
translated, it may still be useful. In the case of a client, the
attribute string may be used for local display of ownership.
5.7. Character Case Attributes
With respect to the case_insensitive and case_preserving attributes,
each UCS-4 character (which UTF-8 encodes) has a "long descriptive
name" [RFC 1345] which may or may not included the word "CAPITAL" or
"SMALL". The presence of SMALL or CAPITAL allows an NFS server to
implement unambiguous and efficient table driven mappings for case
insensitive comparisons, and non-case-preserving storage. For
general character handling and internationalization issues, see the
section "Internationalization".
5.8. Quota Attributes
For the attributes related to file system quotas, the following
definitions apply:
quota_avail_soft
The value in bytes which represents the amount of additional
disk space that can be allocated to this file or directory
before the user may reasonably be warned. It is understood
that this space may be consumed by allocations to other files
or directories though there is a rule as to which other files
or directories.
quota_avail_hard
The value in bytes which represent the amount of additional
disk space beyond the current allocation that can be allocated
to this file or directory before further allocations will be
refused. It is understood that this space may be consumed by
allocations to other files or directories.
quota_used
The value in bytes which represent the amount of disc space
used by this file or directory and possibly a number of other
similar files or directories, where the set of "similar" meets
at least the criterion that allocating space to any file or
directory in the set will reduce the "quota_avail_hard" of
every other file or directory in the set.
Note that there may be a number of distinct but overlapping
sets of files or directories for which a quota_used value is
maintained. E.g. "all files with a given owner", "all files
with a given group owner". etc.
Shepler, et al. Standards Track PAGE 39
RFC 3010 NFS version 4 Protocol December 2000
The server is at liberty to choose any of those sets but should
do so in a repeatable way. The rule may be configured per-
filesystem or may be "choose the set with the smallest quota".
5.9. Access Control Lists
The NFS ACL attribute is an array of access control entries (ACE).
There are various access control entry types. The server is able to
communicate which ACE types are supported by returning the
appropriate value within the aclsupport attribute. The types of ACEs
are defined as follows:
Type Description
_____________________________________________________
ALLOW Explicitly grants the access defined in
acemask4 to the file or directory.
DENY Explicitly denies the access defined in
acemask4 to the file or directory.
AUDIT LOG (system dependent) any access
attempt to a file or directory which
uses any of the access methods specified
in acemask4.
ALARM Generate a system ALARM (system
dependent) when any access attempt is
made to a file or directory for the
access methods specified in acemask4.
The NFS ACE attribute is defined as follows:
typedef uint32_t acetype4;
typedef uint32_t aceflag4;
typedef uint32_t acemask4;
struct nfsace4 {
acetype4 type;
aceflag4 flag;
acemask4 access_mask;
utf8string who;
};
To determine if an ACCESS or OPEN request succeeds each nfsace4 entry
is processed in order by the server. Only ACEs which have a "who"
that matches the requester are considered. Each ACE is processed
until all of the bits of the requester's access have been ALLOWED.
Once a bit (see below) has been ALLOWED by an ACCESS_ALLOWED_ACE, it
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RFC 3010 NFS version 4 Protocol December 2000
is no longer considered in the processing of later ACEs. If an
ACCESS_DENIED_ACE is encountered where the requester's mode still has
unALLOWED bits in common with the "access_mask" of the ACE, the
request is denied.
The bitmask constants used to represent the above definitions within
the aclsupport attribute are as follows:
const ACL4_SUPPORT_ALLOW_ACL = 0x00000001;
const ACL4_SUPPORT_DENY_ACL = 0x00000002;
const ACL4_SUPPORT_AUDIT_ACL = 0x00000004;
const ACL4_SUPPORT_ALARM_ACL = 0x00000008;
5.9.1. ACE type
The semantics of the "type" field follow the descriptions provided
above.
The bitmask constants used for the type field are as follows:
const ACE4_ACCESS_ALLOWED_ACE_TYPE = 0x00000000;
const ACE4_ACCESS_DENIED_ACE_TYPE = 0x00000001;
const ACE4_SYSTEM_AUDIT_ACE_TYPE = 0x00000002;
const ACE4_SYSTEM_ALARM_ACE_TYPE = 0x00000003;
5.9.2. ACE flag
The "flag" field contains values based on the following descriptions.
ACE4_FILE_INHERIT_ACE
Can be placed on a directory and indicates that this ACE should be
added to each new non-directory file created.
ACE4_DIRECTORY_INHERIT_ACE
Can be placed on a directory and indicates that this ACE should be
added to each new directory created.
ACE4_INHERIT_ONLY_ACE
Can be placed on a directory but does not apply to the directory,
only to newly created files/directories as specified by the above two
flags.
ACE4_NO_PROPAGATE_INHERIT_ACE
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RFC 3010 NFS version 4 Protocol December 2000
Can be placed on a directory. Normally when a new directory is
created and an ACE exists on the parent directory which is marked
ACL4_DIRECTORY_INHERIT_ACE, two ACEs are placed on the new directory.
One for the directory itself and one which is an inheritable ACE for
newly created directories. This flag tells the server to not place
an ACE on the newly created directory which is inheritable by
subdirectories of the created directory.
ACE4_SUCCESSFUL_ACCESS_ACE_FLAG
ACL4_FAILED_ACCESS_ACE_FLAG
Both indicate for AUDIT and ALARM which state to log the event. On
every ACCESS or OPEN call which occurs on a file or directory which
has an ACL that is of type ACE4_SYSTEM_AUDIT_ACE_TYPE or
ACE4_SYSTEM_ALARM_ACE_TYPE, the attempted access is compared to the
ace4mask of these ACLs. If the access is a subset of ace4mask and the
identifier match, an AUDIT trail or an ALARM is generated. By
default this happens regardless of the success or failure of the
ACCESS or OPEN call.
The flag ACE4_SUCCESSFUL_ACCESS_ACE_FLAG only produces the AUDIT or
ALARM if the ACCESS or OPEN call is successful. The
ACE4_FAILED_ACCESS_ACE_FLAG causes the ALARM or AUDIT if the ACCESS
or OPEN call fails.
ACE4_IDENTIFIER_GROUP
Indicates that the "who" refers to a GROUP as defined under Unix.
The bitmask constants used for the flag field are as follows:
const ACE4_FILE_INHERIT_ACE = 0x00000001;
const ACE4_DIRECTORY_INHERIT_ACE = 0x00000002;
const ACE4_NO_PROPAGATE_INHERIT_ACE = 0x00000004;
const ACE4_INHERIT_ONLY_ACE = 0x00000008;
const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG = 0x00000010;
const ACE4_FAILED_ACCESS_ACE_FLAG = 0x00000020;
const ACE4_IDENTIFIER_GROUP = 0x00000040;
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RFC 3010 NFS version 4 Protocol December 2000
5.9.3. ACE Access Mask
The access_mask field contains values based on the following:
Access Description
_______________________________________________________________
READ_DATA Permission to read the data of the file
LIST_DIRECTORY Permission to list the contents of a
directory
WRITE_DATA Permission to modify the file's data
ADD_FILE Permission to add a new file to a
directory
APPEND_DATA Permission to append data to a file
ADD_SUBDIRECTORY Permission to create a subdirectory to a
directory
READ_NAMED_ATTRS Permission to read the named attributes
of a file
WRITE_NAMED_ATTRS Permission to write the named attributes
of a file
EXECUTE Permission to execute a file
DELETE_CHILD Permission to delete a file or directory
within a directory
READ_ATTRIBUTES The ability to read basic attributes
(non-acls) of a file
WRITE_ATTRIBUTES Permission to change basic attributes
(non-acls) of a file
DELETE Permission to Delete the file
READ_ACL Permission to Read the ACL
WRITE_ACL Permission to Write the ACL
WRITE_OWNER Permission to change the owner
SYNCHRONIZE Permission to access file locally at the
server with synchronous reads and writes
The bitmask constants used for the access mask field are as follows:
const ACE4_READ_DATA = 0x00000001;
const ACE4_LIST_DIRECTORY = 0x00000001;
const ACE4_WRITE_DATA = 0x00000002;
const ACE4_ADD_FILE = 0x00000002;
const ACE4_APPEND_DATA = 0x00000004;
const ACE4_ADD_SUBDIRECTORY = 0x00000004;
const ACE4_READ_NAMED_ATTRS = 0x00000008;
const ACE4_WRITE_NAMED_ATTRS = 0x00000010;
const ACE4_EXECUTE = 0x00000020;
const ACE4_DELETE_CHILD = 0x00000040;
const ACE4_READ_ATTRIBUTES = 0x00000080;
const ACE4_WRITE_ATTRIBUTES = 0x00000100;
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const ACE4_DELETE = 0x00010000;
const ACE4_READ_ACL = 0x00020000;
const ACE4_WRITE_ACL = 0x00040000;
const ACE4_WRITE_OWNER = 0x00080000;
const ACE4_SYNCHRONIZE = 0x00100000;
5.9.4. ACE who
There are several special identifiers ("who") which need to be
understood universally. Some of these identifiers cannot be
understood when an NFS client accesses the server, but have meaning
when a local process accesses the file. The ability to display and
modify these permissions is permitted over NFS.
Who Description
_______________________________________________________________
"OWNER" The owner of the file.
"GROUP" The group associated with the file.
"EVERYONE" The world.
"INTERACTIVE" Accessed from an interactive terminal.
"NETWORK" Accessed via the network.
"DIALUP" Accessed as a dialup user to the server.
"BATCH" Accessed from a batch job.
"ANONYMOUS" Accessed without any authentication.
"AUTHENTICATED" Any authenticated user (opposite of
ANONYMOUS)
"SERVICE" Access from a system service.
To avoid conflict, these special identifiers are distinguish by an
appended "@" and should appear in the form "xxxx@" (note: no domain
name after the "@"). For example: ANONYMOUS@.
6. File System Migration and Replication
With the use of the recommended attribute "fs_locations", the NFS
version 4 server has a method of providing file system migration or
replication services. For the purposes of migration and replication,
a file system will be defined as all files that share a given fsid
(both major and minor values are the same).
The fs_locations attribute provides a list of file system locations.
These locations are specified by providing the server name (either
DNS domain or IP address) and the path name representing the root of
the file system. Depending on the type of service being provided,
the list will provide a new location or a set of alternate locations
for the file system. The client will use this information to
redirect its requests to the new server.
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6.1. Replication
It is expected that file system replication will be used in the case
of read-only data. Typically, the file system will be replicated on
two or more servers. The fs_locations attribute will provide the
list of these locations to the client. On first access of the file
system, the client should obtain the value of the fs_locations
attribute. If, in the future, the client finds the server
unresponsive, the client may attempt to use another server specified
by fs_locations.
If applicable, the client must take the appropriate steps to recover
valid filehandles from the new server. This is described in more
detail in the following sections.
6.2. Migration
File system migration is used to move a file system from one server
to another. Migration is typically used for a file system that is
writable and has a single copy. The expected use of migration is for
load balancing or general resource reallocation. The protocol does
not specify how the file system will be moved between servers. This
server-to-server transfer mechanism is left to the server
implementor. However, the method used to communicate the migration
event between client and server is specified here.
Once the servers participating in the migration have completed the
move of the file system, the error NFS4ERR_MOVED will be returned for
subsequent requests received by the original server. The
NFS4ERR_MOVED error is returned for all operations except GETATTR.
Upon receiving the NFS4ERR_MOVED error, the client will obtain the
value of the fs_locations attribute. The client will then use the
contents of the attribute to redirect its requests to the specified
server. To facilitate the use of GETATTR, operations such as PUTFH
must also be accepted by the server for the migrated file system's
filehandles. Note that if the server returns NFS4ERR_MOVED, the
server MUST support the fs_locations attribute.
If the client requests more attributes than just fs_locations, the
server may return fs_locations only. This is to be expected since
the server has migrated the file system and may not have a method of
obtaining additional attribute data.
The server implementor needs to be careful in developing a migration
solution. The server must consider all of the state information
clients may have outstanding at the server. This includes but is not
limited to locking/share state, delegation state, and asynchronous
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RFC 3010 NFS version 4 Protocol December 2000
file writes which are represented by WRITE and COMMIT verifiers. The
server should strive to minimize the impact on its clients during and
after the migration process.
6.3. Interpretation of the fs_locations Attribute
The fs_location attribute is structured in the following way:
struct fs_location {
utf8string server<>;
pathname4 rootpath;
};
struct fs_locations {
pathname4 fs_root;
fs_location locations<>;
};
The fs_location struct is used to represent the location of a file
system by providing a server name and the path to the root of the
file system. For a multi-homed server or a set of servers that use
the same rootpath, an array of server names may be provided. An
entry in the server array is an UTF8 string and represents one of a
traditional DNS host name, IPv4 address, or IPv6 address. It is not
a requirement that all servers that share the same rootpath be listed
in one fs_location struct. The array of server names is provided for
convenience. Servers that share the same rootpath may also be listed
in separate fs_location entries in the fs_locations attribute.
The fs_locations struct and attribute then contains an array of
locations. Since the name space of each server may be constructed
differently, the "fs_root" field is provided. The path represented
by fs_root represents the location of the file system in the server's
name space. Therefore, the fs_root path is only associated with the
server from which the fs_locations attribute was obtained. The
fs_root path is meant to aid the client in locating the file system
at the various servers listed.
As an example, there is a replicated file system located at two
servers (servA and servB). At servA the file system is located at
path "/a/b/c". At servB the file system is located at path "/x/y/z".
In this example the client accesses the file system first at servA
with a multi-component lookup path of "/a/b/c/d". Since the client
used a multi-component lookup to obtain the filehandle at "/a/b/c/d",
it is unaware that the file system's root is located in servA's name
space at "/a/b/c". When the client switches to servB, it will need
to determine that the directory it first referenced at servA is now
represented by the path "/x/y/z/d" on servB. To facilitate this, the
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RFC 3010 NFS version 4 Protocol December 2000
fs_locations attribute provided by servA would have a fs_root value
of "/a/b/c" and two entries in fs_location. One entry in fs_location
will be for itself (servA) and the other will be for servB with a
path of "/x/y/z". With this information, the client is able to
substitute "/x/y/z" for the "/a/b/c" at the beginning of its access
path and construct "/x/y/z/d" to use for the new server.
6.4. Filehandle Recovery for Migration or Replication
Filehandles for file systems that are replicated or migrated
generally have the same semantics as for file systems that are not
replicated or migrated. For example, if a file system has persistent
filehandles and it is migrated to another server, the filehandle
values for the file system will be valid at the new server.
For volatile filehandles, the servers involved likely do not have a
mechanism to transfer filehandle format and content between
themselves. Therefore, a server may have difficulty in determining
if a volatile filehandle from an old server should return an error of
NFS4ERR_FHEXPIRED. Therefore, the client is informed, with the use
of the fh_expire_type attribute, whether volatile filehandles will
expire at the migration or replication event. If the bit
FH4_VOL_MIGRATION is set in the fh_expire_type attribute, the client
must treat the volatile filehandle as if the server had returned the
NFS4ERR_FHEXPIRED error. At the migration or replication event in
the presence of the FH4_VOL_MIGRATION bit, the client will not
present the original or old volatile file handle to the new server.
The client will start its communication with the new server by
recovering its filehandles using the saved file names.
7. NFS Server Name Space
7.1. Server Exports
On a UNIX server the name space describes all the files reachable by
pathnames under the root directory or "/". On a Windows NT server
the name space constitutes all the files on disks named by mapped
disk letters. NFS server administrators rarely make the entire
server's file system name space available to NFS clients. More often
portions of the name space are made available via an "export"
feature. In previous versions of the NFS protocol, the root
filehandle for each export is obtained through the MOUNT protocol;
the client sends a string that identifies the export of name space
and the server returns the root filehandle for it. The MOUNT
protocol supports an EXPORTS procedure that will enumerate the
server's exports.
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7.2. Browsing Exports
The NFS version 4 protocol provides a root filehandle that clients
can use to obtain filehandles for these exports via a multi-component
LOOKUP. A common user experience is to use a graphical user
interface (perhaps a file "Open" dialog window) to find a file via
progressive browsing through a directory tree. The client must be
able to move from one export to another export via single-component,
progressive LOOKUP operations.
This style of browsing is not well supported by the NFS version 2 and
3 protocols. The client expects all LOOKUP operations to remain
within a single server file system. For example, the device
attribute will not change. This prevents a client from taking name
space paths that span exports.
An automounter on the client can obtain a snapshot of the server's
name space using the EXPORTS procedure of the MOUNT protocol. If it
understands the server's pathname syntax, it can create an image of
the server's name space on the client. The parts of the name space
that are not exported by the server are filled in with a "pseudo file
system" that allows the user to browse from one mounted file system
to another. There is a drawback to this representation of the
server's name space on the client: it is static. If the server
administrator adds a new export the client will be unaware of it.
7.3. Server Pseudo File System
NFS version 4 servers avoid this name space inconsistency by
presenting all the exports within the framework of a single server
name space. An NFS version 4 client uses LOOKUP and READDIR
operations to browse seamlessly from one export to another. Portions
of the server name space that are not exported are bridged via a
"pseudo file system" that provides a view of exported directories
only. A pseudo file system has a unique fsid and behaves like a
normal, read only file system.
Based on the construction of the server's name space, it is possible
that multiple pseudo file systems may exist. For example,
/a pseudo file system
/a/b real file system
/a/b/c pseudo file system
/a/b/c/d real file system
Each of the pseudo file systems are consider separate entities and
therefore will have a unique fsid.
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7.4. Multiple Roots
The DOS and Windows operating environments are sometimes described as
having "multiple roots". File systems are commonly represented as
disk letters. MacOS represents file systems as top level names. NFS
version 4 servers for these platforms can construct a pseudo file
system above these root names so that disk letters or volume names
are simply directory names in the pseudo root.
7.5. Filehandle Volatility
The nature of the server's pseudo file system is that it is a logical
representation of file system(s) available from the server.
Therefore, the pseudo file system is most likely constructed
dynamically when the server is first instantiated. It is expected
that the pseudo file system may not have an on disk counterpart from
which persistent filehandles could be constructed. Even though it is
preferable that the server provide persistent filehandles for the
pseudo file system, the NFS client should expect that pseudo file
system filehandles are volatile. This can be confirmed by checking
the associated "fh_expire_type" attribute for those filehandles in
question. If the filehandles are volatile, the NFS client must be
prepared to recover a filehandle value (e.g. with a multi-component
LOOKUP) when receiving an error of NFS4ERR_FHEXPIRED.
7.6. Exported Root
If the server's root file system is exported, one might conclude that
a pseudo-file system is not needed. This would be wrong. Assume the
following file systems on a server:
/ disk1 (exported)
/a disk2 (not exported)
/a/b disk3 (exported)
Because disk2 is not exported, disk3 cannot be reached with simple
LOOKUPs. The server must bridge the gap with a pseudo-file system.
7.7. Mount Point Crossing
The server file system environment may be constructed in such a way
that one file system contains a directory which is 'covered' or
mounted upon by a second file system. For example:
/a/b (file system 1)
/a/b/c/d (file system 2)
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RFC 3010 NFS version 4 Protocol December 2000
The pseudo file system for this server may be constructed to look
like:
/ (place holder/not exported)
/a/b (file system 1)
/a/b/c/d (file system 2)
It is the server's responsibility to present the pseudo file system
that is complete to the client. If the client sends a lookup request
for the path "/a/b/c/d", the server's response is the filehandle of
the file system "/a/b/c/d". In previous versions of the NFS
protocol, the server would respond with the directory "/a/b/c/d"
within the file system "/a/b".
The NFS client will be able to determine if it crosses a server mount
point by a change in the value of the "fsid" attribute.
7.8. Security Policy and Name Space Presentation
The application of the server's security policy needs to be carefully
considered by the implementor. One may choose to limit the
viewability of portions of the pseudo file system based on the
server's perception of the client's ability to authenticate itself
properly. However, with the support of multiple security mechanisms
and the ability to negotiate the appropriate use of these mechanisms,
the server is unable to properly determine if a client will be able
to authenticate itself. If, based on its policies, the server
chooses to limit the contents of the pseudo file system, the server
may effectively hide file systems from a client that may otherwise
have legitimate access.
8. File Locking and Share Reservations
Integrating locking into the NFS protocol necessarily causes it to be
state-full. With the inclusion of "share" file locks the protocol
becomes substantially more dependent on state than the traditional
combination of NFS and NLM [XNFS]. There are three components to
making this state manageable:
o Clear division between client and server
o Ability to reliably detect inconsistency in state between client
and server
o Simple and robust recovery mechanisms
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RFC 3010 NFS version 4 Protocol December 2000
In this model, the server owns the state information. The client
communicates its view of this state to the server as needed. The
client is also able to detect inconsistent state before modifying a
file.
To support Win32 "share" locks it is necessary to atomically OPEN or
CREATE files. Having a separate share/unshare operation would not
allow correct implementation of the Win32 OpenFile API. In order to
correctly implement share semantics, the previous NFS protocol
mechanisms used when a file is opened or created (LOOKUP, CREATE,
ACCESS) need to be replaced. The NFS version 4 protocol has an OPEN
operation that subsumes the functionality of LOOKUP, CREATE, and
ACCESS. However, because many operations require a filehandle, the
traditional LOOKUP is preserved to map a file name to filehandle
without establishing state on the server. The policy of granting
access or modifying files is managed by the server based on the
client's state. These mechanisms can implement policy ranging from
advisory only locking to full mandatory locking.
8.1. Locking
It is assumed that manipulating a lock is rare when compared to READ
and WRITE operations. It is also assumed that crashes and network
partitions are relatively rare. Therefore it is important that the
READ and WRITE operations have a lightweight mechanism to indicate if
they possess a held lock. A lock request contains the heavyweight
information required to establish a lock and uniquely define the lock
owner.
The following sections describe the transition from the heavy weight
information to the eventual stateid used for most client and server
locking and lease interactions.
8.1.1. Client ID
For each LOCK request, the client must identify itself to the server.
This is done in such a way as to allow for correct lock
identification and crash recovery. Client identification is
accomplished with two values.
o A verifier that is used to detect client reboots.
o A variable length opaque array to uniquely define a client.
For an operating system this may be a fully qualified host name
or IP address. For a user level NFS client it may additionally
contain a process id or other unique sequence.
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RFC 3010 NFS version 4 Protocol December 2000
The data structure for the Client ID would then appear as:
struct nfs_client_id {
opaque verifier[4];
opaque id<>;
}
It is possible through the mis-configuration of a client or the
existence of a rogue client that two clients end up using the same
nfs_client_id. This situation is avoided by "negotiating" the
nfs_client_id between client and server with the use of the
SETCLIENTID and SETCLIENTID_CONFIRM operations. The following
describes the two scenarios of negotiation.
1 Client has never connected to the server
In this case the client generates an nfs_client_id and unless
another client has the same nfs_client_id.id field, the server
accepts the request. The server also records the principal (or
principal to uid mapping) from the credential in the RPC request
that contains the nfs_client_id negotiation request (SETCLIENTID
operation).
Two clients might still use the same nfs_client_id.id due to
perhaps configuration error. For example, a High Availability
configuration where the nfs_client_id.id is derived from the
ethernet controller address and both systems have the same
address. In this case, the result is a switched union that
returns, in addition to NFS4ERR_CLID_INUSE, the network address
(the rpcbind netid and universal address) of the client that is
using the id.
2 Client is re-connecting to the server after a client reboot
In this case, the client still generates an nfs_client_id but the
nfs_client_id.id field will be the same as the nfs_client_id.id
generated prior to reboot. If the server finds that the
principal/uid is equal to the previously "registered"
nfs_client_id.id, then locks associated with the old nfs_client_id
are immediately released. If the principal/uid is not equal, then
this is a rogue client and the request is returned in error. For
more discussion of crash recovery semantics, see the section on
"Crash Recovery".
It is possible for a retransmission of request to be received by
the server after the server has acted upon and responded to the
original client request. Therefore to mitigate effects of the
retransmission of the SETCLIENTID operation, the client and server
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RFC 3010 NFS version 4 Protocol December 2000
use a confirmation step. The server returns a confirmation
verifier that the client then sends to the server in the
SETCLIENTID_CONFIRM operation. Once the server receives the
confirmation from the client, the locking state for the client is
released.
In both cases, upon success, NFS4_OK is returned. To help reduce the
amount of data transferred on OPEN and LOCK, the server will also
return a unique 64-bit clientid value that is a shorthand reference
to the nfs_client_id values presented by the client. From this point
forward, the client will use the clientid to refer to itself.
The clientid assigned by the server should be chosen so that it will
not conflict with a clientid previously assigned by the server. This
applies across server restarts or reboots. When a clientid is
presented to a server and that clientid is not recognized, as would
happen after a server reboot, the server will reject the request with
the error NFS4ERR_STALE_CLIENTID. When this happens, the client must
obtain a new clientid by use of the SETCLIENTID operation and then
proceed to any other necessary recovery for the server reboot case
(See the section "Server Failure and Recovery").
The client must also employ the SETCLIENTID operation when it
receives a NFS4ERR_STALE_STATEID error using a stateid derived from
its current clientid, since this also indicates a server reboot which
has invalidated the existing clientid (see the next section
"nfs_lockowner and stateid Definition" for details).
8.1.2. Server Release of Clientid
If the server determines that the client holds no associated state
for its clientid, the server may choose to release the clientid. The
server may make this choice for an inactive client so that resources
are not consumed by those intermittently active clients. If the
client contacts the server after this release, the server must ensure
the client receives the appropriate error so that it will use the
SETCLIENTID/SETCLIENTID_CONFIRM sequence to establish a new identity.
It should be clear that the server must be very hesitant to release a
clientid since the resulting work on the client to recover from such
an event will be the same burden as if the server had failed and
restarted. Typically a server would not release a clientid unless
there had been no activity from that client for many minutes.
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8.1.3. nfs_lockowner and stateid Definition
When requesting a lock, the client must present to the server the
clientid and an identifier for the owner of the requested lock.
These two fields are referred to as the nfs_lockowner and the
definition of those fields are:
o A clientid returned by the server as part of the client's use of
the SETCLIENTID operation.
o A variable length opaque array used to uniquely define the owner
of a lock managed by the client.
This may be a thread id, process id, or other unique value.
When the server grants the lock, it responds with a unique 64-bit
stateid. The stateid is used as a shorthand reference to the
nfs_lockowner, since the server will be maintaining the
correspondence between them.
The server is free to form the stateid in any manner that it chooses
as long as it is able to recognize invalid and out-of-date stateids.
This requirement includes those stateids generated by earlier
instances of the server. From this, the client can be properly
notified of a server restart. This notification will occur when the
client presents a stateid to the server from a previous
instantiation.
The server must be able to distinguish the following situations and
return the error as specified:
o The stateid was generated by an earlier server instance (i.e.
before a server reboot). The error NFS4ERR_STALE_STATEID should
be returned.
o The stateid was generated by the current server instance but the
stateid no longer designates the current locking state for the
lockowner-file pair in question (i.e. one or more locking
operations has occurred). The error NFS4ERR_OLD_STATEID should be
returned.
This error condition will only occur when the client issues a
locking request which changes a stateid while an I/O request that
uses that stateid is outstanding.
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RFC 3010 NFS version 4 Protocol December 2000
o The stateid was generated by the current server instance but the
stateid does not designate a locking state for any active
lockowner-file pair. The error NFS4ERR_BAD_STATEID should be
returned.
This error condition will occur when there has been a logic error
on the part of the client or server. This should not happen.
One mechanism that may be used to satisfy these requirements is for
the server to divide stateids into three fields:
o A server verifier which uniquely designates a particular server
instantiation.
o An index into a table of locking-state structures.
o A sequence value which is incremented for each stateid that is
associated with the same index into the locking-state table.
By matching the incoming stateid and its field values with the state
held at the server, the server is able to easily determine if a
stateid is valid for its current instantiation and state. If the
stateid is not valid, the appropriate error can be supplied to the
client.
8.1.4. Use of the stateid
All READ and WRITE operations contain a stateid. If the
nfs_lockowner performs a READ or WRITE on a range of bytes within a
locked range, the stateid (previously returned by the server) must be
used to indicate that the appropriate lock (record or share) is held.
If no state is established by the client, either record lock or share
lock, a stateid of all bits 0 is used. If no conflicting locks are
held on the file, the server may service the READ or WRITE operation.
If a conflict with an explicit lock occurs, an error is returned for
the operation (NFS4ERR_LOCKED). This allows "mandatory locking" to be
implemented.
A stateid of all bits 1 (one) allows READ operations to bypass record
locking checks at the server. However, WRITE operations with stateid
with bits all 1 (one) do not bypass record locking checks. File
locking checks are handled by the OPEN operation (see the section
"OPEN/CLOSE Operations").
An explicit lock may not be granted while a READ or WRITE operation
with conflicting implicit locking is being performed.
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8.1.5. Sequencing of Lock Requests
Locking is different than most NFS operations as it requires "at-
most-one" semantics that are not provided by ONCRPC. ONCRPC over a
reliable transport is not sufficient because a sequence of locking
requests may span multiple TCP connections. In the face of
retransmission or reordering, lock or unlock requests must have a
well defined and consistent behavior. To accomplish this, each lock
request contains a sequence number that is a consecutively increasing
integer. Different nfs_lockowners have different sequences. The
server maintains the last sequence number (L) received and the
response that was returned.
Note that for requests that contain a sequence number, for each
nfs_lockowner, there should be no more than one outstanding request.
If a request with a previous sequence number (r < L) is received, it
is rejected with the return of error NFS4ERR_BAD_SEQID. Given a
properly-functioning client, the response to (r) must have been
received before the last request (L) was sent. If a duplicate of
last request (r == L) is received, the stored response is returned.
If a request beyond the next sequence (r == L + 2) is received, it is
rejected with the return of error NFS4ERR_BAD_SEQID. Sequence
history is reinitialized whenever the client verifier changes.
Since the sequence number is represented with an unsigned 32-bit
integer, the arithmetic involved with the sequence number is mod
2^32.
It is critical the server maintain the last response sent to the
client to provide a more reliable cache of duplicate non-idempotent
requests than that of the traditional cache described in [Juszczak].
The traditional duplicate request cache uses a least recently used
algorithm for removing unneeded requests. However, the last lock
request and response on a given nfs_lockowner must be cached as long
as the lock state exists on the server.
8.1.6. Recovery from Replayed Requests
As described above, the sequence number is per nfs_lockowner. As
long as the server maintains the last sequence number received and
follows the methods described above, there are no risks of a
Byzantine router re-sending old requests. The server need only
maintain the nfs_lockowner, sequence number state as long as there
are open files or closed files with locks outstanding.
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RFC 3010 NFS version 4 Protocol December 2000
LOCK, LOCKU, OPEN, OPEN_DOWNGRADE, and CLOSE each contain a sequence
number and therefore the risk of the replay of these operations
resulting in undesired effects is non-existent while the server
maintains the nfs_lockowner state.
8.1.7. Releasing nfs_lockowner State
When a particular nfs_lockowner no longer holds open or file locking
state at the server, the server may choose to release the sequence
number state associated with the nfs_lockowner. The server may make
this choice based on lease expiration, for the reclamation of server
memory, or other implementation specific details. In any event, the
server is able to do this safely only when the nfs_lockowner no
longer is being utilized by the client. The server may choose to
hold the nfs_lockowner state in the event that retransmitted requests
are received. However, the period to hold this state is
implementation specific.
In the case that a LOCK, LOCKU, OPEN_DOWNGRADE, or CLOSE is
retransmitted after the server has previously released the
nfs_lockowner state, the server will find that the nfs_lockowner has
no files open and an error will be returned to the client. If the
nfs_lockowner does have a file open, the stateid will not match and
again an error is returned to the client.
In the case that an OPEN is retransmitted and the nfs_lockowner is
being used for the first time or the nfs_lockowner state has been
previously released by the server, the use of the OPEN_CONFIRM
operation will prevent incorrect behavior. When the server observes
the use of the nfs_lockowner for the first time, it will direct the
client to perform the OPEN_CONFIRM for the corresponding OPEN. This
sequence establishes the use of an nfs_lockowner and associated
sequence number. See the section "OPEN_CONFIRM - Confirm Open" for
further details.
8.2. Lock Ranges
The protocol allows a lock owner to request a lock with one byte
range and then either upgrade or unlock a sub-range of the initial
lock. It is expected that this will be an uncommon type of request.
In any case, servers or server file systems may not be able to
support sub-range lock semantics. In the event that a server
receives a locking request that represents a sub-range of current
locking state for the lock owner, the server is allowed to return the
error NFS4ERR_LOCK_RANGE to signify that it does not support sub-
range lock operations. Therefore, the client should be prepared to
receive this error and, if appropriate, report the error to the
requesting application.
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The client is discouraged from combining multiple independent locking
ranges that happen to be adjacent into a single request since the
server may not support sub-range requests and for reasons related to
the recovery of file locking state in the event of server failure.
As discussed in the section "Server Failure and Recovery" below, the
server may employ certain optimizations during recovery that work
effectively only when the client's behavior during lock recovery is
similar to the client's locking behavior prior to server failure.
8.3. Blocking Locks
Some clients require the support of blocking locks. The NFS version
4 protocol must not rely on a callback mechanism and therefore is
unable to notify a client when a previously denied lock has been
granted. Clients have no choice but to continually poll for the
lock. This presents a fairness problem. Two new lock types are
added, READW and WRITEW, and are used to indicate to the server that
the client is requesting a blocking lock. The server should maintain
an ordered list of pending blocking locks. When the conflicting lock
is released, the server may wait the lease period for the first
waiting client to re-request the lock. After the lease period
expires the next waiting client request is allowed the lock. Clients
are required to poll at an interval sufficiently small that it is
likely to acquire the lock in a timely manner. The server is not
required to maintain a list of pending blocked locks as it is used to
increase fairness and not correct operation. Because of the
unordered nature of crash recovery, storing of lock state to stable
storage would be required to guarantee ordered granting of blocking
locks.
Servers may also note the lock types and delay returning denial of
the request to allow extra time for a conflicting lock to be
released, allowing a successful return. In this way, clients can
avoid the burden of needlessly frequent polling for blocking locks.
The server should take care in the length of delay in the event the
client retransmits the request.
8.4. Lease Renewal
The purpose of a lease is to allow a server to remove stale locks
that are held by a client that has crashed or is otherwise
unreachable. It is not a mechanism for cache consistency and lease
renewals may not be denied if the lease interval has not expired.
The following events cause implicit renewal of all of the leases for
a given client (i.e. all those sharing a given clientid). Each of
these is a positive indication that the client is still active and
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that the associated state held at the server, for the client, is
still valid.
o An OPEN with a valid clientid.
o Any operation made with a valid stateid (CLOSE, DELEGRETURN, LOCK,
LOCKU, OPEN, OPEN_CONFIRM, READ, RENEW, SETATTR, WRITE). This
does not include the special stateids of all bits 0 or all bits 1.
Note that if the client had restarted or rebooted, the client
would not be making these requests without issuing the
SETCLIENTID operation. The use of the SETCLIENTID operation
(possibly with the addition of the optional SETCLIENTID_CONFIRM
operation) notifies the server to drop the locking state
associated with the client.
If the server has rebooted, the stateids (NFS4ERR_STALE_STATEID
error) or the clientid (NFS4ERR_STALE_CLIENTID error) will not
be valid hence preventing spurious renewals.
This approach allows for low overhead lease renewal which scales
well. In the typical case no extra RPC calls are required for lease
renewal and in the worst case one RPC is required every lease period
(i.e. a RENEW operation). The number of locks held by the client is
not a factor since all state for the client is involved with the
lease renewal action.
Since all operations that create a new lease also renew existing
leases, the server must maintain a common lease expiration time for
all valid leases for a given client. This lease time can then be
easily updated upon implicit lease renewal actions.
8.5. Crash Recovery
The important requirement in crash recovery is that both the client
and the server know when the other has failed. Additionally, it is
required that a client sees a consistent view of data across server
restarts or reboots. All READ and WRITE operations that may have
been queued within the client or network buffers must wait until the
client has successfully recovered the locks protecting the READ and
WRITE operations.
8.5.1. Client Failure and Recovery
In the event that a client fails, the server may recover the client's
locks when the associated leases have expired. Conflicting locks
from another client may only be granted after this lease expiration.
If the client is able to restart or reinitialize within the lease
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period the client may be forced to wait the remainder of the lease
period before obtaining new locks.
To minimize client delay upon restart, lock requests are associated
with an instance of the client by a client supplied verifier. This
verifier is part of the initial SETCLIENTID call made by the client.
The server returns a clientid as a result of the SETCLIENTID
operation. The client then confirms the use of the verifier with
SETCLIENTID_CONFIRM. The clientid in combination with an opaque
owner field is then used by the client to identify the lock owner for
OPEN. This chain of associations is then used to identify all locks
for a particular client.
Since the verifier will be changed by the client upon each
initialization, the server can compare a new verifier to the verifier
associated with currently held locks and determine that they do not
match. This signifies the client's new instantiation and subsequent
loss of locking state. As a result, the server is free to release
all locks held which are associated with the old clientid which was
derived from the old verifier.
For secure environments, a change in the verifier must only cause the
release of locks associated with the authenticated requester. This
is required to prevent a rogue entity from freeing otherwise valid
locks.
Note that the verifier must have the same uniqueness properties of
the verifier for the COMMIT operation.
8.5.2. Server Failure and Recovery
If the server loses locking state (usually as a result of a restart
or reboot), it must allow clients time to discover this fact and re-
establish the lost locking state. The client must be able to re-
establish the locking state without having the server deny valid
requests because the server has granted conflicting access to another
client. Likewise, if there is the possibility that clients have not
yet re-established their locking state for a file, the server must
disallow READ and WRITE operations for that file. The duration of
this recovery period is equal to the duration of the lease period.
A client can determine that server failure (and thus loss of locking
state) has occurred, when it receives one of two errors. The
NFS4ERR_STALE_STATEID error indicates a stateid invalidated by a
reboot or restart. The NFS4ERR_STALE_CLIENTID error indicates a
clientid invalidated by reboot or restart. When either of these are
received, the client must establish a new clientid (See the section
"Client ID") and re-establish the locking state as discussed below.
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The period of special handling of locking and READs and WRITEs, equal
in duration to the lease period, is referred to as the "grace
period". During the grace period, clients recover locks and the
associated state by reclaim-type locking requests (i.e. LOCK requests
with reclaim set to true and OPEN operations with a claim type of
CLAIM_PREVIOUS). During the grace period, the server must reject
READ and WRITE operations and non-reclaim locking requests (i.e.
other LOCK and OPEN operations) with an error of NFS4ERR_GRACE.
If the server can reliably determine that granting a non-reclaim
request will not conflict with reclamation of locks by other clients,
the NFS4ERR_GRACE error does not have to be returned and the non-
reclaim client request can be serviced. For the server to be able to
service READ and WRITE operations during the grace period, it must
again be able to guarantee that no possible conflict could arise
between an impending reclaim locking request and the READ or WRITE
operation. If the server is unable to offer that guarantee, the
NFS4ERR_GRACE error must be returned to the client.
For a server to provide simple, valid handling during the grace
period, the easiest method is to simply reject all non-reclaim
locking requests and READ and WRITE operations by returning the
NFS4ERR_GRACE error. However, a server may keep information about
granted locks in stable storage. With this information, the server
could determine if a regular lock or READ or WRITE operation can be
safely processed.
For example, if a count of locks on a given file is available in
stable storage, the server can track reclaimed locks for the file and
when all reclaims have been processed, non-reclaim locking requests
may be processed. This way the server can ensure that non-reclaim
locking requests will not conflict with potential reclaim requests.
With respect to I/O requests, if the server is able to determine that
there are no outstanding reclaim requests for a file by information
from stable storage or another similar mechanism, the processing of
I/O requests could proceed normally for the file.
To reiterate, for a server that allows non-reclaim lock and I/O
requests to be processed during the grace period, it MUST determine
that no lock subsequently reclaimed will be rejected and that no lock
subsequently reclaimed would have prevented any I/O operation
processed during the grace period.
Clients should be prepared for the return of NFS4ERR_GRACE errors for
non-reclaim lock and I/O requests. In this case the client should
employ a retry mechanism for the request. A delay (on the order of
several seconds) between retries should be used to avoid overwhelming
the server. Further discussion of the general is included in
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[Floyd]. The client must account for the server that is able to
perform I/O and non-reclaim locking requests within the grace period
as well as those that can not do so.
A reclaim-type locking request outside the server's grace period can
only succeed if the server can guarantee that no conflicting lock or
I/O request has been granted since reboot or restart.
8.5.3. Network Partitions and Recovery
If the duration of a network partition is greater than the lease
period provided by the server, the server will have not received a
lease renewal from the client. If this occurs, the server may free
all locks held for the client. As a result, all stateids held by the
client will become invalid or stale. Once the client is able to
reach the server after such a network partition, all I/O submitted by
the client with the now invalid stateids will fail with the server
returning the error NFS4ERR_EXPIRED. Once this error is received,
the client will suitably notify the application that held the lock.
As a courtesy to the client or as an optimization, the server may
continue to hold locks on behalf of a client for which recent
communication has extended beyond the lease period. If the server
receives a lock or I/O request that conflicts with one of these
courtesy locks, the server must free the courtesy lock and grant the
new request.
If the server continues to hold locks beyond the expiration of a
client's lease, the server MUST employ a method of recording this
fact in its stable storage. Conflicting locks requests from another
client may be serviced after the lease expiration. There are various
scenarios involving server failure after such an event that require
the storage of these lease expirations or network partitions. One
scenario is as follows:
A client holds a lock at the server and encounters a network
partition and is unable to renew the associated lease. A
second client obtains a conflicting lock and then frees the
lock. After the unlock request by the second client, the
server reboots or reinitializes. Once the server recovers, the
network partition heals and the original client attempts to
reclaim the original lock.
In this scenario and without any state information, the server will
allow the reclaim and the client will be in an inconsistent state
because the server or the client has no knowledge of the conflicting
lock.
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The server may choose to store this lease expiration or network
partitioning state in a way that will only identify the client as a
whole. Note that this may potentially lead to lock reclaims being
denied unnecessarily because of a mix of conflicting and non-
conflicting locks. The server may also choose to store information
about each lock that has an expired lease with an associated
conflicting lock. The choice of the amount and type of state
information that is stored is left to the implementor. In any case,
the server must have enough state information to enable correct
recovery from multiple partitions and multiple server failures.
8.6. Recovery from a Lock Request Timeout or Abort
In the event a lock request times out, a client may decide to not
retry the request. The client may also abort the request when the
process for which it was issued is terminated (e.g. in UNIX due to a
signal. It is possible though that the server received the request
and acted upon it. This would change the state on the server without
the client being aware of the change. It is paramount that the
client re-synchronize state with server before it attempts any other
operation that takes a seqid and/or a stateid with the same
nfs_lockowner. This is straightforward to do without a special re-
synchronize operation.
Since the server maintains the last lock request and response
received on the nfs_lockowner, for each nfs_lockowner, the client
should cache the last lock request it sent such that the lock request
did not receive a response. From this, the next time the client does
a lock operation for the nfs_lockowner, it can send the cached
request, if there is one, and if the request was one that established
state (e.g. a LOCK or OPEN operation) the client can follow up with a
request to remove the state (e.g. a LOCKU or CLOSE operation). With
this approach, the sequencing and stateid information on the client
and server for the given nfs_lockowner will re-synchronize and in
turn the lock state will re-synchronize.
8.7. Server Revocation of Locks
At any point, the server can revoke locks held by a client and the
client must be prepared for this event. When the client detects that
its locks have been or may have been revoked, the client is
responsible for validating the state information between itself and
the server. Validating locking state for the client means that it
must verify or reclaim state for each lock currently held.
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The first instance of lock revocation is upon server reboot or re-
initialization. In this instance the client will receive an error
(NFS4ERR_STALE_STATEID or NFS4ERR_STALE_CLIENTID) and the client will
proceed with normal crash recovery as described in the previous
section.
The second lock revocation event is the inability to renew the lease
period. While this is considered a rare or unusual event, the client
must be prepared to recover. Both the server and client will be able
to detect the failure to renew the lease and are capable of
recovering without data corruption. For the server, it tracks the
last renewal event serviced for the client and knows when the lease
will expire. Similarly, the client must track operations which will
renew the lease period. Using the time that each such request was
sent and the time that the corresponding reply was received, the
client should bound the time that the corresponding renewal could
have occurred on the server and thus determine if it is possible that
a lease period expiration could have occurred.
The third lock revocation event can occur as a result of
administrative intervention within the lease period. While this is
considered a rare event, it is possible that the server's
administrator has decided to release or revoke a particular lock held
by the client. As a result of revocation, the client will receive an
error of NFS4ERR_EXPIRED and the error is received within the lease
period for the lock. In this instance the client may assume that
only the nfs_lockowner's locks have been lost. The client notifies
the lock holder appropriately. The client may not assume the lease
period has been renewed as a result of failed operation.
When the client determines the lease period may have expired, the
client must mark all locks held for the associated lease as
"unvalidated". This means the client has been unable to re-establish
or confirm the appropriate lock state with the server. As described
in the previous section on crash recovery, there are scenarios in
which the server may grant conflicting locks after the lease period
has expired for a client. When it is possible that the lease period
has expired, the client must validate each lock currently held to
ensure that a conflicting lock has not been granted. The client may
accomplish this task by issuing an I/O request, either a pending I/O
or a zero-length read, specifying the stateid associated with the
lock in question. If the response to the request is success, the
client has validated all of the locks governed by that stateid and
re-established the appropriate state between itself and the server.
If the I/O request is not successful, then one or more of the locks
associated with the stateid was revoked by the server and the client
must notify the owner.
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8.8. Share Reservations
A share reservation is a mechanism to control access to a file. It
is a separate and independent mechanism from record locking. When a
client opens a file, it issues an OPEN operation to the server
specifying the type of access required (READ, WRITE, or BOTH) and the
type of access to deny others (deny NONE, READ, WRITE, or BOTH). If
the OPEN fails the client will fail the application's open request.
Pseudo-code definition of the semantics:
if ((request.access & file_state.deny)) ||
(request.deny & file_state.access))
return (NFS4ERR_DENIED)
The constants used for the OPEN and OPEN_DOWNGRADE operations for the
access and deny fields are as follows:
const OPEN4_SHARE_ACCESS_READ = 0x00000001;
const OPEN4_SHARE_ACCESS_WRITE = 0x00000002;
const OPEN4_SHARE_ACCESS_BOTH = 0x00000003;
const OPEN4_SHARE_DENY_NONE = 0x00000000;
const OPEN4_SHARE_DENY_READ = 0x00000001;
const OPEN4_SHARE_DENY_WRITE = 0x00000002;
const OPEN4_SHARE_DENY_BOTH = 0x00000003;
8.9. OPEN/CLOSE Operations
To provide correct share semantics, a client MUST use the OPEN
operation to obtain the initial filehandle and indicate the desired
access and what if any access to deny. Even if the client intends to
use a stateid of all 0's or all 1's, it must still obtain the
filehandle for the regular file with the OPEN operation so the
appropriate share semantics can be applied. For clients that do not
have a deny mode built into their open programming interfaces, deny
equal to NONE should be used.
The OPEN operation with the CREATE flag, also subsumes the CREATE
operation for regular files as used in previous versions of the NFS
protocol. This allows a create with a share to be done atomically.
The CLOSE operation removes all share locks held by the nfs_lockowner
on that file. If record locks are held, the client SHOULD release
all locks before issuing a CLOSE. The server MAY free all
outstanding locks on CLOSE but some servers may not support the CLOSE
of a file that still has record locks held. The server MUST return
failure if any locks would exist after the CLOSE.
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The LOOKUP operation will return a filehandle without establishing
any lock state on the server. Without a valid stateid, the server
will assume the client has the least access. For example, a file
opened with deny READ/WRITE cannot be accessed using a filehandle
obtained through LOOKUP because it would not have a valid stateid
(i.e. using a stateid of all bits 0 or all bits 1).
8.10. Open Upgrade and Downgrade
When an OPEN is done for a file and the lockowner for which the open
is being done already has the file open, the result is to upgrade the
open file status maintained on the server to include the access and
deny bits specified by the new OPEN as well as those for the existing
OPEN. The result is that there is one open file, as far as the
protocol is concerned, and it includes the union of the access and
deny bits for all of the OPEN requests completed. Only a single
CLOSE will be done to reset the effects of both OPEN's. Note that
the client, when issuing the OPEN, may not know that the same file is
in fact being opened. The above only applies if both OPEN's result
in the OPEN'ed object being designated by the same filehandle.
When the server chooses to export multiple filehandles corresponding
to the same file object and returns different filehandles on two
different OPEN's of the same file object, the server MUST NOT "OR"
together the access and deny bits and coalesce the two open files.
Instead the server must maintain separate OPEN's with separate
stateid's and will require separate CLOSE's to free them.
When multiple open files on the client are merged into a single open
file object on the server, the close of one of the open files (on the
client) may necessitate change of the access and deny status of the
open file on the server. This is because the union of the access and
deny bits for the remaining open's may be smaller (i.e. a proper
subset) than previously. The OPEN_DOWNGRADE operation is used to
make the necessary change and the client should use it to update the
server so that share reservation requests by other clients are
handled properly.
8.11. Short and Long Leases
When determining the time period for the server lease, the usual
lease tradeoffs apply. Short leases are good for fast server
recovery at a cost of increased RENEW or READ (with zero length)
requests. Longer leases are certainly kinder and gentler to large
internet servers trying to handle very large numbers of clients. The
number of RENEW requests drop in proportion to the lease time. The
disadvantages of long leases are slower recovery after server failure
(server must wait for leases to expire and grace period before
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granting new lock requests) and increased file contention (if client
fails to transmit an unlock request then server must wait for lease
expiration before granting new locks).
Long leases are usable if the server is able to store lease state in
non-volatile memory. Upon recovery, the server can reconstruct the
lease state from its non-volatile memory and continue operation with
its clients and therefore long leases are not an issue.
8.12. Clocks and Calculating Lease Expiration
To avoid the need for synchronized clocks, lease times are granted by
the server as a time delta. However, there is a requirement that the
client and server clocks do not drift excessively over the duration
of the lock. There is also the issue of propagation delay across the
network which could easily be several hundred milliseconds as well as
the possibility that requests will be lost and need to be
retransmitted.
To take propagation delay into account, the client should subtract it
from lease times (e.g. if the client estimates the one-way
propagation delay as 200 msec, then it can assume that the lease is
already 200 msec old when it gets it). In addition, it will take
another 200 msec to get a response back to the server. So the client
must send a lock renewal or write data back to the server 400 msec
before the lease would expire.
8.13. Migration, Replication and State
When responsibility for handling a given file system is transferred
to a new server (migration) or the client chooses to use an alternate
server (e.g. in response to server unresponsiveness) in the context
of file system replication, the appropriate handling of state shared
between the client and server (i.e. locks, leases, stateid's, and
clientid's) is as described below. The handling differs between
migration and replication. For related discussion of file server
state and recover of such see the sections under "File Locking and
Share Reservations"
8.13.1. Migration and State
In the case of migration, the servers involved in the migration of a
file system SHOULD transfer all server state from the original to the
new server. This must be done in a way that is transparent to the
client. This state transfer will ease the client's transition when a
file system migration occurs. If the servers are successful in
transferring all state, the client will continue to use stateid's
assigned by the original server. Therefore the new server must
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recognize these stateid's as valid. This holds true for the clientid
as well. Since responsibility for an entire file system is
transferred with a migration event, there is no possibility that
conflicts will arise on the new server as a result of the transfer of
locks.
As part of the transfer of information between servers, leases would
be transferred as well. The leases being transferred to the new
server will typically have a different expiration time from those for
the same client, previously on the new server. To maintain the
property that all leases on a given server for a given client expire
at the same time, the server should advance the expiration time to
the later of the leases being transferred or the leases already
present. This allows the client to maintain lease renewal of both
classes without special effort.
The servers may choose not to transfer the state information upon
migration. However, this choice is discouraged. In this case, when
the client presents state information from the original server, the
client must be prepared to receive either NFS4ERR_STALE_CLIENTID or
NFS4ERR_STALE_STATEID from the new server. The client should then
recover its state information as it normally would in response to a
server failure. The new server must take care to allow for the
recovery of state information as it would in the event of server
restart.
8.13.2. Replication and State
Since client switch-over in the case of replication is not under
server control, the handling of state is different. In this case,
leases, stateid's and clientid's do not have validity across a
transition from one server to another. The client must re-establish
its locks on the new server. This can be compared to the re-
establishment of locks by means of reclaim-type requests after a
server reboot. The difference is that the server has no provision to
distinguish requests reclaiming locks from those obtaining new locks
or to defer the latter. Thus, a client re-establishing a lock on the
new server (by means of a LOCK or OPEN request), may have the
requests denied due to a conflicting lock. Since replication is
intended for read-only use of filesystems, such denial of locks
should not pose large difficulties in practice. When an attempt to
re-establish a lock on a new server is denied, the client should
treat the situation as if his original lock had been revoked.
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8.13.3. Notification of Migrated Lease
In the case of lease renewal, the client may not be submitting
requests for a file system that has been migrated to another server.
This can occur because of the implicit lease renewal mechanism. The
client renews leases for all file systems when submitting a request
to any one file system at the server.
In order for the client to schedule renewal of leases that may have
been relocated to the new server, the client must find out about
lease relocation before those leases expire. To accomplish this, all
operations which implicitly renew leases for a client (i.e. OPEN,
CLOSE, READ, WRITE, RENEW, LOCK, LOCKT, LOCKU), will return the error
NFS4ERR_LEASE_MOVED if responsibility for any of the leases to be
renewed has been transferred to a new server. This condition will
continue until the client receives an NFS4ERR_MOVED error and the
server receives the subsequent GETATTR(fs_locations) for an access to
each file system for which a lease has been moved to a new server.
When a client receives an NFS4ERR_LEASE_MOVED error, it should
perform some operation, such as a RENEW, on each file system
associated with the server in question. When the client receives an
NFS4ERR_MOVED error, the client can follow the normal process to
obtain the new server information (through the fs_locations
attribute) and perform renewal of those leases on the new server. If
the server has not had state transferred to it transparently, it will
receive either NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID from
the new server, as described above, and can then recover state
information as it does in the event of server failure.
9. Client-Side Caching
Client-side caching of data, of file attributes, and of file names is
essential to providing good performance with the NFS protocol.
Providing distributed cache coherence is a difficult problem and
previous versions of the NFS protocol have not attempted it.
Instead, several NFS client implementation techniques have been used
to reduce the problems that a lack of coherence poses for users.
These techniques have not been clearly defined by earlier protocol
specifications and it is often unclear what is valid or invalid
client behavior.
The NFS version 4 protocol uses many techniques similar to those that
have been used in previous protocol versions. The NFS version 4
protocol does not provide distributed cache coherence. However, it
defines a more limited set of caching guarantees to allow locks and
share reservations to be used without destructive interference from
client side caching.
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In addition, the NFS version 4 protocol introduces a delegation
mechanism which allows many decisions normally made by the server to
be made locally by clients. This mechanism provides efficient
support of the common cases where sharing is infrequent or where
sharing is read-only.
9.1. Performance Challenges for Client-Side Caching
Caching techniques used in previous versions of the NFS protocol have
been successful in providing good performance. However, several
scalability challenges can arise when those techniques are used with
very large numbers of clients. This is particularly true when
clients are geographically distributed which classically increases
the latency for cache revalidation requests.
The previous versions of the NFS protocol repeat their file data
cache validation requests at the time the file is opened. This
behavior can have serious performance drawbacks. A common case is
one in which a file is only accessed by a single client. Therefore,
sharing is infrequent.
In this case, repeated reference to the server to find that no
conflicts exist is expensive. A better option with regards to
performance is to allow a client that repeatedly opens a file to do
so without reference to the server. This is done until potentially
conflicting operations from another client actually occur.
A similar situation arises in connection with file locking. Sending
file lock and unlock requests to the server as well as the read and
write requests necessary to make data caching consistent with the
locking semantics (see the section "Data Caching and File Locking")
can severely limit performance. When locking is used to provide
protection against infrequent conflicts, a large penalty is incurred.
This penalty may discourage the use of file locking by applications.
The NFS version 4 protocol provides more aggressive caching
strategies with the following design goals:
o Compatibility with a large range of server semantics.
o Provide the same caching benefits as previous versions of the NFS
protocol when unable to provide the more aggressive model.
o Requirements for aggressive caching are organized so that a large
portion of the benefit can be obtained even when not all of the
requirements can be met.
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The appropriate requirements for the server are discussed in later
sections in which specific forms of caching are covered. (see the
section "Open Delegation").
9.2. Delegation and Callbacks
Recallable delegation of server responsibilities for a file to a
client improves performance by avoiding repeated requests to the
server in the absence of inter-client conflict. With the use of a
"callback" RPC from server to client, a server recalls delegated
responsibilities when another client engages in sharing of a
delegated file.
A delegation is passed from the server to the client, specifying the
object of the delegation and the type of delegation. There are
different types of delegations but each type contains a stateid to be
used to represent the delegation when performing operations that
depend on the delegation. This stateid is similar to those
associated with locks and share reservations but differs in that the
stateid for a delegation is associated with a clientid and may be
used on behalf of all the nfs_lockowners for the given client. A
delegation is made to the client as a whole and not to any specific
process or thread of control within it.
Because callback RPCs may not work in all environments (due to
firewalls, for example), correct protocol operation does not depend
on them. Preliminary testing of callback functionality by means of a
CB_NULL procedure determines whether callbacks can be supported. The
CB_NULL procedure checks the continuity of the callback path. A
server makes a preliminary assessment of callback availability to a
given client and avoids delegating responsibilities until it has
determined that callbacks are supported. Because the granting of a
delegation is always conditional upon the absence of conflicting
access, clients must not assume that a delegation will be granted and
they must always be prepared for OPENs to be processed without any
delegations being granted.
Once granted, a delegation behaves in most ways like a lock. There
is an associated lease that is subject to renewal together with all
of the other leases held by that client.
Unlike locks, an operation by a second client to a delegated file
will cause the server to recall a delegation through a callback.
On recall, the client holding the delegation must flush modified
state (such as modified data) to the server and return the
delegation. The conflicting request will not receive a response
until the recall is complete. The recall is considered complete when
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the client returns the delegation or the server times out on the
recall and revokes the delegation as a result of the timeout.
Following the resolution of the recall, the server has the
information necessary to grant or deny the second client's request.
At the time the client receives a delegation recall, it may have
substantial state that needs to be flushed to the server. Therefore,
the server should allow sufficient time for the delegation to be
returned since it may involve numerous RPCs to the server. If the
server is able to determine that the client is diligently flushing
state to the server as a result of the recall, the server may extend
the usual time allowed for a recall. However, the time allowed for
recall completion should not be unbounded.
An example of this is when responsibility to mediate opens on a given
file is delegated to a client (see the section "Open Delegation").
The server will not know what opens are in effect on the client.
Without this knowledge the server will be unable to determine if the
access and deny state for the file allows any particular open until
the delegation for the file has been returned.
A client failure or a network partition can result in failure to
respond to a recall callback. In this case, the server will revoke
the delegation which in turn will render useless any modified state
still on the client.
9.2.1. Delegation Recovery
There are three situations that delegation recovery must deal with:
o Client reboot or restart
o Server reboot or restart
o Network partition (full or callback-only)
In the event the client reboots or restarts, the failure to renew
leases will result in the revocation of record locks and share
reservations. Delegations, however, may be treated a bit
differently.
There will be situations in which delegations will need to be
reestablished after a client reboots or restarts. The reason for
this is the client may have file data stored locally and this data
was associated with the previously held delegations. The client will
need to reestablish the appropriate file state on the server.
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To allow for this type of client recovery, the server may extend the
period for delegation recovery beyond the typical lease expiration
period. This implies that requests from other clients that conflict
with these delegations will need to wait. Because the normal recall
process may require significant time for the client to flush changed
state to the server, other clients need be prepared for delays that
occur because of a conflicting delegation. This longer interval
would increase the window for clients to reboot and consult stable
storage so that the delegations can be reclaimed. For open
delegations, such delegations are reclaimed using OPEN with a claim
type of CLAIM_DELEGATE_PREV. (see the sections on "Data Caching and
Revocation" and "Operation 18: OPEN" for discussion of open
delegation and the details of OPEN respectively).
When the server reboots or restarts, delegations are reclaimed (using
the OPEN operation with CLAIM_DELEGATE_PREV) in a similar fashion to
record locks and share reservations. However, there is a slight
semantic difference. In the normal case if the server decides that a
delegation should not be granted, it performs the requested action
(e.g. OPEN) without granting any delegation. For reclaim, the server
grants the delegation but a special designation is applied so that
the client treats the delegation as having been granted but recalled
by the server. Because of this, the client has the duty to write all
modified state to the server and then return the delegation. This
process of handling delegation reclaim reconciles three principles of
the NFS Version 4 protocol:
o Upon reclaim, a client reporting resources assigned to it by an
earlier server instance must be granted those resources.
o The server has unquestionable authority to determine whether
delegations are to be granted and, once granted, whether they are
to be continued.
o The use of callbacks is not to be depended upon until the client
has proven its ability to receive them.
When a network partition occurs, delegations are subject to freeing
by the server when the lease renewal period expires. This is similar
to the behavior for locks and share reservations. For delegations,
however, the server may extend the period in which conflicting
requests are held off. Eventually the occurrence of a conflicting
request from another client will cause revocation of the delegation.
A loss of the callback path (e.g. by later network configuration
change) will have the same effect. A recall request will fail and
revocation of the delegation will result.
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A client normally finds out about revocation of a delegation when it
uses a stateid associated with a delegation and receives the error
NFS4ERR_EXPIRED. It also may find out about delegation revocation
after a client reboot when it attempts to reclaim a delegation and
receives that same error. Note that in the case of a revoked write
open delegation, there are issues because data may have been modified
by the client whose delegation is revoked and separately by other
clients. See the section "Revocation Recovery for Write Open
Delegation" for a discussion of such issues. Note also that when
delegations are revoked, information about the revoked delegation
will be written by the server to stable storage (as described in the
section "Crash Recovery"). This is done to deal with the case in
which a server reboots after revoking a delegation but before the
client holding the revoked delegation is notified about the
revocation.
9.3. Data Caching
When applications share access to a set of files, they need to be
implemented so as to take account of the possibility of conflicting
access by another application. This is true whether the applications
in question execute on different clients or reside on the same
client.
Share reservations and record locks are the facilities the NFS
version 4 protocol provides to allow applications to coordinate
access by providing mutual exclusion facilities. The NFS version 4
protocol's data caching must be implemented such that it does not
invalidate the assumptions that those using these facilities depend
upon.
9.3.1. Data Caching and OPENs
In order to avoid invalidating the sharing assumptions that
applications rely on, NFS version 4 clients should not provide cached
data to applications or modify it on behalf of an application when it
would not be valid to obtain or modify that same data via a READ or
WRITE operation.
Furthermore, in the absence of open delegation (see the section "Open
Delegation") two additional rules apply. Note that these rules are
obeyed in practice by many NFS version 2 and version 3 clients.
o First, cached data present on a client must be revalidated after
doing an OPEN. This is to ensure that the data for the OPENed
file is still correctly reflected in the client's cache. This
validation must be done at least when the client's OPEN operation
includes DENY=WRITE or BOTH thus terminating a period in which
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other clients may have had the opportunity to open the file with
WRITE access. Clients may choose to do the revalidation more
often (i.e. at OPENs specifying DENY=NONE) to parallel the NFS
version 3 protocol's practice for the benefit of users assuming
this degree of cache revalidation.
o Second, modified data must be flushed to the server before closing
a file OPENed for write. This is complementary to the first rule.
If the data is not flushed at CLOSE, the revalidation done after
client OPENs as file is unable to achieve its purpose. The other
aspect to flushing the data before close is that the data must be
committed to stable storage, at the server, before the CLOSE
operation is requested by the client. In the case of a server
reboot or restart and a CLOSEd file, it may not be possible to
retransmit the data to be written to the file. Hence, this
requirement.
9.3.2. Data Caching and File Locking
For those applications that choose to use file locking instead of
share reservations to exclude inconsistent file access, there is an
analogous set of constraints that apply to client side data caching.
These rules are effective only if the file locking is used in a way
that matches in an equivalent way the actual READ and WRITE
operations executed. This is as opposed to file locking that is
based on pure convention. For example, it is possible to manipulate
a two-megabyte file by dividing the file into two one-megabyte
regions and protecting access to the two regions by file locks on
bytes zero and one. A lock for write on byte zero of the file would
represent the right to do READ and WRITE operations on the first
region. A lock for write on byte one of the file would represent the
right to do READ and WRITE operations on the second region. As long
as all applications manipulating the file obey this convention, they
will work on a local file system. However, they may not work with
the NFS version 4 protocol unless clients refrain from data caching.
The rules for data caching in the file locking environment are:
o First, when a client obtains a file lock for a particular region,
the data cache corresponding to that region (if any cache data
exists) must be revalidated. If the change attribute indicates
that the file may have been updated since the cached data was
obtained, the client must flush or invalidate the cached data for
the newly locked region. A client might choose to invalidate all
of non-modified cached data that it has for the file but the only
requirement for correct operation is to invalidate all of the data
in the newly locked region.
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o Second, before releasing a write lock for a region, all modified
data for that region must be flushed to the server. The modified
data must also be written to stable storage.
Note that flushing data to the server and the invalidation of cached
data must reflect the actual byte ranges locked or unlocked.
Rounding these up or down to reflect client cache block boundaries
will cause problems if not carefully done. For example, writing a
modified block when only half of that block is within an area being
unlocked may cause invalid modification to the region outside the
unlocked area. This, in turn, may be part of a region locked by
another client. Clients can avoid this situation by synchronously
performing portions of write operations that overlap that portion
(initial or final) that is not a full block. Similarly, invalidating
a locked area which is not an integral number of full buffer blocks
would require the client to read one or two partial blocks from the
server if the revalidation procedure shows that the data which the
client possesses may not be valid.
The data that is written to the server as a pre-requisite to the
unlocking of a region must be written, at the server, to stable
storage. The client may accomplish this either with synchronous
writes or by following asynchronous writes with a COMMIT operation.
This is required because retransmission of the modified data after a
server reboot might conflict with a lock held by another client.
A client implementation may choose to accommodate applications which
use record locking in non-standard ways (e.g. using a record lock as
a global semaphore) by flushing to the server more data upon an LOCKU
than is covered by the locked range. This may include modified data
within files other than the one for which the unlocks are being done.
In such cases, the client must not interfere with applications whose
READs and WRITEs are being done only within the bounds of record
locks which the application holds. For example, an application locks
a single byte of a file and proceeds to write that single byte. A
client that chose to handle a LOCKU by flushing all modified data to
the server could validly write that single byte in response to an
unrelated unlock. However, it would not be valid to write the entire
block in which that single written byte was located since it includes
an area that is not locked and might be locked by another client.
Client implementations can avoid this problem by dividing files with
modified data into those for which all modifications are done to
areas covered by an appropriate record lock and those for which there
are modifications not covered by a record lock. Any writes done for
the former class of files must not include areas not locked and thus
not modified on the client.
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9.3.3. Data Caching and Mandatory File Locking
Client side data caching needs to respect mandatory file locking when
it is in effect. The presence of mandatory file locking for a given
file is indicated in the result flags for an OPEN. When mandatory
locking is in effect for a file, the client must check for an
appropriate file lock for data being read or written. If a lock
exists for the range being read or written, the client may satisfy
the request using the client's validated cache. If an appropriate
file lock is not held for the range of the read or write, the read or
write request must not be satisfied by the client's cache and the
request must be sent to the server for processing. When a read or
write request partially overlaps a locked region, the request should
be subdivided into multiple pieces with each region (locked or not)
treated appropriately.
9.3.4. Data Caching and File Identity
When clients cache data, the file data needs to organized according
to the file system object to which the data belongs. For NFS version
3 clients, the typical practice has been to assume for the purpose of
caching that distinct filehandles represent distinct file system
objects. The client then has the choice to organize and maintain the
data cache on this basis.
In the NFS version 4 protocol, there is now the possibility to have
significant deviations from a "one filehandle per object" model
because a filehandle may be constructed on the basis of the object's
pathname. Therefore, clients need a reliable method to determine if
two filehandles designate the same file system object. If clients
were simply to assume that all distinct filehandles denote distinct
objects and proceed to do data caching on this basis, caching
inconsistencies would arise between the distinct client side objects
which mapped to the same server side object.
By providing a method to differentiate filehandles, the NFS version 4
protocol alleviates a potential functional regression in comparison
with the NFS version 3 protocol. Without this method, caching
inconsistencies within the same client could occur and this has not
been present in previous versions of the NFS protocol. Note that it
is possible to have such inconsistencies with applications executing
on multiple clients but that is not the issue being addressed here.
For the purposes of data caching, the following steps allow an NFS
version 4 client to determine whether two distinct filehandles denote
the same server side object:
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o If GETATTR directed to two filehandles have different values of
the fsid attribute, then the filehandles represent distinct
objects.
o If GETATTR for any file with an fsid that matches the fsid of the
two filehandles in question returns a unique_handles attribute
with a value of TRUE, then the two objects are distinct.
o If GETATTR directed to the two filehandles does not return the
fileid attribute for one or both of the handles, then the it
cannot be determined whether the two objects are the same.
Therefore, operations which depend on that knowledge (e.g. client
side data caching) cannot be done reliably.
o If GETATTR directed to the two filehandles returns different
values for the fileid attribute, then they are distinct objects.
o Otherwise they are the same object.
9.4. Open Delegation
When a file is being OPENed, the server may delegate further handling
of opens and closes for that file to the opening client. Any such
delegation is recallable, since the circumstances that allowed for
the delegation are subject to change. In particular, the server may
receive a conflicting OPEN from another client, the server must
recall the delegation before deciding whether the OPEN from the other
client may be granted. Making a delegation is up to the server and
clients should not assume that any particular OPEN either will or
will not result in an open delegation. The following is a typical
set of conditions that servers might use in deciding whether OPEN
should be delegated:
o The client must be able to respond to the server's callback
requests. The server will use the CB_NULL procedure for a test of
callback ability.
o The client must have responded properly to previous recalls.
o There must be no current open conflicting with the requested
delegation.
o There should be no current delegation that conflicts with the
delegation being requested.
o The probability of future conflicting open requests should be low
based on the recent history of the file.
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o The existence of any server-specific semantics of OPEN/CLOSE that
would make the required handling incompatible with the prescribed
handling that the delegated client would apply (see below).
There are two types of open delegations, read and write. A read open
delegation allows a client to handle, on its own, requests to open a
file for reading that do not deny read access to others. Multiple
read open delegations may be outstanding simultaneously and do not
conflict. A write open delegation allows the client to handle, on
its own, all opens. Only one write open delegation may exist for a
given file at a given time and it is inconsistent with any read open
delegations.
When a client has a read open delegation, it may not make any changes
to the contents or attributes of the file but it is assured that no
other client may do so. When a client has a write open delegation,
it may modify the file data since no other client will be accessing
the file's data. The client holding a write delegation may only
affect file attributes which are intimately connected with the file
data: object_size, time_modify, change.
When a client has an open delegation, it does not send OPENs or
CLOSEs to the server but updates the appropriate status internally.
For a read open delegation, opens that cannot be handled locally
(opens for write or that deny read access) must be sent to the
server.
When an open delegation is made, the response to the OPEN contains an
open delegation structure which specifies the following:
o the type of delegation (read or write)
o space limitation information to control flushing of data on close
(write open delegation only, see the section "Open Delegation and
Data Caching")
o an nfsace4 specifying read and write permissions
o a stateid to represent the delegation for READ and WRITE
The stateid is separate and distinct from the stateid for the OPEN
proper. The standard stateid, unlike the delegation stateid, is
associated with a particular nfs_lockowner and will continue to be
valid after the delegation is recalled and the file remains open.
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When a request internal to the client is made to open a file and open
delegation is in effect, it will be accepted or rejected solely on
the basis of the following conditions. Any requirement for other
checks to be made by the delegate should result in open delegation
being denied so that the checks can be made by the server itself.
o The access and deny bits for the request and the file as described
in the section "Share Reservations".
o The read and write permissions as determined below.
The nfsace4 passed with delegation can be used to avoid frequent
ACCESS calls. The permission check should be as follows:
o If the nfsace4 indicates that the open may be done, then it should
be granted without reference to the server.
o If the nfsace4 indicates that the open may not be done, then an
ACCESS request must be sent to the server to obtain the definitive
answer.
The server may return an nfsace4 that is more restrictive than the
actual ACL of the file. This includes an nfsace4 that specifies
denial of all access. Note that some common practices such as
mapping the traditional user "root" to the user "nobody" may make it
incorrect to return the actual ACL of the file in the delegation
response.
The use of delegation together with various other forms of caching
creates the possibility that no server authentication will ever be
performed for a given user since all of the user's requests might be
satisfied locally. Where the client is depending on the server for
authentication, the client should be sure authentication occurs for
each user by use of the ACCESS operation. This should be the case
even if an ACCESS operation would not be required otherwise. As
mentioned before, the server may enforce frequent authentication by
returning an nfsace4 denying all access with every open delegation.
9.4.1. Open Delegation and Data Caching
OPEN delegation allows much of the message overhead associated with
the opening and closing files to be eliminated. An open when an open
delegation is in effect does not require that a validation message be
sent to the server. The continued endurance of the "read open
delegation" provides a guarantee that no OPEN for write and thus no
write has occurred. Similarly, when closing a file opened for write
and if write open delegation is in effect, the data written does not
have to be flushed to the server until the open delegation is
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recalled. The continued endurance of the open delegation provides a
guarantee that no open and thus no read or write has been done by
another client.
For the purposes of open delegation, READs and WRITEs done without an
OPEN are treated as the functional equivalents of a corresponding
type of OPEN. This refers to the READs and WRITEs that use the
special stateids consisting of all zero bits or all one bits.
Therefore, READs or WRITEs with a special stateid done by another
client will force the server to recall a write open delegation. A
WRITE with a special stateid done by another client will force a
recall of read open delegations.
With delegations, a client is able to avoid writing data to the
server when the CLOSE of a file is serviced. The CLOSE operation is
the usual point at which the client is notified of a lack of stable
storage for the modified file data generated by the application. At
the CLOSE, file data is written to the server and through normal
accounting the server is able to determine if the available file
system space for the data has been exceeded (i.e. server returns
NFS4ERR_NOSPC or NFS4ERR_DQUOT). This accounting includes quotas.
The introduction of delegations requires that a alternative method be
in place for the same type of communication to occur between client
and server.
In the delegation response, the server provides either the limit of
the size of the file or the number of modified blocks and associated
block size. The server must ensure that the client will be able to
flush data to the server of a size equal to that provided in the
original delegation. The server must make this assurance for all
outstanding delegations. Therefore, the server must be careful in
its management of available space for new or modified data taking
into account available file system space and any applicable quotas.
The server can recall delegations as a result of managing the
available file system space. The client should abide by the server's
state space limits for delegations. If the client exceeds the stated
limits for the delegation, the server's behavior is undefined.
Based on server conditions, quotas or available file system space,
the server may grant write open delegations with very restrictive
space limitations. The limitations may be defined in a way that will
always force modified data to be flushed to the server on close.
With respect to authentication, flushing modified data to the server
after a CLOSE has occurred may be problematic. For example, the user
of the application may have logged off of the client and unexpired
authentication credentials may not be present. In this case, the
client may need to take special care to ensure that local unexpired
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credentials will in fact be available. This may be accomplished by
tracking the expiration time of credentials and flushing data well in
advance of their expiration or by making private copies of
credentials to assure their availability when needed.
9.4.2. Open Delegation and File Locks
When a client holds a write open delegation, lock operations are
performed locally. This includes those required for mandatory file
locking. This can be done since the delegation implies that there
can be no conflicting locks. Similarly, all of the revalidations
that would normally be associated with obtaining locks and the
flushing of data associated with the releasing of locks need not be
done.
9.4.3. Recall of Open Delegation
The following events necessitate recall of an open delegation:
o Potentially conflicting OPEN request (or READ/WRITE done with
"special" stateid)
o SETATTR issued by another client
o REMOVE request for the file
o RENAME request for the file as either source or target of the
RENAME
Whether a RENAME of a directory in the path leading to the file
results in recall of an open delegation depends on the semantics of
the server file system. If that file system denies such RENAMEs when
a file is open, the recall must be performed to determine whether the
file in question is, in fact, open.
In addition to the situations above, the server may choose to recall
open delegations at any time if resource constraints make it
advisable to do so. Clients should always be prepared for the
possibility of recall.
The server needs to employ special handling for a GETATTR where the
target is a file that has a write open delegation in effect. In this
case, the client holding the delegation needs to be interrogated.
The server will use a CB_GETATTR callback, if the GETATTR attribute
bits include any of the attributes that a write open delegate may
modify (object_size, time_modify, change).
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When a client receives a recall for an open delegation, it needs to
update state on the server before returning the delegation. These
same updates must be done whenever a client chooses to return a
delegation voluntarily. The following items of state need to be
dealt with:
o If the file associated with the delegation is no longer open and
no previous CLOSE operation has been sent to the server, a CLOSE
operation must be sent to the server.
o If a file has other open references at the client, then OPEN
operations must be sent to the server. The appropriate stateids
will be provided by the server for subsequent use by the client
since the delegation stateid will not longer be valid. These OPEN
requests are done with the claim type of CLAIM_DELEGATE_CUR. This
will allow the presentation of the delegation stateid so that the
client can establish the appropriate rights to perform the OPEN.
(see the section "Operation 18: OPEN" for details.)
o If there are granted file locks, the corresponding LOCK operations
need to be performed. This applies to the write open delegation
case only.
o For a write open delegation, if at the time of recall the file is
not open for write, all modified data for the file must be flushed
to the server. If the delegation had not existed, the client
would have done this data flush before the CLOSE operation.
o For a write open delegation when a file is still open at the time
of recall, any modified data for the file needs to be flushed to
the server.
o With the write open delegation in place, it is possible that the
file was truncated during the duration of the delegation. For
example, the truncation could have occurred as a result of an OPEN
UNCHECKED with a object_size attribute value of zero. Therefore,
if a truncation of the file has occurred and this operation has
not been propagated to the server, the truncation must occur
before any modified data is written to the server.
In the case of write open delegation, file locking imposes some
additional requirements. The flushing of any modified data in any
region for which a write lock was released while the write open
delegation was in effect is what is required to precisely maintain
the associated invariant. However, because the write open delegation
implies no other locking by other clients, a simpler implementation
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is to flush all modified data for the file (as described just above)
if any write lock has been released while the write open delegation
was in effect.
9.4.4. Delegation Revocation
At the point a delegation is revoked, if there are associated opens
on the client, the applications holding these opens need to be
notified. This notification usually occurs by returning errors for
READ/WRITE operations or when a close is attempted for the open file.
If no opens exist for the file at the point the delegation is
revoked, then notification of the revocation is unnecessary.
However, if there is modified data present at the client for the
file, the user of the application should be notified. Unfortunately,
it may not be possible to notify the user since active applications
may not be present at the client. See the section "Revocation
Recovery for Write Open Delegation" for additional details.
9.5. Data Caching and Revocation
When locks and delegations are revoked, the assumptions upon which
successful caching depend are no longer guaranteed. The owner of the
locks or share reservations which have been revoked needs to be
notified. This notification includes applications with a file open
that has a corresponding delegation which has been revoked. Cached
data associated with the revocation must be removed from the client.
In the case of modified data existing in the client's cache, that
data must be removed from the client without it being written to the
server. As mentioned, the assumptions made by the client are no
longer valid at the point when a lock or delegation has been revoked.
For example, another client may have been granted a conflicting lock
after the revocation of the lock at the first client. Therefore, the
data within the lock range may have been modified by the other
client. Obviously, the first client is unable to guarantee to the
application what has occurred to the file in the case of revocation.
Notification to a lock owner will in many cases consist of simply
returning an error on the next and all subsequent READs/WRITEs to the
open file or on the close. Where the methods available to a client
make such notification impossible because errors for certain
operations may not be returned, more drastic action such as signals
or process termination may be appropriate. The justification for
this is that an invariant for which an application depends on may be
violated. Depending on how errors are typically treated for the
client operating environment, further levels of notification
including logging, console messages, and GUI pop-ups may be
appropriate.
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9.5.1. Revocation Recovery for Write Open Delegation
Revocation recovery for a write open delegation poses the special
issue of modified data in the client cache while the file is not
open. In this situation, any client which does not flush modified
data to the server on each close must ensure that the user receives
appropriate notification of the failure as a result of the
revocation. Since such situations may require human action to
correct problems, notification schemes in which the appropriate user
or administrator is notified may be necessary. Logging and console
messages are typical examples.
If there is modified data on the client, it must not be flushed
normally to the server. A client may attempt to provide a copy of
the file data as modified during the delegation under a different
name in the file system name space to ease recovery. Unless the
client can determine that the file has not modified by any other
client, this technique must be limited to situations in which a
client has a complete cached copy of the file in question. Use of
such a technique may be limited to files under a certain size or may
only be used when sufficient disk space is guaranteed to be available
within the target file system and when the client has sufficient
buffering resources to keep the cached copy available until it is
properly stored to the target file system.
9.6. Attribute Caching
The attributes discussed in this section do not include named
attributes. Individual named attributes are analogous to files and
caching of the data for these needs to be handled just as data
caching is for ordinary files. Similarly, LOOKUP results from an
OPENATTR directory are to be cached on the same basis as any other
pathnames and similarly for directory contents.
Clients may cache file attributes obtained from the server and use
them to avoid subsequent GETATTR requests. Such caching is write
through in that modification to file attributes is always done by
means of requests to the server and should not be done locally and
cached. The exception to this are modifications to attributes that
are intimately connected with data caching. Therefore, extending a
file by writing data to the local data cache is reflected immediately
in the object_size as seen on the client without this change being
immediately reflected on the server. Normally such changes are not
propagated directly to the server but when the modified data is
flushed to the server, analogous attribute changes are made on the
server. When open delegation is in effect, the modified attributes
may be returned to the server in the response to a CB_RECALL call.
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The result of local caching of attributes is that the attribute
caches maintained on individual clients will not be coherent. Changes
made in one order on the server may be seen in a different order on
one client and in a third order on a different client.
The typical file system application programming interfaces do not
provide means to atomically modify or interrogate attributes for
multiple files at the same time. The following rules provide an
environment where the potential incoherences mentioned above can be
reasonably managed. These rules are derived from the practice of
previous NFS protocols.
o All attributes for a given file (per-fsid attributes excepted) are
cached as a unit at the client so that no non-serializability can
arise within the context of a single file.
o An upper time boundary is maintained on how long a client cache
entry can be kept without being refreshed from the server.
o When operations are performed that change attributes at the
server, the updated attribute set is requested as part of the
containing RPC. This includes directory operations that update
attributes indirectly. This is accomplished by following the
modifying operation with a GETATTR operation and then using the
results of the GETATTR to update the client's cached attributes.
Note that if the full set of attributes to be cached is requested by
READDIR, the results can be cached by the client on the same basis as
attributes obtained via GETATTR.
A client may validate its cached version of attributes for a file by
fetching only the change attribute and assuming that if the change
attribute has the same value as it did when the attributes were
cached, then no attributes have changed. The possible exception is
the attribute time_access.
9.7. Name Caching
The results of LOOKUP and READDIR operations may be cached to avoid
the cost of subsequent LOOKUP operations. Just as in the case of
attribute caching, inconsistencies may arise among the various client
caches. To mitigate the effects of these inconsistencies and given
the context of typical file system APIs, the following rules should
be followed:
o The results of unsuccessful LOOKUPs should not be cached, unless
they are specifically reverified at the point of use.
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o An upper time boundary is maintained on how long a client name
cache entry can be kept without verifying that the entry has not
been made invalid by a directory change operation performed by
another client.
When a client is not making changes to a directory for which there
exist name cache entries, the client needs to periodically fetch
attributes for that directory to ensure that it is not being
modified. After determining that no modification has occurred, the
expiration time for the associated name cache entries may be updated
to be the current time plus the name cache staleness bound.
When a client is making changes to a given directory, it needs to
determine whether there have been changes made to the directory by
other clients. It does this by using the change attribute as
reported before and after the directory operation in the associated
change_info4 value returned for the operation. The server is able to
communicate to the client whether the change_info4 data is provided
atomically with respect to the directory operation. If the change
values are provided atomically, the client is then able to compare
the pre-operation change value with the change value in the client's
name cache. If the comparison indicates that the directory was
updated by another client, the name cache associated with the
modified directory is purged from the client. If the comparison
indicates no modification, the name cache can be updated on the
client to reflect the directory operation and the associated timeout
extended. The post-operation change value needs to be saved as the
basis for future change_info4 comparisons.
As demonstrated by the scenario above, name caching requires that the
client revalidate name cache data by inspecting the change attribute
of a directory at the point when the name cache item was cached.
This requires that the server update the change attribute for
directories when the contents of the corresponding directory is
modified. For a client to use the change_info4 information
appropriately and correctly, the server must report the pre and post
operation change attribute values atomically. When the server is
unable to report the before and after values atomically with respect
to the directory operation, the server must indicate that fact in the
change_info4 return value. When the information is not atomically
reported, the client should not assume that other clients have not
changed the directory.
9.8. Directory Caching
The results of READDIR operations may be used to avoid subsequent
READDIR operations. Just as in the cases of attribute and name
caching, inconsistencies may arise among the various client caches.
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To mitigate the effects of these inconsistencies, and given the
context of typical file system APIs, the following rules should be
followed:
o Cached READDIR information for a directory which is not obtained
in a single READDIR operation must always be a consistent snapshot
of directory contents. This is determined by using a GETATTR
before the first READDIR and after the last of READDIR that
contributes to the cache.
o An upper time boundary is maintained to indicate the length of
time a directory cache entry is considered valid before the client
must revalidate the cached information.
The revalidation technique parallels that discussed in the case of
name caching. When the client is not changing the directory in
question, checking the change attribute of the directory with GETATTR
is adequate. The lifetime of the cache entry can be extended at
these checkpoints. When a client is modifying the directory, the
client needs to use the change_info4 data to determine whether there
are other clients modifying the directory. If it is determined that
no other client modifications are occurring, the client may update
its directory cache to reflect its own changes.
As demonstrated previously, directory caching requires that the
client revalidate directory cache data by inspecting the change
attribute of a directory at the point when the directory was cached.
This requires that the server update the change attribute for
directories when the contents of the corresponding directory is
modified. For a client to use the change_info4 information
appropriately and correctly, the server must report the pre and post
operation change attribute values atomically. When the server is
unable to report the before and after values atomically with respect
to the directory operation, the server must indicate that fact in the
change_info4 return value. When the information is not atomically
reported, the client should not assume that other clients have not
changed the directory.
10. Minor Versioning
To address the requirement of an NFS protocol that can evolve as the
need arises, the NFS version 4 protocol contains the rules and
framework to allow for future minor changes or versioning.
The base assumption with respect to minor versioning is that any
future accepted minor version must follow the IETF process and be
documented in a standards track RFC. Therefore, each minor version
number will correspond to an RFC. Minor version zero of the NFS
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version 4 protocol is represented by this RFC. The COMPOUND
procedure will support the encoding of the minor version being
requested by the client.
The following items represent the basic rules for the development of
minor versions. Note that a future minor version may decide to
modify or add to the following rules as part of the minor version
definition.
1 Procedures are not added or deleted
To maintain the general RPC model, NFS version 4 minor versions
will not add or delete procedures from the NFS program.
2 Minor versions may add operations to the COMPOUND and
CB_COMPOUND procedures.
The addition of operations to the COMPOUND and CB_COMPOUND
procedures does not affect the RPC model.
2.1 Minor versions may append attributes to GETATTR4args, bitmap4,
and GETATTR4res.
This allows for the expansion of the attribute model to allow
for future growth or adaptation.
2.2 Minor version X must append any new attributes after the last
documented attribute.
Since attribute results are specified as an opaque array of
per-attribute XDR encoded results, the complexity of adding new
attributes in the midst of the current definitions will be too
burdensome.
3 Minor versions must not modify the structure of an existing
operation's arguments or results.
Again the complexity of handling multiple structure definitions
for a single operation is too burdensome. New operations should
be added instead of modifying existing structures for a minor
version.
This rule does not preclude the following adaptations in a minor
version.
o adding bits to flag fields such as new attributes to
GETATTR's bitmap4 data type
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o adding bits to existing attributes like ACLs that have flag
words
o extending enumerated types (including NFS4ERR_*) with new
values
4 Minor versions may not modify the structure of existing
attributes.
5 Minor versions may not delete operations.
This prevents the potential reuse of a particular operation
"slot" in a future minor version.
6 Minor versions may not delete attributes.
7 Minor versions may not delete flag bits or enumeration values.
8 Minor versions may declare an operation as mandatory to NOT
implement.
Specifying an operation as "mandatory to not implement" is
equivalent to obsoleting an operation. For the client, it means
that the operation should not be sent to the server. For the
server, an NFS error can be returned as opposed to "dropping"
the request as an XDR decode error. This approach allows for
the obsolescence of an operation while maintaining its structure
so that a future minor version can reintroduce the operation.
8.1 Minor versions may declare attributes mandatory to NOT
implement.
8.2 Minor versions may declare flag bits or enumeration values as
mandatory to NOT implement.
9 Minor versions may downgrade features from mandatory to
recommended, or recommended to optional.
10 Minor versions may upgrade features from optional to recommended
or recommended to mandatory.
11 A client and server that support minor version X must support
minor versions 0 (zero) through X-1 as well.
12 No new features may be introduced as mandatory in a minor
version.
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This rule allows for the introduction of new functionality and
forces the use of implementation experience before designating a
feature as mandatory.
13 A client MUST NOT attempt to use a stateid, file handle, or
similar returned object from the COMPOUND procedure with minor
version X for another COMPOUND procedure with minor version Y,
where X != Y.
11. Internationalization
The primary issue in which NFS needs to deal with
internationalization, or I18n, is with respect to file names and
other strings as used within the protocol. The choice of string
representation must allow reasonable name/string access to clients
which use various languages. The UTF-8 encoding of the UCS as
defined by [ISO10646] allows for this type of access and follows the
policy described in "IETF Policy on Character Sets and Languages",
[RFC 2277]. This choice is explained further in the following.
11.1. Universal Versus Local Character Sets
[RFC 1345] describes a table of 16 bit characters for many different
languages (the bit encodings match Unicode, though of course RFC 1345
is somewhat out of date with respect to current Unicode assignments).
Each character from each language has a unique 16 bit value in the 16
bit character set. Thus this table can be thought of as a universal
character set. [RFC 1345] then talks about groupings of subsets of
the entire 16 bit character set into "Charset Tables". For example
one might take all the Greek characters from the 16 bit table (which
are consecutively allocated), and normalize their offsets to a table
that fits in 7 bits. Thus it is determined that "lower case alpha"
is in the same position as "upper case a" in the US-ASCII table, and
"upper case alpha" is in the same position as "lower case a" in the
US-ASCII table.
These normalized subset character sets can be thought of as "local
character sets", suitable for an operating system locale.
Local character sets are not suitable for the NFS protocol. Consider
someone who creates a file with a name in a Swedish character set.
If someone else later goes to access the file with their locale set
to the Swedish language, then there are no problems. But if someone
in say the US-ASCII locale goes to access the file, the file name
will look very different, because the Swedish characters in the 7 bit
table will now be represented in US-ASCII characters on the display.
It would be preferable to give the US-ASCII user a way to display the
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file name using Swedish glyphs. In order to do that, the NFS protocol
would have to include the locale with the file name on each operation
to create a file.
But then what of the situation when there is a path name on the
server like:
/component-1/component-2/component-3
Each component could have been created with a different locale. If
one issues CREATE with multi-component path name, and if some of the
leading components already exist, what is to be done with the
existing components? Is the current locale attribute replaced with
the user's current one? These types of situations quickly become too
complex when there is an alternate solution.
If the NFS version 4 protocol used a universal 16 bit or 32 bit
character set (or an encoding of a 16 bit or 32 bit character set
into octets), then the server and client need not care if the locale
of the user accessing the file is different than the locale of the
user who created the file. The unique 16 bit or 32 bit encoding of
the character allows for determination of what language the character
is from and also how to display that character on the client. The
server need not know what locales are used.
11.2. Overview of Universal Character Set Standards
The previous section makes a case for using a universal character
set. This section makes the case for using UTF-8 as the specific
universal character set for the NFS version 4 protocol.
[RFC 2279] discusses UTF-* (UTF-8 and other UTF-XXX encodings),
Unicode, and UCS-*. There are two standards bodies managing
universal code sets:
o ISO/IEC which has the standard 10646-1
o Unicode which has the Unicode standard
Both standards bodies have pledged to track each other's assignments
of character codes.
The following is a brief analysis of the various standards.
UCS Universal Character Set. This is ISO/IEC 10646-1: "a
multi-octet character set called the Universal Character
Set (UCS), which encompasses most of the world's writing
systems."
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UCS-2 a two octet per character encoding that addresses the first
2^16 characters of UCS. Currently there are no UCS
characters beyond that range.
UCS-4 a four octet per character encoding that permits the
encoding of up to 2^31 characters.
UTF UTF is an abbreviation of the term "UCS transformation
format" and is used in the naming of various standards for
encoding of UCS characters as described below.
UTF-1 Only historical interest; it has been removed from 10646-1
UTF-7 Encodes the entire "repertoire" of UCS "characters using
only octets with the higher order bit clear". [RFC 2152]
describes UTF-7. UTF-7 accomplishes this by reserving one
of the 7bit US-ASCII characters as a "shift" character to
indicate non-US-ASCII characters.
UTF-8 Unlike UTF-7, uses all 8 bits of the octets. US-ASCII
characters are encoded as before unchanged. Any octet with
the high bit cleared can only mean a US-ASCII character.
The high bit set means that a UCS character is being
encoded.
UTF-16 Encodes UCS-4 characters into UCS-2 characters using a
reserved range in UCS-2.
Unicode Unicode and UCS-2 are the same; [RFC 2279] states:
Up to the present time, changes in Unicode and amendments
to ISO/IEC 10646 have tracked each other, so that the
character repertoires and code point assignments have
remained in sync. The relevant standardization committees
have committed to maintain this very useful synchronism.
11.3. Difficulties with UCS-4, UCS-2, Unicode
Adapting existing applications, and file systems to multi-octet
schemes like UCS and Unicode can be difficult. A significant amount
of code has been written to process streams of bytes. Also there are
many existing stored objects described with 7 bit or 8 bit
characters. Doubling or quadrupling the bandwidth and storage
requirements seems like an expensive way to accomplish I18N.
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RFC 3010 NFS version 4 Protocol December 2000
UCS-2 and Unicode are "only" 16 bits long. That might seem to be
enough but, according to [Unicode1], 49,194 Unicode characters are
already assigned. According to [Unicode2] there are still more
languages that need to be added.
11.4. UTF-8 and its solutions
UTF-8 solves problems for NFS that exist with the use of UCS and
Unicode. UTF-8 will encode 16 bit and 32 bit characters in a way
that will be compact for most users. The encoding table from UCS-4 to
UTF-8, as copied from [RFC 2279]:
UCS-4 range (hex.) UTF-8 octet sequence (binary)
0000 0000-0000 007F 0xxxxxxx
0000 0080-0000 07FF 110xxxxx 10xxxxxx
0000 0800-0000 FFFF 1110xxxx 10xxxxxx 10xxxxxx
0001 0000-001F FFFF 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
0020 0000-03FF FFFF 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
0400 0000-7FFF FFFF 1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
10xxxxxx
See [RFC 2279] for precise encoding and decoding rules. Note because
of UTF-16, the algorithm from Unicode/UCS-2 to UTF-8 needs to account
for the reserved range between D800 and DFFF.
Note that the 16 bit UCS or Unicode characters require no more than 3
octets to encode into UTF-8
Interestingly, UTF-8 has room to handle characters larger than 31
bits, because the leading octet of form:
1111111x
is not defined. If needed, ISO could either use that octet to
indicate a sequence of an encoded 8 octet character, or perhaps use
11111110 to permit the next octet to indicate an even more expandable
character set.
So using UTF-8 to represent character encodings means never having to
run out of room.
11.5. Normalization
The client and server operating environments may differ in their
policies and operational methods with respect to character
normalization (See [Unicode1] for a discussion of normalization
forms). This difference may also exist between applications on the
same client. This adds to the difficulty of providing a single
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RFC 3010 NFS version 4 Protocol December 2000
normalization policy for the protocol that allows for maximal
interoperability. This issue is similar to the character case issues
where the server may or may not support case insensitive file name
matching and may or may not preserve the character case when storing
file names. The protocol does not mandate a particular behavior but
allows for the various permutations.
The NFS version 4 protocol does not mandate the use of a particular
normalization form at this time. A later revision of this
specification may specify a particular normalization form.
Therefore, the server and client can expect that they may receive
unnormalized characters within protocol requests and responses. If
the operating environment requires normalization, then the
implementation must normalize the various UTF-8 encoded strings
within the protocol before presenting the information to an
application (at the client) or local file system (at the server).
12. Error Definitions
NFS error numbers are assigned to failed operations within a compound
request. A compound request contains a number of NFS operations that
have their results encoded in sequence in a compound reply. The
results of successful operations will consist of an NFS4_OK status
followed by the encoded results of the operation. If an NFS
operation fails, an error status will be entered in the reply and the
compound request will be terminated.
A description of each defined error follows:
NFS4_OK Indicates the operation completed successfully.
NFS4ERR_ACCES Permission denied. The caller does not have the
correct permission to perform the requested
operation. Contrast this with NFS4ERR_PERM,
which restricts itself to owner or privileged
user permission failures.
NFS4ERR_BADHANDLE Illegal NFS file handle. The file handle failed
internal consistency checks.
NFS4ERR_BADTYPE An attempt was made to create an object of a
type not supported by the server.
NFS4ERR_BAD_COOKIE READDIR cookie is stale.
NFS4ERR_BAD_SEQID The sequence number in a locking request is
neither the next expected number or the last
number processed.
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NFS4ERR_BAD_STATEID A stateid generated by the current server
instance, but which does not designate any
locking state (either current or superseded)
for a current lockowner-file pair, was used.
NFS4ERR_CLID_INUSE The SETCLIENTID procedure has found that a
client id is already in use by another client.
NFS4ERR_DELAY The server initiated the request, but was not
able to complete it in a timely fashion. The
client should wait and then try the request
with a new RPC transaction ID. For example,
this error should be returned from a server
that supports hierarchical storage and receives
a request to process a file that has been
migrated. In this case, the server should start
the immigration process and respond to client
with this error. This error may also occur
when a necessary delegation recall makes
processing a request in a timely fashion
impossible.
NFS4ERR_DENIED An attempt to lock a file is denied. Since
this may be a temporary condition, the client
is encouraged to retry the lock request until
the lock is accepted.
NFS4ERR_DQUOT Resource (quota) hard limit exceeded. The
user's resource limit on the server has been
exceeded.
NFS4ERR_EXIST File exists. The file specified already exists.
NFS4ERR_EXPIRED A lease has expired that is being used in the
current procedure.
NFS4ERR_FBIG File too large. The operation would have caused
a file to grow beyond the server's limit.
NFS4ERR_FHEXPIRED The file handle provided is volatile and has
expired at the server.
NFS4ERR_GRACE The server is in its recovery or grace period
which should match the lease period of the
server.
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NFS4ERR_INVAL Invalid argument or unsupported argument for an
operation. Two examples are attempting a
READLINK on an object other than a symbolic
link or attempting to SETATTR a time field on a
server that does not support this operation.
NFS4ERR_IO I/O error. A hard error (for example, a disk
error) occurred while processing the requested
operation.
NFS4ERR_ISDIR Is a directory. The caller specified a
directory in a non-directory operation.
NFS4ERR_LEASE_MOVED A lease being renewed is associated with a file
system that has been migrated to a new server.
NFS4ERR_LOCKED A read or write operation was attempted on a
locked file.
NFS4ERR_LOCK_RANGE A lock request is operating on a sub-range of a
current lock for the lock owner and the server
does not support this type of request.
NFS4ERR_MINOR_VERS_MISMATCH
The server has received a request that
specifies an unsupported minor version. The
server must return a COMPOUND4res with a zero
length operations result array.
NFS4ERR_MLINK Too many hard links.
NFS4ERR_MOVED The filesystem which contains the current
filehandle object has been relocated or
migrated to another server. The client may
obtain the new filesystem location by obtaining
the "fs_locations" attribute for the current
filehandle. For further discussion, refer to
the section "Filesystem Migration or
Relocation".
NFS4ERR_NAMETOOLONG The filename in an operation was too long.
NFS4ERR_NODEV No such device.
NFS4ERR_NOENT No such file or directory. The file or
directory name specified does not exist.
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NFS4ERR_NOFILEHANDLE The logical current file handle value has not
been set properly. This may be a result of a
malformed COMPOUND operation (i.e. no PUTFH or
PUTROOTFH before an operation that requires the
current file handle be set).
NFS4ERR_NOSPC No space left on device. The operation would
have caused the server's file system to exceed
its limit.
NFS4ERR_NOTDIR Not a directory. The caller specified a non-
directory in a directory operation.
NFS4ERR_NOTEMPTY An attempt was made to remove a directory that
was not empty.
NFS4ERR_NOTSUPP Operation is not supported.
NFS4ERR_NOT_SAME This error is returned by the VERIFY operation
to signify that the attributes compared were
not the same as provided in the client's
request.
NFS4ERR_NXIO I/O error. No such device or address.
NFS4ERR_OLD_STATEID A stateid which designates the locking state
for a lockowner-file at an earlier time was
used.
NFS4ERR_PERM Not owner. The operation was not allowed
because the caller is either not a privileged
user (root) or not the owner of the target of
the operation.
NFS4ERR_READDIR_NOSPC The encoded response to a READDIR request
exceeds the size limit set by the initial
request.
NFS4ERR_RESOURCE For the processing of the COMPOUND procedure,
the server may exhaust available resources and
can not continue processing procedures within
the COMPOUND operation. This error will be
returned from the server in those instances of
resource exhaustion related to the processing
of the COMPOUND procedure.
NFS4ERR_ROFS Read-only file system. A modifying operation
was attempted on a read-only file system.
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NFS4ERR_SAME This error is returned by the NVERIFY operation
to signify that the attributes compared were
the same as provided in the client's request.
NFS4ERR_SERVERFAULT An error occurred on the server which does not
map to any of the legal NFS version 4 protocol
error values. The client should translate this
into an appropriate error. UNIX clients may
choose to translate this to EIO.
NFS4ERR_SHARE_DENIED An attempt to OPEN a file with a share
reservation has failed because of a share
conflict.
NFS4ERR_STALE Invalid file handle. The file handle given in
the arguments was invalid. The file referred to
by that file handle no longer exists or access
to it has been revoked.
NFS4ERR_STALE_CLIENTID A clientid not recognized by the server was
used in a locking or SETCLIENTID_CONFIRM
request.
NFS4ERR_STALE_STATEID A stateid generated by an earlier server
instance was used.
NFS4ERR_SYMLINK The current file handle provided for a LOOKUP
is not a directory but a symbolic link. Also
used if the final component of the OPEN path is
a symbolic link.
NFS4ERR_TOOSMALL Buffer or request is too
small.
NFS4ERR_WRONGSEC The security mechanism being used by the client
for the procedure does not match the server's
security policy. The client should change the
security mechanism being used and retry the
operation.
NFS4ERR_XDEV Attempt to do a cross-device hard link.
13. NFS Version 4 Requests
For the NFS version 4 RPC program, there are two traditional RPC
procedures: NULL and COMPOUND. All other functionality is defined as
a set of operations and these operations are defined in normal
XDR/RPC syntax and semantics. However, these operations are
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RFC 3010 NFS version 4 Protocol December 2000
encapsulated within the COMPOUND procedure. This requires that the
client combine one or more of the NFS version 4 operations into a
single request.
The NFS4_CALLBACK program is used to provide server to client
signaling and is constructed in a similar fashion as the NFS version
4 program. The procedures CB_NULL and CB_COMPOUND are defined in the
same way as NULL and COMPOUND are within the NFS program. The
CB_COMPOUND request also encapsulates the remaining operations of the
NFS4_CALLBACK program. There is no predefined RPC program number for
the NFS4_CALLBACK program. It is up to the client to specify a
program number in the "transient" program range. The program and
port number of the NFS4_CALLBACK program are provided by the client
as part of the SETCLIENTID operation and therefore is fixed for the
life of the client instantiation.
13.1. Compound Procedure
The COMPOUND procedure provides the opportunity for better
performance within high latency networks. The client can avoid
cumulative latency of multiple RPCs by combining multiple dependent
operations into a single COMPOUND procedure. A compound operation
may provide for protocol simplification by allowing the client to
combine basic procedures into a single request that is customized for
the client's environment.
The CB_COMPOUND procedure precisely parallels the features of
COMPOUND as described above.
The basics of the COMPOUND procedures construction is:
+-----------+-----------+-----------+--
| op + args | op + args | op + args |
+-----------+-----------+-----------+--
and the reply looks like this:
+------------+-----------------------+-----------------------+--
|last status | status + op + results | status + op + results |
+------------+-----------------------+-----------------------+--
13.2. Evaluation of a Compound Request
The server will process the COMPOUND procedure by evaluating each of
the operations within the COMPOUND procedure in order. Each
component operation consists of a 32 bit operation code, followed by
the argument of length determined by the type of operation. The
results of each operation are encoded in sequence into a reply
Shepler, et al. Standards Track PAGE 100
RFC 3010 NFS version 4 Protocol December 2000
buffer. The results of each operation are preceded by the opcode and
a status code (normally zero). If an operation results in a non-zero
status code, the status will be encoded and evaluation of the
compound sequence will halt and the reply will be returned. Note
that evaluation stops even in the event of "non error" conditions
such as NFS4ERR_SAME.
There are no atomicity requirements for the operations contained
within the COMPOUND procedure. The operations being evaluated as
part of a COMPOUND request may be evaluated simultaneously with other
COMPOUND requests that the server receives.
It is the client's responsibility for recovering from any partially
completed COMPOUND procedure. Partially completed COMPOUND
procedures may occur at any point due to errors such as
NFS4ERR_RESOURCE and NFS4ERR_LONG_DELAY. This may occur even given
an otherwise valid operation string. Further, a server reboot which
occurs in the middle of processing a COMPOUND procedure may leave the
client with the difficult task of determining how far COMPOUND
processing has proceeded. Therefore, the client should avoid overly
complex COMPOUND procedures in the event of the failure of an
operation within the procedure.
Each operation assumes a "current" and "saved" filehandle that is
available as part of the execution context of the compound request.
Operations may set, change, or return the current filehandle. The
"saved" filehandle is used for temporary storage of a filehandle
value and as operands for the RENAME and LINK operations.
13.3. Synchronous Modifying Operations
NFS version 4 operations that modify the file system are synchronous.
When an operation is successfully completed at the server, the client
can depend that any data associated with the request is now on stable
storage (the one exception is in the case of the file data in a WRITE
operation with the UNSTABLE option specified).
This implies that any previous operations within the same compound
request are also reflected in stable storage. This behavior enables
the client's ability to recover from a partially executed compound
request which may resulted from the failure of the server. For
example, if a compound request contains operations A and B and the
server is unable to send a response to the client, depending on the
progress the server made in servicing the request the result of both
operations may be reflected in stable storage or just operation A may
be reflected. The server must not have just the results of operation
B in stable storage.
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RFC 3010 NFS version 4 Protocol December 2000
13.4. Operation Values
The operations encoded in the COMPOUND procedure are identified by
operation values. To avoid overlap with the RPC procedure numbers,
operations 0 (zero) and 1 are not defined. Operation 2 is not
defined but reserved for future use with minor versioning.
14. NFS Version 4 Procedures
14.1. Procedure 0: NULL - No Operation
SYNOPSIS
<null>
ARGUMENT
void;
RESULT
void;
DESCRIPTION
Standard NULL procedure. Void argument, void response. This
procedure has no functionality associated with it. Because of
this it is sometimes used to measure the overhead of processing a
service request. Therefore, the server should ensure that no
unnecessary work is done in servicing this procedure.
ERRORS
None.
14.2. Procedure 1: COMPOUND - Compound Operations
SYNOPSIS
compoundargs -> compoundres
ARGUMENT
union nfs_argop4 switch (nfs_opnum4 argop) {
case <OPCODE>: <argument>;
...
};
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RFC 3010 NFS version 4 Protocol December 2000
struct COMPOUND4args {
utf8string tag;
uint32_t minorversion;
nfs_argop4 argarray<>;
};
RESULT
union nfs_resop4 switch (nfs_opnum4 resop){
case <OPCODE>: <result>;
...
};
struct COMPOUND4res {
nfsstat4 status;
utf8string tag;
nfs_resop4 resarray<>;
};
DESCRIPTION
The COMPOUND procedure is used to combine one or more of the NFS
operations into a single RPC request. The main NFS RPC program
has two main procedures: NULL and COMPOUND. All other operations
use the COMPOUND procedure as a wrapper.
The COMPOUND procedure is used to combine individual operations
into a single RPC request. The server interprets each of the
operations in turn. If an operation is executed by the server and
the status of that operation is NFS4_OK, then the next operation
in the COMPOUND procedure is executed. The server continues this
process until there are no more operations to be executed or one
of the operations has a status value other than NFS4_OK.
In the processing of the COMPOUND procedure, the server may find
that it does not have the available resources to execute any or
all of the operations within the COMPOUND sequence. In this case,
the error NFS4ERR_RESOURCE will be returned for the particular
operation within the COMPOUND procedure where the resource
exhaustion occurred. This assumes that all previous operations
within the COMPOUND sequence have been evaluated successfully.
The results for all of the evaluated operations must be returned
to the client.
The COMPOUND arguments contain a "minorversion" field. The
initial and default value for this field is 0 (zero). This field
will be used by future minor versions such that the client can
communicate to the server what minor version is being requested.
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RFC 3010 NFS version 4 Protocol December 2000
If the server receives a COMPOUND procedure with a minorversion
field value that it does not support, the server MUST return an
error of NFS4ERR_MINOR_VERS_MISMATCH and a zero length resultdata
array.
Contained within the COMPOUND results is a "status" field. If the
results array length is non-zero, this status must be equivalent
to the status of the last operation that was executed within the
COMPOUND procedure. Therefore, if an operation incurred an error
then the "status" value will be the same error value as is being
returned for the operation that failed.
Note that operations, 0 (zero) and 1 (one) are not defined for the
COMPOUND procedure. If the server receives an operation array
with either of these included, an error of NFS4ERR_NOTSUPP must be
returned. Operation 2 is not defined but reserved for future
definition and use with minor versioning. If the server receives
a operation array that contains operation 2 and the minorversion
field has a value of 0 (zero), an error of NFS4ERR_NOTSUPP is
returned. If an operation array contains an operation 2 and the
minorversion field is non-zero and the server does not support the
minor version, the server returns an error of
NFS4ERR_MINOR_VERS_MISMATCH. Therefore, the
NFS4ERR_MINOR_VERS_MISMATCH error takes precedence over all other
errors.
IMPLEMENTATION
Note that the definition of the "tag" in both the request and
response are left to the implementor. It may be used to summarize
the content of the compound request for the benefit of packet
sniffers and engineers debugging implementations.
Since an error of any type may occur after only a portion of the
operations have been evaluated, the client must be prepared to
recover from any failure. If the source of an NFS4ERR_RESOURCE
error was a complex or lengthy set of operations, it is likely
that if the number of operations were reduced the server would be
able to evaluate them successfully. Therefore, the client is
responsible for dealing with this type of complexity in recovery.
ERRORS
All errors defined in the protocol
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RFC 3010 NFS version 4 Protocol December 2000
14.2.1. Operation 3: ACCESS - Check Access Rights
SYNOPSIS
(cfh), accessreq -> supported, accessrights
ARGUMENT
const ACCESS4_READ = 0x00000001;
const ACCESS4_LOOKUP = 0x00000002;
const ACCESS4_MODIFY = 0x00000004;
const ACCESS4_EXTEND = 0x00000008;
const ACCESS4_DELETE = 0x00000010;
const ACCESS4_EXECUTE = 0x00000020;
struct ACCESS4args {
/* CURRENT_FH: object */
uint32_t access;
};
RESULT
struct ACCESS4resok {
uint32_t supported;
uint32_t access;
};
union ACCESS4res switch (nfsstat4 status) {
case NFS4_OK:
ACCESS4resok resok4;
default:
void;
};
DESCRIPTION
ACCESS determines the access rights that a user, as identified by
the credentials in the RPC request, has with respect to the file
system object specified by the current filehandle. The client
encodes the set of access rights that are to be checked in the bit
mask "access". The server checks the permissions encoded in the
bit mask. If a status of NFS4_OK is returned, two bit masks are
included in the response. The first, "supported", represents the
access rights for which the server can verify reliably. The
second, "access", represents the access rights available to the
user for the filehandle provided. On success, the current
filehandle retains its value.
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RFC 3010 NFS version 4 Protocol December 2000
Note that the supported field will contain only as many values as
was originally sent in the arguments. For example, if the client
sends an ACCESS operation with only the ACCESS4_READ value set and
the server supports this value, the server will return only
ACCESS4_READ even if it could have reliably checked other values.
The results of this operation are necessarily advisory in nature.
A return status of NFS4_OK and the appropriate bit set in the bit
mask does not imply that such access will be allowed to the file
system object in the future. This is because access rights can be
revoked by the server at any time.
The following access permissions may be requested:
ACCESS4_READ Read data from file or read a directory.
ACCESS4_LOOKUP Look up a name in a directory (no meaning for non-
directory objects).
ACCESS4_MODIFY Rewrite existing file data or modify existing
directory entries.
ACCESS4_EXTEND Write new data or add directory entries.
ACCESS4_DELETE Delete an existing directory entry (no meaning for
non-directory objects).
ACCESS4_EXECUTE Execute file (no meaning for a directory).
On success, the current filehandle retains its value.
IMPLEMENTATION
For the NFS version 4 protocol, the use of the ACCESS procedure
when opening a regular file is deprecated in favor of using OPEN.
In general, it is not sufficient for the client to attempt to
deduce access permissions by inspecting the uid, gid, and mode
fields in the file attributes or by attempting to interpret the
contents of the ACL attribute. This is because the server may
perform uid or gid mapping or enforce additional access control
restrictions. It is also possible that the server may not be in
the same ID space as the client. In these cases (and perhaps
others), the client can not reliably perform an access check with
only current file attributes.
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RFC 3010 NFS version 4 Protocol December 2000
In the NFS version 2 protocol, the only reliable way to determine
whether an operation was allowed was to try it and see if it
succeeded or failed. Using the ACCESS procedure in the NFS
version 4 protocol, the client can ask the server to indicate
whether or not one or more classes of operations are permitted.
The ACCESS operation is provided to allow clients to check before
doing a series of operations which will result in an access
failure. The OPEN operation provides a point where the server can
verify access to the file object and method to return that
information to the client. The ACCESS operation is still useful
for directory operations or for use in the case the UNIX API
"access" is used on the client.
The information returned by the server in response to an ACCESS
call is not permanent. It was correct at the exact time that the
server performed the checks, but not necessarily afterwards. The
server can revoke access permission at any time.
The client should use the effective credentials of the user to
build the authentication information in the ACCESS request used to
determine access rights. It is the effective user and group
credentials that are used in subsequent read and write operations.
Many implementations do not directly support the ACCESS4_DELETE
permission. Operating systems like UNIX will ignore the
ACCESS4_DELETE bit if set on an access request on a non-directory
object. In these systems, delete permission on a file is
determined by the access permissions on the directory in which the
file resides, instead of being determined by the permissions of
the file itself. Therefore, the mask returned enumerating which
access rights can be determined will have the ACCESS4_DELETE value
set to 0. This indicates to the client that the server was unable
to check that particular access right. The ACCESS4_DELETE bit in
the access mask returned will then be ignored by the client.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
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RFC 3010 NFS version 4 Protocol December 2000
14.2.2. Operation 4: CLOSE - Close File
SYNOPSIS
(cfh), seqid, stateid -> stateid
ARGUMENT
struct CLOSE4args {
/* CURRENT_FH: object */
seqid4 seqid
stateid4 stateid;
};
RESULT
union CLOSE4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 stateid;
default:
void;
};
DESCRIPTION
The CLOSE operation releases share reservations for the file as
specified by the current filehandle. The share reservations and
other state information released at the server as a result of this
CLOSE is only associated with the supplied stateid. The sequence
id provides for the correct ordering. State associated with other
OPENs is not affected.
If record locks are held, the client SHOULD release all locks
before issuing a CLOSE. The server MAY free all outstanding locks
on CLOSE but some servers may not support the CLOSE of a file that
still has record locks held. The server MUST return failure if
any locks would exist after the CLOSE.
On success, the current filehandle retains its value.
IMPLEMENTATION
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_BAD_SEQID
NFS4ERR_BAD_STATEID
NFS4ERR_DELAY
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RFC 3010 NFS version 4 Protocol December 2000
NFS4ERR_EXPIRED
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_INVAL
NFS4ERR_ISDIR
NFS4ERR_LEASE_MOVED
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_OLD_STATEID
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_STATEID
14.2.3. Operation 5: COMMIT - Commit Cached Data
SYNOPSIS
(cfh), offset, count -> verifier
ARGUMENT
struct COMMIT4args {
/* CURRENT_FH: file */
offset4 offset;
count4 count;
};
RESULT
struct COMMIT4resok {
verifier4 writeverf;
};
union COMMIT4res switch (nfsstat4 status) {
case NFS4_OK:
COMMIT4resok resok4;
default:
void;
};
DESCRIPTION
The COMMIT operation forces or flushes data to stable storage for
the file specified by the current file handle. The flushed data
is that which was previously written with a WRITE operation which
had the stable field set to UNSTABLE4.
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RFC 3010 NFS version 4 Protocol December 2000
The offset specifies the position within the file where the flush
is to begin. An offset value of 0 (zero) means to flush data
starting at the beginning of the file. The count specifies the
number of bytes of data to flush. If count is 0 (zero), a flush
from offset to the end of the file is done.
The server returns a write verifier upon successful completion of
the COMMIT. The write verifier is used by the client to determine
if the server has restarted or rebooted between the initial
WRITE(s) and the COMMIT. The client does this by comparing the
write verifier returned from the initial writes and the verifier
returned by the COMMIT procedure. The server must vary the value
of the write verifier at each server event or instantiation that
may lead to a loss of uncommitted data. Most commonly this occurs
when the server is rebooted; however, other events at the server
may result in uncommitted data loss as well.
On success, the current filehandle retains its value.
IMPLEMENTATION
The COMMIT procedure is similar in operation and semantics to the
POSIX fsync(2) system call that synchronizes a file's state with
the disk (file data and metadata is flushed to disk or stable
storage). COMMIT performs the same operation for a client,
flushing any unsynchronized data and metadata on the server to the
server's disk or stable storage for the specified file. Like
fsync(2), it may be that there is some modified data or no
modified data to synchronize. The data may have been synchronized
by the server's normal periodic buffer synchronization activity.
COMMIT should return NFS4_OK, unless there has been an unexpected
error.
COMMIT differs from fsync(2) in that it is possible for the client
to flush a range of the file (most likely triggered by a buffer-
reclamation scheme on the client before file has been completely
written).
The server implementation of COMMIT is reasonably simple. If the
server receives a full file COMMIT request, that is starting at
offset 0 and count 0, it should do the equivalent of fsync()'ing
the file. Otherwise, it should arrange to have the cached data in
the range specified by offset and count to be flushed to stable
storage. In both cases, any metadata associated with the file
must be flushed to stable storage before returning. It is not an
error for there to be nothing to flush on the server. This means
that the data and metadata that needed to be flushed have already
been flushed or lost during the last server failure.
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RFC 3010 NFS version 4 Protocol December 2000
The client implementation of COMMIT is a little more complex.
There are two reasons for wanting to commit a client buffer to
stable storage. The first is that the client wants to reuse a
buffer. In this case, the offset and count of the buffer are sent
to the server in the COMMIT request. The server then flushes any
cached data based on the offset and count, and flushes any
metadata associated with the file. It then returns the status of
the flush and the write verifier. The other reason for the client
to generate a COMMIT is for a full file flush, such as may be done
at close. In this case, the client would gather all of the
buffers for this file that contain uncommitted data, do the COMMIT
operation with an offset of 0 and count of 0, and then free all of
those buffers. Any other dirty buffers would be sent to the
server in the normal fashion.
After a buffer is written by the client with the stable parameter
set to UNSTABLE4, the buffer must be considered as modified by the
client until the buffer has either been flushed via a COMMIT
operation or written via a WRITE operation with stable parameter
set to FILE_SYNC4 or DATA_SYNC4. This is done to prevent the
buffer from being freed and reused before the data can be flushed
to stable storage on the server.
When a response is returned from either a WRITE or a COMMIT
operation and it contains a write verifier that is different than
previously returned by the server, the client will need to
retransmit all of the buffers containing uncommitted cached data
to the server. How this is to be done is up to the implementor.
If there is only one buffer of interest, then it should probably
be sent back over in a WRITE request with the appropriate stable
parameter. If there is more than one buffer, it might be
worthwhile retransmitting all of the buffers in WRITE requests
with the stable parameter set to UNSTABLE4 and then retransmitting
the COMMIT operation to flush all of the data on the server to
stable storage. The timing of these retransmissions is left to
the implementor.
The above description applies to page-cache-based systems as well
as buffer-cache-based systems. In those systems, the virtual
memory system will need to be modified instead of the buffer
cache.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_FHEXPIRED
NFS4ERR_IO
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RFC 3010 NFS version 4 Protocol December 2000
NFS4ERR_ISDIR
NFS4ERR_LOCKED
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.4. Operation 6: CREATE - Create a Non-Regular File Object
SYNOPSIS
(cfh), name, type -> (cfh), change_info
ARGUMENT
union createtype4 switch (nfs_ftype4 type) {
case NF4LNK:
linktext4 linkdata;
case NF4BLK:
case NF4CHR:
specdata4 devdata;
case NF4SOCK:
case NF4FIFO:
case NF4DIR:
void;
};
struct CREATE4args {
/* CURRENT_FH: directory for creation */
component4 objname;
createtype4 objtype;
};
RESULT
struct CREATE4resok {
change_info4 cinfo;
};
union CREATE4res switch (nfsstat4 status) {
case NFS4_OK:
CREATE4resok resok4;
default:
void;
};
Shepler, et al. Standards Track PAGE 112
RFC 3010 NFS version 4 Protocol December 2000
DESCRIPTION
The CREATE operation creates a non-regular file object in a
directory with a given name. The OPEN procedure MUST be used to
create a regular file.
The objname specifies the name for the new object. If the objname
has a length of 0 (zero), the error NFS4ERR_INVAL will be
returned. The objtype determines the type of object to be
created: directory, symlink, etc.
If an object of the same name already exists in the directory, the
server will return the error NFS4ERR_EXIST.
For the directory where the new file object was created, the
server returns change_info4 information in cinfo. With the atomic
field of the change_info4 struct, the server will indicate if the
before and after change attributes were obtained atomically with
respect to the file object creation.
If the objname has a length of 0 (zero), or if objname does not
obey the UTF-8 definition, the error NFS4ERR_INVAL will be
returned.
The current filehandle is replaced by that of the new object.
IMPLEMENTATION
If the client desires to set attribute values after the create, a
SETATTR operation can be added to the COMPOUND request so that the
appropriate attributes will be set.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_BADTYPE
NFS4ERR_DQUOT
NFS4ERR_EXIST
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOSPC
NFS4ERR_NOTDIR
NFS4ERR_NOTSUPP
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NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.5. Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery
SYNOPSIS
clientid ->
ARGUMENT
struct DELEGPURGE4args {
clientid4 clientid;
};
RESULT
struct DELEGPURGE4res {
nfsstat4 status;
};
DESCRIPTION
Purges all of the delegations awaiting recovery for a given
client. This is useful for clients which do not commit delegation
information to stable storage to indicate that conflicting
requests need not be delayed by the server awaiting recovery of
delegation information.
This operation should be used by clients that record delegation
information on stable storage on the client. In this case,
DELEGPURGE should be issued immediately after doing delegation
recovery on all delegations know to the client. Doing so will
notify the server that no additional delegations for the client
will be recovered allowing it to free resources, and avoid
delaying other clients who make requests that conflict with the
unrecovered delegations. The set of delegations known to the
server and the client may be different. The reason for this is
that a client may fail after making a request which resulted in
delegation but before it received the results and committed them
to the client's stable storage.
ERRORS
NFS4ERR_RESOURCE
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RFC 3010 NFS version 4 Protocol December 2000
NFS4ERR_SERVERFAULT
NFS4ERR_STALE_CLIENTID
14.2.6. Operation 8: DELEGRETURN - Return Delegation
SYNOPSIS
stateid ->
ARGUMENT
struct DELEGRETURN4args {
stateid4 stateid;
};
RESULT
struct DELEGRETURN4res {
nfsstat4 status;
};
DESCRIPTION
Returns the delegation represented by the given stateid.
ERRORS
NFS4ERR_BAD_STATEID
NFS4ERR_OLD_STATEID
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE_STATEID
14.2.7. Operation 9: GETATTR - Get Attributes
SYNOPSIS
(cfh), attrbits -> attrbits, attrvals
ARGUMENT
struct GETATTR4args {
/* CURRENT_FH: directory or file */
bitmap4 attr_request;
};
RESULT
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RFC 3010 NFS version 4 Protocol December 2000
struct GETATTR4resok {
fattr4 obj_attributes;
};
union GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
GETATTR4resok resok4;
default:
void;
};
DESCRIPTION
The GETATTR operation will obtain attributes for the file system
object specified by the current filehandle. The client sets a bit
in the bitmap argument for each attribute value that it would like
the server to return. The server returns an attribute bitmap that
indicates the attribute values for which it was able to return,
followed by the attribute values ordered lowest attribute number
first.
The server must return a value for each attribute that the client
requests if the attribute is supported by the server. If the
server does not support an attribute or cannot approximate a
useful value then it must not return the attribute value and must
not set the attribute bit in the result bitmap. The server must
return an error if it supports an attribute but cannot obtain its
value. In that case no attribute values will be returned.
All servers must support the mandatory attributes as specified in
the section "File Attributes".
On success, the current filehandle retains its value.
IMPLEMENTATION
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
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NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.8. Operation 10: GETFH - Get Current Filehandle
SYNOPSIS
(cfh) -> filehandle
ARGUMENT
/* CURRENT_FH: */
void;
RESULT
struct GETFH4resok {
nfs_fh4 object;
};
union GETFH4res switch (nfsstat4 status) {
case NFS4_OK:
GETFH4resok resok4;
default:
void;
};
DESCRIPTION
This operation returns the current filehandle value.
On success, the current filehandle retains its value.
IMPLEMENTATION
Operations that change the current filehandle like LOOKUP or
CREATE do not automatically return the new filehandle as a result.
For instance, if a client needs to lookup a directory entry and
obtain its filehandle then the following request is needed.
PUTFH (directory filehandle)
LOOKUP (entry name)
GETFH
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_FHEXPIRED
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RFC 3010 NFS version 4 Protocol December 2000
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.9. Operation 11: LINK - Create Link to a File
SYNOPSIS
(sfh), (cfh), newname -> (cfh), change_info
ARGUMENT
struct LINK4args {
/* SAVED_FH: source object */
/* CURRENT_FH: target directory */
component4 newname;
};
RESULT
struct LINK4resok {
change_info4 cinfo;
};
union LINK4res switch (nfsstat4 status) {
case NFS4_OK:
LINK4resok resok4;
default:
void;
};
DESCRIPTION
The LINK operation creates an additional newname for the file
represented by the saved filehandle, as set by the SAVEFH
operation, in the directory represented by the current filehandle.
The existing file and the target directory must reside within the
same file system on the server. On success, the current
filehandle will continue to be the target directory.
For the target directory, the server returns change_info4
information in cinfo. With the atomic field of the change_info4
struct, the server will indicate if the before and after change
attributes were obtained atomically with respect to the link
creation.
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RFC 3010 NFS version 4 Protocol December 2000
If the newname has a length of 0 (zero), or if newname does not
obey the UTF-8 definition, the error NFS4ERR_INVAL will be
returned.
IMPLEMENTATION
Changes to any property of the "hard" linked files are reflected
in all of the linked files. When a link is made to a file, the
attributes for the file should have a value for numlinks that is
one greater than the value before the LINK operation.
The comments under RENAME regarding object and target residing on
the same file system apply here as well. The comments regarding
the target name applies as well.
Note that symbolic links are created with the CREATE operation.
ERRORS
NFS4ERR_ACCES NFS4ERR_BADHANDLE NFS4ERR_DELAY NFS4ERR_DQUOT
NFS4ERR_EXIST NFS4ERR_FHEXPIRED NFS4ERR_INVAL NFS4ERR_IO
NFS4ERR_ISDIR NFS4ERR_MLINK NFS4ERR_MOVED NFS4ERR_NAMETOOLONG
NFS4ERR_NOFILEHANDLE NFS4ERR_NOSPC NFS4ERR_NOTDIR NFS4ERR_NOTSUPP
NFS4ERR_RESOURCE NFS4ERR_ROFS NFS4ERR_SERVERFAULT NFS4ERR_STALE
NFS4ERR_WRONGSEC NFS4ERR_XDEV
14.2.10. Operation 12: LOCK - Create Lock
SYNOPSIS
(cfh) type, seqid, reclaim, stateid, offset, length -> stateid,
access
ARGUMENT
enum nfs4_lock_type {
READ_LT = 1,
WRITE_LT = 2,
READW_LT = 3, /* blocking read */
WRITEW_LT = 4 /* blocking write */ };
struct LOCK4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
seqid4 seqid;
bool reclaim;
stateid4 stateid;
offset4 offset;
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RFC 3010 NFS version 4 Protocol December 2000
length4 length; };
RESULT
struct LOCK4denied {
nfs_lockowner4 owner;
offset4 offset;
length4 length; };
union LOCK4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 stateid;
case NFS4ERR_DENIED:
LOCK4denied denied;
default:
void; };
DESCRIPTION
The LOCK operation requests a record lock for the byte range
specified by the offset and length parameters. The lock type is
also specified to be one of the nfs4_lock_types. If this is a
reclaim request, the reclaim parameter will be TRUE;
Bytes in a file may be locked even if those bytes are not
currently allocated to the file. To lock the file from a specific
offset through the end-of-file (no matter how long the file
actually is) use a length field with all bits set to 1 (one). To
lock the entire file, use an offset of 0 (zero) and a length with
all bits set to 1. A length of 0 is reserved and should not be
used.
In the case that the lock is denied, the owner, offset, and length
of a conflicting lock are returned.
On success, the current filehandle retains its value.
IMPLEMENTATION
If the server is unable to determine the exact offset and length
of the conflicting lock, the same offset and length that were
provided in the arguments should be returned in the denied
results. The File Locking section contains a full description of
this and the other file locking operations.
ERRORS
NFS4ERR_ACCES NFS4ERR_BADHANDLE NFS4ERR_BAD_SEQID
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RFC 3010 NFS version 4 Protocol December 2000
NFS4ERR_BAD_STATEID NFS4ERR_DELAY NFS4ERR_DENIED NFS4ERR_EXPIRED
NFS4ERR_FHEXPIRED NFS4ERR_GRACE NFS4ERR_INVAL NFS4ERR_ISDIR
NFS4ERR_LEASE_MOVED NFS4ERR_LOCK_RANGE NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE NFS4ERR_OLD_STATEID NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT NFS4ERR_STALE NFS4ERR_STALE_CLIENTID
NFS4ERR_STALE_STATEID NFS4ERR_WRONGSEC
14.2.11. Operation 13: LOCKT - Test For Lock
SYNOPSIS
(cfh) type, owner, offset, length -> {void, NFS4ERR_DENIED ->
owner}
ARGUMENT
struct LOCKT4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
nfs_lockowner4 owner;
offset4 offset;
length4 length; };
RESULT
union LOCKT4res switch (nfsstat4 status) {
case NFS4ERR_DENIED:
LOCK4denied denied;
case NFS4_OK:
void;
default:
void; };
DESCRIPTION
The LOCKT operation tests the lock as specified in the arguments.
If a conflicting lock exists, the owner, offset, and length of the
conflicting lock are returned; if no lock is held, nothing other
than NFS4_OK is returned.
On success, the current filehandle retains its value.
IMPLEMENTATION
If the server is unable to determine the exact offset and length
of the conflicting lock, the same offset and length that were
provided in the arguments should be returned in the denied
Shepler, et al. Standards Track PAGE 121
RFC 3010 NFS version 4 Protocol December 2000
results. The File Locking section contains further discussion of
the file locking mechanisms.
LOCKT uses nfs_lockowner4 instead of a stateid4, as LOCK does, to
identify the owner so that the client does not have to open the
file to test for the existence of a lock.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_DELAY
NFS4ERR_DENIED
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_INVAL
NFS4ERR_ISDIR
NFS4ERR_LEASE_MOVED
NFS4ERR_LOCK_RANGE
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_CLIENTID
NFS4ERR_WRONGSEC
14.2.12. Operation 14: LOCKU - Unlock File
SYNOPSIS
(cfh) type, seqid, stateid, offset, length -> stateid
ARGUMENT
struct LOCKU4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
seqid4 seqid;
stateid4 stateid;
offset4 offset;
length4 length;
};
RESULT
union LOCKU4res switch (nfsstat4 status) {
case NFS4_OK:
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RFC 3010 NFS version 4 Protocol December 2000
stateid4 stateid;
default:
void;
};
DESCRIPTION
The LOCKU operation unlocks the record lock specified by the
parameters.
On success, the current filehandle retains its value.
IMPLEMENTATION
The File Locking section contains a full description of this and
the other file locking procedures.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_BAD_SEQID
NFS4ERR_BAD_STATEID
NFS4ERR_EXPIRED
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_INVAL
NFS4ERR_LOCK_RANGE
NFS4ERR_LEASE_MOVED
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_OLD_STATEID
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_CLIENTID
NFS4ERR_STALE_STATEID
14.2.13. Operation 15: LOOKUP - Lookup Filename
SYNOPSIS
(cfh), filenames -> (cfh)
ARGUMENT
struct LOOKUP4args {
/* CURRENT_FH: directory */
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RFC 3010 NFS version 4 Protocol December 2000
pathname4 path;
};
RESULT
struct LOOKUP4res {
/* CURRENT_FH: object */
nfsstat4 status;
};
DESCRIPTION
This operation LOOKUPs or finds a file system object starting from
the directory specified by the current filehandle. LOOKUP
evaluates the pathname contained in the array of names and obtains
a new current filehandle from the final name. All but the final
name in the list must be the names of directories.
If the pathname cannot be evaluated either because a component
does not exist or because the client does not have permission to
evaluate a component of the path, then an error will be returned
and the current filehandle will be unchanged.
If the path is a zero length array, if any component does not obey
the UTF-8 definition, or if any component in the path is of zero
length, the error NFS4ERR_INVAL will be returned.
IMPLEMENTATION
If the client prefers a partial evaluation of the path then a
sequence of LOOKUP operations can be substituted e.g.
PUTFH (directory filehandle)
LOOKUP "pub" "foo" "bar"
GETFH
or, if the client wishes to obtain the intermediate filehandles
PUTFH (directory filehandle)
LOOKUP "pub"
GETFH
LOOKUP "foo"
GETFH
LOOKUP "bar"
GETFH
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RFC 3010 NFS version 4 Protocol December 2000
NFS version 4 servers depart from the semantics of previous NFS
versions in allowing LOOKUP requests to cross mountpoints on the
server. The client can detect a mountpoint crossing by comparing
the fsid attribute of the directory with the fsid attribute of the
directory looked up. If the fsids are different then the new
directory is a server mountpoint. Unix clients that detect a
mountpoint crossing will need to mount the server's filesystem.
This needs to be done to maintain the file object identity
checking mechanisms common to Unix clients.
Servers that limit NFS access to "shares" or "exported"
filesystems should provide a pseudo-filesystem into which the
exported filesystems can be integrated, so that clients can browse
the server's name space. The clients view of a pseudo filesystem
will be limited to paths that lead to exported filesystems.
Note: previous versions of the protocol assigned special semantics
to the names "." and "..". NFS version 4 assigns no special
semantics to these names. The LOOKUPP operator must be used to
lookup a parent directory.
Note that this procedure does not follow symbolic links. The
client is responsible for all parsing of filenames including
filenames that are modified by symbolic links encountered during
the lookup process.
If the current file handle supplied is not a directory but a
symbolic link, the error NFS4ERR_SYMLINK is returned as the error.
For all other non-directory file types, the error NFS4ERR_NOTDIR
is returned.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTDIR
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_SYMLINK
NFS4ERR_WRONGSEC
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RFC 3010 NFS version 4 Protocol December 2000
14.2.14. Operation 16: LOOKUPP - Lookup Parent Directory
SYNOPSIS
(cfh) -> (cfh)
ARGUMENT
/* CURRENT_FH: object */
void;
RESULT
struct LOOKUPP4res {
/* CURRENT_FH: directory */
nfsstat4 status;
};
DESCRIPTION
The current filehandle is assumed to refer to a regular directory
or a named attribute directory. LOOKUPP assigns the filehandle
for its parent directory to be the current filehandle. If there
is no parent directory an NFS4ERR_ENOENT error must be returned.
Therefore, NFS4ERR_ENOENT will be returned by the server when the
current filehandle is at the root or top of the server's file
tree.
IMPLEMENTATION
As for LOOKUP, LOOKUPP will also cross mountpoints.
If the current filehandle is not a directory or named attribute
directory, the error NFS4ERR_NOTDIR is returned.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTDIR
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
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RFC 3010 NFS version 4 Protocol December 2000
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.15. Operation 17: NVERIFY - Verify Difference in Attributes
SYNOPSIS
(cfh), fattr -> -
ARGUMENT
struct NVERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
RESULT
struct NVERIFY4res {
nfsstat4 status;
};
DESCRIPTION
This operation is used to prefix a sequence of operations to be
performed if one or more attributes have changed on some
filesystem object. If all the attributes match then the error
NFS4ERR_SAME must be returned.
On success, the current filehandle retains its value.
IMPLEMENTATION
This operation is useful as a cache validation operator. If the
object to which the attributes belong has changed then the
following operations may obtain new data associated with that
object. For instance, to check if a file has been changed and
obtain new data if it has:
PUTFH (public)
LOOKUP "pub" "foo" "bar"
NVERIFY attrbits attrs
READ 0 32767
In the case that a recommended attribute is specified in the
NVERIFY operation and the server does not support that attribute
for the file system object, the error NFS4ERR_NOTSUPP is returned
to the client.
Shepler, et al. Standards Track PAGE 127
RFC 3010 NFS version 4 Protocol December 2000
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTSUPP
NFS4ERR_RESOURCE
NFS4ERR_SAME
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.16. Operation 18: OPEN - Open a Regular File
SYNOPSIS
(cfh), claim, openhow, owner, seqid, access, deny -> (cfh),
stateid, cinfo, rflags, open_confirm, delegation
ARGUMENT
struct OPEN4args {
open_claim4 claim;
openflag4 openhow;
nfs_lockowner4 owner;
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
};
enum createmode4 {
UNCHECKED4 = 0,
GUARDED4 = 1,
EXCLUSIVE4 = 2
};
union createhow4 switch (createmode4 mode) {
case UNCHECKED4:
case GUARDED4:
fattr4 createattrs;
case EXCLUSIVE4:
verifier4 createverf;
};
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RFC 3010 NFS version 4 Protocol December 2000
enum opentype4 {
OPEN4_NOCREATE = 0,
OPEN4_CREATE = 1
};
union openflag4 switch (opentype4 opentype) {
case OPEN4_CREATE:
createhow4 how;
default:
void;
};
/* Next definitions used for OPEN delegation */
enum limit_by4 {
NFS_LIMIT_SIZE = 1,
NFS_LIMIT_BLOCKS = 2
/* others as needed */
};
struct nfs_modified_limit4 {
uint32_t num_blocks;
uint32_t bytes_per_block;
};
union nfs_space_limit4 switch (limit_by4 limitby) {
/* limit specified as file size */
case NFS_LIMIT_SIZE:
uint64_t filesize;
/* limit specified by number of blocks */
case NFS_LIMIT_BLOCKS:
nfs_modified_limit4 mod_blocks;
} ;
enum open_delegation_type4 {
OPEN_DELEGATE_NONE = 0,
OPEN_DELEGATE_READ = 1,
OPEN_DELEGATE_WRITE = 2
};
enum open_claim_type4 {
CLAIM_NULL = 0,
CLAIM_PREVIOUS = 1,
CLAIM_DELEGATE_CUR = 2,
CLAIM_DELEGATE_PREV = 3
};
struct open_claim_delegate_cur4 {
pathname4 file;
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RFC 3010 NFS version 4 Protocol December 2000
stateid4 delegate_stateid;
};
union open_claim4 switch (open_claim_type4 claim) {
/*
* No special rights to file. Ordinary OPEN of the specified file.
*/
case CLAIM_NULL:
/* CURRENT_FH: directory */
pathname4 file;
/*
* Right to the file established by an open previous to server
* reboot. File identified by filehandle obtained at that time
* rather than by name.
*/
case CLAIM_PREVIOUS:
/* CURRENT_FH: file being reclaimed */
uint32_t delegate_type;
/*
* Right to file based on a delegation granted by the server.
* File is specified by name.
*/
case CLAIM_DELEGATE_CUR:
/* CURRENT_FH: directory */
open_claim_delegate_cur4 delegate_cur_info;
/* Right to file based on a delegation granted to a previous boot
* instance of the client. File is specified by name.
*/
case CLAIM_DELEGATE_PREV:
/* CURRENT_FH: directory */
pathname4 file_delegate_prev;
};
RESULT
struct open_read_delegation4 {
stateid4 stateid; /* Stateid for delegation*/
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim
(CLAIM_PREVIOUS) */
nfsace4 permissions; /* Defines users who don't
need an ACCESS call to
open for read */
};
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RFC 3010 NFS version 4 Protocol December 2000
struct open_write_delegation4 {
stateid4 stateid; /* Stateid for delegation*/
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim
(CLAIM_PREVIOUS) */
nfs_space_limit4 space_limit; /* Defines condition that
the client must check to
determine whether the
file needs to be flushed
to the server on close.
*/
nfsace4 permissions; /* Defines users who don't
need an ACCESS call as
part of a delegated
open. */
};
union open_delegation4
switch (open_delegation_type4 delegation_type) {
case OPEN_DELEGATE_NONE:
void;
case OPEN_DELEGATE_READ:
open_read_delegation4 read;
case OPEN_DELEGATE_WRITE:
open_write_delegation4 write;
};
const OPEN4_RESULT_MLOCK = 0x00000001;
const OPEN4_RESULT_CONFIRM= 0x00000002;
struct OPEN4resok {
stateid4 stateid; /* Stateid for open */
change_info4 cinfo; /* Directory Change Info */
uint32_t rflags; /* Result flags */
verifier4 open_confirm; /* OPEN_CONFIRM verifier */
open_delegation4 delegation; /* Info on any open
delegation */
};
union OPEN4res switch (nfsstat4 status) {
case NFS4_OK:
/* CURRENT_FH: opened file */
OPEN4resok resok4;
default:
void;
};
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RFC 3010 NFS version 4 Protocol December 2000
WARNING TO CLIENT IMPLEMENTORS
OPEN resembles LOOKUP in that it generates a filehandle for the
client to use. Unlike LOOKUP though, OPEN creates server state on
the filehandle. In normal circumstances, the client can only
release this state with a CLOSE operation. CLOSE uses the current
filehandle to determine which file to close. Therefore the client
MUST follow every OPEN operation with a GETFH operation in the
same COMPOUND procedure. This will supply the client with the
filehandle such that CLOSE can be used appropriately.
Simply waiting for the lease on the file to expire is insufficient
because the server may maintain the state indefinitely as long as
another client does not attempt to make a conflicting access to
the same file.
DESCRIPTION
The OPEN operation creates and/or opens a regular file in a
directory with the provided name. If the file does not exist at
the server and creation is desired, specification of the method of
creation is provided by the openhow parameter. The client has the
choice of three creation methods: UNCHECKED, GUARDED, or
EXCLUSIVE.
UNCHECKED means that the file should be created if a file of that
name does not exist and encountering an existing regular file of
that name is not an error. For this type of create, createattrs
specifies the initial set of attributes for the file. The set of
attributes may includes any writable attribute valid for regular
files. When an UNCHECKED create encounters an existing file, the
attributes specified by createattrs is not used, except that when
an object_size of zero is specified, the existing file is
truncated. If GUARDED is specified, the server checks for the
presence of a duplicate object by name before performing the
create. If a duplicate exists, an error of NFS4ERR_EXIST is
returned as the status. If the object does not exist, the request
is performed as described for UNCHECKED.
EXCLUSIVE specifies that the server is to follow exclusive
creation semantics, using the verifier to ensure exclusive
creation of the target. The server should check for the presence
of a duplicate object by name. If the object does not exist, the
server creates the object and stores the verifier with the object.
If the object does exist and the stored verifier matches the
client provided verifier, the server uses the existing object as
the newly created object. If the stored verifier does not match,
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RFC 3010 NFS version 4 Protocol December 2000
then an error of NFS4ERR_EXIST is returned. No attributes may be
provided in this case, since the server may use an attribute of
the target object to store the verifier.
For the target directory, the server returns change_info4
information in cinfo. With the atomic field of the change_info4
struct, the server will indicate if the before and after change
attributes were obtained atomically with respect to the link
creation.
Upon successful creation, the current filehandle is replaced by
that of the new object.
The OPEN procedure provides for DOS SHARE capability with the use
of the access and deny fields of the OPEN arguments. The client
specifies at OPEN the required access and deny modes. For clients
that do not directly support SHAREs (i.e. Unix), the expected deny
value is DENY_NONE. In the case that there is a existing SHARE
reservation that conflicts with the OPEN request, the server
returns the error NFS4ERR_DENIED. For a complete SHARE request,
the client must provide values for the owner and seqid fields for
the OPEN argument. For additional discussion of SHARE semantics
see the section on 'Share Reservations'.
In the case that the client is recovering state from a server
failure, the reclaim field of the OPEN argument is used to signify
that the request is meant to reclaim state previously held.
The "claim" field of the OPEN argument is used to specify the file
to be opened and the state information which the client claims to
possess. There are four basic claim types which cover the various
situations for an OPEN. They are as follows:
CLAIM_NULL
For the client, this is a new OPEN
request and there is no previous state
associate with the file for the client.
CLAIM_PREVIOUS
The client is claiming basic OPEN state
for a file that was held previous to a
server reboot. Generally used when a
server is returning persistent file
handles; the client may not have the
file name to reclaim the OPEN.
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RFC 3010 NFS version 4 Protocol December 2000
CLAIM_DELEGATE_CUR
The client is claiming a delegation for
OPEN as granted by the server.
Generally this is done as part of
recalling a delegation.
CLAIM_DELEGATE_PREV
The client is claiming a delegation
granted to a previous client instance;
used after the client reboots.
For OPEN requests whose claim type is other than CLAIM_PREVIOUS
(i.e. requests other than those devoted to reclaiming opens after
a server reboot) that reach the server during its grace or lease
expiration period, the server returns an error of NFS4ERR_GRACE.
For any OPEN request, the server may return an open delegation,
which allows further opens and closes to be handled locally on the
client as described in the section Open Delegation. Note that
delegation is up to the server to decide. The client should never
assume that delegation will or will not be granted in a particular
instance. It should always be prepared for either case. A
partial exception is the reclaim (CLAIM_PREVIOUS) case, in which a
delegation type is claimed. In this case, delegation will always
be granted, although the server may specify an immediate recall in
the delegation structure.
The rflags returned by a successful OPEN allow the server to
return information governing how the open file is to be handled.
OPEN4_RESULT_MLOCK indicates to the caller that mandatory locking
is in effect for this file and the client should act appropriately
with regard to data cached on the client. OPEN4_RESULT_CONFIRM
indicates that the client MUST execute an OPEN_CONFIRM operation
before using the open file.
If the file is a zero length array, if any component does not obey
the UTF-8 definition, or if any component in the path is of zero
length, the error NFS4ERR_INVAL will be returned.
When an OPEN is done and the specified lockowner already has the
resulting filehandle open, the result is to "OR" together the new
share and deny status together with the existing status. In this
case, only a single CLOSE need be done, even though multiple
OPEN's were completed.
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RFC 3010 NFS version 4 Protocol December 2000
IMPLEMENTATION
The OPEN procedure contains support for EXCLUSIVE create. The
mechanism is similar to the support in NFS version 3 [RFC 1813].
As in NFS version 3, this mechanism provides reliable exclusive
creation. Exclusive create is invoked when the how parameter is
EXCLUSIVE. In this case, the client provides a verifier that can
reasonably be expected to be unique. A combination of a client
identifier, perhaps the client network address, and a unique
number generated by the client, perhaps the RPC transaction
identifier, may be appropriate.
If the object does not exist, the server creates the object and
stores the verifier in stable storage. For file systems that do
not provide a mechanism for the storage of arbitrary file
attributes, the server may use one or more elements of the object
meta-data to store the verifier. The verifier must be stored in
stable storage to prevent erroneous failure on retransmission of
the request. It is assumed that an exclusive create is being
performed because exclusive semantics are critical to the
application. Because of the expected usage, exclusive CREATE does
not rely solely on the normally volatile duplicate request cache
for storage of the verifier. The duplicate request cache in
volatile storage does not survive a crash and may actually flush
on a long network partition, opening failure windows. In the UNIX
local file system environment, the expected storage location for
the verifier on creation is the meta-data (time stamps) of the
object. For this reason, an exclusive object create may not
include initial attributes because the server would have nowhere
to store the verifier.
If the server can not support these exclusive create semantics,
possibly because of the requirement to commit the verifier to
stable storage, it should fail the OPEN request with the error,
NFS4ERR_NOTSUPP.
During an exclusive CREATE request, if the object already exists,
the server reconstructs the object's verifier and compares it with
the verifier in the request. If they match, the server treats the
request as a success. The request is presumed to be a duplicate of
an earlier, successful request for which the reply was lost and
that the server duplicate request cache mechanism did not detect.
If the verifiers do not match, the request is rejected with the
status, NFS4ERR_EXIST.
Once the client has performed a successful exclusive create, it
must issue a SETATTR to set the correct object attributes. Until
it does so, it should not rely upon any of the object attributes,
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RFC 3010 NFS version 4 Protocol December 2000
since the server implementation may need to overload object meta-
data to store the verifier. The subsequent SETATTR must not occur
in the same COMPOUND request as the OPEN. This separation will
guarantee that the exclusive create mechanism will continue to
function properly in the face of retransmission of the request.
Use of the GUARDED attribute does not provide exactly-once
semantics. In particular, if a reply is lost and the server does
not detect the retransmission of the request, the procedure can
fail with NFS4ERR_EXIST, even though the create was performed
successfully.
For SHARE reservations, the client must specify a value for access
that is one of READ, WRITE, or BOTH. For deny, the client must
specify one of NONE, READ, WRITE, or BOTH. If the client fails to
do this, the server must return NFS4ERR_INVAL.
If the final component provided to OPEN is a symbolic link, the
error NFS4ERR_SYMLINK will be returned to the client. If an
intermediate component of the pathname provided to OPEN is a
symbolic link, the error NFS4ERR_NOTDIR will be returned to the
client.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BAD_SEQID
NFS4ERR_DELAY
NFS4ERR_DQUOT
NFS4ERR_EXIST
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_IO
NFS4ERR_ISDIR
NFS4ERR_LEASE_MOVED
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOSPC
NFS4ERR_NOTDIR
NFS4ERR_NOTSUPP
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_SHARE_DENIED
NFS4ERR_STALE_CLIENTID
NFS4ERR_SYMLINK
Shepler, et al. Standards Track PAGE 136
RFC 3010 NFS version 4 Protocol December 2000
14.2.17. Operation 19: OPENATTR - Open Named Attribute Directory
SYNOPSIS
(cfh) -> (cfh)
ARGUMENT
/* CURRENT_FH: file or directory */
void;
RESULT
struct OPENATTR4res {
/* CURRENT_FH: name attr directory*/
nfsstat4 status;
};
DESCRIPTION
The OPENATTR operation is used to obtain the filehandle of the
named attribute directory associated with the current filehandle.
The result of the OPENATTR will be a filehandle to an object of
type NF4ATTRDIR. From this filehandle, READDIR and LOOKUP
procedures can be used to obtain filehandles for the various named
attributes associated with the original file system object.
Filehandles returned within the named attribute directory will
have a type of NF4NAMEDATTR.
IMPLEMENTATION
If the server does not support named attributes for the current
filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
client.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTSUPP
NFS4ERR_RESOURCE
Shepler, et al. Standards Track PAGE 137
RFC 3010 NFS version 4 Protocol December 2000
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.18. Operation 20: OPEN_CONFIRM - Confirm Open
SYNOPSIS
(cfh), seqid, open_confirm-> stateid
ARGUMENT
struct OPEN_CONFIRM4args {
/* CURRENT_FH: opened file */
seqid4 seqid;
verifier4 open_confirm; /* OPEN_CONFIRM verifier */
};
RESULT
struct OPEN_CONFIRM4resok {
stateid4 stateid;
};
union OPEN_CONFIRM4res switch (nfsstat4 status) {
case NFS4_OK:
OPEN_CONFIRM4resok resok4;
default:
void;
};
DESCRIPTION
This operation is used to confirm the sequence id usage for the
first time that a nfs_lockowner is used by a client. The OPEN
operation returns a opaque confirmation verifier that is then
passed to this operation along with the next sequence id for the
nfs_lockowner. The sequence id passed to the OPEN_CONFIRM must be
1 (one) greater than the seqid passed to the OPEN operation from
which the open_confirm value was obtained. If the server receives
an unexpected sequence id with respect to the original open, then
the server assumes that the client will not confirm the original
OPEN and all state associated with the original OPEN is released
by the server.
On success, the current filehandle retains its value.
Shepler, et al. Standards Track PAGE 138
RFC 3010 NFS version 4 Protocol December 2000
IMPLEMENTATION
A given client might generate many nfs_lockowner data structures
for a given clientid. The client will periodically either dispose
of its nfs_lockowners or stop using them for indefinite periods of
time. The latter situation is why the NFS version 4 protocol does
not have a an explicit operation to exit an nfs_lockowner: such an
operation is of no use in that situation. Instead, to avoid
unbounded memory use, the server needs to implement a strategy for
disposing of nfs_lockowners that have no current lock, open, or
delegation state for any files and have not been used recently.
The time period used to determine when to dispose of
nfs_lockowners is an implementation choice. The time period
should certainly be no less than the lease time plus any grace
period the server wishes to implement beyond a lease time. The
OPEN_CONFIRM operation allows the server to safely dispose of
unused nfs_lockowner data structures.
In the case that a client issues an OPEN operation and the server
no longer has a record of the nfs_lockowner, the server needs
ensure that this is a new OPEN and not a replay or retransmission.
A lazy server implementation might require confirmation for every
nfs_lockowner for which it has no record. However, this is not
necessary until the server records the fact that it has disposed
of one nfs_lockowner for the given clientid.
The server must hold unconfirmed OPEN state until one of three
events occur. First, the client sends an OPEN_CONFIRM request
with the appropriate sequence id and confirmation verifier within
the lease period. In this case, the OPEN state on the server goes
to confirmed, and the nfs_lockowner on the server is fully
established.
Second, the client sends another OPEN request with a sequence id
that is incorrect for the nfs_lockowner (out of sequence). In
this case, the server assumes the second OPEN request is valid and
the first one is a replay. The server cancels the OPEN state of
the first OPEN request, establishes an unconfirmed OPEN state for
the second OPEN request, and responds to the second OPEN request
with an indication that an OPEN_CONFIRM is needed. The process
then repeats itself. While there is a potential for a denial of
service attack on the client, it is mitigated if the client and
server require the use of a security flavor based on Kerberos V5,
LIPKEY, or some other flavor that uses cryptography.
Shepler, et al. Standards Track PAGE 139
RFC 3010 NFS version 4 Protocol December 2000
What if the server is in the unconfirmed OPEN state for a given
nfs_lockowner, and it receives an operation on the nfs_lockowner
that has a stateid but the operation is not OPEN, or it is
OPEN_CONFIRM but with the wrong confirmation verifier? Then, even
if the seqid is correct, the server returns NFS4ERR_BAD_STATEID,
because the server assumes the operation is a replay: if the
server has no established OPEN state, then there is no way, for
example, a LOCK operation could be valid.
Third, neither of the two aforementioned events occur for the
nfs_lockowner within the lease period. In this case, the OPEN
state is cancelled and disposal of the nfs_lockowner can occur.
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_BAD_SEQID
NFS4ERR_EXPIRED
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_INVAL
NFS4ERR_MOVED
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTSUPP
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.19. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access
SYNOPSIS
(cfh), stateid, seqid, access, deny -> stateid
ARGUMENT
struct OPEN_DOWNGRADE4args {
/* CURRENT_FH: opened file */
stateid4 stateid;
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
};
RESULT
Shepler, et al. Standards Track PAGE 140
RFC 3010 NFS version 4 Protocol December 2000
struct OPEN_DOWNGRADE4resok {
stateid4 stateid;
};
union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
case NFS4_OK:
OPEN_DOWNGRADE4resok resok4;
default:
void;
};
This operation is used to adjust the access and deny bits for a given
open. This is necessary when a given lockowner opens the same file
multiple times with different access and deny flags. In this
situation, a close of one of the open's may change the appropriate
access and deny flags to remove bits associated with open's no longer
in effect.
The access and deny bits specified in this operation replace the
current ones for the specified open file. If either the access or
the deny mode specified includes bits not in effect for the open, the
error NFS4ERR_INVAL should be returned. Since access and deny bits
are subsets of those already granted, it is not possible for this
request to be denied because of conflicting share reservations.
On success, the current filehandle retains its value.
ERRORS
NFS4ERR_BADHANDLE NFS4ERR_BAD_SEQID NFS4ERR_BAD_STATEID
NFS4ERR_EXPIRED NFS4ERR_FHEXPIRED NFS4ERR_INVAL NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE NFS4ERR_OLD_STATEID NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT NFS4ERR_STALE NFS4ERR_STALE_STATEID
14.2.20. Operation 22: PUTFH - Set Current Filehandle
SYNOPSIS
filehandle -> (cfh)
ARGUMENT
struct PUTFH4args {
nfs4_fh object; };
RESULT
struct PUTFH4res {
Shepler, et al. Standards Track PAGE 141
RFC 3010 NFS version 4 Protocol December 2000
/* CURRENT_FH: */
nfsstat4 status; };
DESCRIPTION
Replaces the current filehandle with the filehandle provided as an
argument.
IMPLEMENTATION
Commonly used as the first operator in an NFS request to set the
context for following operations.
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_FHEXPIRED
NFS4ERR_MOVED
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.21. Operation 23: PUTPUBFH - Set Public Filehandle
SYNOPSIS
- -> (cfh)
ARGUMENT
void;
RESULT
struct PUTPUBFH4res {
/* CURRENT_FH: public fh */
nfsstat4 status;
};
DESCRIPTION
Replaces the current filehandle with the filehandle that
represents the public filehandle of the server's name space. This
filehandle may be different from the "root" filehandle which may
be associated with some other directory on the server.
Shepler, et al. Standards Track PAGE 142
RFC 3010 NFS version 4 Protocol December 2000
IMPLEMENTATION
Used as the first operator in an NFS request to set the context
for following operations.
ERRORS
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_WRONGSEC
14.2.22. Operation 24: PUTROOTFH - Set Root Filehandle
SYNOPSIS
- -> (cfh)
ARGUMENT
void;
RESULT
struct PUTROOTFH4res {
/* CURRENT_FH: root fh */
nfsstat4 status;
};
DESCRIPTION
Replaces the current filehandle with the filehandle that
represents the root of the server's name space. From this
filehandle a LOOKUP operation can locate any other filehandle on
the server. This filehandle may be different from the "public"
filehandle which may be associated with some other directory on
the server.
IMPLEMENTATION
Commonly used as the first operator in an NFS request to set the
context for following operations.
ERRORS
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_WRONGSEC
Shepler, et al. Standards Track PAGE 143
RFC 3010 NFS version 4 Protocol December 2000
14.2.23. Operation 25: READ - Read from File
SYNOPSIS
(cfh), offset, count, stateid -> eof, data
ARGUMENT
struct READ4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
count4 count;
};
RESULT
struct READ4resok {
bool eof;
opaque data<>;
};
union READ4res switch (nfsstat4 status) {
case NFS4_OK:
READ4resok resok4;
default:
void;
};
DESCRIPTION
The READ operation reads data from the regular file identified by
the current filehandle.
The client provides an offset of where the READ is to start and a
count of how many bytes are to be read. An offset of 0 (zero)
means to read data starting at the beginning of the file. If
offset is greater than or equal to the size of the file, the
status, NFS4_OK, is returned with a data length set to 0 (zero)
and eof is set to TRUE. The READ is subject to access permissions
checking.
If the client specifies a count value of 0 (zero), the READ
succeeds and returns 0 (zero) bytes of data again subject to
access permissions checking. The server may choose to return
fewer bytes than specified by the client. The client needs to
check for this condition and handle the condition appropriately.
Shepler, et al. Standards Track PAGE 144
RFC 3010 NFS version 4 Protocol December 2000
The stateid value for a READ request represents a value returned
from a previous record lock or share reservation request. Used by
the server to verify that the associated lock is still valid and
to update lease timeouts for the client.
If the read ended at the end-of-file (formally, in a correctly
formed READ request, if offset + count is equal to the size of the
file), or the read request extends beyond the size of the file (if
offset + count is greater than the size of the file), eof is
returned as TRUE; otherwise it is FALSE. A successful READ of an
empty file will always return eof as TRUE.
On success, the current filehandle retains its value.
IMPLEMENTATION
It is possible for the server to return fewer than count bytes of
data. If the server returns less than the count requested and eof
set to FALSE, the client should issue another READ to get the
remaining data. A server may return less data than requested
under several circumstances. The file may have been truncated by
another client or perhaps on the server itself, changing the file
size from what the requesting client believes to be the case.
This would reduce the actual amount of data available to the
client. It is possible that the server may back off the transfer
size and reduce the read request return. Server resource
exhaustion may also occur necessitating a smaller read return.
If the file is locked the server will return an NFS4ERR_LOCKED
error. Since the lock may be of short duration, the client may
choose to retransmit the READ request (with exponential backoff)
until the operation succeeds.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_BAD_STATEID
NFS4ERR_DELAY
NFS4ERR_DENIED
NFS4ERR_EXPIRED
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_LOCKED
NFS4ERR_LEASE_MOVED
NFS4ERR_MOVED
Shepler, et al. Standards Track PAGE 145
RFC 3010 NFS version 4 Protocol December 2000
NFS4ERR_NOFILEHANDLE
NFS4ERR_NXIO
NFS4ERR_OLD_STATEID
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_STATEID
NFS4ERR_WRONGSEC
14.2.24. Operation 26: READDIR - Read Directory
SYNOPSIS
(cfh), cookie, cookieverf, dircount, maxcount, attrbits ->
cookieverf { cookie, filename, attrbits, attributes }
ARGUMENT
struct READDIR4args {
/* CURRENT_FH: directory */
nfs_cookie4 cookie;
verifier4 cookieverf;
count4 dircount;
count4 maxcount;
bitmap4 attr_request;
};
RESULT
struct entry4 {
nfs_cookie4 cookie;
component4 name;
fattr4 attrs;
entry4 *nextentry;
};
struct dirlist4 {
entry4 *entries;
bool eof;
};
struct READDIR4resok {
verifier4 cookieverf;
dirlist4 reply;
};
union READDIR4res switch (nfsstat4 status) {
Shepler, et al. Standards Track PAGE 146
RFC 3010 NFS version 4 Protocol December 2000
case NFS4_OK:
READDIR4resok resok4;
default:
void;
};
DESCRIPTION
The READDIR operation retrieves a variable number of entries from
a file system directory and returns client requested attributes
for each entry along with information to allow the client to
request additional directory entries in a subsequent READDIR.
The arguments contain a cookie value that represents where the
READDIR should start within the directory. A value of 0 (zero)
for the cookie is used to start reading at the beginning of the
directory. For subsequent READDIR requests, the client specifies
a cookie value that is provided by the server on a previous
READDIR request.
The cookieverf value should be set to 0 (zero) when the cookie
value is 0 (zero) (first directory read). On subsequent requests,
it should be a cookieverf as returned by the server. The
cookieverf must match that returned by the READDIR in which the
cookie was acquired.
The dircount portion of the argument is a hint of the maximum
number of bytes of directory information that should be returned.
This value represents the length of the names of the directory
entries and the cookie value for these entries. This length
represents the XDR encoding of the data (names and cookies) and
not the length in the native format of the server. The server may
return less data.
The maxcount value of the argument is the maximum number of bytes
for the result. This maximum size represents all of the data
being returned and includes the XDR overhead. The server may
return less data. If the server is unable to return a single
directory entry within the maxcount limit, the error
NFS4ERR_READDIR_NOSPC will be returned to the client.
Finally, attrbits represents the list of attributes to be returned
for each directory entry supplied by the server.
On successful return, the server's response will provide a list of
directory entries. Each of these entries contains the name of the
directory entry, a cookie value for that entry, and the associated
attributes as requested.
Shepler, et al. Standards Track PAGE 147
RFC 3010 NFS version 4 Protocol December 2000
The cookie value is only meaningful to the server and is used as a
"bookmark" for the directory entry. As mentioned, this cookie is
used by the client for subsequent READDIR operations so that it
may continue reading a directory. The cookie is similar in
concept to a READ offset but should not be interpreted as such by
the client. Ideally, the cookie value should not change if the
directory is modified since the client may be caching these
values.
In some cases, the server may encounter an error while obtaining
the attributes for a directory entry. Instead of returning an
error for the entire READDIR operation, the server can instead
return the attribute 'fattr4_rdattr_error'. With this, the server
is able to communicate the failure to the client and not fail the
entire operation in the instance of what might be a transient
failure. Obviously, the client must request the
fattr4_rdattr_error attribute for this method to work properly.
If the client does not request the attribute, the server has no
choice but to return failure for the entire READDIR operation.
For some file system environments, the directory entries "." and
".." have special meaning and in other environments, they may
not. If the server supports these special entries within a
directory, they should not be returned to the client as part of
the READDIR response. To enable some client environments, the
cookie values of 0, 1, and 2 are to be considered reserved. Note
that the Unix client will use these values when combining the
server's response and local representations to enable a fully
formed Unix directory presentation to the application.
For READDIR arguments, cookie values of 1 and 2 should not be used
and for READDIR results cookie values of 0, 1, and 2 should not
returned.
On success, the current filehandle retains its value.
IMPLEMENTATION
The server's file system directory representations can differ
greatly. A client's programming interfaces may also be bound to
the local operating environment in a way that does not translate
well into the NFS protocol. Therefore the use of the dircount and
maxcount fields are provided to allow the client the ability to
provide guidelines to the server. If the client is aggressive
about attribute collection during a READDIR, the server has an
idea of how to limit the encoded response. The dircount field
provides a hint on the number of entries based solely on the names
of the directory entries. Since it is a hint, it may be possible
Shepler, et al. Standards Track PAGE 148
RFC 3010 NFS version 4 Protocol December 2000
that a dircount value is zero. In this case, the server is free
to ignore the dircount value and return directory information
based on the specified maxcount value.
The cookieverf may be used by the server to help manage cookie
values that may become stale. It should be a rare occurrence that
a server is unable to continue properly reading a directory with
the provided cookie/cookieverf pair. The server should make every
effort to avoid this condition since the application at the client
may not be able to properly handle this type of failure.
The use of the cookieverf will also protect the client from using
READDIR cookie values that may be stale. For example, if the file
system has been migrated, the server may or may not be able to use
the same cookie values to service READDIR as the previous server
used. With the client providing the cookieverf, the server is
able to provide the appropriate response to the client. This
prevents the case where the server may accept a cookie value but
the underlying directory has changed and the response is invalid
from the client's context of its previous READDIR.
Since some servers will not be returning "." and ".." entries as
has been done with previous versions of the NFS protocol, the
client that requires these entries be present in READDIR responses
must fabricate them.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_BAD_COOKIE
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTDIR
NFS4ERR_NOTSUPP
NFS4ERR_READDIR_NOSPC
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_TOOSMALL
NFS4ERR_WRONGSEC
Shepler, et al. Standards Track PAGE 149
RFC 3010 NFS version 4 Protocol December 2000
14.2.25. Operation 27: READLINK - Read Symbolic Link
SYNOPSIS
(cfh) -> linktext
ARGUMENT
/* CURRENT_FH: symlink */
void;
RESULT
struct READLINK4resok {
linktext4 link;
};
union READLINK4res switch (nfsstat4 status) {
case NFS4_OK:
READLINK4resok resok4;
default:
void;
};
DESCRIPTION
READLINK reads the data associated with a symbolic link. The data
is a UTF-8 string that is opaque to the server. That is, whether
created by an NFS client or created locally on the server, the
data in a symbolic link is not interpreted when created, but is
simply stored.
On success, the current filehandle retains its value.
IMPLEMENTATION
A symbolic link is nominally a pointer to another file. The data
is not necessarily interpreted by the server, just stored in the
file. It is possible for a client implementation to store a path
name that is not meaningful to the server operating system in a
symbolic link. A READLINK operation returns the data to the
client for interpretation. If different implementations want to
share access to symbolic links, then they must agree on the
interpretation of the data in the symbolic link.
The READLINK operation is only allowed on objects of type NF4LNK.
The server should return the error, NFS4ERR_INVAL, if the object
is not of type, NF4LNK.
Shepler, et al. Standards Track PAGE 150
RFC 3010 NFS version 4 Protocol December 2000
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTSUPP
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.26. Operation 28: REMOVE - Remove Filesystem Object
SYNOPSIS
(cfh), filename -> change_info
ARGUMENT
struct REMOVE4args {
/* CURRENT_FH: directory */
component4 target;
};
RESULT
struct REMOVE4resok {
change_info4 cinfo;
}
union REMOVE4res switch (nfsstat4 status) {
case NFS4_OK:
REMOVE4resok resok4;
default:
void;
}
DESCRIPTION
The REMOVE operation removes (deletes) a directory entry named by
filename from the directory corresponding to the current
filehandle. If the entry in the directory was the last reference
Shepler, et al. Standards Track PAGE 151
RFC 3010 NFS version 4 Protocol December 2000
to the corresponding file system object, the object may be
destroyed.
For the directory where the filename was removed, the server
returns change_info4 information in cinfo. With the atomic field
of the change_info4 struct, the server will indicate if the before
and after change attributes were obtained atomically with respect
to the removal.
If the target has a length of 0 (zero), or if target does not obey
the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
On success, the current filehandle retains its value.
IMPLEMENTATION
NFS versions 2 and 3 required a different operator RMDIR for
directory removal. NFS version 4 REMOVE can be used to delete any
directory entry independent of its file type.
The concept of last reference is server specific. However, if the
numlinks field in the previous attributes of the object had the
value 1, the client should not rely on referring to the object via
a file handle. Likewise, the client should not rely on the
resources (disk space, directory entry, and so on) formerly
associated with the object becoming immediately available. Thus,
if a client needs to be able to continue to access a file after
using REMOVE to remove it, the client should take steps to make
sure that the file will still be accessible. The usual mechanism
used is to RENAME the file from its old name to a new hidden name.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTDIR
NFS4ERR_NOTEMPTY
NFS4ERR_NOTSUPP
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
Shepler, et al. Standards Track PAGE 152
RFC 3010 NFS version 4 Protocol December 2000
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.27. Operation 29: RENAME - Rename Directory Entry
SYNOPSIS
(sfh), oldname (cfh), newname -> source_change_info,
target_change_info
ARGUMENT
struct RENAME4args {
/* SAVED_FH: source directory */
component4 oldname;
/* CURRENT_FH: target directory */
component4 newname;
};
RESULT
struct RENAME4resok {
change_info4 source_cinfo;
change_info4 target_cinfo;
};
union RENAME4res switch (nfsstat4 status) {
case NFS4_OK:
RENAME4resok resok4;
default:
void;
};
DESCRIPTION
The RENAME operation renames the object identified by oldname in
the source directory corresponding to the saved filehandle, as set
by the SAVEFH operation, to newname in the target directory
corresponding to the current filehandle. The operation is
required to be atomic to the client. Source and target
directories must reside on the same file system on the server. On
success, the current filehandle will continue to be the target
directory.
If the target directory already contains an entry with the name,
newname, the source object must be compatible with the target:
either both are non-directories or both are directories and the
target must be empty. If compatible, the existing target is
Shepler, et al. Standards Track PAGE 153
RFC 3010 NFS version 4 Protocol December 2000
removed before the rename occurs. If they are not compatible or
if the target is a directory but not empty, the server will return
the error, NFS4ERR_EXIST.
If oldname and newname both refer to the same file (they might be
hard links of each other), then RENAME should perform no action
and return success.
For both directories involved in the RENAME, the server returns
change_info4 information. With the atomic field of the
change_info4 struct, the server will indicate if the before and
after change attributes were obtained atomically with respect to
the rename.
If the oldname or newname has a length of 0 (zero), or if oldname
or newname does not obey the UTF-8 definition, the error
NFS4ERR_INVAL will be returned.
IMPLEMENTATION
The RENAME operation must be atomic to the client. The statement
"source and target directories must reside on the same file system
on the server" means that the fsid fields in the attributes for
the directories are the same. If they reside on different file
systems, the error, NFS4ERR_XDEV, is returned.
A filehandle may or may not become stale or expire on a rename.
However, server implementors are strongly encouraged to attempt to
keep file handles from becoming stale or expiring in this fashion.
On some servers, the filenames, "." and "..", are illegal as
either oldname or newname. In addition, neither oldname nor
newname can be an alias for the source directory. These servers
will return the error, NFS4ERR_INVAL, in these cases.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_DELAY
NFS4ERR_DQUOT
NFS4ERR_EXIST
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_ISDIR
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
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NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOSPC
NFS4ERR_NOTDIR
NFS4ERR_NOTEMPTY
NFS4ERR_NOTSUPP
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
NFS4ERR_XDEV
14.2.28. Operation 30: RENEW - Renew a Lease
SYNOPSIS
stateid -> ()
ARGUMENT
struct RENEW4args {
stateid4 stateid;
};
RESULT
struct RENEW4res {
nfsstat4 status;
};
DESCRIPTION
The RENEW operation is used by the client to renew leases which it
currently holds at a server. In processing the RENEW request, the
server renews all leases associated with the client. The
associated leases are determined by the client id provided via the
SETCLIENTID procedure.
The stateid for RENEW may not be one of the special stateids
consisting of all bits 0 (zero) or all bits 1.
IMPLEMENTATION
ERRORS
NFS4ERR_BAD_STATEID
NFS4ERR_EXPIRED
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NFS4ERR_GRACE
NFS4ERR_INVAL
NFS4ERR_LEASE_MOVED
NFS4ERR_MOVED
NFS4ERR_OLD_STATEID
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE_STATEID
NFS4ERR_WRONGSEC
14.2.29. Operation 31: RESTOREFH - Restore Saved Filehandle
SYNOPSIS
(sfh) -> (cfh)
ARGUMENT
/* SAVED_FH: */
void;
RESULT
struct RESTOREFH4res {
/* CURRENT_FH: value of saved fh */
nfsstat4 status;
};
DESCRIPTION
Set the current filehandle to the value in the saved filehandle.
If there is no saved filehandle then return an error
NFS4ERR_NOFILEHANDLE.
IMPLEMENTATION
Operations like OPEN and LOOKUP use the current filehandle to
represent a directory and replace it with a new filehandle.
Assuming the previous filehandle was saved with a SAVEFH operator,
the previous filehandle can be restored as the current filehandle.
This is commonly used to obtain post-operation attributes for the
directory, e.g.
PUTFH (directory filehandle)
SAVEFH
GETATTR attrbits (pre-op dir attrs)
CREATE optbits "foo" attrs
GETATTR attrbits (file attributes)
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RESTOREFH
GETATTR attrbits (post-op dir attrs)
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_FHEXPIRED
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.30. Operation 32: SAVEFH - Save Current Filehandle
SYNOPSIS
(cfh) -> (sfh)
ARGUMENT
/* CURRENT_FH: */
void;
RESULT
struct SAVEFH4res {
/* SAVED_FH: value of current fh */
nfsstat4 status;
};
DESCRIPTION
Save the current filehandle. If a previous filehandle was saved
then it is no longer accessible. The saved filehandle can be
restored as the current filehandle with the RESTOREFH operator.
On success, the current filehandle retains its value.
IMPLEMENTATION
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_FHEXPIRED
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
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NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.31. Operation 33: SECINFO - Obtain Available Security
SYNOPSIS
(cfh), name -> { secinfo }
ARGUMENT
struct SECINFO4args {
/* CURRENT_FH: */
component4 name;
};
RESULT
enum rpc_gss_svc_t {
RPC_GSS_SVC_NONE = 1,
RPC_GSS_SVC_INTEGRITY = 2,
RPC_GSS_SVC_PRIVACY = 3
};
struct rpcsec_gss_info {
sec_oid4 oid;
qop4 qop;
rpc_gss_svc_t service;
};
struct secinfo4 {
uint32_t flavor;
opaque flavor_info<>; /* null for AUTH_SYS, AUTH_NONE;
contains rpcsec_gss_info for
RPCSEC_GSS. */
};
typedef secinfo4 SECINFO4resok<>;
union SECINFO4res switch (nfsstat4 status) {
case NFS4_OK:
SECINFO4resok resok4;
default:
void;
};
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DESCRIPTION
The SECINFO operation is used by the client to obtain a list of
valid RPC authentication flavors for a specific file handle, file
name pair. The result will contain an array which represents the
security mechanisms available. The array entries are represented
by the secinfo4 structure. The field 'flavor' will contain a
value of AUTH_NONE, AUTH_SYS (as defined in [RFC 1831]), or
RPCSEC_GSS (as defined in [RFC 2203]).
For the flavors, AUTH_NONE, and AUTH_SYS no additional security
information is returned. For a return value of RPCSEC_GSS, a
security triple is returned that contains the mechanism object id
(as defined in [RFC 2078]), the quality of protection (as defined
in [RFC 2078]) and the service type (as defined in [RFC 2203]). It
is possible for SECINFO to return multiple entries with flavor
equal to RPCSEC_GSS with different security triple values.
On success, the current filehandle retains its value.
IMPLEMENTATION
The SECINFO operation is expected to be used by the NFS client
when the error value of NFS4ERR_WRONGSEC is returned from another
NFS operation. This signifies to the client that the server's
security policy is different from what the client is currently
using. At this point, the client is expected to obtain a list of
possible security flavors and choose what best suits its policies.
It is recommended that the client issue the SECINFO call protected
by a security triple that uses either rpc_gss_svc_integrity or
rpc_gss_svc_privacy service. The use of rpc_gss_svc_none would
allow an attacker in the middle to modify the SECINFO results such
that the client might select a weaker algorithm in the set allowed
by server, making the client and/or server vulnerable to further
attacks.
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_FHEXPIRED
NFS4ERR_MOVED
NFS4ERR_NAMETOOLONG
NFS4ERR_NOENT
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTDIR
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
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NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.32. Operation 34: SETATTR - Set Attributes
SYNOPSIS
(cfh), attrbits, attrvals -> -
ARGUMENT
struct SETATTR4args {
/* CURRENT_FH: target object */
stateid4 stateid;
fattr4 obj_attributes;
};
RESULT
struct SETATTR4res {
nfsstat4 status;
bitmap4 attrsset;
};
DESCRIPTION
The SETATTR operation changes one or more of the attributes of a
file system object. The new attributes are specified with a
bitmap and the attributes that follow the bitmap in bit order.
The stateid is necessary for SETATTRs that change the size of a
file (modify the attribute object_size). This stateid represents
a record lock, share reservation, or delegation which must be
valid for the SETATTR to modify the file data. A valid stateid
would always be specified. When the file size is not changed, the
special stateid consisting of all bits 0 (zero) should be used.
On either success or failure of the operation, the server will
return the attrsset bitmask to represent what (if any) attributes
were successfully set.
On success, the current filehandle retains its value.
IMPLEMENTATION
The file size attribute is used to request changes to the size of
a file. A value of 0 (zero) causes the file to be truncated, a
value less than the current size of the file causes data from new
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RFC 3010 NFS version 4 Protocol December 2000
size to the end of the file to be discarded, and a size greater
than the current size of the file causes logically zeroed data
bytes to be added to the end of the file. Servers are free to
implement this using holes or actual zero data bytes. Clients
should not make any assumptions regarding a server's
implementation of this feature, beyond that the bytes returned
will be zeroed. Servers must support extending the file size via
SETATTR.
SETATTR is not guaranteed atomic. A failed SETATTR may partially
change a file's attributes.
Changing the size of a file with SETATTR indirectly changes the
time_modify. A client must account for this as size changes can
result in data deletion.
If server and client times differ, programs that compare client
time to file times can break. A time maintenance protocol should
be used to limit client/server time skew.
If the server cannot successfully set all the attributes it must
return an NFS4ERR_INVAL error. If the server can only support 32
bit offsets and sizes, a SETATTR request to set the size of a file
to larger than can be represented in 32 bits will be rejected with
this same error.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_BAD_STATEID
NFS4ERR_DELAY
NFS4ERR_DENIED
NFS4ERR_DQUOT
NFS4ERR_EXPIRED
NFS4ERR_FBIG
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOSPC
NFS4ERR_NOTSUPP
NFS4ERR_OLD_STATEID
NFS4ERR_PERM
NFS4ERR_RESOURCE
NFS4ERR_ROFS
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NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_STATEID
NFS4ERR_WRONGSEC
14.2.33. Operation 35: SETCLIENTID - Negotiate Clientid
SYNOPSIS
client, callback -> clientid, setclientid_confirm
ARGUMENT
struct SETCLIENTID4args {
nfs_client_id4 client;
cb_client4 callback;
};
RESULT
struct SETCLIENTID4resok {
clientid4 clientid;
verifier4 setclientid_confirm;
};
union SETCLIENTID4res switch (nfsstat4 status) {
case NFS4_OK:
SETCLIENTID4resok resok4;
case NFS4ERR_CLID_INUSE:
clientaddr4 client_using;
default:
void;
};
DESCRIPTION
The SETCLIENTID operation introduces the ability of the client to
notify the server of its intention to use a particular client
identifier and verifier pair. Upon successful completion the
server will return a clientid which is used in subsequent file
locking requests and a confirmation verifier. The client will use
the SETCLIENTID_CONFIRM operation to return the verifier to the
server. At that point, the client may use the clientid in
subsequent operations that require an nfs_lockowner.
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The callback information provided in this operation will be used
if the client is provided an open delegation at a future point.
Therefore, the client must correctly reflect the program and port
numbers for the callback program at the time SETCLIENTID is used.
IMPLEMENTATION
The server takes the verifier and client identification supplied
in the nfs_client_id4 and searches for a match of the client
identification. If no match is found the server saves the
principal/uid information along with the verifier and client
identification and returns a unique clientid that is used as a
shorthand reference to the supplied information.
If the server finds matching client identification and a
corresponding match in principal/uid, the server releases all
locking state for the client and returns a new clientid.
The principal, or principal to user-identifier mapping is taken
from the credential presented in the RPC. As mentioned, the
server will use the credential and associated principal for the
matching with existing clientids. If the client is a traditional
host-based client like a Unix NFS client, then the credential
presented may be the host credential. If the client is a user
level client or lightweight client, the credential used may be the
end user's credential. The client should take care in choosing an
appropriate credential since denial of service attacks could be
attempted by a rogue client that has access to the credential.
ERRORS
NFS4ERR_CLID_INUSE
NFS4ERR_INVAL
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
14.2.34. Operation 36: SETCLIENTID_CONFIRM - Confirm Clientid
SYNOPSIS
setclientid_confirm -> -
ARGUMENT
struct SETCLIENTID_CONFIRM4args {
verifier4 setclientid_confirm;
};
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RFC 3010 NFS version 4 Protocol December 2000
RESULT
struct SETCLIENTID_CONFIRM4res {
nfsstat4 status;
};
DESCRIPTION
This operation is used by the client to confirm the results from a
previous call to SETCLIENTID. The client provides the server
supplied (from a SETCLIENTID response) opaque confirmation
verifier. The server responds with a simple status of success or
failure.
IMPLEMENTATION
The client must use the SETCLIENTID_CONFIRM operation to confirm
its use of client identifier. If the server is holding state for
a client which has presented a new verifier via SETCLIENTID, then
the state will not be released, as described in the section
"Client Failure and Recovery", until a valid SETCLIENTID_CONFIRM
is received. Upon successful confirmation the server will release
the previous state held on behalf of the client. The server
should choose a confirmation cookie value that is reasonably
unique for the client.
ERRORS
NFS4ERR_CLID_INUSE
NFS4ERR_INVAL
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE_CLIENTID
14.2.35. Operation 37: VERIFY - Verify Same Attributes
SYNOPSIS
(cfh), fattr -> -
ARGUMENT
struct VERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
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RESULT
struct VERIFY4res {
nfsstat4 status;
};
DESCRIPTION
The VERIFY operation is used to verify that attributes have a
value assumed by the client before proceeding with following
operations in the compound request. If any of the attributes do
not match then the error NFS4ERR_NOT_SAME must be returned. The
current filehandle retains its value after successful completion
of the operation.
IMPLEMENTATION
One possible use of the VERIFY operation is the following compound
sequence. With this the client is attempting to verify that the
file being removed will match what the client expects to be
removed. This sequence can help prevent the unintended deletion
of a file.
PUTFH (directory filehandle)
LOOKUP (file name)
VERIFY (filehandle == fh)
PUTFH (directory filehandle)
REMOVE (file name)
This sequence does not prevent a second client from removing and
creating a new file in the middle of this sequence but it does
help avoid the unintended result.
In the case that a recommended attribute is specified in the
VERIFY operation and the server does not support that attribute
for the file system object, the error NFS4ERR_NOTSUPP is returned
to the client.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_DELAY
NFS4ERR_FHEXPIRED
NFS4ERR_INVAL
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOTSUPP
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NFS4ERR_NOT_SAME
NFS4ERR_RESOURCE
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_WRONGSEC
14.2.36. Operation 38: WRITE - Write to File
SYNOPSIS
(cfh), offset, count, stability, stateid, data -> count, committed,
verifier
ARGUMENT
enum stable_how4 {
UNSTABLE4 = 0,
DATA_SYNC4 = 1,
FILE_SYNC4 = 2
};
struct WRITE4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
stable_how4 stable;
opaque data<>;
};
RESULT
struct WRITE4resok {
count4 count;
stable_how4 committed;
verifier4 writeverf;
};
union WRITE4res switch (nfsstat4 status) {
case NFS4_OK:
WRITE4resok resok4;
default:
void;
};
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DESCRIPTION
The WRITE operation is used to write data to a regular file. The
target file is specified by the current filehandle. The offset
specifies the offset where the data should be written. An offset
of 0 (zero) specifies that the write should start at the beginning
of the file. The count represents the number of bytes of data
that are to be written. If the count is 0 (zero), the WRITE will
succeed and return a count of 0 (zero) subject to permissions
checking. The server may choose to write fewer bytes than
requested by the client.
Part of the write request is a specification of how the write is
to be performed. The client specifies with the stable parameter
the method of how the data is to be processed by the server. If
stable is FILE_SYNC4, the server must commit the data written plus
all file system metadata to stable storage before returning
results. This corresponds to the NFS version 2 protocol
semantics. Any other behavior constitutes a protocol violation.
If stable is DATA_SYNC4, then the server must commit all of the
data to stable storage and enough of the metadata to retrieve the
data before returning. The server implementor is free to
implement DATA_SYNC4 in the same fashion as FILE_SYNC4, but with a
possible performance drop. If stable is UNSTABLE4, the server is
free to commit any part of the data and the metadata to stable
storage, including all or none, before returning a reply to the
client. There is no guarantee whether or when any uncommitted data
will subsequently be committed to stable storage. The only
guarantees made by the server are that it will not destroy any
data without changing the value of verf and that it will not
commit the data and metadata at a level less than that requested
by the client.
The stateid returned from a previous record lock or share
reservation request is provided as part of the argument. The
stateid is used by the server to verify that the associated lock
is still valid and to update lease timeouts for the client.
Upon successful completion, the following results are returned.
The count result is the number of bytes of data written to the
file. The server may write fewer bytes than requested. If so, the
actual number of bytes written starting at location, offset, is
returned.
The server also returns an indication of the level of commitment
of the data and metadata via committed. If the server committed
all data and metadata to stable storage, committed should be set
to FILE_SYNC4. If the level of commitment was at least as strong
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RFC 3010 NFS version 4 Protocol December 2000
as DATA_SYNC4, then committed should be set to DATA_SYNC4.
Otherwise, committed must be returned as UNSTABLE4. If stable was
FILE4_SYNC, then committed must also be FILE_SYNC4: anything else
constitutes a protocol violation. If stable was DATA_SYNC4, then
committed may be FILE_SYNC4 or DATA_SYNC4: anything else
constitutes a protocol violation. If stable was UNSTABLE4, then
committed may be either FILE_SYNC4, DATA_SYNC4, or UNSTABLE4.
The final portion of the result is the write verifier, verf. The
write verifier is a cookie that the client can use to determine
whether the server has changed state between a call to WRITE and a
subsequent call to either WRITE or COMMIT. This cookie must be
consistent during a single instance of the NFS version 4 protocol
service and must be unique between instances of the NFS version 4
protocol server, where uncommitted data may be lost.
If a client writes data to the server with the stable argument set
to UNSTABLE4 and the reply yields a committed response of
DATA_SYNC4 or UNSTABLE4, the client will follow up some time in
the future with a COMMIT operation to synchronize outstanding
asynchronous data and metadata with the server's stable storage,
barring client error. It is possible that due to client crash or
other error that a subsequent COMMIT will not be received by the
server.
On success, the current filehandle retains its value.
IMPLEMENTATION
It is possible for the server to write fewer than count bytes of
data. In this case, the server should not return an error unless
no data was written at all. If the server writes less than count
bytes, the client should issue another WRITE to write the
remaining data.
It is assumed that the act of writing data to a file will cause
the time_modified of the file to be updated. However, the
time_modified of the file should not be changed unless the
contents of the file are changed. Thus, a WRITE request with
count set to 0 should not cause the time_modified of the file to
be updated.
The definition of stable storage has been historically a point of
contention. The following expected properties of stable storage
may help in resolving design issues in the implementation. Stable
storage is persistent storage that survives:
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RFC 3010 NFS version 4 Protocol December 2000
1. Repeated power failures.
2. Hardware failures (of any board, power supply, etc.).
3. Repeated software crashes, including reboot cycle.
This definition does not address failure of the stable storage
module itself.
The verifier is defined to allow a client to detect different
instances of an NFS version 4 protocol server over which cached,
uncommitted data may be lost. In the most likely case, the
verifier allows the client to detect server reboots. This
information is required so that the client can safely determine
whether the server could have lost cached data. If the server
fails unexpectedly and the client has uncommitted data from
previous WRITE requests (done with the stable argument set to
UNSTABLE4 and in which the result committed was returned as
UNSTABLE4 as well) it may not have flushed cached data to stable
storage. The burden of recovery is on the client and the client
will need to retransmit the data to the server.
A suggested verifier would be to use the time that the server was
booted or the time the server was last started (if restarting the
server without a reboot results in lost buffers).
The committed field in the results allows the client to do more
effective caching. If the server is committing all WRITE requests
to stable storage, then it should return with committed set to
FILE_SYNC4, regardless of the value of the stable field in the
arguments. A server that uses an NVRAM accelerator may choose to
implement this policy. The client can use this to increase the
effectiveness of the cache by discarding cached data that has
already been committed on the server.
Some implementations may return NFS4ERR_NOSPC instead of
NFS4ERR_DQUOT when a user's quota is exceeded.
ERRORS
NFS4ERR_ACCES
NFS4ERR_BADHANDLE
NFS4ERR_BAD_STATEID
NFS4ERR_DELAY
NFS4ERR_DENIED
NFS4ERR_DQUOT
NFS4ERR_EXPIRED
NFS4ERR_FBIG
NFS4ERR_FHEXPIRED
NFS4ERR_GRACE
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NFS4ERR_INVAL
NFS4ERR_IO
NFS4ERR_LEASE_MOVED
NFS4ERR_LOCKED
NFS4ERR_MOVED
NFS4ERR_NOFILEHANDLE
NFS4ERR_NOSPC
NFS4ERR_OLD_STATEID
NFS4ERR_RESOURCE
NFS4ERR_ROFS
NFS4ERR_SERVERFAULT
NFS4ERR_STALE
NFS4ERR_STALE_STATEID
NFS4ERR_WRONGSEC
15. NFS Version 4 Callback Procedures
The procedures used for callbacks are defined in the following
sections. In the interest of clarity, the terms "client" and
"server" refer to NFS clients and servers, despite the fact that for
an individual callback RPC, the sense of these terms would be
precisely the opposite.
15.1. Procedure 0: CB_NULL - No Operation
SYNOPSIS
<null>
ARGUMENT
void;
RESULT
void;
DESCRIPTION
Standard NULL procedure. Void argument, void response. Even
though there is no direct functionality associated with this
procedure, the server will use CB_NULL to confirm the existence of
a path for RPCs from server to client.
ERRORS
None.
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15.2. Procedure 1: CB_COMPOUND - Compound Operations
SYNOPSIS
compoundargs -> compoundres
ARGUMENT
enum nfs_cb_opnum4 {
OP_CB_GETATTR = 3,
OP_CB_RECALL = 4 };
union nfs_cb_argop4 switch (unsigned argop) {
case OP_CB_GETATTR: CB_GETATTR4args opcbgetattr;
case OP_CB_RECALL: CB_RECALL4args opcbrecall; };
struct CB_COMPOUND4args {
utf8string tag;
uint32_t minorversion;
nfs_cb_argop4 argarray<>; };
RESULT
union nfs_cb_resop4 switch (unsigned resop){
case OP_CB_GETATTR: CB_GETATTR4res opcbgetattr;
case OP_CB_RECALL: CB_RECALL4res opcbrecall; };
struct CB_COMPOUND4res {
nfsstat4 status;
utf8string tag;
nfs_cb_resop4 resarray<>; };
DESCRIPTION
The CB_COMPOUND procedure is used to combine one or more of the
callback procedures into a single RPC request. The main callback
RPC program has two main procedures: CB_NULL and CB_COMPOUND. All
other operations use the CB_COMPOUND procedure as a wrapper.
In the processing of the CB_COMPOUND procedure, the client may
find that it does not have the available resources to execute any
or all of the operations within the CB_COMPOUND sequence. In this
case, the error NFS4ERR_RESOURCE will be returned for the
particular operation within the CB_COMPOUND procedure where the
resource exhaustion occurred. This assumes that all previous
operations within the CB_COMPOUND sequence have been evaluated
successfully.
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Contained within the CB_COMPOUND results is a 'status' field.
This status must be equivalent to the status of the last operation
that was executed within the CB_COMPOUND procedure. Therefore, if
an operation incurred an error then the 'status' value will be the
same error value as is being returned for the operation that
failed.
IMPLEMENTATION
The CB_COMPOUND procedure is used to combine individual operations
into a single RPC request. The client interprets each of the
operations in turn. If an operation is executed by the client and
the status of that operation is NFS4_OK, then the next operation
in the CB_COMPOUND procedure is executed. The client continues
this process until there are no more operations to be executed or
one of the operations has a status value other than NFS4_OK.
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_BAD_STATEID
NFS4ERR_RESOURCE
15.2.1. Operation 3: CB_GETATTR - Get Attributes
SYNOPSIS
fh, attrbits -> attrbits, attrvals
ARGUMENT
struct CB_GETATTR4args {
nfs_fh4 fh;
bitmap4 attr_request;
};
RESULT
struct CB_GETATTR4resok {
fattr4 obj_attributes;
};
union CB_GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
CB_GETATTR4resok resok4;
default:
void;
};
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RFC 3010 NFS version 4 Protocol December 2000
DESCRIPTION
The CB_GETATTR operation is used to obtain the attributes modified
by an open delegate to allow the server to respond to GETATTR
requests for a file which is the subject of an open delegation.
If the handle specified is not one for which the client holds a
write open delegation, an NFS4ERR_BADHANDLE error is returned.
IMPLEMENTATION
The client returns attrbits and the associated attribute values
only for attributes that it may change (change, time_modify,
object_size).
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_RESOURCE
15.2.2. Operation 4: CB_RECALL - Recall an Open Delegation
SYNOPSIS
stateid, truncate, fh -> status
ARGUMENT
struct CB_RECALL4args {
stateid4 stateid;
bool truncate;
nfs_fh4 fh;
};
RESULT
struct CB_RECALL4res {
nfsstat4 status;
};
DESCRIPTION
The CB_RECALL operation is used to begin the process of recalling
an open delegation and returning it to the server.
Shepler, et al. Standards Track PAGE 173
RFC 3010 NFS version 4 Protocol December 2000
The truncate flag is used to optimize recall for a file which is
about to be truncated to zero. When it is set, the client is
freed of obligation to propagate modified data for the file to the
server, since this data is irrelevant.
If the handle specified is not one for which the client holds an
open delegation, an NFS4ERR_BADHANDLE error is returned.
If the stateid specified is not one corresponding to an open
delegation for the file specified by the filehandle, an
NFS4ERR_BAD_STATEID is returned.
IMPLEMENTATION
The client should reply to the callback immediately. Replying
does not complete the recall. The recall is not complete until
the delegation is returned using a DELEGRETURN.
ERRORS
NFS4ERR_BADHANDLE
NFS4ERR_BAD_STATEID
NFS4ERR_RESOURCE
16. Security Considerations
The major security feature to consider is the authentication of the
user making the request of NFS service. Consideration should also be
given to the integrity and privacy of this NFS request. These
specific issues are discussed as part of the section on "RPC and
Security Flavor".
17. IANA Considerations
17.1. Named Attribute Definition
The NFS version 4 protocol provides for the association of named
attributes to files. The name space identifiers for these attributes
are defined as string names. The protocol does not define the
specific assignment of the name space for these file attributes; the
application developer or system vendor is allowed to define the
attribute, its semantics, and the associated name. Even though this
name space will not be specifically controlled to prevent collisions,
the application developer or system vendor is strongly encouraged to
provide the name assignment and associated semantics for attributes
via an Informational RFC. This will provide for interoperability
where common interests exist.
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RFC 3010 NFS version 4 Protocol December 2000
18. RPC definition file
/*
* Copyright © The Internet Society (1998,1999,2000).
* All Rights Reserved.
*/
/*
* nfs4_prot.x
*
*/
%#pragma ident "@(#)nfs4_prot.x 1.97 00/06/12"
/*
* Basic typedefs for RFC 1832 data type definitions
*/
typedef int int32_t;
typedef unsigned int uint32_t;
typedef hyper int64_t;
typedef unsigned hyper uint64_t;
/*
* Sizes
*/
const NFS4_FHSIZE = 128;
const NFS4_VERIFIER_SIZE = 8;
/*
* File types
*/
enum nfs_ftype4 {
NF4REG = 1, /* Regular File */
NF4DIR = 2, /* Directory */
NF4BLK = 3, /* Special File - block device */
NF4CHR = 4, /* Special File - character device */
NF4LNK = 5, /* Symbolic Link */
NF4SOCK = 6, /* Special File - socket */
NF4FIFO = 7, /* Special File - fifo */
NF4ATTRDIR = 8, /* Attribute Directory */
NF4NAMEDATTR = 9 /* Named Attribute */
};
/*
* Error status
*/
enum nfsstat4 {
NFS4_OK = 0,
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RFC 3010 NFS version 4 Protocol December 2000
NFS4ERR_PERM = 1,
NFS4ERR_NOENT = 2,
NFS4ERR_IO = 5,
NFS4ERR_NXIO = 6,
NFS4ERR_ACCES = 13,
NFS4ERR_EXIST = 17,
NFS4ERR_XDEV = 18,
NFS4ERR_NODEV = 19,
NFS4ERR_NOTDIR = 20,
NFS4ERR_ISDIR = 21,
NFS4ERR_INVAL = 22,
NFS4ERR_FBIG = 27,
NFS4ERR_NOSPC = 28,
NFS4ERR_ROFS = 30,
NFS4ERR_MLINK = 31,
NFS4ERR_NAMETOOLONG = 63,
NFS4ERR_NOTEMPTY = 66,
NFS4ERR_DQUOT = 69,
NFS4ERR_STALE = 70,
NFS4ERR_BADHANDLE = 10001,
NFS4ERR_BAD_COOKIE = 10003,
NFS4ERR_NOTSUPP = 10004,
NFS4ERR_TOOSMALL = 10005,
NFS4ERR_SERVERFAULT = 10006,
NFS4ERR_BADTYPE = 10007,
NFS4ERR_DELAY = 10008,
NFS4ERR_SAME = 10009,/* nverify says attrs same */
NFS4ERR_DENIED = 10010,/* lock unavailable */
NFS4ERR_EXPIRED = 10011,/* lock lease expired */
NFS4ERR_LOCKED = 10012,/* I/O failed due to lock */
NFS4ERR_GRACE = 10013,/* in grace period */
NFS4ERR_FHEXPIRED = 10014,/* file handle expired */
NFS4ERR_SHARE_DENIED = 10015,/* share reserve denied */
NFS4ERR_WRONGSEC = 10016,/* wrong security flavor */
NFS4ERR_CLID_INUSE = 10017,/* clientid in use */
NFS4ERR_RESOURCE = 10018,/* resource exhaustion */
NFS4ERR_MOVED = 10019,/* filesystem relocated */
NFS4ERR_NOFILEHANDLE = 10020,/* current FH is not set */
NFS4ERR_MINOR_VERS_MISMATCH = 10021,/* minor vers not supp */
NFS4ERR_STALE_CLIENTID = 10022,
NFS4ERR_STALE_STATEID = 10023,
NFS4ERR_OLD_STATEID = 10024,
NFS4ERR_BAD_STATEID = 10025,
NFS4ERR_BAD_SEQID = 10026,
NFS4ERR_NOT_SAME = 10027,/* verify - attrs not same */
NFS4ERR_LOCK_RANGE = 10028,
NFS4ERR_SYMLINK = 10029,
NFS4ERR_READDIR_NOSPC = 10030,
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RFC 3010 NFS version 4 Protocol December 2000
NFS4ERR_LEASE_MOVED = 10031
};
/*
* Basic data types
*/
typedef uint32_t bitmap4<>;
typedef uint64_t offset4;
typedef uint32_t count4;
typedef uint64_t length4;
typedef uint64_t clientid4;
typedef uint64_t stateid4;
typedef uint32_t seqid4;
typedef opaque utf8string<>;
typedef utf8string component4;
typedef component4 pathname4<>;
typedef uint64_t nfs_lockid4;
typedef uint64_t nfs_cookie4;
typedef utf8string linktext4;
typedef opaque sec_oid4<>;
typedef uint32_t qop4;
typedef uint32_t mode4;
typedef uint64_t changeid4;
typedef opaque verifier4[NFS4_VERIFIER_SIZE];
/*
* Timeval
*/
struct nfstime4 {
int64_t seconds;
uint32_t nseconds;
};
enum time_how4 {
SET_TO_SERVER_TIME4 = 0,
SET_TO_CLIENT_TIME4 = 1
};
union settime4 switch (time_how4 set_it) {
case SET_TO_CLIENT_TIME4:
nfstime4 time;
default:
void;
};
/*
* File access handle
*/
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RFC 3010 NFS version 4 Protocol December 2000
typedef opaque nfs_fh4<NFS4_FHSIZE>;
/*
* File attribute definitions
*/
/*
* FSID structure for major/minor
*/
struct fsid4 {
uint64_t major;
uint64_t minor;
};
/*
* Filesystem locations attribute for relocation/migration
*/
struct fs_location4 {
utf8string server<>;
pathname4 rootpath;
};
struct fs_locations4 {
pathname4 fs_root;
fs_location4 locations<>;
};
/*
* Various Access Control Entry definitions
*/
/*
* Mask that indicates which Access Control Entries are supported.
* Values for the fattr4_aclsupport attribute.
*/
const ACL4_SUPPORT_ALLOW_ACL = 0x00000001;
const ACL4_SUPPORT_DENY_ACL = 0x00000002;
const ACL4_SUPPORT_AUDIT_ACL = 0x00000004;
const ACL4_SUPPORT_ALARM_ACL = 0x00000008;
typedef uint32_t acetype4;
/*
* acetype4 values, others can be added as needed.
*/
const ACE4_ACCESS_ALLOWED_ACE_TYPE = 0x00000000;
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RFC 3010 NFS version 4 Protocol December 2000
const ACE4_ACCESS_DENIED_ACE_TYPE = 0x00000001;
const ACE4_SYSTEM_AUDIT_ACE_TYPE = 0x00000002;
const ACE4_SYSTEM_ALARM_ACE_TYPE = 0x00000003;
/*
* ACE flag
*/
typedef uint32_t aceflag4;
/*
* ACE flag values
*/
const ACE4_FILE_INHERIT_ACE = 0x00000001;
const ACE4_DIRECTORY_INHERIT_ACE = 0x00000002;
const ACE4_NO_PROPAGATE_INHERIT_ACE = 0x00000004;
const ACE4_INHERIT_ONLY_ACE = 0x00000008;
const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG = 0x00000010;
const ACE4_FAILED_ACCESS_ACE_FLAG = 0x00000020;
const ACE4_IDENTIFIER_GROUP = 0x00000040;
/*
* ACE mask
*/
typedef uint32_t acemask4;
/*
* ACE mask values
*/
const ACE4_READ_DATA = 0x00000001;
const ACE4_LIST_DIRECTORY = 0x00000001;
const ACE4_WRITE_DATA = 0x00000002;
const ACE4_ADD_FILE = 0x00000002;
const ACE4_APPEND_DATA = 0x00000004;
const ACE4_ADD_SUBDIRECTORY = 0x00000004;
const ACE4_READ_NAMED_ATTRS = 0x00000008;
const ACE4_WRITE_NAMED_ATTRS = 0x00000010;
const ACE4_EXECUTE = 0x00000020;
const ACE4_DELETE_CHILD = 0x00000040;
const ACE4_READ_ATTRIBUTES = 0x00000080;
const ACE4_WRITE_ATTRIBUTES = 0x00000100;
const ACE4_DELETE = 0x00010000;
const ACE4_READ_ACL = 0x00020000;
const ACE4_WRITE_ACL = 0x00040000;
const ACE4_WRITE_OWNER = 0x00080000;
const ACE4_SYNCHRONIZE = 0x00100000;
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RFC 3010 NFS version 4 Protocol December 2000
/*
* ACE4_GENERIC_READ -- defined as combination of
* ACE4_READ_ACL |
* ACE4_READ_DATA |
* ACE4_READ_ATTRIBUTES |
* ACE4_SYNCHRONIZE
*/
const ACE4_GENERIC_READ = 0x00120081;
/*
* ACE4_GENERIC_WRITE -- defined as combination of
* ACE4_READ_ACL |
* ACE4_WRITE_DATA |
* ACE4_WRITE_ATTRIBUTES |
* ACE4_WRITE_ACL |
* ACE4_APPEND_DATA |
* ACE4_SYNCHRONIZE
*/
const ACE4_GENERIC_WRITE = 0x00160106;
/*
* ACE4_GENERIC_EXECUTE -- defined as combination of
* ACE4_READ_ACL
* ACE4_READ_ATTRIBUTES
* ACE4_EXECUTE
* ACE4_SYNCHRONIZE
*/
const ACE4_GENERIC_EXECUTE = 0x001200A0;
/*
* Access Control Entry definition
*/
struct nfsace4 {
acetype4 type;
aceflag4 flag;
acemask4 access_mask;
utf8string who;
};
/*
* Special data/attribute associated with
* file types NF4BLK and NF4CHR.
*/
struct specdata4 {
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RFC 3010 NFS version 4 Protocol December 2000
uint32_t specdata1;
uint32_t specdata2;
};
/*
* Values for fattr4_fh_expire_type
*/
const FH4_PERSISTENT = 0x00000000;
const FH4_NOEXPIRE_WITH_OPEN = 0x00000001;
const FH4_VOLATILE_ANY = 0x00000002;
const FH4_VOL_MIGRATION = 0x00000004;
const FH4_VOL_RENAME = 0x00000008;
typedef bitmap4 fattr4_supported_attrs;
typedef nfs_ftype4 fattr4_type;
typedef uint32_t fattr4_fh_expire_type;
typedef changeid4 fattr4_change;
typedef uint64_t fattr4_size;
typedef bool fattr4_link_support;
typedef bool fattr4_symlink_support;
typedef bool fattr4_named_attr;
typedef fsid4 fattr4_fsid;
typedef bool fattr4_unique_handles;
typedef uint32_t fattr4_lease_time;
typedef nfsstat4 fattr4_rdattr_error;
typedef nfsace4 fattr4_acl<>;
typedef uint32_t fattr4_aclsupport;
typedef bool fattr4_archive;
typedef bool fattr4_cansettime;
typedef bool fattr4_case_insensitive;
typedef bool fattr4_case_preserving;
typedef bool fattr4_chown_restricted;
typedef uint64_t fattr4_fileid;
typedef uint64_t fattr4_files_avail;
typedef nfs_fh4 fattr4_filehandle;
typedef uint64_t fattr4_files_free;
typedef uint64_t fattr4_files_total;
typedef fs_locations4 fattr4_fs_locations;
typedef bool fattr4_hidden;
typedef bool fattr4_homogeneous;
typedef uint64_t fattr4_maxfilesize;
typedef uint32_t fattr4_maxlink;
typedef uint32_t fattr4_maxname;
typedef uint64_t fattr4_maxread;
typedef uint64_t fattr4_maxwrite;
typedef utf8string fattr4_mimetype;
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RFC 3010 NFS version 4 Protocol December 2000
typedef mode4 fattr4_mode;
typedef bool fattr4_no_trunc;
typedef uint32_t fattr4_numlinks;
typedef utf8string fattr4_owner;
typedef utf8string fattr4_owner_group;
typedef uint64_t fattr4_quota_avail_hard;
typedef uint64_t fattr4_quota_avail_soft;
typedef uint64_t fattr4_quota_used;
typedef specdata4 fattr4_rawdev;
typedef uint64_t fattr4_space_avail;
typedef uint64_t fattr4_space_free;
typedef uint64_t fattr4_space_total;
typedef uint64_t fattr4_space_used;
typedef bool fattr4_system;
typedef nfstime4 fattr4_time_access;
typedef settime4 fattr4_time_access_set;
typedef nfstime4 fattr4_time_backup;
typedef nfstime4 fattr4_time_create;
typedef nfstime4 fattr4_time_delta;
typedef nfstime4 fattr4_time_metadata;
typedef nfstime4 fattr4_time_modify;
typedef settime4 fattr4_time_modify_set;
/*
* Mandatory Attributes
*/
const FATTR4_SUPPORTED_ATTRS = 0;
const FATTR4_TYPE = 1;
const FATTR4_FH_EXPIRE_TYPE = 2;
const FATTR4_CHANGE = 3;
const FATTR4_SIZE = 4;
const FATTR4_LINK_SUPPORT = 5;
const FATTR4_SYMLINK_SUPPORT = 6;
const FATTR4_NAMED_ATTR = 7;
const FATTR4_FSID = 8;
const FATTR4_UNIQUE_HANDLES = 9;
const FATTR4_LEASE_TIME = 10;
const FATTR4_RDATTR_ERROR = 11;
/*
* Recommended Attributes
*/
const FATTR4_ACL = 12;
const FATTR4_ACLSUPPORT = 13;
const FATTR4_ARCHIVE = 14;
const FATTR4_CANSETTIME = 15;
const FATTR4_CASE_INSENSITIVE = 16;
Shepler, et al. Standards Track PAGE 182
RFC 3010 NFS version 4 Protocol December 2000
const FATTR4_CASE_PRESERVING = 17;
const FATTR4_CHOWN_RESTRICTED = 18;
const FATTR4_FILEHANDLE = 19;
const FATTR4_FILEID = 20;
const FATTR4_FILES_AVAIL = 21;
const FATTR4_FILES_FREE = 22;
const FATTR4_FILES_TOTAL = 23;
const FATTR4_FS_LOCATIONS = 24;
const FATTR4_HIDDEN = 25;
const FATTR4_HOMOGENEOUS = 26;
const FATTR4_MAXFILESIZE = 27;
const FATTR4_MAXLINK = 28;
const FATTR4_MAXNAME = 29;
const FATTR4_MAXREAD = 30;
const FATTR4_MAXWRITE = 31;
const FATTR4_MIMETYPE = 32;
const FATTR4_MODE = 33;
const FATTR4_NO_TRUNC = 34;
const FATTR4_NUMLINKS = 35;
const FATTR4_OWNER = 36;
const FATTR4_OWNER_GROUP = 37;
const FATTR4_QUOTA_AVAIL_HARD = 38;
const FATTR4_QUOTA_AVAIL_SOFT = 39;
const FATTR4_QUOTA_USED = 40;
const FATTR4_RAWDEV = 41;
const FATTR4_SPACE_AVAIL = 42;
const FATTR4_SPACE_FREE = 43;
const FATTR4_SPACE_TOTAL = 44;
const FATTR4_SPACE_USED = 45;
const FATTR4_SYSTEM = 46;
const FATTR4_TIME_ACCESS = 47;
const FATTR4_TIME_ACCESS_SET = 48;
const FATTR4_TIME_BACKUP = 49;
const FATTR4_TIME_CREATE = 50;
const FATTR4_TIME_DELTA = 51;
const FATTR4_TIME_METADATA = 52;
const FATTR4_TIME_MODIFY = 53;
const FATTR4_TIME_MODIFY_SET = 54;
typedef opaque attrlist4<>;
/*
* File attribute container
*/
struct fattr4 {
bitmap4 attrmask;
attrlist4 attr_vals;
Shepler, et al. Standards Track PAGE 183
RFC 3010 NFS version 4 Protocol December 2000
};
/*
* Change info for the client
*/
struct change_info4 {
bool atomic;
changeid4 before;
changeid4 after;
};
struct clientaddr4 {
/* see struct rpcb in RFC 1833 */
string r_netid<>; /* network id */
string r_addr<>; /* universal address */
};
/*
* Callback program info as provided by the client
*/
struct cb_client4 {
unsigned int cb_program;
clientaddr4 cb_location;
};
/*
* Client ID
*/
struct nfs_client_id4 {
verifier4 verifier;
opaque id<>;
};
struct nfs_lockowner4 {
clientid4 clientid;
opaque owner<>;
};
enum nfs_lock_type4 {
READ_LT = 1,
WRITE_LT = 2,
READW_LT = 3, /* blocking read */
WRITEW_LT = 4 /* blocking write */
};
/*
* ACCESS: Check access permission
*/
Shepler, et al. Standards Track PAGE 184
RFC 3010 NFS version 4 Protocol December 2000
const ACCESS4_READ = 0x00000001;
const ACCESS4_LOOKUP = 0x00000002;
const ACCESS4_MODIFY = 0x00000004;
const ACCESS4_EXTEND = 0x00000008;
const ACCESS4_DELETE = 0x00000010;
const ACCESS4_EXECUTE = 0x00000020;
struct ACCESS4args {
/* CURRENT_FH: object */
uint32_t access;
};
struct ACCESS4resok {
uint32_t supported;
uint32_t access;
};
union ACCESS4res switch (nfsstat4 status) {
case NFS4_OK:
ACCESS4resok resok4;
default:
void;
};
/*
* CLOSE: Close a file and release share locks
*/
struct CLOSE4args {
/* CURRENT_FH: object */
seqid4 seqid;
stateid4 stateid;
};
union CLOSE4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 stateid;
default:
void;
};
/*
* COMMIT: Commit cached data on server to stable storage
*/
struct COMMIT4args {
/* CURRENT_FH: file */
offset4 offset;
count4 count;
};
Shepler, et al. Standards Track PAGE 185
RFC 3010 NFS version 4 Protocol December 2000
struct COMMIT4resok {
verifier4 writeverf;
};
union COMMIT4res switch (nfsstat4 status) {
case NFS4_OK:
COMMIT4resok resok4;
default:
void;
};
/*
* CREATE: Create a file
*/
union createtype4 switch (nfs_ftype4 type) {
case NF4LNK:
linktext4 linkdata;
case NF4BLK:
case NF4CHR:
specdata4 devdata;
case NF4SOCK:
case NF4FIFO:
case NF4DIR:
void;
};
struct CREATE4args {
/* CURRENT_FH: directory for creation */
component4 objname;
createtype4 objtype;
};
struct CREATE4resok {
change_info4 cinfo;
};
union CREATE4res switch (nfsstat4 status) {
case NFS4_OK:
CREATE4resok resok4;
default:
void;
};
/*
* DELEGPURGE: Purge Delegations Awaiting Recovery
*/
struct DELEGPURGE4args {
Shepler, et al. Standards Track PAGE 186
RFC 3010 NFS version 4 Protocol December 2000
clientid4 clientid;
};
struct DELEGPURGE4res {
nfsstat4 status;
};
/*
* DELEGRETURN: Return a delegation
*/
struct DELEGRETURN4args {
stateid4 stateid;
};
struct DELEGRETURN4res {
nfsstat4 status;
};
/*
* GETATTR: Get file attributes
*/
struct GETATTR4args {
/* CURRENT_FH: directory or file */
bitmap4 attr_request;
};
struct GETATTR4resok {
fattr4 obj_attributes;
};
union GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
GETATTR4resok resok4;
default:
void;
};
/*
* GETFH: Get current filehandle
*/
struct GETFH4resok {
nfs_fh4 object;
};
union GETFH4res switch (nfsstat4 status) {
case NFS4_OK:
GETFH4resok resok4;
default:
Shepler, et al. Standards Track PAGE 187
RFC 3010 NFS version 4 Protocol December 2000
void;
};
/*
* LINK: Create link to an object
*/
struct LINK4args {
/* SAVED_FH: source object */
/* CURRENT_FH: target directory */
component4 newname;
};
struct LINK4resok {
change_info4 cinfo;
};
union LINK4res switch (nfsstat4 status) {
case NFS4_OK:
LINK4resok resok4;
default:
void;
};
/*
* LOCK/LOCKT/LOCKU: Record lock management
*/
struct LOCK4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
seqid4 seqid;
bool reclaim;
stateid4 stateid;
offset4 offset;
length4 length;
};
struct LOCK4denied {
nfs_lockowner4 owner;
offset4 offset;
length4 length;
};
union LOCK4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 stateid;
case NFS4ERR_DENIED:
LOCK4denied denied;
default:
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RFC 3010 NFS version 4 Protocol December 2000
void;
};
struct LOCKT4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
nfs_lockowner4 owner;
offset4 offset;
length4 length;
};
union LOCKT4res switch (nfsstat4 status) {
case NFS4ERR_DENIED:
LOCK4denied denied;
case NFS4_OK:
void;
default:
void;
};
struct LOCKU4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
seqid4 seqid;
stateid4 stateid;
offset4 offset;
length4 length;
};
union LOCKU4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 stateid;
default:
void;
};
/*
* LOOKUP: Lookup filename
*/
struct LOOKUP4args {
/* CURRENT_FH: directory */
pathname4 path;
};
struct LOOKUP4res {
/* CURRENT_FH: object */
nfsstat4 status;
};
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RFC 3010 NFS version 4 Protocol December 2000
/*
* LOOKUPP: Lookup parent directory
*/
struct LOOKUPP4res {
/* CURRENT_FH: directory */
nfsstat4 status;
};
/*
* NVERIFY: Verify attributes different
*/
struct NVERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
struct NVERIFY4res {
nfsstat4 status;
};
/*
* Various definitions for OPEN
*/
enum createmode4 {
UNCHECKED4 = 0,
GUARDED4 = 1,
EXCLUSIVE4 = 2
};
union createhow4 switch (createmode4 mode) {
case UNCHECKED4:
case GUARDED4:
fattr4 createattrs;
case EXCLUSIVE4:
verifier4 createverf;
};
enum opentype4 {
OPEN4_NOCREATE = 0,
OPEN4_CREATE = 1
};
union openflag4 switch (opentype4 opentype) {
case OPEN4_CREATE:
createhow4 how;
default:
void;
};
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RFC 3010 NFS version 4 Protocol December 2000
/* Next definitions used for OPEN delegation */
enum limit_by4 {
NFS_LIMIT_SIZE = 1,
NFS_LIMIT_BLOCKS = 2
/* others as needed */
};
struct nfs_modified_limit4 {
uint32_t num_blocks;
uint32_t bytes_per_block;
};
union nfs_space_limit4 switch (limit_by4 limitby) {
/* limit specified as file size */
case NFS_LIMIT_SIZE:
uint64_t filesize;
/* limit specified by number of blocks */
case NFS_LIMIT_BLOCKS:
nfs_modified_limit4 mod_blocks;
} ;
/*
* Share Access and Deny constants for open argument
*/
const OPEN4_SHARE_ACCESS_READ = 0x00000001;
const OPEN4_SHARE_ACCESS_WRITE = 0x00000002;
const OPEN4_SHARE_ACCESS_BOTH = 0x00000003;
const OPEN4_SHARE_DENY_NONE = 0x00000000;
const OPEN4_SHARE_DENY_READ = 0x00000001;
const OPEN4_SHARE_DENY_WRITE = 0x00000002;
const OPEN4_SHARE_DENY_BOTH = 0x00000003;
enum open_delegation_type4 {
OPEN_DELEGATE_NONE = 0,
OPEN_DELEGATE_READ = 1,
OPEN_DELEGATE_WRITE = 2
};
enum open_claim_type4 {
CLAIM_NULL = 0,
CLAIM_PREVIOUS = 1,
CLAIM_DELEGATE_CUR = 2,
CLAIM_DELEGATE_PREV = 3
};
struct open_claim_delegate_cur4 {
pathname4 file;
Shepler, et al. Standards Track PAGE 191
RFC 3010 NFS version 4 Protocol December 2000
stateid4 delegate_stateid;
};
union open_claim4 switch (open_claim_type4 claim) {
/*
* No special rights to file. Ordinary OPEN of the specified file.
*/
case CLAIM_NULL:
/* CURRENT_FH: directory */
pathname4 file;
/*
* Right to the file established by an open previous to server
* reboot. File identified by filehandle obtained at that time
* rather than by name.
*/
case CLAIM_PREVIOUS:
/* CURRENT_FH: file being reclaimed */
uint32_t delegate_type;
/*
* Right to file based on a delegation granted by the server.
* File is specified by name.
*/
case CLAIM_DELEGATE_CUR:
/* CURRENT_FH: directory */
open_claim_delegate_cur4 delegate_cur_info;
/* Right to file based on a delegation granted to a previous boot
* instance of the client. File is specified by name.
*/
case CLAIM_DELEGATE_PREV:
/* CURRENT_FH: directory */
pathname4 file_delegate_prev;
};
/*
* OPEN: Open a file, potentially receiving an open delegation
*/
struct OPEN4args {
open_claim4 claim;
openflag4 openhow;
nfs_lockowner4 owner;
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
};
Shepler, et al. Standards Track PAGE 192
RFC 3010 NFS version 4 Protocol December 2000
struct open_read_delegation4 {
stateid4 stateid; /* Stateid for delegation*/
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim
(CLAIM_PREVIOUS) */
nfsace4 permissions; /* Defines users who don't
need an ACCESS call to
open for read */
};
struct open_write_delegation4 {
stateid4 stateid; /* Stateid for delegation */
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim
(CLAIM_PREVIOUS) */
nfs_space_limit4 space_limit; /* Defines condition that
the client must check to
determine whether the
file needs to be flushed
to the server on close.
*/
nfsace4 permissions; /* Defines users who don't
need an ACCESS call as
part of a delegated
open. */
};
union open_delegation4
switch (open_delegation_type4 delegation_type) {
case OPEN_DELEGATE_NONE:
void;
case OPEN_DELEGATE_READ:
open_read_delegation4 read;
case OPEN_DELEGATE_WRITE:
open_write_delegation4 write;
};
/*
* Result flags
*/
/* Mandatory locking is in effect for this file. */
const OPEN4_RESULT_MLOCK = 0x00000001;
/* Client must confirm open */
const OPEN4_RESULT_CONFIRM = 0x00000002;
struct OPEN4resok {
Shepler, et al. Standards Track PAGE 193
RFC 3010 NFS version 4 Protocol December 2000
stateid4 stateid; /* Stateid for open */
change_info4 cinfo; /* Directory Change Info */
uint32_t rflags; /* Result flags */
verifier4 open_confirm; /* OPEN_CONFIRM verifier */
open_delegation4 delegation; /* Info on any open
delegation */
};
union OPEN4res switch (nfsstat4 status) {
case NFS4_OK:
/* CURRENT_FH: opened file */
OPEN4resok resok4;
default:
void;
};
/*
* OPENATTR: open named attributes directory
*/
struct OPENATTR4res {
/* CURRENT_FH: name attr directory*/
nfsstat4 status;
};
/*
* OPEN_CONFIRM: confirm the open
*/
struct OPEN_CONFIRM4args {
/* CURRENT_FH: opened file */
seqid4 seqid;
verifier4 open_confirm; /* OPEN_CONFIRM verifier */
};
struct OPEN_CONFIRM4resok {
stateid4 stateid;
};
union OPEN_CONFIRM4res switch (nfsstat4 status) {
case NFS4_OK:
OPEN_CONFIRM4resok resok4;
default:
void;
};
/*
* OPEN_DOWNGRADE: downgrade the access/deny for a file
*/
struct OPEN_DOWNGRADE4args {
Shepler, et al. Standards Track PAGE 194
RFC 3010 NFS version 4 Protocol December 2000
/* CURRENT_FH: opened file */
stateid4 stateid;
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
};
struct OPEN_DOWNGRADE4resok {
stateid4 stateid;
};
union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
case NFS4_OK:
OPEN_DOWNGRADE4resok resok4;
default:
void;
};
/*
* PUTFH: Set current filehandle
*/
struct PUTFH4args {
nfs_fh4 object;
};
struct PUTFH4res {
/* CURRENT_FH: */
nfsstat4 status;
};
/*
* PUTPUBFH: Set public filehandle
*/
struct PUTPUBFH4res {
/* CURRENT_FH: public fh */
nfsstat4 status;
};
/*
* PUTROOTFH: Set root filehandle
*/
struct PUTROOTFH4res {
/* CURRENT_FH: root fh */
nfsstat4 status;
};
/*
* READ: Read from file
Shepler, et al. Standards Track PAGE 195
RFC 3010 NFS version 4 Protocol December 2000
*/
struct READ4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
count4 count;
};
struct READ4resok {
bool eof;
opaque data<>;
};
union READ4res switch (nfsstat4 status) {
case NFS4_OK:
READ4resok resok4;
default:
void;
};
/*
* READDIR: Read directory
*/
struct READDIR4args {
/* CURRENT_FH: directory */
nfs_cookie4 cookie;
verifier4 cookieverf;
count4 dircount;
count4 maxcount;
bitmap4 attr_request;
};
struct entry4 {
nfs_cookie4 cookie;
component4 name;
fattr4 attrs;
entry4 *nextentry;
};
struct dirlist4 {
entry4 *entries;
bool eof;
};
struct READDIR4resok {
verifier4 cookieverf;
dirlist4 reply;
};
Shepler, et al. Standards Track PAGE 196
RFC 3010 NFS version 4 Protocol December 2000
union READDIR4res switch (nfsstat4 status) {
case NFS4_OK:
READDIR4resok resok4;
default:
void;
};
/*
* READLINK: Read symbolic link
*/
struct READLINK4resok {
linktext4 link;
};
union READLINK4res switch (nfsstat4 status) {
case NFS4_OK:
READLINK4resok resok4;
default:
void;
};
/*
* REMOVE: Remove filesystem object
*/
struct REMOVE4args {
/* CURRENT_FH: directory */
component4 target;
};
struct REMOVE4resok {
change_info4 cinfo;
};
union REMOVE4res switch (nfsstat4 status) {
case NFS4_OK:
REMOVE4resok resok4;
default:
void;
};
/*
* RENAME: Rename directory entry
*/
struct RENAME4args {
/* SAVED_FH: source directory */
component4 oldname;
/* CURRENT_FH: target directory */
Shepler, et al. Standards Track PAGE 197
RFC 3010 NFS version 4 Protocol December 2000
component4 newname;
};
struct RENAME4resok {
change_info4 source_cinfo;
change_info4 target_cinfo;
};
union RENAME4res switch (nfsstat4 status) {
case NFS4_OK:
RENAME4resok resok4;
default:
void;
};
/*
* RENEW: Renew a Lease
*/
struct RENEW4args {
stateid4 stateid;
};
struct RENEW4res {
nfsstat4 status;
};
/*
* RESTOREFH: Restore saved filehandle
*/
struct RESTOREFH4res {
/* CURRENT_FH: value of saved fh */
nfsstat4 status;
};
/*
* SAVEFH: Save current filehandle
*/
struct SAVEFH4res {
/* SAVED_FH: value of current fh */
nfsstat4 status;
};
/*
* SECINFO: Obtain Available Security Mechanisms
*/
struct SECINFO4args {
Shepler, et al. Standards Track PAGE 198
RFC 3010 NFS version 4 Protocol December 2000
/* CURRENT_FH: */
component4 name;
};
/*
* From RFC 2203
*/
enum rpc_gss_svc_t {
RPC_GSS_SVC_NONE = 1,
RPC_GSS_SVC_INTEGRITY = 2,
RPC_GSS_SVC_PRIVACY = 3
};
struct rpcsec_gss_info {
sec_oid4 oid;
qop4 qop;
rpc_gss_svc_t service;
};
struct secinfo4 {
uint32_t flavor;
/* null for AUTH_SYS, AUTH_NONE;
contains rpcsec_gss_info for
RPCSEC_GSS. */
opaque flavor_info<>;
};
typedef secinfo4 SECINFO4resok<>;
union SECINFO4res switch (nfsstat4 status) {
case NFS4_OK:
SECINFO4resok resok4;
default:
void;
};
/*
* SETATTR: Set attributes
*/
struct SETATTR4args {
/* CURRENT_FH: target object */
stateid4 stateid;
fattr4 obj_attributes;
};
struct SETATTR4res {
nfsstat4 status;
Shepler, et al. Standards Track PAGE 199
RFC 3010 NFS version 4 Protocol December 2000
bitmap4 attrsset;
};
/*
* SETCLIENTID
*/
struct SETCLIENTID4args {
nfs_client_id4 client;
cb_client4 callback;
};
struct SETCLIENTID4resok {
clientid4 clientid;
verifier4 setclientid_confirm;
};
union SETCLIENTID4res switch (nfsstat4 status) {
case NFS4_OK:
SETCLIENTID4resok resok4;
case NFS4ERR_CLID_INUSE:
clientaddr4 client_using;
default:
void;
};
struct SETCLIENTID_CONFIRM4args {
verifier4 setclientid_confirm;
};
struct SETCLIENTID_CONFIRM4res {
nfsstat4 status;
};
/*
* VERIFY: Verify attributes same
*/
struct VERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
struct VERIFY4res {
nfsstat4 status;
};
/*
* WRITE: Write to file
*/
Shepler, et al. Standards Track PAGE 200
RFC 3010 NFS version 4 Protocol December 2000
enum stable_how4 {
UNSTABLE4 = 0,
DATA_SYNC4 = 1,
FILE_SYNC4 = 2
};
struct WRITE4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
stable_how4 stable;
opaque data<>;
};
struct WRITE4resok {
count4 count;
stable_how4 committed;
verifier4 writeverf;
};
union WRITE4res switch (nfsstat4 status) {
case NFS4_OK:
WRITE4resok resok4;
default:
void;
};
/*
* Operation arrays
*/
enum nfs_opnum4 {
OP_ACCESS = 3,
OP_CLOSE = 4,
OP_COMMIT = 5,
OP_CREATE = 6,
OP_DELEGPURGE = 7,
OP_DELEGRETURN = 8,
OP_GETATTR = 9,
OP_GETFH = 10,
OP_LINK = 11,
OP_LOCK = 12,
OP_LOCKT = 13,
OP_LOCKU = 14,
OP_LOOKUP = 15,
OP_LOOKUPP = 16,
OP_NVERIFY = 17,
OP_OPEN = 18,
Shepler, et al. Standards Track PAGE 201
RFC 3010 NFS version 4 Protocol December 2000
OP_OPENATTR = 19,
OP_OPEN_CONFIRM = 20,
OP_OPEN_DOWNGRADE = 21,
OP_PUTFH = 22,
OP_PUTPUBFH = 23,
OP_PUTROOTFH = 24,
OP_READ = 25,
OP_READDIR = 26,
OP_READLINK = 27,
OP_REMOVE = 28,
OP_RENAME = 29,
OP_RENEW = 30,
OP_RESTOREFH = 31,
OP_SAVEFH = 32,
OP_SECINFO = 33,
OP_SETATTR = 34,
OP_SETCLIENTID = 35,
OP_SETCLIENTID_CONFIRM = 36,
OP_VERIFY = 37,
OP_WRITE = 38
};
union nfs_argop4 switch (nfs_opnum4 argop) {
case OP_ACCESS: ACCESS4args opaccess;
case OP_CLOSE: CLOSE4args opclose;
case OP_COMMIT: COMMIT4args opcommit;
case OP_CREATE: CREATE4args opcreate;
case OP_DELEGPURGE: DELEGPURGE4args opdelegpurge;
case OP_DELEGRETURN: DELEGRETURN4args opdelegreturn;
case OP_GETATTR: GETATTR4args opgetattr;
case OP_GETFH: void;
case OP_LINK: LINK4args oplink;
case OP_LOCK: LOCK4args oplock;
case OP_LOCKT: LOCKT4args oplockt;
case OP_LOCKU: LOCKU4args oplocku;
case OP_LOOKUP: LOOKUP4args oplookup;
case OP_LOOKUPP: void;
case OP_NVERIFY: NVERIFY4args opnverify;
case OP_OPEN: OPEN4args opopen;
case OP_OPENATTR: void;
case OP_OPEN_CONFIRM: OPEN_CONFIRM4args opopen_confirm;
case OP_OPEN_DOWNGRADE: OPEN_DOWNGRADE4args opopen_downgrade;
case OP_PUTFH: PUTFH4args opputfh;
case OP_PUTPUBFH: void;
case OP_PUTROOTFH: void;
case OP_READ: READ4args opread;
case OP_READDIR: READDIR4args opreaddir;
case OP_READLINK: void;
Shepler, et al. Standards Track PAGE 202
RFC 3010 NFS version 4 Protocol December 2000
case OP_REMOVE: REMOVE4args opremove;
case OP_RENAME: RENAME4args oprename;
case OP_RENEW: RENEW4args oprenew;
case OP_RESTOREFH: void;
case OP_SAVEFH: void;
case OP_SECINFO: SECINFO4args opsecinfo;
case OP_SETATTR: SETATTR4args opsetattr;
case OP_SETCLIENTID: SETCLIENTID4args opsetclientid;
case OP_SETCLIENTID_CONFIRM: SETCLIENTID_CONFIRM4args
opsetclientid_confirm;
case OP_VERIFY: VERIFY4args opverify;
case OP_WRITE: WRITE4args opwrite;
};
union nfs_resop4 switch (nfs_opnum4 resop){
case OP_ACCESS: ACCESS4res opaccess;
case OP_CLOSE: CLOSE4res opclose;
case OP_COMMIT: COMMIT4res opcommit;
case OP_CREATE: CREATE4res opcreate;
case OP_DELEGPURGE: DELEGPURGE4res opdelegpurge;
case OP_DELEGRETURN: DELEGRETURN4res opdelegreturn;
case OP_GETATTR: GETATTR4res opgetattr;
case OP_GETFH: GETFH4res opgetfh;
case OP_LINK: LINK4res oplink;
case OP_LOCK: LOCK4res oplock;
case OP_LOCKT: LOCKT4res oplockt;
case OP_LOCKU: LOCKU4res oplocku;
case OP_LOOKUP: LOOKUP4res oplookup;
case OP_LOOKUPP: LOOKUPP4res oplookupp;
case OP_NVERIFY: NVERIFY4res opnverify;
case OP_OPEN: OPEN4res opopen;
case OP_OPENATTR: OPENATTR4res opopenattr;
case OP_OPEN_CONFIRM: OPEN_CONFIRM4res opopen_confirm;
case OP_OPEN_DOWNGRADE: OPEN_DOWNGRADE4res opopen_downgrade;
case OP_PUTFH: PUTFH4res opputfh;
case OP_PUTPUBFH: PUTPUBFH4res opputpubfh;
case OP_PUTROOTFH: PUTROOTFH4res opputrootfh;
case OP_READ: READ4res opread;
case OP_READDIR: READDIR4res opreaddir;
case OP_READLINK: READLINK4res opreadlink;
case OP_REMOVE: REMOVE4res opremove;
case OP_RENAME: RENAME4res oprename;
case OP_RENEW: RENEW4res oprenew;
case OP_RESTOREFH: RESTOREFH4res oprestorefh;
case OP_SAVEFH: SAVEFH4res opsavefh;
case OP_SECINFO: SECINFO4res opsecinfo;
case OP_SETATTR: SETATTR4res opsetattr;
case OP_SETCLIENTID: SETCLIENTID4res opsetclientid;
Shepler, et al. Standards Track PAGE 203
RFC 3010 NFS version 4 Protocol December 2000
case OP_SETCLIENTID_CONFIRM: SETCLIENTID_CONFIRM4res
opsetclientid_confirm;
case OP_VERIFY: VERIFY4res opverify;
case OP_WRITE: WRITE4res opwrite;
};
struct COMPOUND4args {
utf8string tag;
uint32_t minorversion;
nfs_argop4 argarray<>;
};
struct COMPOUND4res {
nfsstat4 status;
utf8string tag;
nfs_resop4 resarray<>;
};
/*
* Remote file service routines
*/
program NFS4_PROGRAM {
version NFS_V4 {
void
NFSPROC4_NULL(void) = 0;
COMPOUND4res
NFSPROC4_COMPOUND(COMPOUND4args) = 1;
} = 4;
} = 100003;
/*
* NFS4 Callback Procedure Definitions and Program
*/
/*
* CB_GETATTR: Get Current Attributes
*/
struct CB_GETATTR4args {
nfs_fh4 fh;
bitmap4 attr_request;
};
struct CB_GETATTR4resok {
fattr4 obj_attributes;
Shepler, et al. Standards Track PAGE 204
RFC 3010 NFS version 4 Protocol December 2000
};
union CB_GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
CB_GETATTR4resok resok4;
default:
void;
};
/*
* CB_RECALL: Recall an Open Delegation
*/
struct CB_RECALL4args {
stateid4 stateid;
bool truncate;
nfs_fh4 fh;
};
struct CB_RECALL4res {
nfsstat4 status;
};
/*
* Various definitions for CB_COMPOUND
*/
enum nfs_cb_opnum4 {
OP_CB_GETATTR = 3,
OP_CB_RECALL = 4
};
union nfs_cb_argop4 switch (unsigned argop) {
case OP_CB_GETATTR: CB_GETATTR4args opcbgetattr;
case OP_CB_RECALL: CB_RECALL4args opcbrecall;
};
union nfs_cb_resop4 switch (unsigned resop){
case OP_CB_GETATTR: CB_GETATTR4res opcbgetattr;
case OP_CB_RECALL: CB_RECALL4res opcbrecall;
};
struct CB_COMPOUND4args {
utf8string tag;
uint32_t minorversion;
nfs_cb_argop4 argarray<>;
};
struct CB_COMPOUND4res {
nfsstat4 status;
Shepler, et al. Standards Track PAGE 205
RFC 3010 NFS version 4 Protocol December 2000
utf8string tag;
nfs_cb_resop4 resarray<>;
};
/*
* Program number is in the transient range since the client
* will assign the exact transient program number and provide
* that to the server via the SETCLIENTID operation.
*/
program NFS4_CALLBACK {
version NFS_CB {
void
CB_NULL(void) = 0;
CB_COMPOUND4res
CB_COMPOUND(CB_COMPOUND4args) = 1;
} = 1;
} = 40000000;
19. Bibliography
[Floyd] S. Floyd, V. Jacobson, "The Synchronization of Periodic
Routing Messages," IEEE/ACM Transactions on Networking,
2(2), pp. 122-136, April 1994.
[Gray] C. Gray, D. Cheriton, "Leases: An Efficient Fault-
Tolerant Mechanism for Distributed File Cache
Consistency," Proceedings of the Twelfth Symposium on
Operating Systems Principles, p. 202-210, December 1989.
[ISO10646] "ISO/IEC 10646-1:1993. International Standard --
Information technology -- Universal Multiple-Octet Coded
Character Set (UCS) -- Part 1: Architecture and Basic
Multilingual Plane."
[Juszczak] Juszczak, Chet, "Improving the Performance and
Correctness of an NFS Server," USENIX Conference
Proceedings, USENIX Association, Berkeley, CA, June
1990, pages 53-63. Describes reply cache implementation
that avoids work in the server by handling duplicate
requests. More important, though listed as a side-
effect, the reply cache aids in the avoidance of
destructive non-idempotent operation re-application --
improving correctness.
Shepler, et al. Standards Track PAGE 206
RFC 3010 NFS version 4 Protocol December 2000
[Kazar] Kazar, Michael Leon, "Synchronization and Caching Issues
in the Andrew File System," USENIX Conference
Proceedings, USENIX Association, Berkeley, CA, Dallas
Winter 1988, pages 27-36. A description of the cache
consistency scheme in AFS. Contrasted with other
distributed file systems.
[Macklem] Macklem, Rick, "Lessons Learned Tuning the 4.3BSD Reno
Implementation of the NFS Protocol," Winter USENIX
Conference Proceedings, USENIX Association, Berkeley,
CA, January 1991. Describes performance work in tuning
the 4.3BSD Reno NFS implementation. Describes
performance improvement (reduced CPU loading) through
elimination of data copies.
[Mogul] Mogul, Jeffrey C., "A Recovery Protocol for Spritely
NFS," USENIX File System Workshop Proceedings, Ann
Arbor, MI, USENIX Association, Berkeley, CA, May 1992.
Second paper on Spritely NFS proposes a lease-based
scheme for recovering state of consistency protocol.
[Nowicki] Nowicki, Bill, "Transport Issues in the Network File
System," ACM SIGCOMM newsletter Computer Communication
Review, April 1989. A brief description of the basis
for the dynamic retransmission work.
[Pawlowski] Pawlowski, Brian, Ron Hixon, Mark Stein, Joseph
Tumminaro, "Network Computing in the UNIX and IBM
Mainframe Environment," Uniforum `89 Conf. Proc.,
(1989) Description of an NFS server implementation for
IBM's MVS operating system.
[RFC 1094] Sun Microsystems, Inc., "NFS: Network File System
Protocol Specification", RFC 1094, March 1989.
[RFC 1345] Simonsen, K., "Character Mnemonics & Character Sets",
RFC 1345, June 1992.
[RFC 1700] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2,
RFC 1700, October 1994.
[RFC 1813] Callaghan, B., Pawlowski, B. and P. Staubach, "NFS
Version 3 Protocol Specification", RFC 1813, June 1995.
[RFC 1831] Srinivasan, R., "RPC: Remote Procedure Call Protocol
Specification Version 2", RFC 1831, August 1995.
Shepler, et al. Standards Track PAGE 207
RFC 3010 NFS version 4 Protocol December 2000
[RFC 1832] Srinivasan, R., "XDR: External Data Representation
Standard", RFC 1832, August 1995.
[RFC 1833] Srinivasan, R., "Binding Protocols for ONC RPC Version
2", RFC 1833, August 1995.
[RFC 2025] Adams, C., "The Simple Public-Key GSS-API Mechanism
(SPKM)", RFC 2025, October 1996.
[RFC 2054] Callaghan, B., "WebNFS Client Specification", RFC 2054,
October 1996.
[RFC 2055] Callaghan, B., "WebNFS Server Specification", RFC 2055,
October 1996.
[RFC 2078] Linn, J., "Generic Security Service Application Program
Interface, Version 2", RFC 2078, January 1997.
[RFC 2152] Goldsmith, D., "UTF-7 A Mail-Safe Transformation Format
of Unicode", RFC 2152, May 1997.
[RFC 2203] Eisler, M., Chiu, A. and L. Ling, "RPCSEC_GSS Protocol
Specification", RFC 2203, August 1995.
[RFC 2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.
[RFC 2279] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 2279, January 1998.
[RFC 2623] Eisler, M., "NFS Version 2 and Version 3 Security Issues
and the NFS Protocol's Use of RPCSEC_GSS and Kerberos
V5", RFC 2623, June 1999.
[RFC 2624] Shepler, S., "NFS Version 4 Design Considerations", RFC
2624, June 1999.
[RFC 2847] Eisler, M., "LIPKEY - A Low Infrastructure Public Key
Mechanism Using SPKM", RFC 2847, June 2000.
[Sandberg] Sandberg, R., D. Goldberg, S. Kleiman, D. Walsh, B.
Lyon, "Design and Implementation of the Sun Network
Filesystem," USENIX Conference Proceedings, USENIX
Association, Berkeley, CA, Summer 1985. The basic paper
describing the SunOS implementation of the NFS version 2
protocol, and discusses the goals, protocol
specification and trade-offs.
Shepler, et al. Standards Track PAGE 208
RFC 3010 NFS version 4 Protocol December 2000
[Srinivasan] Srinivasan, V., Jeffrey C. Mogul, "Spritely NFS:
Implementation and Performance of Cache Consistency
Protocols", WRL Research Report 89/5, Digital Equipment
Corporation Western Research Laboratory, 100 Hamilton
Ave., Palo Alto, CA, 94301, May 1989. This paper
analyzes the effect of applying a Sprite-like
consistency protocol applied to standard NFS. The issues
of recovery in a stateful environment are covered in
[Mogul].
[Unicode1] The Unicode Consortium, "The Unicode Standard, Version
3.0", Addison-Wesley Developers Press, Reading, MA,
2000. ISBN 0-201-61633-5.
More information available at: http://www.unicode.org/
[Unicode2] "Unsupported Scripts" Unicode, Inc., The Unicode
Consortium, P.O. Box 700519, San Jose, CA 95710-0519
USA, September 1999
http://www.unicode.org/unicode/standard/unsupported.html
[XNFS] The Open Group, Protocols for Interworking: XNFS,
Version 3W, The Open Group, 1010 El Camino Real Suite
380, Menlo Park, CA 94025, ISBN 1-85912-184-5, February
1998.
HTML version available: http://www.opengroup.org
Shepler, et al. Standards Track PAGE 209
RFC 3010 NFS version 4 Protocol December 2000
20. Authors
20.1. Editor's Address
Spencer Shepler
Sun Microsystems, Inc.
7808 Moonflower Drive
Austin, Texas 78750
Phone: +1 512-349-9376
EMail: spencer.shepler@sun.com
20.2. Authors' Addresses
Carl Beame
Hummingbird Ltd.
EMail: beame@bws.com
Brent Callaghan
Sun Microsystems, Inc.
901 San Antonio Road
Palo Alto, CA 94303
Phone: +1 650-786-5067
EMail: brent.callaghan@sun.com
Mike Eisler
5565 Wilson Road
Colorado Springs, CO 80919
Phone: +1 719-599-9026
EMail: mike@eisler.com
David Noveck
Network Appliance
375 Totten Pond Road
Waltham, MA 02451
Phone: +1 781-895-4949
E-mail: dnoveck@netapp.com
Shepler, et al. Standards Track PAGE 210
RFC 3010 NFS version 4 Protocol December 2000
David Robinson
Sun Microsystems, Inc.
901 San Antonio Road
Palo Alto, CA 94303
Phone: +1 650-786-5088
EMail: david.robinson@sun.com
Robert Thurlow
Sun Microsystems, Inc.
901 San Antonio Road
Palo Alto, CA 94303
Phone: +1 650-786-5096
EMail: robert.thurlow@sun.com
20.3. Acknowledgements
The author thanks and acknowledges:
Neil Brown for his extensive review and comments of various drafts.
Shepler, et al. Standards Track PAGE 211
RFC 3010 NFS version 4 Protocol December 2000
21. Full Copyright Statement
Copyright © The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
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included on all such copies and derivative works. However, this
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the copyright notice or references to the Internet Society or other
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The limited permissions granted above are perpetual and will not be
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This document and the information contained herein is provided on an
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Shepler, et al. Standards Track PAGE 212
NFS version 4 Protocol
RFC TOTAL SIZE: 450434 bytes
PUBLICATION DATE: Tuesday, December 5th, 2000
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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