Internet RFC/STD/FYI/BCP Archives
Alternate Formats: rfc3530.txt | rfc3530.txt.pdf
Network Working Group S. Shepler
Request for Comments: 3530 B. Callaghan
Obsoletes: 3010 D. Robinson
Category: Standards Track R. Thurlow
Sun Microsystems, Inc.
C. Beame
Hummingbird Ltd.
M. Eisler
D. Noveck
Network Appliance, Inc.
April 2003
Network File System (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 (C) The Internet Society (2003). All Rights Reserved.
Abstract
The Network File System (NFS) version 4 is a distributed filesystem
protocol which owes heritage to NFS protocol version 2, RFC 1094, and
version 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.
This document replaces RFC 3010 as the definition of the NFS version
4 protocol.
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 [RFC2119].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 8
1.1. Changes since RFC 3010 . . . . . . . . . . . . . . . 8
1.2. NFS version 4 Goals. . . . . . . . . . . . . . . . . 9
1.3. Inconsistencies of this Document with Section 18 . . 9
1.4. Overview of NFS version 4 Features . . . . . . . . . 10
1.4.1. RPC and Security . . . . . . . . . . . . . . 10
1.4.2. Procedure and Operation Structure. . . . . . 10
1.4.3. Filesystem Mode. . . . . . . . . . . . . . . 11
1.4.3.1. Filehandle Types . . . . . . . . . 11
1.4.3.2. Attribute Types. . . . . . . . . . 12
1.4.3.3. Filesystem Replication and
Migration. . . . . . . . . . . . . 13
1.4.4. OPEN and CLOSE . . . . . . . . . . . . . . . 13
1.4.5. File locking . . . . . . . . . . . . . . . . 13
1.4.6. Client Caching and Delegation. . . . . . . . 13
1.5. General Definitions. . . . . . . . . . . . . . . . . 14
2. Protocol Data Types. . . . . . . . . . . . . . . . . . . . 16
2.1. Basic Data Types . . . . . . . . . . . . . . . . . . 16
2.2. Structured Data Types. . . . . . . . . . . . . . . . 18
3. RPC and Security Flavor. . . . . . . . . . . . . . . . . . 23
3.1. Ports and Transports . . . . . . . . . . . . . . . . 23
3.1.1. Client Retransmission Behavior . . . . . . . 24
3.2. Security Flavors . . . . . . . . . . . . . . . . . . 25
3.2.1. Security mechanisms for NFS version 4. . . . 25
3.2.1.1. Kerberos V5 as a security triple . 25
3.2.1.2. LIPKEY as a security triple. . . . 26
3.2.1.3. SPKM-3 as a security triple. . . . 27
3.3. Security Negotiation . . . . . . . . . . . . . . . . 27
3.3.1. SECINFO. . . . . . . . . . . . . . . . . . . 28
3.3.2. Security Error . . . . . . . . . . . . . . . 28
3.4. Callback RPC Authentication. . . . . . . . . . . . . 28
4. Filehandles . . . . . . . . . . . . . . . . . . . . . . . . 30
4.1. Obtaining the First Filehandle . . . . . . . . . . . 30
4.1.1. Root Filehandle. . . . . . . . . . . . . . . 31
4.1.2. Public Filehandle. . . . . . . . . . . . . . 31
4.2. Filehandle Types . . . . . . . . . . . . . . . . . . 31
4.2.1. General Properties of a Filehandle . . . . . 32
4.2.2. Persistent Filehandle. . . . . . . . . . . . 32
4.2.3. Volatile Filehandle. . . . . . . . . . . . . 33
4.2.4. One Method of Constructing a
Volatile Filehandle. . . . . . . . . . . . . 34
4.3. Client Recovery from Filehandle Expiration . . . . . 35
5. File Attributes. . . . . . . . . . . . . . . . . . . . . . 35
5.1. Mandatory Attributes . . . . . . . . . . . . . . . . 37
5.2. Recommended Attributes . . . . . . . . . . . . . . . 37
5.3. Named Attributes . . . . . . . . . . . . . . . . . . 37
5.4. Classification of Attributes . . . . . . . . . . . . 38
5.5. Mandatory Attributes - Definitions . . . . . . . . . 39
5.6. Recommended Attributes - Definitions . . . . . . . . 41
5.7. Time Access. . . . . . . . . . . . . . . . . . . . . 46
5.8. Interpreting owner and owner_group . . . . . . . . . 47
5.9. Character Case Attributes. . . . . . . . . . . . . . 49
5.10. Quota Attributes . . . . . . . . . . . . . . . . . . 49
5.11. Access Control Lists . . . . . . . . . . . . . . . . 50
5.11.1. ACE type . . . . . . . . . . . . . . . . . 51
5.11.2. ACE Access Mask. . . . . . . . . . . . . . 52
5.11.3. ACE flag . . . . . . . . . . . . . . . . . 54
5.11.4. ACE who . . . . . . . . . . . . . . . . . 55
5.11.5. Mode Attribute . . . . . . . . . . . . . . 56
5.11.6. Mode and ACL Attribute . . . . . . . . . . 57
5.11.7. mounted_on_fileid. . . . . . . . . . . . . 57
6. Filesystem Migration and Replication . . . . . . . . . . . 58
6.1. Replication. . . . . . . . . . . . . . . . . . . . . 58
6.2. Migration. . . . . . . . . . . . . . . . . . . . . . 59
6.3. Interpretation of the fs_locations Attribute . . . . 60
6.4. Filehandle Recovery for Migration or Replication . . 61
7. NFS Server Name Space . . . . . . . . . . . . . . . . . . . 61
7.1. Server Exports . . . . . . . . . . . . . . . . . . . 61
7.2. Browsing Exports . . . . . . . . . . . . . . . . . . 62
7.3. Server Pseudo Filesystem . . . . . . . . . . . . . . 62
7.4. Multiple Roots . . . . . . . . . . . . . . . . . . . 63
7.5. Filehandle Volatility. . . . . . . . . . . . . . . . 63
7.6. Exported Root. . . . . . . . . . . . . . . . . . . . 63
7.7. Mount Point Crossing . . . . . . . . . . . . . . . . 63
7.8. Security Policy and Name Space Presentation. . . . . 64
8. File Locking and Share Reservations. . . . . . . . . . . . 65
8.1. Locking. . . . . . . . . . . . . . . . . . . . . . . 65
8.1.1. Client ID. . . . . . . . . . . . . . . . . 66
8.1.2. Server Release of Clientid . . . . . . . . 69
8.1.3. lock_owner and stateid Definition. . . . . 69
8.1.4. Use of the stateid and Locking . . . . . . 71
8.1.5. Sequencing of Lock Requests. . . . . . . . 73
8.1.6. Recovery from Replayed Requests. . . . . . 74
8.1.7. Releasing lock_owner State . . . . . . . . 74
8.1.8. Use of Open Confirmation . . . . . . . . . 75
8.2. Lock Ranges. . . . . . . . . . . . . . . . . . . . . 76
8.3. Upgrading and Downgrading Locks. . . . . . . . . . . 76
8.4. Blocking Locks . . . . . . . . . . . . . . . . . . . 77
8.5. Lease Renewal. . . . . . . . . . . . . . . . . . . . 77
8.6. Crash Recovery . . . . . . . . . . . . . . . . . . . 78
8.6.1. Client Failure and Recovery. . . . . . . . 79
8.6.2. Server Failure and Recovery. . . . . . . . 79
8.6.3. Network Partitions and Recovery. . . . . . 81
8.7. Recovery from a Lock Request Timeout or Abort . . . 85
8.8. Server Revocation of Locks. . . . . . . . . . . . . 85
8.9. Share Reservations. . . . . . . . . . . . . . . . . 86
8.10. OPEN/CLOSE Operations . . . . . . . . . . . . . . . 87
8.10.1. Close and Retention of State
Information. . . . . . . . . . . . . . . . 88
8.11. Open Upgrade and Downgrade. . . . . . . . . . . . . 88
8.12. Short and Long Leases . . . . . . . . . . . . . . . 89
8.13. Clocks, Propagation Delay, and Calculating Lease
Expiration. . . . . . . . . . . . . . . . . . . . . 89
8.14. Migration, Replication and State. . . . . . . . . . 90
8.14.1. Migration and State. . . . . . . . . . . . 90
8.14.2. Replication and State. . . . . . . . . . . 91
8.14.3. Notification of Migrated Lease . . . . . . 92
8.14.4. Migration and the Lease_time Attribute . . 92
9. Client-Side Caching . . . . . . . . . . . . . . . . . . . . 93
9.1. Performance Challenges for Client-Side Caching. . . 93
9.2. Delegation and Callbacks. . . . . . . . . . . . . . 94
9.2.1. Delegation Recovery . . . . . . . . . . . . 96
9.3. Data Caching. . . . . . . . . . . . . . . . . . . . 98
9.3.1. Data Caching and OPENs . . . . . . . . . . 98
9.3.2. Data Caching and File Locking. . . . . . . 99
9.3.3. Data Caching and Mandatory File Locking. . 101
9.3.4. Data Caching and File Identity . . . . . . 101
9.4. Open Delegation . . . . . . . . . . . . . . . . . . 102
9.4.1. Open Delegation and Data Caching . . . . . 104
9.4.2. Open Delegation and File Locks . . . . . . 106
9.4.3. Handling of CB_GETATTR . . . . . . . . . . 106
9.4.4. Recall of Open Delegation. . . . . . . . . 109
9.4.5. Clients that Fail to Honor
Delegation Recalls . . . . . . . . . . . . 111
9.4.6. Delegation Revocation. . . . . . . . . . . 112
9.5. Data Caching and Revocation . . . . . . . . . . . . 112
9.5.1. Revocation Recovery for Write Open
Delegation . . . . . . . . . . . . . . . . 113
9.6. Attribute Caching . . . . . . . . . . . . . . . . . 113
9.7. Data and Metadata Caching and Memory Mapped Files . 115
9.8. Name Caching . . . . . . . . . . . . . . . . . . . 118
9.9. Directory Caching . . . . . . . . . . . . . . . . . 119
10. Minor Versioning . . . . . . . . . . . . . . . . . . . . . 120
11. Internationalization . . . . . . . . . . . . . . . . . . . 122
11.1. Stringprep profile for the utf8str_cs type. . . . . 123
11.1.1. Intended applicability of the
nfs4_cs_prep profile . . . . . . . . . . . 123
11.1.2. Character repertoire of nfs4_cs_prep . . . 124
11.1.3. Mapping used by nfs4_cs_prep . . . . . . . 124
11.1.4. Normalization used by nfs4_cs_prep . . . . 124
11.1.5. Prohibited output for nfs4_cs_prep . . . . 125
11.1.6. Bidirectional output for nfs4_cs_prep. . . 125
11.2. Stringprep profile for the utf8str_cis type . . . . 125
11.2.1. Intended applicability of the
nfs4_cis_prep profile. . . . . . . . . . . 125
11.2.2. Character repertoire of nfs4_cis_prep . . 125
11.2.3. Mapping used by nfs4_cis_prep . . . . . . 125
11.2.4. Normalization used by nfs4_cis_prep . . . 125
11.2.5. Prohibited output for nfs4_cis_prep . . . 126
11.2.6. Bidirectional output for nfs4_cis_prep . . 126
11.3. Stringprep profile for the utf8str_mixed type . . . 126
11.3.1. Intended applicability of the
nfs4_mixed_prep profile. . . . . . . . . . 126
11.3.2. Character repertoire of nfs4_mixed_prep . 126
11.3.3. Mapping used by nfs4_cis_prep . . . . . . 126
11.3.4. Normalization used by nfs4_mixed_prep . . 127
11.3.5. Prohibited output for nfs4_mixed_prep . . 127
11.3.6. Bidirectional output for nfs4_mixed_prep . 127
11.4. UTF-8 Related Errors. . . . . . . . . . . . . . . . 127
12. Error Definitions . . . . . . . . . . . . . . . . . . . . 128
13. NFS version 4 Requests . . . . . . . . . . . . . . . . . . 134
13.1. Compound Procedure. . . . . . . . . . . . . . . . . 134
13.2. Evaluation of a Compound Request. . . . . . . . . . 135
13.3. Synchronous Modifying Operations. . . . . . . . . . 136
13.4. Operation Values. . . . . . . . . . . . . . . . . . 136
14. NFS version 4 Procedures . . . . . . . . . . . . . . . . . 136
14.1. Procedure 0: NULL - No Operation. . . . . . . . . . 136
14.2. Procedure 1: COMPOUND - Compound Operations . . . . 137
14.2.1. Operation 3: ACCESS - Check Access
Rights. . . . . . . . . . . . . . . . . . 140
14.2.2. Operation 4: CLOSE - Close File . . . . . 142
14.2.3. Operation 5: COMMIT - Commit
Cached Data . . . . . . . . . . . . . . . 144
14.2.4. Operation 6: CREATE - Create a
Non-Regular File Object . . . . . . . . . 147
14.2.5. Operation 7: DELEGPURGE -
Purge Delegations Awaiting Recovery . . . 150
14.2.6. Operation 8: DELEGRETURN - Return
Delegation. . . . . . . . . . . . . . . . 151
14.2.7. Operation 9: GETATTR - Get Attributes . . 152
14.2.8. Operation 10: GETFH - Get Current
Filehandle. . . . . . . . . . . . . . . . 153
14.2.9. Operation 11: LINK - Create Link to a
File. . . . . . . . . . . . . . . . . . . 154
14.2.10. Operation 12: LOCK - Create Lock . . . . 156
14.2.11. Operation 13: LOCKT - Test For Lock . . . 160
14.2.12. Operation 14: LOCKU - Unlock File . . . . 162
14.2.13. Operation 15: LOOKUP - Lookup Filename. . 163
14.2.14. Operation 16: LOOKUPP - Lookup
Parent Directory. . . . . . . . . . . . . 165
14.2.15. Operation 17: NVERIFY - Verify
Difference in Attributes . . . . . . . . 166
14.2.16. Operation 18: OPEN - Open a Regular
File. . . . . . . . . . . . . . . . . . . 168
14.2.17. Operation 19: OPENATTR - Open Named
Attribute Directory . . . . . . . . . . . 178
14.2.18. Operation 20: OPEN_CONFIRM -
Confirm Open . . . . . . . . . . . . . . 180
14.2.19. Operation 21: OPEN_DOWNGRADE -
Reduce Open File Access . . . . . . . . . 182
14.2.20. Operation 22: PUTFH - Set
Current Filehandle. . . . . . . . . . . . 184
14.2.21. Operation 23: PUTPUBFH -
Set Public Filehandle . . . . . . . . . . 185
14.2.22. Operation 24: PUTROOTFH -
Set Root Filehandle . . . . . . . . . . . 186
14.2.23. Operation 25: READ - Read from File . . . 187
14.2.24. Operation 26: READDIR -
Read Directory. . . . . . . . . . . . . . 190
14.2.25. Operation 27: READLINK -
Read Symbolic Link. . . . . . . . . . . . 193
14.2.26. Operation 28: REMOVE -
Remove Filesystem Object. . . . . . . . . 195
14.2.27. Operation 29: RENAME -
Rename Directory Entry. . . . . . . . . . 197
14.2.28. Operation 30: RENEW - Renew a Lease . . . 200
14.2.29. Operation 31: RESTOREFH -
Restore Saved Filehandle. . . . . . . . . 201
14.2.30. Operation 32: SAVEFH - Save
Current Filehandle. . . . . . . . . . . . 202
14.2.31. Operation 33: SECINFO - Obtain
Available Security. . . . . . . . . . . . 203
14.2.32. Operation 34: SETATTR - Set Attributes. . 206
14.2.33. Operation 35: SETCLIENTID -
Negotiate Clientid. . . . . . . . . . . . 209
14.2.34. Operation 36: SETCLIENTID_CONFIRM -
Confirm Clientid. . . . . . . . . . . . . 213
14.2.35. Operation 37: VERIFY -
Verify Same Attributes. . . . . . . . . . 217
14.2.36. Operation 38: WRITE - Write to File . . . 218
14.2.37. Operation 39: RELEASE_LOCKOWNER -
Release Lockowner State . . . . . . . . . 223
14.2.38. Operation 10044: ILLEGAL -
Illegal operation . . . . . . . . . . . . 224
15. NFS version 4 Callback Procedures . . . . . . . . . . . . 225
15.1. Procedure 0: CB_NULL - No Operation . . . . . . . . 225
15.2. Procedure 1: CB_COMPOUND - Compound
Operations. . . . . . . . . . . . . . . . . . . . . 226
15.2.1. Operation 3: CB_GETATTR - Get
Attributes . . . . . . . . . . . . . . . . 228
15.2.2. Operation 4: CB_RECALL -
Recall an Open Delegation. . . . . . . . . 229
15.2.3. Operation 10044: CB_ILLEGAL -
Illegal Callback Operation . . . . . . . . 230
16. Security Considerations . . . . . . . . . . . . . . . . . 231
17. IANA Considerations . . . . . . . . . . . . . . . . . . . 232
17.1. Named Attribute Definition. . . . . . . . . . . . . 232
17.2. ONC RPC Network Identifiers (netids). . . . . . . . 232
18. RPC definition file . . . . . . . . . . . . . . . . . . . 234
19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 268
20. Normative References . . . . . . . . . . . . . . . . . . . 268
21. Informative References . . . . . . . . . . . . . . . . . . 270
22. Authors' Information . . . . . . . . . . . . . . . . . . . 273
22.1. Editor's Address. . . . . . . . . . . . . . . . . . 273
22.2. Authors' Addresses. . . . . . . . . . . . . . . . . 274
23. Full Copyright Statement . . . . . . . . . . . . . . . . . 275
1. Introduction
1.1. Changes since RFC 3010
This definition of the NFS version 4 protocol replaces or obsoletes
the definition present in [RFC3010]. While portions of the two
documents have remained the same, there have been substantive changes
in others. The changes made between [RFC3010] and this document
represent implementation experience and further review of the
protocol. While some modifications were made for ease of
implementation or clarification, most updates represent errors or
situations where the [RFC3010] definition were untenable.
The following list is not all inclusive of all changes but presents
some of the most notable changes or additions made:
o The state model has added an open_owner4 identifier. This was
done to accommodate Posix based clients and the model they use for
file locking. For Posix clients, an open_owner4 would correspond
to a file descriptor potentially shared amongst a set of processes
and the lock_owner4 identifier would correspond to a process that
is locking a file.
o Clarifications and error conditions were added for the handling of
the owner and group attributes. Since these attributes are string
based (as opposed to the numeric uid/gid of previous versions of
NFS), translations may not be available and hence the changes
made.
o Clarifications for the ACL and mode attributes to address
evaluation and partial support.
o For identifiers that are defined as XDR opaque, limits were set on
their size.
o Added the mounted_on_filed attribute to allow Posix clients to
correctly construct local mounts.
o Modified the SETCLIENTID/SETCLIENTID_CONFIRM operations to deal
correctly with confirmation details along with adding the ability
to specify new client callback information. Also added
clarification of the callback information itself.
o Added a new operation LOCKOWNER_RELEASE to enable notifying the
server that a lock_owner4 will no longer be used by the client.
o RENEW operation changes to identify the client correctly and allow
for additional error returns.
o Verify error return possibilities for all operations.
o Remove use of the pathname4 data type from LOOKUP and OPEN in
favor of having the client construct a sequence of LOOKUP
operations to achieive the same effect.
o Clarification of the internationalization issues and adoption of
the new stringprep profile framework.
1.2. NFS Version 4 Goals
The NFS version 4 protocol is a further revision of the NFS protocol
defined already by versions 2 [RFC1094] and 3 [RFC1813]. 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:
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 filesystem model that provides a useful,
common set of features that does not unduly favor one filesystem
or operating system over another.
o Designed for protocol extensions.
The protocol is designed to accept standard extensions that do not
compromise backward compatibility.
1.3. Inconsistencies of this Document with Section 18
Section 18, RPC Definition File, contains the definitions in XDR
description language of the constructs used by the protocol. Prior
to Section 18, several of the constructs are reproduced for purposes
of explanation. The reader is warned of the possibility of errors in
the reproduced constructs outside of Section 18. For any part of the
document that is inconsistent with Section 18, Section 18 is to be
considered authoritative.
1.4. 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
[RFC1831] and [RFC1832]. A basic knowledge of filesystems and
distributed filesystems is expected as well.
1.4.1. 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 [RFC1831] and [RFC1832]. To
meet end to end security requirements, the RPCSEC_GSS framework
[RFC2203] 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 [RFC1964] to provide one
security framework. The LIPKEY GSS-API mechanism described in
[RFC2847] 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 filesystem
resources. With this, the client can securely match the security
mechanism that meets the policies specified at both the client and
server.
1.4.2. 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 filesystem
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 filesystem 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.
1.4.3. Filesystem Model
The general filesystem model used for the NFS version 4 protocol is
the same as previous versions. The server filesystem 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 filesystem tree provided by the server. The server
provides multiple filesystems by gluing them together with pseudo
filesystems. These pseudo filesystems provide for potential gaps in
the path names between real filesystems.
1.4.3.1. 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 filesystem 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 filesystem 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.
1.4.3.2. Attribute Types
The NFS version 4 protocol introduces three classes of filesystem 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 filesystem 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.
Mandatory attributes are the minimal set of file or filesystem
attributes that must be provided by the server and must be properly
represented by the server. Recommended attributes represent
different filesystem 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 filesystem
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.
1.4.3.3. Filesystem Replication and Migration
With the use of a special file attribute, the ability to migrate or
replicate server filesystems is enabled within the protocol. The
filesystem locations attribute provides a method for the client to
probe the server about the location of a filesystem. In the event of
a migration of a filesystem, the client will receive an error when
operating on the filesystem 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 filesystem. From this information, the client can use its
own policies to access the appropriate filesystem location.
1.4.4. 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.
1.4.5. 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
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).
1.4.6. 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 filesystem 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.
1.5. 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
filesystem 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 share reservations unless
specifically stated otherwise.
Server The "Server" is the entity responsible for coordinating
client access to a set of filesystems.
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).
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 128-bit quantity returned by a server that uniquely
defines the open and locking state provided by the server
for a specific open or 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 [RFC1832] and RPC [RFC1831]
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;
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 utf8str_cs 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 utf8str_cs 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
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 [RFC2743] for details.
seqid4 typedef uint32_t seqid4;
Sequence identifier used for file locking
utf8string typedef opaque utf8string<>;
UTF-8 encoding for strings
utf8str_cis typedef opaque utf8str_cis;
Case-insensitive UTF-8 string
utf8str_cs typedef opaque utf8str_cs;
Case-sensitive UTF-8 string
utf8str_mixed typedef opaque utf8str_mixed;
UTF-8 strings with a case sensitive prefix and
a case insensitive suffix.
verifier4 typedef opaque verifier4[NFS4_VERIFIER_SIZE];
Verifier used for various operations (COMMIT,
CREATE, OPEN, READDIR, SETCLIENTID,
SETCLIENTID_CONFIRM, 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 filesystem object is 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; /* major device number */
uint32_t specdata2; /* minor device number */
};
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 filesystem identifier that is used as a mandatory
attribute.
fs_location4
struct fs_location4 {
utf8str_cis 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;
};
This structure is used with the CREATE, LINK, REMOVE, RENAME
operations to let the client know the value of the change attribute
for the directory in which the target filesystem 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 SETCLIENTID
operation to either specify the address of the client that is using a
clientid or as part of the callback registration. The
r_netid and r_addr fields are specified in [RFC1833], but they are
underspecified in [RFC1833] as far as what they should look like for
specific protocols.
For TCP over IPv4 and for UDP over IPv4, the format of r_addr is the
US-ASCII string:
h1.h2.h3.h4.p1.p2
The prefix, "h1.h2.h3.h4", is the standard textual form for
representing an IPv4 address, which is always four octets long.
Assuming big-endian ordering, h1, h2, h3, and h4, are respectively,
the first through fourth octets each converted to ASCII-decimal.
Assuming big-endian ordering, p1 and p2 are, respectively, the first
and second octets each converted to ASCII-decimal. For example, if a
host, in big-endian order, has an address of 0x0A010307 and there is
a service listening on, in big endian order, port 0x020F (decimal
527), then the complete universal address is "10.1.3.7.2.15".
For TCP over IPv4 the value of r_netid is the string "tcp". For UDP
over IPv4 the value of r_netid is the string "udp".
For TCP over IPv6 and for UDP over IPv6, the format of r_addr is the
US-ASCII string:
x1:x2:x3:x4:x5:x6:x7:x8.p1.p2
The suffix "p1.p2" is the service port, and is computed the same way
as with universal addresses for TCP and UDP over IPv4. The prefix,
"x1:x2:x3:x4:x5:x6:x7:x8", is the standard textual form for
representing an IPv6 address as defined in Section 2.2 of [RFC2373].
Additionally, the two alternative forms specified in Section 2.2 of
[RFC2373] are also acceptable.
For TCP over IPv6 the value of r_netid is the string "tcp6". For UDP
over IPv6 the value of r_netid is the string "udp6".
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<NFS4_OPAQUE_LIMIT>;
};
This structure is part of the arguments to the SETCLIENTID operation.
NFS4_OPAQUE_LIMIT is defined as 1024.
open_owner4
struct open_owner4 {
clientid4 clientid;
opaque owner<NFS4_OPAQUE_LIMIT>;
};
This structure is used to identify the owner of open state.
NFS4_OPAQUE_LIMIT is defined as 1024.
lock_owner4
struct lock_owner4 {
clientid4 clientid;
opaque owner<NFS4_OPAQUE_LIMIT>;
};
This structure is used to identify the owner of file locking state.
NFS4_OPAQUE_LIMIT is defined as 1024.
open_to_lock_owner4
struct open_to_lock_owner4 {
seqid4 open_seqid;
stateid4 open_stateid;
seqid4 lock_seqid;
lock_owner4 lock_owner;
};
This structure is used for the first LOCK operation done for an
open_owner4. It provides both the open_stateid and lock_owner such
that the transition is made from a valid open_stateid sequence to
that of the new lock_stateid sequence. Using this mechanism avoids
the confirmation of the lock_owner/lock_seqid pair since it is tied
to established state in the form of the open_stateid/open_seqid.
stateid4
struct stateid4 {
uint32_t seqid;
opaque other[12];
};
This structure is used for the various state sharing mechanisms
between the client and server. For the client, this data structure
is read-only. The starting value of the seqid field is undefined.
The server is required to increment the seqid field monotonically at
each transition of the stateid. This is important since the client
will inspect the seqid in OPEN stateids to determine the order of
OPEN processing done by the server.
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 [RFC1831] and [RFC1832]. The
RPCSEC_GSS security flavor as defined in [RFC2203] 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 [RFC3232] 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 [RFC1833]; this will allow NFS to
transit firewalls.
Where an NFS version 4 implementation supports operation over the IP
network protocol, the supported transports between NFS and IP MUST be
among the IETF-approved congestion control transport protocols, which
include TCP and SCTP. To enhance the possibilities for
interoperability, an NFS version 4 implementation MUST support
operation over the TCP transport protocol, at least until such time
as a standards track RFC revises this requirement to use a different
IETF-approved congestion control transport protocol.
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.
As noted in the Security Considerations section, the authentication
model for NFS version 4 has moved from machine-based to principal-
based. However, this modification of the authentication model does
not imply a technical requirement to move the TCP connection
management model from whole machine-based to one based on a per user
model. In particular, NFS over TCP client implementations have
traditionally multiplexed traffic for multiple users over a common
TCP connection between an NFS client and server. This has been true,
regardless whether the NFS client is using AUTH_SYS, AUTH_DH,
RPCSEC_GSS or any other flavor. Similarly, NFS over TCP server
implementations have assumed such a model and thus scale the
implementation of TCP connection management in proportion to the
number of expected client machines. It is intended that NFS version
4 will not modify this connection management model. NFS version 4
clients that violate this assumption can expect scaling issues on the
server and hence reduced service.
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].
3.1.1. Client Retransmission Behavior
When processing a request received over a reliable transport such as
TCP, the NFS version 4 server MUST NOT silently drop the request,
except if the transport connection has been broken. Given such a
contract between NFS version 4 clients and servers, clients MUST NOT
retry a request unless one or both of the following are true:
o The transport connection has been broken
o The procedure being retried is the NULL procedure
Since reliable transports, such as TCP, do not always synchronously
inform a peer when the other peer has broken the connection (for
example, when an NFS server reboots), the NFS version 4 client may
want to actively "probe" the connection to see if has been broken.
Use of the NULL procedure is one recommended way to do so. So, when
a client experiences a remote procedure call timeout (of some
arbitrary implementation specific amount), rather than retrying the
remote procedure call, it could instead issue a NULL procedure call
to the server. If the server has died, the transport connection
break will eventually be indicated to the NFS version 4 client. The
client can then reconnect, and then retry the original request. If
the NULL procedure call gets a response, the connection has not
broken. The client can decide to wait longer for the original
request's response, or it can break the transport connection and
reconnect before re-sending the original request.
For callbacks from the server to the client, the same rules apply,
but the server doing the callback becomes the client, and the client
receiving the callback becomes the server.
3.2. Security Flavors
Traditional RPC implementations have included AUTH_NONE, AUTH_SYS,
AUTH_DH, and AUTH_KRB4 as security flavors. With [RFC2203] an
additional security flavor of RPCSEC_GSS has been introduced which
uses the functionality of GSS-API [RFC2743]. This allows for the use
of various 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
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 a security triple
The Kerberos V5 GSS-API mechanism as described in [RFC1964] 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 [RFC2623].
Users and implementors are warned that 56 bit DES is no longer
considered state of the art in terms of resistance to brute force
attacks. Once a revision to [RFC1964] is available that adds support
for AES, implementors are urged to incorporate AES into their NFSv4
over Kerberos V5 protocol stacks, and users are similarly urged to
migrate to the use of AES.
3.2.1.2. LIPKEY as a security triple
The LIPKEY GSS-API mechanism as described in [RFC2847] 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
--------------------------------------------------------------------
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 [RFC2847] 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 [RFC2025] 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 server. 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 [RFC2847] for more
details.
3.2.1.3. SPKM-3 as a security triple
The SPKM-3 GSS-API mechanism as described in [RFC2847] 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 [RFC2025] for an
explanation.
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 filesystem 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.
See the section "Security Considerations" for further discussion.
3.3.1. 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
operation 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.
3.3.2. 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 filesystem
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. See the section for the "SECINFO"
operation for further discussion of how the client will respond to
the NFS4ERR_WRONGSEC error and use SECINFO.
3.4. Callback RPC Authentication
Except as noted elsewhere in this section, the callback RPC
(described later) MUST mutually authenticate the NFS server to the
principal that acquired the clientid (also described later), using
the security flavor the original SETCLIENTID operation used.
For AUTH_NONE, there are no principals, so this is a non-issue.
AUTH_SYS has no notions of mutual authentication or a server
principal, so the callback from the server simply uses the AUTH_SYS
credential that the user used when he 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.
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.
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. This is the same
principal the client acquired a GSS-API context for when it issued
the SETCLIENTID operation, therefore, the realm name for the server
principal must be the same for the callback as it was for the
SETCLIENTID.
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
pair, and if the user that the NFS server is authenticating to has a
public key certificate, then it works.
In situations where the 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 filesystem 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 filesystem
object.
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 [RFC1094] and the NFS version 3 protocol [RFC1813], 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 filesystem 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 [RFC2054] and [RFC2055]. With the use
of the public filehandle in combination with the LOOKUP operation 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 filesystem 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 operation. 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 filesystem 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 filesystem 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 filesystem object. The client may not make any
assumptions about this binding. The client uses the PUBLIC
filehandle via the PUTPUBFH operation.
4.2. Filehandle Types
In the NFS version 2 and 3 protocols, there was one type of
filehandle with a single set of semantics. This type of filehandle
is termed "persistent" in NFS Version 4. The semantics of a
persistent filehandle remain the same as before. A new type of
filehandle introduced in NFS Version 4 is the "volatile" filehandle,
which attempts to accommodate certain server environments.
The volatile filehandle type was introduced to address server
functionality or implementation issues which make correct
implementation of a persistent filehandle infeasible. Some server
environments do not provide a filesystem level invariant that can be
used to construct a persistent filehandle. The underlying server
filesystem may not provide the invariant or the server's filesystem
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
filesystem reorganization or migration. However, the volatile
filehandle increases the implementation burden for the client.
Since the client will need to handle persistent and volatile
filehandles 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.
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. 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 filesystem 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 filesystem object to which it refers. Once the
server creates the filehandle for a filesystem 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 filesystem is migrated, the new NFS
server must honor the same filehandle as the old NFS server.
The persistent filehandle will be become stale or invalid when the
filesystem 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
filesystem 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 filesystem in whole
has been destroyed or the filesystem 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.
The mandatory attribute "fh_expire_type" is used by the client to
determine what type of filehandle the server is providing for a
particular filesystem. 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 filesystem. 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_VOLATILE_ANY
The filehandle may expire at any time, except as
specifically excluded (i.e., FH4_NO_EXPIRE_WITH_OPEN).
FH4_NOEXPIRE_WITH_OPEN
May only be set when FH4_VOLATILE_ANY is set. If this bit
is set, then the meaning of FH4_VOLATILE_ANY is qualified
to exclude any expiration of the filehandle when it is
open.
FH4_VOL_MIGRATION
The filehandle will expire as a result of migration. If
FH4_VOL_ANY is set, FH4_VOL_MIGRATION is redundant.
FH4_VOL_RENAME
The filehandle will expire during rename. This includes a
rename by the requesting client or a rename by any other
client. If FH4_VOL_ANY is set, FH4_VOL_RENAME is
redundant.
Servers which provide volatile filehandles that may expire while open
(i.e., if FH4_VOL_MIGRATION or FH4_VOL_RENAME is set or if
FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN not set), should
deny a RENAME or REMOVE that would affect an OPEN file of any of the
components leading to the OPEN file. In addition, the server should
deny all RENAME or REMOVE requests during the grace period upon
server restart.
Note that the bits FH4_VOL_MIGRATION and FH4_VOL_RENAME allow the
client to determine that expiration has occurred whenever a specific
event occurs, without an explicit filehandle expiration error from
the server. FH4_VOL_ANY does not provide this form of information.
In situations where the server will expire many, but not all
filehandles upon migration (e.g., all but those that are open),
FH4_VOLATILE_ANY (in this case with FH4_NOEXPIRE_WITH_OPEN) is a
better choice since the client may not assume that all filehandles
will expire when migration occurs, and it is likely that additional
expirations will occur (as a result of file CLOSE) that are separated
in time from the migration event itself.
4.2.4. One Method of Constructing a Volatile Filehandle
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
When the client presents a volatile filehandle, the server makes the
following checks, which assume that the check for the volatile bit
has passed. 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 filesystem 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 filesystem name space.
If the expired filehandle refers to an object that has been removed
from the filesystem, 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
Note that the COMPOUND procedure does not provide atomicity. This
example only reduces the overhead of recovering from an expired
filehandle.
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 is able query what attributes
the server supports and construct requests with only those supported
attributes (or a subset thereof).
To this end, attributes are 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
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. A server should support as many of the recommended attributes
as possible but by their definition, the server is not required to
support all of them. 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.
Note that the hidden directory returned by OPENATTR is a convenience
for protocol processing. The client should not make any assumptions
about the server's implementation of named attributes and whether the
underlying filesystem at the server has a named attribute directory
or not. Therefore, operations such as SETATTR and GETATTR on the
named attribute directory are undefined.
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
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 the client is better positioned decide whether and how to
fabricate or construct an attribute or whether to 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 filesystem 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 filesystem. 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. Classification of Attributes
Each of the Mandatory and Recommended attributes can be classified in
one of three categories: per server, per filesystem, or per
filesystem object. Note that it is possible that some per filesystem
attributes may vary within the filesystem. See the "homogeneous"
attribute for its definition. Note that the attributes
time_access_set and time_modify_set are not listed in this section
because they are write-only attributes corresponding to time_access
and time_modify, and are used in a special instance of SETATTR.
o The per server attribute is:
lease_time
o The per filesystem attributes are:
supp_attr, fh_expire_type, link_support, symlink_support,
unique_handles, aclsupport, cansettime, case_insensitive,
case_preserving, chown_restricted, files_avail, files_free,
files_total, fs_locations, homogeneous, maxfilesize, maxname,
maxread, maxwrite, no_trunc, space_avail, space_free, space_total,
time_delta
o The per filesystem object attributes are:
type, change, size, named_attr, fsid, rdattr_error, filehandle,
ACL, archive, fileid, hidden, maxlink, mimetype, mode, numlinks,
owner, owner_group, rawdev, space_used, system, time_access,
time_backup, time_create, time_metadata, time_modify,
mounted_on_fileid
For quota_avail_hard, quota_avail_soft, and quota_used see their
definitions below for the appropriate classification.
5.5. 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. The
scope of this
attribute applies to
all objects with a
matching fsid.
type 1 nfs4_ftype READ The type of the object
(file, directory,
symlink, etc.)
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_metadata
attribute for this
attribute's value but
only if the filesystem
object can not be
updated more
frequently than the
resolution of
time_metadata.
size 4 uint64 R/W The size of the object
in bytes.
link_support 5 bool READ True, if the object's
filesystem supports
hard links.
symlink_support 6 bool READ True, if the object's
filesystem supports
symbolic links.
named_attr 7 bool READ True, if this object
has named attributes.
In other words, object
has a non-empty named
attribute directory.
fsid 8 fsid4 READ Unique filesystem
identifier for the
filesystem holding
this object. fsid
contains major and
minor components each
of which are uint64.
unique_handles 9 bool READ True, if two distinct
filehandles guaranteed
to refer to two
different filesystem
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.
filehandle 19 nfs_fh4 READ The filehandle of this
object (primarily for
readdir requests).
5.6. 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 filesystem.
archive 14 bool R/W True, if this file
has been archived
since the time of
last modification
(deprecated in favor
of time_backup).
cansettime 15 bool READ True, if the server
is able to change
the times for a
filesystem object as
specified in a
SETATTR operation.
case_insensitive 16 bool READ True, if filename
comparisons on this
filesystem are case
insensitive.
case_preserving 17 bool READ True, if filename
case on this
filesystem are
preserved.
chown_restricted 18 bool 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
Windows 2000 the
"Take Ownership"
privilege).
fileid 20 uint64 READ A number uniquely
identifying the file
within the
filesystem.
files_avail 21 uint64 READ File slots available
to this user on the
filesystem
containing this
object - this should
be the smallest
relevant limit.
files_free 22 uint64 READ Free file slots on
the filesystem
containing this
object - this should
be the smallest
relevant limit.
files_total 23 uint64 READ Total file slots on
the filesystem
containing this
object.
fs_locations 24 fs_locations READ Locations where this
filesystem may be
found. If the
server returns
NFS4ERR_MOVED
as an error, this
attribute MUST be
supported.
hidden 25 bool R/W True, if the file is
considered hidden
with respect to the
Windows API.
homogeneous 26 bool READ True, if this
object's filesystem
is homogeneous,
i.e., are per
filesystem
attributes the same
for all filesystem's
objects?
maxfilesize 27 uint64 READ Maximum supported
file size for the
filesystem 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
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 mode and
permission bits for
this object.
no_trunc 34 bool READ True, if a name
longer than name_max
is used, an error be
returned and name is
not 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.
If the value of
type is not
NF4BLK or NF4CHR,
the value return
SHOULD NOT be
considered useful.
space_avail 42 uint64 READ Disk space in bytes
available to this
user on the
filesystem
containing this
object - this should
be the smallest
relevant limit.
space_free 43 uint64 READ Free disk space in
bytes on the
filesystem
containing this
object - this should
be the smallest
relevant limit.
space_total 44 uint64 READ Total disk space in
bytes on the
filesystem
containing this
object.
space_used 45 uint64 READ Number of filesystem
bytes allocated to
this object.
system 46 bool R/W True, if this file
is a "system" file
with respect to the
Windows API.
time_access 47 nfstime4 READ The time of last
access to the object
by a read that was
satisfied by the
server.
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".
time_delta 51 nfstime4 READ Smallest useful
server time
granularity.
time_metadata 52 nfstime4 READ 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.
mounted_on_fileid 55 uint64 READ Like fileid, but if
the target
filehandle is the
root of a filesystem
return the fileid of
the underlying
directory.
5.7. Time Access
As defined above, the time_access attribute represents the time of
last access to the object by a read that was satisfied by the server.
The notion of what is an "access" depends on server's operating
environment and/or the server's filesystem semantics. For example,
for servers obeying POSIX semantics, time_access would be updated
only by the READLINK, READ, and READDIR operations and not any of the
operations that modify the content of the object. Of course, setting
the corresponding time_access_set attribute is another way to modify
the time_access attribute.
Whenever the file object resides on a writable filesystem, the server
should make best efforts to record time_access into stable storage.
However, to mitigate the performance effects of doing so, and most
especially whenever the server is satisfying the read of the object's
content from its cache, the server MAY cache access time updates and
lazily write them to stable storage. It is also acceptable to give
administrators of the server the option to disable time_access
updates.
5.8. Interpreting owner and owner_group
The recommended attributes "owner" and "owner_group" (and also users
and groups within the "acl" attribute) 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 [RFC2624]
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.
Similarly, security principals may be represented in different ways
by different security mechanisms. Servers normally translate these
representations into a common format, generally that used by local
storage, to serve as a means of identifying the users corresponding
to these security principals. When these local identifiers are
translated to the form of the owner attribute, associated with files
created by such principals they identify, in a common format, the
users associated with each corresponding set of security principals.
The translation used to interpret owner and group strings 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. A server may
provide a more general service, not limited by any particular
translation (which would only translate a limited set of possible
strings) by storing the owner and owner_group attributes in local
storage without any translation or it may augment a translation
method by storing the entire string for attributes for which no
translation is available while using the local representation for
those cases in which a translation is available.
Servers that do not provide support for all possible values of the
owner and owner_group attributes, should return an error
(NFS4ERR_BADOWNER) when a string is presented that has no
translation, as the value to be set for a SETATTR of the owner,
owner_group, or acl attributes. When a server does accept an owner
or owner_group value as valid on a SETATTR (and similarly for the
owner and group strings in an acl), it is promising to return that
same string when a corresponding GETATTR is done. Configuration
changes and ill-constructed name translations (those that contain
aliasing) may make that promise impossible to honor. Servers should
make appropriate efforts to avoid a situation in which these
attributes have their values changed when no real change to ownership
has occurred.
The "dns_domain" portion of the owner string is meant to be a DNS
domain name. For example, user@ietf.org. Servers should accept as
valid a set of users for at least one domain. A server may treat
other domains as having no valid translations. A more general
service is provided when a server is capable of accepting users for
multiple domains, or for all domains, subject to security
constraints.
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 at the sender
and that the receiver of the attribute should not use that string as
a basis for translation into its own internal format. 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.
To provide a greater degree of compatibility with previous versions
of NFS (i.e., v2 and v3), which identified users and groups by 32-bit
unsigned uid's and gid's, owner and group strings that consist of
decimal numeric values with no leading zeros can be given a special
interpretation by clients and servers which choose to provide such
support. The receiver may treat such a user or group string as
representing the same user as would be represented by a v2/v3 uid or
gid having the corresponding numeric value. A server is not
obligated to accept such a string, but may return an NFS4ERR_BADOWNER
instead. To avoid this mechanism being used to subvert user and
group translation, so that a client might pass all of the owners and
groups in numeric form, a server SHOULD return an NFS4ERR_BADOWNER
error when there is a valid translation for the user or owner
designated in this way. In that case, the client must use the
appropriate name@domain string and not the special form for
compatibility.
The owner string "nobody" may be used to designate an anonymous user,
which will be associated with a file created by a security principal
that cannot be mapped through normal means to the owner attribute.
5.9. 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" [RFC1345] 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".
5.10. Quota Attributes
For the attributes related to filesystem 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.).
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".
5.11. Access Control Lists
The NFS version 4 ACL attribute is an array of access control entries
(ACE). Although, the client can read and write the ACL attribute,
the NFSv4 model is the server does all access control based on the
server's interpretation of the ACL. If at any point the client wants
to check access without issuing an operation that modifies or reads
data or metadata, the client can use the OPEN and ACCESS operations
to do so. There are various access control entry types, as defined
in the Section "ACE type". The server is able to communicate which
ACE types are supported by returning the appropriate value within the
aclsupport attribute. Each ACE covers one or more operations on a
file or directory as described in the Section "ACE Access Mask". It
may also contain one or more flags that modify the semantics of the
ACE as defined in the Section "ACE flag".
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;
utf8str_mixed who;
};
To determine if a 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 is no longer
considered in the processing of later ACEs. If an ACCESS_DENIED_ACE
is encountered where the requester's access still has unALLOWED bits
in common with the "access_mask" of the ACE, the request is denied.
However, unlike the ALLOWED and DENIED ACE types, the ALARM and AUDIT
ACE types do not affect a requester's access, and instead are for
triggering events as a result of a requester's access attempt.
Therefore, all AUDIT and ALARM ACEs are processed until end of the
ACL. When the ACL is fully processed, if there are bits in
requester's mask that have not been considered whether the server
allows or denies the access is undefined. If there is a mode
attribute on the file, then this cannot happen, since the mode's
MODE4_*OTH bits will map to EVERYONE@ ACEs that unambiguously specify
the requester's access.
The NFS version 4 ACL model is quite rich. Some server platforms may
provide access control functionality that goes beyond the UNIX-style
mode attribute, but which is not as rich as the NFS ACL model. So
that users can take advantage of this more limited functionality, the
server may indicate that it supports ACLs as long as it follows the
guidelines for mapping between its ACL model and the NFS version 4
ACL model.
The situation is complicated by the fact that a server may have
multiple modules that enforce ACLs. For example, the enforcement for
NFS version 4 access may be different from the enforcement for local
access, and both may be different from the enforcement for access
through other protocols such as SMB. So it may be useful for a
server to accept an ACL even if not all of its modules are able to
support it.
The guiding principle in all cases is that the server must not accept
ACLs that appear to make the file more secure than it really is.
5.11.1. ACE type
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.
A server need not support all of the above ACE types. 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;
The semantics of the "type" field follow the descriptions provided
above.
The constants used for the type field (acetype4) 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;
Clients should not attempt to set an ACE unless the server claims
support for that ACE type. If the server receives a request to set
an ACE that it cannot store, it MUST reject the request with
NFS4ERR_ATTRNOTSUPP. If the server receives a request to set an ACE
that it can store but cannot enforce, the server SHOULD reject the
request with NFS4ERR_ATTRNOTSUPP.
Example: suppose a server can enforce NFS ACLs for NFS access but
cannot enforce ACLs for local access. If arbitrary processes can run
on the server, then the server SHOULD NOT indicate ACL support. On
the other hand, if only trusted administrative programs run locally,
then the server may indicate ACL support.
5.11.2. 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;
const ACE4_DELETE = 0x00010000;
const ACE4_READ_ACL = 0x00020000;
const ACE4_WRITE_ACL = 0x00040000;
const ACE4_WRITE_OWNER = 0x00080000;
const ACE4_SYNCHRONIZE = 0x00100000;
Server implementations need not provide the granularity of control
that is implied by this list of masks. For example, POSIX-based
systems might not distinguish APPEND_DATA (the ability to append to a
file) from WRITE_DATA (the ability to modify existing contents); both
masks would be tied to a single "write" permission. When such a
server returns attributes to the client, it would show both
APPEND_DATA and WRITE_DATA if and only if the write permission is
enabled.
If a server receives a SETATTR request that it cannot accurately
implement, it should error in the direction of more restricted
access. For example, suppose a server cannot distinguish overwriting
data from appending new data, as described in the previous paragraph.
If a client submits an ACE where APPEND_DATA is set but WRITE_DATA is
not (or vice versa), the server should reject the request with
NFS4ERR_ATTRNOTSUPP. Nonethele