draft-ietf-nfsv4-xattrs-03.txt   draft-ietf-nfsv4-xattrs-04.txt 
NFSv4 Working Group M. Naik NFSv4 Working Group M. Naik
Internet Draft Nutanix Internet Draft Nutanix
Intended Status: Standards Track M. Eshel Intended Status: Standards Track M. Eshel
Expires: March 11, 2017 IBM Almaden Expires: August 4, 2017 IBM Almaden
September 7, 2016 January 31, 2017
File System Extended Attributes in NFSv4 File System Extended Attributes in NFSv4
draft-ietf-nfsv4-xattrs-03 draft-ietf-nfsv4-xattrs-04
Abstract Abstract
This document proposes an OPTIONAL feature extending the NFSv4 This document describes an OPTIONAL feature extending the NFSv4
protocol which allows extended attributes (hereinafter also referred protocol which allows extended attributes (hereinafter also referred
to as xattrs) to be interrogated and manipulated using NFSv4. An to as xattrs) to be interrogated and manipulated using NFSv4 clients.
xattr is a file system feature that allows opaque metadata, not Xattrs are provided by a file system to associate opaque metadata,
interpreted by the file system, to be associated with files and not interpreted by the file system, with files and directories. Such
directories. Such support is present in many modern local file support is present in many modern local file systems. New file
systems. New file attributes are proposed to allow clients to query attributes are provided to allow clients to query the server for
the server for xattr support, and new operations to get and set xattr support, with that support consisting of new operations to get
xattrs on file system objects are provided. and set xattrs on file system objects.
Status of this Memo Status of this Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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Copyright and License Notice Copyright and License Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Current and Potential Uses of Extended Attributes . . . . . . 5 2. Uses of Extended Attributes . . . . . . . . . . . . . . . . . 5
3. File System Support . . . . . . . . . . . . . . . . . . . . . 6 3. Functional Gaps Due to Lack of NFSv4 Extended Attribute
4. Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Support . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Relationship with Named Attributes . . . . . . . . . . . . . . 7 4. File System Support for Extended Attributes . . . . . . . . . 6
6. XDR Description . . . . . . . . . . . . . . . . . . . . . . . 8 5. Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Code Components Licensing Notice . . . . . . . . . . . . . 9 6. Relationship with Named Attributes . . . . . . . . . . . . . . 7
6.2. XDR for Xattr Extension . . . . . . . . . . . . . . . . . 10 7. XDR Description . . . . . . . . . . . . . . . . . . . . . . . 8
7. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 10 7.1. Code Components Licensing Notice . . . . . . . . . . . . . 9
7.1. New definitions . . . . . . . . . . . . . . . . . . . . . 11 7.2. XDR for Xattr Extension . . . . . . . . . . . . . . . . . 10
7.2. New Attribute . . . . . . . . . . . . . . . . . . . . . . 11 8. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 11
7.2.1. xattr_support . . . . . . . . . . . . . . . . . . . . 11 8.1. New definitions . . . . . . . . . . . . . . . . . . . . . 11
7.3. New Error Definitions . . . . . . . . . . . . . . . . . . 12 8.2. New Attribute . . . . . . . . . . . . . . . . . . . . . . 11
7.3.1. NFS4ERR_NOXATTR (Error Code 10095) . . . . . . . . . . 12 8.2.1. xattr_support . . . . . . . . . . . . . . . . . . . . 12
7.3.2. NFS4ERR_XATTR2BIG (Error Code 10096) . . . . . . . . . 12 8.3. New Error Definitions . . . . . . . . . . . . . . . . . . 12
7.4. New Operations . . . . . . . . . . . . . . . . . . . . . . 12 8.3.1. NFS4ERR_NOXATTR (Error Code 10095) . . . . . . . . . . 12
7.4.1. GETXATTR - Get an extended attribute of a file . . . . 13 8.3.2. NFS4ERR_XATTR2BIG (Error Code 10096) . . . . . . . . . 12
7.4.2. SETXATTR - Set an extended attribute of a file . . . . 14 8.4. New Operations . . . . . . . . . . . . . . . . . . . . . . 12
7.4.3. LISTXATTRS - List extended attributes of a file . . . 16 8.4.1. GETXATTR - Get an extended attribute of a file . . . . 13
7.4.4. REMOVEXATTR - Remove an extended attribute of a file . 18 8.4.2. SETXATTR - Set an extended attribute of a file . . . . 14
7.4.5. Valid Errors . . . . . . . . . . . . . . . . . . . . . 19 8.4.3. LISTXATTRS - List extended attributes of a file . . . 16
7.5. Modifications to Existing Operations . . . . . . . . . . . 20 8.4.4. REMOVEXATTR - Remove an extended attribute of a file . 18
7.6. Numeric Values Assigned to Protocol Extensions . . . . . . 22 8.4.5. Valid Errors . . . . . . . . . . . . . . . . . . . . . 19
7.7. Caching . . . . . . . . . . . . . . . . . . . . . . . . . 23 8.5. Modifications to Existing Operations . . . . . . . . . . . 20
7.8. Xattrs and File Locking . . . . . . . . . . . . . . . . . 25 8.6. Numeric Values Assigned to Protocol Extensions . . . . . . 21
7.9. pNFS Considerations . . . . . . . . . . . . . . . . . . . 25 8.7. Caching . . . . . . . . . . . . . . . . . . . . . . . . . 22
8. Security Considerations . . . . . . . . . . . . . . . . . . . 25 8.8. Xattrs and File Locking . . . . . . . . . . . . . . . . . 24
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 8.9. pNFS Considerations . . . . . . . . . . . . . . . . . . . 24
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 9. Security Considerations . . . . . . . . . . . . . . . . . . . 24
10.1. Normative References . . . . . . . . . . . . . . . . . . 26 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
10.2. Informative References . . . . . . . . . . . . . . . . . 26 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.1. Normative References . . . . . . . . . . . . . . . . . . 26
11.2. Informative References . . . . . . . . . . . . . . . . . 27
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 27 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
1. Introduction 1. Introduction
Extended attributes, also called xattrs, are a means to associate Extended attributes, also called xattrs, are a means to associate
opaque metadata with file system objects, organized as key/value opaque metadata with file system objects, organized as key/value
pairs. They are especially useful when they add information that is pairs. They are especially useful when they add information that is
not, or cannot be, present in the associated object itself. User- not, or cannot be, present in the associated object itself. User-
space applications can arbitrarily create, interrogate, and modify space applications can arbitrarily create, interrogate, and modify
the key/value pairs. the key/value pairs.
Extended attributes are file system-agnostic; applications use an Extended attributes are file system-agnostic; applications use an
interface not specific to any file system to manipulate them. interface not specific to any file system to manipulate them.
Applications do not need to be concerned about how the key/value Applications are not concerned about how the key/value pairs are
pairs are stored internally within the underlying file system. All stored internally within the underlying file system. All major
major operating systems provide various flavors of extended operating systems provide facilities to access and modify extended
attributes. Many user space tools allow xattrs to be included in attributes. Many user space tools allow xattrs to be included
regular attributes that need to be preserved when objects are together with regular attributes that need to be preserved when
updated, moved or copied. objects are updated, moved or copied.
Extended attributes have previously been considered unsuitable for Extended attributes have not previously been included within the
inclusion in NFSv4 because some aspects of their handling are not NFSv4 specification. One issue that needs to be addressed as part of
precisely defined and they are not formally documented by any including them is that, as with named attributes, some aspects of
standard (such as POSIX). Nevertheless, it appears that xattrs are their handling are not precisely defined and they are not formally
widely deployed and their support in modern disk-based file systems documented by any standard (such as POSIX). Nevertheless, it appears
is nearly universal. that xattrs are widely deployed and their support in modern disk-
based file systems is nearly universal.
There is no clear specification of how xattrs could be mapped to any There is no current specification of how xattrs could be mapped to
existing file attributes defined in the NFSv4 protocol ([RFC7530], any existing file attributes defined in the NFSv4 protocol
[RFC5661], [NFSv42]). As a result, most NFSv4 client implementations ([RFC7530], [RFC5661], [RFC7862]). As a result, most NFSv4 client
ignore application-specified xattrs. This state of affairs results implementations ignore application-specified xattrs. This state of
in data loss if one copies, over the NFSv4 protocol, a file with affairs results in data loss if one copies, over the NFSv4 protocol,
xattrs from one file system to another that also supports xattrs. a file with xattrs from one file system to another that also supports
xattrs.
There is thus a need to provide a means by which such data loss can There is thus a need to provide a means by which such data loss can
be avoided. This will involve exposing xattrs within the NFSv4 be avoided. This will involve exposing xattrs within the NFSv4
protocol, despite the lack of completely compatible file system protocol, despite the lack of completely compatible file system
implementations. implementations.
This document discusses (in Section 5) the reasons that NFSv4 named This document discusses (in Section 5) the reasons that NFSv4 named
attributes as currently standardized in [RFC7530], are unsuitable for attributes, as currently standardized in [RFC5661], are unsuitable
representing xattrs. Instead, it proposes a separate protocol for representing xattrs. Instead, it describes a separate protocol
mechanism to support xattrs. As a consequence, xattrs and named mechanism to support xattrs. As a consequence, xattrs and named
attributes will both be optional features with servers free to attributes will both be optional features with servers free to
support either, both, or neither. support either, both, or neither.
1.1. Terminology 1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
In this document, these words will appear with that interpretation In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance. interpreted as carrying RFC-2119 significance.
2. Current and Potential Uses of Extended Attributes 2. Uses of Extended Attributes
Applications can store tracking information in extended attributes. Applications can store tracking information in extended attributes.
Examples include storing metadata identifying the application that Examples include storing metadata identifying the application that
created the file, a tag to indicate when the file was last verified created the file, a tag to indicate when the file was last verified
by a data integrity scrubber, or a tag to hold a checksum/crypto hash by a data integrity scrubber, or a tag to hold a checksum/crypto hash
of the file contents along with the date of that signature. Xattrs of the file contents along with the date of that signature. Xattrs
can also be used for decorations or annotations. For example, a file can also be used for decorations or annotations. For example, a file
downloaded from a web server can be tagged with the URL, which can be downloaded from a web server can be tagged with the URL, which can be
convenient if its source has to be determined in the future. convenient if its source has to be determined in the future.
Likewise, an email attachment, when saved, can be tagged with the Likewise, an email attachment, when saved, can be tagged with the
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type by inspecting it (Unix MIME type). Some file managers generate type by inspecting it (Unix MIME type). Some file managers generate
this information on the fly; others generate the information once and this information on the fly; others generate the information once and
then cache it. Those that cache the information tend to put it in a then cache it. Those that cache the information tend to put it in a
custom database. The file manager must work to keep this database in custom database. The file manager must work to keep this database in
sync with the files, which can change without the file manager's sync with the files, which can change without the file manager's
knowledge. A better approach is to dispense with the custom database knowledge. A better approach is to dispense with the custom database
and store such metadata in extended attributes. This is easier to and store such metadata in extended attributes. This is easier to
maintain, provides faster access, and is readily accessible by maintain, provides faster access, and is readily accessible by
applications [Love]. applications [Love].
3. Functional Gaps Due to Lack of NFSv4 Extended Attribute Support
In addition to the prospect of data loss discussed above (in Section
1), arising from use of xattrs on local file systems, application use
of xattrs poses further difficulties given the current lack of xattr
support within NFSv4. As a result, certain applications may not be
supported by NFSv4 or may be supported in an unsatisfactory way.
Some examples are discussed below.
Swift, the OpenStack distributed object store, uses xattrs to store Swift, the OpenStack distributed object store, uses xattrs to store
an object's metadata along with all the data together in one file. an object's metadata along with all the data together in one file.
Swift-on-File [Swift] transfers the responsibility of maintaining Swift-on-File [Swift] transfers the responsibility of maintaining
object durability and availability to the underlying file system. object durability and availability to the underlying file system.
Today, this requires a native file system client to mount the Today, this requires a native file system client to mount the
volumes. Xattr support in NFSv4 would open up the possibility of volumes. Xattr support in NFSv4 would open up the possibility of
storing and consuming data from other storage systems, and facilitate storing and consuming data from other storage systems, and facilitate
the migration of data between different backend storage systems. the migration of data between different backend storage systems.
Baloo, the file indexing and search framework for KDE, has moved to Baloo, the file indexing and search framework for KDE, has moved to
storing metadata such as tags, ratings and comments, in file system storing metadata such as tags, ratings and comments, in file system
xattrs instead of a custom database for simplicity. Starting with xattrs instead of a custom database for simplicity. Starting with
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volumes. Xattr support in NFSv4 would open up the possibility of volumes. Xattr support in NFSv4 would open up the possibility of
storing and consuming data from other storage systems, and facilitate storing and consuming data from other storage systems, and facilitate
the migration of data between different backend storage systems. the migration of data between different backend storage systems.
Baloo, the file indexing and search framework for KDE, has moved to Baloo, the file indexing and search framework for KDE, has moved to
storing metadata such as tags, ratings and comments, in file system storing metadata such as tags, ratings and comments, in file system
xattrs instead of a custom database for simplicity. Starting with xattrs instead of a custom database for simplicity. Starting with
KDE Plasma 5.1, NFS is no longer supported due to its lack of xattr KDE Plasma 5.1, NFS is no longer supported due to its lack of xattr
support [KDE]. support [KDE].
3. File System Support 4. File System Support for Extended Attributes
Extended attributes are supported by most modern file systems. Extended attributes are supported by most modern file systems.
In Linux, ext3, ext4, JFS, XFS, Btrfs, among other file systems, In Linux, ext3, ext4, JFS, XFS, Btrfs, among other file systems,
support extended attributes. The getfattr and setfattr utilities can support extended attributes. The getfattr and setfattr utilities can
be used to retrieve and set xattrs. The names of the extended be used to retrieve and set xattrs. The names of the extended
attributes must be prefixed by the name of the category and a dot; attributes must be prefixed by the name of the category and a dot;
hence these categories are generally qualified as name spaces. hence these categories are generally qualified as name spaces.
Currently, four namespaces exist: user, trusted, security and system Currently, four namespaces exist: user, trusted, security and system
[Linux]. Recommendations on how they should be used have been [Linux]. Recommendations on how they should be used have been
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the NTFS file system, extended attributes may be stored within "file the NTFS file system, extended attributes may be stored within "file
streams" [NTFS]. streams" [NTFS].
Xattrs can be retrieved and set through system calls or shell Xattrs can be retrieved and set through system calls or shell
commands and are generally supported by user-space tools that commands and are generally supported by user-space tools that
preserve other file attributes. For example, the "rsync" remote copy preserve other file attributes. For example, the "rsync" remote copy
program will correctly preserve user extended attributes between program will correctly preserve user extended attributes between
Linux/ext4 and OSX/hfs by stripping off the Linux-specific "user." Linux/ext4 and OSX/hfs by stripping off the Linux-specific "user."
prefix. prefix.
4. Namespaces 5. Namespaces
Operating systems may define multiple "namespaces" in which xattrs Operating systems may define multiple "namespaces" in which xattrs
can be set. Namespaces are more than organizational classes; the can be set. Namespaces are more than organizational classes; the
operating system may enforce different access policies and allow operating system may enforce different access policies and allow
different capabilities depending on the namespace. Linux, for different capabilities depending on the namespace. Linux, for
example, defines "security", "system", "trusted" and "user" example, defines "security", "system", "trusted" and "user"
namespaces, the first three being specific to Linux [freedesktop]. namespaces, the first three being specific to Linux [freedesktop].
Implementations generally agree on the semantics of a "user" Implementations generally agree on the semantics of a "user"
namespace, that allows applications to store arbitrary user attribute namespace, that allows applications to store arbitrary user attribute
data with file system objects. Access to this namespace is data with file system objects. Access to this namespace is
controlled via the normal file system attributes. As such, getting controlled via the normal file system attributes. As such, getting
and setting xattrs from the user namespace can be considered and setting xattrs from the user namespace can be considered
interoperable across platforms and vendor implementations. interoperable across platforms and vendor implementations.
Attributes from other namespaces are typically platform-specific. Attributes from other namespaces are typically platform-specific.
This document provides for namespaces supporting user-managed This document provides support for namespaces related to user-managed
metadata only, thus avoiding the need to specify the semantics metadata only, thus avoiding the need to specify the semantics
applicable to particular system-interpreted xattrs. The values of applicable to particular system-interpreted xattrs. The values of
xattrs are considered application data just as the contents of named xattrs are considered application data just as the contents of named
attributes, files, and symbolic links are. Servers have a attributes, files, and symbolic links are. Servers have a
responsibility to store whatever value the client specifies and to responsibility to store whatever value the client specifies and to
return it on demand. xattr keys and values MUST NOT be interpreted by return it on demand. Xattr keys and values MUST NOT be interpreted by
the NFS clients and servers, as such behavior would lead to non- the NFS clients and servers, as such behavior would lead to non-
interoperable implementations. If there is a need to specify interoperable implementations. If there were to be a need to specify
attributes that servers need to be act upon, the appropriate one or more attributes that servers need to act upon, the appropriate
semantics need to be specified by adding a new attribute for the semantics would be specified by adding a new attribute for the
purpose as provided by [RFC7530] and [NFSv4-vers]. purpose as provided for by [RFC5661] and [NFSv4-vers].
5. Relationship with Named Attributes 6. Relationship with Named Attributes
[RFC7530] defines named attributes as opaque byte streams that are [RFC7530] defines named attributes as opaque byte streams that are
associated with a directory or file and referred to by a string name. associated with a directory or file and referred to by a string name.
Named attributes are intended to be used by client applications as a Named attributes are intended to be used by client applications as a
method to associate application-specific data with a regular file or method to associate application-specific data with a regular file or
directory. In that sense, xattrs are similar in concept and use to directory. Although this makes xattrs similar in concept and use to
named attributes, but there are subtle differences. named attributes, there are important semantic differences.
File systems typically define operations to get and set individual File systems typically define operations to get and set individual
xatrrs as being atomic, although collectively they may be xatrrs as being atomic, although collectively they may be
independent. Xattrs generally have size limits ranging from a few independent. Xattrs generally have size limits ranging from a few
bytes to several kilobytes; the maximum supported size is not bytes to several kilobytes; the maximum supported size is not
universally defined and is usually restricted by the file system. universally defined and is usually restricted by the file system.
Similar to ACLs, the amount of xattr data exchanged between the Similar to ACLs, the amount of xattr data exchanged between the
client and server for get/set operations can be considered to fit in client and server for get/set operations can be considered to fit in
a single COMPOUND request, bounded by the channel's negotiated a single COMPOUND request, bounded by the channel's negotiated
maximum size for requests. Named attributes, on the other hand, are maximum size for requests. Named attributes, on the other hand, are
unbounded data streams and do not impose atomicity requirements. unbounded data streams and do not impose atomicity requirements.
Individual named attributes are analogous to files, and caching of Individual named attributes are analogous to files, and are opened
the data for these needs to be handled just as data caching is for and closed just as files are. Caching of the data for these needs to
ordinary files following close-to-open semantics. Xattrs, on the be handled just as data caching is for ordinary files following
other hand, impose caching requirements like other file attributes. close-to-open semantics. Xattrs, on the other hand, have caching
requirements similar to other file attributes.
Named attributes and xattrs have different semantics and belong to Named attributes and xattrs have different semantics and are treated
disjoint namespaces. As a result, mapping one to another is, at by applications as belonging to disjoint namespaces. As a result,
best, a compromise. Despite these differences, the underlying file mapping from one to the other would be, at best, a compromise.
system structure used to store named attributes is generally capable Despite these differences, the underlying file system structure used
of storing xattrs. However, the converse is typically not the case to store named attributes is generally capable of storing xattrs.
because of the size limits applicable to xattrs. However, the converse is typically not the case because of the size
limits applicable to xattrs.
While it should be possible to write guidance about how a client can While it might be possible to write guidance about how a client can
use the named attribute mechanism to act like xattrs, such as carving use the named attribute mechanism to act like xattrs, such as by
out some namespace and specifying locking primitives to enforce carving out some namespace and specifying locking primitives to
atomicity constraints on individual get/set operations, this is enforce atomicity constraints on individual get/set operations, such
problematic. A client application trying to use xattrs through named an approach is sufficiently problematic that it will not be attempted
here. A client application trying to use xattrs through named
attributes with a server that supported xattrs directly would get a attributes with a server that supported xattrs directly would get a
lower level of service, and could fail to cooperate on a local lower level of service, and could fail to cooperate on a local
application running on the server unless the server file system application running on the server unless the server file system
defined its own interoperability constraints. File systems that defined its own interoperability constraints. File systems that
already implement xattrs and named attributes natively would need already implement xattrs and named attributes natively would need
additional guidance such as reserving named attribute namespace additional guidance such as reserving named attribute namespace
specifically for implementation purposes. specifically for implementation purposes.
6. XDR Description 7. XDR Description
This document contains the external data representation (XDR) This document contains the external data representation (XDR)
[RFC4506] description of the extended attributes. The XDR [RFC4506] description of the extended attributes. The XDR
description is embedded in this document in a way that makes it description is embedded in this document in a way that makes it
simple for the reader to extract into a ready-to-compile form. The simple for the reader to extract into a ready-to-compile form. The
reader can feed this document into the following shell script to reader can feed this document into the following shell script to
produce the machine readable XDR description of extended attributes: produce the machine readable XDR description of extended attributes:
<CODE BEGINS> <CODE BEGINS>
skipping to change at page 8, line 39 skipping to change at page 9, line 4
#! /bin/sh #! /bin/sh
grep '^ *///' $* | sed 's?^ */// ??' | sed 's?^ *///$??' grep '^ *///' $* | sed 's?^ */// ??' | sed 's?^ *///$??'
<CODE ENDS> <CODE ENDS>
That is, if the above script is stored in a file called "extract.sh", That is, if the above script is stored in a file called "extract.sh",
and this document is in a file called "spec.txt", then the reader can and this document is in a file called "spec.txt", then the reader can
do: do:
sh extract.sh < spec.txt > xattr_prot.x sh extract.sh < spec.txt > xattr_prot.x
The effect of the script is to remove leading white space from each The effect of the script is to remove leading white space from each
line, plus a sentinel sequence of "///". line, plus a sentinel sequence of "///".
The initial section of the embedded XDR file header follows. The initial section of the embedded XDR file header follows.
Subsequent XDR descriptions, with the sentinel sequence are embedded Subsequent XDR descriptions, with the sentinel sequence are embedded
throughout the document. throughout the document.
Note that the XDR code contained in this document depends on types Note that the XDR code contained in this document depends on types
from the proposed NFSv4.2 nfs4_prot.x file [NFSv42-dot-x]. This from the proposed NFSv4.2 nfs4_prot.x file [RFC7863]. This includes
includes both nfs types that end with a 4, such as nfs_cookie4, both nfs types that end with a 4, such as nfs_cookie4, count4, etc.,
count4, etc., as well as more generic types such as opaque and bool. as well as more generic types such as opaque and bool.
To produce a compilable XDR file, following procedure is suggested: To produce a compilable XDR file, following procedure is suggested:
o Extract the file nfs4_prot.x as described in [RFC7863].
o Extract the file nfs4_prot.x as described in [NFSv42-dot-x].
o Extract xattr_prot.x from this document as described above. o Extract xattr_prot.x from this document as described above.
o Apply any changes required for other extensions to be included o Apply any changes required for other extensions to be included
together with the xattr extension. together with the xattr extension.
o Perform modifications to nfs4_prot.x as described by comments o Perform modifications to nfs4_prot.x as described by comments
within xattr_prot.x. within xattr_prot.x.
o Extend the unions nfs_argop4 and nfs_resop4 to include cases for o Extend the unions nfs_argop4 and nfs_resop4 to include cases for
the new operations defined in this document. the new operations defined in this document.
o Combine the XDR files for the base v4.2 protocol, and all needed o Combine the XDR files for the base v4.2 protocol, and all needed
extensions by either concatenating the relevant XDR files, or extensions by either concatenating the relevant XDR files, or
using file inclusion. using file inclusion.
6.1. Code Components Licensing Notice 7.1. Code Components Licensing Notice
Both the XDR description and the scripts used for extracting the Both the XDR description and the scripts used for extracting the
XDR description are Code Components as described in Section 4 of XDR description are Code Components as described in Section 4 of
"Legal Provisions Relating to IETF Documents" [LEGAL]. These Code "Legal Provisions Relating to IETF Documents" [LEGAL]. These Code
Components are licensed according to the terms of that document. Components are licensed according to the terms of that document.
<CODE BEGINS> <CODE BEGINS>
/// /* /// /*
/// * Copyright (c) 2012 IETF Trust and the persons identified /// * Copyright (c) 2012 IETF Trust and the persons identified
skipping to change at page 10, line 26 skipping to change at page 10, line 39
/// * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING /// * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
/// * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF /// * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
/// * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. /// * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
/// * /// *
/// * This code was derived from RFCTBD10. /// * This code was derived from RFCTBD10.
/// * Please reproduce this note if possible. /// * Please reproduce this note if possible.
/// */ /// */
<CODE ENDS> <CODE ENDS>
6.2. XDR for Xattr Extension 7.2. XDR for Xattr Extension
<CODE BEGINS> <CODE BEGINS>
/// /* /// /*
/// * xattr_prot.x /// * xattr_prot.x
/// */ /// */
/// /* /// /*
/// * The following include statements are for example only. /// * The following include statements are for example only.
/// * The actual XDR definition files are generated separately /// * The actual XDR definition files are generated separately
/// * and independently and are likely to have a different name. /// * and independently and are likely to have a different name.
/// * %#include <rpc_prot.x> /// * %#include <rpc_prot.x>
/// * %#include <nfsv42.x> /// * %#include <nfsv42.x>
/// */ /// */
<CODE ENDS> <CODE ENDS>
7. Protocol Extensions 8. Protocol Extensions
This section documents extensions to the NFSv4 protocol operations This section documents extensions to the NFSv4 protocol operations
to allow xattrs to be queried and modified by clients. A new to allow xattrs to be queried and modified by clients. A new
attribute is added to allow clients to determine if the file attribute is added to allow clients to determine if the file
system being accessed provides support for xattrs. New operations system being accessed provides support for xattrs. New operations
are defined to allow xattr keys and values to be queried and set. are defined to allow xattr keys and values to be queried and set.
In addition, extension are made to existing operations and In addition, the ACCESS operation is extended by adding new mask
attributes as follows: bits to provide access information relating to xattrs.
o The ACCESS operation is extended by adding new mask bits to
provide access information relating to xattrs.
o The acl attribute is extended by adding new bits to the ACE access
mask field to separately control permissions to query and modify
xattrs.
These changes follow applicable guidelines for valid NFSv4 These changes follow applicable guidelines for valid NFSv4 XDR
protocol extension, whether the extensions occur in a minor protocol extension, as specified in [NFSv4-vers], and obey the
version (as specified in [RFC5661]) or as an extension to an rules for extensions capable of being made without a change in
existing minor version (as specified in [NFSv4-vers]). minor version number.
7.1. New definitions 8.1. New definitions
<CODE BEGINS> <CODE BEGINS>
/// typedef component4 xattrkey4; /// typedef component4 xattrkey4;
/// typedef opaque xattrvalue4<>; /// typedef opaque xattrvalue4<>;
<CODE ENDS> <CODE ENDS>
Each xattr is a key/value pair. xattrkey4 is a string denoting the Each xattr is a key/value pair. xattrkey4 is a string denoting the
xattr key name, and an attrvalue4 which is a variable-length string xattr key name, and an attrvalue4 which is a variable-length string
that identifies the value of the xattr. The handling of xattrkey4 that identifies the value of the xattr. The handling of xattrkey4
with regard to internationalization-related issues is the same as with regard to internationalization-related issues is the same as
that for NFSv4 file names and named attribute names, as described in that for NFSv4 file names and named attribute names, as described in
[RFC7530]. Any regular file or directory may have a set of extended [RFC7530]. Any regular file or directory may have a set of extended
attributes, each consisting of a key and associated value. The NFS attributes, each consisting of a key and associated value. The NFS
client or server MUST NOT interpret the contents of xattrkey4 or client or server MUST NOT interpret the contents of xattrkey4 or
xattrvalue4. xattrvalue4.
7.2. New Attribute 8.2. New Attribute
The per-fs read-only attribute described in Section 7.2.1 may be used The per-fs read-only attribute described below may be used to
to determine if xattrs are supported. Servers need not support this determine if xattrs are supported. Servers need not support this
attribute and some NFSv4.2 servers may be unaware of its existence. attribute and some NFSv4.2 servers may be unaware of its existence.
Before interrogating this attribute using GETATTR, a client should Before interrogating this attribute using GETATTR, a client should
determine whether it is a supported attribute by interrogating the determine whether it is a supported attribute by interrogating the
supported_attrs attribute. supported_attrs attribute.
7.2.1. xattr_support 8.2.1. xattr_support
True, if the object's file system supports extended attributes. True, if the object's file system supports extended attributes.
Since xattr_support is not a REQUIRED attribute, server need not Since xattr_support is not a REQUIRED attribute, server need not
support it. However, a client may reasonably assume that a server support it. However, a client may reasonably assume that a server
(or file system) that does not support the xattr_support attribute (or file system) that does not support the xattr_support attribute
does not provide xattr support and act on that basis. does not provide xattr support and act on that basis.
Note that the protocol does not enforce any limits on the number of Note that the protocol does not enforce any limits on the number of
keys, the length of a key or the size of a value, or the total size keys, the length of a key or the size of a value, or the total size
of xattrs that are allowed for a file. The server file system MAY of xattrs that are allowed for a file. The server file system MAY
impose additional limits. In addition, a single xattr key or value impose additional limits. In addition, a single xattr key or value
exchanged between the client and server for get/set operations is exchanged between the client and server for get/set operations is
limited by the channel's negotiated maximum size for requests and limited by the channel's negotiated maximum size for requests and
responses. responses.
7.3. New Error Definitions 8.3. New Error Definitions
<CODE BEGINS> <CODE BEGINS>
/// /* Following lines are to be added to enum nfsstat4 */ /// /* Following lines are to be added to enum nfsstat4 */
/// /* /// /*
/// NFS4ERR_NOXATTR = 10095 /* xattr does not exist */ /// NFS4ERR_NOXATTR = 10095 /* xattr does not exist */
/// NFS4ERR_XATTR2BIG = 10096 /* xattr value is too big */ /// NFS4ERR_XATTR2BIG = 10096 /* xattr value is too big */
/// */ /// */
<CODE ENDS> <CODE ENDS>
7.3.1. NFS4ERR_NOXATTR (Error Code 10095) 8.3.1. NFS4ERR_NOXATTR (Error Code 10095)
The specified xattr does not exist or the server is unable to The specified xattr does not exist or the server is unable to
retrieve it. retrieve it.
7.3.2. NFS4ERR_XATTR2BIG (Error Code 10096) 8.3.2. NFS4ERR_XATTR2BIG (Error Code 10096)
The size of the xattr value as part of a SETXATTR operation is bigger
than that supported by the underlying file system.
7.4. New Operations
Individual xattrs generally represent separate items of metadata. The size of the xattr value specified as part of a SETXATTR
For various reasons, combining them into a single attribute results operation, or the collective size of all xattrs of the file resulting
in clumsy implementations with significant functional deficits. In from the SETXATTR operation, is bigger than that supported by the
consequence, adding a new attribute to represent the set of xattrs underlying file system.
for an object is not an appropriate way to provide support for
xattrs.
For example, obtaining the value of a single xattr using the bitmap 8.4. New Operations
would require a client implementation to read all the xattrs of the
file and find a match for the one requested. Similarly, replacing or
deleting a single xattr while keeping the others intact would require
a client to read the xattrs first, replacing the existing list with a
modified list that excludes the one to be deleted, and writing out
the remaining xattrs. Such a read-modify-write cycle is subject to
updates being lost in the case of simultaneous updates by multiple
clients. In addition, two clients might simultaneously add the same
xattr key to the same file with each concluding that it did the
initial creation for the common xattr key, when the semantic model
implies that only one could have done so.
Applications need to perform the following operations on a given Applications need to perform the following operations on a given
file's extended attributes [Love]: file's extended attributes [Love]:
o Given a file, return a list of all of the file's assigned extended o Given a file, return a list of all of the file's assigned extended
attribute keys. attribute keys.
o Given a file and a key, return the corresponding value. o Given a file and a key, return the corresponding value.
o Given a file, a key, and a value, assign that value to the key. o Given a file, a key, and a value, assign that value to the key.
o Given a file and a key, remove that extended attribute from the o Given a file and a key, remove that extended attribute from the
file. file.
This section introduces four new OPTIONAL operations, GETXATTR, In order to meet these requirements, this section introduces four new
SETXATTR, LISTXATTRS and REMOVEXATTR, to query, set, list and remove OPTIONAL operations, GETXATTR, SETXATTR, LISTXATTRS and REMOVEXATTR,
xattrs respectively. A server MUST support all four operations when to query, set, list and remove xattrs respectively. A server MUST
they are directed to a file system which supports the xattr_support support all four operations when they are directed to a file system
attribute and returns TRUE when it is interrogated. For file systems which supports the xattr_support attribute and returns TRUE when it
which either do not support the xattr_support attribute or which is interrogated. For file systems which either do not support the
returns FALSE when it is interrogated, all of these operations MUST xattr_support attribute or which returns FALSE when it is
NOT be supported. GETXATTR allows obtaining the value of an xattr interrogated, all of these operations MUST NOT be supported. GETXATTR
key, SETXATTR allows creating or replacing an xattr key with a value, allows obtaining the value of an xattr key, SETXATTR allows creating
LISTXATTRS enumerates all the xattrs names, and REMOVEXATTR allows or replacing an xattr key with a value, LISTXATTRS enumerates all the
deleting a single xattr. xattrs names, and REMOVEXATTR allows deleting a single xattr.
7.4.1. GETXATTR - Get an extended attribute of a file Note that some server implementations may not be aware of the
existence of these operations, thereby a client cannot always expect
that issuing one of them will either succeed or return
NFS4ERR_NOTSUPP. In some cases NFS4ERR_OP_ILLEGAL may be returned or
the request may encounter an XDR decode error on the server. As a
result, clients should only issue these operations after determining
that support is present.
7.4.1.1. ARGUMENTS 8.4.1. GETXATTR - Get an extended attribute of a file
8.4.1.1. ARGUMENTS
<CODE BEGINS> <CODE BEGINS>
/// struct GETXATTR4args { /// struct GETXATTR4args {
/// /* CURRENT_FH: file */ /// /* CURRENT_FH: file */
/// xattrkey4 gxa_name; /// xattrkey4 gxa_name;
/// }; /// };
<CODE ENDS> <CODE ENDS>
7.4.1.2. RESULTS 8.4.1.2. RESULTS
<CODE BEGINS> <CODE BEGINS>
/// union GETXATTR4res switch (nfsstat4 gxr_status) { /// union GETXATTR4res switch (nfsstat4 gxr_status) {
/// case NFS4_OK: /// case NFS4_OK:
/// xattrvalue4 gxr_value; /// xattrvalue4 gxr_value;
/// default: /// default:
/// void; /// void;
/// }; /// };
<CODE ENDS> <CODE ENDS>
7.4.1.3. DESCRIPTION 8.4.1.3. DESCRIPTION
The GETXATTR operation will obtain the value for the given extended The GETXATTR operation will obtain the value for the given extended
attribute key for the file system object specified by the current attribute key for the file system object specified by the current
filehandle. filehandle.
The server will fetch the xattr value for the key that the client The server will fetch the xattr value for the key that the client
requests if xattrs are supported by the server for the target file requests if xattrs are supported by the server for the target file
system. If the server does not support xattrs on the target file system. If the server does not support xattrs on the target file
system, then it MUST NOT return a value and MUST return the system, then it MUST NOT return a value and MUST return the
NFS4ERR_NOTSUPP error. The server also MUST return NFS4ERR_NOXATTR NFS4ERR_NOTSUPP error or another error indicating the request was not
if it supports xattrs on the target but cannot obtain the requested understood. The server also MUST return NFS4ERR_NOXATTR if it
data. If the xattr value contained in the server response is such as supports xattrs on the target but cannot obtain the requested data.
to cause the channel's negotiated maximum response size to be If the xattr value contained in the server response is such as to
exceeded, then the server MUST return NFS4ERR_REP_TOO_BIG in cause the channel's negotiated maximum response size to be exceeded,
gxr_status. then the server MUST return NFS4ERR_REP_TOO_BIG in gxr_status.
7.4.1.4. IMPLEMENTATION 8.4.1.4. IMPLEMENTATION
Clients that have cached an xattr may avoid the need to do a GETXATTR Clients that have cached an xattr may avoid the need to do a GETXATTR
by determining if the change attribute is the same as it was when the by determining if the change attribute is the same as it was when the
xattr was fetched. If the client does not hold a delegation for the xattr was fetched. If the client does not hold a delegation for the
file in question, it can do so with a GETATTR request to obtain the file in question, it can do so with a GETATTR request to obtain the
change attribute and comparing its value to the change attribute change attribute and comparing its value to the change attribute
value fetched when the xattr value was obtained. This handling is value fetched when the xattr value was obtained. This handling is
similar to how a client would revalidate other file attributes such similar to how a client would revalidate other file attributes such
as ACLs. as ACLs.
When responding to such a GETATTR, the server will, if there is an When responding to such a GETATTR, the server will, if there is an
OPEN_DELEGATE_WRITE delegation held by another client for the file in OPEN_DELEGATE_WRITE delegation held by another client for the file in
question, either obtain the actual current value of these attributes question, either obtain the actual current value of these attributes
from the client holding the delegation by using the CB_GETATTR from the client holding the delegation by using the CB_GETATTR
callback, or revoke the delegation. See Section 18.7.4 of [RFC5661] callback, or revoke the delegation. See Section 18.7.4 of [RFC5661]
for details. for details.
7.4.2. SETXATTR - Set an extended attribute of a file 8.4.2. SETXATTR - Set an extended attribute of a file
7.4.2.1. ARGUMENTS 8.4.2.1. ARGUMENTS
<CODE BEGINS> <CODE BEGINS>
/// enum setxattr_option4 { /// enum setxattr_option4 {
/// SETXATTR4_NONE = 0, /// SETXATTR4_EITHER = 0,
/// SETXATTR4_CREATE = 1, /// SETXATTR4_CREATE = 1,
/// SETXATTR4_REPLACE = 2, /// SETXATTR4_REPLACE = 2,
/// }; /// };
/// struct SETXATTR4args { /// struct SETXATTR4args {
/// /* CURRENT_FH: file */ /// /* CURRENT_FH: file */
/// setxattr_option4 sxa_option; /// setxattr_option4 sxa_option;
/// xattrkey4 sxa_key; /// xattrkey4 sxa_key;
/// xattrvalue4 sxa_value; /// xattrvalue4 sxa_value;
/// }; /// };
<CODE ENDS> <CODE ENDS>
7.4.2.2. RESULTS 8.4.2.2. RESULTS
<CODE BEGINS> <CODE BEGINS>
/// struct SETXATTR4res switch (nfsstat4 sxr_status) { /// struct SETXATTR4res switch (nfsstat4 sxr_status) {
/// case NFS4_OK: /// case NFS4_OK:
/// change_info4 sxr_info; /// change_info4 sxr_info;
/// default: /// default:
/// void; /// void;
/// }; /// };
<CODE ENDS> <CODE ENDS>
7.4.2.3. DESCRIPTION 8.4.2.3. DESCRIPTION
The SETXATTR operation changes one extended attribute of a file The SETXATTR operation changes one extended attribute of a file
system object. The change desired is specified by sxa_option. system object. The change desired is specified by sxa_option.
SETXATTR4_CREATE is used to associate the given value with the given SETXATTR4_CREATE is used to associate the given value with the given
extended attribute key for the file system object specified by the extended attribute key for the file system object specified by the
current filehandle. The server MUST return NFS4ERR_EXIST if the current filehandle. The server MUST return NFS4ERR_EXIST if the
attribute key already exists. SETXATTR4_REPLACE is also used to set attribute key already exists. SETXATTR4_REPLACE is also used to set
an xattr, but the server MUST return NFS4ERR_NOXATTR if the attribute an xattr, but the server MUST return NFS4ERR_NOXATTR if the attribute
key does not exist. By default (SETXATTR4_NONE), the extended key does not exist. By default (SETXATTR4_EITHER), the extended
attribute will be created if need be, or its value will be replaced attribute will be created if need be, or its value will be replaced
if the attribute exists. if the attribute exists.
If the xattr key and value contained in the client request are such If the xattr key and value contained in the client request are such
that the request would exceed the channel's negotiated maximum that the request would exceed the channel's negotiated maximum
request size, then the server MUST return NFS4ERR_REQ_TOO_BIG in request size, then the server MUST return NFS4ERR_REQ_TOO_BIG in
sxr_status. If the server file system imposes additional limits on sxr_status. If the server file system imposes additional limits on
the size of key name or value, it MAY return NFS4ERR_XATTR2BIG. the size of key name or value, it MAY return NFS4ERR_XATTR2BIG.
A successful SETXATTR MUST change the file time_metadata and change A successful SETXATTR MUST change the file time_metadata and change
attributes if the xattr is created or the value assigned to xattr attributes if the xattr is created or the value assigned to xattr
changes. However, these attributes SHOULD NOT be changed if this changes. However, it is not NECESSARY to change these attributes if
causes no actual change in the xattr value. there has been no actual change in the xattr value. Avoiding
attribute change in such situation is desirable as it avoids
unnecessary cache invalidation.
On success, the server returns the change_info4 information in On success, the server returns the change_info4 information in
sxr_info. With the atomic field of the change_info4 data type, the sxr_info. With the atomic field of the change_info4 data type, the
server will indicate if the before and after change attributes were server will indicate if the before and after change attributes were
obtained atomically with respect to the SETXATTR operation. This obtained atomically with respect to the SETXATTR operation. This
allows the client to determine if its cached xattrs are still valid allows the client to determine if its cached xattrs are still valid
after the operation. See Section 7.6 for a discussion on xattr after the operation. See Section 8.7 for a discussion on xattr
caching. caching.
7.4.2.4. IMPLEMENTATION 8.4.2.4. IMPLEMENTATION
If the object whose xattr is being changed has a file delegation that If the object whose xattr is being changed has a file delegation that
is held by a client other than the one doing the SETXATTR, the is held by a client other than the one doing the SETXATTR, the
delegation(s) must be recalled, and the operation cannot proceed to delegation(s) must be recalled, and the operation cannot proceed to
actually change the xattr until each such delegation is returned or actually change the xattr until each such delegation is returned or
revoked. In all cases in which delegations are recalled, the server revoked. In all cases in which delegations are recalled, the server
is likely to return one or more NFS4ERR_DELAY errors while the is likely to return one or more NFS4ERR_DELAY errors while the
delegation(s) remains outstanding, although it might not do that if delegation(s) remains outstanding, although it might not do that if
the delegations are returned quickly. the delegations are returned quickly.
7.4.3. LISTXATTRS - List extended attributes of a file 8.4.3. LISTXATTRS - List extended attributes of a file
7.4.3.1. ARGUMENTS 8.4.3.1. ARGUMENTS
<CODE BEGINS> <CODE BEGINS>
/// struct LISTXATTRS4args { /// struct LISTXATTRS4args {
/// /* CURRENT_FH: file */ /// /* CURRENT_FH: file */
/// nfs_cookie4 lxa_cookie; /// nfs_cookie4 lxa_cookie;
/// count4 lxa_maxcount; /// count4 lxa_maxcount;
/// }; /// };
<CODE ENDS> <CODE ENDS>
7.4.3.2. RESULTS 8.4.3.2. RESULTS
<CODE BEGINS> <CODE BEGINS>
/// struct LISTXATTRS4resok { /// struct LISTXATTRS4resok {
/// nfs_cookie4 lxr_cookie; /// nfs_cookie4 lxr_cookie;
/// xattrkey4 lxr_names<>; /// xattrkey4 lxr_names<>;
/// bool lxr_eof; /// bool lxr_eof;
/// }; /// };
/// union LISTXATTRS4res switch (nfsstat4 lxr_status) { /// union LISTXATTRS4res switch (nfsstat4 lxr_status) {
/// case NFS4_OK: /// case NFS4_OK:
/// LISTXATTRS4resok lxr_value; /// LISTXATTRS4resok lxr_value;
/// default: /// default:
/// void; /// void;
/// }; /// };
<CODE ENDS> <CODE ENDS>
7.4.3.3. DESCRIPTION 8.4.3.3. DESCRIPTION
The LISTXATTRS operation retrieves a variable number of extended The LISTXATTRS operation retrieves a variable number of extended
attribute keys from the file system object specified by the current attribute keys from the file system object specified by the current
filehandle, along with information to allow the client to request filehandle, along with information to allow the client to request
additional attribute keys in a subsequent LISTXATTRS. additional attribute keys in a subsequent LISTXATTRS.
The arguments contain a cookie value that represents where the The arguments contain a cookie value that represents where the
LISTXATTRS should start within the list of xattrs. A value of 0 LISTXATTRS should start within the list of xattrs. A value of 0
(zero) for lxa_cookie is used to start reading at the beginning of (zero) for lxa_cookie is used to start reading at the beginning of
the list. For subsequent LISTXATTRS requests, the client specifies a the list. For subsequent LISTXATTRS requests, the client specifies a
skipping to change at page 18, line 7 skipping to change at page 18, line 7
The cookie value is only meaningful to the server and is used as a The cookie value is only meaningful to the server and is used as a
"bookmark" for the xattr key. As mentioned, this cookie is used by "bookmark" for the xattr key. As mentioned, this cookie is used by
the client for subsequent LISTXATTRS operations so that it may the client for subsequent LISTXATTRS operations so that it may
continue listing keys. The cookie is similar in concept to a READDIR continue listing keys. The cookie is similar in concept to a READDIR
cookie or the READ offset but should not be interpreted as such by cookie or the READ offset but should not be interpreted as such by
the client. the client.
On success, the current filehandle retains its value. On success, the current filehandle retains its value.
7.4.3.4. IMPLEMENTATION 8.4.3.4. IMPLEMENTATION
The handling of cookie is similar to that of the READDIR operation. The handling of cookie is similar to that of the READDIR operation.
It should be a rare occurrence that a server is unable to continue It should be a rare occurrence that a server is unable to continue
properly listing xattrs with the provided cookie. The server should properly listing xattrs with the provided cookie. The server should
make every effort to avoid this condition since the application at make every effort to avoid this condition since the application at
the client may not be able to properly handle this type of failure. the client may not be able to properly handle this type of failure.
7.4.4. REMOVEXATTR - Remove an extended attribute of a file 8.4.4. REMOVEXATTR - Remove an extended attribute of a file
7.4.4.1. ARGUMENTS 8.4.4.1. ARGUMENTS
<CODE BEGINS> <CODE BEGINS>
/// struct REMOVEXATTR4args { /// struct REMOVEXATTR4args {
/// /* CURRENT_FH: file */ /// /* CURRENT_FH: file */
/// xattrkey4 rxa_name; /// xattrkey4 rxa_name;
/// }; /// };
<CODE ENDS> <CODE ENDS>
7.4.4.2. RESULTS 8.4.4.2. RESULTS
<CODE BEGINS> <CODE BEGINS>
/// struct REMOVEXATTR4res switch (nfsstat4 rxr_status) { /// struct REMOVEXATTR4res switch (nfsstat4 rxr_status) {
/// case NFS4_OK: /// case NFS4_OK:
/// change_info4 rxr_info; /// change_info4 rxr_info;
/// default: /// default:
/// void; /// void;
/// }; /// };
<CODE ENDS> <CODE ENDS>
7.4.4.3. DESCRIPTION 8.4.4.3. DESCRIPTION
The REMOVEXATTR operation deletes one extended attribute of a file The REMOVEXATTR operation deletes one extended attribute of a file
system object specified by rxa_name. The server MUST return system object specified by rxa_name. The server MUST return
NFS4ERR_NOXATTR if the attribute key does not exist. NFS4ERR_NOXATTR if the attribute key does not exist.
A successful REMOVEXATTR SHOULD change the file time_metadata and A successful REMOVEXATTR MUST change the file time_metadata and
change attributes. change attributes.
Similar to SETXATTR, the server communicates the value of the change Similar to SETXATTR, the server communicates the value of the change
attribute immediately prior to, and immediately following, a attribute immediately prior to, and immediately following, a
successful REMOVEXATTR operation in rxr_info. This allows the client successful REMOVEXATTR operation in rxr_info. This allows the client
to determine if its cached xattrs are still valid after the to determine if its cached xattrs are still valid after the
operation. See Section 7.6 for a discussion on xattr caching. operation. See Section 8.7 for a discussion on xattr caching.
7.4.4.4. IMPLEMENTATION 8.4.4.4. IMPLEMENTATION
If the object whose xattr is being removed has a file delegation that If the object whose xattr is being removed has a file delegation that
is held by a client other than the one doing the REMOVEXATTR, the is held by a client other than the one doing the REMOVEXATTR, the
delegation(s) must be recalled, and the operation cannot proceed to delegation(s) must be recalled, and the operation cannot proceed to
delete the xattr until each such delegation is returned or revoked. delete the xattr until each such delegation is returned or revoked.
In all cases in which delegations are recalled, the server is likely In all cases in which delegations are recalled, the server is likely
to return one or more NFS4ERR_DELAY errors while the delegation(s) to return one or more NFS4ERR_DELAY errors while the delegation(s)
remains outstanding, although it might not do that if the delegations remains outstanding, although it might not do that if the delegations
are returned quickly. are returned quickly.
7.4.5. Valid Errors 8.4.5. Valid Errors
This section contains a table that gives the valid error returns for This section contains a table that gives the valid error returns for
each new protocol operation. The error code NFS4_OK (indicating no each new protocol operation. The error code NFS4_OK (indicating no
error) is not listed but should be understood to be returnable by all error) is not listed but should be understood to be returnable by all
new operations. The error values for all other operations are new operations. The error values for all other operations are
defined in Section 13.2 of [RFC7530]. defined in Section 13.2 of [RFC7530] and Section 11.2 of [RFC7862].
Valid Error Returns for Each New Protocol Operation Valid Error Returns for Each New Protocol Operation
+----------------------+--------------------------------------------+ +----------------------+--------------------------------------------+
| Operation | Errors | | Operation | Errors |
+----------------------+--------------------------------------------+ +----------------------+--------------------------------------------+
| GETXATTR | NFS4ERR_ACCESS, NFS4ERR_BADXDR, | | GETXATTR | NFS4ERR_ACCESS, NFS4ERR_BADXDR, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, | | | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, | | | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_IO, NFS4ERR_MOVED, | | | NFS4ERR_IO, NFS4ERR_MOVED, |
skipping to change at page 20, line 33 skipping to change at page 20, line 33
| | NFS4ERR_LOCKED, NFS4ERR_MOVED, | | | NFS4ERR_LOCKED, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOFILEHANDLE, | | | NFS4ERR_NAMETOOLONG, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOSPC, NFS4ERR_OLD_STATEID, | | | NFS4ERR_NOSPC, NFS4ERR_OLD_STATEID, |
| | NFS4ERR_OPENMODE, | | | NFS4ERR_OPENMODE, |
| | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_PERM, | | | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_PERM, |
| | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS, | | | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, | | | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE | | | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE |
+----------------------+--------------------------------------------+ +----------------------+--------------------------------------------+
7.5. Modifications to Existing Operations 8.5. Modifications to Existing Operations
In order to provide fine-grained access control to query or modify In order to provide fine-grained access control to query or modify
extended attributes, additions are proposed to the set of access extended attributes, additions are proposed to the set of access
rights that can be checked to determine if the client is permitted to rights that can be checked to determine if the client is permitted to
perform the xattr operation. perform the xattr operation.
Note that in general, as explained in Section 18.1.4 of [RFC5661], a Note that in general, as explained in Section 18.1.4 of [RFC5661], a
client cannot reliably perform an access check with only current file client cannot reliably perform an access check with only current file
attributes and must verify access with the server. attributes and must verify access with the server.
skipping to change at page 21, line 12 skipping to change at page 21, line 12
ACCESS4_XAWRITE Modify xattr keys and/or values of a file or ACCESS4_XAWRITE Modify xattr keys and/or values of a file or
directory. directory.
ACCESS4_XALIST Query a file or directory to list its xattr keys. ACCESS4_XALIST Query a file or directory to list its xattr keys.
As with the existing access permissions, the results of ACCESS are As with the existing access permissions, the results of ACCESS are
advisory in nature, with no implication that such access will be advisory in nature, with no implication that such access will be
allowed or denied in the future. allowed or denied in the future.
In addition, two new bitmask constants used for the access mask field
are added:
ACE4_READ_XATTRS Permission to interrogate the extended attributes
of a file with GETXATTR.
ACE4_WRITE_XATTRS Permission to change the extended attributes of a
file with SETXATTR or REMOVEXATTR.
ACE4_LIST_XATTRS Permission to list the extended attributes of a
file with LISTXATTRS.
The rules for the client and server follow: The rules for the client and server follow:
o If the client is sending ACCESS in order to determine if the user o If the client is sending ACCESS in order to determine if the user
can read an xattr of the file with GETXATTR, the client SHOULD set can read an xattr of the file with GETXATTR, the client should set
ACCESS4_XAREAD in the request's access field. ACCESS4_XAREAD in the request's access field.
o If the client is sending ACCESS in order to determine if the user o If the client is sending ACCESS in order to determine if the user
can modify an xattr of the file with SETXATTR or REMOVEXATTR, the can modify an xattr of the file with SETXATTR or REMOVEXATTR, the
client SHOULD set ACCESS4_XAWRITE in the request's access field. client should set ACCESS4_XAWRITE in the request's access field.
o If the client is sending ACCESS in order to determine if the user o If the client is sending ACCESS in order to determine if the user
can list the xattr keys of the file with LISTXATTRS, the client can list the xattr keys of the file with LISTXATTRS, the client
SHOULD set ACCESS4_XALIST in the request's access field. should set ACCESS4_XALIST in the request's access field.
o If the server supports the ACE4_READ_XATTRS permission bit, it
MUST only check for it in the mode, acl, and dacl attributes when
it receives an ACCESS request with ACCESS4_XAREAD set in the
access field.
o If the server supports the ACE4_WRITE_XATTRS permission bit, it
MUST only check for it in the mode, acl, and dacl attributes when
it receives an ACCESS request with ACCESS4_XAWRITE set in the
access field.
o If the server supports the ACE4_LIST_XATTRS permission bit, it
MUST only check for it in the mode, acl, and dacl attributes when
it receives an ACCESS request with ACCESS4_XALIST set in the
access field.
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 ACE4_XAREAD from ACE4_READ_ATTRIBUTES
(or ACE4_READ_DATA); both masks would be tied to a single "stat" (or
"read") permission. When such a server returns attributes to the
client, it would show both ACE4_READ_ATTRIBUTES (or ACE4_READ_DATA)
and ACE4_XAREAD if and only if the stat (or read) permission is
enabled.
If a server receives a SETXATTR request that it cannot accurately
implement, it should err in the direction of more restricted access.
For example, suppose a server supports xattrs, but cannot distinguish
modifying attributes from updating xattr. If a client submits an
ALLOW ACE where ACE4_WRITE_ATTRIBUTES is set but ACE4_WRITE_XATTR is
not (or vice versa), the server should either turn off
ACE4_WRITE_ATTRIBUTES or reject the request with NFS4ERR_ATTRNOTSUPP.
7.6. Numeric Values Assigned to Protocol Extensions
This section lists the numeric values assigned new attributes and
operations to implement the xattr feature. To avoid inconsistent
assignments, these have been checked against the most recent protocol
version [RFC5661], the current minor version [NFSv42], and all
extensions currently approved as working group documents.
Development of interoperable prototypes should be possible using
these values, although it is possible that these values may be
modified before eventual publication as a standard-track document.
<CODE BEGINS>
/// /* 8.6. Numeric Values Assigned to Protocol Extensions
/// * ACCESS - Check Access Rights
/// */
/// const ACCESS4_XAREAD = 0x00000040;
/// const ACCESS4_XAWRITE = 0x00000080;
/// const ACCESS4_XALIST = 0x00000100;
/// /* This section lists the numeric values assigned new attributes and
/// * ACE mask values operations to implement the xattr feature. To avoid inconsistent
/// */ assignments, these have been checked against the most recent
/// const ACE4_READ_XATTRS = 0x00200000; protocol version [RFC5661], the current minor version [RFC7862],
/// const ACE4_WRITE_XATTRS = 0x00400000; and all extensions currently approved as working group documents.
/// const ACE4_LIST_XATTRS = 0x00800000; Development of interoperable prototypes should be possible using
these values, although it is possible that these values may be
modified before eventual publication as a standard-track document.
/// /* <CODE BEGINS>
/// * New NFSv4 attribute
/// */
/// typedef bool fattr4_xattr_support;
/// /* /// /*
/// * New RECOMMENDED Attribute /// * ACCESS - Check Access Rights
/// */ /// */
/// const FATTR4_XATTR_SUPPORT = 81; /// const ACCESS4_XAREAD = 0x00000040;
/// const ACCESS4_XAWRITE = 0x00000080;
/// const ACCESS4_XALIST = 0x00000100;
/// /* /// /*
/// * New NFSv4 operations /// * ACE mask values
/// */ /// */
/// /* Following lines are to be added to enum nfs_opnum4 */ /// const ACE4_READ_XATTRS = 0x00200000;
/// /* /// const ACE4_WRITE_XATTRS = 0x00400000;
/// OP_GETXATTR = 72, /// const ACE4_LIST_XATTRS = 0x00800000;
/// OP_SETXATTR = 73, /// /*
/// OP_LISTXATTRS = 74, /// * New NFSv4 attribute
/// OP_REMOVEXATTR = 75, /// */
/// */ /// typedef bool fattr4_xattr_support;
<CODE ENDS> /// /*
/// * New RECOMMENDED Attribute
/// */
/// const FATTR4_XATTR_SUPPORT = 81;
7.7. Caching /// /*
/// * New NFSv4 operations
/// */
/// /* Following lines are to be added to enum nfs_opnum4 */
/// /*
/// OP_GETXATTR = 72,
/// OP_SETXATTR = 73,
/// OP_LISTXATTRS = 74,
/// OP_REMOVEXATTR = 75,
/// */
The caching behavior for extended attributes is similar to other file <CODE ENDS>
attributes such as ACLs and is affected by whether OPEN delegation
has been granted to a client or not.
Xattrs obtained from, or sent to, the server may be cached and 8.7. Caching
clients can use them to avoid subsequent GETXATTR requests, provided
that the client can ensure that the cached value has not been
subsequently modified by another client. Such assurance can depend
on the client holding a delegation for the file in question or the
client interrogating the change attribute to make sure that any
cached value is still valid. Such caching may be read-only or write-
through.
When a delegation is in effect, some operations by a second client to The caching behavior for extended attributes is similar to other
a delegated file will cause the server to recall the delegation file attributes such as ACLs and is affected by whether OPEN
through a callback. For individual operations, we describe, under delegation has been granted to a client or not.
IMPLEMENTATION, when such operations are required to effect a recall.
The result of local caching is that the individual xattrs maintained Xattrs obtained from, or sent to, the server may be cached and
on clients may not be up-to-date. Changes made in one order on the clients can use them to avoid subsequent GETXATTR requests,
server may be seen in a different order on one client and in a third provided that the client can ensure that the cached value has not
order on another client. In order to limit problems that may arise been subsequently modified by another client. Such assurance can
due to separate operations to obtain individual xattrs and other file be based on the client holding a delegation for the file in
attributes, a client should treat xattrs just like other file question or the client interrogating the change attribute to make
attributes with respect to caching as detailed in section 10.6 of sure that any cached value is still valid. Such caching may be
read-only or write-through.
[RFC7530]. A client may validate its cached version of an xattr for When a delegation is in effect, some operations by a second client
a file by fetching the change attribute and assuming that if the to a delegated file will cause the server to recall the delegation
change attribute has the same value as it did when the attributes through a callback. For individual operations, we describe, under
were cached, then xattrs have not changed. If the client holds a IMPLEMENTATION, when such operations are required to effect a
delegation that ensures that the change attribute cannot be modified recall.
by another client, that it can dispense with actual interrogation of
the change attribute.
When a client is changing xattrs of a file, it needs to determine The result of local caching is that the individual xattrs
whether there have been changes made to the file by other clients. maintained on clients may not be up-to-date. Changes made in one
It does this by using the change attribute as reported before and order on the server may be seen in a different order on one client
after the change operation (SETXATTR or REMOVEXATTR) in the and in a third order on another client. In order to limit
associated change_info4 value returned for the operation. The server problems that may arise due to separate operations to obtain
is able to communicate to the client whether the change_info4 data is individual xattrs and other file attributes, a client should treat
provided atomically with respect to the change operation. If the xattrs just like other file attributes with respect to caching as
change values are provided atomically, the client has a basis for detailed in section 10.6 of [RFC7530]. A client may validate its
determining, given proper care, whether other clients are modifying cached version of an xattr for a file by fetching the change
the file in question. attribute and assuming that if the change attribute has the same
value as it did when the attributes were cached, then xattrs have
not changed. If the client holds a delegation that ensures that
the change attribute cannot be modified by another client, that it
can dispense with actual interrogation of the change attribute.
The simplest way to enable the client to make this determination is When a client is changing xattrs of a file, it needs to determine
for the client to serialize all xattr changes made to a specific whether there have been changes made to the file by other clients.
file. When this is done, and the server provides before and after It does this by using the change attribute as reported before and
values of the change attribute atomically, the client can simply after the change operation (SETXATTR or REMOVEXATTR) in the
compare the after value of the change attribute from one operation associated change_info4 value returned for the operation. The
with the before value on the subsequent change operation modifying server is able to communicate to the client whether the
the file. When these are equal, the client is assured that no other change_info4 data is provided atomically with respect to the
client is modifying the file in question. change operation. If the change values are provided atomically,
the client has a basis for determining, given proper care, whether
other clients are modifying the file in question.
If the comparison indicates that the file was updated by another An effective way to enable the client to make this determination
client, the xattr cache associated with the modified file is purged simply is for it to serialize all xattr changes made to a specific
from the client. If the comparison indicates no modification, the file. When this is done, and the server provides before and after
xattr cache can be updated on the client to reflect the file values of the change attribute atomically, the client can simply
operation and the associated timeout can be extended. The post- compare the after value of the change attribute from one operation
operation change value needs to be saved as the basis for future with the before value on the subsequent change operation modifying
change_info4 comparisons. the file. When these are equal, the client is assured that no
other client is modifying the file in question.
Xattr caching requires that the client revalidate xattr cache data by If the comparison indicates that the file was updated by another
inspecting the change attribute of a file at the point when an xattr client, the xattr cache associated with the modified file is
was cached. This requires that the server update the change purged from the client. If the comparison indicates no
attribute when xattrs are modified. For a client to use the modification, the xattr cache can be updated on the client to
change_info4 information appropriately and correctly, the server must reflect the file operation and the associated timeout can be
report the pre- and post-operation change attribute values extended. The post-operation change value needs to be saved as
atomically. When the server is unable to report the before and after the basis for future change_info4 comparisons.
values atomically with respect to the xattr update operation, the
server must indicate that fact in the change_info4 return value.
When the information is not atomically reported, the client should
not assume that other clients have not changed the xattrs.
The protocol does not provide support for write-back caching of Xattr caching requires that the client revalidate xattr cache data
xattrs. As such, all modifications to xattrs should be done by by inspecting the change attribute of a file at the point when an
requests to the server. The server should perform such updates xattr was cached. This requires that the server update the change
synchronously. attribute when xattrs are modified. For a client to use the
change_info4 information appropriately and correctly, the server
must report the pre- and post-operation change attribute values
atomically. When the server is unable to report the before and
after values atomically with respect to the xattr update
operation, the server must indicate that fact in the change_info4
return value. When the information is not atomically reported,
the client should not assume that other clients have not changed
the xattrs.
7.8. Xattrs and File Locking The protocol does not provide support for write-back caching of
xattrs. As such, all modifications to xattrs should be done by
requests to the server. The server should perform such updates
synchronously.
Xattr operations, for the most part, function independent of 8.8. Xattrs and File Locking
operations related to file locking state. For example, xattrs can be
interrogated and modified without a corresponding OPEN operation.
The server does not need to check for locks that conflict with xattr
access or modify operations. For example, another OPEN specified
with OPEN4_SHARE_DENY_READ or OPEN4_SHARE_DENY_BOTH does not prevent
access to or modification of xattrs. Note that the server MUST still
verify that the client is allowed to perform the xattr operation on
the basis of ACE access permissions.
However, the presence of delegations may dictate how xattr operations Xattr operations, for the most part, function independent of
interact with the state-related logic. Xattrs cannot be modified operations related to file locking state. For example, xattrs can
when a delegation for the corresponding file is held by another be interrogated and modified without a corresponding OPEN
client. On the other hand, xattrs can be interrogated despite the operation. The server does not need to check for locks that
holding of a write delegation by another client since updates are conflict with xattr access or modify operations. For example,
write-through to the server. another OPEN specified with OPEN4_SHARE_DENY_READ or
OPEN4_SHARE_DENY_BOTH does not prevent access to or modification
of xattrs. Note that the server MUST still verify that the client
is allowed to perform the xattr operation on the basis of ACE
access permissions.
7.9. pNFS Considerations However, the presence of delegations may dictate how xattr
operations interact with the state-related logic. Xattrs cannot
be modified when a delegation for the corresponding file is held
by another client. On the other hand, xattrs can be interrogated
despite the holding of a write delegation by another client since
updates are write-through to the server.
All xattr operations are sent to the metadata server, which is 8.9. pNFS Considerations
responsible for fetching data from and effecting necessary changes to
persistent storage.
8. Security Considerations All xattr operations are sent to the metadata server, which is
responsible for fetching data from and effecting necessary changes
to persistent storage.
Since xattrs are application data, security issues are exactly the 9. Security Considerations
same as those relating to the storing of file data and named
attributes. These are all various sorts of application data and the
fact that the means of reference is slightly different in each case
should not be considered security-relevant. As such, the additions
to the NFS protocol for supporting extended attributes do not alter
the security considerations of the NFSv4.2 protocol [NFSv42].
9. IANA Considerations Since xattrs are application data, security issues are exactly the
same as those relating to the storing of file data and named
attributes. These are all various sorts of application data and
the fact that the means of reference is slightly different in each
case should not be considered security-relevant. As such, the
additions to the NFS protocol for supporting extended attributes
do not alter the security considerations of the NFSv4.2 protocol
[RFC7862].
The addition of xattr support to the NFSv4 protocol does not require 10. IANA Considerations
any actions by IANA. This document limits xattr names to the user The addition of xattr support to the NFSv4 protocol does not
namespace, where application developers are allowed to define and use require any actions by IANA. This document limits xattr names to
attributes as needed. Unlike named attributes, there is no namespace the user namespace, where application developers are allowed to
identifier associated with xattrs that may require registration. define and use attributes as needed. Unlike named attributes,
there is no namespace identifier associated with xattrs that may
require registration.
10. References 11. References
10.1. Normative References 11.1. Normative References
[LEGAL] IETF Trust, "Legal Provisions Relating to IETF Documents", [LEGAL] IETF Trust, "Legal Provisions Relating to IETF Documents",
November 2008, <http://trustee.ietf.org/docs/IETF-Trust- November 2008, <http://trustee.ietf.org/docs/IETF-Trust-
License-Policy.pdf>. License-Policy.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI Requirement Levels", BCP 14, RFC 2119, DOI
10.17487/RFC2119, March 1997, <http://www.rfc- 10.17487/RFC2119, March 1997, <http://www.rfc-
editor.org/info/rfc2119>. editor.org/info/rfc2119>.
[RFC4506] Eisler, M., Ed., "XDR: External Data Representation [RFC4506] Eisler, M., Ed., "XDR: External Data Representation
Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May
2006, <http://www.rfc-editor.org/info/rfc4506>. 2006, <http://www.rfc-editor.org/info/rfc4506>.
[RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., [RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1 "Network File System (NFS) Version 4 Minor Version 1
Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010, Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
<http://www.rfc-editor.org/info/rfc5661>. <http://www.rfc-editor.org/info/rfc5661>.
[RFC5662] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., [RFC7530] Haynes, T., Ed., and D. Noveck, Ed., "Network File System
"Network File System (NFS) Version 4 Minor Version 1 (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
External Data Representation Standard (XDR) Description", March 2015, <http://www.rfc-editor.org/info/rfc7530>.
RFC 5662, DOI 10.17487/RFC5662, January 2010,
<http://www.rfc-editor.org/info/rfc5662>.
[RFC7530] Haynes, T. and D. Noveck, "Network File System (NFS)
Version 4 Protocol", RFC 7530, March 2015.
10.2. Informative References
[NFSv42] Haynes, T., Ed., "NFS Version 4 Minor Version 2", January [RFC7862] Haynes, T., "Network File System (NFS) Version 4 Minor
2016, <http://www.ietf.org/id/draft-ietf-nfsv4- Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
minorversion2-41.txt>. November 2016, <http://www.rfc-editor.org/info/rfc7862>.
Work in progress. [RFC7863] Haynes, T., "Network File System (NFS) Version 4 Minor
Version 2 External Data Representation Standard (XDR)
Description", RFC 7863, DOI 10.17487/RFC7863, November
2016, <http://www.rfc-editor.org/info/rfc7863>.
[NFSv42-dot-x] [RFC7862] Haynes, T., "Network File System (NFS) Version 4 Minor
Haynes, T., Ed., "NFS Version 4 Minor Version 2 Protocol Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
External Data Representation Standard (XDR) Description", November 2016, <http://www.rfc-editor.org/info/rfc7862>.
January 2016, <http://www.ietf.org/id/draft-ietf-nfsv4-
minorversion2-dot-x-41.txt>.
Work in progress. [RFC7863] Haynes, T., "Network File System (NFS) Version 4 Minor
Version 2 External Data Representation Standard (XDR)
Description", RFC 7863, DOI 10.17487/RFC7863, November
2016, <http://www.rfc-editor.org/info/rfc7863>.
[NFSv4-vers] [NFSv4-vers]
D. Noveck, "NFSv4 Version Management", January 2016, D. Noveck, "Rules for NFSv4 Extensions and Minor
<http://www.ietf.org/id/draft-ietf-nfsv4-versioning- Versions", December 2016, <http://www.ietf.org/id/draft-
03.txt>. ietf-nfsv4-versioning-09.txt>.
Work in progress. Work in progress.
11.2. Informative References
[freedesktop] [freedesktop]
"Guidelines for extended attributes", "Guidelines for extended attributes",
<http://www.freedesktop.org/wiki/CommonExtendedAttributes>. <http://www.freedesktop.org/wiki/CommonExtendedAttributes>.
[Linux] "Linux Programmer's Manual: xattr(7)", [Linux] "Linux Programmer's Manual: xattr(7)",
<http://man7.org/linux/man-pages/man7/xattr.7.html>. <http://man7.org/linux/man-pages/man7/xattr.7.html>.
[Love] Love, R., "Linux System Programming: Talking Directly to [Love] Love, R., "Linux System Programming: Talking Directly to
the Kernel and C Library", O'Reilly Media, Inc., 2007. the Kernel and C Library", O'Reilly Media, Inc., 2007.
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