draft-ietf-nfsv4-xattrs-00.txt   draft-ietf-nfsv4-xattrs-01.txt 
NFSv4 Working Group M. Naik NFSv4 Working Group M. Naik
Internet Draft M. Eshel Internet Draft M. Eshel
Intended Status: Standards Track IBM Almaden Intended Status: Standards Track IBM Almaden
Expires: February 1, 2016 July 31, 2015 Expires: February 19, 2016 August 18, 2015
Support for File System Extended Attributes in NFSv4 File System Extended Attributes in NFSv4
draft-ietf-nfsv4-xattrs-00 draft-ietf-nfsv4-xattrs-01
Abstract Abstract
This document proposes extensions to existing NFSv4 operations to This document proposes extensions to the NFSv4 protocol which allow
allow file extended attributes (here forth also referred to as file extended attributes (hereinafter also referred to as xattrs) to
xattrs) to be manipulated in the protocol. An xattr is a file system be manipulated using NFSv4. An xattr is a file system feature that
feature that allows opaque metadata, not interpreted by the file allows opaque metadata, not interpreted by the file system, to be
system, to be associated with files and directories and are supported associated with files and directories. Such support is present in
by many modern file systems. New file attributes are proposed to many modern local file systems. New file attributes are proposed to
allow clients to query the server for xattr support, and new allow clients to query the server for xattr support, and new
operations to get and set xattrs on file system objects. operations to get and set xattrs on file system objects are provided.
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as other groups may also distribute working documents as
Internet-Drafts. Internet-Drafts.
skipping to change at page 2, line 17 skipping to change at page 2, line 17
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Table of Contents Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2 Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 File System Support . . . . . . . . . . . . . . . . . . . . . . 5 3. File System Support . . . . . . . . . . . . . . . . . . . . . 5
4 Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5 Differences with Named Attributes . . . . . . . . . . . . . . . 6 5. Differences from Named Attributes . . . . . . . . . . . . . . 6
6 Protocol Enhancements . . . . . . . . . . . . . . . . . . . . . 7 6. XDR Description . . . . . . . . . . . . . . . . . . . . . . . 7
6.1 New Attributes . . . . . . . . . . . . . . . . . . . . . . 7 6.1. Code Components Licensing Notice . . . . . . . . . . . . . 7
6.1.1 Attribute 82: xattr_support . . . . . . . . . . . . . . 7 7. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 9
6.2 New Operations . . . . . . . . . . . . . . . . . . . . . . 7 7.1. New definition . . . . . . . . . . . . . . . . . . . . . . 9
6.2.1 New definitions . . . . . . . . . . . . . . . . . . . . 8 7.1.1. xattr4 . . . . . . . . . . . . . . . . . . . . . . . . 9
6.2.2 Caching . . . . . . . . . . . . . . . . . . . . . . . . 9 7.2. New Attribute . . . . . . . . . . . . . . . . . . . . . . 10
6.2.3 GETXATTR - Get an extended attribute of a file . . . . 9 7.2.1. xattr_support . . . . . . . . . . . . . . . . . . . . 10
6.2.4 SETXATTR - Set an extended attribute of a file . . . . 10 7.3. New Operations . . . . . . . . . . . . . . . . . . . . . . 10
6.2.5 LISTXATTR - List extended attributes of a file . . . . 12 7.3.1. GETXATTR - Get an extended attribute of a file . . . . 11
6.2.6 REMOVEXATTR - Remove an extended attribute of a file . 13 7.3.2. SETXATTR - Set an extended attribute of a file . . . . 12
6.2.7 Valid Errors . . . . . . . . . . . . . . . . . . . . . 14 7.3.3. LISTXATTR - List extended attributes of a file . . . . 14
6.3 Extensions to ACE Access Mask Attributes . . . . . . . . . 16 7.3.4. REMOVEXATTR - Remove an extended attribute of a file . 16
6.4 pNFS Considerations . . . . . . . . . . . . . . . . . . . . 16 7.3.5. Valid Errors . . . . . . . . . . . . . . . . . . . . . 17
7 Security Considerations . . . . . . . . . . . . . . . . . . . . 16 7.4. Modifications to Existing Operations . . . . . . . . . . . 18
8 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 16 7.5. Numeric Values Assigned to Protocol Extensions . . . . . . 20
9 References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 7.6. Caching . . . . . . . . . . . . . . . . . . . . . . . . . 21
9.1 Normative References . . . . . . . . . . . . . . . . . . . 17 7.7. Xattrs and File Locking . . . . . . . . . . . . . . . . . 22
9.2 Informative References . . . . . . . . . . . . . . . . . . 17 7.8. pNFS Considerations . . . . . . . . . . . . . . . . . . . 23
10 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17 8. Security Considerations . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
10.1. Normative References . . . . . . . . . . . . . . . . . . 24
10.2. Informative References . . . . . . . . . . . . . . . . . 24
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
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, typically organized in opaque metadata with file system objects, typically organized in
key/value pairs. They are especially useful when they add information key/value pairs. They are especially useful when they add
that is not, or cannot be, present in the associated object itself. information that is not, or cannot be, present in the associated
User-space applications can arbitrarily create, read from, and write object itself. User-space applications can arbitrarily create,
to the key/value pairs. interrogate, and modify to 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 do not need to be concerned about how the key/value
pairs are stored internally on the underlying file system. All major pairs are stored internally within the underlying file system. All
operating systems provide various flavors of extended attributes. major operating systems provide various flavors of extended
Many user space tools allow xattrs to be included in attributes that attributes. Many user space tools allow xattrs to be included in
need to be preserved when objects are updated, moved or copied. attributes that need to be preserved when objects are updated, moved
or copied.
Extended attributes have long been considered unsuitable for Extended attributes have previously been considered unsuitable for
portability because they are inadequately defined and not formally portable use because some aspects of their handling are not precisely
documented by any standard (such as POSIX). However, evidence defined and they are not formally documented by any standard (such as
suggests that xattrs are widely deployed and their support in modern POSIX). Nevertheless, it appears that xattrs are widely deployed and
disk-based file systems is fairly universal. their support in modern disk-based file systems is nearly universal.
There are no clear indications on how xattrs can be mapped to any There is no clear specification of how xattrs could be mapped to any
existing recommended or optional file attributes defined in RFC 5661 existing file attributes defined in the NFSv4 protocol ([RFC7530],
[2]; thereby most NFS client implementations ignore application- [RFC5661], [NFSv42]). As a result, most NFSv4 client implementations
specified xattrs. This results in data loss if one copies, over the ignore application-specified xattrs. This state of affairs results
NFS protocol, a file with xattrs from one file system to another that in data loss if one copies, over the NFS protocol, a file with xattrs
also supports xattrs. from one file system to another that also supports xattrs.
There is a relatively strong interest in the community in exposing There is thus a need to provide a means by which such data loss can
xattrs over NFS despite the shortcomings. be avoided. This will involve exposing xattrs within the NFSv4
protocol, despite the lack of completely compatible file system
implementations.
This document discusses why the current NFSv4 named attributes as This document discusses (in Section 5) the reasons that NFSv4 named
currently standardized in [2], are unsuitable for representing attributes as currently standardized in [RFC7530], are unsuitable for
xattrs, and proposes alternate language, adjustment and protocol representing xattrs. Instead, it proposes a separate protocol
mechanisms to support them. mechanism to support xattrs. As a consequence, xattrs and named
attributes will both be optional features with servers free to
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 RFC 2119 [1]. 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 Use Cases 2. Use Cases
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
message-id of the email, making it possible to trace the original message-id of the email, making it possible to trace the original
message. message.
Applications may need to behave differently when handling files of Applications may need to behave differently when handling files of
varying types. For example, file managers, such as GNOME's, offer varying types. For example, file managers, such as GNOME's, offer
unique icons, different click behavior, and special lists of unique icons, different click behavior, and special lists of
operations to perform depending on the file format. This can be operations to perform depending on the file format. This can be
achieved by looking at the file extension (Windows), or interpret the achieved by looking at the file extension (Windows), or interpret the
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 jettison the custom database and knowledge. A better approach is to dispense with the custom database
store such metadata in extended attributes: these are easier to and store such metadata in extended attributes. This is easier to
maintain, faster to access, and readily accessible by any application maintain, provides faster access, and is readily accessible by
[5]. applications [Love].
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 [9] transfers the responsibility of maintaining object Swift-on-File [Swift] transfers the responsibility of maintaining
durability and availability to the underlying file system. Today, object durability and availability to the underlying file system.
this requires a native file system client to mount the volumes. Xattr Today, this requires a native file system client to mount the
support in NFS would open up the possibility of storing and consuming volumes. Xattr support in NFS would open up the possibility of
data from other storage systems, and facilitate the migration of data storing and consuming data from other storage systems, and facilitate
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 KDE xattrs instead of a custom database for simplicity. Starting with
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 [10]. support [KDE].
3 File System Support 3. File System Support
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
[5]. Recommendations on how they should be used have been published [Love]. Recommendations on how they should be used have been
[4]. published [freedesktop].
FreeBSD supports extended attributes in two universal namespaces - FreeBSD supports extended attributes in two universal namespaces -
user and system, although individual file systems are allowed to user and system, although individual file systems are allowed to
implement additional namespaces [6]. implement additional namespaces [FreeBSD].
Solaris 9 and later allows files to have extended attributes, but Solaris 9 and later allows files to have extended attributes, but
implements them as "forks", logically represented as files within a implements them as "forks", logically represented as files within a
hidden directory that is associated with the target file [7]. hidden directory that is associated with the target file [fsattr].
In the NTFS file system, extended attributes are one of several In the NTFS file system, extended attributes are one of several
supported "file streams" [8]. supported "file 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 generally supported by user-space tools that preserve commands and generally supported by user-space tools that preserve
other file attributes. For example, the "rsync" remote copy program other file attributes. For example, the "rsync" remote copy program
will correctly preserve user extended attributes between Linux/ext4 will correctly preserve user extended attributes between Linux/ext4
and OSX/hfs by stripping off the Linux-specific "user." prefix. and OSX/hfs by stripping off the Linux-specific "user." prefix.
4 Namespaces 4. 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 [4]. 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 controlled data with file system objects. Access to this namespace is
via the normal file system attributes. As such, getting and setting controlled via the normal file system attributes. As such, getting
xattrs from the user namespace can be considered interoperable across and setting xattrs from the user namespace can be considered
platforms and vendor implementations. Attributes from other interoperable across platforms and vendor implementations.
namespaces are typically platform-specific, but some of them may be Attributes from other namespaces are typically platform-specific.
generalized into well-defined set of names that promote interoperable
implementations. Similarly, attaching the namespace to the attribute
key can avoid conflicting use of attributes.
This document restricts the allowed namespaces to user-managed This document provides for namespaces supporting user-managed
metadata only, in order to prevent the development of non- metadata only, thus avoiding the need to specify the semantics
interoperable implementations. It requires that the attribute applicable to particular system-interpreted xattrs. The values of
key/value MUST not be interpreted by the NFS clients and servers. xattrs are considered application data just as the contents of named
attributes, files, and symbolic links are. Servers have a
responsibility to store whatever value the client specifies and to
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-
interoperable implementations. If there is a need to specify
attributes that servers need to be act upon, the appropriate
semantics need to be specified by adding a new attribute for the
purpose as provided by [RFC7530] and [NFSv4-vers].
5 Differences with Named Attributes 5. Differences from Named Attributes
RFC5661 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.
[2]. Named attributes are intended to be used by client applications Named attributes are intended to be used by client applications as a
as a method to associate application-specific data with a regular method to associate application-specific data with a regular file or
file or directory. In that sense, xattrs are similar in concept and directory. In that sense, xattrs are similar in concept and use to
use to named attributes, but there are subtle differences. named attributes, but there are subtle differences.
File systems typically define individual xattrs "get" and "set" File systems typically define operations to get and set individual
operations 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 caching of
the data for these needs to be handled just as data caching is for the data for these needs to be handled just as data caching is for
ordinary files following close-to-open semantics. Xattrs, on the ordinary files following close-to-open semantics. Xattrs, on the
other hand, impose caching requirements like other file attributes. other hand, impose caching requirements like other file attributes.
Named attributes and xattrs have different semantics and belong to Named attributes and xattrs have different semantics and belong to
disjoint namespaces. As a result, mapping one to another is, at best, disjoint namespaces. As a result, mapping one to another is, at
a compromise. best, a compromise.
While it should be possible to write guidance about how a client can While it should 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 carving
out some namespace and specifying locking primitives to enforce out some namespace and specifying locking primitives to enforce
atomicity constraints on individual get/set operations, this is atomicity constraints on individual get/set operations, this is
problematic. A client application trying to use xattrs through named problematic. 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 Protocol Enhancements 6. XDR Description
This section proposes extensions to the NFSv4 protocol operations to This document contains the external data representation (XDR)
allow xattrs to be queried and modified by clients. A new attribute [RFC4506] description of the extended attributes. The XDR
is added to bitmap4 data type to allow xattr support to be queried. description is embedded in this document in a way that makes it
This follows the guidelines specified in [2] with respect to minor simple for the reader to extract into a ready-to-compile form. The
versioning. In addition, new operations, namely GETXATTR, SETXATTR, reader can feed this document into the following shell script to
LISTXATTR and REMOVEXATTR are defined to allow xattr key/value to be produce the machine readable XDR description of extended attributes:
queried and set.
6.1 New Attributes <CODE BEGINS>
The following RECOMMENDED attribute is proposed for use with GETATTR. #! /bin/sh
A client can query the server to determine if xattrs are supported by grep '^ *///' $* | sed 's?^ */// ??' | sed 's?^ *///$??'
setting the xattr_support bit in the GETATTR request.
+------------------+----+-------------------+-----+----------------+ <CODE ENDS>
|Name | Id | Data Type | Acc | Defined in |
+------------------+----+-------------------+-----+----------------+
| xattr_support | 82 | bool | R | Section 6.1.1 |
+------------------+----+-------------------+-----+----------------+
6.1.1 Attribute 82: xattr_support 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
do:
sh extract.sh < spec.txt > xattr_prot.x
The effect of the script is to remove leading white space from each
line, plus a sentinel sequence of "///".
The embedded XDR file header follows. Subsequent XDR descriptions,
with the sentinel sequence are embedded throughout the document.
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
includes both nfs types that end with a 4, such as verifier4, count4,
etc., as well as more generic types such as opaque and bool.
6.1. Code Components Licensing Notice
Both the XDR description and the scripts used for extracting the XDR
description are Code Components as described in Section 4 of "Legal
Provisions Relating to IETF Documents" [LEGAL]. These Code
Components are licensed according to the terms of that document.
<CODE BEGINS>
/// /*
/// * Copyright (c) 2012 IETF Trust and the persons identified
/// * as authors of the code. All rights reserved.
/// *
/// * Redistribution and use in source and binary forms, with
/// * or without modification, are permitted provided that the
/// * following conditions are met:
/// *
/// * o Redistributions of source code must retain the above
/// * copyright notice, this list of conditions and the
/// * following disclaimer.
/// *
/// * o Redistributions in binary form must reproduce the above
/// * copyright notice, this list of conditions and the
/// * following disclaimer in the documentation and/or other
/// * materials provided with the distribution.
/// *
/// * o Neither the name of Internet Society, IETF or IETF
/// * Trust, nor the names of specific contributors, may be
/// * used to endorse or promote products derived from this
/// * software without specific prior written permission.
/// *
/// * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS
/// * AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED
/// * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
/// * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
/// * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
/// * EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
/// * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
/// * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
/// * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
/// * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
/// * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
/// * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
/// * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
/// * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
/// * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
/// *
/// * This code was derived from RFCTBD10.
/// * Please reproduce this note if possible.
/// */
/// /*
/// * xattr_prot.x
/// */
/// /*
/// * The following include statements are for example only.
/// * The actual XDR definition files are generated separately
/// * and independently and are likely to have a different name.
/// * %#include <nfsv42.x>
/// * %#include <rpc_prot.x>
/// */
<CODE ENDS>
7. Protocol Extensions
This section documents extensions to the NFSv4 protocol operations to
allow xattrs to be queried and modified by clients. A new attribute
is added to allow clients to check if the server supports xattrs.
New operations are defined to allow xattr keys and values to be
queried and set. In addition, new bitmask constants are added to the
ACE access mask field to validate permissions to query and modify
xattrs.
These changes follow applicable guidelines for valid NFSv4 protocol
extension, whether the extensions occur in a minor version (as
specified in [RFC5661]) or as an extension to an existing minor
version (as specified in [NFSv4-vers]).
7.1. New definition
7.1.1. xattr4
The NFSv4 xattr4 structure is defined as follows:
<CODE BEGINS>
/// typedef component4 xattrname4;
/// typedef opaque xattrvalue4<>;
/// struct xattr4 {
/// xattrname4 xa_name;
/// xattrvalue4 xa_value;
/// };
<CODE ENDS>
Each xattr, defined by xattr4, is a key/value pair. An xattr4
consists of an xattrname4 which is a string denoting the xattr key
name, and an attrvalue4 which is a variable-length string that
identifies the value of the xattr. The handling of xattrname4 with
regard to internationalization-related issues is the same as that for
NFSv4 file names and named attribute names, as described in
[RFC7530]. Any regular file or directory may have set of extended
attributes, each consisting of a key and associated value. The NFS
client or server MUST NOT interpret the contents of xattr4.
7.2. New Attribute
The following RECOMMENDED per-fs read-only attribute is proposed for
use. A client can query the server to determine if xattrs are
supported by setting the xattr_support bit in the GETATTR request.
7.2.1. 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
support it. However, a client may reasonably assume that a server
(or file system) that does not support the xattr_support attribute
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.
6.2 New Operations 7.3. New Operations
Unlike other file system attributes, xattrs can represent disparate Individual xattrs generally represent separate items of metadata.
metadata most file systems allow disparate metadata to be associated For various reasons, combining them into a single attribute results
with an object through one or more xattrs, and combining them into a in clumsy implementations with significant functional deficits. In
single attribute is unwieldy. As such, adding new attributes to consequence, adding a new attribute to represent the set of xattrs
bitmap4 for use in GETATTR and SETATTR is inappropriate to support for an object is not an appropriate way to provide support for
xattr operations. For example, obtaining the value of a single xattr xattrs.
using the bitmap would require a client implementation to read all
the xattrs of the file and find a match for the one requested. For example, obtaining the value of a single xattr using the bitmap
Similarly, replacing or deleting a single xattr while keeping the would require a client implementation to read all the xattrs of the
others intact would require a client to read the xattrs first, file and find a match for the one requested. Similarly, replacing or
replacing the existing list with a modified list that excludes the deleting a single xattr while keeping the others intact would require
one to be deleted, and writing out the remaining xattrs. Moreover, a client to read the xattrs first, replacing the existing list with a
distinguishing between creating new and replacing existing xattrs on modified list that excludes the one to be deleted, and writing out
an object is not possible with the existing bitmap. 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 [5]: 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 operations, GETXATTR, SETXATTR, This section introduces four new RECOMMENDED operations, GETXATTR,
LISTXATTR and REMOVEXATTR, to query, set, list and remove xattrs SETXATTR, LISTXATTR and REMOVEXATTR, to query, set, list and remove
respectively. GETXATTR allows obtaining the value of an xattr key, xattrs respectively. GETXATTR allows obtaining the value of an xattr
SETXATTR allows creating or replacing an xattr key with a value, key, SETXATTR allows creating or replacing an xattr key with a value,
LISTXATTR enumerates all the xattrs names, and REMOVEXATTR allows LISTXATTR enumerates all the xattrs names, and REMOVEXATTR allows
deleting a single xattr. deleting a single xattr.
6.2.1 New definitions 7.3.1. GETXATTR - Get an extended attribute of a file
The NFS xattr structure is defined as follows:
typedef utf8str_cis xattrname4;
typedef opaque xattrvalue4<>;
struct xattr4 {
xattrname4 xa_name;
xattrvalue4 xa_value;
};
Each xattr, defined by xattr4, is a key/value pair. xattrname4 is a
UTF-8 string denoting the xattr key name, xattrvalue4 is a variable
length string that identifies the values of a specified xattr. The
size of the xattr is a combination of the size of its name
represented by xattrname4, and its value represented by xattrvalue4.
Any regular file or directory may have an array of xattr4, each
consisting of a key and associated value. The NFS client or server
MUST NOT interpret the contents of xattr4. Similar to ACLs, the
client can use the OPEN or ACCESS operations to check access without
modifying or reading data or metadata.
6.2.2 Caching
The caching behavior for extended attributes is similar to other file
attributes such as ACLs and is affected by whether OPEN delegation
has been granted to a client or not.
When a delegation is in effect, an operation by a second client to a 7.3.1.1. ARGUMENTS
delegated file will cause the server to recall the delegation through
a callback. For individual operations, we will describe, under
IMPLEMENTATION, when such operations are required to effect a recall.
When the client does not hold a delegation on the file, xattrs <CODE BEGINS>
obtained from the server may be cached and clients can use them to
avoid subsequent GETXATTR requests. Such caching is write through in
that modification to xattrs is always done by means of requests to
the server and should not be only done locally. Due to the relative
infrequency of xattr updates, it is suggested that all changes be
propagated synchronously. The client MUST NOT maintain a cache of
modified xattrs.
The result of local caching is that the xattrs maintained on /// struct GETXATTR4args {
individual clients may not be coherent. Changes made in one order on /// /* CURRENT_FH: file */
the server may be seen in a different order on one client and in a /// xattrname4 ga_name;
third order on another client. In order to manage the incoherency /// };
caused by separate operations to obtain xattrs and other file
attributes, a client should treat xattrs just like other file
attributes with respect to caching as detailed in section 10.6 of RFC
5661 [2]. A client may validate its cached version of xattrs for a
file by fetching both the change and time_access attributes and
assuming that if the change attribute has the same value as it did
when the attributes were cached, then xattrs have not changed.
6.2.3 GETXATTR - Get an extended attribute of a file <CODE ENDS>
6.2.3.1 ARGUMENTS 7.3.1.2. RESULTS
struct GETXATTR4args { <CODE BEGINS>
/* CURRENT_FH: file */
xattrname4 ga_name;
};
6.2.3.2 RESULTS /// union GETXATTR4res switch (nfsstat4 gr_status) {
/// case NFS4_OK:
/// xattrvalue4 gr_value;
/// default:
/// void;
/// };
union GETXATTR4res switch (nfsstat4 gr_status) { <CODE ENDS>
case NFS4_OK:
xattrvalue4 gr_value;
default:
void;
};
6.2.3.3 DESCRIPTION 7.3.1.3. 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 MUST return 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 an error. The system, then it MUST NOT return a value and MUST return an error.
server also MUST return an error if it supports xattrs on the target The server also MUST return an error if it supports xattrs on the
but cannot obtain the requested data. In that case, no value will be target but cannot obtain the requested data. In that case, no value
returned. If the xattr value contained in the server response will will be returned. If the xattr value contained in the server
exceed the channel's negotiated maximum response size, then the response is such as to cause the channel's negotiated maximum
server MUST return NFS4ERR_REP_TOO_BIG in gr_status. response size to be exceeded, then the server MUST return
NFS4ERR_REP_TOO_BIG in gr_status.
6.2.3.4 IMPLEMENTATION 7.3.1.4. IMPLEMENTATION
If there is an OPEN_DELEGATE_WRITE delegation held by another client Clients that have cached an xattr may avoid the need to do a GETXATTR
for the file in question, and size and/or change are among the set of by determining if the change attribute is the same as it was when the
attributes being interrogated in GETATTR, the server can either xattr was fetched. If the client does not hold a delegation for the
obtain the actual current value of these attributes from the client file in question, it can do so with a GETATTR request to obtain the
holding the delegation by using the CB_GETATTR callback, or revoke change attribute and comparing its value to the change attribute
the delegation. See Section 18.7.4 of RFC 5661 for details [2]. value fetched when the xattr value was obtained. This handling is
Consequently, if a client needs to verify the list of extended similar to how a client would revalidate other file attributes such
attributes with the server, it must also query the change attribute as ACLs.
of the file with GETATTR. This handling is similar to how a client
would revalidate other file attributes such as ACLs.
6.2.4 SETXATTR - Set an extended attribute of a file 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
question, either obtain the actual current value of these attributes
from the client holding the delegation by using the CB_GETATTR
callback, or revoke the delegation. See Section 18.7.4 of [RFC5661]
for details.
6.2.4.1 ARGUMENTS 7.3.2. SETXATTR - Set an extended attribute of a file
enum setxattr_type4 { 7.3.2.1. ARGUMENTS
SETXATTR4_CREATE = 0,
SETXATTR4_REPLACE = 1,
};
struct SETXATTR4args {
/* CURRENT_FH: file */
setxattr_type4 sa_type;
xattr4 sa_xattr;
};
6.2.4.2 RESULTS <CODE BEGINS>
union SETXATTR4res switch (nfsstat4 sr_status) { /// enum setxattr_type4 {
case NFS4_OK: /// SETXATTR4_CREATE = 0,
void; /// SETXATTR4_REPLACE = 1,
default: /// };
void; /// struct SETXATTR4args {
}; /// /* CURRENT_FH: file */
/// setxattr_type4 sa_type;
/// xattr4 sa_xattr;
/// };
6.2.4.3 DESCRIPTION <CODE ENDS>
7.3.2.2. RESULTS
<CODE BEGINS>
/// struct SETXATTR4res switch (nfsstat4 sr_status) {
/// case NFS4_OK:
/// change_info4 sr_info;
/// default:
/// void;
/// };
<CODE ENDS>
7.3.2.3. 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 sa_type. system object. The change desired is specified by sa_type.
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 an error if the attribute current filehandle. The server MUST return an error if the attribute
key already exists. SETXATTR4_REPLACE is also used to set an xattr, key already exists. SETXATTR4_REPLACE is also used to set an xattr,
but the server MUST return an error if the attribute key does not but the server MUST return an error if the attribute key does not
exist. exist.
If the xattr key and/or value contained in the client request exceeds If the xattr key and value contained in the client request are such
the channel's negotiated maximum request size, then the server MUST that the request would exceed the channel's negotiated maximum
return NFS4ERR_REQ_TOO_BIG in sr_status. If the server file system request size, then the server MUST return NFS4ERR_REQ_TOO_BIG in
imposes additional limits on the size of key name or value, it MAY sr_status. If the server file system imposes additional limits on
return NFS4ERR_ENOSPC. the size of key name or value, it MAY return NFS4ERR_NAMETOOLONG.
A successful SETXATTR SHOULD change the file time_modify and change A successful SETXATTR MUST change the file time_modify and change
attributes. However, these attributes SHOULD NOT be changed unless attributes if the xattr is created or the value assigned to xattr
the xattrs are changed. changes. However, these attributes SHOULD NOT be changed if this
causes no actual change in the xattr value.
6.2.4.4 IMPLEMENTATION On success, the server returns the change_info4 information in
sr_info. With the atomic field of the change_info4 data type, the
server will indicate if the before and after change attributes were
obtained atomically with respect to the SETXATTR operation. This
allows the client to determine if its cached xattrs are still valid
after the operation. See Section 7.6 for a discussion on xattr
caching.
7.3.2.4. 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.
6.2.5 LISTXATTR - List extended attributes of a file 7.3.3. LISTXATTR - List extended attributes of a file
6.2.5.1 ARGUMENTS 7.3.3.1. ARGUMENTS
struct LISTXATTR4args { <CODE BEGINS>
/* CURRENT_FH: file */
nfs_cookie4 la_cookie;
count4 la_maxcount;
};
5.2.5.2 RESULTS /// struct LISTXATTR4args {
/// /* CURRENT_FH: file */
/// nfs_cookie4 la_cookie;
/// verifier4 la_cookieverf;
/// count4 la_maxcount;
/// };
struct LISTXATTR4resok ( <CODE ENDS>
nfs_cookie4 lr_cookie;
verifier4 lr_cookieverf;
bool lr_eof;
xattrname4 lr_names<>;
};
union LISTXATTR4res switch (nfsstat4 lr_status) { 7.3.3.2. RESULTS
case NFS4_OK:
LISTXATTR4resok lr_value;
default:
void;
};
6.2.5.3 DESCRIPTION <CODE BEGINS>
/// struct LISTXATTR4resok (
/// nfs_cookie4 lr_cookie;
/// verifier4 lr_cookieverf;
/// bool lr_eof;
/// xattrname4 lr_names<>;
/// };
/// union LISTXATTR4res switch (nfsstat4 lr_status) {
/// case NFS4_OK:
/// LISTXATTR4resok lr_value;
/// default:
/// void;
/// };
<CODE ENDS>
7.3.3.3. DESCRIPTION
The LISTXATTR operation retrieves a variable number of extended The LISTXATTR 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 LISTXATTR. additional attribute keys in a subsequent LISTXATTR.
The arguments contain a cookie value that represents where the The arguments contain a cookie value that represents where the
LISTXATTR should start within the list of xattrs. A value of 0 LISTXATTR should start within the list of xattrs. A value of 0
(zero) for la_cookie is used to start reading at the beginning of the (zero) for la_cookie is used to start reading at the beginning of the
list. For subsequent LISTXATTR requests, the client specifies a list. For subsequent LISTXATTR requests, the client specifies a
skipping to change at page 13, line 6 skipping to change at page 15, line 28
The la_cookieverf value should be set to 0 (zero) when the la_cookie The la_cookieverf value should be set to 0 (zero) when the la_cookie
value is 0 (zero) (first xattr read). On subsequent requests, it value is 0 (zero) (first xattr read). On subsequent requests, it
should be lr_cookieverf as returned by the server. The la_cookieverf should be lr_cookieverf as returned by the server. The la_cookieverf
must match that returned by the LISTXATTR in which the cookie was must match that returned by the LISTXATTR in which the cookie was
acquired. If the server determines that the la_cookieverf is no acquired. If the server determines that the la_cookieverf is no
longer valid for the directory, the error NFS4ERR_NOT_SAME must be longer valid for the directory, the error NFS4ERR_NOT_SAME must be
returned. returned.
The la_maxcount value of the argument is the maximum number of bytes The la_maxcount value of the argument is the maximum number of bytes
for the result. This maximum size represents all of the data being for the result. This maximum size represents all of the data being
returned within the LISTXATTR4resok structure and includes the XDR returned within the LISTXATTR4resok structure and includes the XDR
overhead. The server may return less data. If the server is unable overhead. The server may return less data. If the server is unable
to return a single xattr name within the maxcount limit, the error to return a single xattr name within the maxcount limit, the error
NFS4ERR_TOOSMALL will be returned to the client. NFS4ERR_TOOSMALL will be returned to the client.
On successful return, the server's response will provide a list of On successful return, the server's response will provide a list of
extended attribute keys. The "lr_eof" flag has a value of TRUE if extended attribute keys. The "lr_eof" flag has a value of TRUE if
there are no more keys for the object. there are no more keys for the object.
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 LISTXATTR operations so that it may the client for subsequent LISTXATTR 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. Ideally, the cookie value should not change if the object the client. Ideally, the cookie value should not change if the
xattr values is modified since the client may be caching these object xattr values is modified since the client may be caching these
values. values.
On success, the current filehandle retains its value. On success, the current filehandle retains its value.
6.2.5.4 IMPLEMENTATION 7.3.3.4. IMPLEMENTATION
The handling of ls_cookie and ls_cookieverf is similar to that of the The handling of ls_cookie and ls_cookieverf is similar to that of the
READDIR operation. The cookieverf may be used by the server to help READDIR operation. The cookieverf may be used by the server to help
manage cookie values that may become stale. It should be a rare manage cookie values that may become stale. It should be a rare
occurrence that a server is unable to continue properly listing occurrence that a server is unable to continue properly listing
xattrs with the provided cookie/cookieverf pair. The server should xattrs with the provided cookie/cookieverf pair. 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.
The use of the ls_cookieverf will also protect the client from using The use of the ls_cookieverf will also protect the client from using
LISTXATTR cookie values that may be stale. For example, if the file LISTXATTR cookie values that may be stale. For example, if the file
system has been migrated, the server may or may not be able to use system has been migrated, the server may or may not be able to use
the same cookie values to service LISTXATTR as the previous server the same cookie values to service LISTXATTR as the previous server
used. With the client providing the ls_cookieverf, the server is used. With the client providing the ls_cookieverf, the server is
able to provide the appropriate response to the client. This able to provide the appropriate response to the client. This
prevents the case where the server may accept a cookie value but the prevents the case where the server may accept a cookie value but the
underlying object xattrs have changed and the response is invalid underlying object xattrs have changed and the response is invalid
from the client's context of its previous LISTXATTR. from the client's context of its previous LISTXATTR.
6.2.6 REMOVEXATTR - Remove an extended attribute of a file 7.3.4. REMOVEXATTR - Remove an extended attribute of a file
6.2.6.1 ARGUMENTS 7.3.4.1. ARGUMENTS
struct REMOVEXATTR4args {
/* CURRENT_FH: file */
xattrname4 ra_name;
};
6.2.6.2 RESULTS <CODE BEGINS>
union REMOVEXATTR4res switch (nfsstat4 rr_status) { /// struct REMOVEXATTR4args {
case NFS4_OK: /// /* CURRENT_FH: file */
void; /// xattrname4 ra_name;
default: /// };
void;
};
6.2.6.3 DESCRIPTION <CODE ENDS>
7.3.4.2. RESULTS
<CODE BEGINS>
/// struct REMOVEXATTR4res switch (nfsstat4 rr_status) {
/// case NFS4_OK:
/// change_info4 rr_info;
/// default:
/// void;
/// };
<CODE ENDS>
7.3.4.3. 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 ra_name. The server MUST return an error system object specified by ra_name. The server MUST return an error
if the attribute key does not exist. If the xattr key contained in if the attribute key does not exist. If the xattr key contained in
the client request exceeds the channel's negotiated maximum request the client request exceeds the channel's negotiated maximum request
size, then the server MUST return NFS4ERR_REQ_TOO_BIG in rr_status. size, then the server MUST return NFS4ERR_REQ_TOO_BIG in rr_status.
A successful REMOVEXATTR SHOULD change the file time_modify and A successful REMOVEXATTR SHOULD change the file time_modify and
change attributes. However, these attributes SHOULD NOT be changed change attributes. However, these attributes SHOULD NOT be changed
unless the xattr is not removed. unless the xattr is not removed.
6.2.6.4 IMPLEMENTATION Similar to SETXATTR, the server communicates the value of the change
attribute immediately prior to, and immediately following, a
successful REMOVEXATTR operation in rr_info. This allows the client
to determine if its cached xattrs are still valid after the
operation. See Section 7.6 for a discussion on xattr caching.
7.3.4.4. 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.
6.2.7 Valid Errors 7.3.5. 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 15.2 of RFC 5661 [2]. defined in Section 13.2 of [RFC7530].
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_GRACE, | | | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR, | | | NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG, | | | NFS4ERR_NAMETOOLONG, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP, | | | NFS4ERR_NOTSUPP, NFS4ERR_OP_NOT_IN_SESSION,|
| | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_NOTDIR, |
| | NFS4ERR_PERM, NFS4ERR_REP_TOO_BIG, | | | NFS4ERR_PERM, NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, | | | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, | | | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, | | | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, | | | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE | | | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE |
| SETXATTR | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, | | SETXATTR | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR, | | | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION, |
| | NFS4ERR_BADOWNER, NFS4ERR_BAD_RANGE, | | | NFS4ERR_DELAY, NFS4ERR_DQUOT, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID, | | | NFS4ERR_EXIST, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, | | | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED, |
| | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT, |
| | NFS4ERR_EXIST, NFS4ERR_EXPIRED, |
| | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_LOCKED, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOFILEHANDLE, | | | NFS4ERR_NAMETOOLONG, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOSPC, NFS4ERR_NOTDIR, | | | NFS4ERR_NOSPC, NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE, | | | NFS4ERR_PERM, NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_PERM, |
| | NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, | | | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, | | | NFS4ERR_REQ_TOO_BIG, |
| | 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_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, | | LISTXATTR | NFS4ERR_ACCESS, NFS4ERR_DEADSESSION, |
| | NFS4ERR_WRONG_TYPE | | | NFS4ERR_DELAY, NFS4ERR_INVAL, NFS4ERR_IO, |
| LISTXATTR | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE, |
| | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR, |
| | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG, | | | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG, |
| | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP, | | | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP, |
| | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_NOTDIR, | | | NFS4ERR_OP_NOT_IN_SESSION, |
| | NFS4ERR_PERM, NFS4ERR_REP_TOO_BIG, | | | NFS4ERR_PERM, NFS4ERR_REP_TOO_BIG, |
| | NFS4ERR_REP_TOO_BIG_TO_CACHE, | | | NFS4ERR_REP_TOO_BIG_TO_CACHE, |
| | NFS4ERR_REQ_TOO_BIG, | | | NFS4ERR_REQ_TOO_BIG, |
| | NFS4ERR_RETRY_UNCACHED_REP, | | | NFS4ERR_RETRY_UNCACHED_REP, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, | | | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE | | | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE |
| REMOVEXATTR | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, | | REMOVEXATTR | NFS4ERR_ACCESS, NFS4ERR_BADCHAR, |
| | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR, | | | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION, |
| | NFS4ERR_BADOWNER, NFS4ERR_BAD_RANGE, | | | NFS4ERR_DELAY, NFS4ERR_DQUOT, |
| | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID, | | | NFS4ERR_EXIST, NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_DEADSESSION, NFS4ERR_DELAY, |
| | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT, |
| | NFS4ERR_EXIST, NFS4ERR_EXPIRED, |
| | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED, |
| | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO, |
| | NFS4ERR_LOCKED, NFS4ERR_MOVED, | | | NFS4ERR_LOCKED, NFS4ERR_MOVED, |
| | NFS4ERR_NAMETOOLONG, NFS4ERR_NOFILEHANDLE, | | | NFS4ERR_NAMETOOLONG, NFS4ERR_NOFILEHANDLE, |
| | NFS4ERR_NOSPC, NFS4ERR_NOTDIR, | | | NFS4ERR_NOSPC, NFS4ERR_OLD_STATEID, |
| | 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_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+--------------------------------------------+ +----------------------+--------------------------------------------+
6.3 Extensions to ACE Access Mask Attributes 7.4. Modifications to Existing Operations
Two new bitmask constants are proposed for the access mask field: In order to provide fine-grained access control to query or modify
extended attributes, additions are proposed to the set of access
rights that can be checked to determine if the client is permitted to
perform the xattr operation.
const ACE4_GET_XATTRS = 0x00200000; Note that in general, as explained in Section 18.1.4 of [RFC5661], a
const ACE4_SET_XATTRS = 0x00400000; client cannot reliably perform an access check with only current file
attributes and must verify access with the server.
Permission to get/list and set/remove the extended attributes of a This section extends the semantics of the ACCESS operation documented
file. The affected operations are GETXATTR/LISTXATTR and in Section 18.1 of [RFC5661]. Two new access permissions can be
SETXATTR/REMOVEXATTR respectively. No additional granularity of requested:
control is implied by these constants for server implementations.
6.4 pNFS Considerations ACCESS4_XAREAD Query a file or directory for its xattr key and/or
value.
ACCESS4_XAWRITE Modify xattr keys and/or values of a file or
directory.
As with the existing access permissions, the results of ACCESS are
advisory in nature, with no implication that such access will be
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 or LISTXATTR.
ACE4_WRITE_XATTRS Permission to change the extended attributes of a
file with SETXATTR or REMOVEXATTR.
The rules for the client and server follow:
o If the client is sending ACCESS in order to determine if the user
can read an xattr of the file with GETXATTR or list the xattr keys
of the file with LISTXATTR, the client SHOULD set ACCESS4_XAREAD
in the request's access field.
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
client SHOULD set ACCESS4_XAWRITE in the request's access field.
o If the server supports 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 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.
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 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.
7.5. 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>
/// /*
/// * ACCESS - Check Access Rights
/// */
/// const ACCESS4_XAREAD = 0x00000040;
/// const ACCESS4_XAWRITE = 0x00000080;
/// /*
/// * ACE flag values
/// */
/// const ACE4_READ_XATTRS = 0x00200000;
/// const ACE4_WRITE_XATTRS = 0x00400000;
/// /*
/// * New NFSv4 attribute
/// */
/// typedef bool fattr4_xattr_support;
/// /*
/// * New RECOMMENDED Attribute
/// */
/// const FATTR4_XATTR_SUPPORT = 81;
/// /*
/// * New NFSv4 operations
/// */
/// /* Following lines are to be added to enum nfs_opnum4 */
/// /*
/// OP_GETXATTR = 72,
/// OP_SETXATTR = 73,
/// OP_LISTXATTR = 74,
/// OP_REMOVEXATTR = 75,
/// */
<CODE ENDS>
7.6. Caching
The caching behavior for extended attributes is similar to other file
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
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
a delegated file will cause the server to recall the delegation
through a callback. For individual operations, we describe, under
IMPLEMENTATION, when such operations are required to effect a recall.
The result of local caching is that the individual xattrs maintained
on clients may not be up-to-date. Changes made in one order on the
server may be seen in a different order on one client and in a third
order on another client. In order to limit problems that may arise
due to separate operations to obtain individual xattrs and other file
attributes, a client should treat xattrs just like other file
attributes with respect to caching as detailed in section 10.6 of
[RFC7530]. A client may validate its cached version of an xattr for
a file by fetching the change 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.
When a client is changing xattrs of a file, it needs to determine
whether there have been changes made to the file by other clients.
It does this by using the change attribute as reported before and
after the change operation (SETXATTR or REMOVEXATTR) in the
associated change_info4 value returned for the operation. The server
is able to communicate to the client whether the change_info4 data is
provided atomically with respect to the 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.
The simplest way to enable the client to make this determination is
for the client to serialize all xattr changes made to a specific
file. When this is done, and the server provides before and after
values of the change attribute atomically, the client can simply
compare the after value of the change attribute from one operation
with the before value on the subsequent change operation modifying
the file. When these are equal, the client is assured that no other
client is modifying the file in question.
If the comparison indicates that the file was updated by another
client, the xattr cache associated with the modified file is purged
from the client. If the comparison indicates no modification, the
xattr cache can be updated on the client to reflect the file
operation and the associated timeout can be extended. The post-
operation change value needs to be saved as the basis for future
change_info4 comparisons.
Xattr caching requires that the client revalidate xattr cache data by
inspecting the change attribute of a file at the point when an xattr
was cached. This requires that the server update the change
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.
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.
7.7. Xattrs and File Locking
Xattr operations, for the most part, function independent of
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
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.
7.8. pNFS Considerations
All xattr operations are sent to the metadata server, which is All xattr operations are sent to the metadata server, which is
responsible for coordinating the changes onto the storage devices. responsible for fetching data from and effecting necessary changes to
persistent storage.
7 Security Considerations 8. Security Considerations
The additions to the NFS protocol for supporting extended attributes Since xattrs are application data, security issues are exactly the
do not alter the security considerations of the NFSv4.1 protocol [2]. 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].
8 IANA Considerations 9. IANA Considerations
All IANA considerations are covered in [2]. The addition of xattr support to the NFSv4 protocol does not require
any actions by IANA. This document limits xattr names to the user
namespace, where application developers are allowed to define and use
attributes as needed. Unlike named attributes, there is no namespace
identifier associated with xattrs that may require registration.
9 References 10. References
9.1 Normative References 10.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [LEGAL] IETF Trust, "Legal Provisions Relating to IETF Documents",
Levels", BCP 14, RFC 2119, March 1997. November 2008, <http://trustee.ietf.org/docs/IETF-Trust-
License-Policy.pdf>.
[2] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., "Network [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
File System (NFS) Version 4 Minor Version 1 Protocol", RFC 5661, Requirement Levels", BCP 14, RFC 2119, DOI
January 2010. 10.17487/RFC2119, March 1997, <http://www.rfc-
editor.org/info/rfc2119>.
[3] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., "Network [RFC4506] Eisler, M., Ed., "XDR: External Data Representation
File System (NFS) Version 4 Minor Version 1 External Data Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May
Representation Standard (XDR) Description", RFC 5662, January 2006, <http://www.rfc-editor.org/info/rfc4506>.
2010.
9.2 Informative References [RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1
Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
<http://www.rfc-editor.org/info/rfc5661>.
[4] http://www.freedesktop.org/wiki/CommonExtendedAttributes, [RFC5662] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Guidelines for extended attributes". "Network File System (NFS) Version 4 Minor Version 1
External Data Representation Standard (XDR) Description",
RFC 5662, DOI 10.17487/RFC5662, January 2010,
<http://www.rfc-editor.org/info/rfc5662>.
[5] Love, R., "Linux System Programming: Talking Directly to the [RFC7530] Haynes, T. and D. Noveck, "Network File System (NFS)
Kernel and C Library", O'Reilly Media, Inc., 2007. Version 4 Protocol", RFC 7530, March 2015.
[6] http://www.freebsd.org/cgi/man.cgi?query=extattr&sektion=9, 10.2. Informative References
"FreeBSD Man Pages - extattr"
[7] http://docs.oracle.com/cd/E19253-01/816-5175/6mbba7f02, [NFSv42] Haynes, T., Ed., "NFS Version 4 Minor Version 2", April
"Oracle Man Pages - fsattr" 2015, <http://www.ietf.org/id/draft-ietf-nfsv4-
minorversion2-38.txt>.
[8] http://msdn.microsoft.com/en- Work in progress.
us/library/windows/desktop/aa364404(v=vs.85).aspx, "File
Streams"
[9] Swift-on-File: https://github.com/stackforge/swiftonfile [NFSv42-dot-x]
Haynes, T., Ed., "NFS Version 4 Minor Version 2 Protocol
External Data Representation Standard (XDR) Description",
April 2015, <http://www.ietf.org/id/draft-ietf-nfsv4-
minorversion2-dot-x-38.txt>.
[10] KDE Planet: http://vhanda.in/blog/2014/08/extended-attributes- Work in progress.
updates/
10 Acknowledgements [NFSv4-vers]
Haynes, T. and D. Noveck, "NFSv4 Version Management", July
2015, <http://www.ietf.org/id/draft-ietf-nfsv4-versioning-
01.txt>.
This draft has attempted to capture the discussion on adding Work in progress.
xattrs to the NFSv4 protocol from many participants on the IETF
NFSv4 mailing list. Valuable input and advice was received on [freedesktop]
earlier revisions of this draft from several people on the NFSv4 "Guidelines for extended attributes",
mailing list, including Tom Haynes, Christoph Hellwig and Nico <http://www.freedesktop.org/wiki/CommonExtendedAttributes>.
Williams.
[Love] Love, R., "Linux System Programming: Talking Directly to
the Kernel and C Library", O'Reilly Media, Inc., 2007.
[FreeBSD] "FreeBSD Man Pages - extattr",
<http://www.freebsd.org/cgi/man.cgi?query=extattr&sektion=9>.
[fsattr] "Oracle Man Pages - fsattr",
<http://docs.oracle.com/cd/E19253-01/816-5175/6mbba7f02>.
[NTFS] "File Streams", <http://msdn.microsoft.com/en-
us/library/windows/desktop/aa364404(v=vs.85).aspx>.
[Swift] "Swift-on-File",
<https://github.com/stackforge/swiftonfile>.
[KDE] Handa, V., "KDE Planet",
<http://vhanda.in/blog/2014/08/extended-attributes-
updates/>.
Appendix A. Acknowledgements
This draft has attempted to capture the discussion on adding xattrs
to the NFSv4 protocol from many participants on the IETF NFSv4
mailing list. Those who provided valuable input and comments on
earlier revisions of this draft include: Tom Haynes, Christoph
Hellwig and Nico Williams. Dave Noveck provided a comprehensive
review of the previous revision of this draft.
Authors' Addresses Authors' Addresses
Manoj Naik Manoj Naik
IBM Almaden IBM Almaden
650 Harry Rd 650 Harry Rd
San Jose, CA 95120 San Jose, CA 95120
Phone: +1 408-927-1707 Phone: +1 408-927-1707
Email: mnaik@us.ibm.com Email: mnaik@us.ibm.com
Marc Eshel Marc Eshel
IBM Almaden IBM Almaden
650 Harry Rd 650 Harry Rd
San Jose, CA 95120 San Jose, CA 95120
Phone: +1 408-927-1894 Phone: +1 408-927-1894
Email: eshel@us.ibm.com Email: eshel@us.ibm.com
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