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Versions: 00 01 02                                                      
NFSv4 Working Group                                              M. Naik
Internet Draft                                                  M. Eshel
Intended Status: Standards Track                             IBM Almaden
Expires: January 19, 2015                                  July 18, 2014

          Support for File System Extended Attributes in NFSv4


   This document proposes extensions to existing NFSv4 operations to
   allow file extended attributes (here forth also referred to as
   xattrs) to be manipulated in the protocol. An xattr is a file system
   feature that allows opaque metadata, not interpreted by the file
   system, to be associated with files and directories and are supported
   by many modern file systems. New file attributes are proposed to
   allow clients to query the server for xattr support, and new
   operations to get and set xattrs on file system objects.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

Copyright and License Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  3
   2  Uses  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3  Namespaces  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4  Differences with Named Attributes . . . . . . . . . . . . . . .  5
   5  Protocol Enhancements . . . . . . . . . . . . . . . . . . . . .  6
     5.1  New Attributes  . . . . . . . . . . . . . . . . . . . . . .  6
       5.1.1  Attribute 82: maxxattrsize  . . . . . . . . . . . . . .  7
       5.1.2  Attribute 83: xattrsize . . . . . . . . . . . . . . . .  7
     5.2  New Operations  . . . . . . . . . . . . . . . . . . . . . .  7
       5.2.1  New definitions . . . . . . . . . . . . . . . . . . . .  8
       5.2.2  Caching . . . . . . . . . . . . . . . . . . . . . . . .  9
       5.2.3  GETXATTR - Get extended attributes of a file  . . . . .  9
       5.2.4  SETXATTR - Set extended attributes for a file . . . . . 11
       5.2.5  Valid Errors  . . . . . . . . . . . . . . . . . . . . . 13
     5.3  Extensions to ACE Access Mask Attributes  . . . . . . . . . 14
     5.4  pNFS Considerations . . . . . . . . . . . . . . . . . . . . 14
   6  Security Considerations . . . . . . . . . . . . . . . . . . . . 14
   7  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 14
   8  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     8.1  Normative References  . . . . . . . . . . . . . . . . . . . 15
     8.2  Informative References  . . . . . . . . . . . . . . . . . . 15
   9  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16

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1  Introduction

   Extended attributes, also called xattrs, are a means to associate
   opaque metadata with file system objects, typically organized in
   key/value pairs. They are especially useful when they add information
   that is not, or cannot be, present in the associated object itself.
   User-space applications can arbitrarily create, read from, and write
   to the key/value pairs.

   Extended attributes are file system-agnostic; applications use an
   interface not specific to any file system to manipulate them.
   Applications do not need to be concerned about how the key/value
   pairs are stored internally on the underlying file system. All major
   operating systems provide various flavors of extended attributes.
   Many user space tools allow xattrs to be included in attributes that
   need to be preserved when objects are updated, moved or copied.

   Extended attributes have long been considered unsuitable for
   portability because they are inadequately defined and not formally
   documented by any standard (such as POSIX). However, evidence
   suggests that xattrs are widely deployed and their support in modern
   disk-based file systems is fairly universal.

   There are no clear indications on how xattrs can be mapped to any
   existing recommended or optional file attributes defined in RFC 5661
   [2]; thereby most NFS client implementations ignore application-
   specified xattrs. This results in data loss if one copies, over the
   NFS protocol, a file with xattrs from one file system to another that
   also supports xattrs.

   There is a relatively strong interest in the community in exposing
   xattrs over NFS despite the shortcomings.

   This document discusses why the current NFSv4 named attributes as
   currently standardized in [2], are unsuitable for representing
   xattrs, and proposes alternate language, adjustment and protocol
   mechanisms to support them.

1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [1].

   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
   interpreted as carrying RFC-2119 significance.

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2  Uses

   Applications can store tracking information in extended attributes.
   Examples include storing metadata identifying the application that
   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
   of the file contents along with the date of that signature. Xattrs
   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
   convenient if its source has to be determined in the future.
   Likewise, an email attachment, when saved, can be tagged with the
   message-id of the email, making it possible to trace the original

   Applications may need to behave differently when handling files of
   varying types. For example, file managers, such as GNOME's, offer
   unique icons, different click behavior, and special lists of
   operations to perform depending on the file format. This can be
   achieved by looking at the file extension (Windows), or interpret the
   type by inspecting it (Unix MIME type). Some file managers generate
   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
   custom database. The file manager must work to keep this database in
   sync with the files, which can change without the file manager's
   knowledge. A better approach is to jettison the custom database and
   store such metadata in extended attributes: these are easier to
   maintain, faster to access, and readily accessible by any application

   On Mac OSX, applications such as Dropbox, Skydrive (Onedrive), and
   Google Drive use the extended attribute interface to assign specific
   tags to folders.

   Xattrs can be retrieved and set through system calls or shell
   commands and generally supported by user-space tools (such as copy
   tools) that preserve other file attributes.

   Extended attributes are supported by many file systems.

   In Linux, ext3, ext4, JFS, XFS, Btrfs, among other file systems
   support extended attributes. The getfattr and setfattr utilities can
   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;
   hence these categories are generally qualified as name spaces.
   Currently, four namespaces exist: user, trusted, security and system
   [5]. Recommendations on how they should be used are published by
   freedesktop.org [4].

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   FreeBSD supports extended attributes in two universal namespaces -
   user and system, although individual file systems are allowed to
   implement additional namespaces [6].

   Solaris 9 and later allows files to have extended attributes, but
   implements them as "forks", logically represented as files within a
   hidden directory that is associated with the target file [7].

   In the NTFS file system, extended attributes are one of several
   supported "file streams" [8].

3  Namespaces

   Operating systems may define multiple "namespaces" in which xattrs
   can be set. Namespaces are more than organizational classes; the
   operating system may enforce different access policies and allow
   different capabilities depending on the namespace. Linux, for
   example, defines "security", "system", "trusted" and "user"
   namespaces, the first three being specific to Linux [4].

   Implementations generally agree on the semantics of a "user"
   namespace, that allows applications to store arbitrary user attribute
   data with file system objects. Access to this namespace is controlled
   via the normal file system attributes. As such, getting and setting
   xattrs from the user namespace can be considered interoperable across
   platforms and vendor implementations. Attributes from other
   namespaces are typically platform-specific, but some of them may be
   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 does not propose any language to restrict the key names
   of extended attributes. Future versions, or other related IETF
   documents, may include additional text to enforce namespace prefix to
   key names, formalize names of some well-defined xattrs, or impose
   additional restrictions on the allowed namespaces to user-managed
   metadata only, in order to prevent the development of non-
   interoperable implementations. This document, however, does require
   that the attribute key/value MUST not be interpreted by the NFS
   clients and servers.

4  Differences with Named Attributes

   RFC5661 defines named attributes as opaque byte streams that are
   associated with a directory or file and referred to by a string name
   [2]. Named attributes are intended to be used by client applications
   as a method to associate application-specific data with a regular
   file or directory. In that sense, xattrs are similar in concept and

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   use to named attributes, but there are subtle differences.

   File systems typically define individual xattrs "get" and "set"
   operations as being atomic, although  collectively they may be
   independent. Xattrs generally have size limits ranging from a few
   bytes to several kilobytes; the maximum supported size is not
   universally defined and is usually restricted by the file system.
   Similar to ACLs, the amount of xattr data exchanged between the
   client and server for get/set operations can be considered to fit in
   a single COMPOUND request, bounded by the channel's negotiated
   maximum size for requests. Named attributes, on the other hand, are
   unbounded data streams and do not impose atomicity requirements.

   Individual named attributes are analogous to files, and caching of
   the data for these needs to be handled just as data caching is for
   ordinary files following close-to-open semantics. Xattrs, on the
   other hand, impose caching requirements like other file attributes.

   Named attributes and xattrs have different semantics and belong to
   disjoint namespaces. As a result, mapping one to another is, at best,
   a compromise.

   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
   out some namespace and specifying locking primitives to enforce
   atomicity constraints on individual get/set operations, this is
   problematic.  A client application trying to use xattrs through named
   attributes with a server that supported xattrs directly would get a
   lower level of service, and could fail to cooperate on a local
   application running on the server unless the server file system
   defined its own interoperability constraints. File systems that
   already implement xattrs and named attributes natively would need
   additional guidance such as reserving named attribute namespace
   specifically for implementation purposes.

5  Protocol Enhancements

   This section proposes extensions to the NFSv4 protocol operations to
   allow xattrs to be queried and set by clients. New attributes are
   added to bitmap4 data type to allow xattr support to be queried. This
   follows the guidelines specified in [2] with respect to minor
   versioning. In addition, new operations, namely GETXATTR and
   SETXATTR, are defined to allow xattr key/value to be queried and

5.1  New Attributes

   The following RECOMMENDED attributes are proposed for use with

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   GETATTR. A client can query the server to determine if xattrs are
   supported, the maximum size of the xattrs that are allowed for a file
   system object, and the total current size of all the xattrs for a
   given file system object.

   A client may ask for any of these attributes to be returned by
   setting a bit in the GETATTR request but MUST handle the case where
   the server does not return them.  A client may ask for the set of
   attributes the server supports and SHOULD NOT request attributes the
   server does not support.

   |Name              | Id | Data Type         | Acc | Defined in     |
   | maxxattrsize     | 82 | uint32_t          | R   | Section 5.1.1  |
   | xattrsize        | 83 | uint32_t          | R   | Section 5.1.2  |

5.1.1  Attribute 82: maxxattrsize

   Maximum size in bytes of all the extended attributes per object that
   the object's file system supports. If maxxattrsize is 0, the server
   does not support extended attributes. The protocol does not enforce
   any limits on the number of keys, the length of a key or the size of
   a value, that are allowed for a file, as long as the total size is
   contained by maxxattrsize. The server file system MAY impose
   additional limits. In addition, the total size of xattrs exchanged
   between the client and server for get/set operations is limited by
   the channel's negotiated maximum size for requests and responses.

5.1.2  Attribute 83: xattrsize

   The total size of all the extended attributes of this object in
   bytes. This MUST be less than or equal to maxxattrsize.

5.2  New Operations

   Unlike other file system attributes, xattrs can represent disparate
   metadata most file systems allow disparate metadata to be associated
   with an object through one or more xattrs, and combining them into a
   single attribute is unwieldy. As such, adding new attributes to
   bitmap4 for use in GETATTR and SETATTR is inappropriate to support
   xattr operations. For example, obtaining the value of a single xattr
   using the bitmap 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

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   one to be deleted, and writing out the remaining xattrs. Moreover,
   distinguishing between creating new and replacing existing xattrs on
   an object is not possible with the existing bitmap.

   Applications need to perform the following operations on a given
   file's extended attributes [5]:

   o  Given a file, return a list of all of the file's assigned extended
      attribute keys.

   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 and a key, remove that extended attribute from the

   This section introduces two new operations, GETXATTR and SETXATTR, to
   query and set xattrs. GETXATTR allows listing all the xattrs names,
   names with values, or querying the value of a single name. SETXATTR
   allows deleting a single xattr or replacing a few without modifying
   the rest.

5.2.1  New definitions

   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.

   Future versions of this document or other related IETF documents may
   define specific values for xattr key names, or mechanisms for

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   encoding namespace in xattrname4.

5.2.2  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
   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.
   For GETXATTR, see Section For SETXATTR, see Section

   When the client does not hold a delegation on the file, xattrs
   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
   individual clients may not be coherent. Changes made in one order on
   the server may be seen in a different order on one client and in a
   third order on 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.

5.2.3  GETXATTR - Get extended attributes of a file         ARGUMENTS

        enum getxattr_type4 {
                GETXATTR4_LIST   = 0,
                GETXATTR4_ONE    = 1,
                GETXATTR4_ALL    = 2

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        union getxattr_args4 switch (getxattr_type4 ga_type) {
         case GETXATTR4_ONE:
                xattrname4    ga_name;

        struct GETXATTR4args {
                /* CURRENT_FH: file */
                getxattr_type4     ga_type;
                getxattr_args4     ga_args;
        }; RESULTS

        union getxattr_res4 switch (getxattr_type4 gr_type) {
         case GETXATTR4_LIST:
                xattrname4    gr_names<>;
         case GETXATTR4_ONE:
                xattrvalue4   gr_value;
         case GETXATTR4_ALL:
                xattr4        gr_xattrs<>;

        union GETXATTR4res switch (nfsstat4 gr_status) {
         case NFS4_OK:
                getxattr_res4 gr_resok4;
        }; DESCRIPTION

   The GETXATTR operation will obtain extended attributes for the file
   system object specified by the current filehandle.  The client
   specifies what kind of xattr information it would like the server to
   return through the ga_type argument. GETXATTR4_LIST is used to
   enumerate the set of extended attribute keys assigned to the file.
   GETXATTR4_ONE returns the value of an extended attribute from the
   file, given the key. GETXATTR4_ALL returns the key/value pairs for
   the set of extended attributes assigned to the file.

   The server MUST return the xattr key and/or value that the client
   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, then it MUST NOT return key and/or value and MUST return an
   error. The server also MUST return an error if it supports xattrs on
   the target but cannot obtain the requested data.  In that case, no

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   key/value will be returned. If the xattr keys and/or values contained
   in the server response will exceed the channel's negotiated maximum
   response size, then the server MUST return NFS4ERR_REP_TOO_BIG in
   gr_status. IMPLEMENTATION

   If there is an OPEN_DELEGATE_WRITE delegation held by another client
   for the file in question, and size and/or change are among the set of
   attributes being interrogated in GETATTR, the server can 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 RFC 5661 for details [2].
   Consequently, if a client needs to verify the list of extended
   attributes with the server, it must also query the change attribute
   of the file with GETATTR. This handling is similar to how a client
   would revalidate other file attributes such as ACLs.

5.2.4  SETXATTR - Set extended attributes for a file         ARGUMENTS

        enum setxattr_type4 {
                SETXATTR4_CREATE      = 0,
                SETXATTR4_REPLACE     = 1,
                SETXATTR4_DELETE      = 2,
                SETXATTR4_REPLACE_ALL = 3,
                SETXATTR4_DELETE_ALL  = 4

        union setxattr_args4 switch (setxattr_type4 sa_type) {
         case SETXATTR4_CREATE:
         case SETXATTR4_REPLACE:
         case SETXATTR4_REPLACE_ALL:
                xattr4 sa_xattrs<>;
         case SETXATTR4_DELETE:
                xattrname4 sa_xattrnames<>;
         case SETXATTR4_DELETE_ALL:

        struct SETXATTR4args {
                /* CURRENT_FH: file */
                setxattr_args4 sa_args;

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        union setxattr_res4 switch (setxattr_type4 sr_type) {
         case SETXATTR4_CREATE:
         case SETXATTR4_REPLACE:
         case SETXATTR4_DELETE:
                nfsstat4 sr_res<>;
         case SETXATTR4_REPLACE_ALL:
         case SETXATTR4_DELETE_ALL:

        union SETXATTR4res switch (nfsstat4 sr_status) {
         case NFS4_OK:
                setxattr_res4 sr_array;
        }; DESCRIPTION

   The SETXATTR operation changes one or more of the extended attributes
   of a file system object. The change desired is specified by sr_type.
   SETXATTR4_CREATE is used to associate the specified values with the
   extended attribute keys for the file system object specified by the
   current filehandle. The server MUST return an error if the attribute
   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
   exist. An application can delete all existing xattrs for a file and
   replace them with a new set by using SETXATTR4_REPLACE_ALL.
   SETXATTR4_DELETE can be used to remove the specified xattr keys, if
   they exist. SETXATTR4_DELETE_ALL removes all the xattr keys for the

   While the SETXATTR request MAY contain multiple attribute keys and/or
   values to be changed for a file, this does not impose any atomicity
   considerations on the server implementation. If the server cannot
   update all the attributes for the file atomically, it MUST set them
   in the order specified. In such cases, it is possible that some keys
   are changed successfully while others encounter errors. To handle
   this, contained within the SETXATTR results is a "status" field.  If
   any of the change operations incur an error, then the "status" value
   MUST NOT be NFS4_OK. In this case, the status of the individual
   change operations is returned in sr_array. If the xattr keys and/or
   values contained in the client request exceeds the channel's
   negotiated maximum request size, then the server MUST return
   NFS4ERR_REQ_TOO_BIG in sr_status.

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   A successful SETXATTR SHOULD change the file time_modify and change
   attributes. However, these attributes SHOULD NOT be changed unless
   the xattrs are changed. IMPLEMENTATION

   If the object whose xattrs are being changed has a file delegation
   that is held by a client other than the one doing the SETXATTR, the
   delegation(s) must be recalled, and the operation cannot proceed to
   actually change the xattrs until each such delegation is returned or
   revoked. In all cases in which delegations are recalled, the server
   is likely to return one or more NFS4ERR_DELAY errors while the
   delegation(s) remains outstanding, although it might not do that if
   the delegations are returned quickly.

5.2.5  Valid Errors

   This section contains a table that gives the valid error returns for
   each new protocol operation.  The error code NFS4_OK (indicating no
   error) is not listed but should be understood to be returnable by all
   new operations.  The error values for all other operations are
   defined in Section 15.2 of RFC 5661 [2].

          Valid Error Returns for Each New Protocol Operation

   | Operation            | Errors                                     |
   | GETXATTR             | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR,  |
   |                      | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP,     |
   |                      | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_NOTDIR, |
   |                      | NFS4ERR_PERM, NFS4ERR_REP_TOO_BIG,         |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE   |
   |                      | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR,      |
   |                      | NFS4ERR_BADOWNER, NFS4ERR_BAD_RANGE,       |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,       |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT,      |
   |                      | NFS4ERR_EXIST, NFS4ERR_EXPIRED,            |

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   |                      | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED,           |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO,  |
   |                      | NFS4ERR_LOCKED, NFS4ERR_MOVED,             |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOFILEHANDLE, |
   |                      | NFS4ERR_NOSPC, NFS4ERR_NOTDIR,             |
   |                      | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE,     |
   |                      | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_PERM,   |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_TYPE                         |

5.3  Extensions to ACE Access Mask Attributes

   Two new bitmask constants are proposed for the access mask field:

         const ACE4_GET_XATTRS          = 0x00200000;
         const ACE4_SET_XATTRS          = 0x00400000;

   Permission to get and set the extended attributes of a file. The
   affected operations are GETXATTR and SETXATTR respectively. No
   additional granularity of control is implied by these constants for
   server implementations.

5.4  pNFS Considerations

   Both GETXATTR and SETXATTR are sent to the metadata server, which is
   responsible for coordinating the changes onto the storage devices.

6  Security Considerations

   The additions to the NFS protocol for supporting extended attributes
   do not alter the security considerations of the NFSv4.1 protocol [2].

7  IANA Considerations

   There are no IANA considerations in this document.  All NFSv4.1 IANA
   considerations are covered in [2].

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8  References

8.1  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., "Network
        File System (NFS) Version 4 Minor Version 1 Protocol", RFC 5661,
        January 2010.

   [3]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., "Network
        File System (NFS) Version 4 Minor Version 1 External Data
        Representation Standard (XDR) Description", RFC 5662, January

8.2  Informative References

   [4]  http://www.freedesktop.org/wiki/CommonExtendedAttributes,
        "Guidelines for extended attributes".

   [5]  Love, R., "Linux System Programming: Talking Directly to the
        Kernel and C Library", O'Reilly Media, Inc., 2007.

   [6]  http://www.freebsd.org/cgi/man.cgi?query=extattr&sektion=9,
        "FreeBSD Man Pages - extattr"

   [7]  http://docs.oracle.com/cd/E19253-01/816-5175/6mbba7f02,
        "Oracle Man Pages - fsattr"

   [8]  http://msdn.microsoft.com/en-
        us/library/windows/desktop/aa364404(v=vs.85).aspx, "File

9  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. Valuable input and advice was received from
        Tom Haynes on the first revision of this draft.

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Authors' Addresses

        Manoj Naik
        IBM Almaden
        650 Harry Rd
        San Jose, CA 95120

        Phone: +1 408-927-1707
        Email: mnaik@us.ibm.com

        Marc Eshel
        IBM Almaden
        650 Harry Rd
        San Jose, CA 95120

        Phone: +1 408-927-1894
        Email: eshel@us.ibm.com

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