Internet DRAFT - draft-naik-nfsv4-xattrs
draft-naik-nfsv4-xattrs
NFSv4 Working Group M. Naik
Internet Draft M. Eshel
Intended Status: Standards Track IBM Almaden
Expires: January 7, 2016 July 6, 2015
Support for File System Extended Attributes in NFSv4
draft-naik-nfsv4-xattrs-02
Abstract
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
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Copyright and License Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 File System Support . . . . . . . . . . . . . . . . . . . . . . 5
4 Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5 Differences with Named Attributes . . . . . . . . . . . . . . . 6
6 Protocol Enhancements . . . . . . . . . . . . . . . . . . . . . 7
6.1 New Attributes . . . . . . . . . . . . . . . . . . . . . . 7
6.1.1 Attribute 82: xattr_support . . . . . . . . . . . . . . 7
6.2 New Operations . . . . . . . . . . . . . . . . . . . . . . 7
6.2.1 New definitions . . . . . . . . . . . . . . . . . . . . 8
6.2.2 Caching . . . . . . . . . . . . . . . . . . . . . . . . 9
6.2.3 GETXATTR - Get an extended attribute of a file . . . . 9
6.2.4 SETXATTR - Set an extended attribute of a file . . . . 10
6.2.5 LISTXATTR - List extended attributes of a file . . . . 12
6.2.6 REMOVEXATTR - Remove an extended attribute of a file . 13
6.2.7 Valid Errors . . . . . . . . . . . . . . . . . . . . . 14
6.3 Extensions to ACE Access Mask Attributes . . . . . . . . . 16
6.4 pNFS Considerations . . . . . . . . . . . . . . . . . . . . 16
7 Security Considerations . . . . . . . . . . . . . . . . . . . . 16
8 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 16
9 References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1 Normative References . . . . . . . . . . . . . . . . . . . 17
9.2 Informative References . . . . . . . . . . . . . . . . . . 17
10 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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 Use Cases
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
message.
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
[5].
Swift, the OpenStack distributed object store, uses xattrs to store
an object's metadata along with all the data together in one file.
Swift-on-File [9] transfers the responsibility of maintaining object
durability and availability to the underlying file system. Today,
this requires a native file system client to mount the volumes. Xattr
support in NFS would open up the possibility of storing and consuming
data from other storage systems, and facilitate the migration of data
between different backend storage systems.
Baloo, the file indexing and search framework for KDE, has moved to
storing metadata such as tags, ratings and comments, in file system
xattrs instead of a custom database for simplicity. Starting with KDE
Plasma 5.1, NFS is no longer supported due to its lack of xattr
support [10].
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3 File System Support
Extended attributes are supported by most modern 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 have been published
[4].
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].
Xattrs can be retrieved and set through system calls or shell
commands and generally supported by user-space tools that preserve
other file attributes. For example, the "rsync" remote copy program
will correctly preserve user extended attributes between Linux/ext4
and OSX/hfs by stripping off the Linux-specific "user." prefix.
4 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
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key can avoid conflicting use of attributes.
This document restricts the allowed namespaces to user-managed
metadata only, in order to prevent the development of non-
interoperable implementations. It requires that the attribute
key/value MUST not be interpreted by the NFS clients and servers.
5 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
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.
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6 Protocol Enhancements
This section proposes extensions to the NFSv4 protocol operations to
allow xattrs to be queried and modified by clients. A new attribute
is 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, SETXATTR,
LISTXATTR and REMOVEXATTR are defined to allow xattr key/value to be
queried and set.
6.1 New Attributes
The following RECOMMENDED attribute is proposed for use with GETATTR.
A client can query the server to determine if xattrs are supported by
setting the xattr_support bit in the GETATTR request.
+------------------+----+-------------------+-----+----------------+
|Name | Id | Data Type | Acc | Defined in |
+------------------+----+-------------------+-----+----------------+
| xattr_support | 82 | bool | R | Section 6.1.1 |
+------------------+----+-------------------+-----+----------------+
6.1.1 Attribute 82: xattr_support
True, if the object's file system supports extended attributes.
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
of xattrs that are allowed for a file. The server file system MAY
impose additional limits. In addition, a single xattr key or value
exchanged between the client and server for get/set operations is
limited by the channel's negotiated maximum size for requests and
responses.
6.2 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
one to be deleted, and writing out the remaining xattrs. Moreover,
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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
file.
This section introduces four new operations, GETXATTR, SETXATTR,
LISTXATTR and REMOVEXATTR, to query, set, list and remove xattrs
respectively. GETXATTR allows obtaining the value of an xattr key,
SETXATTR allows creating or replacing an xattr key with a value,
LISTXATTR enumerates all the xattrs names, and REMOVEXATTR allows
deleting a single xattr.
6.2.1 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.
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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
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
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.
6.2.3 GETXATTR - Get an extended attribute of a file
6.2.3.1 ARGUMENTS
struct GETXATTR4args {
/* CURRENT_FH: file */
xattrname4 ga_name;
};
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6.2.3.2 RESULTS
union GETXATTR4res switch (nfsstat4 gr_status) {
case NFS4_OK:
xattrvalue4 gr_value;
default:
void;
};
6.2.3.3 DESCRIPTION
The GETXATTR operation will obtain the value for the given extended
attribute key for the file system object specified by the current
filehandle.
The server MUST return the xattr value for the key 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 a 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 value will be
returned. If the xattr value 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.
6.2.3.4 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.
6.2.4 SETXATTR - Set an extended attribute of a file
6.2.4.1 ARGUMENTS
enum setxattr_type4 {
SETXATTR4_CREATE = 0,
SETXATTR4_REPLACE = 1,
};
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struct SETXATTR4args {
/* CURRENT_FH: file */
setxattr_type4 sa_type;
xattr4 sa_xattr;
};
6.2.4.2 RESULTS
union SETXATTR4res switch (nfsstat4 sr_status) {
case NFS4_OK:
void;
default:
void;
};
6.2.4.3 DESCRIPTION
The SETXATTR operation changes one extended attribute of a file
system object. The change desired is specified by sa_type.
SETXATTR4_CREATE is used to associate the given value with the given
extended attribute key 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.
If the xattr key and/or value 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. If the server file system
imposes additional limits on the size of key name or value, it MAY
return NFS4ERR_ENOSPC.
A successful SETXATTR SHOULD change the file time_modify and change
attributes. However, these attributes SHOULD NOT be changed unless
the xattrs are changed.
6.2.4.4 IMPLEMENTATION
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
delegation(s) must be recalled, and the operation cannot proceed to
actually change the xattr 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.
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6.2.5 LISTXATTR - List extended attributes of a file
6.2.5.1 ARGUMENTS
struct LISTXATTR4args {
/* CURRENT_FH: file */
nfs_cookie4 la_cookie;
count4 la_maxcount;
};
5.2.5.2 RESULTS
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;
};
6.2.5.3 DESCRIPTION
The LISTXATTR operation retrieves a variable number of extended
attribute keys from the file system object specified by the current
filehandle, along with information to allow the client to request
additional attribute keys in a subsequent LISTXATTR.
The arguments contain a cookie value that represents where the
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
list. For subsequent LISTXATTR requests, the client specifies a
cookie value that is provided by the server on a previous LISTXATTR
request.
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
should be lr_cookieverf as returned by the server. The la_cookieverf
must match that returned by the LISTXATTR in which the cookie was
acquired. If the server determines that the la_cookieverf is no
longer valid for the directory, the error NFS4ERR_NOT_SAME must be
returned.
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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
returned within the LISTXATTR4resok structure and includes the XDR
overhead. The server may return less data. If the server is unable
to return a single xattr name within the maxcount limit, the error
NFS4ERR_TOOSMALL will be returned to the client.
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
there are no more keys for the object.
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
the client for subsequent LISTXATTR operations so that it may
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
the client. Ideally, the cookie value should not change if the object
xattr values is modified since the client may be caching these
values.
On success, the current filehandle retains its value.
6.2.5.4 IMPLEMENTATION
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
manage cookie values that may become stale. It should be a rare
occurrence that a server is unable to continue properly listing
xattrs with the provided cookie/cookieverf pair. The server should
make every effort to avoid this condition since the application at
the client may not be able to properly handle this type of failure.
The use of the ls_cookieverf will also protect the client from using
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
the same cookie values to service LISTXATTR as the previous server
used. With the client providing the ls_cookieverf, the server is
able to provide the appropriate response to the client. This
prevents the case where the server may accept a cookie value but the
underlying object xattrs have changed and the response is invalid
from the client's context of its previous LISTXATTR.
6.2.6 REMOVEXATTR - Remove an extended attribute of a file
6.2.6.1 ARGUMENTS
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struct REMOVEXATTR4args {
/* CURRENT_FH: file */
xattrname4 ra_name;
};
6.2.6.2 RESULTS
union REMOVEXATTR4res switch (nfsstat4 rr_status) {
case NFS4_OK:
void;
default:
void;
};
6.2.6.3 DESCRIPTION
The REMOVEXATTR operation deletes one extended attribute of a file
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
the client request exceeds the channel's negotiated maximum request
size, then the server MUST return NFS4ERR_REQ_TOO_BIG in rr_status.
A successful REMOVEXATTR SHOULD change the file time_modify and
change attributes. However, these attributes SHOULD NOT be changed
unless the xattr is not removed.
6.2.6.4 IMPLEMENTATION
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
delegation(s) must be recalled, and the operation cannot proceed to
delete the xattr 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.
6.2.7 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
+----------------------+--------------------------------------------+
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| 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 |
| SETXATTR | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | 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, |
| | 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 |
| 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_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, |
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| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE |
| REMOVEXATTR | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED, |
| | 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, |
| | 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_RETRY_UNCACHED_REP, NFS4ERR_ROFS, |
| | NFS4ERR_SERVERFAULT, NFS4ERR_STALE, |
| | NFS4ERR_TOO_MANY_OPS, |
| | NFS4ERR_UNKNOWN_LAYOUTTYPE, |
| | NFS4ERR_WRONG_TYPE |
+----------------------+--------------------------------------------+
6.3 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/list and set/remove the extended attributes of a
file. The affected operations are GETXATTR/LISTXATTR and
SETXATTR/REMOVEXATTR respectively. No additional granularity of
control is implied by these constants for server implementations.
6.4 pNFS Considerations
All xattr operations are sent to the metadata server, which is
responsible for coordinating the changes onto the storage devices.
7 Security Considerations
The additions to the NFS protocol for supporting extended attributes
do not alter the security considerations of the NFSv4.1 protocol [2].
8 IANA Considerations
All IANA considerations are covered in [2].
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9 References
9.1 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
2010.
9.2 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
Streams"
[9] Swift-on-File: https://github.com/stackforge/swiftonfile
[10] KDE Planet: http://vhanda.in/blog/2014/08/extended-attributes-
updates/
10 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 on
earlier revisions of this draft from several people on the NFSv4
mailing list, including Tom Haynes, Christoph Hellwig and Nico
Williams.
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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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