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-.\" Copyright (C) Andreas Gruenbacher, February 2001
-.\" Copyright (C) Silicon Graphics Inc, September 2001
-.\" Copyright (C) 2015 Heinrich Schuchardt <xypron.glpk@gmx.de>
-.\"
-.\" SPDX-License-Identifier: GPL-2.0-or-later
-.\"
-.TH listxattr 2 2023-10-31 "Linux man-pages 6.7"
-.SH NAME
-listxattr, llistxattr, flistxattr \- list extended attribute names
-.SH LIBRARY
-Standard C library
-.RI ( libc ", " \-lc )
-.SH SYNOPSIS
-.nf
-.B #include <sys/xattr.h>
-.P
-.BI "ssize_t listxattr(const char *" path ", char *_Nullable " list \
-", size_t " size );
-.BI "ssize_t llistxattr(const char *" path ", char *_Nullable " list \
-", size_t " size );
-.BI "ssize_t flistxattr(int " fd ", char *_Nullable " list ", size_t " size );
-.fi
-.SH DESCRIPTION
-Extended attributes are
-.IR name : value
-pairs associated with inodes (files, directories, symbolic links, etc.).
-They are extensions to the normal attributes which are associated
-with all inodes in the system (i.e., the
-.BR stat (2)
-data).
-A complete overview of extended attributes concepts can be found in
-.BR xattr (7).
-.P
-.BR listxattr ()
-retrieves the list
-of extended attribute names associated with the given
-.I path
-in the filesystem.
-The retrieved list is placed in
-.IR list ,
-a caller-allocated buffer whose size (in bytes) is specified in the argument
-.IR size .
-The list is the set of (null-terminated) names, one after the other.
-Names of extended attributes to which the calling process does not
-have access may be omitted from the list.
-The length of the attribute name
-.I list
-is returned.
-.P
-.BR llistxattr ()
-is identical to
-.BR listxattr (),
-except in the case of a symbolic link, where the list of names of
-extended attributes associated with the link itself is retrieved,
-not the file that it refers to.
-.P
-.BR flistxattr ()
-is identical to
-.BR listxattr (),
-only the open file referred to by
-.I fd
-(as returned by
-.BR open (2))
-is interrogated in place of
-.IR path .
-.P
-A single extended attribute
-.I name
-is a null-terminated string.
-The name includes a namespace prefix; there may be several, disjoint
-namespaces associated with an individual inode.
-.P
-If
-.I size
-is specified as zero, these calls return the current size of the
-list of extended attribute names (and leave
-.I list
-unchanged).
-This can be used to determine the size of the buffer that
-should be supplied in a subsequent call.
-(But, bear in mind that there is a possibility that the
-set of extended attributes may change between the two calls,
-so that it is still necessary to check the return status
-from the second call.)
-.SS Example
-The
-.I list
-of names is returned as an unordered array of null-terminated character strings
-(attribute names are separated by null bytes (\[aq]\e0\[aq])),
-like this:
-.P
-.in +4n
-.EX
-user.name1\e0system.name1\e0user.name2\e0
-.EE
-.in
-.P
-Filesystems that implement POSIX ACLs using
-extended attributes might return a
-.I list
-like this:
-.P
-.in +4n
-.EX
-system.posix_acl_access\e0system.posix_acl_default\e0
-.EE
-.in
-.SH RETURN VALUE
-On success, a nonnegative number is returned indicating the size of the
-extended attribute name list.
-On failure, \-1 is returned and
-.I errno
-is set to indicate the error.
-.SH ERRORS
-.TP
-.B E2BIG
-The size of the list of extended attribute names is larger than the maximum
-size allowed; the list cannot be retrieved.
-This can happen on filesystems that support an unlimited number of
-extended attributes per file such as XFS, for example.
-See BUGS.
-.TP
-.B ENOTSUP
-Extended attributes are not supported by the filesystem, or are disabled.
-.TP
-.B ERANGE
-The
-.I size
-of the
-.I list
-buffer is too small to hold the result.
-.P
-In addition, the errors documented in
-.BR stat (2)
-can also occur.
-.SH STANDARDS
-Linux.
-.SH HISTORY
-Linux 2.4,
-glibc 2.3.
-.\" .SH AUTHORS
-.\" Andreas Gruenbacher,
-.\" .RI < a.gruenbacher@computer.org >
-.\" and the SGI XFS development team,
-.\" .RI < linux-xfs@oss.sgi.com >.
-.\" Please send any bug reports or comments to these addresses.
-.SH BUGS
-.\" The xattr(7) page refers to this text:
-As noted in
-.BR xattr (7),
-the VFS imposes a limit of 64\ kB on the size of the extended
-attribute name list returned by
-.BR listxattr ().
-If the total size of attribute names attached to a file exceeds this limit,
-it is no longer possible to retrieve the list of attribute names.
-.SH EXAMPLES
-The following program demonstrates the usage of
-.BR listxattr ()
-and
-.BR getxattr (2).
-For the file whose pathname is provided as a command-line argument,
-it lists all extended file attributes and their values.
-.P
-To keep the code simple, the program assumes that attribute keys and
-values are constant during the execution of the program.
-A production program should expect and handle changes during
-execution of the program.
-For example,
-the number of bytes required for attribute keys
-might increase between the two calls to
-.BR listxattr ().
-An application could handle this possibility using
-a loop that retries the call
-(perhaps up to a predetermined maximum number of attempts)
-with a larger buffer each time it fails with the error
-.BR ERANGE .
-Calls to
-.BR getxattr (2)
-could be handled similarly.
-.P
-The following output was recorded by first creating a file, setting
-some extended file attributes,
-and then listing the attributes with the example program.
-.SS Example output
-.in +4n
-.EX
-$ \fBtouch /tmp/foo\fP
-$ \fBsetfattr \-n user.fred \-v chocolate /tmp/foo\fP
-$ \fBsetfattr \-n user.frieda \-v bar /tmp/foo\fP
-$ \fBsetfattr \-n user.empty /tmp/foo\fP
-$ \fB./listxattr /tmp/foo\fP
-user.fred: chocolate
-user.frieda: bar
-user.empty: <no value>
-.EE
-.in
-.SS Program source (listxattr.c)
-.\" SRC BEGIN (listxattr.c)
-.EX
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/xattr.h>
-\&
-int
-main(int argc, char *argv[])
-{
- char *buf, *key, *val;
- ssize_t buflen, keylen, vallen;
-\&
- if (argc != 2) {
- fprintf(stderr, "Usage: %s path\en", argv[0]);
- exit(EXIT_FAILURE);
- }
-\&
- /*
- * Determine the length of the buffer needed.
- */
- buflen = listxattr(argv[1], NULL, 0);
- if (buflen == \-1) {
- perror("listxattr");
- exit(EXIT_FAILURE);
- }
- if (buflen == 0) {
- printf("%s has no attributes.\en", argv[1]);
- exit(EXIT_SUCCESS);
- }
-\&
- /*
- * Allocate the buffer.
- */
- buf = malloc(buflen);
- if (buf == NULL) {
- perror("malloc");
- exit(EXIT_FAILURE);
- }
-\&
- /*
- * Copy the list of attribute keys to the buffer.
- */
- buflen = listxattr(argv[1], buf, buflen);
- if (buflen == \-1) {
- perror("listxattr");
- exit(EXIT_FAILURE);
- }
-\&
- /*
- * Loop over the list of zero terminated strings with the
- * attribute keys. Use the remaining buffer length to determine
- * the end of the list.
- */
- key = buf;
- while (buflen > 0) {
-\&
- /*
- * Output attribute key.
- */
- printf("%s: ", key);
-\&
- /*
- * Determine length of the value.
- */
- vallen = getxattr(argv[1], key, NULL, 0);
- if (vallen == \-1)
- perror("getxattr");
-\&
- if (vallen > 0) {
-\&
- /*
- * Allocate value buffer.
- * One extra byte is needed to append 0x00.
- */
- val = malloc(vallen + 1);
- if (val == NULL) {
- perror("malloc");
- exit(EXIT_FAILURE);
- }
-\&
- /*
- * Copy value to buffer.
- */
- vallen = getxattr(argv[1], key, val, vallen);
- if (vallen == \-1) {
- perror("getxattr");
- } else {
- /*
- * Output attribute value.
- */
- val[vallen] = 0;
- printf("%s", val);
- }
-\&
- free(val);
- } else if (vallen == 0) {
- printf("<no value>");
- }
-\&
- printf("\en");
-\&
- /*
- * Forward to next attribute key.
- */
- keylen = strlen(key) + 1;
- buflen \-= keylen;
- key += keylen;
- }
-\&
- free(buf);
- exit(EXIT_SUCCESS);
-}
-.EE
-.\" SRC END
-.SH SEE ALSO
-.BR getfattr (1),
-.BR setfattr (1),
-.BR getxattr (2),
-.BR open (2),
-.BR removexattr (2),
-.BR setxattr (2),
-.BR stat (2),
-.BR symlink (7),
-.BR xattr (7)
generated by cgit v1.2.3 (git 2.39.1) at 2024-10-31 11:04:29 +0000