+.\" Copyright (C) Andreas Gruenbacher, February 2001
+.\" Copyright (C) Silicon Graphics Inc, September 2001
+.\" Copyright (C) 2015 Heinrich Schuchardt <xypron.glpk@gmx.de>
.\"
-.\" Extended attributes system calls manual pages
-.\"
-.\" (C) Andreas Gruenbacher, February 2001
-.\" (C) Silicon Graphics Inc, September 2001
-.\"
+.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public
-.\" License along with this manual; if not, write to the Free
-.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
-.\" USA.
+.\" License along with this manual; if not, see
+.\" <http://www.gnu.org/licenses/>.
+.\" %%%LICENSE_END
.\"
-.TH LISTXATTR 2 2001-12-01 "Linux" "Linux Programmer's Manual"
+.TH LISTXATTR 2 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
listxattr, llistxattr, flistxattr \- list extended attribute names
.SH SYNOPSIS
.fam C
.nf
.B #include <sys/types.h>
-.B #include <attr/xattr.h>
-.sp
+.B #include <sys/xattr.h>
+.PP
.BI "ssize_t listxattr(const char\ *" path ", char\ *" list \
", size_t " size );
.BI "ssize_t llistxattr(const char\ *" path ", char\ *" list \
.fi
.fam T
.SH DESCRIPTION
-Extended attributes are name:value
+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 attr (5).
+.BR xattr (7).
.PP
.BR listxattr ()
-retrieves the
-.I list
+retrieves the list
of extended attribute names associated with the given
.I path
-in the file system.
+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.
.PP
A single extended attribute
.I name
-is a simple null-terminated string.
+is a null-terminated string.
The name includes a namespace prefix; there may be several, disjoint
namespaces associated with an individual inode.
.PP
-An empty buffer of
+If
.I size
-zero can be passed into these calls to return the current size of the
-list of extended attribute names, which can be used to estimate the
-size of a buffer which is sufficiently large to hold the list of names.
+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 (\'\\0\')), like this:
-.fam C
-.RS
-.nf
-
+strings (attribute names are separated by null bytes (\(aq\\0\(aq)), like this:
+.PP
+.in +4n
+.EX
user.name1\\0system.name1\\0user.name2\\0
-.fi
-.RE
-.fam T
-.P
-Filesystems like ext2, ext3 and XFS which implement POSIX ACLs using
-extended attributes, might return a
+.EE
+.in
+.PP
+Filesystems that implement POSIX ACLs using
+extended attributes might return a
.I list
like this:
-.fam C
-.RS
-.nf
-
+.PP
+.in +4n
+.EX
system.posix_acl_access\\0system.posix_acl_default\\0
-.fi
-.RE
-.fam T
+.EE
+.in
.SH RETURN VALUE
-On success, a positive number is returned indicating the size of the
+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 appropriately.
-.PP
-If the
+.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,
-.I errno
-is set to
-.BR ERANGE .
+buffer is too small to hold the result.
.PP
-If extended attributes are not supported by the file system, or are disabled,
-.I errno
-is set to
-.BR ENOTSUP .
-.PP
-The errors documented for the
+In addition, the errors documented in
.BR stat (2)
-system call are also applicable here.
+can also occur.
.SH VERSIONS
These system calls have been available on Linux since kernel 2.4;
glibc support is provided since version 2.3.
-.SH "CONFORMING TO"
+.SH CONFORMING TO
These system calls are Linux-specific.
.\" .SH AUTHORS
.\" Andreas Gruenbacher,
.\" 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 (7).
+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 EXAMPLE
+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.
+.PP
+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.
+.PP
+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)
+.EX
+#include <malloc.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/xattr.h>
+
+int
+main(int argc, char *argv[])
+{
+ ssize_t buflen, keylen, vallen;
+ char *buf, *key, *val;
+
+ if (argc != 2) {
+ fprintf(stderr, "Usage: %s path\\n", 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.\\n", 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("\\n");
+
+ /*
+ * Forward to next attribute key.
+ */
+ keylen = strlen(key) + 1;
+ buflen \-= keylen;
+ key += keylen;
+ }
+
+ free(buf);
+ exit(EXIT_SUCCESS);
+}
+.EE
.SH SEE ALSO
.BR getfattr (1),
.BR setfattr (1),
.BR removexattr (2),
.BR setxattr (2),
.BR stat (2),
-.BR attr (5)
+.BR symlink (7),
+.BR xattr (7)
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