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Diffstat (limited to 'man2/listxattr.2')
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diff --git a/man2/listxattr.2 b/man2/listxattr.2 new file mode 100644 index 0000000..58f5ce0 --- /dev/null +++ b/man2/listxattr.2 @@ -0,0 +1,322 @@ +.\" 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 2023-05-03 "Linux man-pages 6.05.01" +.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> +.PP +.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). +.PP +.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. +.PP +.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. +.PP +.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 . +.PP +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. +.PP +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: +.PP +.in +4n +.EX +user.name1\e0system.name1\e0user.name2\e0 +.EE +.in +.PP +Filesystems that implement POSIX ACLs using +extended attributes might return a +.I list +like this: +.PP +.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. +.PP +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. +.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) +.\" 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) |