Provided by: manpages-dev_5.02-1_all bug

NAME

       listxattr, llistxattr, flistxattr - list extended attribute names

SYNOPSIS

       #include <sys/types.h>
       #include <sys/xattr.h>

       ssize_t listxattr(const char *path, char *list, size_t size);
       ssize_t llistxattr(const char *path, char *list, size_t size);
       ssize_t flistxattr(int fd, char *list, size_t size);

DESCRIPTION

       Extended  attributes  are  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 stat(2) data).  A complete overview of extended
       attributes concepts can be found in xattr(7).

       listxattr() retrieves the list of extended attribute names associated with the given  path
       in  the filesystem.  The retrieved list is placed in list, a caller-allocated buffer whose
       size (in bytes) is specified in the  argument  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 list is returned.

       llistxattr() is identical to 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.

       flistxattr()  is  identical  to  listxattr(),  only  the  open  file referred to by fd (as
       returned by open(2)) is interrogated in place of path.

       A single extended attribute name  is  a  null-terminated  string.   The  name  includes  a
       namespace  prefix; there may be several, disjoint namespaces associated with an individual
       inode.

       If size is specified as zero, these calls return the current size of the list of  extended
       attribute names (and leave 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.)

   Example
       The list of names is returned as an unordered array of null-terminated  character  strings
       (attribute names are separated by null bytes ('\0')), like this:

           user.name1\0system.name1\0user.name2\0

       Filesystems  that  implement POSIX ACLs using extended attributes might return a list like
       this:

           system.posix_acl_access\0system.posix_acl_default\0

RETURN VALUE

       On success, a nonnegative number is returned indicating the size of the extended attribute
       name list.  On failure, -1 is returned and errno is set appropriately.

ERRORS

       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.

       ENOTSUP
              Extended attributes are not supported by the filesystem, or are disabled.

       ERANGE The size of the list buffer is too small to hold the result.

       In addition, the errors documented in stat(2) can also occur.

VERSIONS

       These system calls have been available  on  Linux  since  kernel  2.4;  glibc  support  is
       provided since version 2.3.

CONFORMING TO

       These system calls are Linux-specific.

BUGS

       As  noted  in  xattr(7),  the  VFS  imposes  a  limit of 64 kB on the size of the extended
       attribute name list returned by 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.

EXAMPLE

       The following program demonstrates the usage of listxattr() and getxattr(2).  For the file
       whose  pathname  is  provided  as  a  command-line  argument,  it  lists all extended file
       attributes and their values.

       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 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 ERANGE.
       Calls to getxattr(2) could be handled similarly.

       The following output was recorded by first creating a file,  setting  some  extended  file
       attributes, and then listing the attributes with the example program.

   Example output
           $ touch /tmp/foo
           $ setfattr -n user.fred -v chocolate /tmp/foo
           $ setfattr -n user.frieda -v bar /tmp/foo
           $ setfattr -n user.empty /tmp/foo
           $ ./listxattr /tmp/foo
           user.fred: chocolate
           user.frieda: bar
           user.empty: <no value>

   Program source (listxattr.c)
       #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);
       }

SEE ALSO

       getfattr(1),  setfattr(1),  getxattr(2),  open(2),  removexattr(2),  setxattr(2), stat(2),
       symlink(7), xattr(7)

COLOPHON

       This page is part of release 5.02 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at https://www.kernel.org/doc/man-pages/.