getxattr, lgetxattr, fgetxattr - retrieve an extended attribute value
#include <sys/types.h>
#include <sys/xattr.h>
ssize_t getxattr(const char *path, const char *name,
void *value, size_t size);
ssize_t lgetxattr(const char *path, const char *name,
void *value, size_t size);
ssize_t fgetxattr(int fd, const char *name,
void *value, size_t size);
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).
getxattr() retrieves the value of the extended attribute identified by
name and associated with the given
path in the filesystem. The
attribute value is placed in the buffer pointed to by
value;
size specifies the size of that buffer. The return value of the call is
the number of bytes placed in
value.
lgetxattr() is identical to
getxattr(), except in the case of a
symbolic link, where the link itself is interrogated, not the file that it
refers to.
fgetxattr() is identical to
getxattr(), only the open file
referred to by
fd (as returned by
open(2)) is interrogated in
place of
path.
An 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. The value of an extended attribute is a chunk of
arbitrary textual or binary data that was assigned using
setxattr(2).
If
size is specified as zero, these calls return the current size of the
named extended attribute (and leave
value 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 attribute value
may change between the two calls, so that it is still necessary to check the
return status from the second call.)
On success, these calls return a nonnegative value which is the size (in bytes)
of the extended attribute value. On failure, -1 is returned and
errno
is set appropriately.
- E2BIG
- The size of the attribute value is larger than the maximum size allowed;
the attribute cannot be retrieved. This can happen on filesystems that
support very large attribute values such as NFSv4, for example.
- ENODATA
- The named attribute does not exist, or the process has no access to this
attribute.
- ENOTSUP
- Extended attributes are not supported by the filesystem, or are
disabled.
- ERANGE
- The size of the value buffer is too small to hold the
result.
In addition, the errors documented in
stat(2) can also occur.
These system calls have been available on Linux since kernel 2.4; glibc support
is provided since version 2.3.
These system calls are Linux-specific.
See
listxattr(2).
getfattr(1),
setfattr(1),
listxattr(2),
open(2),
removexattr(2),
setxattr(2),
stat(2),
symlink(7),
xattr(7)