Extended attributes are
name:
value pairs associated with inodes (files, directories, symlinks, 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
attr(5).
setxattr() sets the
value of the extended attribute identified by
name and associated with the given
path in the filesystem.
The
size of the
value must be specified.
lsetxattr() is identical to
setxattr(), except in the case of a symbolic link, where the extended attribute is
set on the link itself, not the file that it refers to.
fsetxattr() is identical to
setxattr(), only the extended attribute is set on the open file pointed to by
filedes (as returned by
open(2))
in place of
path.
An extended attribute name is a simple 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 of specified length.
The
flags parameter can be used to refine the semantics of the operation.
XATTR_CREATE specifies a pure create, which fails if the named
attribute exists already.
XATTR_REPLACE specifies a pure replace operation, which fails if the
named attribute does not already exist.
By default (no flags), the extended attribute will be created if
need be, or will simply replace the value if the attribute exists.
On success, zero is returned.
On failure, -1 is returned and
errno is set appropriately.
If XATTR_CREATE is specified, and the attribute exists already,
errno is set to EEXIST.
If XATTR_REPLACE is specified, and the attribute does not exist,
errno is set to ENOATTR.
If there is insufficient space remaining to store the extended attribute,
errno is set to either ENOSPC, or EDQUOT if quota enforcement was the cause.
If extended attributes are not supported by the filesystem, or are disabled,
errno is set to ENOTSUP.
The errors documented for the
stat(2)
system call are also applicable here.