SETXATTR(2) System Calls Manual SETXATTR(2)

setxattr, fsetxattr — set an extended attribute value

#include <sys/xattr.h>

int
setxattr(const char *path, const char *name, void *value, size_t size, u_int32_t position, int options);

int
fsetxattr(int fd, const char *name, void *value, size_t size, u_int32_t position, int options);

Extended attributes extend the basic attributes associated with files and directories in the file system. They are stored as name:data pairs associated with file system objects (files, directories, symlinks, etc).

() associates name and data together as an attribute of path.

An extended attribute's name is a simple NULL-terminated UTF-8 string. Value is a pointer to a data buffer of size bytes containing textual or binary data to be associated with the extended attribute. Position specifies the offset within the extended attribute. In the current implementation, only the resource fork extended attribute makes use of this argument. For all others, position is reserved and should be set to zero.

options controls how the attribute is set:

do not follow symbolic links. () normally sets attributes on the target of path if it is a symbolic link. With this option, setxattr() will act on the link itself.
do not follow any symbolic links encountered during pathname resolution. An error is returned if a symlink is encountered before the last component of path.
fail if the named attribute already exists.
fail if the named attribute does not exist. Failure to specify XATTR_REPLACE or XATTR_CREATE allows creation and replacement.

() is identical to setxattr(), except that it sets an extended attribute on an open file referenced by file descriptor fd.

On some filesystems, such as HFS+, setting the extended attribute com.apple.ResourceFork will update the modification time (``mtime'') of the file.

Due to historical reasons, the XATTR_FINDERINFO_NAME (defined to be “com.apple.FinderInfo”) extended attribute must be 32 bytes; see the ATTR_CMN_FNDRINFO section in getattrlist(2).

The maximum supported size of extended attribute can be found out using pathconf(2) with _PC_XATTR_SIZE_BITS option.

On success, 0 is returned. On failure, -1 is returned and the global variable errno is set as follows.

[]
options contains XATTR_CREATE and the named attribute already exists.
[]
options is set to XATTR_REPLACE and the named attribute does not exist.
[]
The file system does not support extended attributes or has them disabled.
[]
The file system is mounted read-only.
[]
The data size of the attribute is out of range (some attributes have size restrictions).
[]
Attributes cannot be associated with this type of object. For example, attributes are not allowed for resource forks.
[]
name or options is invalid. name must be valid UTF-8 and options must make sense.
[]
XATTR_NOFOLLOW or XATTR_NOFOLLOW_ANY option was passed in fsetxattr().
[]
A component of path is not a directory.
[]
name exceeded XATTR_MAXNAMELEN UTF-8 bytes, or a component of path exceeded NAME_MAX characters, or the entire path exceeded PATH_MAX characters.
[]
Search permission is denied for a component of path or permission to set the attribute is denied.
[]
Too many symbolic links were encountered resolving path.
[]
If XATTR_NOFOLLOW_ANY option was passed and a symbolic link was encountered in translating the pathname.
[]
path or name points to an invalid address.
[]
An I/O error occurred while reading from or writing to the file system.
[]
The data size of the extended attribute is too large.
[]
Not enough space left on the file system.

getxattr(2), listxattr(2), removexattr(2), pathconf(2)

setxattr() and fsetxattr() first appeared in Mac OS X 10.4.

October 19, 2004 Mac OS X