#include <sys/types.h>
#include <sys/xattr.h>
int setxattr(const char *path, const char *name,
const void *value, size_t size, int flags);
int lsetxattr(const char *path, const char *name,
const void *value, size_t size, int flags);
int fsetxattr(int fd, const char *name,
const void *value, size_t size, int flags);
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 referred to by fd (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 argument 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.
In addition, the errors documented in stat(2) can also occur.