Retrieve an extended attribute value
#include <sys/types.h> #include <attr/xattr.h> ssize_t getxattr (const char *path, const char *name, \t\t\t\t void *value, size_t size); ssize_t lgetxattr (const char *path, const char *name, \t\t\t\t void *value, size_t size); ssize_t fgetxattr (int filedes, const char *name, \t\t\t\t void *value, size_t size);
Extended attributes are name:.Ivalue 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).
getxattr retrieves the value of the extended attribute identified by name and associated with the given path in the filesystem. The length of the attribute value is returned.
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 pointed to by filedes (as returned by open(2)) is interrogated 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.
An empty buffer of size zero can be passed into these calls to return the current size of the named extended attribute, which can be used to estimate the size of a buffer which is sufficiently large to hold the value associated with the extended attribute.
The interface is designed to allow guessing of initial buffer sizes, and to enlarge buffers when the return value indicates that the buffer provided was too small.
On success, a positive number is returned indicating the size of the extended attribute value. On failure, -1 is returned and errno is set appropriately.
If the named attribute does not exist, or the process has no access to this attribute, errno is set to ENOATTR.
If the size of the value buffer is too small to hold the result, errno is set to ERANGE.
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.
Andreas Gruenbacher, <[email protected]> and the SGI XFS development team, <[email protected]>. Please send any bug reports or comments to these addresses.