List extended attribute names
#include <sys/types.h> #include <attr/xattr.h> ssize_t listxattr (const char *path, \t\t\t\t char *list, size_t size); ssize_t llistxattr (const char *path, \t\t\t\t char *list, size_t size); ssize_t flistxattr (int filedes, \t\t\t\t char *list, size_t size);
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).
listxattr retrieves the list of extended attribute names associated with the given path in the filesystem. The list is the set of (NULL-terminated) names, one after the other. Names of extended attributes to which the calling process does not have access may be omitted from the list. The length of the attribute name list is returned.
llistxattr is identical to listxattr, except in the case of a symbolic link, where the list of names of extended attributes associated with the link itself is retrieved, not the file that it refers to. list is a caller-allocated buffer of size size.
flistxattr is identical to listxattr, only the open file pointed to by filedes (as returned by open(2)) is interrogated in place of path.
A single 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.
An empty buffer of size zero can be passed into these calls to return the current size of the list of extended attribute names, which can be used to estimate the size of a buffer which is sufficiently large to hold the list of names.
The list of names is returned as an unordered array of NULL-terminated character strings (attribute names are separated by NULL characters), like this:
user.name1\0system.name1\0user.name2\0
Filesystems like ext2, ext3 and XFS which implement POSIX ACLs using extended attributes, might return a list like this:
system.posix_acl_access\0system.posix_acl_default\0
On success, a positive number is returned indicating the size of the extended attribute name list. On failure, -1 is returned and errno is set appropriately.
If the size of the list 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.