afs: Get an AFS3 ACL as an xattr

Implement an xattr on AFS files called "afs.acl" that retrieves a file's
ACL.  It returns the raw AFS3 ACL from the result of calling FS.FetchACL,
leaving any interpretation to userspace.

Note that whilst YFS servers will respond to FS.FetchACL, this will render
a more-advanced YFS ACL down.  Use "afs.yfs.acl" instead for that.

Signed-off-by: David Howells <dhowells@redhat.com>

fs/afs/internal.h

@@ -977,6 +977,13 @@ extern int afs_fs_fetch_status(struct afs_fs_cursor *, struct afs_net *,
 			       struct afs_fid *, struct afs_file_status *,
 			       struct afs_callback *, struct afs_volsync *);
 
+struct afs_acl {
+	u32	size;
+	u8	data[];
+};
+
+extern struct afs_acl *afs_fs_fetch_acl(struct afs_fs_cursor *);
+
 /*
  * fs_probe.c
  */