afs: Add metadata xattrs

Add xattrs to allow the user to get/set metadata in lieu of having pioctl()
available.  The following xattrs are now available:

 - "afs.cell"

   The name of the cell in which the vnode's volume resides.

 - "afs.fid"

   The volume ID, vnode ID and vnode uniquifier of the file as three hex
   numbers separated by colons.

 - "afs.volume"

   The name of the volume in which the vnode resides.

For example:

	# getfattr -d -m ".*" /mnt/scratch
	getfattr: Removing leading '/' from absolute path names
	# file: mnt/scratch
	afs.cell="mycell.myorg.org"
	afs.fid="10000b:1:1"
	afs.volume="scratch"

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 4e25566..82e1655 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -731,6 +731,11 @@
 extern int afs_flush(struct file *, fl_owner_t);
 extern int afs_fsync(struct file *, loff_t, loff_t, int);
 
+/*
+ * xattr.c
+ */
+extern const struct xattr_handler *afs_xattr_handlers[];
+extern ssize_t afs_listxattr(struct dentry *, char *, size_t);
 
 /*****************************************************************************/
 /*