afs: Implement sillyrename for unlink and rename

Implement sillyrename for AFS unlink and rename, using the NFS variant
implementation as a basis.

Note that the asynchronous file locking extender/releaser has to be
notified with a state change to stop it complaining if there's a race
between that and the actual file deletion.

A tracepoint, afs_silly_rename, is also added to note the silly rename and
the cleanup.  The afs_edit_dir tracepoint is given some extra reason
indicators and the afs_flock_ev tracepoint is given a silly-delete file
lock cancellation indicator.

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

fs/afs/super.c

@@ -45,7 +45,7 @@ struct file_system_type afs_fs_type = {
 	.init_fs_context	= afs_init_fs_context,
 	.parameters		= &afs_fs_parameters,
 	.kill_sb		= afs_kill_super,
-	.fs_flags		= 0,
+	.fs_flags		= FS_RENAME_DOES_D_MOVE,
 };
 MODULE_ALIAS_FS("afs");
 
@@ -656,6 +656,8 @@ static struct inode *afs_alloc_inode(struct super_block *sb)
 	vnode->cb_type		= 0;
 	vnode->lock_state	= AFS_VNODE_LOCK_NONE;
 
+	init_rwsem(&vnode->rmdir_lock);
+
 	_leave(" = %p", &vnode->vfs_inode);
 	return &vnode->vfs_inode;
 }