fuse: lockd support

If fuse filesystem doesn't define it's own lock operations, then allow the
lock manager to work with fuse.

Adding lockd support for remote locking is also possible, but more rarely
used, so leave it till later.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: David Teigland <teigland@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/fuse/file.c

@@ -1341,6 +1341,11 @@ static int fuse_setlk(struct file *file, struct file_lock *fl, int flock)
 	pid_t pid = fl->fl_type != F_UNLCK ? current->tgid : 0;
 	int err;
 
+	if (fl->fl_lmops && fl->fl_lmops->fl_grant) {
+		/* NLM needs asynchronous locks, which we don't support yet */
+		return -ENOLCK;
+	}
+
 	/* Unlock on close is handled by the flush method */
 	if (fl->fl_flags & FL_CLOSE)
 		return 0;
@@ -1365,7 +1370,9 @@ static int fuse_file_lock(struct file *file, int cmd, struct file_lock *fl)
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	int err;
 
-	if (cmd == F_GETLK) {
+	if (cmd == F_CANCELLK) {
+		err = 0;
+	} else if (cmd == F_GETLK) {
 		if (fc->no_lock) {
 			posix_test_lock(file, fl);
 			err = 0;
@@ -1373,7 +1380,7 @@ static int fuse_file_lock(struct file *file, int cmd, struct file_lock *fl)
 			err = fuse_getlk(file, fl);
 	} else {
 		if (fc->no_lock)
-			err = posix_lock_file_wait(file, fl);
+			err = posix_lock_file(file, fl, NULL);
 		else
 			err = fuse_setlk(file, fl, 0);
 	}