fuse: add support for mandatory locking

For mandatory locking the userspace filesystem needs to know the lock
ownership for read, write and truncate operations.

This patch adds the necessary fields to the protocol.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 052327b..6c83ed0 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1108,6 +1108,11 @@
 		inarg.valid |= FATTR_FH;
 		inarg.fh = ff->fh;
 	}
+	if (attr->ia_valid & ATTR_SIZE) {
+		/* For mandatory locking in truncate */
+		inarg.valid |= FATTR_LOCKOWNER;
+		inarg.lock_owner = fuse_lock_owner_id(fc, current->files);
+	}
 	req->in.h.opcode = FUSE_SETATTR;
 	req->in.h.nodeid = get_node_id(inode);
 	req->in.numargs = 1;