[PATCH] fuse: add O_ASYNC support to FUSE device

This adds asynchronous notification to FUSE - a FUSE server can request
O_ASYNC on a /dev/fuse file descriptor and receive SIGIO when there is input
available.

One subtlety - fuse_dev_fasync, which is called when O_ASYNC is requested,
does no locking, unlink the other methods.  I think it's unnecessary, as the
fuse_conn.fasync list is manipulated only by fasync_helper and kill_fasync,
which provide their own locking.  It would also be wrong to use the fuse_lock,
as it's a spin lock and fasync_helper can sleep.  My one concern with this is
the fuse_conn going away underneath fuse_dev_fasync - sys_fcntl takes a
reference on the file struct, so this seems not to be a problem.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/fuse/inode.c

@@ -216,6 +216,7 @@ static void fuse_put_super(struct super_block *sb)
 	spin_unlock(&fuse_lock);
 	up_write(&fc->sbput_sem);
 	/* Flush all readers on this fs */
+	kill_fasync(&fc->fasync, SIGIO, POLL_IN);
 	wake_up_all(&fc->waitq);
 	kobject_del(&fc->kobj);
 	kobject_put(&fc->kobj);