[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>

1 files changed, 16 insertions, 1 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index b2e8613a26d8..438770f8867f 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -317,6 +317,7 @@ static void queue_request(struct fuse_conn *fc, struct fuse_req *req)
         list_add_tail(&req->list, &fc->pending);
         req->state = FUSE_REQ_PENDING;
         wake_up(&fc->waitq);
+        kill_fasync(&fc->fasync, SIGIO, POLL_IN);
 }
 
 /*
@@ -901,6 +902,7 @@ void fuse_abort_conn(struct fuse_conn *fc)
                 end_requests(fc, &fc->pending);
                 end_requests(fc, &fc->processing);
                 wake_up_all(&fc->waitq);
+                kill_fasync(&fc->fasync, SIGIO, POLL_IN);
         }
         spin_unlock(&fuse_lock);
 }
@@ -917,12 +919,24 @@ static int fuse_dev_release(struct inode *inode, struct file *file)
                 end_requests(fc, &fc->processing);
         }
         spin_unlock(&fuse_lock);
-        if (fc)
+        if (fc) {
+                fasync_helper(-1, file, 0, &fc->fasync);
                 kobject_put(&fc->kobj);
+        }
 
         return 0;
 }
 
+static int fuse_dev_fasync(int fd, struct file *file, int on)
+{
+        struct fuse_conn *fc = fuse_get_conn(file);
+        if (!fc)
+                return -ENODEV;
+
+        /* No locking - fasync_helper does its own locking */
+        return fasync_helper(fd, file, on, &fc->fasync);
+}
+
 const struct file_operations fuse_dev_operations = {
         .owner          = THIS_MODULE,
         .llseek         = no_llseek,
@@ -932,6 +946,7 @@ const struct file_operations fuse_dev_operations = {
         .writev         = fuse_dev_writev,
         .poll           = fuse_dev_poll,
         .release        = fuse_dev_release,
+        .fasync         = fuse_dev_fasync,
 };
 
 static struct miscdevice fuse_miscdevice = {