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, unlike 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 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.
One possible bug - there is a wakeup in inode.c:fuse_put_super, but
sticking a kill_fasync there causes BUGs because the /dev/fuse
file struct seems to have gone away. So, this may be lacking when a
FUSE mount is unmounted from underneath the server (is that
possible, or must the server be killed in order to do the umount?).
Signed-off-by: Jeff Dike <[email protected]>
Index: host-2.6.15-fuse/fs/fuse/dev.c
===================================================================
--- host-2.6.15-fuse.orig/fs/fuse/dev.c 2006-02-18 12:19:07.000000000 -0500
+++ host-2.6.15-fuse/fs/fuse/dev.c 2006-02-27 13:19:10.000000000 -0500
@@ -311,6 +311,7 @@ static void queue_request(struct fuse_co
list_add_tail(&req->list, &fc->pending);
req->state = FUSE_REQ_PENDING;
wake_up(&fc->waitq);
+ kill_fasync(&fc->fasync, SIGIO, POLL_IN);
}
/*
@@ -894,6 +895,7 @@ void fuse_abort_conn(struct fuse_conn *f
end_requests(fc, &fc->pending);
end_requests(fc, &fc->processing);
wake_up_all(&fc->waitq);
+ kill_fasync(&fc->fasync, SIGIO, POLLIN);
}
spin_unlock(&fuse_lock);
}
@@ -913,9 +915,20 @@ static int fuse_dev_release(struct inode
if (fc)
kobject_put(&fc->kobj);
+ fasync_helper(-1, file, 0, &fc->fasync);
+
return 0;
}
+static int fuse_dev_fasync(int fd, struct file *file, int on)
+{
+ struct fuse_conn *fc;
+
+ /* No locking - fasync_helper does its own locking */
+ fc = file->private_data;
+ return(fasync_helper(fd, file, on, &fc->fasync));
+}
+
struct file_operations fuse_dev_operations = {
.owner = THIS_MODULE,
.llseek = no_llseek,
@@ -925,6 +938,7 @@ struct file_operations fuse_dev_operatio
.writev = fuse_dev_writev,
.poll = fuse_dev_poll,
.release = fuse_dev_release,
+ .fasync = fuse_dev_fasync,
};
static struct miscdevice fuse_miscdevice = {
Index: host-2.6.15-fuse/fs/fuse/fuse_i.h
===================================================================
--- host-2.6.15-fuse.orig/fs/fuse/fuse_i.h 2006-02-24 17:46:47.000000000 -0500
+++ host-2.6.15-fuse/fs/fuse/fuse_i.h 2006-02-24 18:24:49.000000000 -0500
@@ -318,6 +318,9 @@ struct fuse_conn {
/** kobject */
struct kobject kobj;
+
+ /** O_ASYNC requests */
+ struct fasync_struct *fasync;
};
static inline struct fuse_conn *get_fuse_conn_super(struct super_block *sb)
Index: host-2.6.15-fuse/fs/fuse/inode.c
===================================================================
--- host-2.6.15-fuse.orig/fs/fuse/inode.c 2006-02-18 12:19:07.000000000 -0500
+++ host-2.6.15-fuse/fs/fuse/inode.c 2006-02-27 13:17:50.000000000 -0500
@@ -17,6 +17,7 @@
#include <linux/module.h>
#include <linux/parser.h>
#include <linux/statfs.h>
+#include <linux/poll.h>
MODULE_AUTHOR("Miklos Szeredi <[email protected]>");
MODULE_DESCRIPTION("Filesystem in Userspace");
@@ -377,6 +378,7 @@ static void fuse_conn_release(struct kob
list_del(&req->list);
fuse_request_free(req);
}
+
kfree(fc);
}
@@ -409,6 +411,7 @@ static struct fuse_conn *new_conn(void)
fc->bdi.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
fc->bdi.unplug_io_fn = default_unplug_io_fn;
fc->reqctr = 0;
+ fc->fasync = NULL;
}
return fc;
}
> 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, unlike 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.
Yes, but you need to use fuse_get_conn() and check the result (see
fuse_dev_poll()).
> It would also be wrong to use 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.
Yes, file holds a reference to fuse_conn.
> One possible bug - there is a wakeup in inode.c:fuse_put_super, but
> sticking a kill_fasync there causes BUGs because the /dev/fuse
> file struct seems to have gone away.
I don't see how that could happen. fuse_dev_release() removes the
file from fc->fasync, and fasync_helper() and kill_fasync() are
protected with fasync_lock against racing with each other.
Although it may be possible that kill_fasync() races with the final
fput(), but as I see kill_fasync() only uses the file->f_owner field
which should still be valid before and during file->release().
Which BUG is triggered?
> So, this may be lacking when a FUSE mount is unmounted from
> underneath the server (is that possible, or must the server be
> killed in order to do the umount?).
Yes it's possible, it is how a normal unmount happens:
- umount() called on the filesystem, filesystem unmounted
- read on /dev/fuse returns -ENODEV
- userspace filesystem exits gracefuly
> @@ -894,6 +895,7 @@ void fuse_abort_conn(struct fuse_conn *f
> end_requests(fc, &fc->pending);
> end_requests(fc, &fc->processing);
> wake_up_all(&fc->waitq);
> + kill_fasync(&fc->fasync, SIGIO, POLLIN);
This should be POLL_IN too, no?
> +static int fuse_dev_fasync(int fd, struct file *file, int on)
> +{
> + struct fuse_conn *fc;
> +
> + /* No locking - fasync_helper does its own locking */
> + fc = file->private_data;
> + return(fasync_helper(fd, file, on, &fc->fasync));
I like this style better:
return fasync_helper(fd, file, on, &fc->fasync);
Thanks,
Miklos
Updated patch below...
On Tue, Feb 28, 2006 at 11:15:16AM +0100, Miklos Szeredi wrote:
> Yes, but you need to use fuse_get_conn() and check the result (see
> fuse_dev_poll()).
Fixed.
> Although it may be possible that kill_fasync() races with the final
> fput(), but as I see kill_fasync() only uses the file->f_owner field
> which should still be valid before and during file->release().
>
> Which BUG is triggered?
I cleaned up a couple things, and I can't make it break any more.
> This should be POLL_IN too, no?
Duh, yes.
> I like this style better:
Fixed.
Jeff
# 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 <[email protected]>
Index: host-2.6.15-fuse/fs/fuse/dev.c
===================================================================
--- host-2.6.15-fuse.orig/fs/fuse/dev.c 2006-02-18 12:19:07.000000000 -0500
+++ host-2.6.15-fuse/fs/fuse/dev.c 2006-02-28 21:04:40.000000000 -0500
@@ -311,6 +311,7 @@ static void queue_request(struct fuse_co
list_add_tail(&req->list, &fc->pending);
req->state = FUSE_REQ_PENDING;
wake_up(&fc->waitq);
+ kill_fasync(&fc->fasync, SIGIO, POLL_IN);
}
/*
@@ -894,6 +895,7 @@ void fuse_abort_conn(struct fuse_conn *f
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);
}
@@ -910,12 +912,26 @@ static int fuse_dev_release(struct inode
end_requests(fc, &fc->processing);
}
spin_unlock(&fuse_lock);
- if (fc)
+ if (fc) {
kobject_put(&fc->kobj);
+ fasync_helper(-1, file, 0, &fc->fasync);
+ fc->fasync = NULL;
+ }
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);
+}
+
struct file_operations fuse_dev_operations = {
.owner = THIS_MODULE,
.llseek = no_llseek,
@@ -925,6 +941,7 @@ struct file_operations fuse_dev_operatio
.writev = fuse_dev_writev,
.poll = fuse_dev_poll,
.release = fuse_dev_release,
+ .fasync = fuse_dev_fasync,
};
static struct miscdevice fuse_miscdevice = {
Index: host-2.6.15-fuse/fs/fuse/fuse_i.h
===================================================================
--- host-2.6.15-fuse.orig/fs/fuse/fuse_i.h 2006-02-24 17:46:47.000000000 -0500
+++ host-2.6.15-fuse/fs/fuse/fuse_i.h 2006-02-24 18:24:49.000000000 -0500
@@ -318,6 +318,9 @@ struct fuse_conn {
/** kobject */
struct kobject kobj;
+
+ /** O_ASYNC requests */
+ struct fasync_struct *fasync;
};
static inline struct fuse_conn *get_fuse_conn_super(struct super_block *sb)
Index: host-2.6.15-fuse/fs/fuse/inode.c
===================================================================
--- host-2.6.15-fuse.orig/fs/fuse/inode.c 2006-02-18 12:19:07.000000000 -0500
+++ host-2.6.15-fuse/fs/fuse/inode.c 2006-02-28 21:00:55.000000000 -0500
@@ -17,6 +17,7 @@
#include <linux/module.h>
#include <linux/parser.h>
#include <linux/statfs.h>
+#include <linux/poll.h>
MODULE_AUTHOR("Miklos Szeredi <[email protected]>");
MODULE_DESCRIPTION("Filesystem in Userspace");
@@ -216,6 +217,7 @@ static void fuse_put_super(struct super_
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);
@@ -409,6 +411,7 @@ static struct fuse_conn *new_conn(void)
fc->bdi.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
fc->bdi.unplug_io_fn = default_unplug_io_fn;
fc->reqctr = 0;
+ fc->fasync = NULL;
}
return fc;
}