Re: [PATCH v9 10/17] fuse: Add io-uring sqe commit and fetch support

[Pavel Begunkov <asml.silence@gmail.com>]

On 1/7/25 00:25, Bernd Schubert wrote:
> This adds support for fuse request completion through ring SQEs
> (FUSE_URING_CMD_COMMIT_AND_FETCH handling). After committing
> the ring entry it becomes available for new fuse requests.
> Handling of requests through the ring (SQE/CQE handling)
> is complete now.
> 
> Fuse request data are copied through the mmaped ring buffer,
> there is no support for any zero copy yet.

Reviewed-by: Pavel Begunkov <asml.silence@gmail.com> # io_uring

> 
> Signed-off-by: Bernd Schubert <bschubert@ddn.com>
> ---
>   fs/fuse/dev_uring.c   | 450 ++++++++++++++++++++++++++++++++++++++++++++++++++
>   fs/fuse/dev_uring_i.h |  12 ++
>   fs/fuse/fuse_i.h      |   4 +
>   3 files changed, 466 insertions(+)
> 
> diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
> index b44ba4033615e01041313c040035b6da6af0ee17..f44e66a7ea577390da87e9ac7d118a9416898c28 100644
> --- a/fs/fuse/dev_uring.c
> +++ b/fs/fuse/dev_uring.c
> @@ -26,6 +26,19 @@ bool fuse_uring_enabled(void)
...
> +
> +/*
> + * Write data to the ring buffer and send the request to userspace,
> + * userspace will read it
> + * This is comparable with classical read(/dev/fuse)
> + */
> +static int fuse_uring_send_next_to_ring(struct fuse_ring_ent *ring_ent,
> +					unsigned int issue_flags)
> +{
> +	int err = 0;
> +	struct fuse_ring_queue *queue = ring_ent->queue;
> +
> +	err = fuse_uring_prepare_send(ring_ent);
> +	if (err)
> +		goto err;
> +
> +	spin_lock(&queue->lock);
> +	ring_ent->state = FRRS_USERSPACE;
> +	list_move(&ring_ent->list, &queue->ent_in_userspace);
> +	spin_unlock(&queue->lock);
> +
> +	io_uring_cmd_done(ring_ent->cmd, 0, 0, issue_flags);
> +	ring_ent->cmd = NULL;

I haven't checked if it races with some reallocation, but
you might want to consider clearing it under the spin.

spin_lock(&queue->lock);
...
cmd = ring_ent->cmd;
ring_ent->cmd = NULL;
spin_unlock(&queue->lock);

io_uring_cmd_done(cmd);

Can be done on top if even needed.

-- 
Pavel Begunkov