Re: [PATCH v2 2/8] fuse: refactor io-uring logic for getting next fuse request

[Bernd Schubert <bschubert@ddn.com>]

On 10/27/25 23:28, Joanne Koong wrote:
> Simplify the logic for getting the next fuse request.
> 
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> ---
>  fs/fuse/dev_uring.c | 78 ++++++++++++++++-----------------------------
>  1 file changed, 28 insertions(+), 50 deletions(-)
> 
> diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
> index f6b12aebb8bb..415924b346c0 100644
> --- a/fs/fuse/dev_uring.c
> +++ b/fs/fuse/dev_uring.c
> @@ -710,34 +710,6 @@ static int fuse_uring_prepare_send(struct fuse_ring_ent *ent,
>  	return err;
>  }
>  
> -/*
> - * 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 *ent,
> -					struct fuse_req *req,
> -					unsigned int issue_flags)
> -{
> -	struct fuse_ring_queue *queue = ent->queue;
> -	int err;
> -	struct io_uring_cmd *cmd;
> -
> -	err = fuse_uring_prepare_send(ent, req);
> -	if (err)
> -		return err;
> -
> -	spin_lock(&queue->lock);
> -	cmd = ent->cmd;
> -	ent->cmd = NULL;
> -	ent->state = FRRS_USERSPACE;
> -	list_move_tail(&ent->list, &queue->ent_in_userspace);
> -	spin_unlock(&queue->lock);
> -
> -	io_uring_cmd_done(cmd, 0, issue_flags);
> -	return 0;
> -}
> -
>  /*
>   * Make a ring entry available for fuse_req assignment
>   */
> @@ -834,11 +806,13 @@ static void fuse_uring_commit(struct fuse_ring_ent *ent, struct fuse_req *req,
>  }
>  
>  /*
> - * Get the next fuse req and send it
> + * Get the next fuse req.
> + *
> + * Returns true if the next fuse request has been assigned to the ent.
> + * Else, there is no next fuse request and this returns false.
>   */
> -static void fuse_uring_next_fuse_req(struct fuse_ring_ent *ent,
> -				     struct fuse_ring_queue *queue,
> -				     unsigned int issue_flags)
> +static bool fuse_uring_get_next_fuse_req(struct fuse_ring_ent *ent,
> +					 struct fuse_ring_queue *queue)
>  {
>  	int err;
>  	struct fuse_req *req;
> @@ -850,10 +824,12 @@ static void fuse_uring_next_fuse_req(struct fuse_ring_ent *ent,
>  	spin_unlock(&queue->lock);
>  
>  	if (req) {
> -		err = fuse_uring_send_next_to_ring(ent, req, issue_flags);
> +		err = fuse_uring_prepare_send(ent, req);
>  		if (err)
>  			goto retry;
>  	}
> +
> +	return req != NULL;
>  }
>  
>  static int fuse_ring_ent_set_commit(struct fuse_ring_ent *ent)
> @@ -871,6 +847,20 @@ static int fuse_ring_ent_set_commit(struct fuse_ring_ent *ent)
>  	return 0;
>  }
>  
> +static void fuse_uring_send(struct fuse_ring_ent *ent, struct io_uring_cmd *cmd,
> +			    ssize_t ret, unsigned int issue_flags)
> +{
> +	struct fuse_ring_queue *queue = ent->queue;
> +
> +	spin_lock(&queue->lock);
> +	ent->state = FRRS_USERSPACE;
> +	list_move_tail(&ent->list, &queue->ent_in_userspace);
> +	ent->cmd = NULL;
> +	spin_unlock(&queue->lock);
> +
> +	io_uring_cmd_done(cmd, ret, issue_flags);
> +}
> +
>  /* FUSE_URING_CMD_COMMIT_AND_FETCH handler */
>  static int fuse_uring_commit_fetch(struct io_uring_cmd *cmd, int issue_flags,
>  				   struct fuse_conn *fc)
> @@ -942,7 +932,8 @@ static int fuse_uring_commit_fetch(struct io_uring_cmd *cmd, int issue_flags,
>  	 * and fetching is done in one step vs legacy fuse, which has separated
>  	 * read (fetch request) and write (commit result).
>  	 */
> -	fuse_uring_next_fuse_req(ent, queue, issue_flags);
> +	if (fuse_uring_get_next_fuse_req(ent, queue))
> +		fuse_uring_send(ent, cmd, 0, issue_flags);
>  	return 0;
>  }
>  
> @@ -1190,20 +1181,6 @@ int fuse_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
>  	return -EIOCBQUEUED;
>  }
>  
> -static void fuse_uring_send(struct fuse_ring_ent *ent, struct io_uring_cmd *cmd,
> -			    ssize_t ret, unsigned int issue_flags)
> -{
> -	struct fuse_ring_queue *queue = ent->queue;
> -
> -	spin_lock(&queue->lock);
> -	ent->state = FRRS_USERSPACE;
> -	list_move_tail(&ent->list, &queue->ent_in_userspace);
> -	ent->cmd = NULL;
> -	spin_unlock(&queue->lock);
> -
> -	io_uring_cmd_done(cmd, ret, issue_flags);
> -}
> -
>  /*
>   * This prepares and sends the ring request in fuse-uring task context.
>   * User buffers are not mapped yet - the application does not have permission
> @@ -1219,8 +1196,9 @@ static void fuse_uring_send_in_task(struct io_uring_cmd *cmd,
>  	if (!(issue_flags & IO_URING_F_TASK_DEAD)) {
>  		err = fuse_uring_prepare_send(ent, ent->fuse_req);
>  		if (err) {
> -			fuse_uring_next_fuse_req(ent, queue, issue_flags);
> -			return;
> +			if (!fuse_uring_get_next_fuse_req(ent, queue))
> +				return;
> +			err = 0;
>  		}
>  	} else {
>  		err = -ECANCELED;

LGTM

(I had already start to go into this direction
https://lore.kernel.org/all/20250403-fuse-io-uring-trace-points-v3-3-35340aa31d9c@ddn.com/)


Reviewed-by: Bernd Schubert <bschubert@ddn.com>