Re: [PATCH 5/8] ublk: factor out ublk_start_io() helper

[Ming Lei <ming.lei@redhat.com>]

On Sat, Apr 26, 2025 at 10:58:00PM -0600, Caleb Sander Mateos wrote:
> In preparation for calling it from outside ublk_dispatch_req(), factor
> out the code responsible for setting up an incoming ublk I/O request.
> 
> Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
> ---
>  drivers/block/ublk_drv.c | 53 ++++++++++++++++++++++------------------
>  1 file changed, 29 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 01fc92051754..90a38a82f8cc 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -1151,17 +1151,44 @@ static inline void __ublk_abort_rq(struct ublk_queue *ubq,
>  		blk_mq_requeue_request(rq, false);
>  	else
>  		blk_mq_end_request(rq, BLK_STS_IOERR);
>  }
>  
> +static void ublk_start_io(struct ublk_queue *ubq, struct request *req,
> +			  struct ublk_io *io)
> +{
> +	unsigned mapped_bytes = ublk_map_io(ubq, req, io);
> +
> +	/* partially mapped, update io descriptor */
> +	if (unlikely(mapped_bytes != blk_rq_bytes(req))) {
> +		/*
> +		 * Nothing mapped, retry until we succeed.
> +		 *
> +		 * We may never succeed in mapping any bytes here because
> +		 * of OOM. TODO: reserve one buffer with single page pinned
> +		 * for providing forward progress guarantee.
> +		 */
> +		if (unlikely(!mapped_bytes)) {
> +			blk_mq_requeue_request(req, false);
> +			blk_mq_delay_kick_requeue_list(req->q,
> +					UBLK_REQUEUE_DELAY_MS);
> +			return;
> +		}
> +
> +		ublk_get_iod(ubq, req->tag)->nr_sectors =
> +			mapped_bytes >> 9;
> +	}
> +
> +	ublk_init_req_ref(ubq, req);
> +}
> +
>  static void ublk_dispatch_req(struct ublk_queue *ubq,
>  			      struct request *req,
>  			      unsigned int issue_flags)
>  {
>  	int tag = req->tag;
>  	struct ublk_io *io = &ubq->ios[tag];
> -	unsigned int mapped_bytes;
>  
>  	pr_devel("%s: complete: qid %d tag %d io_flags %x addr %llx\n",
>  			__func__, ubq->q_id, req->tag, io->flags,
>  			ublk_get_iod(ubq, req->tag)->addr);
>  
> @@ -1204,33 +1231,11 @@ static void ublk_dispatch_req(struct ublk_queue *ubq,
>  		pr_devel("%s: update iod->addr: qid %d tag %d io_flags %x addr %llx\n",
>  				__func__, ubq->q_id, req->tag, io->flags,
>  				ublk_get_iod(ubq, req->tag)->addr);
>  	}
>  
> -	mapped_bytes = ublk_map_io(ubq, req, io);
> -
> -	/* partially mapped, update io descriptor */
> -	if (unlikely(mapped_bytes != blk_rq_bytes(req))) {
> -		/*
> -		 * Nothing mapped, retry until we succeed.
> -		 *
> -		 * We may never succeed in mapping any bytes here because
> -		 * of OOM. TODO: reserve one buffer with single page pinned
> -		 * for providing forward progress guarantee.
> -		 */
> -		if (unlikely(!mapped_bytes)) {
> -			blk_mq_requeue_request(req, false);
> -			blk_mq_delay_kick_requeue_list(req->q,
> -					UBLK_REQUEUE_DELAY_MS);
> -			return;
> -		}

Here it needs to break ublk_dispatch_req() for not completing the
uring_cmd, however ublk_start_io() can't support it.


Thanks,
Ming