Re: [PATCH 10/25] loop: zero-fill bio on the submitting cpu

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

On Thu, Apr 06, 2017 at 05:39:29PM +0200, Christoph Hellwig wrote:
> In thruth I've just audited which blk-mq drivers don't currently have a
> complete callback, but I think this change is at least borderline useful.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/block/loop.c | 30 ++++++++++++++----------------
>  drivers/block/loop.h |  1 +
>  2 files changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index cc981f34e017..6924ec611a49 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -445,32 +445,27 @@ static int lo_req_flush(struct loop_device *lo, struct request *rq)
>  	return ret;
>  }
>  
> -static inline void handle_partial_read(struct loop_cmd *cmd, long bytes)
> +static void lo_complete_rq(struct request *rq)
>  {
> -	if (bytes < 0 || op_is_write(req_op(cmd->rq)))
> -		return;
> +	struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
>  
> -	if (unlikely(bytes < blk_rq_bytes(cmd->rq))) {
> +	if (unlikely(req_op(cmd->rq) == REQ_OP_READ && cmd->use_aio &&
> +		     cmd->ret >= 0 && cmd->ret < blk_rq_bytes(cmd->rq))) {
>  		struct bio *bio = cmd->rq->bio;
>  
> -		bio_advance(bio, bytes);
> +		bio_advance(bio, cmd->ret);
>  		zero_fill_bio(bio);
>  	}
> +
> +	blk_mq_end_request(rq, cmd->ret < 0 ? -EIO : 0);
>  }
>  
>  static void lo_rw_aio_complete(struct kiocb *iocb, long ret, long ret2)
>  {
>  	struct loop_cmd *cmd = container_of(iocb, struct loop_cmd, iocb);
> -	struct request *rq = cmd->rq;
> -
> -	handle_partial_read(cmd, ret);
>  
> -	if (ret > 0)
> -		ret = 0;
> -	else if (ret < 0)
> -		ret = -EIO;
> -
> -	blk_mq_complete_request(rq, ret);
> +	cmd->ret = ret;
> +	blk_mq_complete_request(cmd->rq, 0);
>  }
>  
>  static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
> @@ -1686,8 +1681,10 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
>  	ret = do_req_filebacked(lo, cmd->rq);
>   failed:
>  	/* complete non-aio request */
> -	if (!cmd->use_aio || ret)
> -		blk_mq_complete_request(cmd->rq, ret ? -EIO : 0);
> +	if (!cmd->use_aio || ret) {
> +		cmd->ret = ret ? -EIO : 0;
> +		blk_mq_complete_request(cmd->rq, 0);
> +	}
>  }
>  
>  static void loop_queue_work(struct kthread_work *work)
> @@ -1713,6 +1710,7 @@ static int loop_init_request(void *data, struct request *rq,
>  static const struct blk_mq_ops loop_mq_ops = {
>  	.queue_rq       = loop_queue_rq,
>  	.init_request	= loop_init_request,
> +	.complete	= lo_complete_rq,
>  };
>  
>  static int loop_add(struct loop_device **l, int i)
> diff --git a/drivers/block/loop.h b/drivers/block/loop.h
> index fb2237c73e61..fecd3f97ef8c 100644
> --- a/drivers/block/loop.h
> +++ b/drivers/block/loop.h
> @@ -70,6 +70,7 @@ struct loop_cmd {
>  	struct request *rq;
>  	struct list_head list;
>  	bool use_aio;           /* use AIO interface to handle I/O */
> +	long ret;
>  	struct kiocb iocb;
>  };

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming