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

Ming Lei
2017-04-12T10:24:35Z

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