Re: [PATCH 10/19] rnbd-srv: simplify bio mapping in process_rdma

[Jinpu Wang <jinpu.wang@xxxxxxxxx>]

Hi Christoph,

Thanks for the patch.

On Tue, Jan 18, 2022 at 8:20 AM Christoph Hellwig <hch@xxxxxx> wrote:
>
> The memory mapped in process_rdma is contiguous, so there is no need
> to loop over bio_add_page.  Remove rnbd_bio_map_kern and just open code
> the bio allocation and mapping in the caller.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  drivers/block/rnbd/rnbd-srv-dev.c | 57 -------------------------------
>  drivers/block/rnbd/rnbd-srv-dev.h |  5 ---
>  drivers/block/rnbd/rnbd-srv.c     | 20 ++++++++---
>  3 files changed, 15 insertions(+), 67 deletions(-)
>
> diff --git a/drivers/block/rnbd/rnbd-srv-dev.c 
> b/drivers/block/rnbd/rnbd-srv-dev.c
> index b241a099aeae2..98d3e591a0885 100644
> --- a/drivers/block/rnbd/rnbd-srv-dev.c
> +++ b/drivers/block/rnbd/rnbd-srv-dev.c
> @@ -44,60 +44,3 @@ void rnbd_dev_close(struct rnbd_dev *dev)
>         blkdev_put(dev->bdev, dev->blk_open_flags);
>         kfree(dev);
>  }
> -
> -void rnbd_dev_bi_end_io(struct bio *bio)
> -{
> -       struct rnbd_dev_blk_io *io = bio->bi_private;
> -
> -       rnbd_endio(io->priv, blk_status_to_errno(bio->bi_status));
> -       bio_put(bio);
> -}
> -
> -/**
> - *     rnbd_bio_map_kern       -       map kernel address into bio
> - *     @data: pointer to buffer to map
> - *     @bs: bio_set to use.
> - *     @len: length in bytes
> - *     @gfp_mask: allocation flags for bio allocation
> - *
> - *     Map the kernel address into a bio suitable for io to a block
> - *     device. Returns an error pointer in case of error.
> - */
> -struct bio *rnbd_bio_map_kern(void *data, struct bio_set *bs,
> -                             unsigned int len, gfp_t gfp_mask)
> -{
> -       unsigned long kaddr = (unsigned long)data;
> -       unsigned long end = (kaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
> -       unsigned long start = kaddr >> PAGE_SHIFT;
> -       const int nr_pages = end - start;
> -       int offset, i;
> -       struct bio *bio;
> -
> -       bio = bio_alloc_bioset(gfp_mask, nr_pages, bs);
> -       if (!bio)
> -               return ERR_PTR(-ENOMEM);
> -
> -       offset = offset_in_page(kaddr);
> -       for (i = 0; i < nr_pages; i++) {
> -               unsigned int bytes = PAGE_SIZE - offset;
> -
> -               if (len <= 0)
> -                       break;
> -
> -               if (bytes > len)
> -                       bytes = len;
> -
> -               if (bio_add_page(bio, virt_to_page(data), bytes,
> -                                   offset) < bytes) {
> -                       /* we don't support partial mappings */
> -                       bio_put(bio);
> -                       return ERR_PTR(-EINVAL);
> -               }
> -
> -               data += bytes;
> -               len -= bytes;
> -               offset = 0;
> -       }
> -
> -       return bio;
> -}
> diff --git a/drivers/block/rnbd/rnbd-srv-dev.h 
> b/drivers/block/rnbd/rnbd-srv-dev.h
> index 0eb23850afb95..1a14ece0be726 100644
> --- a/drivers/block/rnbd/rnbd-srv-dev.h
> +++ b/drivers/block/rnbd/rnbd-srv-dev.h
> @@ -41,11 +41,6 @@ void rnbd_dev_close(struct rnbd_dev *dev);
>
>  void rnbd_endio(void *priv, int error);
>
> -void rnbd_dev_bi_end_io(struct bio *bio);
> -
> -struct bio *rnbd_bio_map_kern(void *data, struct bio_set *bs,
> -                             unsigned int len, gfp_t gfp_mask);
> -
>  static inline int rnbd_dev_get_max_segs(const struct rnbd_dev *dev)
>  {
>         return queue_max_segments(bdev_get_queue(dev->bdev));
> diff --git a/drivers/block/rnbd/rnbd-srv.c b/drivers/block/rnbd/rnbd-srv.c
> index 1ee808fc600cf..65c670e96075b 100644
> --- a/drivers/block/rnbd/rnbd-srv.c
> +++ b/drivers/block/rnbd/rnbd-srv.c
> @@ -114,6 +114,14 @@ rnbd_get_sess_dev(int dev_id, struct rnbd_srv_session 
> *srv_sess)
>         return sess_dev;
>  }
>
> +static void rnbd_dev_bi_end_io(struct bio *bio)
> +{
> +       struct rnbd_dev_blk_io *io = bio->bi_private;
> +
> +       rnbd_endio(io->priv, blk_status_to_errno(bio->bi_status));
> +       bio_put(bio);
> +}
> +
>  static int process_rdma(struct rnbd_srv_session *srv_sess,
>                         struct rtrs_srv_op *id, void *data, u32 datalen,
>                         const void *usr, size_t usrlen)
> @@ -144,11 +152,11 @@ static int process_rdma(struct rnbd_srv_session 
> *srv_sess,
>         priv->sess_dev = sess_dev;
>         priv->id = id;
>
> -       /* Generate bio with pages pointing to the rdma buffer */
> -       bio = rnbd_bio_map_kern(data, sess_dev->rnbd_dev->ibd_bio_set, 
> datalen, GFP_KERNEL);
> -       if (IS_ERR(bio)) {
> -               err = PTR_ERR(bio);
> -               rnbd_srv_err(sess_dev, "Failed to generate bio, err: %d\n", 
> err);
> +       bio = bio_alloc_bioset(GFP_KERNEL, 1, 
> sess_dev->rnbd_dev->ibd_bio_set);
> +       if (bio_add_page(bio, virt_to_page(data), datalen,
> +                       offset_in_page(data))) {
this changes lead to IO error all the time, because bio_add_page return len.
We need  if (bio_add_page(bio, virt_to_page(data), datalen,
                     offset_in_page(data)) < datalen)

Thanks!
> +               rnbd_srv_err(sess_dev, "Failed to map data to bio\n");
> +               err = -EINVAL;
>                 goto sess_dev_put;
>         }
>
> @@ -170,6 +178,8 @@ static int process_rdma(struct rnbd_srv_session *srv_sess,
>
>         return 0;
>
> +bio_put:
> +       bio_put(bio);
>  sess_dev_put:
>         rnbd_put_sess_dev(sess_dev);
>  err:
> --
> 2.30.2
>