Re: [PATCH v1 1/1] virtio-block: switch to blk_get_max_hw_transfer

[Ilya Dryomov]

On Thu, Dec 9, 2021 at 10:34 AM Or Ozeri <oro@il.ibm.com> wrote:
>
> The blk_get_max_hw_transfer API was recently added in 6.1.0.
> It allows querying an underlying block device its max transfer capability.
> This commit changes virtio-blk to use this.
>
> Signed-off-by: Or Ozeri <oro@il.ibm.com>
> ---
>  hw/block/virtio-blk.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index f139cd7cc9..1ba9a06888 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -458,7 +458,7 @@ static void virtio_blk_submit_multireq(BlockBackend *blk, 
> MultiReqBuffer *mrb)
>          return;
>      }
>
> -    max_transfer = blk_get_max_transfer(mrb->reqs[0]->dev->blk);
> +    max_transfer = blk_get_max_hw_transfer(mrb->reqs[0]->dev->blk);
>
>      qsort(mrb->reqs, mrb->num_reqs, sizeof(*mrb->reqs),
>            &multireq_compare);
> --
> 2.25.1
>
>

Hi Or,

Superficially, this makes sense to me.  A couple of things to consider:

- Move the explanation from the cover letter into the patch
  description.  The current patch description is pretty much
  meaningless.
- Should the actual limit be consulted for the number of segments
  as well?  IOW should blk_get_max_hw_iov() be called instead of
  blk_get_max_iov() a dozen lines below?

I'm adding Stefan and Kevin to CC to get more eyes on this patch as it
fixes a regression.  I believe this was encountered with the following
NBD device, Or please correct me if I'm wrong:

$ cat /sys/block/nbd0/queue/max_sectors_kb
128
$ cat /sys/block/nbd0/queue/max_segments
65535

Thanks,

                Ilya