Re: [Qemu-devel] [PATCH v3 19/22] block: Split bdrv_merge_limits() from bdrv_refresh_limits()

[Fam Zheng <famz@redhat.com>]

On Thu, 06/23 16:37, Eric Blake wrote:
> During bdrv_merge_limits(), we were computing initial limits
> based on another BDS in two places.  At first glance, the two
> computations are not identical (one is doing straight copying,
> the other is doing merging towards or away from zero) - but
> when you realize that the first round is starting with all-0
> memory, all of the merging happens to work.  Factoring out the
> merging makes it easier to track how two BDS limits are merged,
> in case we have future reasons to merge in even more limits.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> ---
> v3: Split raw block driver changes to its own patch, make new
> function static
> v2: new patch
> ---
>  block/io.c | 31 +++++++++++++------------------
>  1 file changed, 13 insertions(+), 18 deletions(-)
> 
> diff --git a/block/io.c b/block/io.c
> index 0f15d05..69dbbd3 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -67,6 +67,17 @@ static void bdrv_parent_drained_end(BlockDriverState *bs)
>      }
>  }
> 
> +static void bdrv_merge_limits(BlockLimits *dst, const BlockLimits *src)
> +{
> +    dst->opt_transfer = MAX(dst->opt_transfer, src->opt_transfer);
> +    dst->max_transfer = MIN_NON_ZERO(dst->max_transfer, src->max_transfer);
> +    dst->opt_mem_alignment = MAX(dst->opt_mem_alignment,
> +                                 src->opt_mem_alignment);
> +    dst->min_mem_alignment = MAX(dst->min_mem_alignment,
> +                                 src->min_mem_alignment);
> +    dst->max_iov = MIN_NON_ZERO(dst->max_iov, src->max_iov);
> +}
> +
>  void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
>  {
>      BlockDriver *drv = bs->drv;
> @@ -88,11 +99,7 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
>              error_propagate(errp, local_err);
>              return;
>          }
> -        bs->bl.opt_transfer = bs->file->bs->bl.opt_transfer;
> -        bs->bl.max_transfer = bs->file->bs->bl.max_transfer;
> -        bs->bl.min_mem_alignment = bs->file->bs->bl.min_mem_alignment;
> -        bs->bl.opt_mem_alignment = bs->file->bs->bl.opt_mem_alignment;
> -        bs->bl.max_iov = bs->file->bs->bl.max_iov;
> +        bdrv_merge_limits(&bs->bl, &bs->file->bs->bl);
>      } else {
>          bs->bl.min_mem_alignment = 512;
>          bs->bl.opt_mem_alignment = getpagesize();
> @@ -107,19 +114,7 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
>              error_propagate(errp, local_err);
>              return;
>          }
> -        bs->bl.opt_transfer = MAX(bs->bl.opt_transfer,
> -                                  bs->backing->bs->bl.opt_transfer);
> -        bs->bl.max_transfer = MIN_NON_ZERO(bs->bl.max_transfer,
> -                                           bs->backing->bs->bl.max_transfer);
> -        bs->bl.opt_mem_alignment =
> -            MAX(bs->bl.opt_mem_alignment,
> -                bs->backing->bs->bl.opt_mem_alignment);
> -        bs->bl.min_mem_alignment =
> -            MAX(bs->bl.min_mem_alignment,
> -                bs->backing->bs->bl.min_mem_alignment);
> -        bs->bl.max_iov =
> -            MIN(bs->bl.max_iov,
> -                bs->backing->bs->bl.max_iov);
> +        bdrv_merge_limits(&bs->bl, &bs->backing->bs->bl);
>      }
> 
>      /* Then let the driver override it */
> -- 
> 2.5.5
> 

Reviewed-by: Fam Zheng <famz@redhat.com>