Commit d9e0dfa2 authored by Eric Blake's avatar Eric Blake Committed by Kevin Wolf
Browse files

block: Split bdrv_merge_limits() from bdrv_refresh_limits() 



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: default avatarEric Blake <eblake@redhat.com>
Reviewed-by: default avatarFam Zheng <famz@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent ad82be2f

block/io.c

+13 −18
Original line number Diff line number Diff line
@@ -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 */