Re: [Qemu-devel] [PATCH 2/3] qcow2: Fix write_zeroes with partially allocated backing file cluster

["Denis V. Lunev" <den@openvz.org>]

On 05/17/2016 07:51 PM, Kevin Wolf wrote:
> In order to correctly check whether a given cluster is read as zero, we
> don't only need to check whether bdrv_get_block_status_above() sets
> BDRV_BLOCK_ZERO, but also if all sectors for the whole cluster have the
> same status.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   block/qcow2.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/block/qcow2.c b/block/qcow2.c
> index a6012dc..c197ff3 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -2412,7 +2412,7 @@ static bool is_zero_cluster(BlockDriverState *bs, int64_t start)
>       BlockDriverState *file;
>       int64_t res = bdrv_get_block_status_above(bs, NULL, start,
>                                                 s->cluster_sectors, &nr, &file);
> -    return res >= 0 && (res & BDRV_BLOCK_ZERO);
> +    return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == s->cluster_sectors;
>   }
>   
>   static bool is_zero_cluster_top_locked(BlockDriverState *bs, int64_t start)
> @@ -2423,6 +2423,7 @@ static bool is_zero_cluster_top_locked(BlockDriverState *bs, int64_t start)
>       int ret;
>   
>       ret = qcow2_get_cluster_offset(bs, start << BDRV_SECTOR_BITS, &nr, &off);
> +    assert(nr == s->cluster_sectors);
>       return ret == QCOW2_CLUSTER_UNALLOCATED || ret == QCOW2_CLUSTER_ZERO;
>   }
>   
Reviewed-by: Denis V. Lunev <den@openvz.org>

I have had this kludge in the revision one and I have lost them in 
revision 3 :(