Re: [PATCH v2 08/11] qcow2: zeroize the entire cluster when there're no non-zero subclusters

[Alexander Ivanov]

On 5/13/24 08:32, Andrey Drobyshev wrote:
> When zeroizing the last non-zero subclusters within single cluster, it
> makes sense to go zeroize the entire cluster and go down zero_in_l2_slice()
> path right away.  That way we'd also update the corresponding refcount
> table.
>
> Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
> Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
> ---
>   block/qcow2-cluster.c | 17 ++++++++++++++---
>   1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 475f167035..8d39e2f960 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -2221,7 +2221,7 @@ zero_in_l2_slice(BlockDriverState *bs, uint64_t offset,
>   
>   static int coroutine_fn GRAPH_RDLOCK
>   zero_l2_subclusters(BlockDriverState *bs, uint64_t offset,
> -                    unsigned nb_subclusters)
> +                    unsigned nb_subclusters, int flags)
>   {
>       BDRVQcow2State *s = bs->opaque;
>       uint64_t new_l2_bitmap;
> @@ -2237,6 +2237,16 @@ zero_l2_subclusters(BlockDriverState *bs, uint64_t 
> offset,
>       new_l2_bitmap |=  QCOW_OFLAG_SUB_ZERO_RANGE(sc, sc + nb_subclusters);
>       new_l2_bitmap &= ~QCOW_OFLAG_SUB_ALLOC_RANGE(sc, sc + nb_subclusters);
>   
> +    /*
> +     * If there're no non-zero subclusters left, we might as well zeroize
> +     * the entire cluster.  That way we'd also update the refcount table.
> +     */
> +    if ((new_l2_bitmap & QCOW_L2_BITMAP_ALL_ZEROES) ==
> +        QCOW_L2_BITMAP_ALL_ZEROES) {
> +        return zero_in_l2_slice(bs, QEMU_ALIGN_DOWN(offset, s->cluster_size),
> +                                1, flags);
> +    }
> +
>       if (new_l2_bitmap != scri.l2_bitmap) {
>           set_l2_bitmap(s, scri.l2_slice, scri.l2_index, new_l2_bitmap);
>           qcow2_cache_entry_mark_dirty(s->l2_table_cache, scri.l2_slice);
> @@ -2293,7 +2303,7 @@ int coroutine_fn 
> qcow2_subcluster_zeroize(BlockDriverState *bs, uint64_t offset,
>   
>       if (head) {
>           ret = zero_l2_subclusters(bs, offset - head,
> -                                  size_to_subclusters(s, head));
> +                                  size_to_subclusters(s, head), flags);
>           if (ret < 0) {
>               goto fail;
>           }
> @@ -2314,7 +2324,8 @@ int coroutine_fn 
> qcow2_subcluster_zeroize(BlockDriverState *bs, uint64_t offset,
>       }
>   
>       if (tail) {
> -        ret = zero_l2_subclusters(bs, end_offset, size_to_subclusters(s, 
> tail));
> +        ret = zero_l2_subclusters(bs, end_offset,
> +                                  size_to_subclusters(s, tail), flags);
>           if (ret < 0) {
>               goto fail;
>           }
Reviewed-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>

--
Best regards,
Alexander Ivanov