Re: [RFC PATCH v2 15/26] qcow2: Add subcluster support to zero_in_l2_slice()

[Max Reitz]

On 26.10.19 23:25, Alberto Garcia wrote:
> Setting the QCOW_OFLAG_ZERO bit of the L2 entry is forbidden if an
> image has subclusters. Instead, the individual 'all zeroes' bits must
> be used.
> 
> Signed-off-by: Alberto Garcia <address@hidden>
> ---
>  block/qcow2-cluster.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index e67559152f..3e4ba8d448 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -1852,7 +1852,7 @@ static int zero_in_l2_slice(BlockDriverState *bs, 
> uint64_t offset,
>      assert(nb_clusters <= INT_MAX);
>  
>      for (i = 0; i < nb_clusters; i++) {
> -        uint64_t old_offset;
> +        uint64_t old_offset, l2_entry = 0;
>          QCow2ClusterType cluster_type;
>  
>          old_offset = get_l2_entry(s, l2_slice, l2_index + i);
> @@ -1869,12 +1869,18 @@ static int zero_in_l2_slice(BlockDriverState *bs, 
> uint64_t offset,
>  
>          qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
>          if (cluster_type == QCOW2_CLUSTER_COMPRESSED || unmap) {
> -            set_l2_entry(s, l2_slice, l2_index + i, QCOW_OFLAG_ZERO);
>              qcow2_free_any_clusters(bs, old_offset, 1, 
> QCOW2_DISCARD_REQUEST);

It feels wrong to me to free the cluster before updating the L2 entry.

Max

>          } else {
> -            uint64_t entry = get_l2_entry(s, l2_slice, l2_index + i);
> -            set_l2_entry(s, l2_slice, l2_index + i, entry | QCOW_OFLAG_ZERO);
> +            l2_entry = get_l2_entry(s, l2_slice, l2_index + i);
>          }
> +
> +        if (has_subclusters(s)) {
> +            set_l2_bitmap(s, l2_slice, l2_index + i, 
> QCOW_L2_BITMAP_ALL_ZEROES);
> +        } else {
> +            l2_entry |= QCOW_OFLAG_ZERO;
> +        }
> +
> +        set_l2_entry(s, l2_slice, l2_index + i, l2_entry);
>      }
>  
>      qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
>

signature.asc
Description: OpenPGP digital signature