17.03.2020 21:16, 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 <berto@igalia.com>
> Reviewed-by: Max Reitz <mreitz@redhat.com>
anyway:
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
still, some comments below
> ---
> 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 6f2643ba53..746006a117 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -1897,7 +1897,7 @@ static int zero_in_l2_slice(BlockDriverState *bs, uint64_t offset,
As I see, function is not prepared to handle unaligned offset. Worth add an assertion while being here?
> assert(nb_clusters <= INT_MAX);
>
> for (i = 0; i < nb_clusters; i++) {
> - uint64_t old_offset;
> + uint64_t old_offset, l2_entry = 0;
I'd rename s/old_offset/old_l2_entry
> QCow2ClusterType cluster_type;
>
> old_offset = get_l2_entry(s, l2_slice, l2_index + i);
more context:
> /*
> * Minimize L2 changes if the cluster already reads back as
> * zeroes with correct allocation.
> */
> cluster_type = qcow2_get_cluster_type(bs, old_offset);
> if (cluster_type == QCOW2_CLUSTER_ZERO_PLAIN ||
> (cluster_type == QCOW2_CLUSTER_ZERO_ALLOC && !unmap)) {
Worth assert !has_subclusters(s), or mark image corrupted?
> continue;
> }
> @@ -1914,12 +1914,18 @@ 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);
> } 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);
For subclasters & !unmap case we set the same value.. And we even don't need to get it.
may be
if (cluster_type == QCOW2_CLUSTER_COMPRESSED || unmap) {
qcow2_free_any_clusters(bs, old_offset, 1, QCOW2_DISCARD_REQUEST);
set_l2_entry(s, l2_slice, l2_index + i,
has_subclusters(s) ? 0 : QCOW_OFLAG_ZERO);
} else if (!has_subclusters(s)) {
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);
}
if (has_subclusters(s)) {
set_l2_bitmap(s, l2_slice, l2_index + i, QCOW_L2_BITMAP_ALL_ZEROES);
}
> }
>
> qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
>
--
Best regards,
Vladimir