When the discard-no-unref flag is enabled, we keep the reference for normal discard requests. But when a discard is executed on a snapshot/qcow2 image with backing, the discards are saved as zero clusters in the snapshot image.
When committing the snapshot to the backing file, not discard_in_l2_slice is called but zero_in_l2_slice. Which did not had any logic to keep the reference when discard-no-unref is enabled. Therefor we add logic in the zero_in_l2_slice call to keep the reference on commit. Next to that we also revert some logic from 42a2890a and just call qcow2_free_any_cluster. As this will just decrease the refcount but not remove the reference itself. And it will also send the discard further to the lower layer. Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1621 Signed-off-by: Jean-Louis Dupond <[email protected]> --- block/qcow2-cluster.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index f4f6cd6ad0..48532ca3c2 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -1975,16 +1975,7 @@ static int discard_in_l2_slice(BlockDriverState *bs, uint64_t offset, if (has_subclusters(s)) { set_l2_bitmap(s, l2_slice, l2_index + i, new_l2_bitmap); } - if (!keep_reference) { - /* Then decrease the refcount */ - qcow2_free_any_cluster(bs, old_l2_entry, type); - } else if (s->discard_passthrough[type] && - (cluster_type == QCOW2_CLUSTER_NORMAL || - cluster_type == QCOW2_CLUSTER_ZERO_ALLOC)) { - /* If we keep the reference, pass on the discard still */ - bdrv_pdiscard(s->data_file, old_l2_entry & L2E_OFFSET_MASK, - s->cluster_size); - } + qcow2_free_any_cluster(bs, old_l2_entry, type); } qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice); @@ -2062,9 +2053,14 @@ zero_in_l2_slice(BlockDriverState *bs, uint64_t offset, QCow2ClusterType type = qcow2_get_cluster_type(bs, old_l2_entry); bool unmap = (type == QCOW2_CLUSTER_COMPRESSED) || ((flags & BDRV_REQ_MAY_UNMAP) && qcow2_cluster_is_allocated(type)); - uint64_t new_l2_entry = unmap ? 0 : old_l2_entry; + uint64_t new_l2_entry = old_l2_entry; uint64_t new_l2_bitmap = old_l2_bitmap; + if (unmap && + !(s->discard_no_unref && type != QCOW2_CLUSTER_COMPRESSED)) { + new_l2_entry = 0; + } + if (has_subclusters(s)) { new_l2_bitmap = QCOW_L2_BITMAP_ALL_ZEROES; } else { -- 2.42.0
