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qcow2: keep reference on zeroize with discard-no-unref enabled

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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.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1621
Signed-off-by: Jean-Louis Dupond <jean-louis@dupond.be>
Message-Id: <20231003125236.216473-2-jean-louis@dupond.be>
[hreitz: Made the documentation change more verbose, as discussed
         on-list]
Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
This commit is contained in:
Jean-Louis Dupond 2023-10-03 14:52:37 +02:00 • committed by Hanna Czenczek
parent 3e01f1147a
commit b2b109041e
3 changed files with 39 additions and 17 deletions
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22
block/qcow2-cluster.c
View file

@ -1983,7 +1983,7 @@ discard_in_l2_slice(BlockDriverState *bs, uint64_t offset, uint64_t nb_clusters,
/* 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_cache_put(s->l2_table_cache, (void **) &l2_slice);
@ -2061,9 +2061,15 @@ 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;
bool keep_reference =
(s->discard_no_unref && type != QCOW2_CLUSTER_COMPRESSED);
uint64_t new_l2_entry = old_l2_entry;
uint64_t new_l2_bitmap = old_l2_bitmap;
if (unmap && !keep_reference) {
new_l2_entry = 0;
}
if (has_subclusters(s)) {
new_l2_bitmap = QCOW_L2_BITMAP_ALL_ZEROES;
} else {
@ -2081,9 +2087,17 @@ zero_in_l2_slice(BlockDriverState *bs, uint64_t offset,
set_l2_bitmap(s, l2_slice, l2_index + i, new_l2_bitmap);
}
/* Then decrease the refcount */
if (unmap) {
qcow2_free_any_cluster(bs, old_l2_entry, QCOW2_DISCARD_REQUEST);
if (!keep_reference) {
/* Then decrease the refcount */
qcow2_free_any_cluster(bs, old_l2_entry, QCOW2_DISCARD_REQUEST);
} else if (s->discard_passthrough[QCOW2_DISCARD_REQUEST] &&
(type == QCOW2_CLUSTER_NORMAL ||
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);
}
}
}