Two things need to be taken into account here:
1) With full_discard == true the L2 entry must be cleared completely.
This also includes the L2 bitmap if the image has extended L2
entries.
2) With full_discard == false we have to make the discarded cluster
read back as zeroes. With normal L2 entries this is done with the
QCOW_OFLAG_ZERO bit, whereas with extended L2 entries this is done
with the individual 'all zeroes' bits for each subcluster.
Note however that QCOW_OFLAG_ZERO is not supported in v2 qcow2
images so, if there is a backing file, discard cannot guarantee
that the image will read back as zeroes. If this is important for
the caller it should forbid it as qcow2_co_pdiscard() does (see
80f5c01183 for more details).
Signed-off-by: Alberto Garcia
---
block/qcow2-cluster.c | 52 +++
1 file changed, 23 insertions(+), 29 deletions(-)
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 4e59bbd545..edfc8ea91c 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1847,11 +1847,17 @@ static int discard_in_l2_slice(BlockDriverState *bs,
uint64_t offset,
assert(nb_clusters <= INT_MAX);
for (i = 0; i < nb_clusters; i++) {
-uint64_t old_l2_entry;
-
-old_l2_entry = get_l2_entry(s, l2_slice, l2_index + i);
+uint64_t old_l2_entry = get_l2_entry(s, l2_slice, l2_index + i);
+uint64_t old_l2_bitmap = get_l2_bitmap(s, l2_slice, l2_index + i);
+uint64_t new_l2_entry = old_l2_entry;
+uint64_t new_l2_bitmap = old_l2_bitmap;
+QCow2ClusterType cluster_type =
+qcow2_get_cluster_type(bs, old_l2_entry);
/*
+ * If full_discard is true, the cluster should not read back as zeroes,
+ * but rather fall through to the backing file.
+ *
* If full_discard is false, make sure that a discarded area reads back
* as zeroes for v3 images (we cannot do it for v2 without actually
* writing a zero-filled buffer). We can skip the operation if the
@@ -1860,40 +1866,28 @@ static int discard_in_l2_slice(BlockDriverState *bs,
uint64_t offset,
*
* TODO We might want to use bdrv_block_status(bs) here, but we're
* holding s->lock, so that doesn't work today.
- *
- * If full_discard is true, the sector should not read back as zeroes,
- * but rather fall through to the backing file.
*/
-switch (qcow2_get_cluster_type(bs, old_l2_entry)) {
-case QCOW2_CLUSTER_UNALLOCATED:
-if (full_discard || !bs->backing) {
-continue;
+if (full_discard) {
+new_l2_entry = new_l2_bitmap = 0;
+} else if (bs->backing || qcow2_cluster_is_allocated(cluster_type)) {
+if (has_subclusters(s)) {
+new_l2_entry = 0;
+new_l2_bitmap = QCOW_L2_BITMAP_ALL_ZEROES;
+} else {
+new_l2_entry = s->qcow_version >= 3 ? QCOW_OFLAG_ZERO : 0;
}
-break;
+}
-case QCOW2_CLUSTER_ZERO_PLAIN:
-if (!full_discard) {
-continue;
-}
-break;
-
-case QCOW2_CLUSTER_ZERO_ALLOC:
-case QCOW2_CLUSTER_NORMAL:
-case QCOW2_CLUSTER_COMPRESSED:
-break;
-
-default:
-abort();
+if (old_l2_entry == new_l2_entry && old_l2_bitmap == new_l2_bitmap) {
+continue;
}
/* First remove L2 entries */
qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
-if (!full_discard && s->qcow_version >= 3) {
-set_l2_entry(s, l2_slice, l2_index + i, QCOW_OFLAG_ZERO);
-} else {
-set_l2_entry(s, l2_slice, l2_index + i, 0);
+set_l2_entry(s, l2_slice, l2_index + i, new_l2_entry);
+if (has_subclusters(s)) {
+set_l2_bitmap(s, l2_slice, l2_index + i, new_l2_bitmap);
}
-
/* Then decrease the refcount */
qcow2_free_any_clusters(bs, old_l2_entry, 1, type);
}
--
2.20.1
