[PATCH 3/7] qcow2: zeroize the entire cluster when there're no non-zero subclusters

[Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>]

When zeroizing the last non-zero subclusters within single cluster, it
makes sense to go zeroize the entire cluster and go down zero_in_l2_slice()
path right away.  That way we'd also update the corresponding refcount
table.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 block/qcow2-cluster.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 8801856b93..7c6fa5524c 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -2145,7 +2145,7 @@ zero_in_l2_slice(BlockDriverState *bs, uint64_t offset,
 
 static int coroutine_fn GRAPH_RDLOCK
 zero_l2_subclusters(BlockDriverState *bs, uint64_t offset,
-                    unsigned nb_subclusters)
+                    unsigned nb_subclusters, int flags)
 {
     BDRVQcow2State *s = bs->opaque;
     uint64_t new_l2_bitmap;
@@ -2161,6 +2161,17 @@ zero_l2_subclusters(BlockDriverState *bs, uint64_t offset,
     new_l2_bitmap |=  QCOW_OFLAG_SUB_ZERO_RANGE(sc, sc + nb_subclusters);
     new_l2_bitmap &= ~QCOW_OFLAG_SUB_ALLOC_RANGE(sc, sc + nb_subclusters);
 
+    /*
+     * If there're no non-zero subclusters left, we might as well zeroize
+     * the entire cluster.  That way we'd also update the refcount table.
+     */
+    if ((new_l2_bitmap & QCOW_L2_BITMAP_ALL_ZEROES) ==
+        QCOW_L2_BITMAP_ALL_ZEROES) {
+        qcow2_cache_put(s->l2_table_cache, (void **) &scri.l2_slice);
+        return zero_in_l2_slice(bs, QEMU_ALIGN_DOWN(offset, s->cluster_size),
+                                1, flags);
+    }
+
     if (new_l2_bitmap != scri.l2_bitmap) {
         set_l2_bitmap(s, scri.l2_slice, scri.l2_index, new_l2_bitmap);
         qcow2_cache_entry_mark_dirty(s->l2_table_cache, scri.l2_slice);
@@ -2221,7 +2232,7 @@ int coroutine_fn qcow2_subcluster_zeroize(BlockDriverState *bs, uint64_t offset,
 
     if (head) {
         ret = zero_l2_subclusters(bs, offset - head,
-                                  size_to_subclusters(s, head));
+                                  size_to_subclusters(s, head), flags);
         if (ret < 0) {
             goto fail;
         }
@@ -2242,7 +2253,8 @@ int coroutine_fn qcow2_subcluster_zeroize(BlockDriverState *bs, uint64_t offset,
     }
 
     if (tail) {
-        ret = zero_l2_subclusters(bs, end_offset, size_to_subclusters(s, tail));
+        ret = zero_l2_subclusters(bs, end_offset,
+                                  size_to_subclusters(s, tail), flags);
         if (ret < 0) {
             goto fail;
         }
-- 
2.39.3