qcow2-refcount: fix_l2_entry_by_zero(): also zero L2 entry bitmap

We'll reuse the function to fix wrong L2 entry bitmap. Support it now.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20210914122454.141075-6-vsementsov@virtuozzo.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

block/qcow2-refcount.c

@@ -1588,7 +1588,8 @@ enum {
 };
 
 /*
- * Fix L2 entry by making it QCOW2_CLUSTER_ZERO_PLAIN.
+ * Fix L2 entry by making it QCOW2_CLUSTER_ZERO_PLAIN (or making all its present
+ * subclusters QCOW2_SUBCLUSTER_ZERO_PLAIN).
  *
  * This function decrements res->corruptions on success, so the caller is
  * responsible to increment res->corruptions prior to the call.
@@ -1605,9 +1606,20 @@ static int fix_l2_entry_by_zero(BlockDriverState *bs, BdrvCheckResult *res,
     int idx = l2_index * (l2_entry_size(s) / sizeof(uint64_t));
     uint64_t l2e_offset = l2_offset + (uint64_t)l2_index * l2_entry_size(s);
     int ign = active ? QCOW2_OL_ACTIVE_L2 : QCOW2_OL_INACTIVE_L2;
-    uint64_t l2_entry = has_subclusters(s) ? 0 : QCOW_OFLAG_ZERO;
 
-    set_l2_entry(s, l2_table, l2_index, l2_entry);
+    if (has_subclusters(s)) {
+        uint64_t l2_bitmap = get_l2_bitmap(s, l2_table, l2_index);
+
+        /* Allocated subclusters become zero */
+        l2_bitmap |= l2_bitmap << 32;
+        l2_bitmap &= QCOW_L2_BITMAP_ALL_ZEROES;
+
+        set_l2_bitmap(s, l2_table, l2_index, l2_bitmap);
+        set_l2_entry(s, l2_table, l2_index, 0);
+    } else {
+        set_l2_entry(s, l2_table, l2_index, QCOW_OFLAG_ZERO);
+    }
+
     ret = qcow2_pre_write_overlap_check(bs, ign, l2e_offset, l2_entry_size(s),
                                         false);
     if (metadata_overlap) {