1 files changed, 19 insertions, 16 deletions

diff --git a/block/qcow2.c b/block/qcow2.c
index b6cb4db8bb..4274806a2a 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2387,26 +2387,26 @@ static bool merge_cow(uint64_t offset, unsigned bytes,
     return false;
 }
 
-static bool is_unallocated(BlockDriverState *bs, int64_t offset, int64_t bytes)
-{
-    int64_t nr;
-    return !bytes ||
-        (!bdrv_is_allocated_above(bs, NULL, false, offset, bytes, &nr) &&
-         nr == bytes);
-}
-
-static bool is_zero_cow(BlockDriverState *bs, QCowL2Meta *m)
+/*
+ * Return 1 if the COW regions read as zeroes, 0 if not, < 0 on error.
+ * Note that returning 0 does not guarantee non-zero data.
+ */
+static int is_zero_cow(BlockDriverState *bs, QCowL2Meta *m)
 {
     /*
      * This check is designed for optimization shortcut so it must be
      * efficient.
-     * Instead of is_zero(), use is_unallocated() as it is faster (but not
-     * as accurate and can result in false negatives).
+     * Instead of is_zero(), use bdrv_co_is_zero_fast() as it is
+     * faster (but not as accurate and can result in false negatives).
      */
-    return is_unallocated(bs, m->offset + m->cow_start.offset,
-                          m->cow_start.nb_bytes) &&
-           is_unallocated(bs, m->offset + m->cow_end.offset,
-                          m->cow_end.nb_bytes);
+    int ret = bdrv_co_is_zero_fast(bs, m->offset + m->cow_start.offset,
+                                   m->cow_start.nb_bytes);
+    if (ret <= 0) {
+        return ret;
+    }
+
+    return bdrv_co_is_zero_fast(bs, m->offset + m->cow_end.offset,
+                                m->cow_end.nb_bytes);
 }
 
 static int handle_alloc_space(BlockDriverState *bs, QCowL2Meta *l2meta)
@@ -2432,7 +2432,10 @@ static int handle_alloc_space(BlockDriverState *bs, QCowL2Meta *l2meta)
             continue;
         }
 
-        if (!is_zero_cow(bs, m)) {
+        ret = is_zero_cow(bs, m);
+        if (ret < 0) {
+            return ret;
+        } else if (ret == 0) {
             continue;
         }