Ideally it should be possible to zero individual subclusters using
this function, but this is currently not implemented.

Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 block/qcow2.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/block/qcow2.c b/block/qcow2.c
index 01322ca449..537569ce88 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -3704,6 +3704,12 @@ static coroutine_fn int qcow2_co_pwrite_zeroes(BlockDriverState *bs,
         bytes = s->cluster_size;
         nr = s->cluster_size;
         ret = qcow2_get_cluster_offset(bs, offset, &nr, &off);
+        /* TODO: allow zeroing separate subclusters, we only allow
+         * zeroing full clusters at the moment. */
+        if (nr != bytes) {
+            qemu_co_mutex_unlock(&s->lock);
+            return -ENOTSUP;
+        }
         if (ret != QCOW2_CLUSTER_UNALLOCATED &&
             ret != QCOW2_CLUSTER_UNALLOCATED_SUBCLUSTER &&
             ret != QCOW2_CLUSTER_ZERO_PLAIN &&
-- 
2.20.1