qcow2: Allow updating no refcounts

There's absolutely no problem with updating the refcounts of 0 clusters.
At least snapshot code is doing this and would fail once the result of
update_refcount isn't ignored any more.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index a84620ffe2681e141bac2e7b6a8df254100f1cf0..da7d3f2401dc7ec885cab5596fb9a3d22a4ac502 100644 (file)
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -284,8 +284,12 @@ static int update_refcount(BlockDriverState *bs,
     printf("update_refcount: offset=%" PRId64 " size=%" PRId64 " addend=%d\n",
            offset, length, addend);
 #endif
-    if (length <= 0)
+    if (length < 0) {
         return -EINVAL;
+    } else if (length == 0) {
+        return 0;
+    }
+
     start = offset & ~(s->cluster_size - 1);
     last = (offset + length - 1) & ~(s->cluster_size - 1);
     for(cluster_offset = start; cluster_offset <= last;