diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index d9ef60ef0337c300bb2dcf1a32217983ea493ecd..56f988ab3d017e0eaae0f18bc0d0f49556e4b99a 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -28,6 +28,7 @@ sys.path.append(os.path.join(os.path.dirname(__file__), '..', '..', 'scripts', '
 import qmp
 import qtest
 import struct
+import json
 
 
 # This will not work if arguments contain spaces but is necessary if we
@@ -103,6 +104,11 @@ def create_image(name, size):
         i = i + 512
     file.close()
 
+def image_size(img):
+    '''Return image's virtual size'''
+    r = qemu_img_pipe('info', '--output=json', '-f', imgfmt, img)
+    return json.loads(r)['virtual-size']
+
 test_dir_re = re.compile(r"%s" % test_dir)
 def filter_test_dir(msg):
     return test_dir_re.sub("TEST_DIR", msg)