qemu-iotests: add no-op streaming test

This patch tests that in a partial block-stream operation, no data is
ever copied from the base image.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 5272a2aa57bc0b3f981f8b3e0c813e58a88c974b.1458566441.git.berto@igalia.com
Signed-off-by: Jeff Cody <jcody@redhat.com>

tests/qemu-iotests/030

@@ -91,6 +91,24 @@ class TestSingleDrive(iotests.QMPTestCase):
                          qemu_io('-f', iotests.imgfmt, '-c', 'map', test_img),
                          'image file map does not match backing file after streaming')
 
+    def test_stream_no_op(self):
+        self.assert_no_active_block_jobs()
+
+        # The image map is empty before the operation
+        empty_map = qemu_io('-f', iotests.imgfmt, '-c', 'map', test_img)
+
+        # This is a no-op: no data should ever be copied from the base image
+        result = self.vm.qmp('block-stream', device='drive0', base=mid_img)
+        self.assert_qmp(result, 'return', {})
+
+        self.wait_until_completed()
+
+        self.assert_no_active_block_jobs()
+        self.vm.shutdown()
+
+        self.assertEqual(qemu_io('-f', iotests.imgfmt, '-c', 'map', test_img),
+                         empty_map, 'image file map changed after a no-op')
+
     def test_stream_partial(self):
         self.assert_no_active_block_jobs()
 

tests/qemu-iotests/030.out

@@ -1,5 +1,5 @@
-.............
+..............
 ----------------------------------------------------------------------
-Ran 13 tests
+Ran 14 tests
 
 OK