qemu-iotests: Test the reopening of overlay_bs in 'block-commit'

The 'block-commit' command needs the overlay image of 'top' to
be opened in read-write mode in order to update the backing file
string. If 'top' is not the active layer or its backing file then its
overlay needs to be reopened during the block job.

This is a test case for that scenario.
Signed-off-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/040

@@ -41,6 +41,7 @@ class ImageCommitTestCase(iotests.QMPTestCase):
         while not completed:
             for event in self.vm.get_qmp_events(wait=True):
                 if event['event'] == 'BLOCK_JOB_COMPLETED':
+                    self.assert_qmp_absent(event, 'data/error')
                     self.assert_qmp(event, 'data/type', 'commit')
                     self.assert_qmp(event, 'data/device', 'drive0')
                     self.assert_qmp(event, 'data/offset', event['data']['len'])
@@ -251,5 +252,34 @@ class TestSetSpeed(ImageCommitTestCase):
 class TestActiveZeroLengthImage(TestSingleDrive):
     image_len = 0
 
+class TestReopenOverlay(ImageCommitTestCase):
+    image_len = 1024 * 1024
+    img0 = os.path.join(iotests.test_dir, '0.img')
+    img1 = os.path.join(iotests.test_dir, '1.img')
+    img2 = os.path.join(iotests.test_dir, '2.img')
+    img3 = os.path.join(iotests.test_dir, '3.img')
+
+    def setUp(self):
+        iotests.create_image(self.img0, self.image_len)
+        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % self.img0, self.img1)
+        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % self.img1, self.img2)
+        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % self.img2, self.img3)
+        qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0xab 0 128K', self.img1)
+        self.vm = iotests.VM().add_drive(self.img3)
+        self.vm.launch()
+
+    def tearDown(self):
+        self.vm.shutdown()
+        os.remove(self.img0)
+        os.remove(self.img1)
+        os.remove(self.img2)
+        os.remove(self.img3)
+
+    # This tests what happens when the overlay image of the 'top' node
+    # needs to be reopened in read-write mode in order to update the
+    # backing image string.
+    def test_reopen_overlay(self):
+        self.run_commit_test(self.img1, self.img0)
+
 if __name__ == '__main__':
     iotests.main(supported_fmts=['qcow2', 'qed'])

tests/qemu-iotests/040.out

-........................
+.........................
 ----------------------------------------------------------------------
-Ran 24 tests
+Ran 25 tests
 
 OK