qemu-iotests: extract wait_until_completed() into iotests.py

The 'drive-mirror' tests often issue 'block-job-complete' and wait for
the QMP completion event.  Other types of block jobs also want to wait
for completion but they may not need to issue 'block-job-complete'.

Extract wait_until_completed() from 041 and put it into iotests.py.
Return the QMP event object so the caller can make additional
assertions, if necessary.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/041

@@ -57,18 +57,8 @@ class ImageMirroringTestCase(iotests.QMPTestCase):
         result = self.vm.qmp('block-job-complete', device=drive)
         self.assert_qmp(result, 'return', {})
 
-        completed = False
-        while not completed:
-            for event in self.vm.get_qmp_events(wait=True):
-                if event['event'] == 'BLOCK_JOB_COMPLETED':
-                    self.assert_qmp(event, 'data/type', 'mirror')
-                    self.assert_qmp(event, 'data/device', drive)
-                    self.assert_qmp_absent(event, 'data/error')
-                    self.assert_qmp(event, 'data/offset', self.image_len)
-                    self.assert_qmp(event, 'data/len', self.image_len)
-                    completed = True
-
-        self.assert_no_active_block_jobs()
+        event = self.wait_until_completed()
+        self.assert_qmp(event, 'data/type', 'mirror')
 
 class TestSingleDrive(ImageMirroringTestCase):
     image_len = 1 * 1024 * 1024 # MB

tests/qemu-iotests/iotests.py

@@ -208,6 +208,21 @@ def cancel_and_wait(self, drive='drive0', force=False):
         self.assert_no_active_block_jobs()
         return result
 
+    def wait_until_completed(self, drive='drive0'):
+        '''Wait for a block job to finish, returning the event'''
+        completed = False
+        while not completed:
+            for event in self.vm.get_qmp_events(wait=True):
+                if event['event'] == 'BLOCK_JOB_COMPLETED':
+                    self.assert_qmp(event, 'data/device', drive)
+                    self.assert_qmp_absent(event, 'data/error')
+                    self.assert_qmp(event, 'data/offset', self.image_len)
+                    self.assert_qmp(event, 'data/len', self.image_len)
+                    completed = True
+
+        self.assert_no_active_block_jobs()
+        return event
+
 def notrun(reason):
     '''Skip this test suite'''
     # Each test in qemu-iotests has a number ("seq")