[Qemu-block] [PATCH] qemu-iotests: fix 203 migration completion race

[Stefan Hajnoczi]

There is a race between the test's 'query-migrate' QMP command after the
QMP 'STOP' event and completing the migration:

The test case invokes 'query-migrate' upon receiving 'STOP'.  At this
point the migration thread may still be in the process of completing.
Therefore 'query-migrate' can return 'status': 'active' for a brief
window of time instead of 'status': 'completed'.  This results in
qemu-iotests 203 hanging.

Solve the race by enabling the 'events' migration capability, which
causes QEMU to emit migration-specific QMP events that do not suffer
from this race condition.  Wait for the QMP 'MIGRATION' event with
'status': 'completed'.

Reported-by: Max Reitz <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 tests/qemu-iotests/203     | 15 +++++++++++----
 tests/qemu-iotests/203.out |  5 +++++
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/tests/qemu-iotests/203 b/tests/qemu-iotests/203
index 2c811917d8..4874a1a0d8 100755
--- a/tests/qemu-iotests/203
+++ b/tests/qemu-iotests/203
@@ -49,11 +49,18 @@ with iotests.FilePath('disk0.img') as disk0_img_path, \
                        node_name='drive1-node', iothread='iothread0',
                        force=True))
 
+    iotests.log('Enabling migration QMP events...')
+    iotests.log(vm.qmp('migrate-set-capabilities', capabilities=[
+        {
+            'capability': 'events',
+            'state': True
+        }
+    ]))
+
     iotests.log('Starting migration...')
     iotests.log(vm.qmp('migrate', uri='exec:cat >/dev/null'))
     while True:
-        vm.get_qmp_event(wait=60.0)
-        result = vm.qmp('query-migrate')
-        status = result.get('return', {}).get('status', None)
-        if status == 'completed':
+        event = vm.event_wait('MIGRATION')
+        iotests.log(event, filters=[iotests.filter_qmp_event])
+        if event['data']['status'] == 'completed':
             break
diff --git a/tests/qemu-iotests/203.out b/tests/qemu-iotests/203.out
index 3f1ff900e4..1a11f0975c 100644
--- a/tests/qemu-iotests/203.out
+++ b/tests/qemu-iotests/203.out
@@ -2,5 +2,10 @@ Launching VM...
 Setting IOThreads...
 {u'return': {}}
 {u'return': {}}
+Enabling migration QMP events...
+{u'return': {}}
 Starting migration...
 {u'return': {}}
+{u'timestamp': {u'seconds': 'SECS', u'microseconds': 'USECS'}, u'data': 
{u'status': u'setup'}, u'event': u'MIGRATION'}
+{u'timestamp': {u'seconds': 'SECS', u'microseconds': 'USECS'}, u'data': 
{u'status': u'active'}, u'event': u'MIGRATION'}
+{u'timestamp': {u'seconds': 'SECS', u'microseconds': 'USECS'}, u'data': 
{u'status': u'completed'}, u'event': u'MIGRATION'}
-- 
2.14.3