libvirt: Fix infinite loop waiting for block job

Libvirt may return an empty dict when a block job has completed.
In this case, _wait_for_block_job will return True, causing
its callers to loop.

Affects volume_snapshot_delete, swap_volume, and live_snapshot.

(See http://libvirt.org/git/?p=libvirt.git;a=commit;h=0f9e67bf )

Closes-Bug: #1260123
Change-Id: Iab81299f0ce32a14e46aee0fd389ed29f7e503b8
(cherry picked from commit e3ac20fca7)

nova/tests/virt/libvirt/fakelibvirt.py

@@ -498,6 +498,9 @@ class Domain(object):
     def maxMemory(self):
         return self._def['memory']
 
+    def blockJobInfo(self, disk, flags):
+        return {}
+
 
 class DomainSnapshot(object):
     def __init__(self, name, domain):

nova/tests/virt/libvirt/test_libvirt.py

@@ -7301,6 +7301,7 @@ class LibvirtVolumeSnapshotTestCase(test.TestCase):
         self.mox.StubOutWithMock(self.conn, 'has_min_version')
         self.mox.StubOutWithMock(domain, 'blockRebase')
         self.mox.StubOutWithMock(domain, 'blockCommit')
+        self.mox.StubOutWithMock(domain, 'blockJobInfo')
 
         self.conn._lookup_by_name('instance-%s' % instance['id']).\
             AndReturn(domain)
@@ -7308,6 +7309,9 @@ class LibvirtVolumeSnapshotTestCase(test.TestCase):
 
         domain.blockRebase('vda', 'snap.img', 0, 0)
 
+        domain.blockJobInfo('vda', 0).AndReturn({'cur': 1, 'end': 1000})
+        domain.blockJobInfo('vda', 0).AndReturn({'cur': 1000, 'end': 1000})
+
         self.mox.ReplayAll()
 
         self.conn._volume_snapshot_delete(self.c, instance, self.volume_uuid,
@@ -7329,6 +7333,7 @@ class LibvirtVolumeSnapshotTestCase(test.TestCase):
         self.mox.StubOutWithMock(self.conn, 'has_min_version')
         self.mox.StubOutWithMock(domain, 'blockRebase')
         self.mox.StubOutWithMock(domain, 'blockCommit')
+        self.mox.StubOutWithMock(domain, 'blockJobInfo')
 
         self.conn._lookup_by_name('instance-%s' % instance['id']).\
             AndReturn(domain)
@@ -7336,6 +7341,9 @@ class LibvirtVolumeSnapshotTestCase(test.TestCase):
 
         domain.blockCommit('vda', 'other-snap.img', 'snap.img', 0, 0)
 
+        domain.blockJobInfo('vda', 0).AndReturn({'cur': 1, 'end': 1000})
+        domain.blockJobInfo('vda', 0).AndReturn({})
+
         self.mox.ReplayAll()
 
         self.conn._volume_snapshot_delete(self.c, instance, self.volume_uuid,

nova/virt/libvirt/driver.py

@@ -1429,6 +1429,16 @@ class LibvirtDriver(driver.ComputeDriver):
 
     @staticmethod
     def _wait_for_block_job(domain, disk_path, abort_on_error=False):
+        """Wait for libvirt block job to complete.
+
+        Libvirt may return either cur==end or an empty dict when
+        the job is complete, depending on whether the job has been
+        cleaned up by libvirt yet, or not.
+
+        :returns: True if still in progress
+                  False if completed
+        """
+
         status = domain.blockJobInfo(disk_path, 0)
         if status == -1 and abort_on_error:
             msg = _('libvirt error while requesting blockjob info.')
@@ -1439,7 +1449,7 @@ class LibvirtDriver(driver.ComputeDriver):
         except Exception:
             return False
 
-        if cur == end and cur != 0 and end != 0:
+        if cur == end:
             return False
         else:
             return True