Change livesnapshot to true by default

Because of past qemu bugs we set this to default off and required a
workaround to enable it. However these issues appear to be fixed, and
we should enable this by default for people (with the ability to turn
it off if it's causing crashes in their environment). Metacloud/Cisco
has been running default this way the entire time without issue.

Change-Id: I4545cc99683d311c41c8d6d8dc9787ea6ec6cbc9

nova/conf/workarounds.py

@@ -66,7 +66,7 @@ Interdependencies to other options:
 
     cfg.BoolOpt(
         'disable_libvirt_livesnapshot',
-        default=True,
+        default=False,
         help="""
 Disable live snapshots when using the libvirt driver.
 

nova/tests/unit/virt/libvirt/fake_libvirt_utils.py

@@ -30,7 +30,7 @@ def create_image(disk_format, path, size):
     pass
 
 
-def create_cow_image(backing_file, path):
+def create_cow_image(backing_file, path, size=None):
     pass
 
 

nova/tests/unit/virt/libvirt/test_driver.py

@@ -454,6 +454,7 @@ class FakeVirtDomain(object):
         else:
             self._fake_dom_xml = """
                 <domain type='kvm'>
+                    <name>testinstance1</name>
                     <devices>
                         <disk type='file'>
                             <source file='filename'/>
@@ -510,6 +511,9 @@ class FakeVirtDomain(object):
     def blockJobInfo(self, path, flags):
         pass
 
+    def blockJobAbort(self, path, flags):
+        pass
+
     def resume(self):
         pass
 
@@ -528,6 +532,9 @@ class FakeVirtDomain(object):
     def isPersistent(self):
         return True
 
+    def undefine(self):
+        return True
+
 
 class CacheConcurrencyTestCase(test.NoDBTestCase):
     def setUp(self):
@@ -18998,6 +19005,14 @@ class _BaseSnapshotTests(test.NoDBTestCase):
 
 
 class LibvirtSnapshotTests(_BaseSnapshotTests):
+
+    def setUp(self):
+        super(LibvirtSnapshotTests, self).setUp()
+        # All paths through livesnapshot trigger a chown behind privsep
+        self.privsep_chown = mock.patch.object(nova.privsep.path, 'chown')
+        self.addCleanup(self.privsep_chown.stop)
+        self.privsep_chown.start()
+
     def test_ami(self):
         # Assign different image_ref from nova/images/fakes for testing ami
         self.instance_ref.image_ref = 'c905cedb-7281-47e4-8a62-f26bc5fc4c77'

releasenotes/notes/live_snapshot_by_default-f231485fc2bf77f1.yaml

@@ -0,0 +1,10 @@
+---
+upgrade:
+  - |
+    Nova now defaults to using the live snapshot feature of libvirt
+    when taking snapshots. This was previously disabled by default due
+    to crashes on load seen with older libvirt versions. It has been
+    used in production by many clouds, and appears stable in real
+    world environments. If you see crashes of guests during snapshots,
+    you can disable this with the ``disable_libvirt_livesnapshot``
+    config value in ``[workarounds]``.