Merge "xenapi: Add efficient impl of instance_exists()"

nova/tests/virt/xenapi/test_xenapi.py

@@ -377,6 +377,20 @@ class XenAPIVMTestCase(stubs.XenAPITestBase):
         self.conn.init_host(None)
         self.assertEquals(set(xenapi_fake.get_all('VBD')), set([vbd0, vbd2]))
 
+    def test_instance_exists(self):
+        self.mox.StubOutWithMock(vm_utils, 'lookup')
+        vm_utils.lookup(mox.IgnoreArg(), 'foo').AndReturn(True)
+        self.mox.ReplayAll()
+
+        self.assertTrue(self.conn.instance_exists('foo'))
+
+    def test_instance_not_exists(self):
+        self.mox.StubOutWithMock(vm_utils, 'lookup')
+        vm_utils.lookup(mox.IgnoreArg(), 'bar').AndReturn(None)
+        self.mox.ReplayAll()
+
+        self.assertFalse(self.conn.instance_exists('bar'))
+
     def test_list_instances_0(self):
         instances = self.conn.list_instances()
         self.assertEquals(instances, [])

nova/virt/xenapi/driver.py

@@ -163,6 +163,19 @@ class XenAPIDriver(driver.ComputeDriver):
         except Exception:
             LOG.exception(_('Failure while cleaning up attached VDIs'))
 
+    def instance_exists(self, instance_name):
+        """Checks existence of an instance on the host.
+
+        :param instance_name: The name of the instance to lookup
+
+        Returns True if an instance with the supplied name exists on
+        the host, False otherwise.
+
+        NOTE(belliott): This is an override of the base method for
+        efficiency.
+        """
+        return self._vmops.instance_exists(instance_name)
+
     def list_instances(self):
         """List VM instances."""
         return self._vmops.list_instances()

nova/virt/xenapi/vmops.py

@@ -211,6 +211,9 @@ class VMOps(object):
                                                instance, vm_ref)
         raise exception.NovaException(_("Error: Agent is disabled"))
 
+    def instance_exists(self, name_label):
+        return vm_utils.lookup(self._session, name_label) is not None
+
     def list_instances(self):
         """List VM instances."""
         # TODO(justinsb): Should we just always use the details method?