Allows xenapi 'lookup' to look for rescue mode VMs

When you lookup a VM by name, you can specify if you want it to check if
it has a rescue mode instance running.

If it finds the rescue mode instance, it'll return that one instead
of the original name.

This is useful for operations that should work on the rescue mode vm if
it's there, or the normal one, if it's not.

Work towards bug: 1170237
Change-Id: I41b31e59631b78a62faadb9970b6b824929e7061

nova/tests/virt/xenapi/test_vm_utils.py

@@ -63,6 +63,33 @@ def test_too_many(self):
                           vm_utils.lookup,
                           self.session, self.name_label)
 
+    def test_rescue_none(self):
+        self.session.call_xenapi(
+            "VM.get_by_name_label", self.name_label + '-rescue').AndReturn([])
+        self._do_mock(['x'])
+        result = vm_utils.lookup(self.session, self.name_label,
+                                 check_rescue=True)
+        self.assertEqual('x', result)
+
+    def test_rescue_found(self):
+        self.session.call_xenapi(
+            "VM.get_by_name_label",
+            self.name_label + '-rescue').AndReturn(['y'])
+        self.mox.ReplayAll()
+        result = vm_utils.lookup(self.session, self.name_label,
+                                 check_rescue=True)
+        self.assertEqual('y', result)
+
+    def test_rescue_too_many(self):
+        self.session.call_xenapi(
+            "VM.get_by_name_label",
+            self.name_label + '-rescue').AndReturn(['a', 'b', 'c'])
+        self.mox.ReplayAll()
+        self.assertRaises(exception.InstanceExists,
+                          vm_utils.lookup,
+                          self.session, self.name_label,
+                          check_rescue=True)
+
 
 class GenerateConfigDriveTestCase(test.TestCase):
     def test_no_admin_pass(self):

nova/virt/xenapi/vm_utils.py

@@ -1394,8 +1394,15 @@ def lookup_vm_vdis(session, vm_ref):
     return vdi_refs
 
 
-def lookup(session, name_label):
-    """Look the instance up and return it if available."""
+def lookup(session, name_label, check_rescue=False):
+    """Look the instance up and return it if available.
+    :param check_rescue: if True will return the 'name'-rescue vm if it
+                         exists, instead of just 'name'
+    """
+    if check_rescue:
+        result = lookup(session, name_label + '-rescue', False)
+        if result:
+            return result
     vm_refs = session.call_xenapi("VM.get_by_name_label", name_label)
     n = len(vm_refs)
     if n == 0: