Merge "Remedies LP Bug #928910 - Use libvirt lookupByName() to check existence"

3 files changed, 24 insertions, 1 deletions

diff --git a/nova/compute/manager.py b/nova/compute/manager.py
index 90a6a84ec..078f53928 100644
--- a/nova/compute/manager.py
+++ b/nova/compute/manager.py
@@ -440,7 +440,7 @@ class ComputeManager(manager.SchedulerDependentManager):
 
     def _check_instance_not_already_created(self, context, instance):
         """Ensure an instance with the same name is not already present."""
-        if instance['name'] in self.driver.list_instances():
+        if self.driver.instance_exists(instance['name']):
             raise exception.Error(_("Instance has already been created"))
 
     def _check_image_size(self, context, instance):
diff --git a/nova/virt/driver.py b/nova/virt/driver.py
index 200bada29..f1d382ac4 100644
--- a/nova/virt/driver.py
+++ b/nova/virt/driver.py
@@ -122,6 +122,21 @@ class ComputeDriver(object):
         # TODO(Vek): Need to pass context in for access to auth_token
         raise NotImplementedError()
 
+    def instance_exists(self, instance_id):
+        """Checks existence of an instance on the host.
+
+        Returns True if an instance with the supplied ID exists on
+        the host, False otherwise.
+
+        :note This implementation works for all drivers, but it is
+              not particularly efficient. Maintainers of the virt drivers are
+              encouraged to override this method with something more
+              efficient.
+
+        :param instance_id: The ID / name of the instance to lookup
+        """
+        return instance_id in self.list_instances()
+
     def list_instances(self):
         """
         Return the names of all the instances known to the virtualization
diff --git a/nova/virt/libvirt/connection.py b/nova/virt/libvirt/connection.py
index 3e8dbb8c1..087dba446 100644
--- a/nova/virt/libvirt/connection.py
+++ b/nova/virt/libvirt/connection.py
@@ -281,6 +281,14 @@ class LibvirtConnection(driver.ComputeDriver):
         else:
             return libvirt.openAuth(uri, auth, 0)
 
+    def instance_exists(self, instance_id):
+        """Efficient override of base instance_exists method."""
+        try:
+            _ignored = self._conn.lookupByName(instance_id)
+            return True
+        except libvirt.libvirtError:
+            return False
+
     def list_instances(self):
         return [self._conn.lookupByID(x).name()
                 for x in self._conn.listDomainsID()