Fix nova-network MAC collision logic

The exception being caught and transformed in sqlalchemy/api.py
was incorrect, causing nova-network to miss it in the MAC
collision retry loop.

This patch corrects that and adds a test of the collision logic.

Backports the fix for bug 1059366

Change-Id: I89d17eb8606a18f102e4de0dc76c77205cafbc8d

nova/db/sqlalchemy/api.py

@@ -1278,7 +1278,7 @@ def virtual_interface_create(context, values):
         vif_ref = models.VirtualInterface()
         vif_ref.update(values)
         vif_ref.save()
-    except IntegrityError:
+    except exception.DBError:
         raise exception.VirtualInterfaceCreateException()
 
     return vif_ref

nova/tests/network/test_manager.py

@@ -22,6 +22,7 @@
 
 from nova import context
 from nova import db
+from nova.db.sqlalchemy import models
 from nova import exception
 from nova.network import linux_net
 from nova.network import manager as network_manager
@@ -1752,6 +1753,38 @@ def fake_domains(context):
         self.network.delete_dns_domain(context_admin, domain1)
         self.network.delete_dns_domain(context_admin, domain2)
 
+    def test_mac_conflicts(self):
+        """Make sure MAC collisions are retried"""
+        self.flags(create_unique_mac_address_attempts=3)
+        ctxt = context.RequestContext('testuser', 'testproject', is_admin=True)
+        macs = ['bb:bb:bb:bb:bb:bb', 'aa:aa:aa:aa:aa:aa']
+
+        # Create a VIF with aa:aa:aa:aa:aa:aa
+        crash_test_dummy_vif = {
+            'address': macs[1],
+            'instance_uuid': 'fake_uuid',
+            'network_id': 'fake_net',
+            'uuid': 'fake_uuid',
+            }
+        self.network.db.virtual_interface_create(ctxt, crash_test_dummy_vif)
+
+        # Hand out a collision first, then a legit MAC
+        def fake_gen_mac():
+            return macs.pop()
+        self.stubs.Set(utils, 'generate_mac_address', fake_gen_mac)
+
+        # SQLite doesn't seem to honor the uniqueness constraint on the
+        # address column, so fake the collision-avoidance here
+        def fake_vif_save(vif):
+            if vif.address == crash_test_dummy_vif['address']:
+                raise exception.DBError("If you're smart, you'll retry!")
+        self.stubs.Set(models.VirtualInterface, 'save', fake_vif_save)
+
+        # Attempt to add another and make sure that both MACs are consumed
+        # by the retry loop
+        self.network.add_virtual_interface(ctxt, 'fake_uuid', 'fake_net')
+        self.assertEqual(macs, [])
+
 
 class NetworkPolicyTestCase(test.TestCase):
     def setUp(self):