DHCP agent should check interface is UP before adding route

The DHCP agent should check not only that an interface for
network's DHCP exists but also make sure that is UP before
adding a default route.
For this purpose a method "ensure_device_is_ready" was
added to ip_lib.

Change-Id: I9af06aa0f39634fe7b63c064337cd4191db5c026
Closes-bug: #1302312

neutron/agent/linux/dhcp.py

@@ -815,7 +815,7 @@ class DeviceManager(object):
         port = self.setup_dhcp_port(network)
         interface_name = self.get_interface_name(network, port)
 
-        if ip_lib.device_exists(interface_name,
+        if ip_lib.ensure_device_is_ready(interface_name,
                                          self.root_helper,
                                          network.namespace):
             LOG.debug(_('Reusing existing device: %s.'), interface_name)

neutron/agent/linux/ip_lib.py

@@ -482,6 +482,17 @@ def device_exists(device_name, root_helper=None, namespace=None):
     return bool(address)
 
 
+def ensure_device_is_ready(device_name, root_helper=None, namespace=None):
+    dev = IPDevice(device_name, root_helper, namespace)
+    try:
+        # Ensure the device is up, even if it is already up. If the device
+        # doesn't exist, a RuntimeError will be raised.
+        dev.link.set_up()
+    except RuntimeError:
+        return False
+    return True
+
+
 def iproute_arg_supported(command, arg, root_helper=None):
     command += ['help']
     stdout, stderr = utils.execute(command, root_helper=root_helper,

neutron/tests/unit/test_dhcp_agent.py

@@ -1088,9 +1088,9 @@ class TestDeviceManager(base.BaseTestCase):
         cfg.CONF.set_override('use_namespaces', True)
         cfg.CONF.set_override('enable_isolated_metadata', True)
 
-        self.device_exists_p = mock.patch(
-            'neutron.agent.linux.ip_lib.device_exists')
-        self.device_exists = self.device_exists_p.start()
+        self.ensure_device_is_ready_p = mock.patch(
+            'neutron.agent.linux.ip_lib.ensure_device_is_ready')
+        self.ensure_device_is_ready = (self.ensure_device_is_ready_p.start())
 
         self.dvr_cls_p = mock.patch('neutron.agent.linux.interface.NullDriver')
         self.iproute_cls_p = mock.patch('neutron.agent.linux.'
@@ -1104,13 +1104,13 @@ class TestDeviceManager(base.BaseTestCase):
         driver_cls.return_value = self.mock_driver
         iproute_cls.return_value = self.mock_iproute
 
-    def _test_setup_helper(self, device_exists, net=None, port=None):
+    def _test_setup_helper(self, device_is_ready, net=None, port=None):
         net = net or fake_network
         port = port or fake_port1
         plugin = mock.Mock()
         plugin.create_dhcp_port.return_value = port or fake_port1
         plugin.get_dhcp_port.return_value = port or fake_port1
-        self.device_exists.return_value = device_exists
+        self.ensure_device_is_ready.return_value = device_is_ready
         self.mock_driver.get_device_name.return_value = 'tap12345678-12'
 
         dh = dhcp.DeviceManager(cfg.CONF, cfg.CONF.root_helper, plugin)
@@ -1135,7 +1135,7 @@ class TestDeviceManager(base.BaseTestCase):
                 expected_ips,
                 namespace=net.namespace)]
 
-        if not device_exists:
+        if not device_is_ready:
             expected.insert(1,
                             mock.call.plug(net.id,
                                            port.id,
@@ -1152,7 +1152,7 @@ class TestDeviceManager(base.BaseTestCase):
         cfg.CONF.set_override('enable_metadata_network', True)
         self._test_setup_helper(False)
 
-    def test_setup_device_exists(self):
+    def test_setup_device_is_ready(self):
         self._test_setup_helper(True)
 
     def test_create_dhcp_port_raise_conflict(self):

neutron/tests/unit/test_linux_ip_lib.py

@@ -789,3 +789,13 @@ class TestDeviceExists(base.BaseTestCase):
             _execute.return_value = ''
             _execute.side_effect = RuntimeError
             self.assertFalse(ip_lib.device_exists('eth0'))
+
+    def test_ensure_device_is_ready(self):
+        ip_lib_mock = mock.Mock()
+        with mock.patch.object(ip_lib, 'IPDevice', return_value=ip_lib_mock):
+            self.assertTrue(ip_lib.ensure_device_is_ready("eth0"))
+            self.assertTrue(ip_lib_mock.link.set_up.called)
+            ip_lib_mock.reset_mock()
+            # device doesn't exists
+            ip_lib_mock.link.set_up.side_effect = RuntimeError
+            self.assertFalse(ip_lib.ensure_device_is_ready("eth0"))