Import IP implementation modules outside privsep context

If the IP module is loaded inside the privsep context, the following
error will occur:
  return getattr(sys.modules[mod_str], class_str)
  "AttributeError: 'module' object has no attribute 'PyRoute2'

Change-Id: I1852038b8d40d4aa52c4f8e661bc78e54e0fc966
Closes-Bug: #1812090

os_vif/internal/command/ip/__init__.py

@@ -16,24 +16,22 @@ from os_vif.internal.command.ip import api
 def set(device, check_exit_code=None, state=None, mtu=None, address=None,
         promisc=None):
     """Method to set a parameter in an interface."""
-    return api._get_impl().set(device, check_exit_code=check_exit_code,
-                               state=state, mtu=mtu, address=address,
-                               promisc=promisc)
+    return api.ip.set(device, check_exit_code=check_exit_code, state=state,
+                      mtu=mtu, address=address, promisc=promisc)
 
 
 def add(device, dev_type, check_exit_code=None, peer=None, link=None,
         vlan_id=None):
     """Method to add an interface."""
-    return api._get_impl().add(device, dev_type,
-                               check_exit_code=check_exit_code, peer=peer,
-                               link=link, vlan_id=vlan_id)
+    return api.ip.add(device, dev_type, check_exit_code=check_exit_code,
+                      peer=peer, link=link, vlan_id=vlan_id)
 
 
 def delete(device, check_exit_code=None):
     """Method to delete an interface."""
-    return api._get_impl().delete(device, check_exit_code=check_exit_code)
+    return api.ip.delete(device, check_exit_code=check_exit_code)
 
 
 def exists(device):
     """Method to check if an interface exists."""
-    return api._get_impl().exists(device)
+    return api.ip.exists(device)

os_vif/internal/command/ip/api.py

@@ -13,16 +13,15 @@
 import os
 
 from oslo_log import log as logging
-from oslo_utils import importutils
+
+if os.name == 'nt':
+    from os_vif.internal.command.ip.windows.impl_netifaces import \
+        Netifaces as ip_lib_class
+else:
+    from os_vif.internal.command.ip.linux.impl_pyroute2 import \
+        PyRoute2 as ip_lib_class
 
 
 LOG = logging.getLogger(__name__)
 
-
-def _get_impl():
-    if os.name == 'nt':
-        impl = 'os_vif.internal.command.ip.windows.impl_netifaces.Netifaces'
-    else:
-        impl = 'os_vif.internal.command.ip.linux.impl_pyroute2.PyRoute2'
-
-    return importutils.import_object(impl)
+ip = ip_lib_class()

os_vif/tests/functional/internal/command/ip/test_impl_pyroute2.py

@@ -15,7 +15,7 @@ import re
 from oslo_concurrency import processutils
 from oslo_utils import excutils
 
-from os_vif.internal.command.ip.linux import impl_pyroute2
+from os_vif.internal.command import ip as ip_lib
 from os_vif.tests.functional import base
 from os_vif.tests.functional import privsep
 
@@ -96,17 +96,17 @@ class ShellIpCommands(object):
 
 @privsep.os_vif_pctxt.entrypoint
 def _ip_cmd_set(*args, **kwargs):
-    impl_pyroute2.PyRoute2().set(*args, **kwargs)
+    ip_lib.set(*args, **kwargs)
 
 
 @privsep.os_vif_pctxt.entrypoint
 def _ip_cmd_add(*args, **kwargs):
-    impl_pyroute2.PyRoute2().add(*args, **kwargs)
+    ip_lib.add(*args, **kwargs)
 
 
 @privsep.os_vif_pctxt.entrypoint
 def _ip_cmd_delete(*args, **kwargs):
-    impl_pyroute2.PyRoute2().delete(*args, **kwargs)
+    ip_lib.delete(*args, **kwargs)
 
 
 class TestIpCommand(ShellIpCommands, base.BaseFunctionalTestCase):

os_vif/tests/unit/internal/command/ip/test_api.py

@@ -11,22 +11,28 @@
 #    under the License.
 
 import mock
-
-from os_vif.tests.unit import base
+from six import moves
 
 from os_vif.internal.command.ip import api
-from os_vif.internal.command.ip.linux import impl_pyroute2 as linux_ip_lib
-from os_vif.internal.command.ip.windows import impl_netifaces as win_ip_lib
+from os_vif.tests.unit import base
 
 
 class TestIpApi(base.TestCase):
 
-    @mock.patch("os.name", "nt")
-    def test_get_impl_windows(self):
-        ip_lib = api._get_impl()
-        self.assertIsInstance(ip_lib, win_ip_lib.Netifaces)
+    @staticmethod
+    def _reload_original_os_module():
+        moves.reload_module(api)
+
+    def test_get_impl_windows(self):
+        self.addCleanup(self._reload_original_os_module)
+        with mock.patch('os.name', 'nt'):
+            moves.reload_module(api)
+            from os_vif.internal.command.ip.windows import impl_netifaces
+            self.assertIsInstance(api.ip, impl_netifaces.Netifaces)
 
-    @mock.patch("os.name", "posix")
     def test_get_impl_linux(self):
-        ip_lib = api._get_impl()
-        self.assertIsInstance(ip_lib, linux_ip_lib.PyRoute2)
+        self.addCleanup(self._reload_original_os_module)
+        with mock.patch('os.name', 'posix'):
+            moves.reload_module(api)
+            from os_vif.internal.command.ip.linux import impl_pyroute2
+            self.assertIsInstance(api.ip, impl_pyroute2.PyRoute2)