Move "get_cdll" to a common place in privileged.agent.linux

That method could be used outside the library where currently is
implemented. This patch relocates it in a common place for all
privileged.agent.linux libraries.

Change-Id: I5a6124eca3b57ee36479c106b62d101f538c12eb
Story: #2007686
Task: #40047

neutron/privileged/agent/linux/__init__.py

@@ -0,0 +1,32 @@
+# Copyright 2020 Red Hat, Inc.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import ctypes
+from ctypes import util as ctypes_util
+
+
+_CDLL = None
+
+
+def get_cdll():
+    global _CDLL
+    if not _CDLL:
+        # NOTE(ralonsoh): from https://docs.python.org/3.6/library/
+        # ctypes.html#ctypes.PyDLL: "Instances of this class behave like CDLL
+        # instances, except that the Python GIL is not released during the
+        # function call, and after the function execution the Python error
+        # flag is checked."
+        # Check https://bugs.launchpad.net/neutron/+bug/1870352
+        _CDLL = ctypes.PyDLL(ctypes_util.find_library('c'), use_errno=True)
+    return _CDLL

neutron/privileged/agent/linux/ip_lib.py

@@ -10,8 +10,6 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-import ctypes
-from ctypes import util as ctypes_util
 import errno
 import os
 import socket
@@ -29,6 +27,7 @@ from pyroute2 import netns
 
 from neutron._i18n import _
 from neutron import privileged
+from neutron.privileged.agent import linux as priv_linux
 
 
 LOG = logging.getLogger(__name__)
@@ -37,21 +36,6 @@ _IP_VERSION_FAMILY_MAP = {4: socket.AF_INET, 6: socket.AF_INET6}
 
 NETNS_RUN_DIR = '/var/run/netns'
 
-_CDLL = None
-
-
-def _get_cdll():
-    global _CDLL
-    if not _CDLL:
-        # NOTE(ralonsoh): from https://docs.python.org/3.6/library/
-        # ctypes.html#ctypes.PyDLL: "Instances of this class behave like CDLL
-        # instances, except that the Python GIL is not released during the
-        # function call, and after the function execution the Python error
-        # flag is checked."
-        # Check https://bugs.launchpad.net/neutron/+bug/1870352
-        _CDLL = ctypes.PyDLL(ctypes_util.find_library('c'), use_errno=True)
-    return _CDLL
-
 
 def _get_scope_name(scope):
     """Return the name of the scope (given as a number), or the scope number
@@ -532,7 +516,7 @@ def create_netns(name, **kwargs):
     :param name: The name of the namespace to create
     """
     try:
-        netns.create(name, libc=_get_cdll())
+        netns.create(name, libc=priv_linux.get_cdll())
     except OSError as e:
         if e.errno != errno.EEXIST:
             raise
@@ -545,7 +529,7 @@ def remove_netns(name, **kwargs):
     :param name: The name of the namespace to remove
     """
     try:
-        netns.remove(name, libc=_get_cdll())
+        netns.remove(name, libc=priv_linux.get_cdll())
     except OSError as e:
         if e.errno != errno.ENOENT:
             raise