Refactor the selinux guard to aid in mocking

1. Adjust the test_util after this mocking to be cleaner

cloudinit/util.py

@@ -46,19 +46,13 @@ import urlparse
 
 import yaml
 
+from cloudinit import importer
 from cloudinit import log as logging
 from cloudinit import url_helper as uhelp
 
 from cloudinit.settings import (CFG_BUILTIN, CLOUD_CONFIG)
 
 
-try:
-    import selinux
-    HAVE_LIBSELINUX = True
-except ImportError:
-    HAVE_LIBSELINUX = False
-
-
 LOG = logging.getLogger(__name__)
 
 # Helps cleanup filenames to ensure they aren't FS incompatible
@@ -126,31 +120,37 @@ class ProcessExecutionError(IOError):
 
 class SeLinuxGuard(object):
     def __init__(self, path, recursive=False):
+        # Late import since it might not always
+        # be possible to use this
+        try:
+            self.selinux = importer.import_module('selinux')
+        except ImportError:
+            self.selinux = None
         self.path = path
         self.recursive = recursive
-        self.enabled = False
-        if HAVE_LIBSELINUX and selinux.is_selinux_enabled():
-            self.enabled = True
 
     def __enter__(self):
-        return self.enabled
+        if self.selinux:
+            return True
+        else:
+            return False
 
     def __exit__(self, excp_type, excp_value, excp_traceback):
-        if self.enabled:
+        if self.selinux:
             path = os.path.realpath(os.path.expanduser(self.path))
             do_restore = False
             try:
                 # See if even worth restoring??
                 stats = os.lstat(path)
                 if stat.ST_MODE in stats:
-                    selinux.matchpathcon(path, stats[stat.ST_MODE])
+                    self.selinux.matchpathcon(path, stats[stat.ST_MODE])
                     do_restore = True
             except OSError:
                 pass
             if do_restore:
                 LOG.debug("Restoring selinux mode for %s (recursive=%s)",
                           path, self.recursive)
-                selinux.restorecon(path, recursive=self.recursive)
+                self.selinux.restorecon(path, recursive=self.recursive)
 
 
 class MountFailedError(Exception):

tests/unittests/test_util.py

@@ -5,6 +5,26 @@ from unittest import TestCase
 from mocker import MockerTestCase
 
 from cloudinit import util
+from cloudinit import importer
+
+
+class FakeSelinux(object):
+
+    def __init__(self, match_what):
+        self.match_what = match_what
+        self.restored = []
+
+    def matchpathcon(self, path, mode):
+        if path == self.match_what:
+            return
+        else:
+            raise OSError("No match!")
+
+    def is_selinux_enabled(self):
+        return True
+
+    def restorecon(self, path, recursive):
+        self.restored.append(path)
 
 
 class TestMergeDict(MockerTestCase):
@@ -159,22 +179,16 @@ class TestWriteFile(MockerTestCase):
 
     def test_restorecon_if_possible_is_called(self):
         """Make sure the selinux guard is called correctly."""
-        try:
-            # We can only mock these out if selinux actually
-            # exists, so thats why we catch the import
-            mock_restorecon = self.mocker.replace(
-                "selinux.restorecon", passthrough=False)
-            mock_is_selinux_enabled = self.mocker.replace(
-                "selinux.is_selinux_enabled", passthrough=False)
-            mock_is_selinux_enabled()
-            self.mocker.result(True)
-            mock_restorecon("/etc/hosts", recursive=False)
-            self.mocker.result(True)
-            self.mocker.replay()
-            with util.SeLinuxGuard("/etc/hosts") as is_on:
-                self.assertTrue(is_on)
-        except ImportError:
-            pass
+        import_mock = self.mocker.replace(importer.import_module,
+                                          passthrough=False)
+        import_mock('selinux')
+        fake_se = FakeSelinux('/etc/hosts')
+        self.mocker.result(fake_se)
+        self.mocker.replay()
+        with util.SeLinuxGuard("/etc/hosts") as is_on:
+            self.assertTrue(is_on)
+        self.assertEqual(1, len(fake_se.restored))
+        self.assertEqual('/etc/hosts', fake_se.restored[0])
 
 
 class TestDeleteDirContents(MockerTestCase):