virt: osinfo will report once if libosinfo is not loaded

Currently osinfo module emits multiple error messages when libosinfo
module cannot be loaded. Since loading the libosinfo module is optional,
it should only report this once as an INFO log message.

Change-Id: If4b582d1ec39ba79b4f993543da11ec8c6bd023b
Closes-bug: #1543288

nova/tests/unit/virt/test_osinfo.py

@@ -35,6 +35,9 @@ class LibvirtOsInfoTest(test.NoDBTestCase):
         self.useFixture(fixtures.MonkeyPatch(
             'nova.virt.osinfo.libosinfo',
             fakelibosinfo))
+        self.useFixture(fixtures.MonkeyPatch(
+            'nova.virt.osinfo._OsInfoDatabase._instance',
+            None))
 
     def test_get_os(self):
         os_info_db = osinfo._OsInfoDatabase.get_instance()
@@ -47,6 +50,22 @@ class LibvirtOsInfoTest(test.NoDBTestCase):
                           os_info_db.get_os,
                           'test33')
 
+    def test_module_load_failed(self):
+        self.useFixture(fixtures.MonkeyPatch(
+            'nova.virt.osinfo.libosinfo',
+            None))
+        with test.nested(
+            mock.patch.object(osinfo.importutils, 'import_module',
+                        side_effect=ImportError('gi.repository.Libosinfo')),
+            mock.patch.object(osinfo.LOG, 'info')) as (mock_import, mock_log):
+
+            os_info_db = osinfo._OsInfoDatabase.get_instance()
+            self.assertIsNone(os_info_db.get_os('fedora22'))
+
+            os_info_db = osinfo._OsInfoDatabase.get_instance()
+            self.assertIsNone(os_info_db.get_os('fedora19'))
+            self.assertEqual(1, mock_log.call_count)
+
     def test_hardware_properties_from_osinfo(self):
         """Verifies that HardwareProperties attributes are being set
            from libosinfo.

nova/virt/osinfo.py

@@ -16,7 +16,7 @@ from oslo_log import log as logging
 from oslo_utils import importutils
 
 from nova import exception
-from nova.i18n import _, _LE
+from nova.i18n import _LW, _LI
 
 libosinfo = None
 LOG = logging.getLogger(__name__)
@@ -35,14 +35,13 @@ class _OsInfoDatabase(object):
     def __init__(self):
 
         global libosinfo
-        if libosinfo is None:
         try:
+            if libosinfo is None:
                 libosinfo = importutils.import_module(
                                              'gi.repository.Libosinfo')
         except ImportError as exp:
-                raise exception.NovaException(
-                                _("Cannot load Libosinfo: (%s)") % exp)
-
+            LOG.info(_LI("Cannot load Libosinfo: (%s)"), exp)
+        else:
             self.loader = libosinfo.Loader()
             self.loader.process_default_path()
 
@@ -69,6 +68,8 @@ class _OsInfoDatabase(object):
            :returns: The operation system object Libosinfo.Os
            :raise exception.OsInfoNotFound: If os hasn't been found
         """
+        if libosinfo is None:
+            return
         if not os_name:
             raise exception.OsInfoNotFound(os_name='Empty')
         fltr = libosinfo.Filter.new()
@@ -92,7 +93,7 @@ class OsInfo(object):
         try:
             return _OsInfoDatabase.get_instance().get_os(os_name)
         except exception.NovaException as e:
-            LOG.error(_LE("Cannot find OS information - Reason: (%s)"), e)
+            LOG.warning(_LW("Cannot find OS information - Reason: (%s)"), e)
 
     @property
     def network_model(self):