Add a 'none' datasource as a last resort fallback

1. This will allow a basically empty datasource to be
   activated (as the last datasource) when no other
   datasources work. This allows modules to still
   run (if they can, new function added to the datasource
   if modules want to check if cloud-init is in this
   'disconnected' state).

cloudinit/settings.py

@@ -35,7 +35,9 @@ CFG_BUILTIN = {
         'OVF',
         'MAAS',
         'Ec2',
-        'CloudStack'
+        'CloudStack',
+        # At the end to act as a 'catch' when none of the above work...
+        'None',
     ],
     'def_log_file': '/var/log/cloud-init.log',
     'log_cfgs': [],

cloudinit/sources/DataSourceNone.py

@@ -0,0 +1,59 @@
+# vi: ts=4 expandtab
+#
+#    Copyright (C) 2012 Yahoo! Inc.
+#
+#    Author: Joshua Harlow <harlowja@yahoo-inc.com>
+#
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License version 3, as
+#    published by the Free Software Foundation.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+#    You should have received a copy of the GNU General Public License
+#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+from cloudinit import log as logging
+from cloudinit import sources
+from cloudinit import util
+
+LOG = logging.getLogger(__name__)
+
+NONE_IID = 'iid-datasource-none'
+
+
+class DataSourceNone(sources.DataSource):
+    def __init__(self, sys_cfg, distro, paths, ud_proc=None):
+        sources.DataSource.__init__(self, sys_cfg, distro, paths, ud_proc)
+        self.userdata = {}
+        self.metadata = {}
+        self.userdata_raw = ''
+
+    def get_data(self):
+        return True
+
+    def get_instance_id(self):
+        return NONE_IID
+
+    def __str__(self):
+        return util.obj_name(self)
+
+    @property
+    def is_disconnected(self):
+        return True
+
+
+# Used to match classes to dependencies (this will always match)
+datasources = [
+  (DataSourceNone, (sources.DEP_FILESYSTEM, sources.DEP_NETWORK)),
+  (DataSourceNone, (sources.DEP_FILESYSTEM,)),
+  (DataSourceNone, []),
+]
+
+
+# Return a list of data sources that match this set of dependencies
+def get_datasource_list(depends):
+    return sources.list_from_depends(depends, datasources)

cloudinit/sources/__init__.py

@@ -65,6 +65,10 @@ class DataSource(object):
             self.userdata = self.ud_proc.process(raw_data)
         return self.userdata
 
+    @property
+    def is_disconnected(self):
+        return False
+
     def get_userdata_raw(self):
         return self.userdata_raw