Merge lp:~harlowja/cloud-init/notify-on-reload into lp:~cloud-init-dev/cloud-init/trunk

[Joshua Harlow]

Use a notify/subscribe model for configuration/distro reloading.

  Instead of the previous way where we reached into the datasource
  object and messed with its properties its cleaner to create a
  tiny set of functions that can be used to notify others of changes
  and let them use those changes as they wish. So instead of messing
  with the datasource properties, just notify it something has changed
  and have the datasource modify itself instead.

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review: Needs Fixing (continuous-integration)

[Chad Smith (chad.smith)]

Hello,
Thank you for taking the time to contribute to cloud-init. Cloud-init has moved its revision control system to git. We are cleaning up old reviews that no longer apply to the current codebase. As a result, we are marking all bzr merge proposals as 'rejected'. If you would like to re-submit this proposal for review, please do so by following the current HACKING documentation at http://cloudinit.readthedocs.io/en/latest/topics/hacking.html.

review: Needs Fixing

Unmerged revisions

752. By Joshua Harlow on 2012-12-18

Use a notify/subscribe model for configuration/distro reloading.

Instead of the previous way where we reached into the datasource
object and messed with its properties its cleaner to create a
tiny set of functions that can be used to notify others of changes
and let them use those changes as they wish. So instead of messing
with the datasource properties, just notify it something has changed
and have the datasource modify itself instead.

=== modified file 'cloudinit/sources/__init__.py'
--- cloudinit/sources/__init__.py	2012-11-12 17:26:49 +0000
+++ cloudinit/sources/__init__.py	2012-12-18 07:45:25 +0000
@@ -52,16 +52,24 @@
         self.userdata = None
         self.metadata = None
         self.userdata_raw = None
-        name = util.obj_name(self)
-        if name.startswith(DS_PREFIX):
-            name = name[len(DS_PREFIX):]
+        self.name = util.obj_name(self)
+        if self.name.startswith(DS_PREFIX):
+            self.name = self.name[len(DS_PREFIX):]
         self.ds_cfg = util.get_cfg_by_path(self.sys_cfg,
-                                          ("datasource", name), {})
+                                          ("datasource", self.name), {})
         if not ud_proc:
             self.ud_proc = ud.UserDataProcessor(self.paths)
         else:
             self.ud_proc = ud_proc
 
+    def notify_reloaded(self, distro, system_config, _cloud_config):
+        if system_config:
+            self.sys_cfg = system_config
+            self.ds_cfg = util.get_cfg_by_path(self.sys_cfg,
+                                               ("datasource", self.name), {})
+        if distro:
+            self.distro = distro
+
     def get_userdata(self, apply_filter=False):
         if self.userdata is None:
             self.userdata = self.ud_proc.process(self.get_userdata_raw())

=== modified file 'cloudinit/stages.py'
--- cloudinit/stages.py	2012-12-17 13:41:11 +0000
+++ cloudinit/stages.py	2012-12-18 07:45:25 +0000
@@ -62,6 +62,7 @@
         self._distro = None
         # Changed only when a fetch occurs
         self.datasource = NULL_DATA_SOURCE
+        self.notify_listeners = []
 
     def _reset(self, reset_ds=False):
         # Recreated on access
@@ -74,20 +75,24 @@
     @property
     def distro(self):
         if not self._distro:
-            # Try to find the right class to use
+            # Try to find the right class to use  
             system_config = self._extract_cfg('system')
             distro_name = system_config.pop('distro', 'ubuntu')
             distro_cls = distros.fetch(distro_name)
             LOG.debug("Using distro class %s", distro_cls)
             self._distro = distro_cls(distro_name, system_config, self.paths)
-            # If we have an active datasource we need to adjust
-            # said datasource and move its distro/system config
-            # from whatever it was to a new set...
-            if self.datasource is not NULL_DATA_SOURCE:
-                self.datasource.distro = self._distro
-                self.datasource.sys_cfg = system_config
+            # Let any listener know that we have reloaded
+            self._notify_reloaded(self._distro, system_config, self.cfg)
         return self._distro
 
+    def add_reloaded_listener(self, listener):
+        if listener not in self.notify_listeners:
+            self.notify_listeners.append(listener)
+
+    def _notify_reloaded(self, distro, system_config, cloud_config):
+        for i in self.notify_listeners:
+            i.notify_reloaded(distro, system_config, cloud_config)
+
     @property
     def cfg(self):
         return self._extract_cfg('restricted')
@@ -161,9 +166,11 @@
         # None check so that we don't keep on re-loading if empty
         if self._cfg is None:
             self._cfg = self._read_cfg(extra_fns)
-            # LOG.debug("Loaded 'init' config %s", self._cfg)
 
     def _read_cfg(self, extra_fns):
+        # A no config path object is used since at the point where this
+        # function is called, it is loading the configuration to be so
+        # it doesn't have access to any previous configuration...
         no_cfg_paths = helpers.Paths({}, self.datasource)
         merger = helpers.ConfigMerger(paths=no_cfg_paths,
                                       datasource=self.datasource,
@@ -235,8 +242,10 @@
                                                pkg_list)
             LOG.debug("Loaded datasource %s - %s", dsname, ds)
         self.datasource = ds
-        # Ensure we adjust our path members datasource
-        # now that we have one (thus allowing ipath to be used)
+        # Automatically add the loaded datasource to the reload notification
+        # listener list so that it gets notified when configuration and distro
+        # reloads happen...
+        self.add_reloaded_listener(ds)
         self._reset()
         return ds
 
@@ -420,6 +429,7 @@
         #
         # They will be recreated on future access...
         self._reset()
+
         # Note(harlowja): the 'active' datasource will have
         # references to the previous config, distro, paths
         # objects before the load of the userdata happened,