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[ganeti-local] / lib / asyncnotifier.py

diff --git a/lib/asyncnotifier.py b/lib/asyncnotifier.py
index 63c020f..f4b0815 100644 (file)
--- a/lib/asyncnotifier.py
+++ b/lib/asyncnotifier.py
@@ -23,19 +23,26 @@
 
 
 import asyncore
+import logging
 
 try:
-  # pylint: disable-msg=E0611
+  # pylint: disable=E0611
   from pyinotify import pyinotify
 except ImportError:
   import pyinotify
 
+from ganeti import daemon
+from ganeti import errors
 
+
+# We contributed the AsyncNotifier class back to python-pyinotify, and it's
+# part of their codebase since version 0.8.7. This code can be removed once
+# we'll be ready to depend on python-pyinotify >= 0.8.7
 class AsyncNotifier(asyncore.file_dispatcher):
   """An asyncore dispatcher for inotify events.
 
   """
-  # pylint: disable-msg=W0622,W0212
+  # pylint: disable=W0622,W0212
   def __init__(self, watch_manager, default_proc_fun=None, map=None):
     """Initializes this class.
 
@@ -58,3 +65,131 @@ class AsyncNotifier(asyncore.file_dispatcher):
   def handle_read(self):
     self.notifier.read_events()
     self.notifier.process_events()
+
+
+class ErrorLoggingAsyncNotifier(AsyncNotifier,
+                                daemon.GanetiBaseAsyncoreDispatcher):
+  """An asyncnotifier that can survive errors in the callbacks.
+
+  We define this as a separate class, since we don't want to make AsyncNotifier
+  diverge from what we contributed upstream.
+
+  """
+
+
+class FileEventHandlerBase(pyinotify.ProcessEvent):
+  """Base class for file event handlers.
+
+  @ivar watch_manager: Inotify watch manager
+
+  """
+  def __init__(self, watch_manager):
+    """Initializes this class.
+
+    @type watch_manager: pyinotify.WatchManager
+    @param watch_manager: inotify watch manager
+
+    """
+    # pylint: disable=W0231
+    # no need to call the parent's constructor
+    self.watch_manager = watch_manager
+
+  def process_default(self, event):
+    logging.error("Received unhandled inotify event: %s", event)
+
+  def AddWatch(self, filename, mask):
+    """Adds a file watch.
+
+    @param filename: Path to file
+    @param mask: Inotify event mask
+    @return: Result
+
+    """
+    result = self.watch_manager.add_watch(filename, mask)
+
+    ret = result.get(filename, -1)
+    if ret <= 0:
+      raise errors.InotifyError("Could not add inotify watcher (error code %s);"
+                                " increasing fs.inotify.max_user_watches sysctl"
+                                " might be necessary" % ret)
+
+    return result[filename]
+
+  def RemoveWatch(self, handle):
+    """Removes a handle from the watcher.
+
+    @param handle: Inotify handle
+    @return: Whether removal was successful
+
+    """
+    result = self.watch_manager.rm_watch(handle)
+
+    return result[handle]
+
+
+class SingleFileEventHandler(FileEventHandlerBase):
+  """Handle modify events for a single file.
+
+  """
+  def __init__(self, watch_manager, callback, filename):
+    """Constructor for SingleFileEventHandler
+
+    @type watch_manager: pyinotify.WatchManager
+    @param watch_manager: inotify watch manager
+    @type callback: function accepting a boolean
+    @param callback: function to call when an inotify event happens
+    @type filename: string
+    @param filename: config file to watch
+
+    """
+    FileEventHandlerBase.__init__(self, watch_manager)
+
+    self._callback = callback
+    self._filename = filename
+
+    self._watch_handle = None
+
+  def enable(self):
+    """Watch the given file.
+
+    """
+    if self._watch_handle is not None:
+      return
+
+    # Different Pyinotify versions have the flag constants at different places,
+    # hence not accessing them directly
+    mask = (pyinotify.EventsCodes.ALL_FLAGS["IN_MODIFY"] |
+            pyinotify.EventsCodes.ALL_FLAGS["IN_IGNORED"])
+
+    self._watch_handle = self.AddWatch(self._filename, mask)
+
+  def disable(self):
+    """Stop watching the given file.
+
+    """
+    if self._watch_handle is not None and self.RemoveWatch(self._watch_handle):
+      self._watch_handle = None
+
+  # pylint: disable=C0103
+  # this overrides a method in pyinotify.ProcessEvent
+  def process_IN_IGNORED(self, event):
+    # Since we monitor a single file rather than the directory it resides in,
+    # when that file is replaced with another one (which is what happens when
+    # utils.WriteFile, the most normal way of updating files in ganeti, is
+    # called) we're going to receive an IN_IGNORED event from inotify, because
+    # of the file removal (which is contextual with the replacement). In such a
+    # case we'll need to create a watcher for the "new" file. This can be done
+    # by the callback by calling "enable" again on us.
+    logging.debug("Received 'ignored' inotify event for %s", event.path)
+    self._watch_handle = None
+    self._callback(False)
+
+  # pylint: disable=C0103
+  # this overrides a method in pyinotify.ProcessEvent
+  def process_IN_MODIFY(self, event):
+    # This gets called when the monitored file is modified. Note that this
+    # doesn't usually happen in Ganeti, as most of the time we're just
+    # replacing any file with a new one, at filesystem level, rather than
+    # actually changing it. (see utils.WriteFile)
+    logging.debug("Received 'modify' inotify event for %s", event.path)
+    self._callback(True)