Synnefo » snf-ganeti » ganeti-local

import logging

from ganeti import errors

class SingleFileEventHandler(pyinotify.ProcessEvent):

  """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

    """

    # pylint: disable-msg=W0231

    # no need to call the parent's constructor

    self.watch_manager = watch_manager

    self.callback = callback

    self.mask = pyinotify.EventsCodes.ALL_FLAGS["IN_IGNORED"] | \

                pyinotify.EventsCodes.ALL_FLAGS["IN_MODIFY"]

    self.file = filename

    self.watch_handle = None

  def enable(self):

    """Watch the given file

    """

    if self.watch_handle is None:

      result = self.watch_manager.add_watch(self.file, self.mask)

      if not self.file in result or result[self.file] <= 0:

        raise errors.InotifyError("Could not add inotify watcher")

      else:

        self.watch_handle = result[self.file]

  def disable(self):

    """Stop watching the given file

    """

    if self.watch_handle is not None:

      result = self.watch_manager.rm_watch(self.watch_handle)

      if result[self.watch_handle]:

        self.watch_handle = None

  # pylint: disable-msg=C0103

  # this overrides a method in pyinotify.ProcessEvent

  def process_IN_IGNORED(self, event):

    # Due to the fact that we monitor just for the cluster config file (rather

    # than for the whole data dir) when the file is replaced with another one

    # (which is what happens normally in ganeti) 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 need to create

    # another watcher for the "new" file.

    logging.debug("Received 'ignored' inotify event for %s", event.path)

    self.watch_handle = None

    try:

      # Since the kernel believes the file we were interested in is gone, it's

      # not going to notify us of any other events, until we set up, here, the

      # new watch. This is not a race condition, though, since we're anyway

      # going to realod the file after setting up the new watch.

      self.callback(False)

    except: # pylint: disable-msg=W0702

      # we need to catch any exception here, log it, but proceed, because even

      # if we failed handling a single request, we still want our daemon to

      # proceed.

      logging.error("Unexpected exception", exc_info=True)

  # pylint: disable-msg=C0103

  # this overrides a method in pyinotify.ProcessEvent

  def process_IN_MODIFY(self, event):

    # This gets called when the config file is modified. Note that this doesn't

    # usually happen in Ganeti, as the config file is normally replaced by a

    # new one, at filesystem level, rather than actually modified (see

    # utils.WriteFile)

    logging.debug("Received 'modify' inotify event for %s", event.path)

    try:

      self.callback(True)

    except: # pylint: disable-msg=W0702

      # we need to catch any exception here, log it, but proceed, because even

      # if we failed handling a single request, we still want our daemon to

      # proceed.

      logging.error("Unexpected exception", exc_info=True)

  def process_default(self, event):

    logging.error("Received unhandled inotify event: %s", event)