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#

#

# Copyright (C) 2009 Google Inc.

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# 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, write to the Free Software

# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

# 02110-1301, USA.

"""Asynchronous pyinotify implementation"""

import asyncore

import logging

try:

  # pylint: disable-msg=E0611

  from pyinotify import pyinotify

except ImportError:

  import pyinotify

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

  def __init__(self, watch_manager, default_proc_fun=None, map=None):

    """Initializes this class.

    This is a a special asyncore file_dispatcher that actually wraps a

    pyinotify Notifier, making it asyncronous.

    """

    if default_proc_fun is None:

      default_proc_fun = pyinotify.ProcessEvent()

    self.notifier = pyinotify.Notifier(watch_manager, default_proc_fun)

    # here we need to steal the file descriptor from the notifier, so we can

    # use it in the global asyncore select, and avoid calling the

    # check_events() function of the notifier (which doesn't allow us to select

    # together with other file descriptors)

    self.fd = self.notifier._fd

    asyncore.file_dispatcher.__init__(self, self.fd, map)

  def handle_read(self):

    self.notifier.read_events()

    self.notifier.process_events()

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):

    # 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

    try:

      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 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)

    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)