Synnefo » snf-ganeti

#

#

# 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 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

  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 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-msg=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 (%s)" % 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-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

    self._callback(False)

  # 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)

    self._callback(True)