Synnefo » snf-ganeti » ganeti-local

	lib/jstore.py \

#

#

# Copyright (C) 2006, 2007 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.

"""Module implementing the job queue handling."""

import os

import logging

import errno

import re

from ganeti import constants

from ganeti import errors

from ganeti import utils

def _ReadNumericFile(file_name):

  """Reads a file containing a number.

  @rtype: None or int

  @return: None if file is not found, otherwise number

  """

  try:

    fd = open(file_name, "r")

  except IOError, err:

    if err.errno in (errno.ENOENT, ):

      return None

    raise

  try:

    return int(fd.read(128))

  finally:

    fd.close()

def ReadSerial():

  """Read the serial file.

  The queue should be locked while this function is called.

  """

  return _ReadNumericFile(constants.JOB_QUEUE_SERIAL_FILE)

def ReadVersion():

  """Read the queue version.

  The queue should be locked while this function is called.

  """

  return _ReadNumericFile(constants.JOB_QUEUE_VERSION_FILE)

def InitAndVerifyQueue(exclusive):

  """Open and lock job queue.

  If necessary, the queue is automatically initialized.

  @type exclusive: bool

  @param exclusive: Whether to lock the queue in exclusive mode. Shared

                    mode otherwise.

  @rtype: utils.FileLock

  @return: Lock object for the queue. This can be used to change the

           locking mode.

  """

  # Make sure our directories exists

  for path in (constants.QUEUE_DIR, constants.JOB_QUEUE_ARCHIVE_DIR):

    try:

      os.mkdir(path, 0700)

    except OSError, err:

      if err.errno not in (errno.EEXIST, ):

        raise

  # Lock queue

  queue_lock = utils.FileLock(constants.JOB_QUEUE_LOCK_FILE)

  try:

    # Determine locking function and call it

    if exclusive:

      fn = queue_lock.Exclusive

    else:

      fn = queue_lock.Shared

    fn(blocking=False)

    # Verify version

    version = ReadVersion()

    if version is None:

      # Write new version file

      utils.WriteFile(constants.JOB_QUEUE_VERSION_FILE,

                      data="%s\n" % constants.JOB_QUEUE_VERSION)

      # Read again

      version = ReadVersion()

    if version != constants.JOB_QUEUE_VERSION:

      raise errors.JobQueueError("Found job queue version %s, expected %s",

                                 version, constants.JOB_QUEUE_VERSION)

    serial = ReadSerial()

    if serial is None:

      # Write new serial file

      utils.WriteFile(constants.JOB_QUEUE_SERIAL_FILE,

                      data="%s\n" % 0)

      # Read again

      serial = ReadSerial()

    if serial is None:

      # There must be a serious problem

      raise errors.JobQueueError("Can't read/parse the job queue serial file")

  except:

    queue_lock.Close()

    raise

  return queue_lock