Synnefo » snf-ganeti

#

#

# 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 errno

from ganeti import constants

from ganeti import errors

from ganeti import runtime

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:

    return int(utils.ReadFile(file_name))

  except EnvironmentError, err:

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

      return None

    raise

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(must_lock):

  """Open and lock job queue.

  If necessary, the queue is automatically initialized.

  @type must_lock: bool

  @param must_lock: Whether an exclusive lock must be held.

  @rtype: utils.FileLock

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

           locking mode.

  """

  getents = runtime.GetEnts()

  # Lock queue

  queue_lock = utils.FileLock.Open(constants.JOB_QUEUE_LOCK_FILE)

  try:

    # The queue needs to be locked in exclusive mode to write to the serial and

    # version files.

    if must_lock:

      queue_lock.Exclusive(blocking=True)

      holding_lock = True

    else:

      try:

        queue_lock.Exclusive(blocking=False)

        holding_lock = True

      except errors.LockError:

        # Ignore errors and assume the process keeping the lock checked

        # everything.

        holding_lock = False

    if holding_lock:

      # Verify version

      version = ReadVersion()

      if version is None:

        # Write new version file

        utils.WriteFile(constants.JOB_QUEUE_VERSION_FILE,

                        uid=getents.masterd_uid, gid=getents.masterd_gid,

                        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,

                        uid=getents.masterd_uid, gid=getents.masterd_gid,

                        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")

      if not must_lock:

        # There's no need for more error handling. Closing the lock

        # file below in case of an error will unlock it anyway.

        queue_lock.Unlock()

  except:

    queue_lock.Close()

    raise

  return queue_lock