#
#

# Copyright (C) 2009, 2010, 2011 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.

"""Wrapper around mlockall(2).

"""

import os
import logging

from ganeti import errors

try:
  # pylint: disable-msg=F0401
  import ctypes
except ImportError:
  ctypes = None


# Flags for mlockall() (from bits/mman.h)
_MCL_CURRENT = 1
_MCL_FUTURE = 2


def Mlockall(_ctypes=ctypes):
  """Lock current process' virtual address space into RAM.

  This is equivalent to the C call mlockall(MCL_CURRENT|MCL_FUTURE),
  see mlock(2) for more details. This function requires ctypes module.

  @raises errors.NoCtypesError: if ctypes module is not found

  """
  if _ctypes is None:
    raise errors.NoCtypesError()

  try:
    libc = _ctypes.cdll.LoadLibrary("libc.so.6")
  except EnvironmentError, err:
    logging.error("Failure trying to load libc: %s", err)
    libc = None
  if libc is None:
    logging.error("Cannot set memory lock, ctypes cannot load libc")
    return

  # Some older version of the ctypes module don't have built-in functionality
  # to access the errno global variable, where function error codes are stored.
  # By declaring this variable as a pointer to an integer we can then access
  # its value correctly, should the mlockall call fail, in order to see what
  # the actual error code was.
  # pylint: disable-msg=W0212
  libc.__errno_location.restype = _ctypes.POINTER(_ctypes.c_int)

  if libc.mlockall(_MCL_CURRENT | _MCL_FUTURE):
    # pylint: disable-msg=W0212
    logging.error("Cannot set memory lock: %s",
                  os.strerror(libc.__errno_location().contents.value))
    return

  logging.debug("Memory lock set")