Synnefo » snf-ganeti » ganeti-local

#

#

# Copyright (C) 2006, 2007, 2010, 2011, 2012 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.

"""Utility functions for processes.

"""

import os

import sys

import subprocess

import errno

import select

import logging

import signal

import resource

from cStringIO import StringIO

from ganeti import errors

from ganeti import constants

from ganeti import compat

from ganeti.utils import retry as utils_retry

from ganeti.utils import wrapper as utils_wrapper

from ganeti.utils import text as utils_text

from ganeti.utils import io as utils_io

from ganeti.utils import algo as utils_algo

#: when set to True, L{RunCmd} is disabled

_no_fork = False

(_TIMEOUT_NONE,

 _TIMEOUT_TERM,

 _TIMEOUT_KILL) = range(3)

def DisableFork():

  """Disables the use of fork(2).

  """

  global _no_fork # pylint: disable=W0603

  _no_fork = True

class RunResult(object):

  """Holds the result of running external programs.

  @type exit_code: int

  @ivar exit_code: the exit code of the program, or None (if the program

      didn't exit())

  @type signal: int or None

  @ivar signal: the signal that caused the program to finish, or None

      (if the program wasn't terminated by a signal)

  @type stdout: str

  @ivar stdout: the standard output of the program

  @type stderr: str

  @ivar stderr: the standard error of the program

  @type failed: boolean

  @ivar failed: True in case the program was

      terminated by a signal or exited with a non-zero exit code

  @ivar fail_reason: a string detailing the termination reason

  """

  __slots__ = ["exit_code", "signal", "stdout", "stderr",

               "failed", "fail_reason", "cmd"]

  def __init__(self, exit_code, signal_, stdout, stderr, cmd, timeout_action,

               timeout):

    self.cmd = cmd

    self.exit_code = exit_code

    self.signal = signal_

    self.stdout = stdout

    self.stderr = stderr

    self.failed = (signal_ is not None or exit_code != 0)

    fail_msgs = []

    if self.signal is not None:

      fail_msgs.append("terminated by signal %s" % self.signal)

    elif self.exit_code is not None:

      fail_msgs.append("exited with exit code %s" % self.exit_code)

    else:

      fail_msgs.append("unable to determine termination reason")

    if timeout_action == _TIMEOUT_TERM:

      fail_msgs.append("terminated after timeout of %.2f seconds" % timeout)

    elif timeout_action == _TIMEOUT_KILL:

      fail_msgs.append(("force termination after timeout of %.2f seconds"

                        " and linger for another %.2f seconds") %

                       (timeout, constants.CHILD_LINGER_TIMEOUT))

    if fail_msgs and self.failed:

      self.fail_reason = utils_text.CommaJoin(fail_msgs)

    if self.failed:

      logging.debug("Command '%s' failed (%s); output: %s",

                    self.cmd, self.fail_reason, self.output)

  def _GetOutput(self):

    """Returns the combined stdout and stderr for easier usage.

    """

    return self.stdout + self.stderr

  output = property(_GetOutput, None, None, "Return full output")

def _BuildCmdEnvironment(env, reset):

  """Builds the environment for an external program.

  """

  if reset:

    cmd_env = {}

  else:

    cmd_env = os.environ.copy()

    cmd_env["LC_ALL"] = "C"

  if env is not None:

    cmd_env.update(env)

  return cmd_env

def RunCmd(cmd, env=None, output=None, cwd="/", reset_env=False,

           interactive=False, timeout=None, noclose_fds=None,

           input_fd=None, postfork_fn=None):

  """Execute a (shell) command.

  The command should not read from its standard input, as it will be

  closed.

  @type cmd: string or list

  @param cmd: Command to run

  @type env: dict

  @param env: Additional environment variables

  @type output: str

  @param output: if desired, the output of the command can be

      saved in a file instead of the RunResult instance; this

      parameter denotes the file name (if not None)

  @type cwd: string

  @param cwd: if specified, will be used as the working

      directory for the command; the default will be /

  @type reset_env: boolean

  @param reset_env: whether to reset or keep the default os environment

  @type interactive: boolean

  @param interactive: whether we pipe stdin, stdout and stderr

                      (default behaviour) or run the command interactive

  @type timeout: int

  @param timeout: If not None, timeout in seconds until child process gets

                  killed

  @type noclose_fds: list

  @param noclose_fds: list of additional (fd >=3) file descriptors to leave

                      open for the child process

  @type input_fd: C{file}-like object or numeric file descriptor

  @param input_fd: File descriptor for process' standard input

  @type postfork_fn: Callable receiving PID as parameter

  @param postfork_fn: Callback run after fork but before timeout

  @rtype: L{RunResult}

  @return: RunResult instance

  @raise errors.ProgrammerError: if we call this when forks are disabled

  """

  if _no_fork:

    raise errors.ProgrammerError("utils.RunCmd() called with fork() disabled")

  if output and interactive:

    raise errors.ProgrammerError("Parameters 'output' and 'interactive' can"

                                 " not be provided at the same time")

  if not (output is None or input_fd is None):

    # The current logic in "_RunCmdFile", which is used when output is defined,

    # does not support input files (not hard to implement, though)

    raise errors.ProgrammerError("Parameters 'output' and 'input_fd' can"

                                 " not be used at the same time")

  if isinstance(cmd, basestring):

    strcmd = cmd

    shell = True

  else:

    cmd = [str(val) for val in cmd]

    strcmd = utils_text.ShellQuoteArgs(cmd)

    shell = False

  if output:

    logging.info("RunCmd %s, output file '%s'", strcmd, output)

  else:

    logging.info("RunCmd %s", strcmd)

  cmd_env = _BuildCmdEnvironment(env, reset_env)

  try:

    if output is None:

      out, err, status, timeout_action = _RunCmdPipe(cmd, cmd_env, shell, cwd,

                                                     interactive, timeout,

                                                     noclose_fds, input_fd,

                                                     postfork_fn=postfork_fn)

    else:

      if postfork_fn:

        raise errors.ProgrammerError("postfork_fn is not supported if output"

                                     " should be captured")

      assert input_fd is None

      timeout_action = _TIMEOUT_NONE

      status = _RunCmdFile(cmd, cmd_env, shell, output, cwd, noclose_fds)

      out = err = ""

  except OSError, err:

    if err.errno == errno.ENOENT:

      raise errors.OpExecError("Can't execute '%s': not found (%s)" %

                               (strcmd, err))

    else:

      raise

  if status >= 0:

    exitcode = status

    signal_ = None

  else:

    exitcode = None

    signal_ = -status

  return RunResult(exitcode, signal_, out, err, strcmd, timeout_action, timeout)

def SetupDaemonEnv(cwd="/", umask=077):

  """Setup a daemon's environment.

  This should be called between the first and second fork, due to

  setsid usage.

  @param cwd: the directory to which to chdir

  @param umask: the umask to setup

  """

  os.chdir(cwd)

  os.umask(umask)

  os.setsid()

def SetupDaemonFDs(output_file, output_fd):

  """Setups up a daemon's file descriptors.

  @param output_file: if not None, the file to which to redirect

      stdout/stderr

  @param output_fd: if not None, the file descriptor for stdout/stderr

  """

  # check that at most one is defined

  assert [output_file, output_fd].count(None) >= 1

  # Open /dev/null (read-only, only for stdin)

  devnull_fd = os.open(os.devnull, os.O_RDONLY)

  output_close = True

  if output_fd is not None:

    output_close = False

  elif output_file is not None:

    # Open output file

    try:

      output_fd = os.open(output_file,

                          os.O_WRONLY | os.O_CREAT | os.O_APPEND, 0600)

    except EnvironmentError, err:

      raise Exception("Opening output file failed: %s" % err)

  else:

    output_fd = os.open(os.devnull, os.O_WRONLY)

  # Redirect standard I/O

  os.dup2(devnull_fd, 0)

  os.dup2(output_fd, 1)

  os.dup2(output_fd, 2)

  if devnull_fd > 2:

    utils_wrapper.CloseFdNoError(devnull_fd)

  if output_close and output_fd > 2:

    utils_wrapper.CloseFdNoError(output_fd)

def StartDaemon(cmd, env=None, cwd="/", output=None, output_fd=None,

                pidfile=None):

  """Start a daemon process after forking twice.

  @type cmd: string or list

  @param cmd: Command to run

  @type env: dict

  @param env: Additional environment variables

  @type cwd: string

  @param cwd: Working directory for the program

  @type output: string

  @param output: Path to file in which to save the output

  @type output_fd: int

  @param output_fd: File descriptor for output

  @type pidfile: string

  @param pidfile: Process ID file

  @rtype: int

  @return: Daemon process ID

  @raise errors.ProgrammerError: if we call this when forks are disabled

  """

  if _no_fork:

    raise errors.ProgrammerError("utils.StartDaemon() called with fork()"

                                 " disabled")

  if output and not (bool(output) ^ (output_fd is not None)):

    raise errors.ProgrammerError("Only one of 'output' and 'output_fd' can be"

                                 " specified")

  if isinstance(cmd, basestring):

    cmd = ["/bin/sh", "-c", cmd]

  strcmd = utils_text.ShellQuoteArgs(cmd)

  if output:

    logging.debug("StartDaemon %s, output file '%s'", strcmd, output)

  else:

    logging.debug("StartDaemon %s", strcmd)

  cmd_env = _BuildCmdEnvironment(env, False)

  # Create pipe for sending PID back

  (pidpipe_read, pidpipe_write) = os.pipe()

  try:

    try:

      # Create pipe for sending error messages

      (errpipe_read, errpipe_write) = os.pipe()

      try:

        try:

          # First fork

          pid = os.fork()

          if pid == 0:

            try:

              # Child process, won't return

              _StartDaemonChild(errpipe_read, errpipe_write,

                                pidpipe_read, pidpipe_write,

                                cmd, cmd_env, cwd,

                                output, output_fd, pidfile)

            finally:

              # Well, maybe child process failed

              os._exit(1) # pylint: disable=W0212

        finally:

          utils_wrapper.CloseFdNoError(errpipe_write)

        # Wait for daemon to be started (or an error message to

        # arrive) and read up to 100 KB as an error message

        errormsg = utils_wrapper.RetryOnSignal(os.read, errpipe_read,

                                               100 * 1024)

      finally:

        utils_wrapper.CloseFdNoError(errpipe_read)

    finally:

      utils_wrapper.CloseFdNoError(pidpipe_write)

    # Read up to 128 bytes for PID

    pidtext = utils_wrapper.RetryOnSignal(os.read, pidpipe_read, 128)

  finally:

    utils_wrapper.CloseFdNoError(pidpipe_read)

  # Try to avoid zombies by waiting for child process

  try:

    os.waitpid(pid, 0)

  except OSError:

    pass

  if errormsg:

    raise errors.OpExecError("Error when starting daemon process: %r" %

                             errormsg)

  try:

    return int(pidtext)

  except (ValueError, TypeError), err:

    raise errors.OpExecError("Error while trying to parse PID %r: %s" %

                             (pidtext, err))

def _StartDaemonChild(errpipe_read, errpipe_write,

                      pidpipe_read, pidpipe_write,

                      args, env, cwd,

                      output, fd_output, pidfile):

  """Child process for starting daemon.

  """

  try:

    # Close parent's side

    utils_wrapper.CloseFdNoError(errpipe_read)

    utils_wrapper.CloseFdNoError(pidpipe_read)

    # First child process

    SetupDaemonEnv()

    # And fork for the second time

    pid = os.fork()

    if pid != 0:

      # Exit first child process

      os._exit(0) # pylint: disable=W0212

    # Make sure pipe is closed on execv* (and thereby notifies

    # original process)

    utils_wrapper.SetCloseOnExecFlag(errpipe_write, True)

    # List of file descriptors to be left open

    noclose_fds = [errpipe_write]

    # Open PID file

    if pidfile:

      fd_pidfile = utils_io.WritePidFile(pidfile)

      # Keeping the file open to hold the lock

      noclose_fds.append(fd_pidfile)

      utils_wrapper.SetCloseOnExecFlag(fd_pidfile, False)

    else:

      fd_pidfile = None

    SetupDaemonFDs(output, fd_output)

    # Send daemon PID to parent

    utils_wrapper.RetryOnSignal(os.write, pidpipe_write, str(os.getpid()))

    # Close all file descriptors except stdio and error message pipe

    CloseFDs(noclose_fds=noclose_fds)

    # Change working directory

    os.chdir(cwd)

    if env is None:

      os.execvp(args[0], args)

    else:

      os.execvpe(args[0], args, env)

  except: # pylint: disable=W0702

    try:

      # Report errors to original process

      WriteErrorToFD(errpipe_write, str(sys.exc_info()[1]))

    except: # pylint: disable=W0702

      # Ignore errors in error handling

      pass

  os._exit(1) # pylint: disable=W0212

def WriteErrorToFD(fd, err):

  """Possibly write an error message to a fd.

  @type fd: None or int (file descriptor)

  @param fd: if not None, the error will be written to this fd

  @param err: string, the error message

  """

  if fd is None:

    return

  if not err:

    err = "<unknown error>"

  utils_wrapper.RetryOnSignal(os.write, fd, err)

def _CheckIfAlive(child):

  """Raises L{utils_retry.RetryAgain} if child is still alive.

  @raises utils_retry.RetryAgain: If child is still alive

  """

  if child.poll() is None:

    raise utils_retry.RetryAgain()

def _WaitForProcess(child, timeout):

  """Waits for the child to terminate or until we reach timeout.

  """

  try:

    utils_retry.Retry(_CheckIfAlive, (1.0, 1.2, 5.0), max(0, timeout),

                      args=[child])

  except utils_retry.RetryTimeout:

    pass

def _RunCmdPipe(cmd, env, via_shell, cwd, interactive, timeout, noclose_fds,

                input_fd, postfork_fn=None,

                _linger_timeout=constants.CHILD_LINGER_TIMEOUT):

  """Run a command and return its output.

  @type  cmd: string or list

  @param cmd: Command to run

  @type env: dict

  @param env: The environment to use

  @type via_shell: bool

  @param via_shell: if we should run via the shell

  @type cwd: string

  @param cwd: the working directory for the program

  @type interactive: boolean

  @param interactive: Run command interactive (without piping)

  @type timeout: int

  @param timeout: Timeout after the programm gets terminated

  @type noclose_fds: list

  @param noclose_fds: list of additional (fd >=3) file descriptors to leave

                      open for the child process

  @type input_fd: C{file}-like object or numeric file descriptor

  @param input_fd: File descriptor for process' standard input

  @type postfork_fn: Callable receiving PID as parameter

  @param postfork_fn: Function run after fork but before timeout

  @rtype: tuple

  @return: (out, err, status)

  """

  poller = select.poll()

  if interactive:

    stderr = None

    stdout = None

  else:

    stderr = subprocess.PIPE

    stdout = subprocess.PIPE

  if input_fd:

    stdin = input_fd

  elif interactive:

    stdin = None

  else:

    stdin = subprocess.PIPE

  if noclose_fds:

    preexec_fn = lambda: CloseFDs(noclose_fds)

    close_fds = False

  else:

    preexec_fn = None

    close_fds = True

  child = subprocess.Popen(cmd, shell=via_shell,

                           stderr=stderr,

                           stdout=stdout,

                           stdin=stdin,

                           close_fds=close_fds, env=env,

                           cwd=cwd,

                           preexec_fn=preexec_fn)

  if postfork_fn:

    postfork_fn(child.pid)

  out = StringIO()

  err = StringIO()

  linger_timeout = None

  if timeout is None:

    poll_timeout = None

  else:

    poll_timeout = utils_algo.RunningTimeout(timeout, True).Remaining

  msg_timeout = ("Command %s (%d) run into execution timeout, terminating" %

                 (cmd, child.pid))

  msg_linger = ("Command %s (%d) run into linger timeout, killing" %

                (cmd, child.pid))

  timeout_action = _TIMEOUT_NONE

  # subprocess: "If the stdin argument is PIPE, this attribute is a file object

  # that provides input to the child process. Otherwise, it is None."

  assert (stdin == subprocess.PIPE) ^ (child.stdin is None), \

    "subprocess' stdin did not behave as documented"

  if not interactive:

    if child.stdin is not None:

      child.stdin.close()

    poller.register(child.stdout, select.POLLIN)

    poller.register(child.stderr, select.POLLIN)

    fdmap = {

      child.stdout.fileno(): (out, child.stdout),

      child.stderr.fileno(): (err, child.stderr),

      }

    for fd in fdmap:

      utils_wrapper.SetNonblockFlag(fd, True)

    while fdmap:

      if poll_timeout:

        pt = poll_timeout() * 1000

        if pt < 0:

          if linger_timeout is None:

            logging.warning(msg_timeout)

            if child.poll() is None:

              timeout_action = _TIMEOUT_TERM

              utils_wrapper.IgnoreProcessNotFound(os.kill, child.pid,

                                                  signal.SIGTERM)

            linger_timeout = \

              utils_algo.RunningTimeout(_linger_timeout, True).Remaining

          pt = linger_timeout() * 1000

          if pt < 0:

            break

      else:

        pt = None

      pollresult = utils_wrapper.RetryOnSignal(poller.poll, pt)

      for fd, event in pollresult:

        if event & select.POLLIN or event & select.POLLPRI:

          data = fdmap[fd][1].read()

          # no data from read signifies EOF (the same as POLLHUP)

          if not data:

            poller.unregister(fd)

            del fdmap[fd]

            continue

          fdmap[fd][0].write(data)

        if (event & select.POLLNVAL or event & select.POLLHUP or

            event & select.POLLERR):

          poller.unregister(fd)

          del fdmap[fd]

  if timeout is not None:

    assert callable(poll_timeout)

    # We have no I/O left but it might still run

    if child.poll() is None:

      _WaitForProcess(child, poll_timeout())

    # Terminate if still alive after timeout

    if child.poll() is None:

      if linger_timeout is None:

        logging.warning(msg_timeout)

        timeout_action = _TIMEOUT_TERM

        utils_wrapper.IgnoreProcessNotFound(os.kill, child.pid, signal.SIGTERM)

        lt = _linger_timeout

      else:

        lt = linger_timeout()

      _WaitForProcess(child, lt)

    # Okay, still alive after timeout and linger timeout? Kill it!

    if child.poll() is None:

      timeout_action = _TIMEOUT_KILL

      logging.warning(msg_linger)

      utils_wrapper.IgnoreProcessNotFound(os.kill, child.pid, signal.SIGKILL)

  out = out.getvalue()

  err = err.getvalue()

  status = child.wait()

  return out, err, status, timeout_action

def _RunCmdFile(cmd, env, via_shell, output, cwd, noclose_fds):

  """Run a command and save its output to a file.

  @type  cmd: string or list

  @param cmd: Command to run

  @type env: dict

  @param env: The environment to use

  @type via_shell: bool

  @param via_shell: if we should run via the shell

  @type output: str

  @param output: the filename in which to save the output

  @type cwd: string

  @param cwd: the working directory for the program

  @type noclose_fds: list

  @param noclose_fds: list of additional (fd >=3) file descriptors to leave

                      open for the child process

  @rtype: int

  @return: the exit status

  """

  fh = open(output, "a")

  if noclose_fds:

    preexec_fn = lambda: CloseFDs(noclose_fds + [fh.fileno()])

    close_fds = False

  else:

    preexec_fn = None

    close_fds = True

  try:

    child = subprocess.Popen(cmd, shell=via_shell,

                             stderr=subprocess.STDOUT,

                             stdout=fh,

                             stdin=subprocess.PIPE,

                             close_fds=close_fds, env=env,

                             cwd=cwd,

                             preexec_fn=preexec_fn)

    child.stdin.close()

    status = child.wait()

  finally:

    fh.close()

  return status

def RunParts(dir_name, env=None, reset_env=False):

  """Run Scripts or programs in a directory

  @type dir_name: string

  @param dir_name: absolute path to a directory

  @type env: dict

  @param env: The environment to use

  @type reset_env: boolean

  @param reset_env: whether to reset or keep the default os environment

  @rtype: list of tuples

  @return: list of (name, (one of RUNDIR_STATUS), RunResult)

  """

  rr = []

  try:

    dir_contents = utils_io.ListVisibleFiles(dir_name)

  except OSError, err:

    logging.warning("RunParts: skipping %s (cannot list: %s)", dir_name, err)

    return rr

  for relname in sorted(dir_contents):

    fname = utils_io.PathJoin(dir_name, relname)

    if not (constants.EXT_PLUGIN_MASK.match(relname) is not None and

            utils_wrapper.IsExecutable(fname)):

      rr.append((relname, constants.RUNPARTS_SKIP, None))

    else:

      try:

        result = RunCmd([fname], env=env, reset_env=reset_env)

      except Exception, err: # pylint: disable=W0703

        rr.append((relname, constants.RUNPARTS_ERR, str(err)))

      else:

        rr.append((relname, constants.RUNPARTS_RUN, result))

  return rr

def _GetProcStatusPath(pid):

  """Returns the path for a PID's proc status file.

  @type pid: int

  @param pid: Process ID

  @rtype: string

  """

  return "/proc/%d/status" % pid

def IsProcessAlive(pid):

  """Check if a given pid exists on the system.

  @note: zombie status is not handled, so zombie processes

      will be returned as alive

  @type pid: int

  @param pid: the process ID to check

  @rtype: boolean

  @return: True if the process exists

  """

  def _TryStat(name):

    try:

      os.stat(name)

      return True

    except EnvironmentError, err:

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

        return False

      elif err.errno == errno.EINVAL:

        raise utils_retry.RetryAgain(err)

      raise

  assert isinstance(pid, int), "pid must be an integer"

  if pid <= 0:

    return False

  # /proc in a multiprocessor environment can have strange behaviors.

  # Retry the os.stat a few times until we get a good result.

  try:

    return utils_retry.Retry(_TryStat, (0.01, 1.5, 0.1), 0.5,

                             args=[_GetProcStatusPath(pid)])

  except utils_retry.RetryTimeout, err:

    err.RaiseInner()

def _ParseSigsetT(sigset):

  """Parse a rendered sigset_t value.

  This is the opposite of the Linux kernel's fs/proc/array.c:render_sigset_t

  function.

  @type sigset: string

  @param sigset: Rendered signal set from /proc/$pid/status

  @rtype: set

  @return: Set of all enabled signal numbers

  """

  result = set()

  signum = 0

  for ch in reversed(sigset):

    chv = int(ch, 16)

    # The following could be done in a loop, but it's easier to read and

    # understand in the unrolled form

    if chv & 1:

      result.add(signum + 1)

    if chv & 2:

      result.add(signum + 2)

    if chv & 4:

      result.add(signum + 3)

    if chv & 8:

      result.add(signum + 4)

    signum += 4

  return result

def _GetProcStatusField(pstatus, field):

  """Retrieves a field from the contents of a proc status file.

  @type pstatus: string

  @param pstatus: Contents of /proc/$pid/status

  @type field: string

  @param field: Name of field whose value should be returned

  @rtype: string

  """

  for line in pstatus.splitlines():

    parts = line.split(":", 1)

    if len(parts) < 2 or parts[0] != field:

      continue

    return parts[1].strip()

  return None

def IsProcessHandlingSignal(pid, signum, status_path=None):

  """Checks whether a process is handling a signal.

  @type pid: int

  @param pid: Process ID

  @type signum: int

  @param signum: Signal number

  @rtype: bool

  """

  if status_path is None:

    status_path = _GetProcStatusPath(pid)

  try:

    proc_status = utils_io.ReadFile(status_path)

  except EnvironmentError, err:

    # In at least one case, reading /proc/$pid/status failed with ESRCH.

    if err.errno in (errno.ENOENT, errno.ENOTDIR, errno.EINVAL, errno.ESRCH):

      return False

    raise

  sigcgt = _GetProcStatusField(proc_status, "SigCgt")

  if sigcgt is None:

    raise RuntimeError("%s is missing 'SigCgt' field" % status_path)

  # Now check whether signal is handled

  return signum in _ParseSigsetT(sigcgt)

def Daemonize(logfile):

  """Daemonize the current process.

  This detaches the current process from the controlling terminal and

  runs it in the background as a daemon.

  @type logfile: str

  @param logfile: the logfile to which we should redirect stdout/stderr

  @rtype: tuple; (int, callable)

  @return: File descriptor of pipe(2) which must be closed to notify parent

    process and a callable to reopen log files

  """

  # pylint: disable=W0212

  # yes, we really want os._exit

  # TODO: do another attempt to merge Daemonize and StartDaemon, or at

  # least abstract the pipe functionality between them

  # Create pipe for sending error messages

  (rpipe, wpipe) = os.pipe()

  # this might fail

  pid = os.fork()

  if (pid == 0):  # The first child.

    SetupDaemonEnv()

    # this might fail

    pid = os.fork() # Fork a second child.

    if (pid == 0):  # The second child.

      utils_wrapper.CloseFdNoError(rpipe)

    else:

      # exit() or _exit()?  See below.

      os._exit(0) # Exit parent (the first child) of the second child.

  else:

    utils_wrapper.CloseFdNoError(wpipe)

    # Wait for daemon to be started (or an error message to

    # arrive) and read up to 100 KB as an error message

    errormsg = utils_wrapper.RetryOnSignal(os.read, rpipe, 100 * 1024)

    if errormsg:

      sys.stderr.write("Error when starting daemon process: %r\n" % errormsg)

      rcode = 1

    else:

      rcode = 0

    os._exit(rcode) # Exit parent of the first child.

  reopen_fn = compat.partial(SetupDaemonFDs, logfile, None)

  # Open logs for the first time

  reopen_fn()

  return (wpipe, reopen_fn)

def KillProcess(pid, signal_=signal.SIGTERM, timeout=30,

                waitpid=False):

  """Kill a process given by its pid.

  @type pid: int

  @param pid: The PID to terminate.

  @type signal_: int

  @param signal_: The signal to send, by default SIGTERM

  @type timeout: int

  @param timeout: The timeout after which, if the process is still alive,

                  a SIGKILL will be sent. If not positive, no such checking

                  will be done

  @type waitpid: boolean

  @param waitpid: If true, we should waitpid on this process after

      sending signals, since it's our own child and otherwise it

      would remain as zombie

  """

  def _helper(pid, signal_, wait):

    """Simple helper to encapsulate the kill/waitpid sequence"""

    if utils_wrapper.IgnoreProcessNotFound(os.kill, pid, signal_) and wait:

      try:

        os.waitpid(pid, os.WNOHANG)

      except OSError:

        pass

  if pid <= 0:

    # kill with pid=0 == suicide

    raise errors.ProgrammerError("Invalid pid given '%s'" % pid)

  if not IsProcessAlive(pid):

    return

  _helper(pid, signal_, waitpid)

  if timeout <= 0:

    return

  def _CheckProcess():

    if not IsProcessAlive(pid):

      return

    try:

      (result_pid, _) = os.waitpid(pid, os.WNOHANG)

    except OSError:

      raise utils_retry.RetryAgain()

    if result_pid > 0:

      return

    raise utils_retry.RetryAgain()

  try:

    # Wait up to $timeout seconds

    utils_retry.Retry(_CheckProcess, (0.01, 1.5, 0.1), timeout)

  except utils_retry.RetryTimeout:

    pass

  if IsProcessAlive(pid):

    # Kill process if it's still alive

    _helper(pid, signal.SIGKILL, waitpid)

def RunInSeparateProcess(fn, *args):

  """Runs a function in a separate process.

  Note: Only boolean return values are supported.

  @type fn: callable

  @param fn: Function to be called

  @rtype: bool

  @return: Function's result

  """

  pid = os.fork()

  if pid == 0:

    # Child process

    try:

      # In case the function uses temporary files

      utils_wrapper.ResetTempfileModule()

      # Call function

      result = int(bool(fn(*args)))

      assert result in (0, 1)

    except: # pylint: disable=W0702

      logging.exception("Error while calling function in separate process")

      # 0 and 1 are reserved for the return value

      result = 33

    os._exit(result) # pylint: disable=W0212

  # Parent process

  # Avoid zombies and check exit code

  (_, status) = os.waitpid(pid, 0)

  if os.WIFSIGNALED(status):

    exitcode = None

    signum = os.WTERMSIG(status)

  else:

    exitcode = os.WEXITSTATUS(status)

    signum = None

  if not (exitcode in (0, 1) and signum is None):

    raise errors.GenericError("Child program failed (code=%s, signal=%s)" %

                              (exitcode, signum))

  return bool(exitcode)

def CloseFDs(noclose_fds=None):

  """Close file descriptors.

  This closes all file descriptors above 2 (i.e. except

  stdin/out/err).

  @type noclose_fds: list or None

  @param noclose_fds: if given, it denotes a list of file descriptor

      that should not be closed

  """

  # Default maximum for the number of available file descriptors.

  if 'SC_OPEN_MAX' in os.sysconf_names:

    try:

      MAXFD = os.sysconf('SC_OPEN_MAX')

      if MAXFD < 0:

        MAXFD = 1024

    except OSError:

      MAXFD = 1024

  else:

    MAXFD = 1024

  maxfd = resource.getrlimit(resource.RLIMIT_NOFILE)[1]

  if (maxfd == resource.RLIM_INFINITY):

    maxfd = MAXFD

  # Iterate through and close all file descriptors (except the standard ones)

  for fd in range(3, maxfd):

    if noclose_fds and fd in noclose_fds:

      continue

    utils_wrapper.CloseFdNoError(fd)