Synnefo » snf-ganeti

#

#

# Copyright (C) 2006, 2007, 2010 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.

"""Ganeti utility module.

This module holds functions that can be used in both daemons (all) and

the command line scripts.

"""

import os

import sys

import time

import subprocess

import re

import socket

import tempfile

import shutil

import errno

import pwd

import itertools

import select

import fcntl

import resource

import logging

import logging.handlers

import signal

import OpenSSL

import datetime

import calendar

import hmac

import collections

from cStringIO import StringIO

try:

  # pylint: disable-msg=F0401

  import ctypes

except ImportError:

  ctypes = None

from ganeti import errors

from ganeti import constants

from ganeti import compat

_locksheld = []

_re_shell_unquoted = re.compile('^[-.,=:/_+@A-Za-z0-9]+$')

debug_locks = False

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

no_fork = False

_RANDOM_UUID_FILE = "/proc/sys/kernel/random/uuid"

HEX_CHAR_RE = r"[a-zA-Z0-9]"

VALID_X509_SIGNATURE_SALT = re.compile("^%s+$" % HEX_CHAR_RE, re.S)

X509_SIGNATURE = re.compile(r"^%s:\s*(?P<salt>%s+)/(?P<sign>%s+)$" %

                            (re.escape(constants.X509_CERT_SIGNATURE_HEADER),

                             HEX_CHAR_RE, HEX_CHAR_RE),

                            re.S | re.I)

_VALID_SERVICE_NAME_RE = re.compile("^[-_.a-zA-Z0-9]{1,128}$")

UUID_RE = re.compile('^[a-f0-9]{8}-[a-f0-9]{4}-[a-f0-9]{4}-'

                     '[a-f0-9]{4}-[a-f0-9]{12}$')

# Certificate verification results

(CERT_WARNING,

 CERT_ERROR) = range(1, 3)

# Flags for mlockall() (from bits/mman.h)

_MCL_CURRENT = 1

_MCL_FUTURE = 2

#: MAC checker regexp

_MAC_CHECK = re.compile("^([0-9a-f]{2}:){5}[0-9a-f]{2}$", re.I)

(_TIMEOUT_NONE,

 _TIMEOUT_TERM,

 _TIMEOUT_KILL) = range(3)

#: Shell param checker regexp

_SHELLPARAM_REGEX = re.compile(r"^[-a-zA-Z0-9._+/:%@]+$")

#: Unit checker regexp

_PARSEUNIT_REGEX = re.compile(r"^([.\d]+)\s*([a-zA-Z]+)?$")

#: ASN1 time regexp

_ASN1_TIME_REGEX = re.compile(r"^(\d+)([-+]\d\d)(\d\d)$")

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 = 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):

  """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: weather 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

  @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 isinstance(cmd, basestring):

    strcmd = cmd

    shell = True

  else:

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

    strcmd = ShellQuoteArgs(cmd)

    shell = False

  if output:

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

  else:

    logging.debug("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)

    else:

      timeout_action = _TIMEOUT_NONE

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

      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)

  if output_fd is not None:

    pass

  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)

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 = 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-msg=W0212

        finally:

          _CloseFDNoErr(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 = RetryOnSignal(os.read, errpipe_read, 100 * 1024)

      finally:

        _CloseFDNoErr(errpipe_read)

    finally:

      _CloseFDNoErr(pidpipe_write)

    # Read up to 128 bytes for PID

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

  finally:

    _CloseFDNoErr(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

    _CloseFDNoErr(errpipe_read)

    _CloseFDNoErr(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-msg=W0212

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

    # original process)

    SetCloseOnExecFlag(errpipe_write, True)

    # List of file descriptors to be left open

    noclose_fds = [errpipe_write]

    # Open PID file

    if pidfile:

      fd_pidfile = WritePidFile(pidfile)

      # Keeping the file open to hold the lock

      noclose_fds.append(fd_pidfile)

      SetCloseOnExecFlag(fd_pidfile, False)

    else:

      fd_pidfile = None

    SetupDaemonFDs(output, fd_output)

    # Send daemon PID to parent

    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-msg=W0702

    try:

      # Report errors to original process

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

    except: # pylint: disable-msg=W0702

      # Ignore errors in error handling

      pass

  os._exit(1) # pylint: disable-msg=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>"

  RetryOnSignal(os.write, fd, err)

def _CheckIfAlive(child):

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

  @raises RetryAgain: If child is still alive

  """

  if child.poll() is None:

    raise RetryAgain()

def _WaitForProcess(child, timeout):

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

  """

  try:

    Retry(_CheckIfAlive, (1.0, 1.2, 5.0), max(0, timeout), args=[child])

  except RetryTimeout:

    pass

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

                _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

  @rtype: tuple

  @return: (out, err, status)

  """

  poller = select.poll()

  stderr = subprocess.PIPE

  stdout = subprocess.PIPE

  stdin = subprocess.PIPE

  if interactive:

    stderr = stdout = stdin = None

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

                           stderr=stderr,

                           stdout=stdout,

                           stdin=stdin,

                           close_fds=True, env=env,

                           cwd=cwd)

  out = StringIO()

  err = StringIO()

  linger_timeout = None

  if timeout is None:

    poll_timeout = None

  else:

    poll_timeout = 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

  if not interactive:

    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:

      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

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

            linger_timeout = RunningTimeout(_linger_timeout, True).Remaining

          pt = linger_timeout() * 1000

          if pt < 0:

            break

      else:

        pt = None

      pollresult = 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

        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)

      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):

  """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

  @rtype: int

  @return: the exit status

  """

  fh = open(output, "a")

  try:

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

                             stderr=subprocess.STDOUT,

                             stdout=fh,

                             stdin=subprocess.PIPE,

                             close_fds=True, env=env,

                             cwd=cwd)

    child.stdin.close()

    status = child.wait()

  finally:

    fh.close()

  return status

def SetCloseOnExecFlag(fd, enable):

  """Sets or unsets the close-on-exec flag on a file descriptor.

  @type fd: int

  @param fd: File descriptor

  @type enable: bool

  @param enable: Whether to set or unset it.

  """

  flags = fcntl.fcntl(fd, fcntl.F_GETFD)

  if enable:

    flags |= fcntl.FD_CLOEXEC

  else:

    flags &= ~fcntl.FD_CLOEXEC

  fcntl.fcntl(fd, fcntl.F_SETFD, flags)

def SetNonblockFlag(fd, enable):

  """Sets or unsets the O_NONBLOCK flag on on a file descriptor.

  @type fd: int

  @param fd: File descriptor

  @type enable: bool

  @param enable: Whether to set or unset it

  """

  flags = fcntl.fcntl(fd, fcntl.F_GETFL)

  if enable:

    flags |= os.O_NONBLOCK

  else:

    flags &= ~os.O_NONBLOCK

  fcntl.fcntl(fd, fcntl.F_SETFL, flags)

def RetryOnSignal(fn, *args, **kwargs):

  """Calls a function again if it failed due to EINTR.

  """

  while True:

    try:

      return fn(*args, **kwargs)

    except EnvironmentError, err:

      if err.errno != errno.EINTR:

        raise

    except (socket.error, select.error), err:

      # In python 2.6 and above select.error is an IOError, so it's handled

      # above, in 2.5 and below it's not, and it's handled here.

      if not (err.args and err.args[0] == errno.EINTR):

        raise

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 = 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 = PathJoin(dir_name, relname)

    if not (os.path.isfile(fname) and os.access(fname, os.X_OK) and

            constants.EXT_PLUGIN_MASK.match(relname) is not None):

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

    else:

      try:

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

      except Exception, err: # pylint: disable-msg=W0703

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

      else:

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

  return rr

def RemoveFile(filename):

  """Remove a file ignoring some errors.

  Remove a file, ignoring non-existing ones or directories. Other

  errors are passed.

  @type filename: str

  @param filename: the file to be removed

  """

  try:

    os.unlink(filename)

  except OSError, err:

    if err.errno not in (errno.ENOENT, errno.EISDIR):

      raise

def RemoveDir(dirname):

  """Remove an empty directory.

  Remove a directory, ignoring non-existing ones.

  Other errors are passed. This includes the case,

  where the directory is not empty, so it can't be removed.

  @type dirname: str

  @param dirname: the empty directory to be removed

  """

  try:

    os.rmdir(dirname)

  except OSError, err:

    if err.errno != errno.ENOENT:

      raise

def RenameFile(old, new, mkdir=False, mkdir_mode=0750):

  """Renames a file.

  @type old: string

  @param old: Original path

  @type new: string

  @param new: New path

  @type mkdir: bool

  @param mkdir: Whether to create target directory if it doesn't exist

  @type mkdir_mode: int

  @param mkdir_mode: Mode for newly created directories

  """

  try:

    return os.rename(old, new)

  except OSError, err:

    # In at least one use case of this function, the job queue, directory

    # creation is very rare. Checking for the directory before renaming is not

    # as efficient.

    if mkdir and err.errno == errno.ENOENT:

      # Create directory and try again

      Makedirs(os.path.dirname(new), mode=mkdir_mode)

      return os.rename(old, new)

    raise

def Makedirs(path, mode=0750):

  """Super-mkdir; create a leaf directory and all intermediate ones.

  This is a wrapper around C{os.makedirs} adding error handling not implemented

  before Python 2.5.

  """

  try:

    os.makedirs(path, mode)

  except OSError, err:

    # Ignore EEXIST. This is only handled in os.makedirs as included in

    # Python 2.5 and above.

    if err.errno != errno.EEXIST or not os.path.exists(path):

      raise

def ResetTempfileModule():

  """Resets the random name generator of the tempfile module.

  This function should be called after C{os.fork} in the child process to

  ensure it creates a newly seeded random generator. Otherwise it would

  generate the same random parts as the parent process. If several processes

  race for the creation of a temporary file, this could lead to one not getting

  a temporary name.

  """

  # pylint: disable-msg=W0212

  if hasattr(tempfile, "_once_lock") and hasattr(tempfile, "_name_sequence"):

    tempfile._once_lock.acquire()

    try:

      # Reset random name generator

      tempfile._name_sequence = None

    finally:

      tempfile._once_lock.release()

  else:

    logging.critical("The tempfile module misses at least one of the"

                     " '_once_lock' and '_name_sequence' attributes")

def _FingerprintFile(filename):

  """Compute the fingerprint of a file.

  If the file does not exist, a None will be returned

  instead.

  @type filename: str

  @param filename: the filename to checksum

  @rtype: str

  @return: the hex digest of the sha checksum of the contents

      of the file

  """

  if not (os.path.exists(filename) and os.path.isfile(filename)):

    return None

  f = open(filename)

  fp = compat.sha1_hash()

  while True:

    data = f.read(4096)

    if not data:

      break

    fp.update(data)

  return fp.hexdigest()

def FingerprintFiles(files):

  """Compute fingerprints for a list of files.

  @type files: list

  @param files: the list of filename to fingerprint

  @rtype: dict

  @return: a dictionary filename: fingerprint, holding only

      existing files

  """

  ret = {}

  for filename in files:

    cksum = _FingerprintFile(filename)

    if cksum:

      ret[filename] = cksum

  return ret

def ForceDictType(target, key_types, allowed_values=None):

  """Force the values of a dict to have certain types.

  @type target: dict

  @param target: the dict to update

  @type key_types: dict

  @param key_types: dict mapping target dict keys to types

                    in constants.ENFORCEABLE_TYPES

  @type allowed_values: list

  @keyword allowed_values: list of specially allowed values

  """

  if allowed_values is None:

    allowed_values = []

  if not isinstance(target, dict):

    msg = "Expected dictionary, got '%s'" % target

    raise errors.TypeEnforcementError(msg)

  for key in target:

    if key not in key_types:

      msg = "Unknown key '%s'" % key

      raise errors.TypeEnforcementError(msg)

    if target[key] in allowed_values:

      continue

    ktype = key_types[key]

    if ktype not in constants.ENFORCEABLE_TYPES:

      msg = "'%s' has non-enforceable type %s" % (key, ktype)

      raise errors.ProgrammerError(msg)

    if ktype in (constants.VTYPE_STRING, constants.VTYPE_MAYBE_STRING):

      if target[key] is None and ktype == constants.VTYPE_MAYBE_STRING:

        pass

      elif not isinstance(target[key], basestring):

        if isinstance(target[key], bool) and not target[key]:

          target[key] = ''

        else:

          msg = "'%s' (value %s) is not a valid string" % (key, target[key])

          raise errors.TypeEnforcementError(msg)

    elif ktype == constants.VTYPE_BOOL:

      if isinstance(target[key], basestring) and target[key]:

        if target[key].lower() == constants.VALUE_FALSE:

          target[key] = False

        elif target[key].lower() == constants.VALUE_TRUE:

          target[key] = True

        else:

          msg = "'%s' (value %s) is not a valid boolean" % (key, target[key])

          raise errors.TypeEnforcementError(msg)

      elif target[key]:

        target[key] = True

      else:

        target[key] = False

    elif ktype == constants.VTYPE_SIZE:

      try:

        target[key] = ParseUnit(target[key])

      except errors.UnitParseError, err:

        msg = "'%s' (value %s) is not a valid size. error: %s" % \

              (key, target[key], err)

        raise errors.TypeEnforcementError(msg)

    elif ktype == constants.VTYPE_INT:

      try:

        target[key] = int(target[key])

      except (ValueError, TypeError):

        msg = "'%s' (value %s) is not a valid integer" % (key, target[key])

        raise errors.TypeEnforcementError(msg)

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 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 Retry(_TryStat, (0.01, 1.5, 0.1), 0.5,

                 args=[_GetProcStatusPath(pid)])

  except 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 = 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: