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+      #
+      #
       # 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.
       """Ganeti utility module.
       This module holds functions that can be used in both daemons (all) and
       the command line scripts.
       """
       import sys
       import os
       import sha
       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 signal
       from cStringIO import StringIO
       from ganeti import errors
       from ganeti import constants
       _locksheld = []
       _re_shell_unquoted = re.compile('^[-.,=:/_+@A-Za-z0-9]+$')
       debug = False
       debug_locks = False
       #: when set to True, L{RunCmd} is disabled
       no_fork = False
       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):
           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)
           if self.signal is not None:
             self.fail_reason = "terminated by signal %s" % self.signal
           elif self.exit_code is not None:
             self.fail_reason = "exited with exit code %s" % self.exit_code
           else:
             self.fail_reason = "unable to determine termination reason"
           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 RunCmd(cmd, env=None, output=None, cwd='/'):
         """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
         @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 /
         @rtype: L{RunResult}
         @return: RunResult instance
         @raise erors.ProgrammerError: if we call this when forks are disabled
         """
         if no_fork:
           raise errors.ProgrammerError("utils.RunCmd() called with fork() disabled")
         if isinstance(cmd, list):
           cmd = [str(val) for val in cmd]
           strcmd = " ".join(cmd)
           shell = False
         else:
           strcmd = cmd
           shell = True
         logging.debug("RunCmd '%s'", strcmd)
         cmd_env = os.environ.copy()
         cmd_env["LC_ALL"] = "C"
         if env is not None:
           cmd_env.update(env)
         if output is None:
           out, err, status = _RunCmdPipe(cmd, cmd_env, shell, cwd)
         else:
           status = _RunCmdFile(cmd, cmd_env, shell, output, cwd)
           out = err = ""
         if status >= 0:
           exitcode = status
           signal_ = None
         else:
           exitcode = None
           signal_ = -status
         return RunResult(exitcode, signal_, out, err, strcmd)
       def _RunCmdPipe(cmd, env, via_shell, cwd):
         """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
         @rtype: tuple
         @return: (out, err, status)
         """
         poller = select.poll()
         child = subprocess.Popen(cmd, shell=via_shell,
                                  stderr=subprocess.PIPE,
                                  stdout=subprocess.PIPE,
                                  stdin=subprocess.PIPE,
                                  close_fds=True, env=env,
                                  cwd=cwd)
         child.stdin.close()
         poller.register(child.stdout, select.POLLIN)
         poller.register(child.stderr, select.POLLIN)
         out = StringIO()
         err = StringIO()
         fdmap = {
           child.stdout.fileno(): (out, child.stdout),
           child.stderr.fileno(): (err, child.stderr),
+          }
         for fd in fdmap:
           status = fcntl.fcntl(fd, fcntl.F_GETFL)
           fcntl.fcntl(fd, fcntl.F_SETFL, status | os.O_NONBLOCK)
         while fdmap:
           try:
             pollresult = poller.poll()
           except EnvironmentError, eerr:
             if eerr.errno == errno.EINTR:
               continue
             raise
           except select.error, serr:
             if serr[0] == errno.EINTR:
               continue
             raise
           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]
         out = out.getvalue()
         err = err.getvalue()
         status = child.wait()
         return out, err, status
       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 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 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
             os.makedirs(os.path.dirname(new), mkdir_mode)
             return os.rename(old, new)
           raise
       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 = sha.sha()
         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 CheckDict(target, template, logname=None):
         """Ensure a dictionary has a required set of keys.
         For the given dictionaries I{target} and I{template}, ensure
         I{target} has all the keys from I{template}. Missing keys are added
         with values from template.
         @type target: dict
         @param target: the dictionary to update
         @type template: dict
         @param template: the dictionary holding the default values
         @type logname: str or None
         @param logname: if not None, causes the missing keys to be
             logged with this name
         """
         missing = []
         for k in template:
           if k not in target:
             missing.append(k)
             target[k] = template[k]
         if missing and logname:
           logging.warning('%s missing keys %s', logname, ', '.join(missing))
       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
         """
         if pid <= 0:
           return False
         try:
           os.stat("/proc/%d/status" % pid)
           return True
         except EnvironmentError, err:
           if err.errno in (errno.ENOENT, errno.ENOTDIR):
             return False
           raise
       def ReadPidFile(pidfile):
         """Read a pid from a file.
         @type  pidfile: string
         @param pidfile: path to the file containing the pid
         @rtype: int
         @return: The process id, if the file exista and contains a valid PID,
                  otherwise 0
         """
         try:
           pf = open(pidfile, 'r')
         except EnvironmentError, err:
           if err.errno != errno.ENOENT:
             logging.exception("Can't read pid file?!")
           return 0
         try:
           pid = int(pf.read())
         except ValueError, err:
           logging.info("Can't parse pid file contents", exc_info=True)
           return 0
         return pid
       def MatchNameComponent(key, name_list):
         """Try to match a name against a list.
         This function will try to match a name like test1 against a list
         like C{['test1.example.com', 'test2.example.com', ...]}. Against
         this list, I{'test1'} as well as I{'test1.example'} will match, but
         not I{'test1.ex'}. A multiple match will be considered as no match
         at all (e.g. I{'test1'} against C{['test1.example.com',
         'test1.example.org']}).
         @type key: str
         @param key: the name to be searched
         @type name_list: list
         @param name_list: the list of strings against which to search the key
         @rtype: None or str
         @return: None if there is no match I{or} if there are multiple matches,
             otherwise the element from the list which matches
         """
         mo = re.compile("^%s(\..*)?$" % re.escape(key))
         names_filtered = [name for name in name_list if mo.match(name) is not None]
         if len(names_filtered) != 1:
           return None
         return names_filtered[0]
       class HostInfo:
         """Class implementing resolver and hostname functionality
         """
         def __init__(self, name=None):
           """Initialize the host name object.
           If the name argument is not passed, it will use this system's
           name.
           """
           if name is None:
             name = self.SysName()
           self.query = name
           self.name, self.aliases, self.ipaddrs = self.LookupHostname(name)
           self.ip = self.ipaddrs[0]
         def ShortName(self):
           """Returns the hostname without domain.
           """
           return self.name.split('.')[0]
         @staticmethod
         def SysName():
           """Return the current system's name.
           This is simply a wrapper over C{socket.gethostname()}.
           """
           return socket.gethostname()
         @staticmethod
         def LookupHostname(hostname):
           """Look up hostname
           @type hostname: str
           @param hostname: hostname to look up
           @rtype: tuple
           @return: a tuple (name, aliases, ipaddrs) as returned by
               C{socket.gethostbyname_ex}
           @raise errors.ResolverError: in case of errors in resolving
           """
           try:
             result = socket.gethostbyname_ex(hostname)
           except socket.gaierror, err:
             # hostname not found in DNS
             raise errors.ResolverError(hostname, err.args[0], err.args[1])
           return result
       def ListVolumeGroups():
         """List volume groups and their size
         @rtype: dict
         @return:
              Dictionary with keys volume name and values
              the size of the volume
         """
         command = "vgs --noheadings --units m --nosuffix -o name,size"
         result = RunCmd(command)
         retval = {}
         if result.failed:
           return retval
         for line in result.stdout.splitlines():
           try:
             name, size = line.split()
             size = int(float(size))
           except (IndexError, ValueError), err:
             logging.error("Invalid output from vgs (%s): %s", err, line)
             continue
           retval[name] = size
         return retval
       def BridgeExists(bridge):
         """Check whether the given bridge exists in the system
         @type bridge: str
         @param bridge: the bridge name to check
         @rtype: boolean
         @return: True if it does
         """
         return os.path.isdir("/sys/class/net/%s/bridge" % bridge)
       def CheckBEParams(beparams):
         """Checks whether the user-supplied be-params are valid,
         and converts them from string format where appropriate.
         @type beparams: dict
         @param beparams: new params dict
         """
         if beparams:
           for item in beparams:
             if item not in constants.BES_PARAMETERS:
               raise errors.OpPrereqError("Unknown backend parameter %s" % item)
             if item in (constants.BE_MEMORY, constants.BE_VCPUS):
               val = beparams[item]
               if val != constants.VALUE_DEFAULT:
                 try:
                   val = int(val)
                 except ValueError, err:
                   raise errors.OpPrereqError("Invalid %s size: %s" % (item, str(err)))
                 beparams[item] = val
             if item in (constants.BE_AUTO_BALANCE):
               val = beparams[item]
               if not isinstance(val, bool):
                 if val == constants.VALUE_TRUE:
                   beparams[item] = True
                 elif val == constants.VALUE_FALSE:
                   beparams[item] = False
                 else:
                   raise errors.OpPrereqError("Invalid %s value: %s" % (item, val))
       def NiceSort(name_list):
         """Sort a list of strings based on digit and non-digit groupings.
         Given a list of names C{['a1', 'a10', 'a11', 'a2']} this function
         will sort the list in the logical order C{['a1', 'a2', 'a10',
         'a11']}.
         The sort algorithm breaks each name in groups of either only-digits
         or no-digits. Only the first eight such groups are considered, and
         after that we just use what's left of the string.
         @type name_list: list
         @param name_list: the names to be sorted
         @rtype: list
         @return: a copy of the name list sorted with our algorithm
         """
         _SORTER_BASE = "(\D+|\d+)"
         _SORTER_FULL = "^%s%s?%s?%s?%s?%s?%s?%s?.*$" % (_SORTER_BASE, _SORTER_BASE,
                                                         _SORTER_BASE, _SORTER_BASE,
                                                         _SORTER_BASE, _SORTER_BASE,
                                                         _SORTER_BASE, _SORTER_BASE)
         _SORTER_RE = re.compile(_SORTER_FULL)
         _SORTER_NODIGIT = re.compile("^\D*$")
         def _TryInt(val):
           """Attempts to convert a variable to integer."""
           if val is None or _SORTER_NODIGIT.match(val):
             return val
           rval = int(val)
           return rval
         to_sort = [([_TryInt(grp) for grp in _SORTER_RE.match(name).groups()], name)
                    for name in name_list]
         to_sort.sort()
         return [tup[1] for tup in to_sort]
       def TryConvert(fn, val):
         """Try to convert a value ignoring errors.
         This function tries to apply function I{fn} to I{val}. If no
         C{ValueError} or C{TypeError} exceptions are raised, it will return
         the result, else it will return the original value. Any other
         exceptions are propagated to the caller.
         @type fn: callable
         @param fn: function to apply to the value
         @param val: the value to be converted
         @return: The converted value if the conversion was successful,
             otherwise the original value.
         """
         try:
           nv = fn(val)
         except (ValueError, TypeError), err:
           nv = val
         return nv
       def IsValidIP(ip):
         """Verifies the syntax of an IPv4 address.
         This function checks if the IPv4 address passes is valid or not based
         on syntax (not IP range, class calculations, etc.).
         @type ip: str
         @param ip: the address to be checked
         @rtype: a regular expression match object
         @return: a regular epression match object, or None if the
             address is not valid
         """
         unit = "(0|[1-9]\d{0,2})"
         #TODO: convert and return only boolean
         return re.match("^%s\.%s\.%s\.%s$" % (unit, unit, unit, unit), ip)
       def IsValidShellParam(word):
         """Verifies is the given word is safe from the shell's p.o.v.
         This means that we can pass this to a command via the shell and be
         sure that it doesn't alter the command line and is passed as such to
         the actual command.
         Note that we are overly restrictive here, in order to be on the safe
         side.
         @type word: str
         @param word: the word to check
         @rtype: boolean
         @return: True if the word is 'safe'
         """
         return bool(re.match("^[-a-zA-Z0-9._+/:%@]+$", word))
       def BuildShellCmd(template, *args):
         """Build a safe shell command line from the given arguments.
         This function will check all arguments in the args list so that they
         are valid shell parameters (i.e. they don't contain shell
         metacharaters). If everything is ok, it will return the result of
         template % args.
         @type template: str
         @param template: the string holding the template for the
             string formatting
         @rtype: str
         @return: the expanded command line
         """
         for word in args:
           if not IsValidShellParam(word):
             raise errors.ProgrammerError("Shell argument '%s' contains"
                                          " invalid characters" % word)
         return template % args
       def FormatUnit(value, units):
         """Formats an incoming number of MiB with the appropriate unit.
         @type value: int
         @param value: integer representing the value in MiB (1048576)
         @type units: char
         @param units: the type of formatting we should do:
             - 'h' for automatic scaling
             - 'm' for MiBs
             - 'g' for GiBs
             - 't' for TiBs
         @rtype: str
         @return: the formatted value (with suffix)
         """
         if units not in ('m', 'g', 't', 'h'):
           raise errors.ProgrammerError("Invalid unit specified '%s'" % str(units))
         suffix = ''
         if units == 'm' or (units == 'h' and value < 1024):
           if units == 'h':
             suffix = 'M'
           return "%d%s" % (round(value, 0), suffix)
         elif units == 'g' or (units == 'h' and value < (1024 * 1024)):
           if units == 'h':
             suffix = 'G'
           return "%0.1f%s" % (round(float(value) / 1024, 1), suffix)
         else:
           if units == 'h':
             suffix = 'T'
           return "%0.1f%s" % (round(float(value) / 1024 / 1024, 1), suffix)
       def ParseUnit(input_string):
         """Tries to extract number and scale from the given string.
         Input must be in the format C{NUMBER+ [DOT NUMBER+] SPACE*
         [UNIT]}. If no unit is specified, it defaults to MiB. Return value
         is always an int in MiB.
         """
         m = re.match('^([.\d]+)\s*([a-zA-Z]+)?$', input_string)
         if not m:
           raise errors.UnitParseError("Invalid format")
         value = float(m.groups()[0])
         unit = m.groups()[1]
         if unit:
           lcunit = unit.lower()
         else:
           lcunit = 'm'
         if lcunit in ('m', 'mb', 'mib'):
           # Value already in MiB
           pass
         elif lcunit in ('g', 'gb', 'gib'):
           value *= 1024
         elif lcunit in ('t', 'tb', 'tib'):
           value *= 1024 * 1024
         else:
           raise errors.UnitParseError("Unknown unit: %s" % unit)
         # Make sure we round up
         if int(value) < value:
           value += 1
         # Round up to the next multiple of 4
         value = int(value)
         if value % 4:
           value += 4 - value % 4
         return value
       def AddAuthorizedKey(file_name, key):
         """Adds an SSH public key to an authorized_keys file.
         @type file_name: str
         @param file_name: path to authorized_keys file
         @type key: str
         @param key: string containing key
         """
         key_fields = key.split()
         f = open(file_name, 'a+')
         try:
           nl = True
           for line in f:
             # Ignore whitespace changes
             if line.split() == key_fields:
               break
             nl = line.endswith('\n')
           else:
             if not nl:
               f.write("\n")
             f.write(key.rstrip('\r\n'))
             f.write("\n")
             f.flush()
         finally:
           f.close()
       def RemoveAuthorizedKey(file_name, key):
         """Removes an SSH public key from an authorized_keys file.
         @type file_name: str
         @param file_name: path to authorized_keys file
         @type key: str
         @param key: string containing key
         """
         key_fields = key.split()
         fd, tmpname = tempfile.mkstemp(dir=os.path.dirname(file_name))
         try:
           out = os.fdopen(fd, 'w')
           try:
             f = open(file_name, 'r')
             try:
               for line in f:
                 # Ignore whitespace changes while comparing lines
                 if line.split() != key_fields:
                   out.write(line)
               out.flush()
               os.rename(tmpname, file_name)
             finally:
               f.close()
           finally:
             out.close()
         except:
           RemoveFile(tmpname)
           raise
       def SetEtcHostsEntry(file_name, ip, hostname, aliases):
         """Sets the name of an IP address and hostname in /etc/hosts.
         @type file_name: str
         @param file_name: path to the file to modify (usually C{/etc/hosts})
         @type ip: str
         @param ip: the IP address
         @type hostname: str
         @param hostname: the hostname to be added
         @type aliases: list
         @param aliases: the list of aliases to add for the hostname
         """
         # Ensure aliases are unique
         aliases = UniqueSequence([hostname] + aliases)[1:]
         fd, tmpname = tempfile.mkstemp(dir=os.path.dirname(file_name))
         try:
           out = os.fdopen(fd, 'w')
           try:
             f = open(file_name, 'r')
             try:
               for line in f:
                 fields = line.split()
                 if fields and not fields[0].startswith('#') and ip == fields[0]:
                   continue
                 out.write(line)
               out.write("%s\t%s" % (ip, hostname))
               if aliases:
                 out.write(" %s" % ' '.join(aliases))
               out.write('\n')
               out.flush()
               os.fsync(out)
               os.rename(tmpname, file_name)
             finally:
               f.close()
           finally:
             out.close()
         except:
           RemoveFile(tmpname)
           raise
       def AddHostToEtcHosts(hostname):
         """Wrapper around SetEtcHostsEntry.
         @type hostname: str
         @param hostname: a hostname that will be resolved and added to
             L{constants.ETC_HOSTS}
         """
         hi = HostInfo(name=hostname)
         SetEtcHostsEntry(constants.ETC_HOSTS, hi.ip, hi.name, [hi.ShortName()])
       def RemoveEtcHostsEntry(file_name, hostname):
         """Removes a hostname from /etc/hosts.
         IP addresses without names are removed from the file.
         @type file_name: str
         @param file_name: path to the file to modify (usually C{/etc/hosts})
         @type hostname: str
         @param hostname: the hostname to be removed
         """
         fd, tmpname = tempfile.mkstemp(dir=os.path.dirname(file_name))
         try:
           out = os.fdopen(fd, 'w')
           try:
             f = open(file_name, 'r')
             try:
               for line in f:
                 fields = line.split()
                 if len(fields) > 1 and not fields[0].startswith('#'):
                   names = fields[1:]
                   if hostname in names:
                     while hostname in names:
                       names.remove(hostname)
                     if names:
                       out.write("%s %s\n" % (fields[0], ' '.join(names)))
                     continue
                 out.write(line)
               out.flush()
               os.fsync(out)
               os.rename(tmpname, file_name)
             finally:
               f.close()
           finally:
             out.close()
         except:
           RemoveFile(tmpname)
           raise
       def RemoveHostFromEtcHosts(hostname):
         """Wrapper around RemoveEtcHostsEntry.
         @type hostname: str
         @param hostname: hostname that will be resolved and its
             full and shot name will be removed from
             L{constants.ETC_HOSTS}
         """
         hi = HostInfo(name=hostname)
         RemoveEtcHostsEntry(constants.ETC_HOSTS, hi.name)
         RemoveEtcHostsEntry(constants.ETC_HOSTS, hi.ShortName())
       def CreateBackup(file_name):
         """Creates a backup of a file.
         @type file_name: str
         @param file_name: file to be backed up
         @rtype: str
         @return: the path to the newly created backup
         @raise errors.ProgrammerError: for invalid file names
         """
         if not os.path.isfile(file_name):
           raise errors.ProgrammerError("Can't make a backup of a non-file '%s'" %
                                       file_name)
         prefix = '%s.backup-%d.' % (os.path.basename(file_name), int(time.time()))
         dir_name = os.path.dirname(file_name)
         fsrc = open(file_name, 'rb')
         try:
           (fd, backup_name) = tempfile.mkstemp(prefix=prefix, dir=dir_name)
           fdst = os.fdopen(fd, 'wb')
           try:
             shutil.copyfileobj(fsrc, fdst)
           finally:
             fdst.close()
         finally:
           fsrc.close()
         return backup_name
       def ShellQuote(value):
         """Quotes shell argument according to POSIX.
         @type value: str
         @param value: the argument to be quoted
         @rtype: str
         @return: the quoted value
         """
         if _re_shell_unquoted.match(value):
           return value
         else:
           return "'%s'" % value.replace("'", "'\\''")
       def ShellQuoteArgs(args):
         """Quotes a list of shell arguments.
         @type args: list
         @param args: list of arguments to be quoted
         @rtype: str
         @return: the quoted arguments concatenaned with spaces
         """
         return ' '.join([ShellQuote(i) for i in args])
       def TcpPing(target, port, timeout=10, live_port_needed=False, source=None):
         """Simple ping implementation using TCP connect(2).
         Check if the given IP is reachable by doing attempting a TCP connect
         to it.
         @type target: str
         @param target: the IP or hostname to ping
         @type port: int
         @param port: the port to connect to
         @type timeout: int
         @param timeout: the timeout on the connection attemp
         @type live_port_needed: boolean
         @param live_port_needed: whether a closed port will cause the
             function to return failure, as if there was a timeout
         @type source: str or None
         @param source: if specified, will cause the connect to be made
             from this specific source address; failures to bind other
             than C{EADDRNOTAVAIL} will be ignored
         """
         sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         success = False
         if source is not None:
           try:
             sock.bind((source, 0))
           except socket.error, (errcode, errstring):
             if errcode == errno.EADDRNOTAVAIL:
               success = False
         sock.settimeout(timeout)
         try:
           sock.connect((target, port))
           sock.close()
           success = True
         except socket.timeout:
           success = False
         except socket.error, (errcode, errstring):
           success = (not live_port_needed) and (errcode == errno.ECONNREFUSED)
         return success
       def OwnIpAddress(address):
         """Check if the current host has the the given IP address.
         Currently this is done by TCP-pinging the address from the loopback
         address.
         @type address: string
         @param address: the addres to check
         @rtype: bool
         @return: True if we own the address
         """
         return TcpPing(address, constants.DEFAULT_NODED_PORT,
                        source=constants.LOCALHOST_IP_ADDRESS)
       def ListVisibleFiles(path):
         """Returns a list of visible files in a directory.
         @type path: str
         @param path: the directory to enumerate
         @rtype: list
         @return: the list of all files not starting with a dot
         """
         files = [i for i in os.listdir(path) if not i.startswith(".")]
         files.sort()
         return files
       def GetHomeDir(user, default=None):
         """Try to get the homedir of the given user.
         The user can be passed either as a string (denoting the name) or as
         an integer (denoting the user id). If the user is not found, the
         'default' argument is returned, which defaults to None.
         """
         try:
           if isinstance(user, basestring):
             result = pwd.getpwnam(user)
           elif isinstance(user, (int, long)):
             result = pwd.getpwuid(user)
           else:
             raise errors.ProgrammerError("Invalid type passed to GetHomeDir (%s)" %
                                          type(user))
         except KeyError:
           return default
         return result.pw_dir
       def NewUUID():
         """Returns a random UUID.
         @note: This is a Linux-specific method as it uses the /proc
             filesystem.
         @rtype: str
         """
         f = open("/proc/sys/kernel/random/uuid", "r")
         try:
           return f.read(128).rstrip("\n")
         finally:
           f.close()
       def GenerateSecret():
         """Generates a random secret.
         This will generate a pseudo-random secret, and return its sha digest
         (so that it can be used where an ASCII string is needed).
         @rtype: str
         @return: a sha1 hexdigest of a block of 64 random bytes
         """
         return sha.new(os.urandom(64)).hexdigest()
       def ReadFile(file_name, size=None):
         """Reads a file.
         @type size: None or int
         @param size: Read at most size bytes
         @rtype: str
         @return: the (possibly partial) conent of the file
         """
         f = open(file_name, "r")
         try:
           if size is None:
             return f.read()
           else:
             return f.read(size)
         finally:
           f.close()
       def WriteFile(file_name, fn=None, data=None,
                     mode=None, uid=-1, gid=-1,
                     atime=None, mtime=None, close=True,
                     dry_run=False, backup=False,
                     prewrite=None, postwrite=None):
         """(Over)write a file atomically.
         The file_name and either fn (a function taking one argument, the
         file descriptor, and which should write the data to it) or data (the
         contents of the file) must be passed. The other arguments are
         optional and allow setting the file mode, owner and group, and the
         mtime/atime of the file.
         If the function doesn't raise an exception, it has succeeded and the
         target file has the new contents. If the file has raised an
         exception, an existing target file should be unmodified and the
         temporary file should be removed.
         @type file_name: str
         @param file_name: the target filename
         @type fn: callable
         @param fn: content writing function, called with
             file descriptor as parameter
         @type data: sr
         @param data: contents of the file
         @type mode: int
         @param mode: file mode
         @type uid: int
         @param uid: the owner of the file
         @type gid: int
         @param gid: the group of the file
         @type atime: int
         @param atime: a custom access time to be set on the file
         @type mtime: int
         @param mtime: a custom modification time to be set on the file
         @type close: boolean
         @param close: whether to close file after writing it
         @type prewrite: callable
         @param prewrite: function to be called before writing content
         @type postwrite: callable
         @param postwrite: function to be called after writing content
         @rtype: None or int
         @return: None if the 'close' parameter evaluates to True,
             otherwise the file descriptor
         @raise errors.ProgrammerError: if an of the arguments are not valid
         """
         if not os.path.isabs(file_name):
           raise errors.ProgrammerError("Path passed to WriteFile is not"
                                        " absolute: '%s'" % file_name)
         if [fn, data].count(None) != 1:
           raise errors.ProgrammerError("fn or data required")
         if [atime, mtime].count(None) == 1:
           raise errors.ProgrammerError("Both atime and mtime must be either"
                                        " set or None")
         if backup and not dry_run and os.path.isfile(file_name):
           CreateBackup(file_name)
         dir_name, base_name = os.path.split(file_name)
         fd, new_name = tempfile.mkstemp('.new', base_name, dir_name)
         # here we need to make sure we remove the temp file, if any error
         # leaves it in place
         try:
           if uid != -1 or gid != -1:
             os.chown(new_name, uid, gid)
           if mode:
             os.chmod(new_name, mode)
           if callable(prewrite):
             prewrite(fd)
           if data is not None:
             os.write(fd, data)
           else:
             fn(fd)
           if callable(postwrite):
             postwrite(fd)
           os.fsync(fd)
           if atime is not None and mtime is not None:
             os.utime(new_name, (atime, mtime))
           if not dry_run:
             os.rename(new_name, file_name)
         finally:
           if close:
             os.close(fd)
             result = None
           else:
             result = fd
           RemoveFile(new_name)
         return result
       def FirstFree(seq, base=0):
         """Returns the first non-existing integer from seq.
         The seq argument should be a sorted list of positive integers. The
         first time the index of an element is smaller than the element
         value, the index will be returned.
         The base argument is used to start at a different offset,
         i.e. C{[3, 4, 6]} with I{offset=3} will return 5.
         Example: C{[0, 1, 3]} will return I{2}.
         @type seq: sequence
         @param seq: the sequence to be analyzed.
         @type base: int
         @param base: use this value as the base index of the sequence
         @rtype: int
         @return: the first non-used index in the sequence
         """
         for idx, elem in enumerate(seq):
           assert elem >= base, "Passed element is higher than base offset"
           if elem > idx + base:
             # idx is not used
             return idx + base
         return None
       def all(seq, pred=bool):
         "Returns True if pred(x) is True for every element in the iterable"
         for elem in itertools.ifilterfalse(pred, seq):
           return False
         return True
       def any(seq, pred=bool):
         "Returns True if pred(x) is True for at least one element in the iterable"
         for elem in itertools.ifilter(pred, seq):
           return True
         return False
       def UniqueSequence(seq):
         """Returns a list with unique elements.
         Element order is preserved.
         @type seq: sequence
         @param seq: the sequence with the source elementes
         @rtype: list
         @return: list of unique elements from seq
         """
         seen = set()
         return [i for i in seq if i not in seen and not seen.add(i)]
       def IsValidMac(mac):
         """Predicate to check if a MAC address is valid.
         Checks wether the supplied MAC address is formally correct, only
         accepts colon separated format.
         @type mac: str
         @param mac: the MAC to be validated
         @rtype: boolean
         @return: True is the MAC seems valid
         """
         mac_check = re.compile("^([0-9a-f]{2}(:|$)){6}$")
         return mac_check.match(mac) is not None
       def TestDelay(duration):
         """Sleep for a fixed amount of time.
         @type duration: float
         @param duration: the sleep duration
         @rtype: boolean
         @return: False for negative value, True otherwise
         """
         if duration < 0:
           return False
         time.sleep(duration)
         return True
       def _CloseFDNoErr(fd, retries=5):
         """Close a file descriptor ignoring errors.
         @type fd: int
         @param fd: the file descriptor
         @type retries: int
         @param retries: how many retries to make, in case we get any
             other error than EBADF
         """
         try:
           os.close(fd)
         except OSError, err:
           if err.errno != errno.EBADF:
             if retries > 0:
               _CloseFDNoErr(fd, retries - 1)
           # else either it's closed already or we're out of retries, so we
           # ignore this and go on
       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
           _CloseFDNoErr(fd)
       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: int
         @returns: the value zero
         """
         UMASK = 077
         WORKDIR = "/"
         # this might fail
         pid = os.fork()
         if (pid == 0):  # The first child.
           os.setsid()
           # this might fail
           pid = os.fork() # Fork a second child.
           if (pid == 0):  # The second child.
             os.chdir(WORKDIR)
             os.umask(UMASK)
           else:
             # exit() or _exit()?  See below.
             os._exit(0) # Exit parent (the first child) of the second child.
         else:
           os._exit(0) # Exit parent of the first child.
         for fd in range(3):
           _CloseFDNoErr(fd)
         i = os.open("/dev/null", os.O_RDONLY) # stdin
         assert i == 0, "Can't close/reopen stdin"
         i = os.open(logfile, os.O_WRONLY|os.O_CREAT|os.O_APPEND, 0600) # stdout
         assert i == 1, "Can't close/reopen stdout"
         # Duplicate standard output to standard error.
         os.dup2(1, 2)
         return 0
       def DaemonPidFileName(name):
         """Compute a ganeti pid file absolute path
         @type name: str
         @param name: the daemon name
         @rtype: str
         @return: the full path to the pidfile corresponding to the given
             daemon name
         """
         return os.path.join(constants.RUN_GANETI_DIR, "%s.pid" % name)
       def WritePidFile(name):
         """Write the current process pidfile.
         The file will be written to L{constants.RUN_GANETI_DIR}I{/name.pid}
         @type name: str
         @param name: the daemon name to use
         @raise errors.GenericError: if the pid file already exists and
             points to a live process
         """
         pid = os.getpid()
         pidfilename = DaemonPidFileName(name)
         if IsProcessAlive(ReadPidFile(pidfilename)):
           raise errors.GenericError("%s contains a live process" % pidfilename)
         WriteFile(pidfilename, data="%d\n" % pid)
       def RemovePidFile(name):
         """Remove the current process pidfile.
         Any errors are ignored.
         @type name: str
         @param name: the daemon name used to derive the pidfile name
         """
         pid = os.getpid()
         pidfilename = DaemonPidFileName(name)
         # TODO: we could check here that the file contains our pid
         try:
           RemoveFile(pidfilename)
         except:
           pass
       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"""
           os.kill(pid, signal_)
           if 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
         # Wait up to $timeout seconds
         end = time.time() + timeout
         wait = 0.01
         while time.time() < end and IsProcessAlive(pid):
           try:
             (result_pid, _) = os.waitpid(pid, os.WNOHANG)
             if result_pid > 0:
               break
           except OSError:
             pass
           time.sleep(wait)
           # Make wait time longer for next try
           if wait < 0.1:
             wait *= 1.5
         if IsProcessAlive(pid):
           # Kill process if it's still alive
           _helper(pid, signal.SIGKILL, waitpid)
       def FindFile(name, search_path, test=os.path.exists):
         """Look for a filesystem object in a given path.
         This is an abstract method to search for filesystem object (files,
         dirs) under a given search path.
         @type name: str
         @param name: the name to look for
         @type search_path: str
         @param search_path: location to start at
         @type test: callable
         @param test: a function taking one argument that should return True
             if the a given object is valid; the default value is
             os.path.exists, causing only existing files to be returned
         @rtype: str or None
         @return: full path to the object if found, None otherwise
         """
         for dir_name in search_path:
           item_name = os.path.sep.join([dir_name, name])
           if test(item_name):
             return item_name
         return None
       def CheckVolumeGroupSize(vglist, vgname, minsize):
         """Checks if the volume group list is valid.
         The function will check if a given volume group is in the list of
         volume groups and has a minimum size.
         @type vglist: dict
         @param vglist: dictionary of volume group names and their size
         @type vgname: str
         @param vgname: the volume group we should check
         @type minsize: int
         @param minsize: the minimum size we accept
         @rtype: None or str
         @return: None for success, otherwise the error message
         """
         vgsize = vglist.get(vgname, None)
         if vgsize is None:
           return "volume group '%s' missing" % vgname
         elif vgsize < minsize:
           return ("volume group '%s' too small (%s MiB required, %d MiB found)" %
                   (vgname, minsize, vgsize))
         return None
       def SplitTime(value):
         """Splits time as floating point number into a tuple.
         @param value: Time in seconds
         @type value: int or float
         @return: Tuple containing (seconds, microseconds)
         """
         (seconds, microseconds) = divmod(int(value * 1000000), 1000000)
         assert 0 <= seconds, \
           "Seconds must be larger than or equal to 0, but are %s" % seconds
         assert 0 <= microseconds <= 999999, \
           "Microseconds must be 0-999999, but are %s" % microseconds
         return (int(seconds), int(microseconds))
       def MergeTime(timetuple):
         """Merges a tuple into time as a floating point number.
         @param timetuple: Time as tuple, (seconds, microseconds)
         @type timetuple: tuple
         @return: Time as a floating point number expressed in seconds
         """
         (seconds, microseconds) = timetuple
         assert 0 <= seconds, \
           "Seconds must be larger than or equal to 0, but are %s" % seconds
         assert 0 <= microseconds <= 999999, \
           "Microseconds must be 0-999999, but are %s" % microseconds
         return float(seconds) + (float(microseconds) * 0.000001)
       def GetNodeDaemonPort():
         """Get the node daemon port for this cluster.
         Note that this routine does not read a ganeti-specific file, but
         instead uses C{socket.getservbyname} to allow pre-customization of
         this parameter outside of Ganeti.
         @rtype: int
         """
         try:
           port = socket.getservbyname("ganeti-noded", "tcp")
         except socket.error:
           port = constants.DEFAULT_NODED_PORT
         return port
       def SetupLogging(logfile, debug=False, stderr_logging=False, program=""):
         """Configures the logging module.
         @type logfile: str
         @param logfile: the filename to which we should log
         @type debug: boolean
         @param debug: whether to enable debug messages too or
             only those at C{INFO} and above level
         @type stderr_logging: boolean
         @param stderr_logging: whether we should also log to the standard error
         @type program: str
         @param program: the name under which we should log messages
         @raise EnvironmentError: if we can't open the log file and
             stderr logging is disabled
         """
         fmt = "%(asctime)s: " + program + " "
         if debug:
           fmt += ("pid=%(process)d/%(threadName)s %(levelname)s"
                  " %(module)s:%(lineno)s %(message)s")
         else:
           fmt += "pid=%(process)d %(levelname)s %(message)s"
         formatter = logging.Formatter(fmt)
         root_logger = logging.getLogger("")
         root_logger.setLevel(logging.NOTSET)
         # Remove all previously setup handlers
         for handler in root_logger.handlers:
           handler.close()
           root_logger.removeHandler(handler)
         if stderr_logging:
           stderr_handler = logging.StreamHandler()
           stderr_handler.setFormatter(formatter)
           if debug:
             stderr_handler.setLevel(logging.NOTSET)
           else:
             stderr_handler.setLevel(logging.CRITICAL)
           root_logger.addHandler(stderr_handler)
         # this can fail, if the logging directories are not setup or we have
         # a permisssion problem; in this case, it's best to log but ignore
         # the error if stderr_logging is True, and if false we re-raise the
         # exception since otherwise we could run but without any logs at all
         try:
           logfile_handler = logging.FileHandler(logfile)
           logfile_handler.setFormatter(formatter)
           if debug:
             logfile_handler.setLevel(logging.DEBUG)
           else:
             logfile_handler.setLevel(logging.INFO)
           root_logger.addHandler(logfile_handler)
         except EnvironmentError, err:
           if stderr_logging:
             logging.exception("Failed to enable logging to file '%s'", logfile)
           else:
             # we need to re-raise the exception
             raise
       def TailFile(fname, lines=20):
         """Return the last lines from a file.
         @note: this function will only read and parse the last 4KB of
             the file; if the lines are very long, it could be that less
             than the requested number of lines are returned
         @param fname: the file name
         @type lines: int
         @param lines: the (maximum) number of lines to return
         """
         fd = open(fname, "r")
         try:
           fd.seek(0, 2)
           pos = fd.tell()
           pos = max(0, pos-4096)
           fd.seek(pos, 0)
           raw_data = fd.read()
         finally:
           fd.close()
         rows = raw_data.splitlines()
         return rows[-lines:]
       def LockedMethod(fn):
         """Synchronized object access decorator.
         This decorator is intended to protect access to an object using the
         object's own lock which is hardcoded to '_lock'.
         """
         def _LockDebug(*args, **kwargs):
           if debug_locks:
             logging.debug(*args, **kwargs)
         def wrapper(self, *args, **kwargs):
           assert hasattr(self, '_lock')
           lock = self._lock
           _LockDebug("Waiting for %s", lock)
           lock.acquire()
           try:
             _LockDebug("Acquired %s", lock)
             result = fn(self, *args, **kwargs)
           finally:
             _LockDebug("Releasing %s", lock)
             lock.release()
             _LockDebug("Released %s", lock)
           return result
         return wrapper
       def LockFile(fd):
         """Locks a file using POSIX locks.
         @type fd: int
         @param fd: the file descriptor we need to lock
         """
         try:
           fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
         except IOError, err:
           if err.errno == errno.EAGAIN:
             raise errors.LockError("File already locked")
           raise
       class FileLock(object):
         """Utility class for file locks.
         """
         def __init__(self, filename):
           """Constructor for FileLock.
           This will open the file denoted by the I{filename} argument.
           @type filename: str
           @param filename: path to the file to be locked
           """
           self.filename = filename
           self.fd = open(self.filename, "w")
         def __del__(self):
           self.Close()
         def Close(self):
           """Close the file and release the lock.
           """
           if self.fd:
             self.fd.close()
             self.fd = None
         def _flock(self, flag, blocking, timeout, errmsg):
           """Wrapper for fcntl.flock.
           @type flag: int
           @param flag: operation flag
           @type blocking: bool
           @param blocking: whether the operation should be done in blocking mode.
           @type timeout: None or float
           @param timeout: for how long the operation should be retried (implies
                           non-blocking mode).
           @type errmsg: string
           @param errmsg: error message in case operation fails.
           """
           assert self.fd, "Lock was closed"
           assert timeout is None or timeout >= 0, \
             "If specified, timeout must be positive"
           if timeout is not None:
             flag |= fcntl.LOCK_NB
             timeout_end = time.time() + timeout
           # Blocking doesn't have effect with timeout
           elif not blocking:
             flag |= fcntl.LOCK_NB
             timeout_end = None
           retry = True
           while retry:
             try:
               fcntl.flock(self.fd, flag)
               retry = False
             except IOError, err:
               if err.errno in (errno.EAGAIN, ):
                 if timeout_end is not None and time.time() < timeout_end:
                   # Wait before trying again
                   time.sleep(max(0.1, min(1.0, timeout)))
                 else:
                   raise errors.LockError(errmsg)
               else:
                 logging.exception("fcntl.flock failed")
                 raise
         def Exclusive(self, blocking=False, timeout=None):
           """Locks the file in exclusive mode.
           @type blocking: boolean
           @param blocking: whether to block and wait until we
               can lock the file or return immediately
           @type timeout: int or None
           @param timeout: if not None, the duration to wait for the lock
               (in blocking mode)
           """
           self._flock(fcntl.LOCK_EX, blocking, timeout,
                       "Failed to lock %s in exclusive mode" % self.filename)
         def Shared(self, blocking=False, timeout=None):
           """Locks the file in shared mode.
           @type blocking: boolean
           @param blocking: whether to block and wait until we
               can lock the file or return immediately
           @type timeout: int or None
           @param timeout: if not None, the duration to wait for the lock
               (in blocking mode)
           """
           self._flock(fcntl.LOCK_SH, blocking, timeout,
                       "Failed to lock %s in shared mode" % self.filename)
         def Unlock(self, blocking=True, timeout=None):
           """Unlocks the file.
           According to C{flock(2)}, unlocking can also be a nonblocking
           operation::
             To make a non-blocking request, include LOCK_NB with any of the above
             operations.
           @type blocking: boolean
           @param blocking: whether to block and wait until we
               can lock the file or return immediately
           @type timeout: int or None
           @param timeout: if not None, the duration to wait for the lock
               (in blocking mode)
           """
           self._flock(fcntl.LOCK_UN, blocking, timeout,
                       "Failed to unlock %s" % self.filename)
       class SignalHandler(object):
         """Generic signal handler class.
         It automatically restores the original handler when deconstructed or
         when L{Reset} is called. You can either pass your own handler
         function in or query the L{called} attribute to detect whether the
         signal was sent.
         @type signum: list
         @ivar signum: the signals we handle
         @type called: boolean
         @ivar called: tracks whether any of the signals have been raised
         """
         def __init__(self, signum):
           """Constructs a new SignalHandler instance.
           @type signum: int or list of ints
           @param signum: Single signal number or set of signal numbers
           """
           if isinstance(signum, (int, long)):
             self.signum = set([signum])
           else:
             self.signum = set(signum)
           self.called = False
           self._previous = {}
           try:
             for signum in self.signum:
               # Setup handler
               prev_handler = signal.signal(signum, self._HandleSignal)
               try:
                 self._previous[signum] = prev_handler
               except:
                 # Restore previous handler
                 signal.signal(signum, prev_handler)
                 raise
           except:
             # Reset all handlers
             self.Reset()
             # Here we have a race condition: a handler may have already been called,
             # but there's not much we can do about it at this point.
             raise
         def __del__(self):
           self.Reset()
         def Reset(self):
           """Restore previous handler.
           This will reset all the signals to their previous handlers.
           """
           for signum, prev_handler in self._previous.items():
             signal.signal(signum, prev_handler)
             # If successful, remove from dict
             del self._previous[signum]
         def Clear(self):
           """Unsets the L{called} flag.
           This function can be used in case a signal may arrive several times.
           """
           self.called = False
         def _HandleSignal(self, signum, frame):
           """Actual signal handling function.
           """
           # This is not nice and not absolutely atomic, but it appears to be the only
           # solution in Python -- there are no atomic types.
           self.called = True
       class FieldSet(object):
         """A simple field set.
         Among the features are:
           - checking if a string is among a list of static string or regex objects
           - checking if a whole list of string matches
           - returning the matching groups from a regex match
         Internally, all fields are held as regular expression objects.
         """
         def __init__(self, *items):
           self.items = [re.compile("^%s$" % value) for value in items]
         def Extend(self, other_set):
           """Extend the field set with the items from another one"""
           self.items.extend(other_set.items)
         def Matches(self, field):
           """Checks if a field matches the current set
           @type field: str
           @param field: the string to match
           @return: either False or a regular expression match object
           """
           for m in itertools.ifilter(None, (val.match(field) for val in self.items)):
             return m
           return False
         def NonMatching(self, items):
           """Returns the list of fields not matching the current set
           @type items: list
           @param items: the list of fields to check
           @rtype: list
           @return: list of non-matching fields
           """
           return [val for val in items if not self.Matches(val)]

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