Synnefo » snf-ganeti

#!/usr/bin/python

#

# Copyright (C) 2006, 2007, 2011 Google Inc.

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful, but

# WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

# General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

# 02110-1301, USA.

"""Program which configures LVM on the Ganeti nodes.

This program wipes disks and creates a volume group on top of them. It

can also show disk information to help you decide which disks you want

to wipe.

The error handling is done by raising our own exceptions from most of

the functions; these exceptions then handled globally in the main()

function. The exceptions that each function can raise are not

documented individually, since almost every error path ends in a

raise.

Another two exceptions that are handled globally are IOError and

OSError. The idea behind this is, since we run as root, we should

usually not get these errors, but if we do it's most probably a system

error, so they should be handled and the user instructed to report

them.

"""

import os

import sys

import optparse

import time

import errno

from ganeti.utils import RunCmd, ReadFile

from ganeti import constants

from ganeti import cli

from ganeti import compat

USAGE = ("\tlvmstrap diskinfo\n"

         "\tlvmstrap [--vgname=NAME] [--allow-removable]"

         " { --alldisks | --disks DISKLIST }"

         " create")

verbose_flag = False

#: Supported disk types (as prefixes)

SUPPORTED_TYPES = [

  "hd",

  "sd",

  "md",

  "ubd",

  ]

#: Excluded filesystem types

EXCLUDED_FS = frozenset([

  "nfs",

  "nfs4",

  "autofs",

  "tmpfs",

  "proc",

  "sysfs",

  "usbfs",

  "devpts",

  ])

#: Minimum partition size to be considered (1 GB)

PART_MINSIZE = 1024 * 1024 * 1024

class Error(Exception):

  """Generic exception"""

  pass

class ProgrammingError(Error):

  """Exception denoting invalid assumptions in programming.

  This should catch sysfs tree changes, or otherwise incorrect

  assumptions about the contents of the /sys/block/... directories.

  """

  pass

class SysconfigError(Error):

  """Exception denoting invalid system configuration.

  If the system configuration is somehow wrong (e.g. /dev files

  missing, or having mismatched major/minor numbers relative to

  /sys/block devices), this exception will be raised.

  This should usually mean that the installation of the Xen node

  failed in some steps.

  """

  pass

class PrereqError(Error):

  """Exception denoting invalid prerequisites.

  If the node does not meet the requirements for cluster membership, this

  exception will be raised. Things like wrong kernel version, or no

  free disks, etc. belong here.

  This should usually mean that the build steps for the Xen node were

  not followed correctly.

  """

  pass

class OperationalError(Error):

  """Exception denoting actual errors.

  Errors during the bootstrapping are signaled using this exception.

  """

  pass

class ParameterError(Error):

  """Exception denoting invalid input from user.

  Wrong disks given as parameters will be signaled using this

  exception.

  """

  pass

def Usage():

  """Shows program usage information and exits the program.

  """

  print >> sys.stderr, "Usage:"

  print >> sys.stderr, USAGE

  sys.exit(2)

def ParseOptions():

  """Parses the command line options.

  In case of command line errors, it will show the usage and exit the

  program.

  @rtype: tuple

  @return: a tuple of (options, args), as returned by

      OptionParser.parse_args

  """

  global verbose_flag # pylint: disable-msg=W0603

  parser = optparse.OptionParser(usage="\n%s" % USAGE,

                                 version="%%prog (ganeti) %s" %

                                 constants.RELEASE_VERSION)

  parser.add_option("--alldisks", dest="alldisks",

                    help="erase ALL disks", action="store_true",

                    default=False)

  parser.add_option("-d", "--disks", dest="disks",

                    help="Choose disks (e.g. hda,hdg)",

                    metavar="DISKLIST")

  parser.add_option(cli.VERBOSE_OPT)

  parser.add_option("-r", "--allow-removable",

                    action="store_true", dest="removable_ok", default=False,

                    help="allow and use removable devices too")

  parser.add_option("-g", "--vg-name", type="string",

                    dest="vgname", default="xenvg", metavar="NAME",

                    help="the volume group to be created [default: xenvg]")

  options, args = parser.parse_args()

  if len(args) != 1:

    Usage()

  verbose_flag = options.verbose

  return options, args

def IsPartitioned(disk):

  """Returns whether a given disk should be used partitioned or as-is.

  Currently only md devices are used as is.

  """

  return not disk.startswith('md')

def DeviceName(disk):

  """Returns the appropriate device name for a disk.

  For non-partitioned devices, it returns the name as is, otherwise it

  returns the first partition.

  """

  if IsPartitioned(disk):

    device = '/dev/%s1' % disk

  else:

    device = '/dev/%s' % disk

  return device

def ExecCommand(command):

  """Executes a command.

  This is just a wrapper around commands.getstatusoutput, with the

  difference that if the command line argument -v has been given, it

  will print the command line and the command output on stdout.

  @param command: the command line to be executed

  @rtype: tuple

  @return: a tuple of (status, output) where status is the exit status

      and output the stdout and stderr of the command together

  """

  if verbose_flag:

    print command

  result = RunCmd(command)

  if verbose_flag:

    print result.output

  return result

def CheckPrereq():

  """Check the prerequisites of this program.

  It check that it runs on Linux 2.6, and that /sys is mounted and the

  fact that /sys/block is a directory.

  """

  if os.getuid() != 0:

    raise PrereqError("This tool runs as root only. Really.")

  osname, _, release, _, _ = os.uname()

  if osname != 'Linux':

    raise PrereqError("This tool only runs on Linux"

                      " (detected OS: %s)." % osname)

  if not release.startswith("2.6."):

    raise PrereqError("Wrong major kernel version (detected %s, needs"

                      " 2.6.*)" % release)

  if not os.path.ismount("/sys"):

    raise PrereqError("Can't find a filesystem mounted at /sys."

                      " Please mount /sys.")

  if not os.path.isdir("/sys/block"):

    raise SysconfigError("Can't find /sys/block directory. Has the"

                         " layout of /sys changed?")

  if not os.path.ismount("/proc"):

    raise PrereqError("Can't find a filesystem mounted at /proc."

                      " Please mount /proc.")

  if not os.path.exists("/proc/mounts"):

    raise SysconfigError("Can't find /proc/mounts")

def CheckVGExists(vgname):

  """Checks to see if a volume group exists.

  @param vgname: the volume group name

  @return: a four-tuple (exists, lv_count, vg_size, vg_free), where:

      - exists: True if the volume exists, otherwise False; if False,

        all other members of the tuple are None

      - lv_count: The number of logical volumes in the volume group

      - vg_size: The total size of the volume group (in gibibytes)

      - vg_free: The available space in the volume group

  """

  result = ExecCommand("vgs --nohead -o lv_count,vg_size,vg_free"

                       " --nosuffix --units g"

                       " --ignorelockingfailure %s" % vgname)

  if not result.failed:

    try:

      lv_count, vg_size, vg_free = result.stdout.strip().split()

    except ValueError:

      # This means the output of vgdisplay can't be parsed

      raise PrereqError("cannot parse output of vgs (%s)" % result.stdout)

  else:

    lv_count = vg_size = vg_free = None

  return not result.failed, lv_count, vg_size, vg_free

def CheckSysDev(name, devnum):

  """Checks consistency between /sys and /dev trees.

  In /sys/block/<name>/dev and /sys/block/<name>/<part>/dev are the

  kernel-known device numbers. The /dev/<name> block/char devices are

  created by userspace and thus could differ from the kernel

  view. This function checks the consistency between the device number

  read from /sys and the actual device number in /dev.

  Note that since the system could be using udev which removes and

  recreates the device nodes on partition table rescan, we need to do

  some retries here. Since we only do a stat, we can afford to do many

  short retries.

  @param name: the device name, e.g. 'sda'

  @param devnum: the device number, e.g. 0x803 (2051 in decimal) for sda3

  @raises L{SysconfigError}: in case of failure of the check

  """

  path = "/dev/%s" % name

  for _ in range(40):

    if os.path.exists(path):

      break

    time.sleep(0.250)

  else:

    raise SysconfigError("the device file %s does not exist, but the block"

                         " device exists in the /sys/block tree" % path)

  rdev = os.stat(path).st_rdev

  if devnum != rdev:

    raise SysconfigError("For device %s, the major:minor in /dev is %04x"

                         " while the major:minor in sysfs is %s" %

                         (path, rdev, devnum))

def ReadDev(syspath):

  """Reads the device number from a sysfs path.

  The device number is given in sysfs under a block device directory

  in a file named 'dev' which contains major:minor (in ASCII). This

  function reads that file and converts the major:minor pair to a dev

  number.

  @type syspath: string

  @param syspath: the path to a block device dir in sysfs,

      e.g. C{/sys/block/sda}

  @return: the device number

  """

  if not os.path.exists("%s/dev" % syspath):

    raise ProgrammingError("Invalid path passed to ReadDev: %s" % syspath)

  f = open("%s/dev" % syspath)

  data = f.read().strip()

  f.close()

  major, minor = data.split(":", 1)

  major = int(major)

  minor = int(minor)

  dev = os.makedev(major, minor)

  return dev

def ReadSize(syspath):

  """Reads the size from a sysfs path.

  The size is given in sysfs under a block device directory in a file

  named 'size' which contains the number of sectors (in ASCII). This

  function reads that file and converts the number in sectors to the

  size in bytes.

  @type syspath: string

  @param syspath: the path to a block device dir in sysfs,

      e.g. C{/sys/block/sda}

  @rtype: int

  @return: the device size in bytes

  """

  if not os.path.exists("%s/size" % syspath):

    raise ProgrammingError("Invalid path passed to ReadSize: %s" % syspath)

  f = open("%s/size" % syspath)

  data = f.read().strip()

  f.close()

  size = 512L * int(data)

  return size

def ReadPV(name):

  """Reads physical volume information.

  This function tries to see if a block device is a physical volume.

  @type name: string

  @param name: the device name (e.g. sda)

  @return: the name of the volume group to which this PV belongs, or

      "" if this PV is not in use, or None if this is not a PV

  """

  result = ExecCommand("pvdisplay -c /dev/%s" % name)

  if result.failed:

    return None

  vgname = result.stdout.strip().split(":")[1]

  return vgname

def GetDiskList(opts):

  """Computes the block device list for this system.

  This function examines the /sys/block tree and using information

  therein, computes the status of the block device.

  @return: a list like [(name, size, dev, partitions, inuse), ...], where:

      - name is the block device name (e.g. sda)

      - size the size in bytes

      - dev is the device number (e.g. 8704 for hdg)

      - partitions is [(name, size, dev), ...] mirroring the disk list

        data inuse is a boolean showing the in-use status of the disk,

        computed as the possibility of re-reading the partition table

        (the meaning of the operation varies with the kernel version,

        but is usually accurate; a mounted disk/partition or swap-area

        or PV with active LVs on it is busy)

  """

  dlist = []

  for name in os.listdir("/sys/block"):

    if not compat.any([name.startswith(pfx) for pfx in SUPPORTED_TYPES]):

      continue

    disksysfsname = "/sys/block/%s" % name

    size = ReadSize(disksysfsname)

    f = open("/sys/block/%s/removable" % name)

    removable = int(f.read().strip())

    f.close()

    if removable and not opts.removable_ok:

      continue

    dev = ReadDev(disksysfsname)

    CheckSysDev(name, dev)

    inuse = InUse(name)

    # Enumerate partitions of the block device

    partitions = []

    for partname in os.listdir(disksysfsname):

      if not partname.startswith(name):

        continue

      partsysfsname = "%s/%s" % (disksysfsname, partname)

      partdev = ReadDev(partsysfsname)

      partsize = ReadSize(partsysfsname)

      if partsize >= PART_MINSIZE:

        CheckSysDev(partname, partdev)

        partitions.append((partname, partsize, partdev))

    partitions.sort()

    dlist.append((name, size, dev, partitions, inuse))

  dlist.sort()

  return dlist

def GetMountInfo():

  """Reads /proc/mounts and computes the mountpoint-devnum mapping.

  This function reads /proc/mounts, finds the mounted filesystems

  (excepting a hard-coded blacklist of network and virtual

  filesystems) and does a stat on these mountpoints. The st_dev number

  of the results is memorised for later matching against the

  /sys/block devices.

  @rtype: dict

  @return: a {mountpoint: device number} dictionary

  """

  mountlines = ReadFile("/proc/mounts").splitlines()

  mounts = {}

  for line in mountlines:

    _, mountpoint, fstype, _ = line.split(None, 3)

    # fs type blacklist

    if fstype in EXCLUDED_FS:

      continue

    try:

      dev = os.stat(mountpoint).st_dev

    except OSError, err:

      # this should be a fairly rare error, since we are blacklisting

      # network filesystems; with this in mind, we'll ignore it,

      # since the rereadpt check catches in-use filesystems,

      # and this is used for disk information only

      print >> sys.stderr, ("Can't stat mountpoint '%s': %s" %

                            (mountpoint, err))

      print >> sys.stderr, "Ignoring."

      continue

    mounts[dev] = mountpoint

  return mounts

def GetSwapInfo():

  """Reads /proc/swaps and returns the list of swap backing stores.

  """

  swaplines = ReadFile("/proc/swaps").splitlines()[1:]

  return [line.split(None, 1)[0] for line in swaplines]

def DevInfo(name, dev, mountinfo):

  """Computes miscellaneous information about a block device.

  @type name: string

  @param name: the device name, e.g. sda

  @return: a tuple (mpath, whatvg, fileinfo), where:

      - mpath is the mount path where this device is mounted or None

      - whatvg is the result of the ReadPV function

      - fileinfo is the output of file -bs on the device

  """

  if dev in mountinfo:

    mpath = mountinfo[dev]

  else:

    mpath = None

  whatvg = ReadPV(name)

  result = ExecCommand("file -bs /dev/%s" % name)

  if result.failed:

    fileinfo = "<error: %s>" % result.stderr

  fileinfo = result.stdout[:45]

  return mpath, whatvg, fileinfo

def ShowDiskInfo(opts):

  """Shows a nicely formatted block device list for this system.

  This function shows the user a table with the information gathered

  by the other functions defined, in order to help the user make a

  choice about which disks should be allocated to our volume group.

  """

  mounts = GetMountInfo()

  dlist = GetDiskList(opts)

  print "------- Disk information -------"

  headers = {

      "name": "Name",

      "size": "Size[M]",

      "used": "Used",

      "mount": "Mount",

      "lvm": "LVM?",

      "info": "Info"

      }

  fields = ["name", "size", "used", "mount", "lvm", "info"]

  flatlist = []

  # Flatten the [(disk, [partition,...]), ...] list

  for name, size, dev, parts, inuse in dlist:

    if inuse:

      str_inuse = "yes"

    else:

      str_inuse = "no"

    flatlist.append((name, size, dev, str_inuse))

    for partname, partsize, partdev in parts:

      flatlist.append((partname, partsize, partdev, ""))

  strlist = []

  for name, size, dev, in_use in flatlist:

    mp, vgname, fileinfo = DevInfo(name, dev, mounts)

    if mp is None:

      mp = "-"

    if vgname is None:

      lvminfo = "-"

    elif vgname == "":

      lvminfo = "yes,free"

    else:

      lvminfo = "in %s" % vgname

    if len(name) > 3:

      # Indent partitions

      name = " %s" % name

    strlist.append([name, "%.2f" % (float(size) / 1024 / 1024),

                    in_use, mp, lvminfo, fileinfo])

  data = cli.GenerateTable(headers, fields, None,

                           strlist, numfields=["size"])

  for line in data:

    print line

def CheckSysfsHolders(name):

  """Check to see if a device is 'hold' at sysfs level.

  This is usually the case for Physical Volumes under LVM.

  @rtype: boolean

  @return: true if the device is available according to sysfs

  """

  try:

    contents = os.listdir("/sys/block/%s/holders/" % name)

  except OSError, err:

    if err.errno == errno.ENOENT:

      contents = []

    else:

      raise

  return not bool(contents)

def CheckReread(name):

  """Check to see if a block device is in use.

  Uses blockdev to reread the partition table of a block device (or

  fuser if the device is not partitionable), and thus compute the

  in-use status.  See the discussion in GetDiskList about the meaning

  of 'in use'.

  @rtype: boolean

  @return: the in-use status of the device

  """

  use_blockdev = IsPartitioned(name)

  if use_blockdev:

    cmd = "blockdev --rereadpt /dev/%s" % name

  else:

    cmd = "fuser -vam /dev/%s" % name

  for _ in range(3):

    result = ExecCommand(cmd)

    if not use_blockdev and result.failed:

      break

    elif not result.failed:

      break

    time.sleep(2)

  if use_blockdev:

    return not result.failed

  else:

    return result.failed

def CheckMounted(name):

  """Check to see if a block device is a mountpoint.

  In recent distros/kernels, this is reported directly via fuser, but

  on older ones not, so we do an additional check here (manually).

  """

  minfo = GetMountInfo()

  dev = ReadDev("/sys/block/%s" % name)

  return dev not in minfo

def CheckSwap(name):

  """Check to see if a block device is being used as swap.

  """

  name = "/dev/%s" % name

  return name not in GetSwapInfo()

def InUse(name):

  """Returns if a disk is in use or not.

  """

  return not (CheckSysfsHolders(name) and CheckReread(name) and

              CheckMounted(name) and CheckSwap(name))

def WipeDisk(name):

  """Wipes a block device.

  This function wipes a block device, by clearing and re-reading the

  partition table. If not successful, it writes back the old partition

  data, and leaves the cleanup to the user.

  @param name: the device name (e.g. sda)

  """

  if InUse(name):

    raise OperationalError("CRITICAL: disk %s you selected seems to be in"

                           " use. ABORTING!" % name)

  fd = os.open("/dev/%s" % name, os.O_RDWR | os.O_SYNC)

  olddata = os.read(fd, 512)

  if len(olddata) != 512:

    raise OperationalError("CRITICAL: Can't read partition table information"

                           " from /dev/%s (needed 512 bytes, got %d" %

                           (name, len(olddata)))

  newdata = "\0" * 512

  os.lseek(fd, 0, 0)

  bytes_written = os.write(fd, newdata)

  os.close(fd)

  if bytes_written != 512:

    raise OperationalError("CRITICAL: Can't write partition table information"

                           " to /dev/%s (tried to write 512 bytes, written"

                           " %d. I don't know how to cleanup. Sorry." %

                           (name, bytes_written))

  if InUse(name):

    # try to restore the data

    fd = os.open("/dev/%s" % name, os.O_RDWR | os.O_SYNC)

    os.write(fd, olddata)

    os.close(fd)

    raise OperationalError("CRITICAL: disk %s which I have just wiped cannot"

                           " reread partition table. Most likely, it is"

                           " in use. You have to clean after this yourself."

                           " I tried to restore the old partition table,"

                           " but I cannot guarantee nothing has broken." %

                           name)

def PartitionDisk(name):

  """Partitions a disk.

  This function creates a single partition spanning the entire disk,

  by means of fdisk.

  @param name: the device name, e.g. sda

  """

  result = ExecCommand(

    'echo ,,8e, | sfdisk /dev/%s' % name)

  if result.failed:

    raise OperationalError("CRITICAL: disk %s which I have just partitioned"

                           " cannot reread its partition table, or there"

                           " is some other sfdisk error. Likely, it is in"

                           " use. You have to clean this yourself. Error"

                           " message from sfdisk: %s" %

                           (name, result.output))

def CreatePVOnDisk(name):

  """Creates a physical volume on a block device.

  This function creates a physical volume on a block device, overriding

  all warnings. So it can wipe existing PVs and PVs which are in a VG.

  @param name: the device name, e.g. sda

  """

  device = DeviceName(name)

  result = ExecCommand("pvcreate -yff %s" % device)

  if result.failed:

    raise OperationalError("I cannot create a physical volume on"

                           " %s. Error message: %s."

                           " Please clean up yourself." %

                           (device, result.output))

def CreateVG(vgname, disks):

  """Creates the volume group.

  This function creates a volume group named `vgname` on the disks

  given as parameters. The physical extent size is set to 64MB.

  @param disks: a list of disk names, e.g. ['sda','sdb']

  """

  pnames = [DeviceName(d) for d in disks]

  result = ExecCommand("vgcreate -s 64MB '%s' %s" % (vgname, " ".join(pnames)))

  if result.failed:

    raise OperationalError("I cannot create the volume group %s from"

                           " disks %s. Error message: %s. Please clean up"

                           " yourself." %

                           (vgname, " ".join(disks), result.output))

def ValidateDiskList(options):

  """Validates or computes the disk list for create.

  This function either computes the available disk list (if the user

  gave --alldisks option), or validates the user-given disk list (by

  using the --disks option) such that all given disks are present and

  not in use.

  @param options: the options returned from OptParser.parse_options

  @return: a list of disk names, e.g. ['sda', 'sdb']

  """

  sysdisks = GetDiskList(options)

  if not sysdisks:

    raise PrereqError("no disks found (I looked for"

                      " non-removable block devices).")

  sysd_free = []

  sysd_used = []

  for name, _, _, _, used in sysdisks:

    if used:

      sysd_used.append(name)

    else:

      sysd_free.append(name)

  if not sysd_free:

    raise PrereqError("no free disks found! (%d in-use disks)" %

                      len(sysd_used))

  if options.alldisks:

    disklist = sysd_free

  elif options.disks:

    disklist = options.disks.split(",")

    for name in disklist:

      if name in sysd_used:

        raise ParameterError("disk %s is in use, cannot wipe!" % name)

      if name not in sysd_free:

        raise ParameterError("cannot find disk %s!" % name)

  else:

    raise ParameterError("Please use either --alldisks or --disks!")

  return disklist

def BootStrap():

  """Actual main routine.

  """

  CheckPrereq()

  options, args = ParseOptions()

  vgname = options.vgname

  command = args.pop(0)

  if command == "diskinfo":

    ShowDiskInfo(options)

    return

  if command != "create":

    Usage()

  exists, lv_count, vg_size, vg_free = CheckVGExists(vgname)

  if exists:

    raise PrereqError("It seems volume group '%s' already exists:\n"

                      "  LV count: %s, size: %s, free: %s." %

                      (vgname, lv_count, vg_size, vg_free))

  disklist = ValidateDiskList(options)

  for disk in disklist:

    WipeDisk(disk)

    if IsPartitioned(disk):

      PartitionDisk(disk)

  for disk in disklist:

    CreatePVOnDisk(disk)

  CreateVG(vgname, disklist)

  status, lv_count, size, _ = CheckVGExists(vgname)

  if status:

    print "Done! %s: size %s GiB, disks: %s" % (vgname, size,

                                              ",".join(disklist))

  else:

    raise OperationalError("Although everything seemed ok, the volume"

                           " group did not get created.")

def main():

  """Application entry point.

  This is just a wrapper over BootStrap, to handle our own exceptions.

  """

  try:

    BootStrap()

  except PrereqError, err:

    print >> sys.stderr, "The prerequisites for running this tool are not met."

    print >> sys.stderr, ("Please make sure you followed all the steps in"

                          " the build document.")

    print >> sys.stderr, "Description: %s" % str(err)

    sys.exit(1)

  except SysconfigError, err:

    print >> sys.stderr, ("This system's configuration seems wrong, at"

                          " least is not what I expect.")

    print >> sys.stderr, ("Please check that the installation didn't fail"

                          " at some step.")

    print >> sys.stderr, "Description: %s" % str(err)

    sys.exit(1)

  except ParameterError, err:

    print >> sys.stderr, ("Some parameters you gave to the program or the"

                          " invocation is wrong. ")

    print >> sys.stderr, "Description: %s" % str(err)

    Usage()

  except OperationalError, err:

    print >> sys.stderr, ("A serious error has happened while modifying"

                          " the system's configuration.")

    print >> sys.stderr, ("Please review the error message below and make"

                          " sure you clean up yourself.")

    print >> sys.stderr, ("It is most likely that the system configuration"

                          " has been partially altered.")

    print >> sys.stderr, str(err)

    sys.exit(1)

  except ProgrammingError, err:

    print >> sys.stderr, ("Internal application error. Please report this"

                          " to the Ganeti developer list.")

    print >> sys.stderr, "Error description: %s" % str(err)

    sys.exit(1)

  except Error, err:

    print >> sys.stderr, "Unhandled application error: %s" % err

    sys.exit(1)

  except (IOError, OSError), err:

    print >> sys.stderr, "I/O error detected, please report."

    print >> sys.stderr, "Description: %s" % str(err)

    sys.exit(1)

if __name__ == "__main__":

  main()