Synnefo » snf-ganeti

#

#

# 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.

"""Functions used by the node daemon"""

import os

import os.path

import shutil

import time

import tempfile

import stat

import errno

import re

import subprocess

from ganeti import logger

from ganeti import errors

from ganeti import utils

from ganeti import ssh

from ganeti import hypervisor

from ganeti import constants

from ganeti import bdev

from ganeti import objects

from ganeti import ssconf

def StartMaster():

  """Activate local node as master node.

  There are two needed steps for this:

    - run the master script

    - register the cron script

  """

  result = utils.RunCmd([constants.MASTER_SCRIPT, "-d", "start"])

  if result.failed:

    logger.Error("could not activate cluster interface with command %s,"

                 " error: '%s'" % (result.cmd, result.output))

    return False

  return True

def StopMaster():

  """Deactivate this node as master.

  This does two things:

    - run the master stop script

    - remove link to master cron script.

  """

  result = utils.RunCmd([constants.MASTER_SCRIPT, "-d", "stop"])

  if result.failed:

    logger.Error("could not deactivate cluster interface with command %s,"

                 " error: '%s'" % (result.cmd, result.output))

    return False

  return True

def AddNode(dsa, dsapub, rsa, rsapub, sshkey, sshpub):

  """Joins this node to the cluster.

  This does the following:

      - updates the hostkeys of the machine (rsa and dsa)

      - adds the ssh private key to the user

      - adds the ssh public key to the users' authorized_keys file

  """

  user_dir = utils.GetHomeDir(constants.GANETI_RUNAS)

  if not user_dir:

    logger.Error("Cannot find home of run-as user %s" % constants.GANETI_RUNAS)

    return False

  sshd_keys =  [("ssh_host_rsa_key", rsa, 0600),

                ("ssh_host_rsa_key.pub", rsapub, 0644),

                ("ssh_host_dsa_key", dsa, 0600),

                ("ssh_host_dsa_key.pub",  dsapub, 0644)]

  for name, content, mode in sshd_keys:

    utils.WriteFile(os.path.join(constants.SSH_CONFIG_DIR, name),

                    data=content, mode=mode)

  user_ssh_dir = os.path.join(user_dir, ".ssh")

  if not os.path.isdir(user_ssh_dir):

    os.mkdir(user_ssh_dir)

  for name, content in [("id_dsa", sshkey), ("id_dsa.pub", sshpub)]:

    utils.WriteFile(os.path.join(user_ssh_dir, name), data=content, mode=0600)

  utils.AddAuthorizedKey(os.path.join(user_ssh_dir, "authorized_keys"), sshpub)

  utils.RunCmd([constants.SSH_INITD_SCRIPT, "restart"])

  return True

def LeaveCluster():

  """Cleans up the current node and prepares it to be removed from the cluster.

  """

  if os.path.isdir(constants.DATA_DIR):

    for rel_name in utils.ListVisibleFiles(constants.DATA_DIR):

      full_name = os.path.join(constants.DATA_DIR, rel_name)

      if os.path.isfile(full_name) and not os.path.islink(full_name):

        utils.RemoveFile(full_name)

  user_dir = utils.GetHomeDir(constants.GANETI_RUNAS)

  if not user_dir:

    logger.Error("Cannot find home of run-as user %s" % constants.GANETI_RUNAS)

    return

  user_ssh_dir = os.path.join(user_dir, ".ssh")

  if not os.path.isdir(user_ssh_dir):

    logger.Error("User's ssh dir '%s' does not exist?!" % user_ssh_dir)

    return

  f = open(os.path.join(user_ssh_dir, "id_dsa.pub"), 'r')

  try:

    utils.RemoveAuthorizedKey(os.path.join(user_ssh_dir, "authorized_keys"),

                              f.read(8192))

  finally:

    f.close()

  utils.RemoveFile(os.path.join(user_ssh_dir, "id_dsa"))

  utils.RemoveFile(os.path.join(user_ssh_dir, "id_dsa.pub"))

def GetNodeInfo(vgname):

  """ gives back a hash with different informations

  about the node

  Returns:

    { 'vg_size' : xxx,  'vg_free' : xxx, 'memory_domain0': xxx,

      'memory_free' : xxx, 'memory_total' : xxx }

    where

    vg_size is the size of the configured volume group in MiB

    vg_free is the free size of the volume group in MiB

    memory_dom0 is the memory allocated for domain0 in MiB

    memory_free is the currently available (free) ram in MiB

    memory_total is the total number of ram in MiB

  """

  outputarray = {}

  vginfo = _GetVGInfo(vgname)

  outputarray['vg_size'] = vginfo['vg_size']

  outputarray['vg_free'] = vginfo['vg_free']

  hyper = hypervisor.GetHypervisor()

  hyp_info = hyper.GetNodeInfo()

  if hyp_info is not None:

    outputarray.update(hyp_info)

  f = open("/proc/sys/kernel/random/boot_id", 'r')

  try:

    outputarray["bootid"] = f.read(128).rstrip("\n")

  finally:

    f.close()

  return outputarray

def VerifyNode(what):

  """Verify the status of the local node.

  Args:

    what - a dictionary of things to check:

      'filelist' : list of files for which to compute checksums

      'nodelist' : list of nodes we should check communication with

      'hypervisor': run the hypervisor-specific verify

  Requested files on local node are checksummed and the result returned.

  The nodelist is traversed, with the following checks being made

  for each node:

  - known_hosts key correct

  - correct resolving of node name (target node returns its own hostname

    by ssh-execution of 'hostname', result compared against name in list.

  """

  result = {}

  if 'hypervisor' in what:

    result['hypervisor'] = hypervisor.GetHypervisor().Verify()

  if 'filelist' in what:

    result['filelist'] = utils.FingerprintFiles(what['filelist'])

  if 'nodelist' in what:

    result['nodelist'] = {}

    for node in what['nodelist']:

      success, message = ssh.VerifyNodeHostname(node)

      if not success:

        result['nodelist'][node] = message

  return result

def GetVolumeList(vg_name):

  """Compute list of logical volumes and their size.

  Returns:

    dictionary of all partions (key) with their size:

    test1: 20.06MiB

  """

  result = utils.RunCmd(["lvs", "--noheadings", "--units=m",

                         "-oname,size", vg_name])

  if result.failed:

    logger.Error("Failed to list logical volumes, lvs output: %s" %

                 result.output)

    return {}

  lvlist = [line.split() for line in result.output.splitlines()]

  return dict(lvlist)

def ListVolumeGroups():

  """List the volume groups and their size

  Returns:

    Dictionary with keys volume name and values the size of the volume

  """

  return utils.ListVolumeGroups()

def NodeVolumes():

  """List all volumes on this node.

  """

  result = utils.RunCmd(["lvs", "--noheadings", "--units=m", "--nosuffix",

                         "--separator=|",

                         "--options=lv_name,lv_size,devices,vg_name"])

  if result.failed:

    logger.Error("Failed to list logical volumes, lvs output: %s" %

                 result.output)

    return {}

  def parse_dev(dev):

    if '(' in dev:

      return dev.split('(')[0]

    else:

      return dev

  def map_line(line):

    return {

      'name': line[0].strip(),

      'size': line[1].strip(),

      'dev': parse_dev(line[2].strip()),

      'vg': line[3].strip(),

    }

  return [map_line(line.split('|')) for line in result.output.splitlines()]

def BridgesExist(bridges_list):

  """Check if a list of bridges exist on the current node

  Returns:

    True if all of them exist, false otherwise

  """

  for bridge in bridges_list:

    if not utils.BridgeExists(bridge):

      return False

  return True

def GetInstanceList():

  """ provides a list of instances

  Returns:

    A list of all running instances on the current node

    - instance1.example.com

    - instance2.example.com

  """

  try:

    names = hypervisor.GetHypervisor().ListInstances()

  except errors.HypervisorError, err:

    logger.Error("error enumerating instances: %s" % str(err))

    raise

  return names

def GetInstanceInfo(instance):

  """ gives back the informations about an instance

  as a dictonary

  Args:

    instance: name of the instance (ex. instance1.example.com)

  Returns:

    { 'memory' : 511, 'state' : '-b---', 'time' : 3188.8, }

    where

    memory: memory size of instance (int)

    state: xen state of instance (string)

    time: cpu time of instance (float)

  """

  output = {}

  iinfo = hypervisor.GetHypervisor().GetInstanceInfo(instance)

  if iinfo is not None:

    output['memory'] = iinfo[2]

    output['state'] = iinfo[4]

    output['time'] = iinfo[5]

  return output

def GetAllInstancesInfo():

  """Gather data about all instances.

  This is the equivalent of `GetInstanceInfo()`, except that it

  computes data for all instances at once, thus being faster if one

  needs data about more than one instance.

  Returns: a dictionary of dictionaries, keys being the instance name,

    and with values:

    { 'memory' : 511, 'state' : '-b---', 'time' : 3188.8, }

    where

    memory: memory size of instance (int)

    state: xen state of instance (string)

    time: cpu time of instance (float)

    vcpus: the number of cpus

  """

  output = {}

  iinfo = hypervisor.GetHypervisor().GetAllInstancesInfo()

  if iinfo:

    for name, inst_id, memory, vcpus, state, times in iinfo:

      output[name] = {

        'memory': memory,

        'vcpus': vcpus,

        'state': state,

        'time': times,

        }

  return output

def AddOSToInstance(instance, os_disk, swap_disk):

  """Add an os to an instance.

  Args:

    instance: the instance object

    os_disk: the instance-visible name of the os device

    swap_disk: the instance-visible name of the swap device

  """

  inst_os = OSFromDisk(instance.os)

  create_script = inst_os.create_script

  os_device = instance.FindDisk(os_disk)

  if os_device is None:

    logger.Error("Can't find this device-visible name '%s'" % os_disk)

    return False

  swap_device = instance.FindDisk(swap_disk)

  if swap_device is None:

    logger.Error("Can't find this device-visible name '%s'" % swap_disk)

    return False

  real_os_dev = _RecursiveFindBD(os_device)

  if real_os_dev is None:

    raise errors.BlockDeviceError("Block device '%s' is not set up" %

                                  str(os_device))

  real_os_dev.Open()

  real_swap_dev = _RecursiveFindBD(swap_device)

  if real_swap_dev is None:

    raise errors.BlockDeviceError("Block device '%s' is not set up" %

                                  str(swap_device))

  real_swap_dev.Open()

  logfile = "%s/add-%s-%s-%d.log" % (constants.LOG_OS_DIR, instance.os,

                                     instance.name, int(time.time()))

  if not os.path.exists(constants.LOG_OS_DIR):

    os.mkdir(constants.LOG_OS_DIR, 0750)

  command = utils.BuildShellCmd("cd %s && %s -i %s -b %s -s %s &>%s",

                                inst_os.path, create_script, instance.name,

                                real_os_dev.dev_path, real_swap_dev.dev_path,

                                logfile)

  result = utils.RunCmd(command)

  if result.failed:

    logger.Error("os create command '%s' returned error: %s"

                 " output: %s" %

                 (command, result.fail_reason, result.output))

    return False

  return True

def RunRenameInstance(instance, old_name, os_disk, swap_disk):

  """Run the OS rename script for an instance.

  Args:

    instance: the instance object

    old_name: the old name of the instance

    os_disk: the instance-visible name of the os device

    swap_disk: the instance-visible name of the swap device

  """

  inst_os = OSFromDisk(instance.os)

  script = inst_os.rename_script

  os_device = instance.FindDisk(os_disk)

  if os_device is None:

    logger.Error("Can't find this device-visible name '%s'" % os_disk)

    return False

  swap_device = instance.FindDisk(swap_disk)

  if swap_device is None:

    logger.Error("Can't find this device-visible name '%s'" % swap_disk)

    return False

  real_os_dev = _RecursiveFindBD(os_device)

  if real_os_dev is None:

    raise errors.BlockDeviceError("Block device '%s' is not set up" %

                                  str(os_device))

  real_os_dev.Open()

  real_swap_dev = _RecursiveFindBD(swap_device)

  if real_swap_dev is None:

    raise errors.BlockDeviceError("Block device '%s' is not set up" %

                                  str(swap_device))

  real_swap_dev.Open()

  logfile = "%s/rename-%s-%s-%s-%d.log" % (constants.LOG_OS_DIR, instance.os,

                                           old_name,

                                           instance.name, int(time.time()))

  if not os.path.exists(constants.LOG_OS_DIR):

    os.mkdir(constants.LOG_OS_DIR, 0750)

  command = utils.BuildShellCmd("cd %s && %s -o %s -n %s -b %s -s %s &>%s",

                                inst_os.path, script, old_name, instance.name,

                                real_os_dev.dev_path, real_swap_dev.dev_path,

                                logfile)

  result = utils.RunCmd(command)

  if result.failed:

    logger.Error("os create command '%s' returned error: %s"

                 " output: %s" %

                 (command, result.fail_reason, result.output))

    return False

  return True

def _GetVGInfo(vg_name):

  """Get informations about the volume group.

  Args:

    vg_name: the volume group

  Returns:

    { 'vg_size' : xxx, 'vg_free' : xxx, 'pv_count' : xxx }

    where

    vg_size is the total size of the volume group in MiB

    vg_free is the free size of the volume group in MiB

    pv_count are the number of physical disks in that vg

  """

  retval = utils.RunCmd(["vgs", "-ovg_size,vg_free,pv_count", "--noheadings",

                         "--nosuffix", "--units=m", "--separator=:", vg_name])

  if retval.failed:

    errmsg = "volume group %s not present" % vg_name

    logger.Error(errmsg)

    raise errors.LVMError(errmsg)

  valarr = retval.stdout.strip().split(':')

  retdic = {

    "vg_size": int(round(float(valarr[0]), 0)),

    "vg_free": int(round(float(valarr[1]), 0)),

    "pv_count": int(valarr[2]),

    }

  return retdic

def _GatherBlockDevs(instance):

  """Set up an instance's block device(s).

  This is run on the primary node at instance startup. The block

  devices must be already assembled.

  """

  block_devices = []

  for disk in instance.disks:

    device = _RecursiveFindBD(disk)

    if device is None:

      raise errors.BlockDeviceError("Block device '%s' is not set up." %

                                    str(disk))

    device.Open()

    block_devices.append((disk, device))

  return block_devices

def StartInstance(instance, extra_args):

  """Start an instance.

  Args:

    instance - name of instance to start.

  """

  running_instances = GetInstanceList()

  if instance.name in running_instances:

    return True

  block_devices = _GatherBlockDevs(instance)

  hyper = hypervisor.GetHypervisor()

  try:

    hyper.StartInstance(instance, block_devices, extra_args)

  except errors.HypervisorError, err:

    logger.Error("Failed to start instance: %s" % err)

    return False

  return True

def ShutdownInstance(instance):

  """Shut an instance down.

  Args:

    instance - name of instance to shutdown.

  """

  running_instances = GetInstanceList()

  if instance.name not in running_instances:

    return True

  hyper = hypervisor.GetHypervisor()

  try:

    hyper.StopInstance(instance)

  except errors.HypervisorError, err:

    logger.Error("Failed to stop instance: %s" % err)

    return False

  # test every 10secs for 2min

  shutdown_ok = False

  time.sleep(1)

  for dummy in range(11):

    if instance.name not in GetInstanceList():

      break

    time.sleep(10)

  else:

    # the shutdown did not succeed

    logger.Error("shutdown of '%s' unsuccessful, using destroy" % instance)

    try:

      hyper.StopInstance(instance, force=True)

    except errors.HypervisorError, err:

      logger.Error("Failed to stop instance: %s" % err)

      return False

    time.sleep(1)

    if instance.name in GetInstanceList():

      logger.Error("could not shutdown instance '%s' even by destroy")

      return False

  return True

def CreateBlockDevice(disk, size, on_primary, info):

  """Creates a block device for an instance.

  Args:

   bdev: a ganeti.objects.Disk object

   size: the size of the physical underlying devices

   do_open: if the device should be `Assemble()`-d and

            `Open()`-ed after creation

  Returns:

    the new unique_id of the device (this can sometime be

    computed only after creation), or None. On secondary nodes,

    it's not required to return anything.

  """

  clist = []

  if disk.children:

    for child in disk.children:

      crdev = _RecursiveAssembleBD(child, on_primary)

      if on_primary or disk.AssembleOnSecondary():

        # we need the children open in case the device itself has to

        # be assembled

        crdev.Open()

      else:

        crdev.Close()

      clist.append(crdev)

  try:

    device = bdev.FindDevice(disk.dev_type, disk.physical_id, clist)

    if device is not None:

      logger.Info("removing existing device %s" % disk)

      device.Remove()

  except errors.BlockDeviceError, err:

    pass

  device = bdev.Create(disk.dev_type, disk.physical_id,

                       clist, size)

  if device is None:

    raise ValueError("Can't create child device for %s, %s" %

                     (disk, size))

  if on_primary or disk.AssembleOnSecondary():

    device.Assemble()

    device.SetSyncSpeed(constants.SYNC_SPEED)

    if on_primary or disk.OpenOnSecondary():

      device.Open(force=True)

  device.SetInfo(info)

  physical_id = device.unique_id

  return physical_id

def RemoveBlockDevice(disk):

  """Remove a block device.

  This is intended to be called recursively.

  """

  try:

    # since we are removing the device, allow a partial match

    # this allows removal of broken mirrors

    rdev = _RecursiveFindBD(disk, allow_partial=True)

  except errors.BlockDeviceError, err:

    # probably can't attach

    logger.Info("Can't attach to device %s in remove" % disk)

    rdev = None

  if rdev is not None:

    result = rdev.Remove()

  else:

    result = True

  if disk.children:

    for child in disk.children:

      result = result and RemoveBlockDevice(child)

  return result

def _RecursiveAssembleBD(disk, as_primary):

  """Activate a block device for an instance.

  This is run on the primary and secondary nodes for an instance.

  This function is called recursively.

  Args:

    disk: a objects.Disk object

    as_primary: if we should make the block device read/write

  Returns:

    the assembled device or None (in case no device was assembled)

  If the assembly is not successful, an exception is raised.

  """

  children = []

  if disk.children:

    for chld_disk in disk.children:

      children.append(_RecursiveAssembleBD(chld_disk, as_primary))

  if as_primary or disk.AssembleOnSecondary():

    r_dev = bdev.AttachOrAssemble(disk.dev_type, disk.physical_id, children)

    r_dev.SetSyncSpeed(constants.SYNC_SPEED)

    result = r_dev

    if as_primary or disk.OpenOnSecondary():

      r_dev.Open()

    else:

      r_dev.Close()

  else:

    result = True

  return result

def AssembleBlockDevice(disk, as_primary):

  """Activate a block device for an instance.

  This is a wrapper over _RecursiveAssembleBD.

  Returns:

    a /dev path for primary nodes

    True for secondary nodes

  """

  result = _RecursiveAssembleBD(disk, as_primary)

  if isinstance(result, bdev.BlockDev):

    result = result.dev_path

  return result

def ShutdownBlockDevice(disk):

  """Shut down a block device.

  First, if the device is assembled (can `Attach()`), then the device

  is shutdown. Then the children of the device are shutdown.

  This function is called recursively. Note that we don't cache the

  children or such, as oppossed to assemble, shutdown of different

  devices doesn't require that the upper device was active.

  """

  r_dev = _RecursiveFindBD(disk)

  if r_dev is not None:

    result = r_dev.Shutdown()

  else:

    result = True

  if disk.children:

    for child in disk.children:

      result = result and ShutdownBlockDevice(child)

  return result

def MirrorAddChild(md_cdev, new_cdev):

  """Extend an MD raid1 array.

  """

  md_bdev = _RecursiveFindBD(md_cdev, allow_partial=True)

  if md_bdev is None:

    logger.Error("Can't find md device")

    return False

  new_bdev = _RecursiveFindBD(new_cdev)

  if new_bdev is None:

    logger.Error("Can't find new device to add")

    return False

  new_bdev.Open()

  md_bdev.AddChild(new_bdev)

  return True

def MirrorRemoveChild(md_cdev, new_cdev):

  """Reduce an MD raid1 array.

  """

  md_bdev = _RecursiveFindBD(md_cdev)

  if md_bdev is None:

    return False

  new_bdev = _RecursiveFindBD(new_cdev)

  if new_bdev is None:

    return False

  new_bdev.Open()

  md_bdev.RemoveChild(new_bdev.dev_path)

  return True

def GetMirrorStatus(disks):

  """Get the mirroring status of a list of devices.

  Args:

    disks: list of `objects.Disk`

  Returns:

    list of (mirror_done, estimated_time) tuples, which

    are the result of bdev.BlockDevice.CombinedSyncStatus()

  """

  stats = []

  for dsk in disks:

    rbd = _RecursiveFindBD(dsk)

    if rbd is None:

      raise errors.BlockDeviceError("Can't find device %s" % str(dsk))

    stats.append(rbd.CombinedSyncStatus())

  return stats

def _RecursiveFindBD(disk, allow_partial=False):

  """Check if a device is activated.

  If so, return informations about the real device.

  Args:

    disk: the objects.Disk instance

    allow_partial: don't abort the find if a child of the

                   device can't be found; this is intended to be

                   used when repairing mirrors

  Returns:

    None if the device can't be found

    otherwise the device instance

  """

  children = []

  if disk.children:

    for chdisk in disk.children:

      children.append(_RecursiveFindBD(chdisk))

  return bdev.FindDevice(disk.dev_type, disk.physical_id, children)

def FindBlockDevice(disk):

  """Check if a device is activated.

  If so, return informations about the real device.

  Args:

    disk: the objects.Disk instance

  Returns:

    None if the device can't be found

    (device_path, major, minor, sync_percent, estimated_time, is_degraded)

  """

  rbd = _RecursiveFindBD(disk)

  if rbd is None:

    return rbd

  sync_p, est_t, is_degr = rbd.GetSyncStatus()

  return rbd.dev_path, rbd.major, rbd.minor, sync_p, est_t, is_degr

def UploadFile(file_name, data, mode, uid, gid, atime, mtime):

  """Write a file to the filesystem.

  This allows the master to overwrite(!) a file. It will only perform

  the operation if the file belongs to a list of configuration files.

  """

  if not os.path.isabs(file_name):

    logger.Error("Filename passed to UploadFile is not absolute: '%s'" %

                 file_name)

    return False

  allowed_files = [constants.CLUSTER_CONF_FILE, "/etc/hosts",

                   constants.SSH_KNOWN_HOSTS_FILE]

  allowed_files.extend(ssconf.SimpleStore().GetFileList())

  if file_name not in allowed_files:

    logger.Error("Filename passed to UploadFile not in allowed"

                 " upload targets: '%s'" % file_name)

    return False

  dir_name, small_name = os.path.split(file_name)

  fd, new_name = tempfile.mkstemp('.new', small_name, dir_name)

  # here we need to make sure we remove the temp file, if any error

  # leaves it in place

  try:

    os.chown(new_name, uid, gid)

    os.chmod(new_name, mode)

    os.write(fd, data)

    os.fsync(fd)

    os.utime(new_name, (atime, mtime))

    os.rename(new_name, file_name)

  finally:

    os.close(fd)

    utils.RemoveFile(new_name)

  return True

def _ErrnoOrStr(err):

  """Format an EnvironmentError exception.

  If the `err` argument has an errno attribute, it will be looked up

  and converted into a textual EXXXX description. Otherwise the string

  representation of the error will be returned.

  """

  if hasattr(err, 'errno'):

    detail = errno.errorcode[err.errno]

  else:

    detail = str(err)

  return detail

def _OSSearch(name, search_path=None):

  """Search for OSes with the given name in the search_path.

  Args:

    name: The name of the OS to look for

    search_path: List of dirs to search (defaults to constants.OS_SEARCH_PATH)

  Returns:

    The base_dir the OS resides in

  """

  if search_path is None:

    search_path = constants.OS_SEARCH_PATH

  for dir in search_path:

    t_os_dir = os.path.sep.join([dir, name])

    if os.path.isdir(t_os_dir):

        return dir

  return None

def _OSOndiskVersion(name, os_dir):

  """Compute and return the api version of a given OS.

  This function will try to read the api version of the os given by

  the 'name' parameter and residing in the 'os_dir' directory.

  Return value will be either an integer denoting the version or None in the

  case when this is not a valid OS name.

  """

  api_file = os.path.sep.join([os_dir, "ganeti_api_version"])

  try:

    st = os.stat(api_file)

  except EnvironmentError, err:

    raise errors.InvalidOS(name, os_dir, "'ganeti_api_version' file not"

                           " found (%s)" % _ErrnoOrStr(err))

  if not stat.S_ISREG(stat.S_IFMT(st.st_mode)):

    raise errors.InvalidOS(name, os_dir, "'ganeti_api_version' file is not"

                           " a regular file")

  try:

    f = open(api_file)

    try:

      api_version = f.read(256)

    finally:

      f.close()

  except EnvironmentError, err:

    raise errors.InvalidOS(name, os_dir, "error while reading the"

                           " API version (%s)" % _ErrnoOrStr(err))

  api_version = api_version.strip()

  try:

    api_version = int(api_version)

  except (TypeError, ValueError), err:

    raise errors.InvalidOS(name, os_dir,

                           "API version is not integer (%s)" % str(err))

  return api_version

def DiagnoseOS(top_dirs=None):

  """Compute the validity for all OSes.

  For each name in all the given top directories (if not given defaults i

  to constants.OS_SEARCH_PATH it will return an object. If this is a valid

  os, the object will be an instance of the object.OS class. If not,

  it will be an instance of errors.InvalidOS and this signifies that

  this name does not correspond to a valid OS.

  Returns:

    list of objects

  """

  if top_dirs is None:

    top_dirs = constants.OS_SEARCH_PATH

  result = []

  for dir in top_dirs:

    if os.path.isdir(dir):

      try:

        f_names = utils.ListVisibleFiles(dir)

      except EnvironmentError, err:

        logger.Error("Can't list the OS directory %s: %s" % (dir,str(err)))

        break

      for name in f_names:

        try:

          os_inst = OSFromDisk(name, base_dir=dir)

          result.append(os_inst)

        except errors.InvalidOS, err:

          result.append(err)

  return result

def OSFromDisk(name, base_dir=None):

  """Create an OS instance from disk.

  This function will return an OS instance if the given name is a

  valid OS name. Otherwise, it will raise an appropriate

  `errors.InvalidOS` exception, detailing why this is not a valid

  OS.

  Args:

    os_dir: Directory containing the OS scripts. Defaults to a search

            in all the OS_SEARCH_PATH directories.

  """

  if base_dir is None:

    base_dir = _OSSearch(name)

  if base_dir is None:

    raise errors.InvalidOS(name, None, "OS dir not found in search path")

  os_dir = os.path.sep.join([base_dir, name])

  api_version = _OSOndiskVersion(name, os_dir)

  if api_version != constants.OS_API_VERSION:

    raise errors.InvalidOS(name, os_dir, "API version mismatch"

                           " (found %s want %s)"

                           % (api_version, constants.OS_API_VERSION))

  # OS Scripts dictionary, we will populate it with the actual script names

  os_scripts = {'create': '', 'export': '', 'import': '', 'rename': ''}

  for script in os_scripts:

    os_scripts[script] = os.path.sep.join([os_dir, script])

    try:

      st = os.stat(os_scripts[script])

    except EnvironmentError, err:

      raise errors.InvalidOS(name, os_dir, "'%s' script missing (%s)" %

                             (script, _ErrnoOrStr(err)))

    if stat.S_IMODE(st.st_mode) & stat.S_IXUSR != stat.S_IXUSR:

      raise errors.InvalidOS(name, os_dir, "'%s' script not executable" %

                             script)

    if not stat.S_ISREG(stat.S_IFMT(st.st_mode)):

      raise errors.InvalidOS(name, os_dir, "'%s' is not a regular file" %

                             script)

  return objects.OS(name=name, path=os_dir,

                    create_script=os_scripts['create'],

                    export_script=os_scripts['export'],

                    import_script=os_scripts['import'],

                    rename_script=os_scripts['rename'],

                    api_version=api_version)

def SnapshotBlockDevice(disk):

  """Create a snapshot copy of a block device.

  This function is called recursively, and the snapshot is actually created

  just for the leaf lvm backend device.

  Args:

    disk: the disk to be snapshotted

  Returns:

    a config entry for the actual lvm device snapshotted.

  """

  if disk.children:

    if len(disk.children) == 1: