backend.py

#
#

# 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

@var _ALLOWED_UPLOAD_FILES: denotes which files are accepted in
     the L{UploadFile} function

"""

# pylint: disable-msg=E1103

# E1103: %s %r has no %r member (but some types could not be
# inferred), because the _TryOSFromDisk returns either (True, os_obj)
# or (False, "string") which confuses pylint


import os
import os.path
import shutil
import time
import stat
import errno
import re
import subprocess
import random
import logging
import tempfile
import zlib
import base64

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


_BOOT_ID_PATH = "/proc/sys/kernel/random/boot_id"


class RPCFail(Exception):
  """Class denoting RPC failure.

  Its argument is the error message.

  """


def _Fail(msg, *args, **kwargs):
  """Log an error and the raise an RPCFail exception.

  This exception is then handled specially in the ganeti daemon and
  turned into a 'failed' return type. As such, this function is a
  useful shortcut for logging the error and returning it to the master
  daemon.

  @type msg: string
  @param msg: the text of the exception
  @raise RPCFail

  """
  if args:
    msg = msg % args
  if "log" not in kwargs or kwargs["log"]: # if we should log this error
    if "exc" in kwargs and kwargs["exc"]:
      logging.exception(msg)
    else:
      logging.error(msg)
  raise RPCFail(msg)


def _GetConfig():
  """Simple wrapper to return a SimpleStore.

  @rtype: L{ssconf.SimpleStore}
  @return: a SimpleStore instance

  """
  return ssconf.SimpleStore()


def _GetSshRunner(cluster_name):
  """Simple wrapper to return an SshRunner.

  @type cluster_name: str
  @param cluster_name: the cluster name, which is needed
      by the SshRunner constructor
  @rtype: L{ssh.SshRunner}
  @return: an SshRunner instance

  """
  return ssh.SshRunner(cluster_name)


def _Decompress(data):
  """Unpacks data compressed by the RPC client.

  @type data: list or tuple
  @param data: Data sent by RPC client
  @rtype: str
  @return: Decompressed data

  """
  assert isinstance(data, (list, tuple))
  assert len(data) == 2
  (encoding, content) = data
  if encoding == constants.RPC_ENCODING_NONE:
    return content
  elif encoding == constants.RPC_ENCODING_ZLIB_BASE64:
    return zlib.decompress(base64.b64decode(content))
  else:
    raise AssertionError("Unknown data encoding")


def _CleanDirectory(path, exclude=None):
  """Removes all regular files in a directory.

  @type path: str
  @param path: the directory to clean
  @type exclude: list
  @param exclude: list of files to be excluded, defaults
      to the empty list

  """
  if not os.path.isdir(path):
    return
  if exclude is None:
    exclude = []
  else:
    # Normalize excluded paths
    exclude = [os.path.normpath(i) for i in exclude]

  for rel_name in utils.ListVisibleFiles(path):
    full_name = os.path.normpath(os.path.join(path, rel_name))
    if full_name in exclude:
      continue
    if os.path.isfile(full_name) and not os.path.islink(full_name):
      utils.RemoveFile(full_name)


def _BuildUploadFileList():
  """Build the list of allowed upload files.

  This is abstracted so that it's built only once at module import time.

  """
  allowed_files = set([
    constants.CLUSTER_CONF_FILE,
    constants.ETC_HOSTS,
    constants.SSH_KNOWN_HOSTS_FILE,
    constants.VNC_PASSWORD_FILE,
    constants.RAPI_CERT_FILE,
    constants.RAPI_USERS_FILE,
    constants.HMAC_CLUSTER_KEY,
    ])

  for hv_name in constants.HYPER_TYPES:
    hv_class = hypervisor.GetHypervisorClass(hv_name)
    allowed_files.update(hv_class.GetAncillaryFiles())

  return frozenset(allowed_files)


_ALLOWED_UPLOAD_FILES = _BuildUploadFileList()


def JobQueuePurge():
  """Removes job queue files and archived jobs.

  @rtype: tuple
  @return: True, None

  """
  _CleanDirectory(constants.QUEUE_DIR, exclude=[constants.JOB_QUEUE_LOCK_FILE])
  _CleanDirectory(constants.JOB_QUEUE_ARCHIVE_DIR)


def GetMasterInfo():
  """Returns master information.

  This is an utility function to compute master information, either
  for consumption here or from the node daemon.

  @rtype: tuple
  @return: master_netdev, master_ip, master_name
  @raise RPCFail: in case of errors

  """
  try:
    cfg = _GetConfig()
    master_netdev = cfg.GetMasterNetdev()
    master_ip = cfg.GetMasterIP()
    master_node = cfg.GetMasterNode()
  except errors.ConfigurationError, err:
    _Fail("Cluster configuration incomplete: %s", err, exc=True)
  return (master_netdev, master_ip, master_node)


def StartMaster(start_daemons, no_voting):
  """Activate local node as master node.

  The function will always try activate the IP address of the master
  (unless someone else has it). It will also start the master daemons,
  based on the start_daemons parameter.

  @type start_daemons: boolean
  @param start_daemons: whether to also start the master
      daemons (ganeti-masterd and ganeti-rapi)
  @type no_voting: boolean
  @param no_voting: whether to start ganeti-masterd without a node vote
      (if start_daemons is True), but still non-interactively
  @rtype: None

  """
  # GetMasterInfo will raise an exception if not able to return data
  master_netdev, master_ip, _ = GetMasterInfo()

  err_msgs = []
  if utils.TcpPing(master_ip, constants.DEFAULT_NODED_PORT):
    if utils.OwnIpAddress(master_ip):
      # we already have the ip:
      logging.debug("Master IP already configured, doing nothing")
    else:
      msg = "Someone else has the master ip, not activating"
      logging.error(msg)
      err_msgs.append(msg)
  else:
    result = utils.RunCmd(["ip", "address", "add", "%s/32" % master_ip,
                           "dev", master_netdev, "label",
                           "%s:0" % master_netdev])
    if result.failed:
      msg = "Can't activate master IP: %s" % result.output
      logging.error(msg)
      err_msgs.append(msg)

    result = utils.RunCmd(["arping", "-q", "-U", "-c 3", "-I", master_netdev,
                           "-s", master_ip, master_ip])
    # we'll ignore the exit code of arping

  # and now start the master and rapi daemons
  if start_daemons:
    if no_voting:
      masterd_args = "--no-voting --yes-do-it"
    else:
      masterd_args = ""

    env = {
      "EXTRA_MASTERD_ARGS": masterd_args,
      }

    result = utils.RunCmd([constants.DAEMON_UTIL, "start-master"], env=env)
    if result.failed:
      msg = "Can't start Ganeti master: %s" % result.output
      logging.error(msg)
      err_msgs.append(msg)

  if err_msgs:
    _Fail("; ".join(err_msgs))


def StopMaster(stop_daemons):
  """Deactivate this node as master.

  The function will always try to deactivate the IP address of the
  master. It will also stop the master daemons depending on the
  stop_daemons parameter.

  @type stop_daemons: boolean
  @param stop_daemons: whether to also stop the master daemons
      (ganeti-masterd and ganeti-rapi)
  @rtype: None

  """
  # TODO: log and report back to the caller the error failures; we
  # need to decide in which case we fail the RPC for this

  # GetMasterInfo will raise an exception if not able to return data
  master_netdev, master_ip, _ = GetMasterInfo()

  result = utils.RunCmd(["ip", "address", "del", "%s/32" % master_ip,
                         "dev", master_netdev])
  if result.failed:
    logging.error("Can't remove the master IP, error: %s", result.output)
    # but otherwise ignore the failure

  if stop_daemons:
    result = utils.RunCmd([constants.DAEMON_UTIL, "stop-master"])
    if result.failed:
      logging.error("Could not stop Ganeti master, command %s had exitcode %s"
                    " and error %s",
                    result.cmd, result.exit_code, result.output)


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

  @type dsa: str
  @param dsa: the DSA private key to write
  @type dsapub: str
  @param dsapub: the DSA public key to write
  @type rsa: str
  @param rsa: the RSA private key to write
  @type rsapub: str
  @param rsapub: the RSA public key to write
  @type sshkey: str
  @param sshkey: the SSH private key to write
  @type sshpub: str
  @param sshpub: the SSH public key to write
  @rtype: boolean
  @return: the success of the operation

  """
  sshd_keys =  [(constants.SSH_HOST_RSA_PRIV, rsa, 0600),
                (constants.SSH_HOST_RSA_PUB, rsapub, 0644),
                (constants.SSH_HOST_DSA_PRIV, dsa, 0600),
                (constants.SSH_HOST_DSA_PUB, dsapub, 0644)]
  for name, content, mode in sshd_keys:
    utils.WriteFile(name, data=content, mode=mode)

  try:
    priv_key, pub_key, auth_keys = ssh.GetUserFiles(constants.GANETI_RUNAS,
                                                    mkdir=True)
  except errors.OpExecError, err:
    _Fail("Error while processing user ssh files: %s", err, exc=True)

  for name, content in [(priv_key, sshkey), (pub_key, sshpub)]:
    utils.WriteFile(name, data=content, mode=0600)

  utils.AddAuthorizedKey(auth_keys, sshpub)

  result = utils.RunCmd([constants.DAEMON_UTIL, "reload-ssh-keys"])
  if result.failed:
    _Fail("Unable to reload SSH keys (command %r, exit code %s, output %r)",
          result.cmd, result.exit_code, result.output)


def LeaveCluster(modify_ssh_setup):
  """Cleans up and remove the current node.

  This function cleans up and prepares the current node to be removed
  from the cluster.

  If processing is successful, then it raises an
  L{errors.QuitGanetiException} which is used as a special case to
  shutdown the node daemon.

  @param modify_ssh_setup: boolean

  """
  _CleanDirectory(constants.DATA_DIR)
  JobQueuePurge()

  if modify_ssh_setup:
    try:
      priv_key, pub_key, auth_keys = ssh.GetUserFiles(constants.GANETI_RUNAS)

      utils.RemoveAuthorizedKey(auth_keys, utils.ReadFile(pub_key))

      utils.RemoveFile(priv_key)
      utils.RemoveFile(pub_key)
    except errors.OpExecError:
      logging.exception("Error while processing ssh files")

  try:
    utils.RemoveFile(constants.HMAC_CLUSTER_KEY)
    utils.RemoveFile(constants.RAPI_CERT_FILE)
    utils.RemoveFile(constants.SSL_CERT_FILE)
  except: # pylint: disable-msg=W0702
    logging.exception("Error while removing cluster secrets")

  result = utils.RunCmd([constants.DAEMON_UTIL, "stop", constants.CONFD])
  if result.failed:
    logging.error("Command %s failed with exitcode %s and error %s",
                  result.cmd, result.exit_code, result.output)

  # Raise a custom exception (handled in ganeti-noded)
  raise errors.QuitGanetiException(True, 'Shutdown scheduled')


def GetNodeInfo(vgname, hypervisor_type):
  """Gives back a hash with different information about the node.

  @type vgname: C{string}
  @param vgname: the name of the volume group to ask for disk space information
  @type hypervisor_type: C{str}
  @param hypervisor_type: the name of the hypervisor to ask for
      memory information
  @rtype: C{dict}
  @return: dictionary with the following keys:
      - 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(hypervisor_type)
  hyp_info = hyper.GetNodeInfo()
  if hyp_info is not None:
    outputarray.update(hyp_info)

  outputarray["bootid"] = utils.ReadFile(_BOOT_ID_PATH, size=128).rstrip("\n")

  return outputarray


def VerifyNode(what, cluster_name):
  """Verify the status of the local node.

  Based on the input L{what} parameter, various checks are done on the
  local node.

  If the I{filelist} key is present, this list of
  files is checksummed and the file/checksum pairs are returned.

  If the I{nodelist} key is present, we check that we have
  connectivity via ssh with the target nodes (and check the hostname
  report).

  If the I{node-net-test} key is present, we check that we have
  connectivity to the given nodes via both primary IP and, if
  applicable, secondary IPs.

  @type what: C{dict}
  @param what: a dictionary of things to check:
      - filelist: list of files for which to compute checksums
      - nodelist: list of nodes we should check ssh communication with
      - node-net-test: list of nodes we should check node daemon port
        connectivity with
      - hypervisor: list with hypervisors to run the verify for
  @rtype: dict
  @return: a dictionary with the same keys as the input dict, and
      values representing the result of the checks

  """
  result = {}

  if constants.NV_HYPERVISOR in what:
    result[constants.NV_HYPERVISOR] = tmp = {}
    for hv_name in what[constants.NV_HYPERVISOR]:
      tmp[hv_name] = hypervisor.GetHypervisor(hv_name).Verify()

  if constants.NV_FILELIST in what:
    result[constants.NV_FILELIST] = utils.FingerprintFiles(
      what[constants.NV_FILELIST])

  if constants.NV_NODELIST in what:
    result[constants.NV_NODELIST] = tmp = {}
    random.shuffle(what[constants.NV_NODELIST])
    for node in what[constants.NV_NODELIST]:
      success, message = _GetSshRunner(cluster_name).VerifyNodeHostname(node)
      if not success:
        tmp[node] = message

  if constants.NV_NODENETTEST in what:
    result[constants.NV_NODENETTEST] = tmp = {}
    my_name = utils.HostInfo().name
    my_pip = my_sip = None
    for name, pip, sip in what[constants.NV_NODENETTEST]:
      if name == my_name:
        my_pip = pip
        my_sip = sip
        break
    if not my_pip:
      tmp[my_name] = ("Can't find my own primary/secondary IP"
                      " in the node list")
    else:
      port = utils.GetDaemonPort(constants.NODED)
      for name, pip, sip in what[constants.NV_NODENETTEST]:
        fail = []
        if not utils.TcpPing(pip, port, source=my_pip):
          fail.append("primary")
        if sip != pip:
          if not utils.TcpPing(sip, port, source=my_sip):
            fail.append("secondary")
        if fail:
          tmp[name] = ("failure using the %s interface(s)" %
                       " and ".join(fail))

  if constants.NV_LVLIST in what:
    result[constants.NV_LVLIST] = GetVolumeList(what[constants.NV_LVLIST])

  if constants.NV_INSTANCELIST in what:
    result[constants.NV_INSTANCELIST] = GetInstanceList(
      what[constants.NV_INSTANCELIST])

  if constants.NV_VGLIST in what:
    result[constants.NV_VGLIST] = utils.ListVolumeGroups()

  if constants.NV_PVLIST in what:
    result[constants.NV_PVLIST] = \
      bdev.LogicalVolume.GetPVInfo(what[constants.NV_PVLIST],
                                   filter_allocatable=False)

  if constants.NV_VERSION in what:
    result[constants.NV_VERSION] = (constants.PROTOCOL_VERSION,
                                    constants.RELEASE_VERSION)

  if constants.NV_HVINFO in what:
    hyper = hypervisor.GetHypervisor(what[constants.NV_HVINFO])
    result[constants.NV_HVINFO] = hyper.GetNodeInfo()

  if constants.NV_DRBDLIST in what:
    try:
      used_minors = bdev.DRBD8.GetUsedDevs().keys()
    except errors.BlockDeviceError, err:
      logging.warning("Can't get used minors list", exc_info=True)
      used_minors = str(err)
    result[constants.NV_DRBDLIST] = used_minors

  if constants.NV_NODESETUP in what:
    result[constants.NV_NODESETUP] = tmpr = []
    if not os.path.isdir("/sys/block") or not os.path.isdir("/sys/class/net"):
      tmpr.append("The sysfs filesytem doesn't seem to be mounted"
                  " under /sys, missing required directories /sys/block"
                  " and /sys/class/net")
    if (not os.path.isdir("/proc/sys") or
        not os.path.isfile("/proc/sysrq-trigger")):
      tmpr.append("The procfs filesystem doesn't seem to be mounted"
                  " under /proc, missing required directory /proc/sys and"
                  " the file /proc/sysrq-trigger")

  if constants.NV_TIME in what:
    result[constants.NV_TIME] = utils.SplitTime(time.time())

  return result


def GetVolumeList(vg_name):
  """Compute list of logical volumes and their size.

  @type vg_name: str
  @param vg_name: the volume group whose LVs we should list
  @rtype: dict
  @return:
      dictionary of all partions (key) with value being a tuple of
      their size (in MiB), inactive and online status::

        {'test1': ('20.06', True, True)}

      in case of errors, a string is returned with the error
      details.

  """
  lvs = {}
  sep = '|'
  result = utils.RunCmd(["lvs", "--noheadings", "--units=m", "--nosuffix",
                         "--separator=%s" % sep,
                         "-olv_name,lv_size,lv_attr", vg_name])
  if result.failed:
    _Fail("Failed to list logical volumes, lvs output: %s", result.output)

  valid_line_re = re.compile("^ *([^|]+)\|([0-9.]+)\|([^|]{6})\|?$")
  for line in result.stdout.splitlines():
    line = line.strip()
    match = valid_line_re.match(line)
    if not match:
      logging.error("Invalid line returned from lvs output: '%s'", line)
      continue
    name, size, attr = match.groups()
    inactive = attr[4] == '-'
    online = attr[5] == 'o'
    virtual = attr[0] == 'v'
    if virtual:
      # we don't want to report such volumes as existing, since they
      # don't really hold data
      continue
    lvs[name] = (size, inactive, online)

  return lvs


def ListVolumeGroups():
  """List the volume groups and their size.

  @rtype: dict
  @return: dictionary with keys volume name and values the
      size of the volume

  """
  return utils.ListVolumeGroups()


def NodeVolumes():
  """List all volumes on this node.

  @rtype: list
  @return:
    A list of dictionaries, each having four keys:
      - name: the logical volume name,
      - size: the size of the logical volume
      - dev: the physical device on which the LV lives
      - vg: the volume group to which it belongs

    In case of errors, we return an empty list and log the
    error.

    Note that since a logical volume can live on multiple physical
    volumes, the resulting list might include a logical volume
    multiple times.

  """
  result = utils.RunCmd(["lvs", "--noheadings", "--units=m", "--nosuffix",
                         "--separator=|",
                         "--options=lv_name,lv_size,devices,vg_name"])
  if result.failed:
    _Fail("Failed to list logical volumes, lvs output: %s",
          result.output)

  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.stdout.splitlines()
          if line.count('|') >= 3]


def BridgesExist(bridges_list):
  """Check if a list of bridges exist on the current node.

  @rtype: boolean
  @return: C{True} if all of them exist, C{False} otherwise

  """
  missing = []
  for bridge in bridges_list:
    if not utils.BridgeExists(bridge):
      missing.append(bridge)

  if missing:
    _Fail("Missing bridges %s", utils.CommaJoin(missing))


def GetInstanceList(hypervisor_list):
  """Provides a list of instances.

  @type hypervisor_list: list
  @param hypervisor_list: the list of hypervisors to query information

  @rtype: list
  @return: a list of all running instances on the current node
    - instance1.example.com
    - instance2.example.com

  """
  results = []
  for hname in hypervisor_list:
    try:
      names = hypervisor.GetHypervisor(hname).ListInstances()
      results.extend(names)
    except errors.HypervisorError, err:
      _Fail("Error enumerating instances (hypervisor %s): %s",
            hname, err, exc=True)

  return results


def GetInstanceInfo(instance, hname):
  """Gives back the information about an instance as a dictionary.

  @type instance: string
  @param instance: the instance name
  @type hname: string
  @param hname: the hypervisor type of the instance

  @rtype: dict
  @return: dictionary with the following keys:
      - memory: memory size of instance (int)
      - state: xen state of instance (string)
      - time: cpu time of instance (float)

  """
  output = {}

  iinfo = hypervisor.GetHypervisor(hname).GetInstanceInfo(instance)
  if iinfo is not None:
    output['memory'] = iinfo[2]
    output['state'] = iinfo[4]
    output['time'] = iinfo[5]

  return output


def GetInstanceMigratable(instance):
  """Gives whether an instance can be migrated.

  @type instance: L{objects.Instance}
  @param instance: object representing the instance to be checked.

  @rtype: tuple
  @return: tuple of (result, description) where:
      - result: whether the instance can be migrated or not
      - description: a description of the issue, if relevant

  """
  hyper = hypervisor.GetHypervisor(instance.hypervisor)
  iname = instance.name
  if iname not in hyper.ListInstances():
    _Fail("Instance %s is not running", iname)

  for idx in range(len(instance.disks)):
    link_name = _GetBlockDevSymlinkPath(iname, idx)
    if not os.path.islink(link_name):
      _Fail("Instance %s was not restarted since ganeti 1.2.5", iname)


def GetAllInstancesInfo(hypervisor_list):
  """Gather data about all instances.

  This is the equivalent of L{GetInstanceInfo}, except that it
  computes data for all instances at once, thus being faster if one
  needs data about more than one instance.

  @type hypervisor_list: list
  @param hypervisor_list: list of hypervisors to query for instance data

  @rtype: dict
  @return: dictionary of instance: data, with data having the following keys:
      - memory: memory size of instance (int)
      - state: xen state of instance (string)
      - time: cpu time of instance (float)
      - vcpus: the number of vcpus

  """
  output = {}

  for hname in hypervisor_list:
    iinfo = hypervisor.GetHypervisor(hname).GetAllInstancesInfo()
    if iinfo:
      for name, _, memory, vcpus, state, times in iinfo:
        value = {
          'memory': memory,
          'vcpus': vcpus,
          'state': state,
          'time': times,
          }
        if name in output:
          # we only check static parameters, like memory and vcpus,
          # and not state and time which can change between the
          # invocations of the different hypervisors
          for key in 'memory', 'vcpus':
            if value[key] != output[name][key]:
              _Fail("Instance %s is running twice"
                    " with different parameters", name)
        output[name] = value

  return output


def InstanceOsAdd(instance, reinstall):
  """Add an OS to an instance.

  @type instance: L{objects.Instance}
  @param instance: Instance whose OS is to be installed
  @type reinstall: boolean
  @param reinstall: whether this is an instance reinstall
  @rtype: None

  """
  inst_os = OSFromDisk(instance.os)

  create_env = OSEnvironment(instance, inst_os)
  if reinstall:
    create_env['INSTANCE_REINSTALL'] = "1"

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

  result = utils.RunCmd([inst_os.create_script], env=create_env,
                        cwd=inst_os.path, output=logfile,)
  if result.failed:
    logging.error("os create command '%s' returned error: %s, logfile: %s,"
                  " output: %s", result.cmd, result.fail_reason, logfile,
                  result.output)
    lines = [utils.SafeEncode(val)
             for val in utils.TailFile(logfile, lines=20)]
    _Fail("OS create script failed (%s), last lines in the"
          " log file:\n%s", result.fail_reason, "\n".join(lines), log=False)


def RunRenameInstance(instance, old_name):
  """Run the OS rename script for an instance.

  @type instance: L{objects.Instance}
  @param instance: Instance whose OS is to be installed
  @type old_name: string
  @param old_name: previous instance name
  @rtype: boolean
  @return: the success of the operation

  """
  inst_os = OSFromDisk(instance.os)

  rename_env = OSEnvironment(instance, inst_os)
  rename_env['OLD_INSTANCE_NAME'] = old_name

  logfile = "%s/rename-%s-%s-%s-%d.log" % (constants.LOG_OS_DIR, instance.os,
                                           old_name,
                                           instance.name, int(time.time()))

  result = utils.RunCmd([inst_os.rename_script], env=rename_env,
                        cwd=inst_os.path, output=logfile)

  if result.failed:
    logging.error("os create command '%s' returned error: %s output: %s",
                  result.cmd, result.fail_reason, result.output)
    lines = [utils.SafeEncode(val)
             for val in utils.TailFile(logfile, lines=20)]
    _Fail("OS rename script failed (%s), last lines in the"
          " log file:\n%s", result.fail_reason, "\n".join(lines), log=False)


def _GetVGInfo(vg_name):
  """Get information about the volume group.

  @type vg_name: str
  @param vg_name: the volume group which we query
  @rtype: dict
  @return:
    A dictionary with the following keys:
      - C{vg_size} is the total size of the volume group in MiB
      - C{vg_free} is the free size of the volume group in MiB
      - C{pv_count} are the number of physical disks in that VG

    If an error occurs during gathering of data, we return the same dict
    with keys all set to None.

  """
  retdic = dict.fromkeys(["vg_size", "vg_free", "pv_count"])

  retval = utils.RunCmd(["vgs", "-ovg_size,vg_free,pv_count", "--noheadings",
                         "--nosuffix", "--units=m", "--separator=:", vg_name])

  if retval.failed:
    logging.error("volume group %s not present", vg_name)
    return retdic
  valarr = retval.stdout.strip().rstrip(':').split(':')
  if len(valarr) == 3:
    try:
      retdic = {
        "vg_size": int(round(float(valarr[0]), 0)),
        "vg_free": int(round(float(valarr[1]), 0)),
        "pv_count": int(valarr[2]),
        }
    except ValueError, err:
      logging.exception("Fail to parse vgs output: %s", err)
  else:
    logging.error("vgs output has the wrong number of fields (expected"
                  " three): %s", str(valarr))
  return retdic


def _GetBlockDevSymlinkPath(instance_name, idx):
  return os.path.join(constants.DISK_LINKS_DIR,
                      "%s:%d" % (instance_name, idx))


def _SymlinkBlockDev(instance_name, device_path, idx):
  """Set up symlinks to a instance's block device.

  This is an auxiliary function run when an instance is start (on the primary
  node) or when an instance is migrated (on the target node).


  @param instance_name: the name of the target instance
  @param device_path: path of the physical block device, on the node
  @param idx: the disk index
  @return: absolute path to the disk's symlink

  """
  link_name = _GetBlockDevSymlinkPath(instance_name, idx)
  try:
    os.symlink(device_path, link_name)
  except OSError, err:
    if err.errno == errno.EEXIST:
      if (not os.path.islink(link_name) or
          os.readlink(link_name) != device_path):
        os.remove(link_name)
        os.symlink(device_path, link_name)
    else:
      raise

  return link_name


def _RemoveBlockDevLinks(instance_name, disks):
  """Remove the block device symlinks belonging to the given instance.

  """
  for idx, _ in enumerate(disks):
    link_name = _GetBlockDevSymlinkPath(instance_name, idx)
    if os.path.islink(link_name):
      try:
        os.remove(link_name)
      except OSError:
        logging.exception("Can't remove symlink '%s'", link_name)


def _GatherAndLinkBlockDevs(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.

  @type instance: L{objects.Instance}
  @param instance: the instance whose disks we shoul assemble
  @rtype: list
  @return: list of (disk_object, device_path)

  """
  block_devices = []
  for idx, disk in enumerate(instance.disks):
    device = _RecursiveFindBD(disk)
    if device is None:
      raise errors.BlockDeviceError("Block device '%s' is not set up." %
                                    str(disk))
    device.Open()
    try:
      link_name = _SymlinkBlockDev(instance.name, device.dev_path, idx)
    except OSError, e:
      raise errors.BlockDeviceError("Cannot create block device symlink: %s" %
                                    e.strerror)

    block_devices.append((disk, link_name))

  return block_devices


def StartInstance(instance):
  """Start an instance.

  @type instance: L{objects.Instance}
  @param instance: the instance object
  @rtype: None

  """
  running_instances = GetInstanceList([instance.hypervisor])

  if instance.name in running_instances:
    logging.info("Instance %s already running, not starting", instance.name)
    return

  try:
    block_devices = _GatherAndLinkBlockDevs(instance)
    hyper = hypervisor.GetHypervisor(instance.hypervisor)
    hyper.StartInstance(instance, block_devices)
  except errors.BlockDeviceError, err:
    _Fail("Block device error: %s", err, exc=True)
  except errors.HypervisorError, err:
    _RemoveBlockDevLinks(instance.name, instance.disks)
    _Fail("Hypervisor error: %s", err, exc=True)


def InstanceShutdown(instance, timeout):
  """Shut an instance down.

  @note: this functions uses polling with a hardcoded timeout.

  @type instance: L{objects.Instance}
  @param instance: the instance object
  @type timeout: integer
  @param timeout: maximum timeout for soft shutdown
  @rtype: None

  """
  hv_name = instance.hypervisor
  hyper = hypervisor.GetHypervisor(hv_name)
  iname = instance.name

  if instance.name not in hyper.ListInstances():
    logging.info("Instance %s not running, doing nothing", iname)
    return

  class _TryShutdown:
    def __init__(self):
      self.tried_once = False

    def __call__(self):
      if iname not in hyper.ListInstances():
        return

      try:
        hyper.StopInstance(instance, retry=self.tried_once)
      except errors.HypervisorError, err:
        if iname not in hyper.ListInstances():
          # if the instance is no longer existing, consider this a
          # success and go to cleanup
          return

        _Fail("Failed to stop instance %s: %s", iname, err)

      self.tried_once = True

      raise utils.RetryAgain()

  try:
    utils.Retry(_TryShutdown(), 5, timeout)
  except utils.RetryTimeout:
    # the shutdown did not succeed
    logging.error("Shutdown of '%s' unsuccessful, forcing", iname)

    try:
      hyper.StopInstance(instance, force=True)
    except errors.HypervisorError, err:
      if iname in hyper.ListInstances():
        # only raise an error if the instance still exists, otherwise
        # the error could simply be "instance ... unknown"!
        _Fail("Failed to force stop instance %s: %s", iname, err)

    time.sleep(1)

    if iname in hyper.ListInstances():
      _Fail("Could not shutdown instance %s even by destroy", iname)

  _RemoveBlockDevLinks(iname, instance.disks)


def InstanceReboot(instance, reboot_type, shutdown_timeout):
  """Reboot an instance.

  @type instance: L{objects.Instance}
  @param instance: the instance object to reboot
  @type reboot_type: str
  @param reboot_type: the type of reboot, one the following
    constants:
      - L{constants.INSTANCE_REBOOT_SOFT}: only reboot the
        instance OS, do not recreate the VM
      - L{constants.INSTANCE_REBOOT_HARD}: tear down and
        restart the VM (at the hypervisor level)
      - the other reboot type (L{constants.INSTANCE_REBOOT_FULL}) is
        not accepted here, since that mode is handled differently, in
        cmdlib, and translates into full stop and start of the
        instance (instead of a call_instance_reboot RPC)