Synnefo » snf-ganeti

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"""Common functions used by multiple logical units."""

import copy

import os

from ganeti import compat

from ganeti import constants

from ganeti import errors

from ganeti import hypervisor

from ganeti import locking

from ganeti import objects

from ganeti import opcodes

from ganeti import pathutils

from ganeti import rpc

from ganeti import ssconf

from ganeti import utils

# States of instance

INSTANCE_DOWN = [constants.ADMINST_DOWN]

INSTANCE_ONLINE = [constants.ADMINST_DOWN, constants.ADMINST_UP]

INSTANCE_NOT_RUNNING = [constants.ADMINST_DOWN, constants.ADMINST_OFFLINE]

#: Instance status in which an instance can be marked as offline/online

CAN_CHANGE_INSTANCE_OFFLINE = (frozenset(INSTANCE_DOWN) | frozenset([

  constants.ADMINST_OFFLINE,

  ]))

def _ExpandItemName(fn, name, kind):

  """Expand an item name.

  @param fn: the function to use for expansion

  @param name: requested item name

  @param kind: text description ('Node' or 'Instance')

  @return: the resolved (full) name

  @raise errors.OpPrereqError: if the item is not found

  """

  full_name = fn(name)

  if full_name is None:

    raise errors.OpPrereqError("%s '%s' not known" % (kind, name),

                               errors.ECODE_NOENT)

  return full_name

def ExpandInstanceName(cfg, name):

  """Wrapper over L{_ExpandItemName} for instance."""

  return _ExpandItemName(cfg.ExpandInstanceName, name, "Instance")

def ExpandNodeName(cfg, name):

  """Wrapper over L{_ExpandItemName} for nodes."""

  return _ExpandItemName(cfg.ExpandNodeName, name, "Node")

def ShareAll():

  """Returns a dict declaring all lock levels shared.

  """

  return dict.fromkeys(locking.LEVELS, 1)

def CheckNodeGroupInstances(cfg, group_uuid, owned_instances):

  """Checks if the instances in a node group are still correct.

  @type cfg: L{config.ConfigWriter}

  @param cfg: The cluster configuration

  @type group_uuid: string

  @param group_uuid: Node group UUID

  @type owned_instances: set or frozenset

  @param owned_instances: List of currently owned instances

  """

  wanted_instances = cfg.GetNodeGroupInstances(group_uuid)

  if owned_instances != wanted_instances:

    raise errors.OpPrereqError("Instances in node group '%s' changed since"

                               " locks were acquired, wanted '%s', have '%s';"

                               " retry the operation" %

                               (group_uuid,

                                utils.CommaJoin(wanted_instances),

                                utils.CommaJoin(owned_instances)),

                               errors.ECODE_STATE)

  return wanted_instances

def GetWantedNodes(lu, nodes):

  """Returns list of checked and expanded node names.

  @type lu: L{LogicalUnit}

  @param lu: the logical unit on whose behalf we execute

  @type nodes: list

  @param nodes: list of node names or None for all nodes

  @rtype: list

  @return: the list of nodes, sorted

  @raise errors.ProgrammerError: if the nodes parameter is wrong type

  """

  if nodes:

    return [ExpandNodeName(lu.cfg, name) for name in nodes]

  return utils.NiceSort(lu.cfg.GetNodeList())

def GetWantedInstances(lu, instances):

  """Returns list of checked and expanded instance names.

  @type lu: L{LogicalUnit}

  @param lu: the logical unit on whose behalf we execute

  @type instances: list

  @param instances: list of instance names or None for all instances

  @rtype: list

  @return: the list of instances, sorted

  @raise errors.OpPrereqError: if the instances parameter is wrong type

  @raise errors.OpPrereqError: if any of the passed instances is not found

  """

  if instances:

    wanted = [ExpandInstanceName(lu.cfg, name) for name in instances]

  else:

    wanted = utils.NiceSort(lu.cfg.GetInstanceList())

  return wanted

def RunPostHook(lu, node_name):

  """Runs the post-hook for an opcode on a single node.

  """

  hm = lu.proc.BuildHooksManager(lu)

  try:

    hm.RunPhase(constants.HOOKS_PHASE_POST, nodes=[node_name])

  except Exception, err: # pylint: disable=W0703

    lu.LogWarning("Errors occurred running hooks on %s: %s",

                  node_name, err)

def RedistributeAncillaryFiles(lu, additional_nodes=None, additional_vm=True):

  """Distribute additional files which are part of the cluster configuration.

  ConfigWriter takes care of distributing the config and ssconf files, but

  there are more files which should be distributed to all nodes. This function

  makes sure those are copied.

  @param lu: calling logical unit

  @param additional_nodes: list of nodes not in the config to distribute to

  @type additional_vm: boolean

  @param additional_vm: whether the additional nodes are vm-capable or not

  """

  # Gather target nodes

  cluster = lu.cfg.GetClusterInfo()

  master_info = lu.cfg.GetNodeInfo(lu.cfg.GetMasterNode())

  online_nodes = lu.cfg.GetOnlineNodeList()

  online_set = frozenset(online_nodes)

  vm_nodes = list(online_set.intersection(lu.cfg.GetVmCapableNodeList()))

  if additional_nodes is not None:

    online_nodes.extend(additional_nodes)

    if additional_vm:

      vm_nodes.extend(additional_nodes)

  # Never distribute to master node

  for nodelist in [online_nodes, vm_nodes]:

    if master_info.name in nodelist:

      nodelist.remove(master_info.name)

  # Gather file lists

  (files_all, _, files_mc, files_vm) = \

    ComputeAncillaryFiles(cluster, True)

  # Never re-distribute configuration file from here

  assert not (pathutils.CLUSTER_CONF_FILE in files_all or

              pathutils.CLUSTER_CONF_FILE in files_vm)

  assert not files_mc, "Master candidates not handled in this function"

  filemap = [

    (online_nodes, files_all),

    (vm_nodes, files_vm),

    ]

  # Upload the files

  for (node_list, files) in filemap:

    for fname in files:

      UploadHelper(lu, node_list, fname)

def ComputeAncillaryFiles(cluster, redist):

  """Compute files external to Ganeti which need to be consistent.

  @type redist: boolean

  @param redist: Whether to include files which need to be redistributed

  """

  # Compute files for all nodes

  files_all = set([

    pathutils.SSH_KNOWN_HOSTS_FILE,

    pathutils.CONFD_HMAC_KEY,

    pathutils.CLUSTER_DOMAIN_SECRET_FILE,

    pathutils.SPICE_CERT_FILE,

    pathutils.SPICE_CACERT_FILE,

    pathutils.RAPI_USERS_FILE,

    ])

  if redist:

    # we need to ship at least the RAPI certificate

    files_all.add(pathutils.RAPI_CERT_FILE)

  else:

    files_all.update(pathutils.ALL_CERT_FILES)

    files_all.update(ssconf.SimpleStore().GetFileList())

  if cluster.modify_etc_hosts:

    files_all.add(pathutils.ETC_HOSTS)

  if cluster.use_external_mip_script:

    files_all.add(pathutils.EXTERNAL_MASTER_SETUP_SCRIPT)

  # Files which are optional, these must:

  # - be present in one other category as well

  # - either exist or not exist on all nodes of that category (mc, vm all)

  files_opt = set([

    pathutils.RAPI_USERS_FILE,

    ])

  # Files which should only be on master candidates

  files_mc = set()

  if not redist:

    files_mc.add(pathutils.CLUSTER_CONF_FILE)

  # File storage

  if (not redist and (constants.ENABLE_FILE_STORAGE or

                        constants.ENABLE_SHARED_FILE_STORAGE)):

    files_all.add(pathutils.FILE_STORAGE_PATHS_FILE)

    files_opt.add(pathutils.FILE_STORAGE_PATHS_FILE)

  # Files which should only be on VM-capable nodes

  files_vm = set(

    filename

    for hv_name in cluster.enabled_hypervisors

    for filename in

    hypervisor.GetHypervisorClass(hv_name).GetAncillaryFiles()[0])

  files_opt |= set(

    filename

    for hv_name in cluster.enabled_hypervisors

    for filename in

    hypervisor.GetHypervisorClass(hv_name).GetAncillaryFiles()[1])

  # Filenames in each category must be unique

  all_files_set = files_all | files_mc | files_vm

  assert (len(all_files_set) ==

          sum(map(len, [files_all, files_mc, files_vm]))), \

    "Found file listed in more than one file list"

  # Optional files must be present in one other category

  assert all_files_set.issuperset(files_opt), \

    "Optional file not in a different required list"

  # This one file should never ever be re-distributed via RPC

  assert not (redist and

              pathutils.FILE_STORAGE_PATHS_FILE in all_files_set)

  return (files_all, files_opt, files_mc, files_vm)

def UploadHelper(lu, nodes, fname):

  """Helper for uploading a file and showing warnings.

  """

  if os.path.exists(fname):

    result = lu.rpc.call_upload_file(nodes, fname)

    for to_node, to_result in result.items():

      msg = to_result.fail_msg

      if msg:

        msg = ("Copy of file %s to node %s failed: %s" %

               (fname, to_node, msg))

        lu.LogWarning(msg)

def MergeAndVerifyHvState(op_input, obj_input):

  """Combines the hv state from an opcode with the one of the object

  @param op_input: The input dict from the opcode

  @param obj_input: The input dict from the objects

  @return: The verified and updated dict

  """

  if op_input:

    invalid_hvs = set(op_input) - constants.HYPER_TYPES

    if invalid_hvs:

      raise errors.OpPrereqError("Invalid hypervisor(s) in hypervisor state:"

                                 " %s" % utils.CommaJoin(invalid_hvs),

                                 errors.ECODE_INVAL)

    if obj_input is None:

      obj_input = {}

    type_check = constants.HVSTS_PARAMETER_TYPES

    return _UpdateAndVerifySubDict(obj_input, op_input, type_check)

  return None

def MergeAndVerifyDiskState(op_input, obj_input):

  """Combines the disk state from an opcode with the one of the object

  @param op_input: The input dict from the opcode

  @param obj_input: The input dict from the objects

  @return: The verified and updated dict

  """

  if op_input:

    invalid_dst = set(op_input) - constants.DS_VALID_TYPES

    if invalid_dst:

      raise errors.OpPrereqError("Invalid storage type(s) in disk state: %s" %

                                 utils.CommaJoin(invalid_dst),

                                 errors.ECODE_INVAL)

    type_check = constants.DSS_PARAMETER_TYPES

    if obj_input is None:

      obj_input = {}

    return dict((key, _UpdateAndVerifySubDict(obj_input.get(key, {}), value,

                                              type_check))

                for key, value in op_input.items())

  return None

def CheckOSParams(lu, required, nodenames, osname, osparams):

  """OS parameters validation.

  @type lu: L{LogicalUnit}

  @param lu: the logical unit for which we check

  @type required: boolean

  @param required: whether the validation should fail if the OS is not

      found

  @type nodenames: list

  @param nodenames: the list of nodes on which we should check

  @type osname: string

  @param osname: the name of the hypervisor we should use

  @type osparams: dict

  @param osparams: the parameters which we need to check

  @raise errors.OpPrereqError: if the parameters are not valid

  """

  nodenames = _FilterVmNodes(lu, nodenames)

  result = lu.rpc.call_os_validate(nodenames, required, osname,

                                   [constants.OS_VALIDATE_PARAMETERS],

                                   osparams)

  for node, nres in result.items():

    # we don't check for offline cases since this should be run only

    # against the master node and/or an instance's nodes

    nres.Raise("OS Parameters validation failed on node %s" % node)

    if not nres.payload:

      lu.LogInfo("OS %s not found on node %s, validation skipped",

                 osname, node)

def CheckHVParams(lu, nodenames, hvname, hvparams):

  """Hypervisor parameter validation.

  This function abstract the hypervisor parameter validation to be

  used in both instance create and instance modify.

  @type lu: L{LogicalUnit}

  @param lu: the logical unit for which we check

  @type nodenames: list

  @param nodenames: the list of nodes on which we should check

  @type hvname: string

  @param hvname: the name of the hypervisor we should use

  @type hvparams: dict

  @param hvparams: the parameters which we need to check

  @raise errors.OpPrereqError: if the parameters are not valid

  """

  nodenames = _FilterVmNodes(lu, nodenames)

  cluster = lu.cfg.GetClusterInfo()

  hvfull = objects.FillDict(cluster.hvparams.get(hvname, {}), hvparams)

  hvinfo = lu.rpc.call_hypervisor_validate_params(nodenames, hvname, hvfull)

  for node in nodenames:

    info = hvinfo[node]

    if info.offline:

      continue

    info.Raise("Hypervisor parameter validation failed on node %s" % node)

def AdjustCandidatePool(lu, exceptions):

  """Adjust the candidate pool after node operations.

  """

  mod_list = lu.cfg.MaintainCandidatePool(exceptions)

  if mod_list:

    lu.LogInfo("Promoted nodes to master candidate role: %s",

               utils.CommaJoin(node.name for node in mod_list))

    for name in mod_list:

      lu.context.ReaddNode(name)

  mc_now, mc_max, _ = lu.cfg.GetMasterCandidateStats(exceptions)

  if mc_now > mc_max:

    lu.LogInfo("Note: more nodes are candidates (%d) than desired (%d)" %

               (mc_now, mc_max))

def CheckNodePVs(nresult, exclusive_storage):

  """Check node PVs.

  """

  pvlist_dict = nresult.get(constants.NV_PVLIST, None)

  if pvlist_dict is None:

    return (["Can't get PV list from node"], None)

  pvlist = map(objects.LvmPvInfo.FromDict, pvlist_dict)

  errlist = []

  # check that ':' is not present in PV names, since it's a

  # special character for lvcreate (denotes the range of PEs to

  # use on the PV)

  for pv in pvlist:

    if ":" in pv.name:

      errlist.append("Invalid character ':' in PV '%s' of VG '%s'" %

                     (pv.name, pv.vg_name))

  es_pvinfo = None

  if exclusive_storage:

    (errmsgs, es_pvinfo) = utils.LvmExclusiveCheckNodePvs(pvlist)

    errlist.extend(errmsgs)

    shared_pvs = nresult.get(constants.NV_EXCLUSIVEPVS, None)

    if shared_pvs:

      for (pvname, lvlist) in shared_pvs:

        # TODO: Check that LVs are really unrelated (snapshots, DRBD meta...)

        errlist.append("PV %s is shared among unrelated LVs (%s)" %

                       (pvname, utils.CommaJoin(lvlist)))

  return (errlist, es_pvinfo)

def _ComputeMinMaxSpec(name, qualifier, ispecs, value):

  """Computes if value is in the desired range.

  @param name: name of the parameter for which we perform the check

  @param qualifier: a qualifier used in the error message (e.g. 'disk/1',

      not just 'disk')

  @param ispecs: dictionary containing min and max values

  @param value: actual value that we want to use

  @return: None or an error string

  """

  if value in [None, constants.VALUE_AUTO]:

    return None

  max_v = ispecs[constants.ISPECS_MAX].get(name, value)

  min_v = ispecs[constants.ISPECS_MIN].get(name, value)

  if value > max_v or min_v > value:

    if qualifier:

      fqn = "%s/%s" % (name, qualifier)

    else:

      fqn = name

    return ("%s value %s is not in range [%s, %s]" %

            (fqn, value, min_v, max_v))

  return None

def ComputeIPolicySpecViolation(ipolicy, mem_size, cpu_count, disk_count,

                                nic_count, disk_sizes, spindle_use,

                                disk_template,

                                _compute_fn=_ComputeMinMaxSpec):

  """Verifies ipolicy against provided specs.

  @type ipolicy: dict

  @param ipolicy: The ipolicy

  @type mem_size: int

  @param mem_size: The memory size

  @type cpu_count: int

  @param cpu_count: Used cpu cores

  @type disk_count: int

  @param disk_count: Number of disks used

  @type nic_count: int

  @param nic_count: Number of nics used

  @type disk_sizes: list of ints

  @param disk_sizes: Disk sizes of used disk (len must match C{disk_count})

  @type spindle_use: int

  @param spindle_use: The number of spindles this instance uses

  @type disk_template: string

  @param disk_template: The disk template of the instance

  @param _compute_fn: The compute function (unittest only)

  @return: A list of violations, or an empty list of no violations are found

  """

  assert disk_count == len(disk_sizes)

  test_settings = [

    (constants.ISPEC_MEM_SIZE, "", mem_size),

    (constants.ISPEC_CPU_COUNT, "", cpu_count),

    (constants.ISPEC_NIC_COUNT, "", nic_count),

    (constants.ISPEC_SPINDLE_USE, "", spindle_use),

    ] + [(constants.ISPEC_DISK_SIZE, str(idx), d)

         for idx, d in enumerate(disk_sizes)]

  if disk_template != constants.DT_DISKLESS:

    # This check doesn't make sense for diskless instances

    test_settings.append((constants.ISPEC_DISK_COUNT, "", disk_count))

  ret = []

  allowed_dts = ipolicy[constants.IPOLICY_DTS]

  if disk_template not in allowed_dts:

    ret.append("Disk template %s is not allowed (allowed templates: %s)" %

               (disk_template, utils.CommaJoin(allowed_dts)))

  min_errs = None

  for minmax in ipolicy[constants.ISPECS_MINMAX]:

    errs = filter(None,

                  (_compute_fn(name, qualifier, minmax, value)

                   for (name, qualifier, value) in test_settings))

    if min_errs is None or len(errs) < len(min_errs):

      min_errs = errs

  assert min_errs is not None

  return ret + min_errs

def ComputeIPolicyInstanceViolation(ipolicy, instance, cfg,

                                    _compute_fn=ComputeIPolicySpecViolation):

  """Compute if instance meets the specs of ipolicy.

  @type ipolicy: dict

  @param ipolicy: The ipolicy to verify against

  @type instance: L{objects.Instance}

  @param instance: The instance to verify

  @type cfg: L{config.ConfigWriter}

  @param cfg: Cluster configuration

  @param _compute_fn: The function to verify ipolicy (unittest only)

  @see: L{ComputeIPolicySpecViolation}

  """

  be_full = cfg.GetClusterInfo().FillBE(instance)

  mem_size = be_full[constants.BE_MAXMEM]

  cpu_count = be_full[constants.BE_VCPUS]

  spindle_use = be_full[constants.BE_SPINDLE_USE]

  disk_count = len(instance.disks)

  disk_sizes = [disk.size for disk in instance.disks]

  nic_count = len(instance.nics)

  disk_template = instance.disk_template

  return _compute_fn(ipolicy, mem_size, cpu_count, disk_count, nic_count,

                     disk_sizes, spindle_use, disk_template)

def _ComputeViolatingInstances(ipolicy, instances, cfg):

  """Computes a set of instances who violates given ipolicy.

  @param ipolicy: The ipolicy to verify

  @type instances: L{objects.Instance}

  @param instances: List of instances to verify

  @type cfg: L{config.ConfigWriter}

  @param cfg: Cluster configuration

  @return: A frozenset of instance names violating the ipolicy

  """

  return frozenset([inst.name for inst in instances

                    if ComputeIPolicyInstanceViolation(ipolicy, inst, cfg)])

def ComputeNewInstanceViolations(old_ipolicy, new_ipolicy, instances, cfg):

  """Computes a set of any instances that would violate the new ipolicy.

  @param old_ipolicy: The current (still in-place) ipolicy

  @param new_ipolicy: The new (to become) ipolicy

  @param instances: List of instances to verify

  @type cfg: L{config.ConfigWriter}

  @param cfg: Cluster configuration

  @return: A list of instances which violates the new ipolicy but

      did not before

  """

  return (_ComputeViolatingInstances(new_ipolicy, instances, cfg) -

          _ComputeViolatingInstances(old_ipolicy, instances, cfg))

def GetUpdatedParams(old_params, update_dict,

                      use_default=True, use_none=False):

  """Return the new version of a parameter dictionary.

  @type old_params: dict

  @param old_params: old parameters

  @type update_dict: dict

  @param update_dict: dict containing new parameter values, or

      constants.VALUE_DEFAULT to reset the parameter to its default

      value

  @param use_default: boolean

  @type use_default: whether to recognise L{constants.VALUE_DEFAULT}

      values as 'to be deleted' values

  @param use_none: boolean

  @type use_none: whether to recognise C{None} values as 'to be

      deleted' values

  @rtype: dict

  @return: the new parameter dictionary

  """

  params_copy = copy.deepcopy(old_params)

  for key, val in update_dict.iteritems():

    if ((use_default and val == constants.VALUE_DEFAULT) or

          (use_none and val is None)):

      try:

        del params_copy[key]

      except KeyError:

        pass

    else:

      params_copy[key] = val

  return params_copy

def GetUpdatedIPolicy(old_ipolicy, new_ipolicy, group_policy=False):

  """Return the new version of an instance policy.

  @param group_policy: whether this policy applies to a group and thus

    we should support removal of policy entries

  """

  ipolicy = copy.deepcopy(old_ipolicy)

  for key, value in new_ipolicy.items():

    if key not in constants.IPOLICY_ALL_KEYS:

      raise errors.OpPrereqError("Invalid key in new ipolicy: %s" % key,

                                 errors.ECODE_INVAL)

    if (not value or value == [constants.VALUE_DEFAULT] or

            value == constants.VALUE_DEFAULT):

      if group_policy:

        if key in ipolicy:

          del ipolicy[key]

      else:

        raise errors.OpPrereqError("Can't unset ipolicy attribute '%s'"

                                   " on the cluster'" % key,

                                   errors.ECODE_INVAL)

    else:

      if key in constants.IPOLICY_PARAMETERS:

        # FIXME: we assume all such values are float

        try:

          ipolicy[key] = float(value)

        except (TypeError, ValueError), err:

          raise errors.OpPrereqError("Invalid value for attribute"

                                     " '%s': '%s', error: %s" %

                                     (key, value, err), errors.ECODE_INVAL)

      elif key == constants.ISPECS_MINMAX:

        for minmax in value:

          for k in minmax.keys():

            utils.ForceDictType(minmax[k], constants.ISPECS_PARAMETER_TYPES)

        ipolicy[key] = value

      elif key == constants.ISPECS_STD:

        if group_policy:

          msg = "%s cannot appear in group instance specs" % key

          raise errors.OpPrereqError(msg, errors.ECODE_INVAL)

        ipolicy[key] = GetUpdatedParams(old_ipolicy.get(key, {}), value,

                                        use_none=False, use_default=False)

        utils.ForceDictType(ipolicy[key], constants.ISPECS_PARAMETER_TYPES)

      else:

        # FIXME: we assume all others are lists; this should be redone

        # in a nicer way

        ipolicy[key] = list(value)

  try:

    objects.InstancePolicy.CheckParameterSyntax(ipolicy, not group_policy)

  except errors.ConfigurationError, err:

    raise errors.OpPrereqError("Invalid instance policy: %s" % err,

                               errors.ECODE_INVAL)

  return ipolicy

def AnnotateDiskParams(instance, devs, cfg):

  """Little helper wrapper to the rpc annotation method.

  @param instance: The instance object

  @type devs: List of L{objects.Disk}

  @param devs: The root devices (not any of its children!)

  @param cfg: The config object

  @returns The annotated disk copies

  @see L{rpc.AnnotateDiskParams}

  """

  return rpc.AnnotateDiskParams(instance.disk_template, devs,

                                cfg.GetInstanceDiskParams(instance))

def SupportsOob(cfg, node):

  """Tells if node supports OOB.

  @type cfg: L{config.ConfigWriter}

  @param cfg: The cluster configuration

  @type node: L{objects.Node}

  @param node: The node

  @return: The OOB script if supported or an empty string otherwise

  """

  return cfg.GetNdParams(node)[constants.ND_OOB_PROGRAM]

def _UpdateAndVerifySubDict(base, updates, type_check):

  """Updates and verifies a dict with sub dicts of the same type.

  @param base: The dict with the old data

  @param updates: The dict with the new data

  @param type_check: Dict suitable to ForceDictType to verify correct types

  @returns: A new dict with updated and verified values

  """

  def fn(old, value):

    new = GetUpdatedParams(old, value)

    utils.ForceDictType(new, type_check)

    return new

  ret = copy.deepcopy(base)

  ret.update(dict((key, fn(base.get(key, {}), value))

                  for key, value in updates.items()))

  return ret

def _FilterVmNodes(lu, nodenames):

  """Filters out non-vm_capable nodes from a list.

  @type lu: L{LogicalUnit}

  @param lu: the logical unit for which we check

  @type nodenames: list

  @param nodenames: the list of nodes on which we should check

  @rtype: list

  @return: the list of vm-capable nodes

  """

  vm_nodes = frozenset(lu.cfg.GetNonVmCapableNodeList())

  return [name for name in nodenames if name not in vm_nodes]

def GetDefaultIAllocator(cfg, ialloc):

  """Decides on which iallocator to use.

  @type cfg: L{config.ConfigWriter}

  @param cfg: Cluster configuration object

  @type ialloc: string or None

  @param ialloc: Iallocator specified in opcode

  @rtype: string

  @return: Iallocator name

  """

  if not ialloc:

    # Use default iallocator

    ialloc = cfg.GetDefaultIAllocator()

  if not ialloc:

    raise errors.OpPrereqError("No iallocator was specified, neither in the"

                               " opcode nor as a cluster-wide default",

                               errors.ECODE_INVAL)

  return ialloc

def CheckInstancesNodeGroups(cfg, instances, owned_groups, owned_nodes,

                             cur_group_uuid):

  """Checks if node groups for locked instances are still correct.