Synnefo » snf-ganeti

#

#

# Copyright (C) 2006, 2007, 2008, 2009, 2010, 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.

"""Inter-node RPC library.

"""

# pylint: disable=C0103,R0201,R0904

# C0103: Invalid name, since call_ are not valid

# R0201: Method could be a function, we keep all rpcs instance methods

# as not to change them back and forth between static/instance methods

# if they need to start using instance attributes

# R0904: Too many public methods

import os

import logging

import zlib

import base64

import pycurl

import threading

from ganeti import utils

from ganeti import objects

from ganeti import http

from ganeti import serializer

from ganeti import constants

from ganeti import errors

from ganeti import netutils

from ganeti import ssconf

from ganeti import runtime

from ganeti import compat

# Special module generated at build time

from ganeti import _generated_rpc

# pylint has a bug here, doesn't see this import

import ganeti.http.client  # pylint: disable=W0611

# Timeout for connecting to nodes (seconds)

_RPC_CONNECT_TIMEOUT = 5

_RPC_CLIENT_HEADERS = [

  "Content-type: %s" % http.HTTP_APP_JSON,

  "Expect:",

  ]

# Various time constants for the timeout table

_TMO_URGENT = 60 # one minute

_TMO_FAST = 5 * 60 # five minutes

_TMO_NORMAL = 15 * 60 # 15 minutes

_TMO_SLOW = 3600 # one hour

_TMO_4HRS = 4 * 3600

_TMO_1DAY = 86400

# Timeout table that will be built later by decorators

# Guidelines for choosing timeouts:

# - call used during watcher: timeout -> 1min, _TMO_URGENT

# - trivial (but be sure it is trivial) (e.g. reading a file): 5min, _TMO_FAST

# - other calls: 15 min, _TMO_NORMAL

# - special calls (instance add, etc.): either _TMO_SLOW (1h) or huge timeouts

_TIMEOUTS = {

}

#: Special value to describe an offline host

_OFFLINE = object()

def Init():

  """Initializes the module-global HTTP client manager.

  Must be called before using any RPC function and while exactly one thread is

  running.

  """

  # curl_global_init(3) and curl_global_cleanup(3) must be called with only

  # one thread running. This check is just a safety measure -- it doesn't

  # cover all cases.

  assert threading.activeCount() == 1, \

         "Found more than one active thread when initializing pycURL"

  logging.info("Using PycURL %s", pycurl.version)

  pycurl.global_init(pycurl.GLOBAL_ALL)

def Shutdown():

  """Stops the module-global HTTP client manager.

  Must be called before quitting the program and while exactly one thread is

  running.

  """

  pycurl.global_cleanup()

def _ConfigRpcCurl(curl):

  noded_cert = str(constants.NODED_CERT_FILE)

  curl.setopt(pycurl.FOLLOWLOCATION, False)

  curl.setopt(pycurl.CAINFO, noded_cert)

  curl.setopt(pycurl.SSL_VERIFYHOST, 0)

  curl.setopt(pycurl.SSL_VERIFYPEER, True)

  curl.setopt(pycurl.SSLCERTTYPE, "PEM")

  curl.setopt(pycurl.SSLCERT, noded_cert)

  curl.setopt(pycurl.SSLKEYTYPE, "PEM")

  curl.setopt(pycurl.SSLKEY, noded_cert)

  curl.setopt(pycurl.CONNECTTIMEOUT, _RPC_CONNECT_TIMEOUT)

def _RpcTimeout(secs):

  """Timeout decorator.

  When applied to a rpc call_* function, it updates the global timeout

  table with the given function/timeout.

  """

  def decorator(f):

    name = f.__name__

    assert name.startswith("call_")

    _TIMEOUTS[name[len("call_"):]] = secs

    return f

  return decorator

def RunWithRPC(fn):

  """RPC-wrapper decorator.

  When applied to a function, it runs it with the RPC system

  initialized, and it shutsdown the system afterwards. This means the

  function must be called without RPC being initialized.

  """

  def wrapper(*args, **kwargs):

    Init()

    try:

      return fn(*args, **kwargs)

    finally:

      Shutdown()

  return wrapper

def _Compress(data):

  """Compresses a string for transport over RPC.

  Small amounts of data are not compressed.

  @type data: str

  @param data: Data

  @rtype: tuple

  @return: Encoded data to send

  """

  # Small amounts of data are not compressed

  if len(data) < 512:

    return (constants.RPC_ENCODING_NONE, data)

  # Compress with zlib and encode in base64

  return (constants.RPC_ENCODING_ZLIB_BASE64,

          base64.b64encode(zlib.compress(data, 3)))

class RpcResult(object):

  """RPC Result class.

  This class holds an RPC result. It is needed since in multi-node

  calls we can't raise an exception just because one one out of many

  failed, and therefore we use this class to encapsulate the result.

  @ivar data: the data payload, for successful results, or None

  @ivar call: the name of the RPC call

  @ivar node: the name of the node to which we made the call

  @ivar offline: whether the operation failed because the node was

      offline, as opposed to actual failure; offline=True will always

      imply failed=True, in order to allow simpler checking if

      the user doesn't care about the exact failure mode

  @ivar fail_msg: the error message if the call failed

  """

  def __init__(self, data=None, failed=False, offline=False,

               call=None, node=None):

    self.offline = offline

    self.call = call

    self.node = node

    if offline:

      self.fail_msg = "Node is marked offline"

      self.data = self.payload = None

    elif failed:

      self.fail_msg = self._EnsureErr(data)

      self.data = self.payload = None

    else:

      self.data = data

      if not isinstance(self.data, (tuple, list)):

        self.fail_msg = ("RPC layer error: invalid result type (%s)" %

                         type(self.data))

        self.payload = None

      elif len(data) != 2:

        self.fail_msg = ("RPC layer error: invalid result length (%d), "

                         "expected 2" % len(self.data))

        self.payload = None

      elif not self.data[0]:

        self.fail_msg = self._EnsureErr(self.data[1])

        self.payload = None

      else:

        # finally success

        self.fail_msg = None

        self.payload = data[1]

    for attr_name in ["call", "data", "fail_msg",

                      "node", "offline", "payload"]:

      assert hasattr(self, attr_name), "Missing attribute %s" % attr_name

  @staticmethod

  def _EnsureErr(val):

    """Helper to ensure we return a 'True' value for error."""

    if val:

      return val

    else:

      return "No error information"

  def Raise(self, msg, prereq=False, ecode=None):

    """If the result has failed, raise an OpExecError.

    This is used so that LU code doesn't have to check for each

    result, but instead can call this function.

    """

    if not self.fail_msg:

      return

    if not msg: # one could pass None for default message

      msg = ("Call '%s' to node '%s' has failed: %s" %

             (self.call, self.node, self.fail_msg))

    else:

      msg = "%s: %s" % (msg, self.fail_msg)

    if prereq:

      ec = errors.OpPrereqError

    else:

      ec = errors.OpExecError

    if ecode is not None:

      args = (msg, ecode)

    else:

      args = (msg, )

    raise ec(*args) # pylint: disable=W0142

def _SsconfResolver(node_list,

                    ssc=ssconf.SimpleStore,

                    nslookup_fn=netutils.Hostname.GetIP):

  """Return addresses for given node names.

  @type node_list: list

  @param node_list: List of node names

  @type ssc: class

  @param ssc: SimpleStore class that is used to obtain node->ip mappings

  @type nslookup_fn: callable

  @param nslookup_fn: function use to do NS lookup

  @rtype: list of tuple; (string, string)

  @return: List of tuples containing node name and IP address

  """

  ss = ssc()

  iplist = ss.GetNodePrimaryIPList()

  family = ss.GetPrimaryIPFamily()

  ipmap = dict(entry.split() for entry in iplist)

  result = []

  for node in node_list:

    ip = ipmap.get(node)

    if ip is None:

      ip = nslookup_fn(node, family=family)

    result.append((node, ip))

  return result

class _StaticResolver:

  def __init__(self, addresses):

    """Initializes this class.

    """

    self._addresses = addresses

  def __call__(self, hosts):

    """Returns static addresses for hosts.

    """

    assert len(hosts) == len(self._addresses)

    return zip(hosts, self._addresses)

def _CheckConfigNode(name, node):

  """Checks if a node is online.

  @type name: string

  @param name: Node name

  @type node: L{objects.Node} or None

  @param node: Node object

  """

  if node is None:

    # Depend on DNS for name resolution

    ip = name

  elif node.offline:

    ip = _OFFLINE

  else:

    ip = node.primary_ip

  return (name, ip)

def _NodeConfigResolver(single_node_fn, all_nodes_fn, hosts):

  """Calculate node addresses using configuration.

  """

  # Special case for single-host lookups

  if len(hosts) == 1:

    (name, ) = hosts

    return [_CheckConfigNode(name, single_node_fn(name))]

  else:

    all_nodes = all_nodes_fn()

    return [_CheckConfigNode(name, all_nodes.get(name, None))

            for name in hosts]

class _RpcProcessor:

  def __init__(self, resolver, port, lock_monitor_cb=None):

    """Initializes this class.

    @param resolver: callable accepting a list of hostnames, returning a list

      of tuples containing name and IP address (IP address can be the name or

      the special value L{_OFFLINE} to mark offline machines)

    @type port: int

    @param port: TCP port

    @param lock_monitor_cb: Callable for registering with lock monitor

    """

    self._resolver = resolver

    self._port = port

    self._lock_monitor_cb = lock_monitor_cb

  @staticmethod

  def _PrepareRequests(hosts, port, procedure, body, read_timeout):

    """Prepares requests by sorting offline hosts into separate list.

    """

    results = {}

    requests = {}

    for (name, ip) in hosts:

      if ip is _OFFLINE:

        # Node is marked as offline

        results[name] = RpcResult(node=name, offline=True, call=procedure)

      else:

        requests[name] = \

          http.client.HttpClientRequest(str(ip), port,

                                        http.HTTP_PUT, str("/%s" % procedure),

                                        headers=_RPC_CLIENT_HEADERS,

                                        post_data=body,

                                        read_timeout=read_timeout,

                                        nicename="%s/%s" % (name, procedure),

                                        curl_config_fn=_ConfigRpcCurl)

    return (results, requests)

  @staticmethod

  def _CombineResults(results, requests, procedure):

    """Combines pre-computed results for offline hosts with actual call results.

    """

    for name, req in requests.items():

      if req.success and req.resp_status_code == http.HTTP_OK:

        host_result = RpcResult(data=serializer.LoadJson(req.resp_body),

                                node=name, call=procedure)

      else:

        # TODO: Better error reporting

        if req.error:

          msg = req.error

        else:

          msg = req.resp_body

        logging.error("RPC error in %s on node %s: %s", procedure, name, msg)

        host_result = RpcResult(data=msg, failed=True, node=name,

                                call=procedure)

      results[name] = host_result

    return results

  def __call__(self, hosts, procedure, body, read_timeout=None,

               _req_process_fn=http.client.ProcessRequests):

    """Makes an RPC request to a number of nodes.

    @type hosts: sequence

    @param hosts: Hostnames

    @type procedure: string

    @param procedure: Request path

    @type body: string

    @param body: Request body

    @type read_timeout: int or None

    @param read_timeout: Read timeout for request

    """

    if read_timeout is None:

      read_timeout = _TIMEOUTS.get(procedure, None)

    assert read_timeout is not None, \

      "Missing RPC read timeout for procedure '%s'" % procedure

    (results, requests) = \

      self._PrepareRequests(self._resolver(hosts), self._port, procedure,

                            str(body), read_timeout)

    _req_process_fn(requests.values(), lock_monitor_cb=self._lock_monitor_cb)

    assert not frozenset(results).intersection(requests)

    return self._CombineResults(results, requests, procedure)

def _EncodeImportExportIO(ieio, ieioargs):

  """Encodes import/export I/O information.

  """

  if ieio == constants.IEIO_RAW_DISK:

    assert len(ieioargs) == 1

    return (ieioargs[0].ToDict(), )

  if ieio == constants.IEIO_SCRIPT:

    assert len(ieioargs) == 2

    return (ieioargs[0].ToDict(), ieioargs[1])

  return ieioargs

class RpcRunner(_generated_rpc.RpcClientDefault):

  """RPC runner class.

  """

  def __init__(self, context):

    """Initialized the RPC runner.

    @type context: C{masterd.GanetiContext}

    @param context: Ganeti context

    """

    _generated_rpc.RpcClientDefault.__init__(self)

    self._cfg = context.cfg

    self._proc = _RpcProcessor(compat.partial(_NodeConfigResolver,

                                              self._cfg.GetNodeInfo,

                                              self._cfg.GetAllNodesInfo),

                               netutils.GetDaemonPort(constants.NODED),

                               lock_monitor_cb=context.glm.AddToLockMonitor)

  def _InstDict(self, instance, hvp=None, bep=None, osp=None):

    """Convert the given instance to a dict.

    This is done via the instance's ToDict() method and additionally

    we fill the hvparams with the cluster defaults.

    @type instance: L{objects.Instance}

    @param instance: an Instance object

    @type hvp: dict or None

    @param hvp: a dictionary with overridden hypervisor parameters

    @type bep: dict or None

    @param bep: a dictionary with overridden backend parameters

    @type osp: dict or None

    @param osp: a dictionary with overridden os parameters

    @rtype: dict

    @return: the instance dict, with the hvparams filled with the

        cluster defaults

    """

    idict = instance.ToDict()

    cluster = self._cfg.GetClusterInfo()

    idict["hvparams"] = cluster.FillHV(instance)

    if hvp is not None:

      idict["hvparams"].update(hvp)

    idict["beparams"] = cluster.FillBE(instance)

    if bep is not None:

      idict["beparams"].update(bep)

    idict["osparams"] = cluster.SimpleFillOS(instance.os, instance.osparams)

    if osp is not None:

      idict["osparams"].update(osp)

    for nic in idict["nics"]:

      nic['nicparams'] = objects.FillDict(

        cluster.nicparams[constants.PP_DEFAULT],

        nic['nicparams'])

    return idict

  def _MultiNodeCall(self, node_list, procedure, args, read_timeout=None):

    """Helper for making a multi-node call

    """

    body = serializer.DumpJson(args, indent=False)

    return self._proc(node_list, procedure, body, read_timeout=read_timeout)

  def _Call(self, node_list, procedure, timeout, args):

    """Entry point for automatically generated RPC wrappers.

    """

    return self._MultiNodeCall(node_list, procedure, args, read_timeout=timeout)

  @staticmethod

  def _StaticMultiNodeCall(node_list, procedure, args,

                           address_list=None, read_timeout=None):

    """Helper for making a multi-node static call

    """

    body = serializer.DumpJson(args, indent=False)

    if address_list is None:

      resolver = _SsconfResolver

    else:

      # Caller provided an address list

      resolver = _StaticResolver(address_list)

    proc = _RpcProcessor(resolver,

                         netutils.GetDaemonPort(constants.NODED))

    return proc(node_list, procedure, body, read_timeout=read_timeout)

  def _SingleNodeCall(self, node, procedure, args, read_timeout=None):

    """Helper for making a single-node call

    """

    body = serializer.DumpJson(args, indent=False)

    return self._proc([node], procedure, body, read_timeout=read_timeout)[node]

  @classmethod

  def _StaticSingleNodeCall(cls, node, procedure, args, read_timeout=None):

    """Helper for making a single-node static call

    """

    body = serializer.DumpJson(args, indent=False)

    proc = _RpcProcessor(_SsconfResolver,

                         netutils.GetDaemonPort(constants.NODED))

    return proc([node], procedure, body, read_timeout=read_timeout)[node]

  @staticmethod

  def _BlockdevFindPostProc(result):

    if not result.fail_msg and result.payload is not None:

      result.payload = objects.BlockDevStatus.FromDict(result.payload)

    return result

  @staticmethod

  def _BlockdevGetMirrorStatusPostProc(result):

    if not result.fail_msg:

      result.payload = [objects.BlockDevStatus.FromDict(i)

                        for i in result.payload]

    return result

  @staticmethod

  def _BlockdevGetMirrorStatusMultiPostProc(result):

    for nres in result.values():

      if nres.fail_msg:

        continue

      for idx, (success, status) in enumerate(nres.payload):

        if success:

          nres.payload[idx] = (success, objects.BlockDevStatus.FromDict(status))

    return result

  @staticmethod

  def _OsGetPostProc(result):

    if not result.fail_msg and isinstance(result.payload, dict):

      result.payload = objects.OS.FromDict(result.payload)

    return result

  @staticmethod

  def _PrepareFinalizeExportDisks(snap_disks):

    flat_disks = []

    for disk in snap_disks:

      if isinstance(disk, bool):

        flat_disks.append(disk)

      else:

        flat_disks.append(disk.ToDict())

    return flat_disks

  @staticmethod

  def _ImpExpStatusPostProc(result):

    """Post-processor for import/export status.

    @rtype: Payload containing list of L{objects.ImportExportStatus} instances

    @return: Returns a list of the state of each named import/export or None if

             a status couldn't be retrieved

    """

    if not result.fail_msg:

      decoded = []

      for i in result.payload:

        if i is None:

          decoded.append(None)

          continue

        decoded.append(objects.ImportExportStatus.FromDict(i))

      result.payload = decoded

    return result

  #

  # Begin RPC calls

  #

  @_RpcTimeout(_TMO_NORMAL)

  def call_storage_list(self, node_list, su_name, su_args, name, fields):

    """Get list of storage units.

    This is a multi-node call.

    """

    return self._MultiNodeCall(node_list, "storage_list",

                               [su_name, su_args, name, fields])

  @_RpcTimeout(_TMO_NORMAL)

  def call_storage_modify(self, node, su_name, su_args, name, changes):

    """Modify a storage unit.

    This is a single-node call.

    """

    return self._SingleNodeCall(node, "storage_modify",

                                [su_name, su_args, name, changes])

  @_RpcTimeout(_TMO_NORMAL)

  def call_storage_execute(self, node, su_name, su_args, name, op):

    """Executes an operation on a storage unit.

    This is a single-node call.

    """

    return self._SingleNodeCall(node, "storage_execute",

                                [su_name, su_args, name, op])

  @_RpcTimeout(_TMO_NORMAL)

  def call_instance_start(self, node, instance, hvp, bep, startup_paused):

    """Starts an instance.

    This is a single-node call.

    """

    idict = self._InstDict(instance, hvp=hvp, bep=bep)

    return self._SingleNodeCall(node, "instance_start", [idict, startup_paused])

  @_RpcTimeout(_TMO_1DAY)

  def call_instance_os_add(self, node, inst, reinstall, debug, osparams=None):

    """Installs an OS on the given instance.

    This is a single-node call.

    """

    return self._SingleNodeCall(node, "instance_os_add",

                                [self._InstDict(inst, osp=osparams),

                                 reinstall, debug])

  @classmethod

  @_RpcTimeout(_TMO_FAST)

  def call_node_start_master_daemons(cls, node, no_voting):

    """Starts master daemons on a node.

    This is a single-node call.

    """

    return cls._StaticSingleNodeCall(node, "node_start_master_daemons",

                                     [no_voting])

  @classmethod

  @_RpcTimeout(_TMO_FAST)

  def call_node_activate_master_ip(cls, node):

    """Activates master IP on a node.

    This is a single-node call.

    """

    return cls._StaticSingleNodeCall(node, "node_activate_master_ip", [])

  @classmethod

  @_RpcTimeout(_TMO_FAST)

  def call_node_stop_master(cls, node):

    """Deactivates master IP and stops master daemons on a node.

    This is a single-node call.

    """

    return cls._StaticSingleNodeCall(node, "node_stop_master", [])

  @classmethod

  @_RpcTimeout(_TMO_FAST)

  def call_node_deactivate_master_ip(cls, node):

    """Deactivates master IP on a node.

    This is a single-node call.

    """

    return cls._StaticSingleNodeCall(node, "node_deactivate_master_ip", [])

  @classmethod

  @_RpcTimeout(_TMO_FAST)

  def call_node_change_master_netmask(cls, node, netmask):

    """Change master IP netmask.

    This is a single-node call.

    """

    return cls._StaticSingleNodeCall(node, "node_change_master_netmask",

                  [netmask])

  @classmethod

  @_RpcTimeout(_TMO_URGENT)

  def call_master_info(cls, node_list):

    """Query master info.

    This is a multi-node call.

    """

    # TODO: should this method query down nodes?

    return cls._StaticMultiNodeCall(node_list, "master_info", [])

  @classmethod

  @_RpcTimeout(_TMO_URGENT)

  def call_version(cls, node_list):

    """Query node version.

    This is a multi-node call.

    """

    return cls._StaticMultiNodeCall(node_list, "version", [])

  @classmethod

  @_RpcTimeout(_TMO_NORMAL)

  def call_upload_file(cls, node_list, file_name, address_list=None):

    """Upload a file.

    The node will refuse the operation in case the file is not on the

    approved file list.

    This is a multi-node call.

    @type node_list: list

    @param node_list: the list of node names to upload to

    @type file_name: str

    @param file_name: the filename to upload

    @type address_list: list or None

    @keyword address_list: an optional list of node addresses, in order

        to optimize the RPC speed

    """

    file_contents = utils.ReadFile(file_name)

    data = _Compress(file_contents)

    st = os.stat(file_name)

    getents = runtime.GetEnts()

    params = [file_name, data, st.st_mode, getents.LookupUid(st.st_uid),

              getents.LookupGid(st.st_gid), st.st_atime, st.st_mtime]

    return cls._StaticMultiNodeCall(node_list, "upload_file", params,

                                    address_list=address_list)

  @classmethod

  @_RpcTimeout(_TMO_NORMAL)

  def call_write_ssconf_files(cls, node_list, values):

    """Write ssconf files.

    This is a multi-node call.

    """

    return cls._StaticMultiNodeCall(node_list, "write_ssconf_files", [values])

  @classmethod

  @_RpcTimeout(_TMO_NORMAL)

  def call_node_leave_cluster(cls, node, modify_ssh_setup):

    """Requests a node to clean the cluster information it has.

    This will remove the configuration information from the ganeti data

    dir.

    This is a single-node call.

    """

    return cls._StaticSingleNodeCall(node, "node_leave_cluster",

                                     [modify_ssh_setup])

  def call_test_delay(self, node_list, duration, read_timeout=None):

    """Sleep for a fixed time on given node(s).

    This is a multi-node call.

    """

    assert read_timeout is None

    return self.call_test_delay(node_list, duration,

                                read_timeout=int(duration + 5))

  @classmethod

  @_RpcTimeout(_TMO_URGENT)

  def call_jobqueue_update(cls, node_list, address_list, file_name, content):

    """Update job queue.

    This is a multi-node call.

    """

    return cls._StaticMultiNodeCall(node_list, "jobqueue_update",

                                    [file_name, _Compress(content)],

                                    address_list=address_list)

  @classmethod

  @_RpcTimeout(_TMO_NORMAL)

  def call_jobqueue_purge(cls, node):

    """Purge job queue.

    This is a single-node call.

    """

    return cls._StaticSingleNodeCall(node, "jobqueue_purge", [])

  @classmethod

  @_RpcTimeout(_TMO_URGENT)

  def call_jobqueue_rename(cls, node_list, address_list, rename):

    """Rename a job queue file.

    This is a multi-node call.

    """

    return cls._StaticMultiNodeCall(node_list, "jobqueue_rename", rename,

                                    address_list=address_list)

  @_RpcTimeout(_TMO_NORMAL)

  def call_hypervisor_validate_params(self, node_list, hvname, hvparams):

    """Validate the hypervisor params.

    This is a multi-node call.

    @type node_list: list

    @param node_list: the list of nodes to query

    @type hvname: string

    @param hvname: the hypervisor name

    @type hvparams: dict

    @param hvparams: the hypervisor parameters to be validated

    """

    cluster = self._cfg.GetClusterInfo()

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

    return self._MultiNodeCall(node_list, "hypervisor_validate_params",

                               [hvname, hv_full])

  @_RpcTimeout(_TMO_NORMAL)

  def call_import_start(self, node, opts, instance, component,

                        dest, dest_args):

    """Starts a listener for an import.

    This is a single-node call.

    @type node: string

    @param node: Node name

    @type instance: C{objects.Instance}

    @param instance: Instance object

    @type component: string

    @param component: which part of the instance is being imported

    """

    return self._SingleNodeCall(node, "import_start",

                                [opts.ToDict(),

                                 self._InstDict(instance), component, dest,

                                 _EncodeImportExportIO(dest, dest_args)])

  @_RpcTimeout(_TMO_NORMAL)

  def call_export_start(self, node, opts, host, port,

                        instance, component, source, source_args):

    """Starts an export daemon.

    This is a single-node call.

    @type node: string

    @param node: Node name

    @type instance: C{objects.Instance}

    @param instance: Instance object

    @type component: string

    @param component: which part of the instance is being imported

    """

    return self._SingleNodeCall(node, "export_start",

                                [opts.ToDict(), host, port,

                                 self._InstDict(instance),

                                 component, source,

                                 _EncodeImportExportIO(source, source_args)])