@wsgi.action('os-migrateLive')
  def _migrate_live(self, req, id, body):
    """Permit admins to (live) migrate a server to a new host."""
    context = req.environ["nova.context"]
    authorize(context, 'migrateLive')

    try:
      block_migration = body["os-migrateLive"]["block_migration"]
      disk_over_commit = body["os-migrateLive"]["disk_over_commit"]
      host = body["os-migrateLive"]["host"]
    except (TypeError, KeyError):
      msg = _("host, block_migration and disk_over_commit must "
          "be specified for live migration.")
      raise exc.HTTPBadRequest(explanation=msg)

    try:
      block_migration = strutils.bool_from_string(block_migration,
                            strict=True)
      disk_over_commit = strutils.bool_from_string(disk_over_commit,
                             strict=True)
    except ValueError as err:
      raise exc.HTTPBadRequest(explanation=str(err))

    try:
      instance = self.compute_api.get(context, id, want_objects=True)
      self.compute_api.live_migrate(context, instance, block_migration,
                     disk_over_commit, host)
    except (exception.ComputeServiceUnavailable,
        exception.InvalidHypervisorType,
        exception.UnableToMigrateToSelf,
        exception.DestinationHypervisorTooOld,
        exception.NoValidHost,
        exception.InvalidLocalStorage,
        exception.InvalidSharedStorage,
        exception.MigrationPreCheckError) as ex:
      raise exc.HTTPBadRequest(explanation=ex.format_message())
    except exception.InstanceNotFound as e:
      raise exc.HTTPNotFound(explanation=e.format_message())
    except exception.InstanceInvalidState as state_error:
      common.raise_http_conflict_for_instance_invalid_state(state_error,
          'os-migrateLive')
    except Exception:
      if host is None:
        msg = _("Live migration of instance %s to another host "
            "failed") % id
      else:
        msg = _("Live migration of instance %(id)s to host %(host)s "
            "failed") % {'id': id, 'host': host}
      LOG.exception(msg)
      # Return messages from scheduler
      raise exc.HTTPBadRequest(explanation=msg)

    return webob.Response(status_int=202)

 {
  "os-migrateLive": {
    "host": "0443e9a1254044d8b99f35eace132080",
    "block_migration": false,
    "disk_over_commit": false
  }
}

self.compute_api.live_migrate(context, instance, block_migration,
                 disk_over_commit, host)

@check_instance_cell
  @check_instance_state(vm_state=[vm_states.ACTIVE])
  def live_migrate(self, context, instance, block_migration,
           disk_over_commit, host_name):
    """Migrate a server lively to a new host."""
    LOG.debug(_("Going to try to live migrate instance to %s"),
         host_name or "another host", instance=instance)

    instance.task_state = task_states.MIGRATING
    instance.save(expected_task_state=[None])

    self.compute_task_api.live_migrate_instance(context, instance,
        host_name, block_migration=block_migration,
        disk_over_commit=disk_over_commit)

def live_migrate_instance(self, context, instance, host_name,
                block_migration, disk_over_commit):
     scheduler_hint = {'host': host_name}
     self._manager.migrate_server(
       context, instance, scheduler_hint, True, False, None,
       block_migration, disk_over_commit, None)

def migrate_server(self, context, instance, scheduler_hint, live, rebuild,
      flavor, block_migration, disk_over_commit, reservations=None):
    if instance and not isinstance(instance, instance_obj.Instance):
      # NOTE(danms): Until v2 of the RPC API, we need to tolerate
      # old-world instance objects here
      attrs = ['metadata', 'system_metadata', 'info_cache',
           'security_groups']
      instance = instance_obj.Instance._from_db_object(
        context, instance_obj.Instance(), instance,
        expected_attrs=attrs)
    if live and not rebuild and not flavor:
      self._live_migrate(context, instance, scheduler_hint,
                block_migration, disk_over_commit)
    elif not live and not rebuild and flavor:
      instance_uuid = instance['uuid']
      with compute_utils.EventReporter(context, self.db,
                     'cold_migrate', instance_uuid):
        self._cold_migrate(context, instance, flavor,
                  scheduler_hint['filter_properties'],
                  reservations)
    else:
      raise NotImplementedError()

self._manager.migrate_server(
       context, instance, scheduler_hint, True, False, None,
       block_migration, disk_over_commit, None)

 if live and not rebuild and not flavor:
       self._live_migrate(context, instance, scheduler_hint,
                block_migration, disk_over_commit) 
　_live_migrate代碼如下：
def _live_migrate(self, context, instance, scheduler_hint,
           block_migration, disk_over_commit):
    destination = scheduler_hint.get("host")
    try:
      live_migrate.execute(context, instance, destination,
               block_migration, disk_over_commit)
    except (exception.NoValidHost,
        exception.ComputeServiceUnavailable,
        exception.InvalidHypervisorType,
        exception.InvalidCPUInfo,
        exception.UnableToMigrateToSelf,
        exception.DestinationHypervisorTooOld,
        exception.InvalidLocalStorage,
        exception.InvalidSharedStorage,
        exception.HypervisorUnavailable,
        exception.MigrationPreCheckError) as ex:
      with excutils.save_and_reraise_exception():
        #TODO(johngarbutt) - eventually need instance actions here
        request_spec = {'instance_properties': {
          'uuid': instance['uuid'], },
        }
        scheduler_utils.set_vm_state_and_notify(context,
            'compute_task', 'migrate_server',
            dict(vm_state=instance['vm_state'],
               task_state=None,
               expected_task_state=task_states.MIGRATING,),
            ex, request_spec, self.db)
    except Exception as ex:
      LOG.error(_('Migration of instance %(instance_id)s to host'
            ' %(dest)s unexpectedly failed.'),
            {'instance_id': instance['uuid'], 'dest': destination},
            exc_info=True)
      raise exception.MigrationError(reason=ex)

def execute(context, instance, destination,
      block_migration, disk_over_commit):
  task = LiveMigrationTask(context, instance,
               destination,
               block_migration,
               disk_over_commit)
  #TODO(johngarbutt) create a superclass that contains a safe_execute call
  return task.execute()

def execute(self):
    self._check_instance_is_running()
    self._check_host_is_up(self.source)

    if not self.destination:
      self.destination = self._find_destination()
    else:
      self._check_requested_destination()

    #TODO(johngarbutt) need to move complexity out of compute manager
    return self.compute_rpcapi.live_migration(self.context,
        host=self.source,
        instance=self.instance,
        dest=self.destination,
        block_migration=self.block_migration,
        migrate_data=self.migrate_data)
        #TODO(johngarbutt) disk_over_commit?

def live_migration(self, ctxt, instance, dest, block_migration, host,
            migrate_data=None):
    # NOTE(russellb) Havana compat
    version = self._get_compat_version('3.0', '2.0')
    instance_p = jsonutils.to_primitive(instance)
    cctxt = self.client.prepare(server=host, version=version)
    cctxt.cast(ctxt, 'live_migration', instance=instance_p,
          dest=dest, block_migration=block_migration,
          migrate_data=migrate_data)

def live_migration(self, context, instance, dest,
            post_method, recover_method, block_migration=False,
            migrate_data=None):
    """Spawning live_migration operation for distributing high-load.

    :param context: security context
    :param instance:
      nova.db.sqlalchemy.models.Instance object
      instance object that is migrated.
    :param dest: destination host
    :param post_method:
      post operation method.
      expected nova.compute.manager.post_live_migration.
    :param recover_method:
      recovery method when any exception occurs.
      expected nova.compute.manager.recover_live_migration.
    :param block_migration: if true, do block migration.
    :param migrate_data: implementation specific params

    """

    greenthread.spawn(self._live_migration, context, instance, dest,
             post_method, recover_method, block_migration,
             migrate_data)

def _live_migration(self, context, instance, dest, post_method,
            recover_method, block_migration=False,
            migrate_data=None):
    """Do live migration.

    :param context: security context
    :param instance:
      nova.db.sqlalchemy.models.Instance object
      instance object that is migrated.
    :param dest: destination host
    :param post_method:
      post operation method.
      expected nova.compute.manager.post_live_migration.
    :param recover_method:
      recovery method when any exception occurs.
      expected nova.compute.manager.recover_live_migration.
    :param block_migration: if true, do block migration.
    :param migrate_data: implementation specific params
    """

    # Do live migration.
    try:
      if block_migration:
        flaglist = CONF.libvirt.block_migration_flag.split(',')
      else:
        flaglist = CONF.libvirt.live_migration_flag.split(',')
      flagvals = [getattr(libvirt, x.strip()) for x in flaglist]
      logical_sum = reduce(lambda x, y: x | y, flagvals)

      dom = self._lookup_by_name(instance["name"])
      dom.migrateToURI(CONF.libvirt.live_migration_uri % dest,
               logical_sum,
               None,
               CONF.libvirt.live_migration_bandwidth)

    except Exception as e:
      with excutils.save_and_reraise_exception():
        LOG.error(_("Live Migration failure: %s"), e,
             instance=instance)
        recover_method(context, instance, dest, block_migration)

    # Waiting for completion of live_migration.
    timer = loopingcall.FixedIntervalLoopingCall(f=None)

if block_migration:
         flaglist = CONF.libvirt.block_migration_flag.split(',')

else:
         flaglist = CONF.libvirt.live_migration_flag.split(',')
       flagvals = [getattr(libvirt, x.strip()) for x in flaglist]
      logical_sum = reduce(lambda x, y: x | y, flagvals)

 dom = self._lookup_by_name(instance["name"])

 timer = loopingcall.FixedIntervalLoopingCall(f=None)