manager.py

# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# Copyright 2011 Justin Santa Barbara
# All Rights Reserved.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

"""Handles all processes relating to instances (guest vms).

The :py:class:`ComputeManager` class is a :py:class:`nova.manager.Manager` that
handles RPC calls relating to creating instances.  It is responsible for
building a disk image, launching it via the underlying virtualization driver,
responding to calls to check its state, attaching persistent storage, and
terminating it.

"""

import base64
import contextlib
import functools
import socket
import sys
import time
import traceback
import uuid

import eventlet.event
from eventlet import greenthread
import eventlet.timeout
from oslo.config import cfg
from oslo import messaging
import six

from nova import block_device
from nova.cells import rpcapi as cells_rpcapi
from nova.cloudpipe import pipelib
from nova import compute
from nova.compute import flavors
from nova.compute import power_state
from nova.compute import resource_tracker
from nova.compute import rpcapi as compute_rpcapi
from nova.compute import task_states
from nova.compute import utils as compute_utils
from nova.compute import vm_states
from nova import conductor
from nova import consoleauth
import nova.context
from nova import exception
from nova import hooks
from nova import image
from nova.image import glance
from nova import manager
from nova import network
from nova.network import model as network_model
from nova.network.security_group import openstack_driver
from nova import objects
from nova.objects import base as obj_base
from nova.objects import instance as instance_obj
from nova.objects import quotas as quotas_obj
from nova.openstack.common import excutils
from nova.openstack.common.gettextutils import _
from nova.openstack.common.gettextutils import _LE
from nova.openstack.common.gettextutils import _LI
from nova.openstack.common.gettextutils import _LW
from nova.openstack.common import jsonutils
from nova.openstack.common import log as logging
from nova.openstack.common import periodic_task
from nova.openstack.common import strutils
from nova.openstack.common import timeutils
from nova import paths
from nova import rpc
from nova import safe_utils
from nova.scheduler import rpcapi as scheduler_rpcapi
from nova import utils
from nova.virt import block_device as driver_block_device
from nova.virt import driver
from nova.virt import event as virtevent
from nova.virt import storage_users
from nova.virt import virtapi
from nova import volume
from nova.volume import encryptors


compute_opts = [
    cfg.StrOpt('console_host',
               default=socket.gethostname(),
               help='Console proxy host to use to connect '
                    'to instances on this host.'),
    cfg.StrOpt('default_access_ip_network_name',
               help='Name of network to use to set access IPs for instances'),
    cfg.BoolOpt('defer_iptables_apply',
                default=False,
                help='Whether to batch up the application of IPTables rules'
                     ' during a host restart and apply all at the end of the'
                     ' init phase'),
    cfg.StrOpt('instances_path',
               default=paths.state_path_def('instances'),
               help='Where instances are stored on disk'),
    cfg.BoolOpt('instance_usage_audit',
                default=False,
                help="Generate periodic compute.instance.exists"
                     " notifications"),
    cfg.IntOpt('live_migration_retry_count',
               default=30,
               help="Number of 1 second retries needed in live_migration"),
    cfg.BoolOpt('resume_guests_state_on_host_boot',
                default=False,
                help='Whether to start guests that were running before the '
                     'host rebooted'),
    cfg.IntOpt('network_allocate_retries',
               default=0,
               help="Number of times to retry network allocation on failures"),
    cfg.IntOpt('block_device_allocate_retries',
               default=60,
               help='Number of times to retry block device'
                    ' allocation on failures')
    ]

interval_opts = [
    cfg.IntOpt('bandwidth_poll_interval',
               default=600,
               help='Interval to pull network bandwidth usage info. Not '
                    'supported on all hypervisors. Set to -1 to disable. '
                    'Setting this to 0 will disable, but this will change in '
                    'the K release to mean "run at the default rate".'),
    # TODO(gilliard): Clean the above message after the K release
    cfg.IntOpt('sync_power_state_interval',
               default=600,
               help='Interval to sync power states between the database and '
                    'the hypervisor. Set to -1 to disable. '
                    'Setting this to 0 will disable, but this will change in '
                    'Juno to mean "run at the default rate".'),
    # TODO(gilliard): Clean the above message after the K release
    cfg.IntOpt("heal_instance_info_cache_interval",
               default=60,
               help="Number of seconds between instance info_cache self "
                    "healing updates"),
    cfg.IntOpt('reclaim_instance_interval',
               default=0,
               help='Interval in seconds for reclaiming deleted instances'),
    cfg.IntOpt('volume_usage_poll_interval',
               default=0,
               help='Interval in seconds for gathering volume usages'),
    cfg.IntOpt('shelved_poll_interval',
               default=3600,
               help='Interval in seconds for polling shelved instances to '
                    'offload. Set to -1 to disable.'
                    'Setting this to 0 will disable, but this will change in '
                    'Juno to mean "run at the default rate".'),
    # TODO(gilliard): Clean the above message after the K release
    cfg.IntOpt('shelved_offload_time',
               default=0,
               help='Time in seconds before a shelved instance is eligible '
                    'for removing from a host.  -1 never offload, 0 offload '
                    'when shelved'),
    cfg.IntOpt('instance_delete_interval',
               default=300,
               help=('Interval in seconds for retrying failed instance file '
                     'deletes')),
    cfg.IntOpt('block_device_allocate_retries_interval',
               default=3,
               help='Waiting time interval (seconds) between block'
                    ' device allocation retries on failures')
]

timeout_opts = [
    cfg.IntOpt("reboot_timeout",
               default=0,
               help="Automatically hard reboot an instance if it has been "
                    "stuck in a rebooting state longer than N seconds. "
                    "Set to 0 to disable."),
    cfg.IntOpt("instance_build_timeout",
               default=0,
               help="Amount of time in seconds an instance can be in BUILD "
                    "before going into ERROR status."
                    "Set to 0 to disable."),
    cfg.IntOpt("rescue_timeout",
               default=0,
               help="Automatically unrescue an instance after N seconds. "
                    "Set to 0 to disable."),
    cfg.IntOpt("resize_confirm_window",
               default=0,
               help="Automatically confirm resizes after N seconds. "
                    "Set to 0 to disable."),
]

running_deleted_opts = [
    cfg.StrOpt("running_deleted_instance_action",
               default="reap",
               help="Action to take if a running deleted instance is detected."
                    "Valid options are 'noop', 'log', 'shutdown', or 'reap'. "
                    "Set to 'noop' to take no action."),
    cfg.IntOpt("running_deleted_instance_poll_interval",
               default=1800,
               help="Number of seconds to wait between runs of the cleanup "
                    "task."),
    cfg.IntOpt("running_deleted_instance_timeout",
               default=0,
               help="Number of seconds after being deleted when a running "
                    "instance should be considered eligible for cleanup."),
]

instance_cleaning_opts = [
    cfg.IntOpt('maximum_instance_delete_attempts',
               default=5,
               help=('The number of times to attempt to reap an instance\'s '
                     'files.')),
]

CONF = cfg.CONF
CONF.register_opts(compute_opts)
CONF.register_opts(interval_opts)
CONF.register_opts(timeout_opts)
CONF.register_opts(running_deleted_opts)
CONF.register_opts(instance_cleaning_opts)
CONF.import_opt('allow_resize_to_same_host', 'nova.compute.api')
CONF.import_opt('console_topic', 'nova.console.rpcapi')
CONF.import_opt('host', 'nova.netconf')
CONF.import_opt('my_ip', 'nova.netconf')
CONF.import_opt('vnc_enabled', 'nova.vnc')
CONF.import_opt('enabled', 'nova.spice', group='spice')
CONF.import_opt('enable', 'nova.cells.opts', group='cells')
CONF.import_opt('image_cache_subdirectory_name', 'nova.virt.imagecache')
CONF.import_opt('image_cache_manager_interval', 'nova.virt.imagecache')
CONF.import_opt('enabled', 'nova.rdp', group='rdp')
CONF.import_opt('html5_proxy_base_url', 'nova.rdp', group='rdp')

LOG = logging.getLogger(__name__)

get_notifier = functools.partial(rpc.get_notifier, service='compute')
wrap_exception = functools.partial(exception.wrap_exception,
                                   get_notifier=get_notifier)


@utils.expects_func_args('migration')
def errors_out_migration(function):
    """Decorator to error out migration on failure."""

    @functools.wraps(function)
    def decorated_function(self, context, *args, **kwargs):
        try:
            return function(self, context, *args, **kwargs)
        except Exception:
            with excutils.save_and_reraise_exception():
                migration = kwargs['migration']
                status = migration.status
                if status not in ['migrating', 'post-migrating']:
                    return
                migration.status = 'error'
                try:
                    migration.save(context.elevated())
                except Exception:
                    LOG.debug('Error setting migration status '
                              'for instance %s.',
                              migration.instance_uuid, exc_info=True)

    return decorated_function


@utils.expects_func_args('instance')
def reverts_task_state(function):
    """Decorator to revert task_state on failure."""

    @functools.wraps(function)
    def decorated_function(self, context, *args, **kwargs):
        try:
            return function(self, context, *args, **kwargs)
        except exception.UnexpectedTaskStateError as e:
            # Note(maoy): unexpected task state means the current
            # task is preempted. Do not clear task state in this
            # case.
            with excutils.save_and_reraise_exception():
                LOG.info(_("Task possibly preempted: %s") % e.format_message())
        except Exception:
            with excutils.save_and_reraise_exception():
                try:
                    self._instance_update(context,
                                          kwargs['instance']['uuid'],
                                          task_state=None)
                except Exception:
                    pass

    return decorated_function


@utils.expects_func_args('instance')
def wrap_instance_fault(function):
    """Wraps a method to catch exceptions related to instances.

    This decorator wraps a method to catch any exceptions having to do with
    an instance that may get thrown. It then logs an instance fault in the db.
    """

    @functools.wraps(function)
    def decorated_function(self, context, *args, **kwargs):
        try:
            return function(self, context, *args, **kwargs)
        except exception.InstanceNotFound:
            raise
        except Exception as e:
            # NOTE(gtt): If argument 'instance' is in args rather than kwargs,
            # we will get a KeyError exception which will cover up the real
            # exception. So, we update kwargs with the values from args first.
            # then, we can get 'instance' from kwargs easily.
            kwargs.update(dict(zip(function.func_code.co_varnames[2:], args)))

            with excutils.save_and_reraise_exception():
                compute_utils.add_instance_fault_from_exc(context,
                        kwargs['instance'], e, sys.exc_info())

    return decorated_function


@utils.expects_func_args('instance')
def wrap_instance_event(function):
    """Wraps a method to log the event taken on the instance, and result.

    This decorator wraps a method to log the start and result of an event, as
    part of an action taken on an instance.
    """

    @functools.wraps(function)
    def decorated_function(self, context, *args, **kwargs):
        wrapped_func = utils.get_wrapped_function(function)
        keyed_args = safe_utils.getcallargs(wrapped_func, context, *args,
                                       **kwargs)
        instance_uuid = keyed_args['instance']['uuid']

        event_name = 'compute_{0}'.format(function.func_name)
        with compute_utils.EventReporter(context, event_name, instance_uuid):
            return function(self, context, *args, **kwargs)

    return decorated_function


@utils.expects_func_args('image_id', 'instance')
def delete_image_on_error(function):
    """Used for snapshot related method to ensure the image created in
    compute.api is deleted when an error occurs.
    """

    @functools.wraps(function)
    def decorated_function(self, context, image_id, instance,
                           *args, **kwargs):
        try:
            return function(self, context, image_id, instance,
                            *args, **kwargs)
        except Exception:
            with excutils.save_and_reraise_exception():
                LOG.debug("Cleaning up image %s", image_id,
                          exc_info=True, instance=instance)
                try:
                    self.image_api.delete(context, image_id)
                except Exception:
                    LOG.exception(_("Error while trying to clean up image %s")
                                  % image_id, instance=instance)

    return decorated_function


# TODO(danms): Remove me after Icehouse
# NOTE(mikal): if the method being decorated has more than one decorator, then
# put this one first. Otherwise the various exception handling decorators do
# not function correctly.
def object_compat(function):
    """Wraps a method that expects a new-world instance

    This provides compatibility for callers passing old-style dict
    instances.
    """

    @functools.wraps(function)
    def decorated_function(self, context, *args, **kwargs):
        def _load_instance(instance_or_dict):
            if isinstance(instance_or_dict, dict):
                instance = objects.Instance._from_db_object(
                    context, objects.Instance(), instance_or_dict,
                    expected_attrs=metas)
                instance._context = context
                return instance
            return instance_or_dict

        metas = ['metadata', 'system_metadata']
        try:
            kwargs['instance'] = _load_instance(kwargs['instance'])
        except KeyError:
            args = (_load_instance(args[0]),) + args[1:]

        migration = kwargs.get('migration')
        if isinstance(migration, dict):
            migration = objects.Migration._from_db_object(
                    context.elevated(), objects.Migration(),
                    migration)
            kwargs['migration'] = migration

        return function(self, context, *args, **kwargs)

    return decorated_function


# TODO(danms): Remove me after Icehouse
def aggregate_object_compat(function):
    """Wraps a method that expects a new-world aggregate."""

    @functools.wraps(function)
    def decorated_function(self, context, *args, **kwargs):
        aggregate = kwargs.get('aggregate')
        if isinstance(aggregate, dict):
            aggregate = objects.Aggregate._from_db_object(
                context.elevated(), objects.Aggregate(),
                aggregate)
            kwargs['aggregate'] = aggregate
        return function(self, context, *args, **kwargs)
    return decorated_function


class InstanceEvents(object):
    def __init__(self):
        self._events = {}

    @staticmethod
    def _lock_name(instance):
        return '%s-%s' % (instance.uuid, 'events')

    def prepare_for_instance_event(self, instance, event_name):
        """Prepare to receive an event for an instance.

        This will register an event for the given instance that we will
        wait on later. This should be called before initiating whatever
        action will trigger the event. The resulting eventlet.event.Event
        object should be wait()'d on to ensure completion.

        :param instance: the instance for which the event will be generated
        :param event_name: the name of the event we're expecting
        :returns: an event object that should be wait()'d on
        """
        @utils.synchronized(self._lock_name(instance))
        def _create_or_get_event():
            if instance.uuid not in self._events:
                self._events.setdefault(instance.uuid, {})
            return self._events[instance.uuid].setdefault(
                event_name, eventlet.event.Event())
        LOG.debug('Preparing to wait for external event %(event)s',
                  {'event': event_name}, instance=instance)
        return _create_or_get_event()

    def pop_instance_event(self, instance, event):
        """Remove a pending event from the wait list.

        This will remove a pending event from the wait list so that it
        can be used to signal the waiters to wake up.

        :param instance: the instance for which the event was generated
        :param event: the nova.objects.external_event.InstanceExternalEvent
                      that describes the event
        :returns: the eventlet.event.Event object on which the waiters
                  are blocked
        """
        @utils.synchronized(self._lock_name(instance))
        def _pop_event():
            events = self._events.get(instance.uuid)
            if not events:
                return None
            _event = events.pop(event.key, None)
            if not events:
                del self._events[instance.uuid]
            return _event
        return _pop_event()

    def clear_events_for_instance(self, instance):
        """Remove all pending events for an instance.

        This will remove all events currently pending for an instance
        and return them (indexed by event name).

        :param instance: the instance for which events should be purged
        :returns: a dictionary of {event_name: eventlet.event.Event}
        """
        @utils.synchronized(self._lock_name(instance))
        def _clear_events():
            # NOTE(danms): Use getitem syntax for the instance until
            # all the callers are using objects
            return self._events.pop(instance['uuid'], {})
        return _clear_events()


class ComputeVirtAPI(virtapi.VirtAPI):
    def __init__(self, compute):
        super(ComputeVirtAPI, self).__init__()
        self._compute = compute

    def provider_fw_rule_get_all(self, context):
        return self._compute.conductor_api.provider_fw_rule_get_all(context)

    def _default_error_callback(self, event_name, instance):
        raise exception.NovaException(_('Instance event failed'))

    @contextlib.contextmanager
    def wait_for_instance_event(self, instance, event_names, deadline=300,
                                error_callback=None):
        """Plan to wait for some events, run some code, then wait.

        This context manager will first create plans to wait for the
        provided event_names, yield, and then wait for all the scheduled
        events to complete.

        Note that this uses an eventlet.timeout.Timeout to bound the
        operation, so callers should be prepared to catch that
        failure and handle that situation appropriately.

        If the event is not received by the specified timeout deadline,
        eventlet.timeout.Timeout is raised.

        If the event is received but did not have a 'completed'
        status, a NovaException is raised.  If an error_callback is
        provided, instead of raising an exception as detailed above
        for the failure case, the callback will be called with the
        event_name and instance, and can return True to continue
        waiting for the rest of the events, False to stop processing,
        or raise an exception which will bubble up to the waiter.

        :param:instance: The instance for which an event is expected
        :param:event_names: A list of event names. Each element can be a
                            string event name or tuple of strings to
                            indicate (name, tag).
        :param:deadline: Maximum number of seconds we should wait for all
                         of the specified events to arrive.
        :param:error_callback: A function to be called if an event arrives
        """

        if error_callback is None:
            error_callback = self._default_error_callback
        events = {}
        for event_name in event_names:
            if isinstance(event_name, tuple):
                name, tag = event_name
                event_name = objects.InstanceExternalEvent.make_key(
                    name, tag)
            events[event_name] = (
                self._compute.instance_events.prepare_for_instance_event(
                    instance, event_name))
        yield
        with eventlet.timeout.Timeout(deadline):
            for event_name, event in events.items():
                actual_event = event.wait()
                if actual_event.status == 'completed':
                    continue
                decision = error_callback(event_name, instance)
                if decision is False:
                    break


class ComputeManager(manager.Manager):
    """Manages the running instances from creation to destruction."""

    target = messaging.Target(version='3.32')

    def __init__(self, compute_driver=None, *args, **kwargs):
        """Load configuration options and connect to the hypervisor."""
        self.virtapi = ComputeVirtAPI(self)
        self.network_api = network.API()
        self.volume_api = volume.API()
        self.image_api = image.API()
        self._last_host_check = 0
        self._last_bw_usage_poll = 0
        self._bw_usage_supported = True
        self._last_bw_usage_cell_update = 0
        self.compute_api = compute.API()
        self.compute_rpcapi = compute_rpcapi.ComputeAPI()
        self.conductor_api = conductor.API()
        self.compute_task_api = conductor.ComputeTaskAPI()
        self.is_neutron_security_groups = (
            openstack_driver.is_neutron_security_groups())
        self.consoleauth_rpcapi = consoleauth.rpcapi.ConsoleAuthAPI()
        self.cells_rpcapi = cells_rpcapi.CellsAPI()
        self.scheduler_rpcapi = scheduler_rpcapi.SchedulerAPI()
        self._resource_tracker_dict = {}
        self.instance_events = InstanceEvents()

        super(ComputeManager, self).__init__(service_name="compute",
                                             *args, **kwargs)

        # NOTE(russellb) Load the driver last.  It may call back into the
        # compute manager via the virtapi, so we want it to be fully
        # initialized before that happens.
        self.driver = driver.load_compute_driver(self.virtapi, compute_driver)
        self.use_legacy_block_device_info = \
                            self.driver.need_legacy_block_device_info

    def _get_resource_tracker(self, nodename):
        rt = self._resource_tracker_dict.get(nodename)
        if not rt:
            if not self.driver.node_is_available(nodename):
                raise exception.NovaException(
                        _("%s is not a valid node managed by this "
                          "compute host.") % nodename)

            rt = resource_tracker.ResourceTracker(self.host,
                                                  self.driver,
                                                  nodename)
            self._resource_tracker_dict[nodename] = rt
        return rt

    def _update_resource_tracker(self, context, instance):
        """Let the resource tracker know that an instance has changed state."""

        if (instance['host'] == self.host and
                self.driver.node_is_available(instance['node'])):
            rt = self._get_resource_tracker(instance.get('node'))
            rt.update_usage(context, instance)

    def _instance_update(self, context, instance_uuid, **kwargs):
        """Update an instance in the database using kwargs as value."""

        instance_ref = self.conductor_api.instance_update(context,
                                                          instance_uuid,
                                                          **kwargs)
        self._update_resource_tracker(context, instance_ref)
        return instance_ref

    def _set_instance_error_state(self, context, instance):
        instance_uuid = instance['uuid']
        try:
            self._instance_update(context, instance_uuid,
                                  vm_state=vm_states.ERROR)
        except exception.InstanceNotFound:
            LOG.debug('Instance has been destroyed from under us while '
                      'trying to set it to ERROR',
                      instance_uuid=instance_uuid)

    def _set_instance_obj_error_state(self, context, instance):
        try:
            instance.vm_state = vm_states.ERROR
            instance.save()
        except exception.InstanceNotFound:
            LOG.debug('Instance has been destroyed from under us while '
                      'trying to set it to ERROR', instance=instance)

    def _get_instances_on_driver(self, context, filters=None):
        """Return a list of instance records for the instances found
        on the hypervisor which satisfy the specified filters. If filters=None
        return a list of instance records for all the instances found on the
        hypervisor.
        """
        if not filters:
            filters = {}
        try:
            driver_uuids = self.driver.list_instance_uuids()
            filters['uuid'] = driver_uuids
            local_instances = objects.InstanceList.get_by_filters(
                context, filters, use_slave=True)
            return local_instances
        except NotImplementedError:
            pass

        # The driver doesn't support uuids listing, so we'll have
        # to brute force.
        driver_instances = self.driver.list_instances()
        instances = objects.InstanceList.get_by_filters(context, filters,
                                                        use_slave=True)
        name_map = dict((instance.name, instance) for instance in instances)
        local_instances = []
        for driver_instance in driver_instances:
            instance = name_map.get(driver_instance)
            if not instance:
                continue
            local_instances.append(instance)
        return local_instances

    def _destroy_evacuated_instances(self, context):
        """Destroys evacuated instances.

        While nova-compute was down, the instances running on it could be
        evacuated to another host. Check that the instances reported
        by the driver are still associated with this host.  If they are
        not, destroy them, with the exception of instances which are in
        the MIGRATING state.
        """
        our_host = self.host
        filters = {'deleted': False}
        local_instances = self._get_instances_on_driver(context, filters)
        for instance in local_instances:
            if instance.host != our_host:
                if instance.task_state in [task_states.MIGRATING]:
                    LOG.debug('Will not delete instance as its host ('
                              '%(instance_host)s) is not equal to our '
                              'host (%(our_host)s) but its state is '
                              '(%(task_state)s)',
                              {'instance_host': instance.host,
                               'our_host': our_host,
                               'task_state': instance.task_state},
                              instance=instance)
                    continue
                LOG.info(_('Deleting instance as its host ('
                           '%(instance_host)s) is not equal to our '
                           'host (%(our_host)s).'),
                         {'instance_host': instance.host,
                          'our_host': our_host}, instance=instance)
                try:
                    network_info = self._get_instance_nw_info(context,
                                                              instance)
                    bdi = self._get_instance_block_device_info(context,
                                                               instance)
                    destroy_disks = not (self._is_instance_storage_shared(
                                                            context, instance))
                except exception.InstanceNotFound:
                    network_info = network_model.NetworkInfo()
                    bdi = {}
                    LOG.info(_('Instance has been marked deleted already, '
                               'removing it from the hypervisor.'),
                             instance=instance)
                    # always destroy disks if the instance was deleted
                    destroy_disks = True
                self.driver.destroy(context, instance,
                                    network_info,
                                    bdi, destroy_disks)

    def _is_instance_storage_shared(self, context, instance):
        shared_storage = True
        data = None
        try:
            data = self.driver.check_instance_shared_storage_local(context,
                                                       instance)
            if data:
                shared_storage = (self.compute_rpcapi.
                                  check_instance_shared_storage(context,
                                  instance, data))
        except NotImplementedError:
            LOG.warning(_('Hypervisor driver does not support '
                          'instance shared storage check, '
                          'assuming it\'s not on shared storage'),
                        instance=instance)
            shared_storage = False
        except Exception:
            LOG.exception(_('Failed to check if instance shared'),
                      instance=instance)
        finally:
            if data:
                self.driver.check_instance_shared_storage_cleanup(context,
                                                                  data)
        return shared_storage

    def _complete_partial_deletion(self, context, instance):
        """Complete deletion for instances in DELETED status but not marked as
        deleted in the DB
        """
        instance.destroy()
        bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                context, instance.uuid)
        quotas = objects.Quotas(context)
        project_id, user_id = quotas_obj.ids_from_instance(context, instance)
        quotas.reserve(context, project_id=project_id, user_id=user_id,
                       instances=-1, cores=-instance.vcpus,
                       ram=-instance.memory_mb)
        self._complete_deletion(context,
                                instance,
                                bdms,
                                quotas,
                                instance.system_metadata)

    def _complete_deletion(self, context, instance, bdms,
                           quotas, system_meta):
        if quotas:
            quotas.commit()

        # ensure block device mappings are not leaked
        for bdm in bdms:
            bdm.destroy()

        self._notify_about_instance_usage(context, instance, "delete.end",
                system_metadata=system_meta)

        if CONF.vnc_enabled or CONF.spice.enabled:
            if CONF.cells.enable:
                self.cells_rpcapi.consoleauth_delete_tokens(context,
                        instance.uuid)
            else:
                self.consoleauth_rpcapi.delete_tokens_for_instance(context,
                        instance.uuid)

    def _init_instance(self, context, instance):
        '''Initialize this instance during service init.'''

        # Instances that are shut down, or in an error state can not be
        # initialized and are not attempted to be recovered. The exception
        # to this are instances that are in RESIZE_MIGRATING or DELETING,
        # which are dealt with further down.
        if (instance.vm_state == vm_states.SOFT_DELETED or
            (instance.vm_state == vm_states.ERROR and
            instance.task_state not in
            (task_states.RESIZE_MIGRATING, task_states.DELETING))):
            LOG.debug("Instance is in %s state.",
                      instance.vm_state, instance=instance)
            return

        if instance.vm_state == vm_states.DELETED:
            try:
                self._complete_partial_deletion(context, instance)
            except Exception:
                # we don't want that an exception blocks the init_host
                msg = _('Failed to complete a deletion')
                LOG.exception(msg, instance=instance)
            return

        if (instance.vm_state == vm_states.BUILDING or
            instance.task_state in [task_states.SCHEDULING,
                                    task_states.BLOCK_DEVICE_MAPPING,
                                    task_states.NETWORKING,
                                    task_states.SPAWNING]):
            # NOTE(dave-mcnally) compute stopped before instance was fully
            # spawned so set to ERROR state. This is safe to do as the state
            # may be set by the api but the host is not so if we get here the
            # instance has already been scheduled to this particular host.
            LOG.debug("Instance failed to spawn correctly, "
                      "setting to ERROR state", instance=instance)
            instance.task_state = None
            instance.vm_state = vm_states.ERROR
            instance.save()
            return

        if (instance.vm_state != vm_states.ERROR and
            instance.task_state in [task_states.IMAGE_SNAPSHOT_PENDING,
                                    task_states.IMAGE_PENDING_UPLOAD,
                                    task_states.IMAGE_UPLOADING,
                                    task_states.IMAGE_SNAPSHOT]):
            LOG.debug("Instance in transitional state %s at start-up "
                      "clearing task state",
                      instance['task_state'], instance=instance)
            instance.task_state = None
            instance.save()

        if instance.task_state == task_states.DELETING:
            try:
                LOG.info(_('Service started deleting the instance during '
                           'the previous run, but did not finish. Restarting '
                           'the deletion now.'), instance=instance)
                instance.obj_load_attr('metadata')
                instance.obj_load_attr('system_metadata')
                bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                        context, instance.uuid)
                # FIXME(comstud): This needs fixed. We should be creating
                # reservations and updating quotas, because quotas
                # wouldn't have been updated for this instance since it is
                # still in DELETING.  See bug 1296414.
                #
                # Create a dummy quota object for now.
                quotas = objects.Quotas.from_reservations(
                        context, None, instance=instance)
                self._delete_instance(context, instance, bdms, quotas)
            except Exception:
                # we don't want that an exception blocks the init_host
                msg = _('Failed to complete a deletion')
                LOG.exception(msg, instance=instance)
                self._set_instance_error_state(context, instance)
            return

        try_reboot, reboot_type = self._retry_reboot(context, instance)
        current_power_state = self._get_power_state(context, instance)

        if try_reboot:
            LOG.debug("Instance in transitional state (%(task_state)s) at "
                      "start-up and power state is (%(power_state)s), "
                      "triggering reboot",
                      {'task_state': instance['task_state'],
                       'power_state': current_power_state},
                      instance=instance)
            self.compute_rpcapi.reboot_instance(context, instance,
                                                block_device_info=None,
                                                reboot_type=reboot_type)
            return

        elif (current_power_state == power_state.RUNNING and
           instance.task_state in [task_states.REBOOT_STARTED,
                                   task_states.REBOOT_STARTED_HARD]):
            LOG.warning(_("Instance in transitional state "
                          "(%(task_state)s) at start-up and power state "
                          "is (%(power_state)s), clearing task state"),
                        {'task_state': instance['task_state'],
                         'power_state': current_power_state},
                        instance=instance)
            instance.task_state = None
            instance.vm_state = vm_states.ACTIVE
            instance.save()

        if instance.task_state == task_states.POWERING_OFF:
            try:
                LOG.debug("Instance in transitional state %s at start-up "
                          "retrying stop request",
                          instance['task_state'], instance=instance)
                self.stop_instance(context, instance)
            except Exception:
                # we don't want that an exception blocks the init_host
                msg = _('Failed to stop instance')
                LOG.exception(msg, instance=instance)
            return

        if instance.task_state == task_states.POWERING_ON:
            try:
                LOG.debug("Instance in transitional state %s at start-up "
                          "retrying start request",
                          instance['task_state'], instance=instance)
                self.start_instance(context, instance)
            except Exception:
                # we don't want that an exception blocks the init_host
                msg = _('Failed to start instance')
                LOG.exception(msg, instance=instance)
            return

        net_info = compute_utils.get_nw_info_for_instance(instance)
        try:
            self.driver.plug_vifs(instance, net_info)
        except NotImplementedError as e:
            LOG.debug(e, instance=instance)
        if instance.task_state == task_states.RESIZE_MIGRATING:
            # We crashed during resize/migration, so roll back for safety
            try:
                # NOTE(mriedem): check old_vm_state for STOPPED here, if it's
                # not in system_metadata we default to True for backwards
                # compatibility
                power_on = (instance.system_metadata.get('old_vm_state') !=
                            vm_states.STOPPED)

                block_dev_info = self._get_instance_block_device_info(context,
                                                                      instance)

                self.driver.finish_revert_migration(context,
                    instance, net_info, block_dev_info, power_on)

            except Exception as e:
                LOG.exception(_('Failed to revert crashed migration'),
                              instance=instance)
            finally:
                LOG.info(_('Instance found in migrating state during '
                           'startup. Resetting task_state'),
                         instance=instance)
                instance.task_state = None
                instance.save()

        db_state = instance.power_state
        drv_state = self._get_power_state(context, instance)
        expect_running = (db_state == power_state.RUNNING and
                          drv_state != db_state)

        LOG.debug('Current state is %(drv_state)s, state in DB is '
                  '%(db_state)s.',
                  {'drv_state': drv_state, 'db_state': db_state},
                  instance=instance)

        if expect_running and CONF.resume_guests_state_on_host_boot:
            LOG.info(_('Rebooting instance after nova-compute restart.'),
                     instance=instance)

            block_device_info = \
                self._get_instance_block_device_info(context, instance)

            try:
                self.driver.resume_state_on_host_boot(
                    context, instance, net_info, block_device_info)
            except NotImplementedError:
                LOG.warning(_('Hypervisor driver does not support '
                              'resume guests'), instance=instance)
            except Exception:
                # NOTE(vish): The instance failed to resume, so we set the
                #             instance to error and attempt to continue.
                LOG.warning(_('Failed to resume instance'), instance=instance)
                self._set_instance_error_state(context, instance)

        elif drv_state == power_state.RUNNING:
            # VMwareAPI drivers will raise an exception
            try:
                self.driver.ensure_filtering_rules_for_instance(
                                       instance, net_info)
            except NotImplementedError:
                LOG.warning(_('Hypervisor driver does not support '
                              'firewall rules'), instance=instance)

    def _retry_reboot(self, context, instance):
        current_power_state = self._get_power_state(context, instance)
        current_task_state = instance.task_state
        retry_reboot = False
        reboot_type = compute_utils.get_reboot_type(current_task_state,
                                                    current_power_state)

        pending_soft = (current_task_state == task_states.REBOOT_PENDING and
                        instance.vm_state in vm_states.ALLOW_SOFT_REBOOT)
        pending_hard = (current_task_state == task_states.REBOOT_PENDING_HARD
                        and instance.vm_state in vm_states.ALLOW_HARD_REBOOT)
        started_not_running = (current_task_state in
                               [task_states.REBOOT_STARTED,
                                task_states.REBOOT_STARTED_HARD] and
                               current_power_state != power_state.RUNNING)

        if pending_soft or pending_hard or started_not_running:
            retry_reboot = True

        return retry_reboot, reboot_type

    def handle_lifecycle_event(self, event):
        LOG.info(_("VM %(state)s (Lifecycle Event)") %
                  {'state': event.get_name()},
                 instance_uuid=event.get_instance_uuid())
        context = nova.context.get_admin_context(read_deleted='yes')
        instance = objects.Instance.get_by_uuid(context,
                                                event.get_instance_uuid())
        vm_power_state = None
        if event.get_transition() == virtevent.EVENT_LIFECYCLE_STOPPED:
            vm_power_state = power_state.SHUTDOWN
        elif event.get_transition() == virtevent.EVENT_LIFECYCLE_STARTED:
            vm_power_state = power_state.RUNNING
        elif event.get_transition() == virtevent.EVENT_LIFECYCLE_PAUSED:
            vm_power_state = power_state.PAUSED
        elif event.get_transition() == virtevent.EVENT_LIFECYCLE_RESUMED:
            vm_power_state = power_state.RUNNING
        else:
            LOG.warning(_("Unexpected power state %d") %
                        event.get_transition())

        if vm_power_state is not None:
            self._sync_instance_power_state(context,
                                            instance,
                                            vm_power_state)

    def handle_events(self, event):
        if isinstance(event, virtevent.LifecycleEvent):
            try:
                self.handle_lifecycle_event(event)
            except exception.InstanceNotFound:
                LOG.debug("Event %s arrived for non-existent instance. The "
                          "instance was probably deleted.", event)
        else:
            LOG.debug("Ignoring event %s", event)

    def init_virt_events(self):
        self.driver.register_event_listener(self.handle_events)

    def init_host(self):
        """Initialization for a standalone compute service."""
        self.driver.init_host(host=self.host)
        context = nova.context.get_admin_context()
        instances = objects.InstanceList.get_by_host(
            context, self.host, expected_attrs=['info_cache'])

        if CONF.defer_iptables_apply:
            self.driver.filter_defer_apply_on()

        self.init_virt_events()

        try:
            # checking that instance was not already evacuated to other host
            self._destroy_evacuated_instances(context)
            for instance in instances:
                self._init_instance(context, instance)
        finally:
            if CONF.defer_iptables_apply:
                self.driver.filter_defer_apply_off()

    def cleanup_host(self):
        self.driver.cleanup_host(host=self.host)

    def pre_start_hook(self):
        """After the service is initialized, but before we fully bring
        the service up by listening on RPC queues, make sure to update
        our available resources (and indirectly our available nodes).
        """
        self.update_available_resource(nova.context.get_admin_context())

    def _get_power_state(self, context, instance):
        """Retrieve the power state for the given instance."""
        LOG.debug('Checking state', instance=instance)
        try:
            return self.driver.get_info(instance)["state"]
        except exception.NotFound:
            return power_state.NOSTATE

    def get_console_topic(self, context):
        """Retrieves the console host for a project on this host.

        Currently this is just set in the flags for each compute host.

        """
        #TODO(mdragon): perhaps make this variable by console_type?
        return '%s.%s' % (CONF.console_topic, CONF.console_host)

    def get_console_pool_info(self, context, console_type):
        return self.driver.get_console_pool_info(console_type)

    @wrap_exception()
    def refresh_security_group_rules(self, context, security_group_id):
        """Tell the virtualization driver to refresh security group rules.

        Passes straight through to the virtualization driver.

        """
        return self.driver.refresh_security_group_rules(security_group_id)

    @wrap_exception()
    def refresh_security_group_members(self, context, security_group_id):
        """Tell the virtualization driver to refresh security group members.

        Passes straight through to the virtualization driver.

        """
        return self.driver.refresh_security_group_members(security_group_id)

    @wrap_exception()
    def refresh_instance_security_rules(self, context, instance):
        """Tell the virtualization driver to refresh security rules for
        an instance.

        Passes straight through to the virtualization driver.

        Synchronise the call because we may still be in the middle of
        creating the instance.
        """
        @utils.synchronized(instance['uuid'])
        def _sync_refresh():
            try:
                return self.driver.refresh_instance_security_rules(instance)
            except NotImplementedError:
                LOG.warning(_('Hypervisor driver does not support '
                              'security groups.'), instance=instance)

        return _sync_refresh()

    @wrap_exception()
    def refresh_provider_fw_rules(self, context):
        """This call passes straight through to the virtualization driver."""
        return self.driver.refresh_provider_fw_rules()

    def _get_instance_nw_info(self, context, instance, use_slave=False):
        """Get a list of dictionaries of network data of an instance."""
        if (not hasattr(instance, 'system_metadata') or
                len(instance['system_metadata']) == 0):
            # NOTE(danms): Several places in the code look up instances without
            # pulling system_metadata for performance, and call this function.
            # If we get an instance without it, re-fetch so that the call
            # to network_api (which requires it for instance_type) will
            # succeed.
            instance = objects.Instance.get_by_uuid(context,
                                                    instance['uuid'],
                                                    use_slave=use_slave)

        network_info = self.network_api.get_instance_nw_info(context,
                                                             instance)
        return network_info

    def _await_block_device_map_created(self, context, vol_id):
        # TODO(yamahata): creating volume simultaneously
        #                 reduces creation time?
        # TODO(yamahata): eliminate dumb polling
        attempts = 0
        start = time.time()
        while attempts < CONF.block_device_allocate_retries:
            volume = self.volume_api.get(context, vol_id)
            volume_status = volume['status']
            if volume_status not in ['creating', 'downloading']:
                if volume_status != 'available':
                    LOG.warn(_("Volume id: %s finished being created but was"
                               " not set as 'available'"), vol_id)
                return attempts + 1
            greenthread.sleep(CONF.block_device_allocate_retries_interval)
            attempts += 1
        # NOTE(harlowja): Should only happen if we ran out of attempts
        raise exception.VolumeNotCreated(volume_id=vol_id,
                                         seconds=int(time.time() - start),
                                         attempts=attempts)

    def _decode_files(self, injected_files):
        """Base64 decode the list of files to inject."""
        if not injected_files:
            return []

        def _decode(f):
            path, contents = f
            try:
                decoded = base64.b64decode(contents)
                return path, decoded
            except TypeError:
                raise exception.Base64Exception(path=path)

        return [_decode(f) for f in injected_files]

    def _run_instance(self, context, request_spec,
                      filter_properties, requested_networks, injected_files,
                      admin_password, is_first_time, node, instance,
                      legacy_bdm_in_spec):
        """Launch a new instance with specified options."""

        extra_usage_info = {}

        def notify(status, msg="", fault=None, **kwargs):
            """Send a create.{start,error,end} notification."""
            type_ = "create.%(status)s" % dict(status=status)
            info = extra_usage_info.copy()
            info['message'] = msg
            self._notify_about_instance_usage(context, instance, type_,
                    extra_usage_info=info, fault=fault, **kwargs)

        try:
            self._prebuild_instance(context, instance)

            if request_spec and request_spec.get('image'):
                image_meta = request_spec['image']
            else:
                image_meta = {}

            extra_usage_info = {"image_name": image_meta.get('name', '')}

            notify("start")  # notify that build is starting

            instance, network_info = self._build_instance(context,
                    request_spec, filter_properties, requested_networks,
                    injected_files, admin_password, is_first_time, node,
                    instance, image_meta, legacy_bdm_in_spec)
            notify("end", msg=_("Success"), network_info=network_info)

        except exception.RescheduledException as e:
            # Instance build encountered an error, and has been rescheduled.
            notify("error", fault=e)

        except exception.BuildAbortException as e:
            # Instance build aborted due to a non-failure
            LOG.info(e)
            notify("end", msg=e.format_message())  # notify that build is done

        except Exception as e:
            # Instance build encountered a non-recoverable error:
            with excutils.save_and_reraise_exception():
                self._set_instance_error_state(context, instance)
                notify("error", fault=e)  # notify that build failed

    def _prebuild_instance(self, context, instance):
        self._check_instance_exists(context, instance)

        try:
            self._start_building(context, instance)
        except (exception.InstanceNotFound,
                exception.UnexpectedDeletingTaskStateError):
            msg = _("Instance disappeared before we could start it")
            # Quickly bail out of here
            raise exception.BuildAbortException(instance_uuid=instance['uuid'],
                    reason=msg)

    def _validate_instance_group_policy(self, context, instance,
            filter_properties):
        # NOTE(russellb) Instance group policy is enforced by the scheduler.
        # However, there is a race condition with the enforcement of
        # anti-affinity.  Since more than one instance may be scheduled at the
        # same time, it's possible that more than one instance with an
        # anti-affinity policy may end up here.  This is a validation step to
        # make sure that starting the instance here doesn't violate the policy.

        scheduler_hints = filter_properties.get('scheduler_hints') or {}
        group_hint = scheduler_hints.get('group')
        if not group_hint:
            return

        @utils.synchronized(group_hint)
        def _do_validation(context, instance, group_hint):
            group = objects.InstanceGroup.get_by_hint(context, group_hint)
            if 'anti-affinity' not in group.policies:
                return

            group_hosts = group.get_hosts(context, exclude=[instance['uuid']])
            if self.host in group_hosts:
                msg = _("Anti-affinity instance group policy was violated.")
                raise exception.RescheduledException(
                        instance_uuid=instance['uuid'],
                        reason=msg)

        _do_validation(context, instance, group_hint)

    def _build_instance(self, context, request_spec, filter_properties,
            requested_networks, injected_files, admin_password, is_first_time,
            node, instance, image_meta, legacy_bdm_in_spec):
        context = context.elevated()

        # If neutron security groups pass requested security
        # groups to allocate_for_instance()
        if request_spec and self.is_neutron_security_groups:
            security_groups = request_spec.get('security_group')
        else:
            security_groups = []

        if node is None:
            node = self.driver.get_available_nodes(refresh=True)[0]
            LOG.debug("No node specified, defaulting to %s", node)

        network_info = None
        bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                context, instance['uuid'])

        # b64 decode the files to inject:
        injected_files_orig = injected_files
        injected_files = self._decode_files(injected_files)

        rt = self._get_resource_tracker(node)
        try:
            limits = filter_properties.get('limits', {})
            with rt.instance_claim(context, instance, limits):
                # NOTE(russellb) It's important that this validation be done
                # *after* the resource tracker instance claim, as that is where
                # the host is set on the instance.
                self._validate_instance_group_policy(context, instance,
                        filter_properties)
                macs = self.driver.macs_for_instance(instance)
                dhcp_options = self.driver.dhcp_options_for_instance(instance)

                network_info = self._allocate_network(context, instance,
                        requested_networks, macs, security_groups,
                        dhcp_options)

                self._instance_update(
                        context, instance['uuid'],
                        vm_state=vm_states.BUILDING,
                        task_state=task_states.BLOCK_DEVICE_MAPPING)

                # Verify that all the BDMs have a device_name set and assign a
                # default to the ones missing it with the help of the driver.
                self._default_block_device_names(context, instance, image_meta,
                                                 bdms)

                block_device_info = self._prep_block_device(
                        context, instance, bdms)

                set_access_ip = (is_first_time and
                                 not instance['access_ip_v4'] and
                                 not instance['access_ip_v6'])

                instance = self._spawn(context, instance, image_meta,
                                       network_info, block_device_info,
                                       injected_files, admin_password,
                                       set_access_ip=set_access_ip)
        except (exception.InstanceNotFound,
                exception.UnexpectedDeletingTaskStateError):
            # the instance got deleted during the spawn
            # Make sure the async call finishes
            if network_info is not None:
                network_info.wait(do_raise=False)
            try:
                self._deallocate_network(context, instance)
            except Exception:
                msg = _('Failed to dealloc network '
                        'for deleted instance')
                LOG.exception(msg, instance=instance)
            raise exception.BuildAbortException(
                instance_uuid=instance['uuid'],
                reason=_("Instance disappeared during build"))
        except (exception.UnexpectedTaskStateError,
                exception.VirtualInterfaceCreateException) as e:
            # Don't try to reschedule, just log and reraise.
            with excutils.save_and_reraise_exception():
                LOG.debug(e.format_message(), instance=instance)
                # Make sure the async call finishes
                if network_info is not None:
                    network_info.wait(do_raise=False)
        except exception.InvalidBDM:
            with excutils.save_and_reraise_exception():
                if network_info is not None:
                    network_info.wait(do_raise=False)
                try:
                    self._deallocate_network(context, instance)
                except Exception:
                    msg = _('Failed to dealloc network '
                            'for failed instance')
                    LOG.exception(msg, instance=instance)
        except Exception:
            exc_info = sys.exc_info()
            # try to re-schedule instance:
            # Make sure the async call finishes
            if network_info is not None:
                network_info.wait(do_raise=False)
            rescheduled = self._reschedule_or_error(context, instance,
                    exc_info, requested_networks, admin_password,
                    injected_files_orig, is_first_time, request_spec,
                    filter_properties, bdms, legacy_bdm_in_spec)
            if rescheduled:
                # log the original build error
                self._log_original_error(exc_info, instance['uuid'])
                raise exception.RescheduledException(
                        instance_uuid=instance['uuid'],
                        reason=unicode(exc_info[1]))
            else:
                # not re-scheduling, go to error:
                raise exc_info[0], exc_info[1], exc_info[2]

        # spawn success
        return instance, network_info

    def _log_original_error(self, exc_info, instance_uuid):
        LOG.error(_('Error: %s') % exc_info[1], instance_uuid=instance_uuid,
                  exc_info=exc_info)

    def _reschedule_or_error(self, context, instance, exc_info,
            requested_networks, admin_password, injected_files, is_first_time,
            request_spec, filter_properties, bdms=None,
            legacy_bdm_in_spec=True):
        """Try to re-schedule the build or re-raise the original build error to
        error out the instance.
        """
        instance_uuid = instance['uuid']
        rescheduled = False

        compute_utils.add_instance_fault_from_exc(context,
                instance, exc_info[1], exc_info=exc_info)
        self._notify_about_instance_usage(context, instance,
                'instance.create.error', fault=exc_info[1])

        try:
            LOG.debug("Clean up resource before rescheduling.",
                      instance=instance)
            if bdms is None:
                bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                        context, instance.uuid)

            self._shutdown_instance(context, instance,
                                    bdms, requested_networks)
            self._cleanup_volumes(context, instance['uuid'], bdms)
        except Exception:
            # do not attempt retry if clean up failed:
            with excutils.save_and_reraise_exception():
                self._log_original_error(exc_info, instance_uuid)

        try:
            method_args = (request_spec, admin_password, injected_files,
                    requested_networks, is_first_time, filter_properties,
                    legacy_bdm_in_spec)
            task_state = task_states.SCHEDULING

            rescheduled = self._reschedule(context, request_spec,
                    filter_properties, instance,
                    self.scheduler_rpcapi.run_instance, method_args,
                    task_state, exc_info)

        except Exception:
            rescheduled = False
            LOG.exception(_("Error trying to reschedule"),
                          instance_uuid=instance_uuid)

        return rescheduled

    def _reschedule(self, context, request_spec, filter_properties,
            instance, scheduler_method, method_args, task_state,
            exc_info=None):
        """Attempt to re-schedule a compute operation."""

        instance_uuid = instance['uuid']
        retry = filter_properties.get('retry', None)
        if not retry:
            # no retry information, do not reschedule.
            LOG.debug("Retry info not present, will not reschedule",
                      instance_uuid=instance_uuid)
            return

        if not request_spec:
            LOG.debug("No request spec, will not reschedule",
                      instance_uuid=instance_uuid)
            return

        request_spec['instance_uuids'] = [instance_uuid]

        LOG.debug("Re-scheduling %(method)s: attempt %(num)d",
                  {'method': scheduler_method.func_name,
                   'num': retry['num_attempts']}, instance_uuid=instance_uuid)

        # reset the task state:
        self._instance_update(context, instance_uuid, task_state=task_state)

        if exc_info:
            # stringify to avoid circular ref problem in json serialization:
            retry['exc'] = traceback.format_exception_only(exc_info[0],
                                    exc_info[1])

        scheduler_method(context, *method_args)
        return True

    @periodic_task.periodic_task
    def _check_instance_build_time(self, context):
        """Ensure that instances are not stuck in build."""
        timeout = CONF.instance_build_timeout
        if timeout == 0:
            return

        filters = {'vm_state': vm_states.BUILDING,
                   'host': self.host}

        building_insts = objects.InstanceList.get_by_filters(context,
                           filters, expected_attrs=[], use_slave=True)

        for instance in building_insts:
            if timeutils.is_older_than(instance['created_at'], timeout):
                self._set_instance_error_state(context, instance)
                LOG.warn(_("Instance build timed out. Set to error state."),
                         instance=instance)

    def _check_instance_exists(self, context, instance):
        """Ensure an instance with the same name is not already present."""
        if self.driver.instance_exists(instance):
            raise exception.InstanceExists(name=instance.name)

    def _start_building(self, context, instance):
        """Save the host and launched_on fields and log appropriately."""
        LOG.audit(_('Starting instance...'), context=context,
                  instance=instance)
        self._instance_update(context, instance['uuid'],
                              vm_state=vm_states.BUILDING,
                              task_state=None,
                              expected_task_state=(task_states.SCHEDULING,
                                                   None))

    def _allocate_network_async(self, context, instance, requested_networks,
                                macs, security_groups, is_vpn, dhcp_options):
        """Method used to allocate networks in the background.

        Broken out for testing.
        """
        LOG.debug("Allocating IP information in the background.",
                  instance=instance)
        retries = CONF.network_allocate_retries
        if retries < 0:
            LOG.warn(_("Treating negative config value (%(retries)s) for "
                       "'network_allocate_retries' as 0."),
                     {'retries': retries})
        attempts = retries > 1 and retries + 1 or 1
        retry_time = 1
        for attempt in range(1, attempts + 1):
            try:
                nwinfo = self.network_api.allocate_for_instance(
                        context, instance, vpn=is_vpn,
                        requested_networks=requested_networks,
                        macs=macs,
                        security_groups=security_groups,
                        dhcp_options=dhcp_options)
                LOG.debug('Instance network_info: |%s|', nwinfo,
                          instance=instance)
                sys_meta = instance.system_metadata
                sys_meta['network_allocated'] = 'True'
                self._instance_update(context, instance.uuid,
                        system_metadata=sys_meta)
                return nwinfo
            except Exception:
                exc_info = sys.exc_info()
                log_info = {'attempt': attempt,
                            'attempts': attempts}
                if attempt == attempts:
                    LOG.exception(_('Instance failed network setup '
                                    'after %(attempts)d attempt(s)'),
                                  log_info)
                    raise exc_info[0], exc_info[1], exc_info[2]
                LOG.warn(_('Instance failed network setup '
                           '(attempt %(attempt)d of %(attempts)d)'),
                         log_info, instance=instance)
                time.sleep(retry_time)
                retry_time *= 2
                if retry_time > 30:
                    retry_time = 30
        # Not reached.

    def _build_networks_for_instance(self, context, instance,
            requested_networks, security_groups):

        # If we're here from a reschedule the network may already be allocated.
        if strutils.bool_from_string(
                instance.system_metadata.get('network_allocated', 'False')):
            return self._get_instance_nw_info(context, instance)

        if not self.is_neutron_security_groups:
            security_groups = []

        macs = self.driver.macs_for_instance(instance)
        dhcp_options = self.driver.dhcp_options_for_instance(instance)
        network_info = self._allocate_network(context, instance,
                requested_networks, macs, security_groups, dhcp_options)

        if not instance.access_ip_v4 and not instance.access_ip_v6:
            # If CONF.default_access_ip_network_name is set, grab the
            # corresponding network and set the access ip values accordingly.
            # Note that when there are multiple ips to choose from, an
            # arbitrary one will be chosen.
            network_name = CONF.default_access_ip_network_name
            if not network_name:
                return network_info

            for vif in network_info:
                if vif['network']['label'] == network_name:
                    for ip in vif.fixed_ips():
                        if ip['version'] == 4:
                            instance.access_ip_v4 = ip['address']
                        if ip['version'] == 6:
                            instance.access_ip_v6 = ip['address']
                    instance.save()
                    break

        return network_info

    def _allocate_network(self, context, instance, requested_networks, macs,
                          security_groups, dhcp_options):
        """Start network allocation asynchronously.  Return an instance
        of NetworkInfoAsyncWrapper that can be used to retrieve the
        allocated networks when the operation has finished.
        """
        # NOTE(comstud): Since we're allocating networks asynchronously,
        # this task state has little meaning, as we won't be in this
        # state for very long.
        instance.vm_state = vm_states.BUILDING
        instance.task_state = task_states.NETWORKING
        instance.save(expected_task_state=[None])
        self._update_resource_tracker(context, instance)

        is_vpn = pipelib.is_vpn_image(instance.image_ref)
        return network_model.NetworkInfoAsyncWrapper(
                self._allocate_network_async, context, instance,
                requested_networks, macs, security_groups, is_vpn,
                dhcp_options)

    def _default_root_device_name(self, instance, image_meta, root_bdm):
        try:
            return self.driver.default_root_device_name(instance,
                                                        image_meta,
                                                        root_bdm)
        except NotImplementedError:
            return compute_utils.get_next_device_name(instance, [])

    def _default_device_names_for_instance(self, instance,
                                           root_device_name,
                                           *block_device_lists):
        try:
            self.driver.default_device_names_for_instance(instance,
                                                          root_device_name,
                                                          *block_device_lists)
        except NotImplementedError:
            compute_utils.default_device_names_for_instance(
                instance, root_device_name, *block_device_lists)

    def _default_block_device_names(self, context, instance,
                                    image_meta, block_devices):
        """Verify that all the devices have the device_name set. If not,
        provide a default name.

        It also ensures that there is a root_device_name and is set to the
        first block device in the boot sequence (boot_index=0).
        """
        root_bdm = block_device.get_root_bdm(block_devices)
        if not root_bdm:
            return

        # Get the root_device_name from the root BDM or the instance
        root_device_name = None
        update_instance = False
        update_root_bdm = False

        if root_bdm.device_name:
            root_device_name = root_bdm.device_name
            instance['root_device_name'] = root_device_name
            update_instance = True
        elif instance['root_device_name']:
            root_device_name = instance['root_device_name']
            root_bdm.device_name = root_device_name
            update_root_bdm = True
        else:
            root_device_name = self._default_root_device_name(instance,
                                                              image_meta,
                                                              root_bdm)

            instance['root_device_name'] = root_device_name
            root_bdm.device_name = root_device_name
            update_instance = update_root_bdm = True

        if update_instance:
            self._instance_update(context, instance['uuid'],
                                  root_device_name=root_device_name)
        if update_root_bdm:
            root_bdm.save()

        def _is_mapping(bdm):
            return (bdm.source_type in ('image', 'volume', 'snapshot') and
                    driver_block_device.is_implemented(bdm))

        ephemerals = filter(block_device.new_format_is_ephemeral,
                            block_devices)
        swap = filter(block_device.new_format_is_swap,
                      block_devices)
        block_device_mapping = filter(_is_mapping, block_devices)

        self._default_device_names_for_instance(instance,
                                                root_device_name,
                                                ephemerals,
                                                swap,
                                                block_device_mapping)

    def _prep_block_device(self, context, instance, bdms):
        """Set up the block device for an instance with error logging."""
        try:
            block_device_info = {
                'root_device_name': instance['root_device_name'],
                'swap': driver_block_device.convert_swap(bdms),
                'ephemerals': driver_block_device.convert_ephemerals(bdms),
                'block_device_mapping': (
                    driver_block_device.attach_block_devices(
                        driver_block_device.convert_volumes(bdms),
                        context, instance, self.volume_api,
                        self.driver) +
                    driver_block_device.attach_block_devices(
                        driver_block_device.convert_snapshots(bdms),
                        context, instance, self.volume_api,
                        self.driver, self._await_block_device_map_created) +
                    driver_block_device.attach_block_devices(
                        driver_block_device.convert_images(bdms),
                        context, instance, self.volume_api,
                        self.driver, self._await_block_device_map_created))
            }

            if self.use_legacy_block_device_info:
                for bdm_type in ('swap', 'ephemerals', 'block_device_mapping'):
                    block_device_info[bdm_type] = \
                        driver_block_device.legacy_block_devices(
                        block_device_info[bdm_type])

            # Get swap out of the list
            block_device_info['swap'] = driver_block_device.get_swap(
                block_device_info['swap'])
            return block_device_info

        except exception.OverQuota:
            msg = ('Failed to create block device for instance due to being '
                   'over volume resource quota')
            LOG.debug(msg, instance=instance)
            raise exception.InvalidBDM()

        except Exception:
            LOG.exception(_('Instance failed block device setup'),
                          instance=instance)
            raise exception.InvalidBDM()

    @object_compat
    def _spawn(self, context, instance, image_meta, network_info,
               block_device_info, injected_files, admin_password,
               set_access_ip=False):
        """Spawn an instance with error logging and update its power state."""
        instance.vm_state = vm_states.BUILDING
        instance.task_state = task_states.SPAWNING
        instance.save(expected_task_state=task_states.BLOCK_DEVICE_MAPPING)

        try:
            self.driver.spawn(context, instance, image_meta,
                              injected_files, admin_password,
                              network_info,
                              block_device_info)
        except Exception:
            with excutils.save_and_reraise_exception():
                LOG.exception(_('Instance failed to spawn'), instance=instance)

        current_power_state = self._get_power_state(context, instance)

        instance.power_state = current_power_state
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.launched_at = timeutils.utcnow()

        def _set_access_ip_values():
            """Add access ip values for a given instance.

            If CONF.default_access_ip_network_name is set, this method will
            grab the corresponding network and set the access ip values
            accordingly. Note that when there are multiple ips to choose
            from, an arbitrary one will be chosen.
            """

            network_name = CONF.default_access_ip_network_name
            if not network_name:
                return

            for vif in network_info:
                if vif['network']['label'] == network_name:
                    for ip in vif.fixed_ips():
                        if ip['version'] == 4:
                            instance.access_ip_v4 = ip['address']
                        if ip['version'] == 6:
                            instance.access_ip_v6 = ip['address']
                    return

        if set_access_ip:
            _set_access_ip_values()

        network_info.wait(do_raise=True)
        instance.info_cache.network_info = network_info
        instance.save(expected_task_state=task_states.SPAWNING)
        return instance

    def _notify_about_instance_usage(self, context, instance, event_suffix,
                                     network_info=None, system_metadata=None,
                                     extra_usage_info=None, fault=None):
        compute_utils.notify_about_instance_usage(
            self.notifier, context, instance, event_suffix,
            network_info=network_info,
            system_metadata=system_metadata,
            extra_usage_info=extra_usage_info, fault=fault)

    def _deallocate_network(self, context, instance,
                            requested_networks=None):
        LOG.debug('Deallocating network for instance', instance=instance)
        self.network_api.deallocate_for_instance(
            context, instance, requested_networks=requested_networks)

    def _get_instance_block_device_info(self, context, instance,
                                        refresh_conn_info=False,
                                        bdms=None):
        """Transform block devices to the driver block_device format."""

        if not bdms:
            bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance['uuid'])
        swap = driver_block_device.convert_swap(bdms)
        ephemerals = driver_block_device.convert_ephemerals(bdms)
        block_device_mapping = (
            driver_block_device.convert_volumes(bdms) +
            driver_block_device.convert_snapshots(bdms) +
            driver_block_device.convert_images(bdms))

        if not refresh_conn_info:
            # if the block_device_mapping has no value in connection_info
            # (returned as None), don't include in the mapping
            block_device_mapping = [
                bdm for bdm in block_device_mapping
                if bdm.get('connection_info')]
        else:
            block_device_mapping = driver_block_device.refresh_conn_infos(
                block_device_mapping, context, instance, self.volume_api,
                self.driver)

        if self.use_legacy_block_device_info:
            swap = driver_block_device.legacy_block_devices(swap)
            ephemerals = driver_block_device.legacy_block_devices(ephemerals)
            block_device_mapping = driver_block_device.legacy_block_devices(
                block_device_mapping)

        # Get swap out of the list
        swap = driver_block_device.get_swap(swap)

        return {'swap': swap,
                'ephemerals': ephemerals,
                'block_device_mapping': block_device_mapping}

    # NOTE(mikal): No object_compat wrapper on this method because its
    # callers all pass objects already
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def build_and_run_instance(self, context, instance, image, request_spec,
                     filter_properties, admin_password=None,
                     injected_files=None, requested_networks=None,
                     security_groups=None, block_device_mapping=None,
                     node=None, limits=None):

        @utils.synchronized(instance.uuid)
        def do_build_and_run_instance(context, instance, image, request_spec,
                filter_properties, admin_password, injected_files,
                requested_networks, security_groups, block_device_mapping,
                node=None, limits=None):

            try:
                LOG.audit(_('Starting instance...'), context=context,
                      instance=instance)
                instance.vm_state = vm_states.BUILDING
                instance.task_state = None
                instance.save(expected_task_state=
                        (task_states.SCHEDULING, None))
            except exception.InstanceNotFound:
                msg = 'Instance disappeared before build.'
                LOG.debug(msg, instance=instance)
                return
            except exception.UnexpectedTaskStateError as e:
                LOG.debug(e.format_message(), instance=instance)
                return

            # b64 decode the files to inject:
            decoded_files = self._decode_files(injected_files)

            if limits is None:
                limits = {}

            if node is None:
                node = self.driver.get_available_nodes(refresh=True)[0]
                LOG.debug('No node specified, defaulting to %s', node,
                          instance=instance)

            try:
                self._build_and_run_instance(context, instance, image,
                        decoded_files, admin_password, requested_networks,
                        security_groups, block_device_mapping, node, limits,
                        filter_properties)
            except exception.RescheduledException as e:
                LOG.debug(e.format_message(), instance=instance)
                retry = filter_properties.get('retry', None)
                if not retry:
                    # no retry information, do not reschedule.
                    LOG.debug("Retry info not present, will not reschedule")
                    self._cleanup_allocated_networks(context, instance,
                        requested_networks)
                    self._set_instance_error_state(context, instance.uuid)
                    return
                retry['exc'] = traceback.format_exception(*sys.exc_info())
                # The MAC address for this instance is tied to the host so if
                # we're going to reschedule we have to free the network details
                # and reallocate on the next host.
                if self.driver.macs_for_instance(instance):
                    self._cleanup_allocated_networks(context, instance,
                            requested_networks)

                instance.task_state = task_states.SCHEDULING
                instance.save()

                self.compute_task_api.build_instances(context, [instance],
                        image, filter_properties, admin_password,
                        injected_files, requested_networks, security_groups,
                        block_device_mapping)
            except (exception.InstanceNotFound,
                    exception.UnexpectedDeletingTaskStateError):
                msg = 'Instance disappeared during build.'
                LOG.debug(msg, instance=instance)
                self._cleanup_allocated_networks(context, instance,
                        requested_networks)
            except exception.BuildAbortException as e:
                LOG.exception(e.format_message(), instance=instance)
                self._cleanup_allocated_networks(context, instance,
                        requested_networks)
                self._set_instance_error_state(context, instance)
            except Exception:
                # Should not reach here.
                msg = _('Unexpected build failure, not rescheduling build.')
                LOG.exception(msg, instance=instance)
                self._cleanup_allocated_networks(context, instance,
                        requested_networks)
                self._set_instance_error_state(context, instance)

        do_build_and_run_instance(context, instance, image, request_spec,
                filter_properties, admin_password, injected_files,
                requested_networks, security_groups, block_device_mapping,
                node, limits)

    def _build_and_run_instance(self, context, instance, image, injected_files,
            admin_password, requested_networks, security_groups,
            block_device_mapping, node, limits, filter_properties):

        image_name = image.get('name')
        self._notify_about_instance_usage(context, instance, 'create.start',
                extra_usage_info={'image_name': image_name})
        try:
            rt = self._get_resource_tracker(node)
            with rt.instance_claim(context, instance, limits):
                # NOTE(russellb) It's important that this validation be done
                # *after* the resource tracker instance claim, as that is where
                # the host is set on the instance.
                self._validate_instance_group_policy(context, instance,
                        filter_properties)
                with self._build_resources(context, instance,
                        requested_networks, security_groups, image,
                        block_device_mapping) as resources:
                    instance.vm_state = vm_states.BUILDING
                    instance.task_state = task_states.SPAWNING
                    instance.save(expected_task_state=
                            task_states.BLOCK_DEVICE_MAPPING)
                    block_device_info = resources['block_device_info']
                    network_info = resources['network_info']
                    self.driver.spawn(context, instance, image,
                                      injected_files, admin_password,
                                      network_info=network_info,
                                      block_device_info=block_device_info)
                    self._notify_about_instance_usage(context, instance,
                            'create.end',
                            extra_usage_info={'message': _('Success')},
                            network_info=network_info)
        except (exception.InstanceNotFound,
                exception.UnexpectedDeletingTaskStateError) as e:
            with excutils.save_and_reraise_exception():
                self._notify_about_instance_usage(context, instance,
                    'create.end', fault=e)
        except exception.ComputeResourcesUnavailable as e:
            LOG.debug(e.format_message(), instance=instance)
            self._notify_about_instance_usage(context, instance,
                    'create.error', fault=e)
            raise exception.RescheduledException(
                    instance_uuid=instance.uuid, reason=e.format_message())
        except exception.BuildAbortException as e:
            with excutils.save_and_reraise_exception():
                LOG.debug(e.format_message(), instance=instance)
                self._notify_about_instance_usage(context, instance,
                    'create.error', fault=e)
        except (exception.FixedIpLimitExceeded,
                exception.NoMoreNetworks) as e:
            LOG.warn(_LW('No more network or fixed IP to be allocated'),
                     instance=instance)
            self._notify_about_instance_usage(context, instance,
                    'create.error', fault=e)
            msg = _('Failed to allocate the network(s) with error %s, '
                    'not rescheduling.') % e.format_message()
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=msg)
        except (exception.VirtualInterfaceCreateException,
                exception.VirtualInterfaceMacAddressException) as e:
            LOG.exception(_('Failed to allocate network(s)'),
                          instance=instance)
            self._notify_about_instance_usage(context, instance,
                    'create.error', fault=e)
            msg = _('Failed to allocate the network(s), not rescheduling.')
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=msg)
        except (exception.FlavorDiskTooSmall,
                exception.FlavorMemoryTooSmall,
                exception.ImageNotActive,
                exception.ImageUnacceptable) as e:
            self._notify_about_instance_usage(context, instance,
                    'create.error', fault=e)
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=e.format_message())
        except Exception as e:
            self._notify_about_instance_usage(context, instance,
                    'create.error', fault=e)
            raise exception.RescheduledException(
                    instance_uuid=instance.uuid, reason=str(e))

        # NOTE(alaski): This is only useful during reschedules, remove it now.
        instance.system_metadata.pop('network_allocated', None)

        instance.power_state = self._get_power_state(context, instance)
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.launched_at = timeutils.utcnow()
        instance.save(expected_task_state=task_states.SPAWNING)

    @contextlib.contextmanager
    def _build_resources(self, context, instance, requested_networks,
            security_groups, image, block_device_mapping):
        resources = {}

        try:
            network_info = self._build_networks_for_instance(context, instance,
                    requested_networks, security_groups)
            resources['network_info'] = network_info
        except (exception.InstanceNotFound,
                exception.UnexpectedDeletingTaskStateError):
            raise
        except exception.UnexpectedTaskStateError as e:
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=e.format_message())
        except Exception:
            # Because this allocation is async any failures are likely to occur
            # when the driver accesses network_info during spawn().
            LOG.exception(_('Failed to allocate network(s)'),
                          instance=instance)
            msg = _('Failed to allocate the network(s), not rescheduling.')
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=msg)

        try:
            # Verify that all the BDMs have a device_name set and assign a
            # default to the ones missing it with the help of the driver.
            self._default_block_device_names(context, instance, image,
                    block_device_mapping)

            instance.vm_state = vm_states.BUILDING
            instance.task_state = task_states.BLOCK_DEVICE_MAPPING
            instance.save()

            block_device_info = self._prep_block_device(context, instance,
                    block_device_mapping)
            resources['block_device_info'] = block_device_info
        except (exception.InstanceNotFound,
                exception.UnexpectedDeletingTaskStateError):
            raise
        except exception.UnexpectedTaskStateError as e:
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=e.format_message())
        except Exception:
            LOG.exception(_('Failure prepping block device'),
                    instance=instance)
            msg = _('Failure prepping block device.')
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=msg)

        try:
            yield resources
        except Exception as exc:
            with excutils.save_and_reraise_exception() as ctxt:
                if not isinstance(exc, (exception.InstanceNotFound,
                    exception.UnexpectedDeletingTaskStateError)):
                        LOG.exception(_('Instance failed to spawn'),
                                instance=instance)
                # Make sure the async call finishes
                if network_info is not None:
                    network_info.wait(do_raise=False)
                try:
                    self._shutdown_instance(context, instance,
                            block_device_mapping, requested_networks,
                            try_deallocate_networks=False)
                    self._cleanup_build_resources(context, instance,
                            block_device_mapping)
                except Exception:
                    ctxt.reraise = False
                    msg = _('Could not clean up failed build,'
                            ' not rescheduling')
                    raise exception.BuildAbortException(
                            instance_uuid=instance.uuid, reason=msg)

    def _cleanup_allocated_networks(self, context, instance,
            requested_networks):
        try:
            self._deallocate_network(context, instance, requested_networks)
        except Exception:
            msg = _('Failed to deallocate networks')
            LOG.exception(msg, instance=instance)
            return

        instance.system_metadata['network_allocated'] = 'False'
        try:
            instance.save()
        except exception.InstanceNotFound:
            # NOTE(alaski): It's possible that we're cleaning up the networks
            # because the instance was deleted.  If that's the case then this
            # exception will be raised by instance.save()
            pass

    def _cleanup_build_resources(self, context, instance,
            block_device_mapping):
        # Don't clean up networks here in case we reschedule
        try:
            self._cleanup_volumes(context, instance.uuid,
                    block_device_mapping)
        except Exception:
            with excutils.save_and_reraise_exception():
                msg = _('Failed to cleanup volumes for failed build,'
                        ' not rescheduling')
                LOG.exception(msg, instance=instance)

    @object_compat
    @messaging.expected_exceptions(exception.BuildAbortException,
                                   exception.UnexpectedTaskStateError,
                                   exception.VirtualInterfaceCreateException,
                                   exception.RescheduledException)
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def run_instance(self, context, instance, request_spec,
                     filter_properties, requested_networks,
                     injected_files, admin_password,
                     is_first_time, node, legacy_bdm_in_spec):
        # NOTE(alaski) This method should be deprecated when the scheduler and
        # compute rpc interfaces are bumped to 4.x, and slated for removal in
        # 5.x as it is no longer used.

        if filter_properties is None:
            filter_properties = {}

        @utils.synchronized(instance.uuid)
        def do_run_instance():
            self._run_instance(context, request_spec,
                    filter_properties, requested_networks, injected_files,
                    admin_password, is_first_time, node, instance,
                    legacy_bdm_in_spec)
        do_run_instance()

    def _try_deallocate_network(self, context, instance,
                                requested_networks=None):
        try:
            # tear down allocated network structure
            self._deallocate_network(context, instance, requested_networks)
        except Exception:
            with excutils.save_and_reraise_exception():
                LOG.error(_('Failed to deallocate network for instance.'),
                          instance=instance)
                self._set_instance_error_state(context, instance)

    def _shutdown_instance(self, context, instance,
                           bdms, requested_networks=None, notify=True,
                           try_deallocate_networks=True):
        """Shutdown an instance on this host.

        :param:context: security context
        :param:instance: a nova.objects.Instance object
        :param:bdms: the block devices for the instance to be torn
                     down
        :param:requested_networks: the networks on which the instance
                                   has ports
        :param:notify: true if a final usage notification should be
                       emitted
        :param:try_deallocate_networks: false if we should avoid
                                        trying to teardown networking
        """
        context = context.elevated()
        LOG.audit(_('%(action_str)s instance') % {'action_str': 'Terminating'},
                  context=context, instance=instance)

        if notify:
            self._notify_about_instance_usage(context, instance,
                                              "shutdown.start")

        network_info = compute_utils.get_nw_info_for_instance(instance)

        # NOTE(vish) get bdms before destroying the instance
        vol_bdms = [bdm for bdm in bdms if bdm.is_volume]
        block_device_info = self._get_instance_block_device_info(
            context, instance, bdms=bdms)

        # NOTE(melwitt): attempt driver destroy before releasing ip, may
        #                want to keep ip allocated for certain failures
        try:
            self.driver.destroy(context, instance, network_info,
                    block_device_info)
        except exception.InstancePowerOffFailure:
            # if the instance can't power off, don't release the ip
            with excutils.save_and_reraise_exception():
                pass
        except Exception:
            with excutils.save_and_reraise_exception():
                # deallocate ip and fail without proceeding to
                # volume api calls, preserving current behavior
                if try_deallocate_networks:
                    self._try_deallocate_network(context, instance,
                                                 requested_networks)

        if try_deallocate_networks:
            self._try_deallocate_network(context, instance, requested_networks)

        for bdm in vol_bdms:
            try:
                # NOTE(vish): actual driver detach done in driver.destroy, so
                #             just tell cinder that we are done with it.
                connector = self.driver.get_volume_connector(instance)
                self.volume_api.terminate_connection(context,
                                                     bdm.volume_id,
                                                     connector)
                self.volume_api.detach(context, bdm.volume_id)
            except exception.DiskNotFound as exc:
                LOG.warn(_('Ignoring DiskNotFound: %s') % exc,
                         instance=instance)
            except exception.VolumeNotFound as exc:
                LOG.warn(_('Ignoring VolumeNotFound: %s') % exc,
                         instance=instance)

        if notify:
            self._notify_about_instance_usage(context, instance,
                                              "shutdown.end")

    def _cleanup_volumes(self, context, instance_uuid, bdms, raise_exc=True):
        exc_info = None

        for bdm in bdms:
            LOG.debug("terminating bdm %s", bdm,
                      instance_uuid=instance_uuid)
            if bdm.volume_id and bdm.delete_on_termination:
                try:
                    self.volume_api.delete(context, bdm.volume_id)
                except Exception as exc:
                    exc_info = sys.exc_info()
                    LOG.warn(_LW('Failed to delete volume: %(volume_id)s due '
                                 'to %(exc)s'), {'volume_id': bdm.volume_id,
                                                  'exc': unicode(exc)})
        if exc_info is not None and raise_exc:
            six.reraise(exc_info[0], exc_info[1], exc_info[2])

    @hooks.add_hook("delete_instance")
    def _delete_instance(self, context, instance, bdms, quotas):
        """Delete an instance on this host.  Commit or rollback quotas
        as necessary.
        """
        instance_uuid = instance['uuid']

        was_soft_deleted = instance['vm_state'] == vm_states.SOFT_DELETED
        if was_soft_deleted:
            # Instances in SOFT_DELETED vm_state have already had quotas
            # decremented.
            try:
                quotas.rollback()
            except Exception:
                pass

        try:
            events = self.instance_events.clear_events_for_instance(instance)
            if events:
                LOG.debug('Events pending at deletion: %(events)s',
                          {'events': ','.join(events.keys())},
                          instance=instance)
            instance.info_cache.delete()
            self._notify_about_instance_usage(context, instance,
                                              "delete.start")
            self._shutdown_instance(context, instance, bdms)
            # NOTE(vish): We have already deleted the instance, so we have
            #             to ignore problems cleaning up the volumes. It
            #             would be nice to let the user know somehow that
            #             the volume deletion failed, but it is not
            #             acceptable to have an instance that can not be
            #             deleted. Perhaps this could be reworked in the
            #             future to set an instance fault the first time
            #             and to only ignore the failure if the instance
            #             is already in ERROR.
            self._cleanup_volumes(context, instance_uuid, bdms,
                    raise_exc=False)
            # if a delete task succeed, always update vm state and task
            # state without expecting task state to be DELETING
            instance.vm_state = vm_states.DELETED
            instance.task_state = None
            instance.terminated_at = timeutils.utcnow()
            instance.save()
            system_meta = instance.system_metadata
            instance.destroy()
        except Exception:
            with excutils.save_and_reraise_exception():
                quotas.rollback()

        self._complete_deletion(context,
                                instance,
                                bdms,
                                quotas,
                                system_meta)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def terminate_instance(self, context, instance, bdms, reservations):
        """Terminate an instance on this host."""
        # NOTE (ndipanov): If we get non-object BDMs, just get them from the
        # db again, as this means they are sent in the old format and we want
        # to avoid converting them back when we can just get them.
        # Remove this when we bump the RPC major version to 4.0
        if (bdms and
            any(not isinstance(bdm, obj_base.NovaObject)
                for bdm in bdms)):
            bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid)

        quotas = objects.Quotas.from_reservations(context,
                                                  reservations,
                                                  instance=instance)

        @utils.synchronized(instance['uuid'])
        def do_terminate_instance(instance, bdms):
            try:
                self._delete_instance(context, instance, bdms, quotas)
            except exception.InstanceNotFound:
                LOG.info(_("Instance disappeared during terminate"),
                         instance=instance)
            except Exception:
                # As we're trying to delete always go to Error if something
                # goes wrong that _delete_instance can't handle.
                with excutils.save_and_reraise_exception():
                    LOG.exception(_('Setting instance vm_state to ERROR'),
                                  instance=instance)
                    self._set_instance_error_state(context, instance)

        do_terminate_instance(instance, bdms)

    # NOTE(johannes): This is probably better named power_off_instance
    # so it matches the driver method, but because of other issues, we
    # can't use that name in grizzly.
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def stop_instance(self, context, instance):
        """Stopping an instance on this host."""

        @utils.synchronized(instance.uuid)
        def do_stop_instance():
            self._notify_about_instance_usage(context, instance,
                                              "power_off.start")
            self.driver.power_off(instance)
            current_power_state = self._get_power_state(context, instance)
            instance.power_state = current_power_state
            instance.vm_state = vm_states.STOPPED
            instance.task_state = None
            instance.save(expected_task_state=task_states.POWERING_OFF)
            self._notify_about_instance_usage(context, instance,
                                              "power_off.end")

        do_stop_instance()

    def _power_on(self, context, instance):
        network_info = self._get_instance_nw_info(context, instance)
        block_device_info = self._get_instance_block_device_info(context,
                                                                 instance)
        self.driver.power_on(context, instance,
                             network_info,
                             block_device_info)

    # NOTE(johannes): This is probably better named power_on_instance
    # so it matches the driver method, but because of other issues, we
    # can't use that name in grizzly.
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def start_instance(self, context, instance):
        """Starting an instance on this host."""
        self._notify_about_instance_usage(context, instance, "power_on.start")
        self._power_on(context, instance)
        current_power_state = self._get_power_state(context, instance)
        instance.power_state = current_power_state
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.save(expected_task_state=task_states.POWERING_ON)
        self._notify_about_instance_usage(context, instance, "power_on.end")

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def soft_delete_instance(self, context, instance, reservations):
        """Soft delete an instance on this host."""

        quotas = objects.Quotas.from_reservations(context,
                                                  reservations,
                                                  instance=instance)
        try:
            self._notify_about_instance_usage(context, instance,
                                              "soft_delete.start")
            try:
                self.driver.soft_delete(instance)
            except NotImplementedError:
                # Fallback to just powering off the instance if the
                # hypervisor doesn't implement the soft_delete method
                self.driver.power_off(instance)
            current_power_state = self._get_power_state(context, instance)
            instance.power_state = current_power_state
            instance.vm_state = vm_states.SOFT_DELETED
            instance.task_state = None
            instance.save(expected_task_state=[task_states.SOFT_DELETING])
        except Exception:
            with excutils.save_and_reraise_exception():
                quotas.rollback()
        quotas.commit()
        self._notify_about_instance_usage(context, instance, "soft_delete.end")

    @object_compat
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def restore_instance(self, context, instance):
        """Restore a soft-deleted instance on this host."""
        self._notify_about_instance_usage(context, instance, "restore.start")
        try:
            self.driver.restore(instance)
        except NotImplementedError:
            # Fallback to just powering on the instance if the hypervisor
            # doesn't implement the restore method
            self._power_on(context, instance)
        current_power_state = self._get_power_state(context, instance)
        instance.power_state = current_power_state
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.save(expected_task_state=task_states.RESTORING)
        self._notify_about_instance_usage(context, instance, "restore.end")

    def _rebuild_default_impl(self, context, instance, image_meta,
                              injected_files, admin_password, bdms,
                              detach_block_devices, attach_block_devices,
                              network_info=None,
                              recreate=False, block_device_info=None,
                              preserve_ephemeral=False):
        if preserve_ephemeral:
            # The default code path does not support preserving ephemeral
            # partitions.
            raise exception.PreserveEphemeralNotSupported()

        detach_block_devices(context, bdms)

        if not recreate:
            self.driver.destroy(context, instance, network_info,
                                block_device_info=block_device_info)

        instance.task_state = task_states.REBUILD_BLOCK_DEVICE_MAPPING
        instance.save(expected_task_state=[task_states.REBUILDING])

        new_block_device_info = attach_block_devices(context, instance, bdms)

        instance.task_state = task_states.REBUILD_SPAWNING
        instance.save(
            expected_task_state=[task_states.REBUILD_BLOCK_DEVICE_MAPPING])

        self.driver.spawn(context, instance, image_meta, injected_files,
                          admin_password, network_info=network_info,
                          block_device_info=new_block_device_info)

    @object_compat
    @messaging.expected_exceptions(exception.PreserveEphemeralNotSupported)
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def rebuild_instance(self, context, instance, orig_image_ref, image_ref,
                         injected_files, new_pass, orig_sys_metadata,
                         bdms, recreate, on_shared_storage,
                         preserve_ephemeral=False):
        """Destroy and re-make this instance.

        A 'rebuild' effectively purges all existing data from the system and
        remakes the VM with given 'metadata' and 'personalities'.

        :param context: `nova.RequestContext` object
        :param instance: Instance object
        :param orig_image_ref: Original image_ref before rebuild
        :param image_ref: New image_ref for rebuild
        :param injected_files: Files to inject
        :param new_pass: password to set on rebuilt instance
        :param orig_sys_metadata: instance system metadata from pre-rebuild
        :param bdms: block-device-mappings to use for rebuild
        :param recreate: True if the instance is being recreated (e.g. the
            hypervisor it was on failed) - cleanup of old state will be
            skipped.
        :param on_shared_storage: True if instance files on shared storage
        :param preserve_ephemeral: True if the default ephemeral storage
                                   partition must be preserved on rebuild
        """
        context = context.elevated()
        # NOTE (ndipanov): If we get non-object BDMs, just get them from the
        # db again, as this means they are sent in the old format and we want
        # to avoid converting them back when we can just get them.
        # Remove this on the next major RPC version bump
        if (bdms and
            any(not isinstance(bdm, obj_base.NovaObject)
                for bdm in bdms)):
            bdms = None

        orig_vm_state = instance.vm_state
        with self._error_out_instance_on_exception(context, instance):
            LOG.audit(_("Rebuilding instance"), context=context,
                      instance=instance)

            if recreate:
                if not self.driver.capabilities["supports_recreate"]:
                    raise exception.InstanceRecreateNotSupported

                self._check_instance_exists(context, instance)

                # To cover case when admin expects that instance files are on
                # shared storage, but not accessible and vice versa
                if on_shared_storage != self.driver.instance_on_disk(instance):
                    raise exception.InvalidSharedStorage(
                            _("Invalid state of instance files on shared"
                              " storage"))

                if on_shared_storage:
                    LOG.info(_('disk on shared storage, recreating using'
                               ' existing disk'))
                else:
                    image_ref = orig_image_ref = instance.image_ref
                    LOG.info(_("disk not on shared storage, rebuilding from:"
                               " '%s'") % str(image_ref))

                # NOTE(mriedem): On a recreate (evacuate), we need to update
                # the instance's host and node properties to reflect it's
                # destination node for the recreate.
                node_name = None
                try:
                    compute_node = self._get_compute_info(context, self.host)
                    node_name = compute_node.hypervisor_hostname
                except exception.NotFound:
                    LOG.exception(_('Failed to get compute_info for %s') %
                                  self.host)
                finally:
                    instance.host = self.host
                    instance.node = node_name
                    instance.save()

            if image_ref:
                image_meta = self.image_api.get(context, image_ref)
            else:
                image_meta = {}

            # This instance.exists message should contain the original
            # image_ref, not the new one.  Since the DB has been updated
            # to point to the new one... we have to override it.
            #TODO(jaypipes): Move generate_image_url() into the nova.image.api
            orig_image_ref_url = glance.generate_image_url(orig_image_ref)
            extra_usage_info = {'image_ref_url': orig_image_ref_url}
            self.conductor_api.notify_usage_exists(context,
                    obj_base.obj_to_primitive(instance),
                    current_period=True, system_metadata=orig_sys_metadata,
                    extra_usage_info=extra_usage_info)

            # This message should contain the new image_ref
            extra_usage_info = {'image_name': image_meta.get('name', '')}
            self._notify_about_instance_usage(context, instance,
                    "rebuild.start", extra_usage_info=extra_usage_info)

            instance.power_state = self._get_power_state(context, instance)
            instance.task_state = task_states.REBUILDING
            instance.save(expected_task_state=[task_states.REBUILDING])

            if recreate:
                self.network_api.setup_networks_on_host(
                        context, instance, self.host)

            network_info = compute_utils.get_nw_info_for_instance(instance)
            if bdms is None:
                bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                        context, instance.uuid)

            block_device_info = \
                self._get_instance_block_device_info(
                        context, instance, bdms=bdms)

            def detach_block_devices(context, bdms):
                for bdm in bdms:
                    if bdm.is_volume:
                        self.volume_api.detach(context, bdm.volume_id)

            files = self._decode_files(injected_files)

            kwargs = dict(
                context=context,
                instance=instance,
                image_meta=image_meta,
                injected_files=files,
                admin_password=new_pass,
                bdms=bdms,
                detach_block_devices=detach_block_devices,
                attach_block_devices=self._prep_block_device,
                block_device_info=block_device_info,
                network_info=network_info,
                preserve_ephemeral=preserve_ephemeral)
            try:
                self.driver.rebuild(**kwargs)
            except NotImplementedError:
                # NOTE(rpodolyaka): driver doesn't provide specialized version
                # of rebuild, fall back to the default implementation
                self._rebuild_default_impl(**kwargs)
            instance.power_state = self._get_power_state(context, instance)
            instance.vm_state = vm_states.ACTIVE
            instance.task_state = None
            instance.launched_at = timeutils.utcnow()
            instance.save(expected_task_state=[task_states.REBUILD_SPAWNING])

            LOG.info(_("bringing vm to original state: '%s'") % orig_vm_state)
            if orig_vm_state == vm_states.STOPPED:
                instance.vm_state = vm_states.ACTIVE
                instance.task_state = task_states.POWERING_OFF
                instance.progress = 0
                instance.save()
                self.stop_instance(context, instance)

            self._notify_about_instance_usage(
                    context, instance, "rebuild.end",
                    network_info=network_info,
                    extra_usage_info=extra_usage_info)

    def _handle_bad_volumes_detached(self, context, instance, bad_devices,
                                     block_device_info):
        """Handle cases where the virt-layer had to detach non-working volumes
        in order to complete an operation.
        """
        for bdm in block_device_info['block_device_mapping']:
            if bdm.get('mount_device') in bad_devices:
                try:
                    volume_id = bdm['connection_info']['data']['volume_id']
                except KeyError:
                    continue

                # NOTE(sirp): ideally we'd just call
                # `compute_api.detach_volume` here but since that hits the
                # DB directly, that's off limits from within the
                # compute-manager.
                #
                # API-detach
                LOG.info(_("Detaching from volume api: %s") % volume_id)
                volume = self.volume_api.get(context, volume_id)
                self.volume_api.check_detach(context, volume)
                self.volume_api.begin_detaching(context, volume_id)

                # Manager-detach
                self.detach_volume(context, volume_id, instance)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def reboot_instance(self, context, instance, block_device_info,
                        reboot_type):
        """Reboot an instance on this host."""
        # acknowledge the request made it to the manager
        if reboot_type == "SOFT":
            instance.task_state = task_states.REBOOT_PENDING
            expected_states = (task_states.REBOOTING,
                               task_states.REBOOT_PENDING,
                               task_states.REBOOT_STARTED)
        else:
            instance.task_state = task_states.REBOOT_PENDING_HARD
            expected_states = (task_states.REBOOTING_HARD,
                               task_states.REBOOT_PENDING_HARD,
                               task_states.REBOOT_STARTED_HARD)
        context = context.elevated()
        LOG.audit(_("Rebooting instance"), context=context, instance=instance)

        block_device_info = self._get_instance_block_device_info(context,
                                                                 instance)

        network_info = self._get_instance_nw_info(context, instance)

        self._notify_about_instance_usage(context, instance, "reboot.start")

        current_power_state = self._get_power_state(context, instance)

        instance.power_state = current_power_state
        instance.save(expected_task_state=expected_states)

        if instance['power_state'] != power_state.RUNNING:
            state = instance['power_state']
            running = power_state.RUNNING
            LOG.warn(_('trying to reboot a non-running instance:'
                       ' (state: %(state)s expected: %(running)s)'),
                     {'state': state, 'running': running},
                     context=context, instance=instance)

        def bad_volumes_callback(bad_devices):
            self._handle_bad_volumes_detached(
                    context, instance, bad_devices, block_device_info)

        try:
            # Don't change it out of rescue mode
            if instance['vm_state'] == vm_states.RESCUED:
                new_vm_state = vm_states.RESCUED
            else:
                new_vm_state = vm_states.ACTIVE
            new_power_state = None
            if reboot_type == "SOFT":
                instance.task_state = task_states.REBOOT_STARTED
                expected_state = task_states.REBOOT_PENDING
            else:
                instance.task_state = task_states.REBOOT_STARTED_HARD
                expected_state = task_states.REBOOT_PENDING_HARD
            instance.save(expected_task_state=expected_state)
            self.driver.reboot(context, instance,
                               network_info,
                               reboot_type,
                               block_device_info=block_device_info,
                               bad_volumes_callback=bad_volumes_callback)

        except Exception as error:
            with excutils.save_and_reraise_exception() as ctxt:
                exc_info = sys.exc_info()
                # if the reboot failed but the VM is running don't
                # put it into an error state
                new_power_state = self._get_power_state(context, instance)
                if new_power_state == power_state.RUNNING:
                    LOG.warning(_('Reboot failed but instance is running'),
                                context=context, instance=instance)
                    compute_utils.add_instance_fault_from_exc(context,
                            instance, error, exc_info)
                    self._notify_about_instance_usage(context, instance,
                            'reboot.error', fault=error)
                    ctxt.reraise = False
                else:
                    LOG.error(_('Cannot reboot instance: %s'), error,
                              context=context, instance=instance)
                    self._set_instance_obj_error_state(context, instance)

        if not new_power_state:
            new_power_state = self._get_power_state(context, instance)
        try:
            instance.power_state = new_power_state
            instance.vm_state = new_vm_state
            instance.task_state = None
            instance.save()
        except exception.InstanceNotFound:
            LOG.warn(_("Instance disappeared during reboot"),
                     context=context, instance=instance)

        self._notify_about_instance_usage(context, instance, "reboot.end")

    @delete_image_on_error
    def _do_snapshot_instance(self, context, image_id, instance, rotation):
        if rotation < 0:
            raise exception.RotationRequiredForBackup()
        self._snapshot_instance(context, image_id, instance,
                                task_states.IMAGE_BACKUP)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def backup_instance(self, context, image_id, instance, backup_type,
                        rotation):
        """Backup an instance on this host.

        :param backup_type: daily | weekly
        :param rotation: int representing how many backups to keep around
        """
        self._do_snapshot_instance(context, image_id, instance, rotation)
        self._rotate_backups(context, instance, backup_type, rotation)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    @delete_image_on_error
    def snapshot_instance(self, context, image_id, instance):
        """Snapshot an instance on this host.

        :param context: security context
        :param instance: a nova.objects.instance.Instance object
        :param image_id: glance.db.sqlalchemy.models.Image.Id
        """
        # NOTE(dave-mcnally) the task state will already be set by the api
        # but if the compute manager has crashed/been restarted prior to the
        # request getting here the task state may have been cleared so we set
        # it again and things continue normally
        try:
            instance.task_state = task_states.IMAGE_SNAPSHOT
            instance.save(
                        expected_task_state=task_states.IMAGE_SNAPSHOT_PENDING)
        except exception.InstanceNotFound:
            # possibility instance no longer exists, no point in continuing
            LOG.debug("Instance not found, could not set state %s "
                      "for instance.",
                      task_states.IMAGE_SNAPSHOT, instance=instance)
            return

        except exception.UnexpectedDeletingTaskStateError:
            LOG.debug("Instance being deleted, snapshot cannot continue",
                      instance=instance)
            return

        self._snapshot_instance(context, image_id, instance,
                                task_states.IMAGE_SNAPSHOT)

    def _snapshot_instance(self, context, image_id, instance,
                           expected_task_state):
        context = context.elevated()

        current_power_state = self._get_power_state(context, instance)
        try:
            instance.power_state = current_power_state
            instance.save()

            LOG.audit(_('instance snapshotting'), context=context,
                  instance=instance)

            if instance.power_state != power_state.RUNNING:
                state = instance.power_state
                running = power_state.RUNNING
                LOG.warn(_('trying to snapshot a non-running instance: '
                       '(state: %(state)s expected: %(running)s)'),
                     {'state': state, 'running': running},
                     instance=instance)

            self._notify_about_instance_usage(
                context, instance, "snapshot.start")

            def update_task_state(task_state,
                                  expected_state=expected_task_state):
                instance.task_state = task_state
                instance.save(expected_task_state=expected_state)

            self.driver.snapshot(context, instance, image_id,
                                 update_task_state)

            instance.task_state = None
            instance.save(expected_task_state=task_states.IMAGE_UPLOADING)

            self._notify_about_instance_usage(context, instance,
                                              "snapshot.end")
        except (exception.InstanceNotFound,
                exception.UnexpectedDeletingTaskStateError):
            # the instance got deleted during the snapshot
            # Quickly bail out of here
            msg = 'Instance disappeared during snapshot'
            LOG.debug(msg, instance=instance)
            try:
                image_service = glance.get_default_image_service()
                image = image_service.show(context, image_id)
                if image['status'] != 'active':
                    image_service.delete(context, image_id)
            except Exception:
                LOG.warning(_("Error while trying to clean up image %s"),
                            image_id, instance=instance)
        except exception.ImageNotFound:
            instance.task_state = None
            instance.save()
            msg = _("Image not found during snapshot")
            LOG.warn(msg, instance=instance)

    @object_compat
    @messaging.expected_exceptions(NotImplementedError)
    def volume_snapshot_create(self, context, instance, volume_id,
                               create_info):
        self.driver.volume_snapshot_create(context, instance, volume_id,
                                           create_info)

    @object_compat
    @messaging.expected_exceptions(NotImplementedError)
    def volume_snapshot_delete(self, context, instance, volume_id,
                               snapshot_id, delete_info):
        self.driver.volume_snapshot_delete(context, instance, volume_id,
                                           snapshot_id, delete_info)

    @wrap_instance_fault
    def _rotate_backups(self, context, instance, backup_type, rotation):
        """Delete excess backups associated to an instance.

        Instances are allowed a fixed number of backups (the rotation number);
        this method deletes the oldest backups that exceed the rotation
        threshold.

        :param context: security context
        :param instance: Instance dict
        :param backup_type: daily | weekly
        :param rotation: int representing how many backups to keep around;
            None if rotation shouldn't be used (as in the case of snapshots)
        """
        filters = {'property-image_type': 'backup',
                   'property-backup_type': backup_type,
                   'property-instance_uuid': instance.uuid}

        images = self.image_api.get_all(context, filters=filters,
                                        sort_key='created_at', sort_dir='desc')
        num_images = len(images)
        LOG.debug("Found %(num_images)d images (rotation: %(rotation)d)",
                  {'num_images': num_images, 'rotation': rotation},
                  instance=instance)

        if num_images > rotation:
            # NOTE(sirp): this deletes all backups that exceed the rotation
            # limit
            excess = len(images) - rotation
            LOG.debug("Rotating out %d backups", excess,
                      instance=instance)
            for i in xrange(excess):
                image = images.pop()
                image_id = image['id']
                LOG.debug("Deleting image %s", image_id,
                          instance=instance)
                self.image_api.delete(context, image_id)

    @object_compat
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def set_admin_password(self, context, instance, new_pass):
        """Set the root/admin password for an instance on this host.

        This is generally only called by API password resets after an
        image has been built.

        @param context: Nova auth context.
        @param instance: Nova instance object.
        @param new_pass: The admin password for the instance.
        """

        context = context.elevated()
        if new_pass is None:
            # Generate a random password
            new_pass = utils.generate_password()

        current_power_state = self._get_power_state(context, instance)
        expected_state = power_state.RUNNING

        if current_power_state != expected_state:
            instance.task_state = None
            instance.save(expected_task_state=task_states.UPDATING_PASSWORD)
            _msg = _('Failed to set admin password. Instance %s is not'
                     ' running') % instance.uuid
            raise exception.InstancePasswordSetFailed(
                instance=instance.uuid, reason=_msg)

        try:
            self.driver.set_admin_password(instance, new_pass)
            LOG.audit(_("Root password set"), instance=instance)
            instance.task_state = None
            instance.save(
                expected_task_state=task_states.UPDATING_PASSWORD)
        except NotImplementedError:
            _msg = _('set_admin_password is not implemented '
                     'by this driver or guest instance.')
            LOG.warn(_msg, instance=instance)
            instance.task_state = None
            instance.save(
                expected_task_state=task_states.UPDATING_PASSWORD)
            raise NotImplementedError(_msg)
        except exception.UnexpectedTaskStateError:
            # interrupted by another (most likely delete) task
            # do not retry
            raise
        except Exception as e:
            # Catch all here because this could be anything.
            LOG.exception(_('set_admin_password failed: %s') % e,
                          instance=instance)
            self._set_instance_obj_error_state(context, instance)
            # We create a new exception here so that we won't
            # potentially reveal password information to the
            # API caller.  The real exception is logged above
            _msg = _('error setting admin password')
            raise exception.InstancePasswordSetFailed(
                instance=instance.uuid, reason=_msg)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def inject_file(self, context, path, file_contents, instance):
        """Write a file to the specified path in an instance on this host."""
        # NOTE(russellb) Remove this method, as well as the underlying virt
        # driver methods, when the compute rpc interface is bumped to 4.x
        # as it is no longer used.
        context = context.elevated()
        current_power_state = self._get_power_state(context, instance)
        expected_state = power_state.RUNNING
        if current_power_state != expected_state:
            LOG.warn(_('trying to inject a file into a non-running (state: '
                       '%(current_state)s expected: %(expected_state)s)'),
                     {'current_state': current_power_state,
                      'expected_state': expected_state},
                     instance=instance)
        LOG.audit(_('injecting file to %s'), path,
                    instance=instance)
        self.driver.inject_file(instance, path, file_contents)

    def _get_rescue_image(self, context, instance, rescue_image_ref=None):
        """Determine what image should be used to boot the rescue VM."""
        # 1. If rescue_image_ref is passed in, use that for rescue.
        # 2. Else, use the base image associated with instance's current image.
        #       The idea here is to provide the customer with a rescue
        #       environment which they are familiar with.
        #       So, if they built their instance off of a Debian image,
        #       their rescue VM will also be Debian.
        # 3. As a last resort, use instance's current image.
        if not rescue_image_ref:
            system_meta = utils.instance_sys_meta(instance)
            rescue_image_ref = system_meta.get('image_base_image_ref')

        if not rescue_image_ref:
            LOG.warn(_('Unable to find a different image to use for rescue VM,'
                       ' using instance\'s current image'), instance=instance)
            rescue_image_ref = instance.image_ref

        image_meta = compute_utils.get_image_metadata(context, self.image_api,
                                                      rescue_image_ref,
                                                      instance)
        # NOTE(belliott) bug #1227350 - xenapi needs the actual image id
        image_meta['id'] = rescue_image_ref
        return image_meta

    @object_compat
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def rescue_instance(self, context, instance, rescue_password,
                        rescue_image_ref=None):
        context = context.elevated()
        LOG.audit(_('Rescuing'), context=context, instance=instance)

        admin_password = (rescue_password if rescue_password else
                      utils.generate_password())

        network_info = self._get_instance_nw_info(context, instance)

        rescue_image_meta = self._get_rescue_image(context, instance,
                                                   rescue_image_ref)

        extra_usage_info = {'rescue_image_name':
                            rescue_image_meta.get('name', '')}
        self._notify_about_instance_usage(context, instance,
                "rescue.start", extra_usage_info=extra_usage_info,
                network_info=network_info)

        try:
            self.driver.rescue(context, instance,
                               network_info,
                               rescue_image_meta, admin_password)
        except Exception as e:
            LOG.exception(_("Error trying to Rescue Instance"),
                          instance=instance)
            raise exception.InstanceNotRescuable(
                instance_id=instance.uuid,
                reason=_("Driver Error: %s") % unicode(e))

        self.conductor_api.notify_usage_exists(context, instance,
                                               current_period=True)

        current_power_state = self._get_power_state(context, instance)
        instance.vm_state = vm_states.RESCUED
        instance.task_state = None
        instance.power_state = current_power_state
        instance.launched_at = timeutils.utcnow()
        instance.save(expected_task_state=task_states.RESCUING)

        self._notify_about_instance_usage(context, instance,
                "rescue.end", extra_usage_info=extra_usage_info,
                network_info=network_info)

    @object_compat
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def unrescue_instance(self, context, instance):
        context = context.elevated()
        LOG.audit(_('Unrescuing'), context=context, instance=instance)

        network_info = self._get_instance_nw_info(context, instance)
        self._notify_about_instance_usage(context, instance,
                "unrescue.start", network_info=network_info)
        with self._error_out_instance_on_exception(context, instance):
            self.driver.unrescue(instance,
                                 network_info)

        current_power_state = self._get_power_state(context, instance)
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.power_state = current_power_state
        instance.save(expected_task_state=task_states.UNRESCUING)

        self._notify_about_instance_usage(context,
                                          instance,
                                          "unrescue.end",
                                          network_info=network_info)

    @object_compat
    @wrap_exception()
    @wrap_instance_fault
    def change_instance_metadata(self, context, diff, instance):
        """Update the metadata published to the instance."""
        LOG.debug("Changing instance metadata according to %r",
                  diff, instance=instance)
        self.driver.change_instance_metadata(context, instance, diff)

    def _cleanup_stored_instance_types(self, migration, instance,
                                       restore_old=False):
        """Clean up "old" and "new" instance_type information stored in
        instance's system_metadata. Optionally update the "current"
        instance_type to the saved old one first.

        Returns the updated system_metadata as a dict, as well as the
        post-cleanup current instance type.
        """
        sys_meta = instance.system_metadata
        if restore_old:
            instance_type = flavors.extract_flavor(instance, 'old_')
            sys_meta = flavors.save_flavor_info(sys_meta, instance_type)
        else:
            instance_type = flavors.extract_flavor(instance)

        flavors.delete_flavor_info(sys_meta, 'old_')
        flavors.delete_flavor_info(sys_meta, 'new_')

        return sys_meta, instance_type

    @wrap_exception()
    @wrap_instance_event
    @wrap_instance_fault
    def confirm_resize(self, context, instance, reservations, migration):

        quotas = objects.Quotas.from_reservations(context,
                                                  reservations,
                                                  instance=instance)

        @utils.synchronized(instance['uuid'])
        def do_confirm_resize(context, instance, migration_id):
            # NOTE(wangpan): Get the migration status from db, if it has been
            #                confirmed, we do nothing and return here
            LOG.debug("Going to confirm migration %s", migration_id,
                      context=context, instance=instance)
            try:
                # TODO(russellb) Why are we sending the migration object just
                # to turn around and look it up from the db again?
                migration = objects.Migration.get_by_id(
                                    context.elevated(), migration_id)
            except exception.MigrationNotFound:
                LOG.error(_("Migration %s is not found during confirmation") %
                            migration_id, context=context, instance=instance)
                return

            if migration.status == 'confirmed':
                LOG.info(_("Migration %s is already confirmed") %
                            migration_id, context=context, instance=instance)
                return
            elif migration.status not in ('finished', 'confirming'):
                LOG.warn(_("Unexpected confirmation status '%(status)s' of "
                           "migration %(id)s, exit confirmation process") %
                           {"status": migration.status, "id": migration_id},
                           context=context, instance=instance)
                return

            # NOTE(wangpan): Get the instance from db, if it has been
            #                deleted, we do nothing and return here
            expected_attrs = ['metadata', 'system_metadata']
            try:
                instance = objects.Instance.get_by_uuid(
                        context, instance.uuid,
                        expected_attrs=expected_attrs)
            except exception.InstanceNotFound:
                LOG.info(_("Instance is not found during confirmation"),
                            context=context, instance=instance)
                return

            self._confirm_resize(context, instance, quotas,
                                 migration=migration)

        do_confirm_resize(context, instance, migration.id)

    def _confirm_resize(self, context, instance, quotas,
                        migration=None):
        """Destroys the source instance."""
        self._notify_about_instance_usage(context, instance,
                                          "resize.confirm.start")

        with self._error_out_instance_on_exception(context, instance,
                                                   quotas=quotas):
            # NOTE(danms): delete stashed migration information
            sys_meta, instance_type = self._cleanup_stored_instance_types(
                migration, instance)
            sys_meta.pop('old_vm_state', None)

            instance.system_metadata = sys_meta
            instance.save()

            # NOTE(tr3buchet): tear down networks on source host
            self.network_api.setup_networks_on_host(context, instance,
                               migration.source_compute, teardown=True)

            network_info = self._get_instance_nw_info(context, instance)
            self.driver.confirm_migration(migration, instance,
                                          network_info)

            migration.status = 'confirmed'
            migration.save(context.elevated())

            rt = self._get_resource_tracker(migration.source_node)
            rt.drop_resize_claim(instance, prefix='old_')

            # NOTE(mriedem): The old_vm_state could be STOPPED but the user
            # might have manually powered up the instance to confirm the
            # resize/migrate, so we need to check the current power state
            # on the instance and set the vm_state appropriately. We default
            # to ACTIVE because if the power state is not SHUTDOWN, we
            # assume _sync_instance_power_state will clean it up.
            p_state = instance.power_state
            vm_state = None
            if p_state == power_state.SHUTDOWN:
                vm_state = vm_states.STOPPED
                LOG.debug("Resized/migrated instance is powered off. "
                          "Setting vm_state to '%s'.", vm_state,
                          instance=instance)
            else:
                vm_state = vm_states.ACTIVE

            instance.vm_state = vm_state
            instance.task_state = None
            instance.save(expected_task_state=[None, task_states.DELETING])

            self._notify_about_instance_usage(
                context, instance, "resize.confirm.end",
                network_info=network_info)

            quotas.commit()

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def revert_resize(self, context, instance, migration, reservations):
        """Destroys the new instance on the destination machine.

        Reverts the model changes, and powers on the old instance on the
        source machine.

        """

        quotas = quotas_obj.Quotas.from_reservations(context,
                                                     reservations,
                                                     instance=instance)

        # NOTE(comstud): A revert_resize is essentially a resize back to
        # the old size, so we need to send a usage event here.
        self.conductor_api.notify_usage_exists(
                context, instance, current_period=True)

        with self._error_out_instance_on_exception(context, instance,
                                                   quotas=quotas):
            # NOTE(tr3buchet): tear down networks on destination host
            self.network_api.setup_networks_on_host(context, instance,
                                                    teardown=True)

            instance_p = obj_base.obj_to_primitive(instance)
            migration_p = obj_base.obj_to_primitive(migration)
            self.network_api.migrate_instance_start(context,
                                                    instance_p,
                                                    migration_p)

            network_info = self._get_instance_nw_info(context, instance)
            bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid)
            block_device_info = self._get_instance_block_device_info(
                                context, instance, bdms=bdms)

            self.driver.destroy(context, instance, network_info,
                                block_device_info)

            self._terminate_volume_connections(context, instance, bdms)

            migration.status = 'reverted'
            migration.save(context.elevated())

            rt = self._get_resource_tracker(instance.node)
            rt.drop_resize_claim(instance)

            self.compute_rpcapi.finish_revert_resize(context, instance,
                    migration, migration.source_compute,
                    quotas.reservations)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def finish_revert_resize(self, context, instance, reservations, migration):
        """Finishes the second half of reverting a resize.

        Bring the original source instance state back (active/shutoff) and
        revert the resized attributes in the database.

        """

        quotas = quotas_obj.Quotas.from_reservations(context,
                                                     reservations,
                                                     instance=instance)

        with self._error_out_instance_on_exception(context, instance,
                                                   quotas=quotas):
            network_info = self._get_instance_nw_info(context, instance)

            self._notify_about_instance_usage(
                    context, instance, "resize.revert.start")

            sys_meta, instance_type = self._cleanup_stored_instance_types(
                migration, instance, True)

            # NOTE(mriedem): delete stashed old_vm_state information; we
            # default to ACTIVE for backwards compatibility if old_vm_state
            # is not set
            old_vm_state = sys_meta.pop('old_vm_state', vm_states.ACTIVE)

            instance.system_metadata = sys_meta
            instance.memory_mb = instance_type['memory_mb']
            instance.vcpus = instance_type['vcpus']
            instance.root_gb = instance_type['root_gb']
            instance.ephemeral_gb = instance_type['ephemeral_gb']
            instance.instance_type_id = instance_type['id']
            instance.host = migration['source_compute']
            instance.node = migration['source_node']
            instance.save()

            self.network_api.setup_networks_on_host(context, instance,
                                            migration['source_compute'])

            block_device_info = self._get_instance_block_device_info(
                    context, instance, refresh_conn_info=True)

            power_on = old_vm_state != vm_states.STOPPED
            self.driver.finish_revert_migration(context, instance,
                                       network_info,
                                       block_device_info, power_on)

            instance.launched_at = timeutils.utcnow()
            instance.save(expected_task_state=task_states.RESIZE_REVERTING)

            instance_p = obj_base.obj_to_primitive(instance)
            migration_p = obj_base.obj_to_primitive(migration)
            self.network_api.migrate_instance_finish(context,
                                                     instance_p,
                                                     migration_p)

            # if the original vm state was STOPPED, set it back to STOPPED
            LOG.info(_("Updating instance to original state: '%s'") %
                     old_vm_state)
            if power_on:
                instance.vm_state = vm_states.ACTIVE
                instance.task_state = None
                instance.save()
            else:
                instance.task_state = task_states.POWERING_OFF
                instance.save()
                self.stop_instance(context, instance=instance)

            self._notify_about_instance_usage(
                    context, instance, "resize.revert.end")
            quotas.commit()

    def _prep_resize(self, context, image, instance, instance_type,
            quotas, request_spec, filter_properties, node):

        if not filter_properties:
            filter_properties = {}

        if not instance['host']:
            self._set_instance_error_state(context, instance)
            msg = _('Instance has no source host')
            raise exception.MigrationError(msg)

        same_host = instance['host'] == self.host
        if same_host and not CONF.allow_resize_to_same_host:
            self._set_instance_error_state(context, instance)
            msg = _('destination same as source!')
            raise exception.MigrationError(msg)

        # NOTE(danms): Stash the new instance_type to avoid having to
        # look it up in the database later
        sys_meta = instance.system_metadata
        flavors.save_flavor_info(sys_meta, instance_type, prefix='new_')
        # NOTE(mriedem): Stash the old vm_state so we can set the
        # resized/reverted instance back to the same state later.
        vm_state = instance['vm_state']
        LOG.debug('Stashing vm_state: %s', vm_state, instance=instance)
        sys_meta['old_vm_state'] = vm_state
        instance.save()

        limits = filter_properties.get('limits', {})
        rt = self._get_resource_tracker(node)
        with rt.resize_claim(context, instance, instance_type,
                             limits=limits) as claim:
            LOG.audit(_('Migrating'), context=context, instance=instance)
            self.compute_rpcapi.resize_instance(
                    context, instance, claim.migration, image,
                    instance_type, quotas.reservations)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def prep_resize(self, context, image, instance, instance_type,
                    reservations, request_spec, filter_properties, node):
        """Initiates the process of moving a running instance to another host.

        Possibly changes the RAM and disk size in the process.

        """
        if node is None:
            node = self.driver.get_available_nodes(refresh=True)[0]
            LOG.debug("No node specified, defaulting to %s", node,
                      instance=instance)

        quotas = quotas_obj.Quotas.from_reservations(context,
                                                     reservations,
                                                     instance=instance)
        with self._error_out_instance_on_exception(context, instance,
                                                   quotas=quotas):
            self.conductor_api.notify_usage_exists(
                    context, instance, current_period=True)
            self._notify_about_instance_usage(
                    context, instance, "resize.prep.start")
            try:
                self._prep_resize(context, image, instance,
                                  instance_type, quotas,
                                  request_spec, filter_properties,
                                  node)
            except Exception:
                # try to re-schedule the resize elsewhere:
                exc_info = sys.exc_info()
                self._reschedule_resize_or_reraise(context, image, instance,
                        exc_info, instance_type, quotas, request_spec,
                        filter_properties)
            finally:
                extra_usage_info = dict(
                        new_instance_type=instance_type['name'],
                        new_instance_type_id=instance_type['id'])

                self._notify_about_instance_usage(
                    context, instance, "resize.prep.end",
                    extra_usage_info=extra_usage_info)

    def _reschedule_resize_or_reraise(self, context, image, instance, exc_info,
            instance_type, quotas, request_spec, filter_properties):
        """Try to re-schedule the resize or re-raise the original error to
        error out the instance.
        """
        if not request_spec:
            request_spec = {}
        if not filter_properties:
            filter_properties = {}

        rescheduled = False
        instance_uuid = instance['uuid']

        try:
            # NOTE(comstud): remove the scheduler RPCAPI method when
            # this is adjusted to send to conductor... and then
            # deprecate the scheduler manager method.
            scheduler_method = self.scheduler_rpcapi.prep_resize
            instance_p = obj_base.obj_to_primitive(instance)
            method_args = (instance_p, instance_type, image, request_spec,
                           filter_properties, quotas.reservations)
            task_state = task_states.RESIZE_PREP

            rescheduled = self._reschedule(context, request_spec,
                    filter_properties, instance, scheduler_method,
                    method_args, task_state, exc_info)
        except Exception as error:
            rescheduled = False
            LOG.exception(_("Error trying to reschedule"),
                          instance_uuid=instance_uuid)
            compute_utils.add_instance_fault_from_exc(context,
                    instance, error,
                    exc_info=sys.exc_info())
            self._notify_about_instance_usage(context, instance,
                    'resize.error', fault=error)

        if rescheduled:
            self._log_original_error(exc_info, instance_uuid)
            compute_utils.add_instance_fault_from_exc(context,
                    instance, exc_info[1], exc_info=exc_info)
            self._notify_about_instance_usage(context, instance,
                    'resize.error', fault=exc_info[1])
        else:
            # not re-scheduling
            raise exc_info[0], exc_info[1], exc_info[2]

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @errors_out_migration
    @wrap_instance_fault
    def resize_instance(self, context, instance, image,
                        reservations, migration, instance_type):
        """Starts the migration of a running instance to another host."""

        quotas = quotas_obj.Quotas.from_reservations(context,
                                                     reservations,
                                                     instance=instance)
        with self._error_out_instance_on_exception(context, instance,
                                                   quotas=quotas):
            if not instance_type:
                instance_type = objects.Flavor.get_by_id(
                    context, migration['new_instance_type_id'])

            network_info = self._get_instance_nw_info(context, instance)

            migration.status = 'migrating'
            migration.save(context.elevated())

            instance.task_state = task_states.RESIZE_MIGRATING
            instance.save(expected_task_state=task_states.RESIZE_PREP)

            self._notify_about_instance_usage(
                context, instance, "resize.start", network_info=network_info)

            bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid)
            block_device_info = self._get_instance_block_device_info(
                                context, instance, bdms=bdms)

            disk_info = self.driver.migrate_disk_and_power_off(
                    context, instance, migration.dest_host,
                    instance_type, network_info,
                    block_device_info)

            self._terminate_volume_connections(context, instance, bdms)

            migration_p = obj_base.obj_to_primitive(migration)
            instance_p = obj_base.obj_to_primitive(instance)
            self.network_api.migrate_instance_start(context,
                                                    instance_p,
                                                    migration_p)

            migration.status = 'post-migrating'
            migration.save(context.elevated())

            instance.host = migration.dest_compute
            instance.node = migration.dest_node
            instance.task_state = task_states.RESIZE_MIGRATED
            instance.save(expected_task_state=task_states.RESIZE_MIGRATING)

            self.compute_rpcapi.finish_resize(context, instance,
                    migration, image, disk_info,
                    migration.dest_compute, reservations=quotas.reservations)

            self._notify_about_instance_usage(context, instance, "resize.end",
                                              network_info=network_info)
            self.instance_events.clear_events_for_instance(instance)

    def _terminate_volume_connections(self, context, instance, bdms):
        connector = self.driver.get_volume_connector(instance)
        for bdm in bdms:
            if bdm.is_volume:
                self.volume_api.terminate_connection(context, bdm.volume_id,
                                                     connector)

    def _finish_resize(self, context, instance, migration, disk_info,
                       image):
        resize_instance = False
        old_instance_type_id = migration['old_instance_type_id']
        new_instance_type_id = migration['new_instance_type_id']
        old_instance_type = flavors.extract_flavor(instance)
        sys_meta = instance.system_metadata
        # NOTE(mriedem): Get the old_vm_state so we know if we should
        # power on the instance. If old_vm_state is not set we need to default
        # to ACTIVE for backwards compatibility
        old_vm_state = sys_meta.get('old_vm_state', vm_states.ACTIVE)
        flavors.save_flavor_info(sys_meta,
                                 old_instance_type,
                                 prefix='old_')

        if old_instance_type_id != new_instance_type_id:
            instance_type = flavors.extract_flavor(instance, prefix='new_')
            flavors.save_flavor_info(sys_meta, instance_type)
            instance.instance_type_id = instance_type['id']
            instance.memory_mb = instance_type['memory_mb']
            instance.vcpus = instance_type['vcpus']
            instance.root_gb = instance_type['root_gb']
            instance.ephemeral_gb = instance_type['ephemeral_gb']
            instance.system_metadata = sys_meta
            instance.save()
            resize_instance = True

        # NOTE(tr3buchet): setup networks on destination host
        self.network_api.setup_networks_on_host(context, instance,
                                                migration['dest_compute'])

        instance_p = obj_base.obj_to_primitive(instance)
        migration_p = obj_base.obj_to_primitive(migration)
        self.network_api.migrate_instance_finish(context,
                                                 instance_p,
                                                 migration_p)

        network_info = self._get_instance_nw_info(context, instance)

        instance.task_state = task_states.RESIZE_FINISH
        instance.system_metadata = sys_meta
        instance.save(expected_task_state=task_states.RESIZE_MIGRATED)

        self._notify_about_instance_usage(
            context, instance, "finish_resize.start",
            network_info=network_info)

        block_device_info = self._get_instance_block_device_info(
                            context, instance, refresh_conn_info=True)

        # NOTE(mriedem): If the original vm_state was STOPPED, we don't
        # automatically power on the instance after it's migrated
        power_on = old_vm_state != vm_states.STOPPED
        self.driver.finish_migration(context, migration, instance,
                                     disk_info,
                                     network_info,
                                     image, resize_instance,
                                     block_device_info, power_on)

        migration.status = 'finished'
        migration.save(context.elevated())

        instance.vm_state = vm_states.RESIZED
        instance.task_state = None
        instance.launched_at = timeutils.utcnow()
        instance.save(expected_task_state=task_states.RESIZE_FINISH)

        self._notify_about_instance_usage(
            context, instance, "finish_resize.end",
            network_info=network_info)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @errors_out_migration
    @wrap_instance_fault
    def finish_resize(self, context, disk_info, image, instance,
                      reservations, migration):
        """Completes the migration process.

        Sets up the newly transferred disk and turns on the instance at its
        new host machine.

        """
        quotas = quotas_obj.Quotas.from_reservations(context,
                                                     reservations,
                                                     instance=instance)
        try:
            self._finish_resize(context, instance, migration,
                                disk_info, image)
            quotas.commit()
        except Exception:
            LOG.exception(_('Setting instance vm_state to ERROR'),
                          instance=instance)
            with excutils.save_and_reraise_exception():
                try:
                    quotas.rollback()
                except Exception as qr_error:
                    LOG.exception(_("Failed to rollback quota for failed "
                                    "finish_resize: %s"),
                                  qr_error, instance=instance)
                self._set_instance_error_state(context, instance)

    @object_compat
    @wrap_exception()
    @wrap_instance_fault
    def add_fixed_ip_to_instance(self, context, network_id, instance):
        """Calls network_api to add new fixed_ip to instance
        then injects the new network info and resets instance networking.

        """
        self._notify_about_instance_usage(
                context, instance, "create_ip.start")

        network_info = self.network_api.add_fixed_ip_to_instance(context,
                                                                 instance,
                                                                 network_id)
        self._inject_network_info(context, instance, network_info)
        self.reset_network(context, instance)

        # NOTE(russellb) We just want to bump updated_at.  See bug 1143466.
        instance.updated_at = timeutils.utcnow()
        instance.save()

        self._notify_about_instance_usage(
            context, instance, "create_ip.end", network_info=network_info)

    @object_compat
    @wrap_exception()
    @wrap_instance_fault
    def remove_fixed_ip_from_instance(self, context, address, instance):
        """Calls network_api to remove existing fixed_ip from instance
        by injecting the altered network info and resetting
        instance networking.
        """
        self._notify_about_instance_usage(
                context, instance, "delete_ip.start")

        network_info = self.network_api.remove_fixed_ip_from_instance(context,
                                                                      instance,
                                                                      address)
        self._inject_network_info(context, instance, network_info)
        self.reset_network(context, instance)

        # NOTE(russellb) We just want to bump updated_at.  See bug 1143466.
        instance.updated_at = timeutils.utcnow()
        instance.save()

        self._notify_about_instance_usage(
            context, instance, "delete_ip.end", network_info=network_info)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def pause_instance(self, context, instance):
        """Pause an instance on this host."""
        context = context.elevated()
        LOG.audit(_('Pausing'), context=context, instance=instance)
        self._notify_about_instance_usage(context, instance, 'pause.start')
        self.driver.pause(instance)
        current_power_state = self._get_power_state(context, instance)
        instance.power_state = current_power_state
        instance.vm_state = vm_states.PAUSED
        instance.task_state = None
        instance.save(expected_task_state=task_states.PAUSING)
        self._notify_about_instance_usage(context, instance, 'pause.end')

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def unpause_instance(self, context, instance):
        """Unpause a paused instance on this host."""
        context = context.elevated()
        LOG.audit(_('Unpausing'), context=context, instance=instance)
        self._notify_about_instance_usage(context, instance, 'unpause.start')
        self.driver.unpause(instance)
        current_power_state = self._get_power_state(context, instance)
        instance.power_state = current_power_state
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.save(expected_task_state=task_states.UNPAUSING)
        self._notify_about_instance_usage(context, instance, 'unpause.end')

    @wrap_exception()
    def host_power_action(self, context, action):
        """Reboots, shuts down or powers up the host."""
        # TODO(russellb) Remove the unused host parameter from the driver API
        return self.driver.host_power_action(None, action)

    @wrap_exception()
    def host_maintenance_mode(self, context, host, mode):
        """Start/Stop host maintenance window. On start, it triggers
        guest VMs evacuation.
        """
        return self.driver.host_maintenance_mode(host, mode)

    @wrap_exception()
    def set_host_enabled(self, context, enabled):
        """Sets the specified host's ability to accept new instances."""
        # TODO(russellb) Remove the unused host parameter from the driver API
        return self.driver.set_host_enabled(None, enabled)

    @wrap_exception()
    def get_host_uptime(self, context):
        """Returns the result of calling "uptime" on the target host."""
        return self.driver.get_host_uptime(self.host)

    @object_compat
    @wrap_exception()
    @wrap_instance_fault
    def get_diagnostics(self, context, instance):
        """Retrieve diagnostics for an instance on this host."""
        current_power_state = self._get_power_state(context, instance)
        if current_power_state == power_state.RUNNING:
            LOG.audit(_("Retrieving diagnostics"), context=context,
                      instance=instance)
            return self.driver.get_diagnostics(instance)
        else:
            raise exception.InstanceInvalidState(
                attr='power_state',
                instance_uuid=instance.uuid,
                state=instance.power_state,
                method='get_diagnostics')

    @object_compat
    @wrap_exception()
    @wrap_instance_fault
    def get_instance_diagnostics(self, context, instance):
        """Retrieve diagnostics for an instance on this host."""
        current_power_state = self._get_power_state(context, instance)
        if current_power_state == power_state.RUNNING:
            LOG.audit(_("Retrieving diagnostics"), context=context,
                      instance=instance)
            diags = self.driver.get_instance_diagnostics(instance)
            return diags.serialize()
        else:
            raise exception.InstanceInvalidState(
                attr='power_state',
                instance_uuid=instance.uuid,
                state=instance.power_state,
                method='get_diagnostics')

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def suspend_instance(self, context, instance):
        """Suspend the given instance."""
        context = context.elevated()

        with self._error_out_instance_on_exception(context, instance,
             instance_state=instance['vm_state']):
            self.driver.suspend(instance)
        current_power_state = self._get_power_state(context, instance)
        instance.power_state = current_power_state
        instance.vm_state = vm_states.SUSPENDED
        instance.task_state = None
        instance.save(expected_task_state=task_states.SUSPENDING)
        self._notify_about_instance_usage(context, instance, 'suspend')

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def resume_instance(self, context, instance):
        """Resume the given suspended instance."""
        context = context.elevated()
        LOG.audit(_('Resuming'), context=context, instance=instance)

        network_info = self._get_instance_nw_info(context, instance)
        block_device_info = self._get_instance_block_device_info(
                            context, instance)

        self.driver.resume(context, instance, network_info,
                           block_device_info)

        instance.power_state = self._get_power_state(context, instance)
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.save(expected_task_state=task_states.RESUMING)
        self._notify_about_instance_usage(context, instance, 'resume')

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def shelve_instance(self, context, instance, image_id):
        """Shelve an instance.

        This should be used when you want to take a snapshot of the instance.
        It also adds system_metadata that can be used by a periodic task to
        offload the shelved instance after a period of time.

        :param context: request context
        :param instance: an Instance object
        :param image_id: an image id to snapshot to.
        """
        self.conductor_api.notify_usage_exists(
            context, obj_base.obj_to_primitive(instance),
            current_period=True)
        self._notify_about_instance_usage(context, instance, 'shelve.start')

        def update_task_state(task_state, expected_state=task_states.SHELVING):
            shelving_state_map = {
                    task_states.IMAGE_PENDING_UPLOAD:
                        task_states.SHELVING_IMAGE_PENDING_UPLOAD,
                    task_states.IMAGE_UPLOADING:
                        task_states.SHELVING_IMAGE_UPLOADING,
                    task_states.SHELVING: task_states.SHELVING}
            task_state = shelving_state_map[task_state]
            expected_state = shelving_state_map[expected_state]
            instance.task_state = task_state
            instance.save(expected_task_state=expected_state)

        self.driver.power_off(instance)
        current_power_state = self._get_power_state(context, instance)
        self.driver.snapshot(context, instance, image_id, update_task_state)

        instance.system_metadata['shelved_at'] = timeutils.strtime()
        instance.system_metadata['shelved_image_id'] = image_id
        instance.system_metadata['shelved_host'] = self.host
        instance.vm_state = vm_states.SHELVED
        instance.task_state = None
        if CONF.shelved_offload_time == 0:
            instance.task_state = task_states.SHELVING_OFFLOADING
        instance.power_state = current_power_state
        instance.save(expected_task_state=[
                task_states.SHELVING,
                task_states.SHELVING_IMAGE_UPLOADING])

        self._notify_about_instance_usage(context, instance, 'shelve.end')

        if CONF.shelved_offload_time == 0:
            self.shelve_offload_instance(context, instance)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def shelve_offload_instance(self, context, instance):
        """Remove a shelved instance from the hypervisor.

        This frees up those resources for use by other instances, but may lead
        to slower unshelve times for this instance.  This method is used by
        volume backed instances since restoring them doesn't involve the
        potentially large download of an image.

        :param context: request context
        :param instance: nova.objects.instance.Instance
        """
        self._notify_about_instance_usage(context, instance,
                'shelve_offload.start')

        self.driver.power_off(instance)
        current_power_state = self._get_power_state(context, instance)

        network_info = self._get_instance_nw_info(context, instance)
        block_device_info = self._get_instance_block_device_info(context,
                                                                 instance)
        self.driver.destroy(context, instance, network_info,
                block_device_info)

        instance.power_state = current_power_state
        instance.host = None
        instance.node = None
        instance.vm_state = vm_states.SHELVED_OFFLOADED
        instance.task_state = None
        instance.save(expected_task_state=[task_states.SHELVING,
                                           task_states.SHELVING_OFFLOADING])
        self._notify_about_instance_usage(context, instance,
                'shelve_offload.end')

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def unshelve_instance(self, context, instance, image,
                          filter_properties=None, node=None):
        """Unshelve the instance.

        :param context: request context
        :param instance: a nova.objects.instance.Instance object
        :param image: an image to build from.  If None we assume a
            volume backed instance.
        :param filter_properties: dict containing limits, retry info etc.
        :param node: target compute node
        """
        if filter_properties is None:
            filter_properties = {}

        @utils.synchronized(instance['uuid'])
        def do_unshelve_instance():
            self._unshelve_instance(context, instance, image,
                                    filter_properties, node)
        do_unshelve_instance()

    def _unshelve_instance_key_scrub(self, instance):
        """Remove data from the instance that may cause side effects."""
        cleaned_keys = dict(
                key_data=instance.key_data,
                auto_disk_config=instance.auto_disk_config)
        instance.key_data = None
        instance.auto_disk_config = False
        return cleaned_keys

    def _unshelve_instance_key_restore(self, instance, keys):
        """Restore previously scrubbed keys before saving the instance."""
        instance.update(keys)

    def _unshelve_instance(self, context, instance, image, filter_properties,
                           node):
        self._notify_about_instance_usage(context, instance, 'unshelve.start')
        instance.task_state = task_states.SPAWNING
        instance.save()

        network_info = self._get_instance_nw_info(context, instance)
        bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                context, instance.uuid)
        block_device_info = self._prep_block_device(context, instance, bdms)
        scrubbed_keys = self._unshelve_instance_key_scrub(instance)

        if node is None:
            node = self.driver.get_available_nodes()[0]
            LOG.debug('No node specified, defaulting to %s', node,
                      instance=instance)

        rt = self._get_resource_tracker(node)
        limits = filter_properties.get('limits', {})

        if image:
            shelved_image_ref = instance.image_ref
            instance.image_ref = image['id']

        try:
            with rt.instance_claim(context, instance, limits):
                self.driver.spawn(context, instance, image, injected_files=[],
                                  admin_password=None,
                                  network_info=network_info,
                                  block_device_info=block_device_info)
        except Exception:
            with excutils.save_and_reraise_exception():
                LOG.exception(_('Instance failed to spawn'), instance=instance)

        if image:
            instance.image_ref = shelved_image_ref
            self.image_api.delete(context, image['id'])

        self._unshelve_instance_key_restore(instance, scrubbed_keys)
        instance.power_state = self._get_power_state(context, instance)
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.launched_at = timeutils.utcnow()
        instance.save(expected_task_state=task_states.SPAWNING)
        self._notify_about_instance_usage(context, instance, 'unshelve.end')

    @wrap_instance_fault
    def reset_network(self, context, instance):
        """Reset networking on the given instance."""
        LOG.debug('Reset network', context=context, instance=instance)
        self.driver.reset_network(instance)

    def _inject_network_info(self, context, instance, network_info):
        """Inject network info for the given instance."""
        LOG.debug('Inject network info', context=context, instance=instance)
        LOG.debug('network_info to inject: |%s|', network_info,
                  instance=instance)

        self.driver.inject_network_info(instance,
                                        network_info)

    @wrap_instance_fault
    def inject_network_info(self, context, instance):
        """Inject network info, but don't return the info."""
        network_info = self._get_instance_nw_info(context, instance)
        self._inject_network_info(context, instance, network_info)

    @object_compat
    @messaging.expected_exceptions(NotImplementedError,
                                   exception.InstanceNotFound)
    @wrap_exception()
    @wrap_instance_fault
    def get_console_output(self, context, instance, tail_length):
        """Send the console output for the given instance."""
        context = context.elevated()
        LOG.audit(_("Get console output"), context=context,
                  instance=instance)
        output = self.driver.get_console_output(context, instance)

        if tail_length is not None:
            output = self._tail_log(output, tail_length)

        return output.decode('utf-8', 'replace').encode('ascii', 'replace')

    def _tail_log(self, log, length):
        try:
            length = int(length)
        except ValueError:
            length = 0

        if length == 0:
            return ''
        else:
            return '\n'.join(log.split('\n')[-int(length):])

    @messaging.expected_exceptions(exception.ConsoleTypeInvalid,
                                   exception.InstanceNotReady,
                                   exception.InstanceNotFound,
                                   exception.ConsoleTypeUnavailable,
                                   NotImplementedError)
    @object_compat
    @wrap_exception()
    @wrap_instance_fault
    def get_vnc_console(self, context, console_type, instance):
        """Return connection information for a vnc console."""
        context = context.elevated()
        LOG.debug("Getting vnc console", instance=instance)
        token = str(uuid.uuid4())

        if not CONF.vnc_enabled:
            raise exception.ConsoleTypeUnavailable(console_type=console_type)

        if console_type == 'novnc':
            # For essex, novncproxy_base_url must include the full path
            # including the html file (like http://myhost/vnc_auto.html)
            access_url = '%s?token=%s' % (CONF.novncproxy_base_url, token)
        elif console_type == 'xvpvnc':
            access_url = '%s?token=%s' % (CONF.xvpvncproxy_base_url, token)
        else:
            raise exception.ConsoleTypeInvalid(console_type=console_type)

        try:
            # Retrieve connect info from driver, and then decorate with our
            # access info token
            connect_info = self.driver.get_vnc_console(context, instance)
            connect_info['token'] = token
            connect_info['access_url'] = access_url
        except exception.InstanceNotFound:
            if instance['vm_state'] != vm_states.BUILDING:
                raise
            raise exception.InstanceNotReady(instance_id=instance['uuid'])

        return connect_info

    @object_compat
    @messaging.expected_exceptions(exception.ConsoleTypeInvalid,
                                   exception.InstanceNotReady,
                                   exception.InstanceNotFound,
                                   exception.ConsoleTypeUnavailable)
    @wrap_exception()
    @wrap_instance_fault
    def get_spice_console(self, context, console_type, instance):
        """Return connection information for a spice console."""
        context = context.elevated()
        LOG.debug("Getting spice console", instance=instance)
        token = str(uuid.uuid4())

        if not CONF.spice.enabled:
            raise exception.ConsoleTypeUnavailable(console_type=console_type)

        if console_type == 'spice-html5':
            # For essex, spicehtml5proxy_base_url must include the full path
            # including the html file (like http://myhost/spice_auto.html)
            access_url = '%s?token=%s' % (CONF.spice.html5proxy_base_url,
                                          token)
        else:
            raise exception.ConsoleTypeInvalid(console_type=console_type)

        try:
            # Retrieve connect info from driver, and then decorate with our
            # access info token
            connect_info = self.driver.get_spice_console(context, instance)
            connect_info['token'] = token
            connect_info['access_url'] = access_url
        except exception.InstanceNotFound:
            if instance['vm_state'] != vm_states.BUILDING:
                raise
            raise exception.InstanceNotReady(instance_id=instance['uuid'])

        return connect_info

    @object_compat
    @messaging.expected_exceptions(exception.ConsoleTypeInvalid,
                                   exception.InstanceNotReady,
                                   exception.InstanceNotFound,
                                   exception.ConsoleTypeUnavailable,
                                   NotImplementedError)
    @wrap_exception()
    @wrap_instance_fault
    def get_rdp_console(self, context, console_type, instance):
        """Return connection information for a RDP console."""
        context = context.elevated()
        LOG.debug("Getting RDP console", instance=instance)
        token = str(uuid.uuid4())

        if not CONF.rdp.enabled:
            raise exception.ConsoleTypeUnavailable(console_type=console_type)

        if console_type == 'rdp-html5':
            access_url = '%s?token=%s' % (CONF.rdp.html5_proxy_base_url,
                                          token)
        else:
            raise exception.ConsoleTypeInvalid(console_type=console_type)

        try:
            # Retrieve connect info from driver, and then decorate with our
            # access info token
            connect_info = self.driver.get_rdp_console(context, instance)
            connect_info['token'] = token
            connect_info['access_url'] = access_url
        except exception.InstanceNotFound:
            if instance['vm_state'] != vm_states.BUILDING:
                raise
            raise exception.InstanceNotReady(instance_id=instance['uuid'])

        return connect_info

    @messaging.expected_exceptions(exception.ConsoleTypeInvalid,
                                   exception.InstanceNotReady,
                                   exception.InstanceNotFound)
    @object_compat
    @wrap_exception()
    @wrap_instance_fault
    def validate_console_port(self, ctxt, instance, port, console_type):
        if console_type == "spice-html5":
            console_info = self.driver.get_spice_console(ctxt, instance)
        elif console_type == "rdp-html5":
            console_info = self.driver.get_rdp_console(ctxt, instance)
        else:
            console_info = self.driver.get_vnc_console(ctxt, instance)

        return console_info['port'] == port

    @object_compat
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def reserve_block_device_name(self, context, instance, device,
                                  volume_id, disk_bus=None, device_type=None):
        # NOTE(ndipanov): disk_bus and device_type will be set to None if not
        # passed (by older clients) and defaulted by the virt driver. Remove
        # default values on the next major RPC version bump.

        @utils.synchronized(instance['uuid'])
        def do_reserve():
            bdms = (
                objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid))

            device_name = compute_utils.get_device_name_for_instance(
                    context, instance, bdms, device)

            # NOTE(vish): create bdm here to avoid race condition
            bdm = objects.BlockDeviceMapping(
                    source_type='volume', destination_type='volume',
                    instance_uuid=instance.uuid,
                    volume_id=volume_id or 'reserved',
                    device_name=device_name,
                    disk_bus=disk_bus, device_type=device_type)
            bdm.create(context)

            return device_name

        return do_reserve()

    @object_compat
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def attach_volume(self, context, volume_id, mountpoint,
                      instance, bdm=None):
        """Attach a volume to an instance."""
        if not bdm:
            bdm = objects.BlockDeviceMapping.get_by_volume_id(
                    context, volume_id)
        driver_bdm = driver_block_device.DriverVolumeBlockDevice(bdm)
        try:
            return self._attach_volume(context, instance, driver_bdm)
        except Exception:
            with excutils.save_and_reraise_exception():
                bdm.destroy(context)

    def _attach_volume(self, context, instance, bdm):
        context = context.elevated()
        LOG.audit(_('Attaching volume %(volume_id)s to %(mountpoint)s'),
                  {'volume_id': bdm.volume_id,
                  'mountpoint': bdm['mount_device']},
                  context=context, instance=instance)
        try:
            bdm.attach(context, instance, self.volume_api, self.driver,
                       do_check_attach=False, do_driver_attach=True)
        except Exception:  # pylint: disable=W0702
            with excutils.save_and_reraise_exception():
                LOG.exception(_("Failed to attach %(volume_id)s "
                                "at %(mountpoint)s"),
                              {'volume_id': bdm.volume_id,
                               'mountpoint': bdm['mount_device']},
                              context=context, instance=instance)
                self.volume_api.unreserve_volume(context, bdm.volume_id)

        info = {'volume_id': bdm.volume_id}
        self._notify_about_instance_usage(
            context, instance, "volume.attach", extra_usage_info=info)

    def _detach_volume(self, context, instance, bdm):
        """Do the actual driver detach using block device mapping."""
        mp = bdm.device_name
        volume_id = bdm.volume_id

        LOG.audit(_('Detach volume %(volume_id)s from mountpoint %(mp)s'),
                  {'volume_id': volume_id, 'mp': mp},
                  context=context, instance=instance)

        connection_info = jsonutils.loads(bdm.connection_info)
        # NOTE(vish): We currently don't use the serial when disconnecting,
        #             but added for completeness in case we ever do.
        if connection_info and 'serial' not in connection_info:
            connection_info['serial'] = volume_id
        try:
            if not self.driver.instance_exists(instance):
                LOG.warn(_('Detaching volume from unknown instance'),
                         context=context, instance=instance)

            encryption = encryptors.get_encryption_metadata(
                context, self.volume_api, volume_id, connection_info)

            self.driver.detach_volume(connection_info,
                                      instance,
                                      mp,
                                      encryption=encryption)
        except Exception:  # pylint: disable=W0702
            with excutils.save_and_reraise_exception():
                LOG.exception(_('Failed to detach volume %(volume_id)s '
                                'from %(mp)s'),
                              {'volume_id': volume_id, 'mp': mp},
                              context=context, instance=instance)
                self.volume_api.roll_detaching(context, volume_id)

    @object_compat
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def detach_volume(self, context, volume_id, instance):
        """Detach a volume from an instance."""
        bdm = objects.BlockDeviceMapping.get_by_volume_id(
                context, volume_id)
        if CONF.volume_usage_poll_interval > 0:
            vol_stats = []
            mp = bdm.device_name
            # Handle bootable volumes which will not contain /dev/
            if '/dev/' in mp:
                mp = mp[5:]
            try:
                vol_stats = self.driver.block_stats(instance.name, mp)
            except NotImplementedError:
                pass

            if vol_stats:
                LOG.debug("Updating volume usage cache with totals",
                          instance=instance)
                rd_req, rd_bytes, wr_req, wr_bytes, flush_ops = vol_stats
                self.conductor_api.vol_usage_update(context, volume_id,
                                                    rd_req, rd_bytes,
                                                    wr_req, wr_bytes,
                                                    instance,
                                                    update_totals=True)

        self._detach_volume(context, instance, bdm)
        connector = self.driver.get_volume_connector(instance)
        self.volume_api.terminate_connection(context, volume_id, connector)
        bdm.destroy()
        info = dict(volume_id=volume_id)
        self._notify_about_instance_usage(
            context, instance, "volume.detach", extra_usage_info=info)
        self.volume_api.detach(context.elevated(), volume_id)

    def _init_volume_connection(self, context, new_volume_id,
                                old_volume_id, connector, instance, bdm):

        new_cinfo = self.volume_api.initialize_connection(context,
                                                          new_volume_id,
                                                          connector)
        old_cinfo = jsonutils.loads(bdm['connection_info'])
        if old_cinfo and 'serial' not in old_cinfo:
            old_cinfo['serial'] = old_volume_id
        new_cinfo['serial'] = old_cinfo['serial']
        return (old_cinfo, new_cinfo)

    def _swap_volume(self, context, instance, bdm, connector, old_volume_id,
                                                              new_volume_id):
        mountpoint = bdm['device_name']
        failed = False
        new_cinfo = None
        try:
            old_cinfo, new_cinfo = self._init_volume_connection(context,
                                                                new_volume_id,
                                                                old_volume_id,
                                                                connector,
                                                                instance,
                                                                bdm)
            self.driver.swap_volume(old_cinfo, new_cinfo, instance, mountpoint)
        except Exception:  # pylint: disable=W0702
            failed = True
            with excutils.save_and_reraise_exception():
                if new_cinfo:
                    msg = _("Failed to swap volume %(old_volume_id)s "
                            "for %(new_volume_id)s")
                    LOG.exception(msg % {'old_volume_id': old_volume_id,
                                         'new_volume_id': new_volume_id},
                                  context=context,
                                  instance=instance)
                else:
                    msg = _("Failed to connect to volume %(volume_id)s "
                            "with volume at %(mountpoint)s")
                    LOG.exception(msg % {'volume_id': new_volume_id,
                                         'mountpoint': bdm['device_name']},
                                  context=context,
                                  instance=instance)
                self.volume_api.roll_detaching(context, old_volume_id)
                self.volume_api.unreserve_volume(context, new_volume_id)
        finally:
            conn_volume = new_volume_id if failed else old_volume_id
            if new_cinfo:
                self.volume_api.terminate_connection(context,
                                                     conn_volume,
                                                     connector)
            # If Cinder initiated the swap, it will keep
            # the original ID
            comp_ret = self.volume_api.migrate_volume_completion(
                                                      context,
                                                      old_volume_id,
                                                      new_volume_id,
                                                      error=failed)

        return (comp_ret, new_cinfo)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def swap_volume(self, context, old_volume_id, new_volume_id, instance):
        """Swap volume for an instance."""
        context = context.elevated()

        bdm = objects.BlockDeviceMapping.get_by_volume_id(
                context, old_volume_id, instance_uuid=instance.uuid)
        connector = self.driver.get_volume_connector(instance)
        comp_ret, new_cinfo = self._swap_volume(context, instance,
                                                         bdm,
                                                         connector,
                                                         old_volume_id,
                                                         new_volume_id)

        save_volume_id = comp_ret['save_volume_id']
        mountpoint = bdm.device_name

        # Update bdm
        values = {
            'connection_info': jsonutils.dumps(new_cinfo),
            'delete_on_termination': False,
            'source_type': 'volume',
            'destination_type': 'volume',
            'snapshot_id': None,
            'volume_id': save_volume_id,
            'volume_size': None,
            'no_device': None}
        bdm.update(values)
        bdm.save()
        self.volume_api.attach(context,
                               new_volume_id,
                               instance.uuid,
                               mountpoint)
        # Remove old connection
        self.volume_api.detach(context.elevated(), old_volume_id)

    @wrap_exception()
    def remove_volume_connection(self, context, volume_id, instance):
        """Remove a volume connection using the volume api."""
        # NOTE(vish): We don't want to actually mark the volume
        #             detached, or delete the bdm, just remove the
        #             connection from this host.

        # NOTE(PhilDay): Can't use object_compat decorator here as
        #                instance is not the second parameter
        if isinstance(instance, dict):
            metas = ['metadata', 'system_metadata']
            instance = objects.Instance._from_db_object(
                    context, objects.Instance(), instance,
                    expected_attrs=metas)
            instance._context = context
        try:
            bdm = objects.BlockDeviceMapping.get_by_volume_id(
                    context, volume_id)
            self._detach_volume(context, instance, bdm)
            connector = self.driver.get_volume_connector(instance)
            self.volume_api.terminate_connection(context, volume_id, connector)
        except exception.NotFound:
            pass

    @object_compat
    def attach_interface(self, context, instance, network_id, port_id,
                         requested_ip):
        """Use hotplug to add an network adapter to an instance."""
        network_info = self.network_api.allocate_port_for_instance(
            context, instance, port_id, network_id, requested_ip)
        if len(network_info) != 1:
            LOG.error(_('allocate_port_for_instance returned %(ports)s ports')
                      % dict(ports=len(network_info)))
            raise exception.InterfaceAttachFailed(instance=instance)
        image_ref = instance.get('image_ref')
        image_meta = compute_utils.get_image_metadata(
            context, self.image_api, image_ref, instance)

        self.driver.attach_interface(instance, image_meta, network_info[0])
        return network_info[0]

    @object_compat
    def detach_interface(self, context, instance, port_id):
        """Detach an network adapter from an instance."""
        network_info = instance.info_cache.network_info
        condemned = None
        for vif in network_info:
            if vif['id'] == port_id:
                condemned = vif
                break
        if condemned is None:
            raise exception.PortNotFound(_("Port %s is not "
                                           "attached") % port_id)

        self.network_api.deallocate_port_for_instance(context, instance,
                                                      port_id)
        self.driver.detach_interface(instance, condemned)

    def _get_compute_info(self, context, host):
        service = objects.Service.get_by_compute_host(context, host)
        try:
            return service.compute_node
        except IndexError:
            raise exception.NotFound(_("Host %s not found") % host)

    @wrap_exception()
    def check_instance_shared_storage(self, ctxt, instance, data):
        """Check if the instance files are shared

        :param context: security context
        :param data: result of driver.check_instance_shared_storage_local

        Returns True if instance disks located on shared storage and
        False otherwise.
        """
        return self.driver.check_instance_shared_storage_remote(ctxt, data)

    @wrap_exception()
    @wrap_instance_fault
    def check_can_live_migrate_destination(self, ctxt, instance,
                                           block_migration, disk_over_commit):
        """Check if it is possible to execute live migration.

        This runs checks on the destination host, and then calls
        back to the source host to check the results.

        :param context: security context
        :param instance: dict of instance data
        :param block_migration: if true, prepare for block migration
        :param disk_over_commit: if true, allow disk over commit
        :returns: a dict containing migration info
        """
        src_compute_info = obj_base.obj_to_primitive(
            self._get_compute_info(ctxt, instance.host))
        dst_compute_info = obj_base.obj_to_primitive(
            self._get_compute_info(ctxt, CONF.host))
        dest_check_data = self.driver.check_can_live_migrate_destination(ctxt,
            instance, src_compute_info, dst_compute_info,
            block_migration, disk_over_commit)
        migrate_data = {}
        try:
            migrate_data = self.compute_rpcapi.\
                                check_can_live_migrate_source(ctxt, instance,
                                                              dest_check_data)
        finally:
            self.driver.check_can_live_migrate_destination_cleanup(ctxt,
                    dest_check_data)
        if 'migrate_data' in dest_check_data:
            migrate_data.update(dest_check_data['migrate_data'])
        return migrate_data

    @wrap_exception()
    @wrap_instance_fault
    def check_can_live_migrate_source(self, ctxt, instance, dest_check_data):
        """Check if it is possible to execute live migration.

        This checks if the live migration can succeed, based on the
        results from check_can_live_migrate_destination.

        :param context: security context
        :param instance: dict of instance data
        :param dest_check_data: result of check_can_live_migrate_destination
        :returns: a dict containing migration info
        """
        is_volume_backed = self.compute_api.is_volume_backed_instance(ctxt,
                                                                      instance)
        dest_check_data['is_volume_backed'] = is_volume_backed
        return self.driver.check_can_live_migrate_source(ctxt, instance,
                                                         dest_check_data)

    @object_compat
    @wrap_exception()
    @wrap_instance_fault
    def pre_live_migration(self, context, instance, block_migration, disk,
                           migrate_data):
        """Preparations for live migration at dest host.

        :param context: security context
        :param instance: dict of instance data
        :param block_migration: if true, prepare for block migration
        :param migrate_data : if not None, it is a dict which holds data
        required for live migration without shared storage.

        """
        block_device_info = self._get_instance_block_device_info(
                            context, instance, refresh_conn_info=True)

        network_info = self._get_instance_nw_info(context, instance)
        self._notify_about_instance_usage(
                     context, instance, "live_migration.pre.start",
                     network_info=network_info)

        pre_live_migration_data = self.driver.pre_live_migration(context,
                                       instance,
                                       block_device_info,
                                       network_info,
                                       disk,
                                       migrate_data)

        # NOTE(tr3buchet): setup networks on destination host
        self.network_api.setup_networks_on_host(context, instance,
                                                         self.host)

        # Creating filters to hypervisors and firewalls.
        # An example is that nova-instance-instance-xxx,
        # which is written to libvirt.xml(Check "virsh nwfilter-list")
        # This nwfilter is necessary on the destination host.
        # In addition, this method is creating filtering rule
        # onto destination host.
        self.driver.ensure_filtering_rules_for_instance(instance,
                                            network_info)

        self._notify_about_instance_usage(
                     context, instance, "live_migration.pre.end",
                     network_info=network_info)

        return pre_live_migration_data

    @wrap_exception()
    @wrap_instance_fault
    def live_migration(self, context, dest, instance, block_migration,
                       migrate_data):
        """Executing live migration.

        :param context: security context
        :param instance: a nova.objects.instance.Instance object
        :param dest: destination host
        :param block_migration: if true, prepare for block migration
        :param migrate_data: implementation specific params

        """

        # NOTE(danms): since instance is not the first parameter, we can't
        # use @object_compat on this method. Since this is the only example,
        # we do this manually instead of complicating the decorator
        if not isinstance(instance, obj_base.NovaObject):
            expected = ['metadata', 'system_metadata',
                        'security_groups', 'info_cache']
            instance = objects.Instance._from_db_object(
                context, objects.Instance(), instance,
                expected_attrs=expected)

        # Create a local copy since we'll be modifying the dictionary
        migrate_data = dict(migrate_data or {})
        try:
            if block_migration:
                disk = self.driver.get_instance_disk_info(instance.name)
            else:
                disk = None

            pre_migration_data = self.compute_rpcapi.pre_live_migration(
                context, instance,
                block_migration, disk, dest, migrate_data)
            migrate_data['pre_live_migration_result'] = pre_migration_data

        except Exception:
            with excutils.save_and_reraise_exception():
                LOG.exception(_('Pre live migration failed at %s'),
                              dest, instance=instance)
                self._rollback_live_migration(context, instance, dest,
                                              block_migration, migrate_data)

        # Executing live migration
        # live_migration might raises exceptions, but
        # nothing must be recovered in this version.
        self.driver.live_migration(context, instance, dest,
                                   self._post_live_migration,
                                   self._rollback_live_migration,
                                   block_migration, migrate_data)

    def _live_migration_cleanup_flags(self, block_migration, migrate_data):
        """Determine whether disks or intance path need to be cleaned up after
        live migration (at source on success, at destination on rollback)

        Block migration needs empty image at destination host before migration
        starts, so if any failure occurs, any empty images has to be deleted.

        Also Volume backed live migration w/o shared storage needs to delete
        newly created instance-xxx dir on the destination as a part of its
        rollback process

        :param block_migration: if true, it was a block migration
        :param migrate_data: implementation specific data
        :returns: (bool, bool) -- do_cleanup, destroy_disks
        """
        # NOTE(angdraug): block migration wouldn't have been allowed if either
        #                 block storage or instance path were shared
        is_shared_block_storage = not block_migration
        is_shared_instance_path = not block_migration
        if migrate_data:
            is_shared_block_storage = migrate_data.get(
                    'is_shared_block_storage', is_shared_block_storage)
            is_shared_instance_path = migrate_data.get(
                    'is_shared_instance_path', is_shared_instance_path)

        # No instance booting at source host, but instance dir
        # must be deleted for preparing next block migration
        # must be deleted for preparing next live migration w/o shared storage
        do_cleanup = block_migration or not is_shared_instance_path
        destroy_disks = not is_shared_block_storage

        return (do_cleanup, destroy_disks)

    @wrap_exception()
    @wrap_instance_fault
    def _post_live_migration(self, ctxt, instance,
                            dest, block_migration=False, migrate_data=None):
        """Post operations for live migration.

        This method is called from live_migration
        and mainly updating database record.

        :param ctxt: security context
        :param instance: instance dict
        :param dest: destination host
        :param block_migration: if true, prepare for block migration
        :param migrate_data: if not None, it is a dict which has data
        required for live migration without shared storage

        """
        LOG.info(_('_post_live_migration() is started..'),
                 instance=instance)

        bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                ctxt, instance['uuid'])

        # Cleanup source host post live-migration
        block_device_info = self._get_instance_block_device_info(
                            ctxt, instance, bdms)
        self.driver.post_live_migration(ctxt, instance, block_device_info,
                                        migrate_data)

        # Detaching volumes.
        connector = self.driver.get_volume_connector(instance)
        for bdm in bdms:
            # NOTE(vish): We don't want to actually mark the volume
            #             detached, or delete the bdm, just remove the
            #             connection from this host.

            # remove the volume connection without detaching from hypervisor
            # because the instance is not running anymore on the current host
            if bdm.is_volume:
                self.volume_api.terminate_connection(ctxt, bdm.volume_id,
                                                     connector)

        # Releasing vlan.
        # (not necessary in current implementation?)

        network_info = self._get_instance_nw_info(ctxt, instance)

        self._notify_about_instance_usage(ctxt, instance,
                                          "live_migration._post.start",
                                          network_info=network_info)
        # Releasing security group ingress rule.
        self.driver.unfilter_instance(instance,
                                      network_info)

        migration = {'source_compute': self.host,
                     'dest_compute': dest, }
        self.network_api.migrate_instance_start(ctxt,
                                                instance,
                                                migration)

        # Define domain at destination host, without doing it,
        # pause/suspend/terminate do not work.
        self.compute_rpcapi.post_live_migration_at_destination(ctxt,
                instance, block_migration, dest)

        do_cleanup, destroy_disks = self._live_migration_cleanup_flags(
                block_migration, migrate_data)

        if do_cleanup:
            self.driver.cleanup(ctxt, instance, network_info,
                                destroy_disks=destroy_disks,
                                migrate_data=migrate_data)
        else:
            # self.driver.cleanup() usually performs  vif unplugging
            # but we must do it explicitly here when block_migration
            # is false, as the network devices at the source must be
            # torn down
            try:
                self.driver.unplug_vifs(instance, network_info)
            except NotImplementedError as e:
                LOG.debug(e, instance=instance)
        # NOTE(tr3buchet): tear down networks on source host
        self.network_api.setup_networks_on_host(ctxt, instance,
                                                self.host, teardown=True)
        self.instance_events.clear_events_for_instance(instance)

        self._notify_about_instance_usage(ctxt, instance,
                                          "live_migration._post.end",
                                          network_info=network_info)
        LOG.info(_('Migrating instance to %s finished successfully.'),
                 dest, instance=instance)
        LOG.info(_("You may see the error \"libvirt: QEMU error: "
                   "Domain not found: no domain with matching name.\" "
                   "This error can be safely ignored."),
                 instance=instance)

        if CONF.vnc_enabled or CONF.spice.enabled or CONF.rdp.enabled:
            if CONF.cells.enable:
                self.cells_rpcapi.consoleauth_delete_tokens(ctxt,
                        instance['uuid'])
            else:
                self.consoleauth_rpcapi.delete_tokens_for_instance(ctxt,
                        instance['uuid'])

    @object_compat
    @wrap_exception()
    @wrap_instance_fault
    def post_live_migration_at_destination(self, context, instance,
                                           block_migration):
        """Post operations for live migration .

        :param context: security context
        :param instance: Instance dict
        :param block_migration: if true, prepare for block migration

        """
        LOG.info(_('Post operation of migration started'),
                 instance=instance)

        # NOTE(tr3buchet): setup networks on destination host
        #                  this is called a second time because
        #                  multi_host does not create the bridge in
        #                  plug_vifs
        self.network_api.setup_networks_on_host(context, instance,
                                                         self.host)
        migration = {'source_compute': instance['host'],
                     'dest_compute': self.host, }
        self.network_api.migrate_instance_finish(context,
                                                 instance,
                                                 migration)

        network_info = self._get_instance_nw_info(context, instance)
        self._notify_about_instance_usage(
                     context, instance, "live_migration.post.dest.start",
                     network_info=network_info)
        block_device_info = self._get_instance_block_device_info(context,
                                                                 instance)

        self.driver.post_live_migration_at_destination(context, instance,
                                            network_info,
                                            block_migration, block_device_info)
        # Restore instance state
        current_power_state = self._get_power_state(context, instance)
        node_name = None
        try:
            compute_node = self._get_compute_info(context, self.host)
            node_name = compute_node.hypervisor_hostname
        except exception.NotFound:
            LOG.exception(_('Failed to get compute_info for %s') % self.host)
        finally:
            instance.host = self.host
            instance.power_state = current_power_state
            instance.vm_state = vm_states.ACTIVE
            instance.task_state = None
            instance.node = node_name
            instance.save(expected_task_state=task_states.MIGRATING)

        # NOTE(vish): this is necessary to update dhcp
        self.network_api.setup_networks_on_host(context, instance, self.host)
        self._notify_about_instance_usage(
                     context, instance, "live_migration.post.dest.end",
                     network_info=network_info)

    @wrap_exception()
    @wrap_instance_fault
    def _rollback_live_migration(self, context, instance,
                                 dest, block_migration, migrate_data=None):
        """Recovers Instance/volume state from migrating -> running.

        :param context: security context
        :param instance: nova.db.sqlalchemy.models.Instance
        :param dest:
            This method is called from live migration src host.
            This param specifies destination host.
        :param block_migration: if true, prepare for block migration
        :param migrate_data:
            if not none, contains implementation specific data.

        """
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.save(expected_task_state=[task_states.MIGRATING])

        # NOTE(tr3buchet): setup networks on source host (really it's re-setup)
        self.network_api.setup_networks_on_host(context, instance, self.host)

        bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                context, instance['uuid'])
        for bdm in bdms:
            if bdm.is_volume:
                self.compute_rpcapi.remove_volume_connection(
                        context, instance, bdm.volume_id, dest)

        self._notify_about_instance_usage(context, instance,
                                          "live_migration._rollback.start")

        do_cleanup, destroy_disks = self._live_migration_cleanup_flags(
                block_migration, migrate_data)

        if do_cleanup:
            self.compute_rpcapi.rollback_live_migration_at_destination(
                    context, instance, dest, destroy_disks=destroy_disks,
                    migrate_data=migrate_data)

        self._notify_about_instance_usage(context, instance,
                                          "live_migration._rollback.end")

    @object_compat
    @wrap_exception()
    @wrap_instance_fault
    def rollback_live_migration_at_destination(self, context, instance,
                                               destroy_disks=True,
                                               migrate_data=None):
        """Cleaning up image directory that is created pre_live_migration.

        :param context: security context
        :param instance: a nova.objects.instance.Instance object sent over rpc
        """
        network_info = self._get_instance_nw_info(context, instance)
        self._notify_about_instance_usage(
                      context, instance, "live_migration.rollback.dest.start",
                      network_info=network_info)

        # NOTE(tr3buchet): tear down networks on destination host
        self.network_api.setup_networks_on_host(context, instance,
                                                self.host, teardown=True)

        # NOTE(vish): The mapping is passed in so the driver can disconnect
        #             from remote volumes if necessary
        block_device_info = self._get_instance_block_device_info(context,
                                                                 instance)
        self.driver.rollback_live_migration_at_destination(
                        context, instance, network_info, block_device_info,
                        destroy_disks=destroy_disks, migrate_data=migrate_data)
        self._notify_about_instance_usage(
                        context, instance, "live_migration.rollback.dest.end",
                        network_info=network_info)

    @periodic_task.periodic_task(
        spacing=CONF.heal_instance_info_cache_interval)
    def _heal_instance_info_cache(self, context):
        """Called periodically.  On every call, try to update the
        info_cache's network information for another instance by
        calling to the network manager.

        This is implemented by keeping a cache of uuids of instances
        that live on this host.  On each call, we pop one off of a
        list, pull the DB record, and try the call to the network API.
        If anything errors don't fail, as it's possible the instance
        has been deleted, etc.
        """
        heal_interval = CONF.heal_instance_info_cache_interval
        if not heal_interval:
            return

        instance_uuids = getattr(self, '_instance_uuids_to_heal', [])
        instance = None

        LOG.debug('Starting heal instance info cache')

        if not instance_uuids:
            # The list of instances to heal is empty so rebuild it
            LOG.debug('Rebuilding the list of instances to heal')
            db_instances = objects.InstanceList.get_by_host(
                context, self.host, expected_attrs=[], use_slave=True)
            for inst in db_instances:
                # We don't want to refersh the cache for instances
                # which are building or deleting so don't put them
                # in the list. If they are building they will get
                # added to the list next time we build it.
                if (inst.vm_state == vm_states.BUILDING):
                    LOG.debug('Skipping network cache update for instance '
                              'because it is Building.', instance=inst)
                    continue
                if (inst.task_state == task_states.DELETING):
                    LOG.debug('Skipping network cache update for instance '
                              'because it is being deleted.', instance=inst)
                    continue

                if not instance:
                    # Save the first one we find so we don't
                    # have to get it again
                    instance = inst
                else:
                    instance_uuids.append(inst['uuid'])

            self._instance_uuids_to_heal = instance_uuids
        else:
            # Find the next valid instance on the list
            while instance_uuids:
                try:
                    inst = objects.Instance.get_by_uuid(
                            context, instance_uuids.pop(0),
                            expected_attrs=['system_metadata', 'info_cache'],
                            use_slave=True)
                except exception.InstanceNotFound:
                    # Instance is gone.  Try to grab another.
                    continue

                # Check the instance hasn't been migrated
                if inst.host != self.host:
                    LOG.debug('Skipping network cache update for instance '
                              'because it has been migrated to another '
                              'host.', instance=inst)
                # Check the instance isn't being deleting
                elif inst.task_state == task_states.DELETING:
                    LOG.debug('Skipping network cache update for instance '
                              'because it is being deleted.', instance=inst)
                else:
                    instance = inst
                    break

        if instance:
            # We have an instance now to refresh
            try:
                # Call to network API to get instance info.. this will
                # force an update to the instance's info_cache
                self._get_instance_nw_info(context, instance, use_slave=True)
                LOG.debug('Updated the network info_cache for instance',
                          instance=instance)
            except Exception:
                LOG.error(_('An error occurred while refreshing the network '
                            'cache.'), instance=instance, exc_info=True)
        else:
            LOG.debug("Didn't find any instances for network info cache "
                      "update.")

    @periodic_task.periodic_task
    def _poll_rebooting_instances(self, context):
        if CONF.reboot_timeout > 0:
            filters = {'task_state': task_states.REBOOTING,
                       'host': self.host}
            rebooting = objects.InstanceList.get_by_filters(
                context, filters, expected_attrs=[], use_slave=True)

            to_poll = []
            for instance in rebooting:
                if timeutils.is_older_than(instance['updated_at'],
                                           CONF.reboot_timeout):
                    to_poll.append(instance)

            self.driver.poll_rebooting_instances(CONF.reboot_timeout, to_poll)

    @periodic_task.periodic_task
    def _poll_rescued_instances(self, context):
        if CONF.rescue_timeout > 0:
            filters = {'vm_state': vm_states.RESCUED,
                       'host': self.host}
            rescued_instances = objects.InstanceList.get_by_filters(
                context, filters, expected_attrs=["system_metadata"],
                use_slave=True)

            to_unrescue = []
            for instance in rescued_instances:
                if timeutils.is_older_than(instance['launched_at'],
                                           CONF.rescue_timeout):
                    to_unrescue.append(instance)

            for instance in to_unrescue:
                self.compute_api.unrescue(context, instance)

    @periodic_task.periodic_task
    def _poll_unconfirmed_resizes(self, context):
        if CONF.resize_confirm_window == 0:
            return

        migrations = objects.MigrationList.get_unconfirmed_by_dest_compute(
                context, CONF.resize_confirm_window, self.host,
                use_slave=True)

        migrations_info = dict(migration_count=len(migrations),
                confirm_window=CONF.resize_confirm_window)

        if migrations_info["migration_count"] > 0:
            LOG.info(_("Found %(migration_count)d unconfirmed migrations "
                       "older than %(confirm_window)d seconds"),
                     migrations_info)

        def _set_migration_to_error(migration, reason, **kwargs):
            LOG.warn(_("Setting migration %(migration_id)s to error: "
                       "%(reason)s"),
                     {'migration_id': migration['id'], 'reason': reason},
                     **kwargs)
            migration.status = 'error'
            migration.save(context.elevated())

        for migration in migrations:
            instance_uuid = migration.instance_uuid
            LOG.info(_("Automatically confirming migration "
                       "%(migration_id)s for instance %(instance_uuid)s"),
                     {'migration_id': migration.id,
                      'instance_uuid': instance_uuid})
            expected_attrs = ['metadata', 'system_metadata']
            try:
                instance = objects.Instance.get_by_uuid(context,
                            instance_uuid, expected_attrs=expected_attrs,
                            use_slave=True)
            except exception.InstanceNotFound:
                reason = (_("Instance %s not found") %
                          instance_uuid)
                _set_migration_to_error(migration, reason)
                continue
            if instance['vm_state'] == vm_states.ERROR:
                reason = _("In ERROR state")
                _set_migration_to_error(migration, reason,
                                        instance=instance)
                continue
            vm_state = instance['vm_state']
            task_state = instance['task_state']
            if vm_state != vm_states.RESIZED or task_state is not None:
                reason = (_("In states %(vm_state)s/%(task_state)s, not "
                           "RESIZED/None") %
                          {'vm_state': vm_state,
                           'task_state': task_state})
                _set_migration_to_error(migration, reason,
                                        instance=instance)
                continue
            try:
                self.compute_api.confirm_resize(context, instance,
                                                migration=migration)
            except Exception as e:
                LOG.info(_("Error auto-confirming resize: %s. "
                           "Will retry later."),
                         e, instance=instance)

    @compute_utils.periodic_task_spacing_warn("shelved_poll_interval")
    @periodic_task.periodic_task(spacing=CONF.shelved_poll_interval)
    def _poll_shelved_instances(self, context):
        if CONF.shelved_offload_time <= 0:
            return

        filters = {'vm_state': vm_states.SHELVED,
                   'host': self.host}
        shelved_instances = objects.InstanceList.get_by_filters(
            context, filters=filters, expected_attrs=['system_metadata'],
            use_slave=True)

        to_gc = []
        for instance in shelved_instances:
            sys_meta = instance.system_metadata
            shelved_at = timeutils.parse_strtime(sys_meta['shelved_at'])
            if timeutils.is_older_than(shelved_at, CONF.shelved_offload_time):
                to_gc.append(instance)

        for instance in to_gc:
            try:
                instance.task_state = task_states.SHELVING_OFFLOADING
                instance.save()
                self.shelve_offload_instance(context, instance)
            except Exception:
                LOG.exception(_('Periodic task failed to offload instance.'),
                        instance=instance)

    @periodic_task.periodic_task
    def _instance_usage_audit(self, context):
        if not CONF.instance_usage_audit:
            return

        if compute_utils.has_audit_been_run(context,
                                            self.conductor_api,
                                            self.host):
            return

        begin, end = utils.last_completed_audit_period()
        instances = objects.InstanceList.get_active_by_window_joined(
            context, begin, end, host=self.host,
            expected_attrs=['system_metadata', 'info_cache', 'metadata'])
        num_instances = len(instances)
        errors = 0
        successes = 0
        LOG.info(_("Running instance usage audit for"
                   " host %(host)s from %(begin_time)s to "
                   "%(end_time)s. %(number_instances)s"
                   " instances."),
                 dict(host=self.host,
                      begin_time=begin,
                      end_time=end,
                      number_instances=num_instances))
        start_time = time.time()
        compute_utils.start_instance_usage_audit(context,
                                      self.conductor_api,
                                      begin, end,
                                      self.host, num_instances)
        for instance in instances:
            try:
                self.conductor_api.notify_usage_exists(
                    context, instance,
                    ignore_missing_network_data=False)
                successes += 1
            except Exception:
                LOG.exception(_('Failed to generate usage '
                                'audit for instance '
                                'on host %s') % self.host,
                              instance=instance)
                errors += 1
        compute_utils.finish_instance_usage_audit(context,
                                      self.conductor_api,
                                      begin, end,
                                      self.host, errors,
                                      "Instance usage audit ran "
                                      "for host %s, %s instances "
                                      "in %s seconds." % (
                                      self.host,
                                      num_instances,
                                      time.time() - start_time))

    @compute_utils.periodic_task_spacing_warn("bandwidth_poll_interval")
    @periodic_task.periodic_task(spacing=CONF.bandwidth_poll_interval)
    def _poll_bandwidth_usage(self, context):

        if (CONF.bandwidth_poll_interval <= 0 or not self._bw_usage_supported):
            return

        prev_time, start_time = utils.last_completed_audit_period()

        curr_time = time.time()
        if (curr_time - self._last_bw_usage_poll >
                CONF.bandwidth_poll_interval):
            self._last_bw_usage_poll = curr_time
            LOG.info(_("Updating bandwidth usage cache"))
            cells_update_interval = CONF.cells.bandwidth_update_interval
            if (cells_update_interval > 0 and
                   curr_time - self._last_bw_usage_cell_update >
                           cells_update_interval):
                self._last_bw_usage_cell_update = curr_time
                update_cells = True
            else:
                update_cells = False

            instances = objects.InstanceList.get_by_host(context,
                                                              self.host,
                                                              use_slave=True)
            try:
                bw_counters = self.driver.get_all_bw_counters(instances)
            except NotImplementedError:
                # NOTE(mdragon): Not all hypervisors have bandwidth polling
                # implemented yet.  If they don't it doesn't break anything,
                # they just don't get the info in the usage events.
                # NOTE(PhilDay): Record that its not supported so we can
                # skip fast on future calls rather than waste effort getting
                # the list of instances.
                LOG.warning(_("Bandwidth usage not supported by hypervisor."))
                self._bw_usage_supported = False
                return

            refreshed = timeutils.utcnow()
            for bw_ctr in bw_counters:
                # Allow switching of greenthreads between queries.
                greenthread.sleep(0)
                bw_in = 0
                bw_out = 0
                last_ctr_in = None
                last_ctr_out = None
                # TODO(geekinutah): Once bw_usage_cache object is created
                #                   need to revisit this and slaveify.
                usage = self.conductor_api.bw_usage_get(context,
                                                        bw_ctr['uuid'],
                                                        start_time,
                                                        bw_ctr['mac_address'])
                if usage:
                    bw_in = usage['bw_in']
                    bw_out = usage['bw_out']
                    last_ctr_in = usage['last_ctr_in']
                    last_ctr_out = usage['last_ctr_out']
                else:
                    # TODO(geekinutah): Same here, pls slaveify
                    usage = self.conductor_api.bw_usage_get(
                        context, bw_ctr['uuid'], prev_time,
                        bw_ctr['mac_address'])
                    if usage:
                        last_ctr_in = usage['last_ctr_in']
                        last_ctr_out = usage['last_ctr_out']

                if last_ctr_in is not None:
                    if bw_ctr['bw_in'] < last_ctr_in:
                        # counter rollover
                        bw_in += bw_ctr['bw_in']
                    else:
                        bw_in += (bw_ctr['bw_in'] - last_ctr_in)

                if last_ctr_out is not None:
                    if bw_ctr['bw_out'] < last_ctr_out:
                        # counter rollover
                        bw_out += bw_ctr['bw_out']
                    else:
                        bw_out += (bw_ctr['bw_out'] - last_ctr_out)

                self.conductor_api.bw_usage_update(context,
                                                   bw_ctr['uuid'],
                                                   bw_ctr['mac_address'],
                                                   start_time,
                                                   bw_in,
                                                   bw_out,
                                                   bw_ctr['bw_in'],
                                                   bw_ctr['bw_out'],
                                                   last_refreshed=refreshed,
                                                   update_cells=update_cells)

    def _get_host_volume_bdms(self, context):
        """Return all block device mappings on a compute host."""
        compute_host_bdms = []
        instances = objects.InstanceList.get_by_host(context, self.host)
        for instance in instances:
            bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid)
            instance_bdms = [bdm for bdm in bdms if bdm.is_volume]
            compute_host_bdms.append(dict(instance=instance,
                                          instance_bdms=instance_bdms))

        return compute_host_bdms

    def _update_volume_usage_cache(self, context, vol_usages):
        """Updates the volume usage cache table with a list of stats."""
        for usage in vol_usages:
            # Allow switching of greenthreads between queries.
            greenthread.sleep(0)
            self.conductor_api.vol_usage_update(context, usage['volume'],
                                                usage['rd_req'],
                                                usage['rd_bytes'],
                                                usage['wr_req'],
                                                usage['wr_bytes'],
                                                usage['instance'])

    @periodic_task.periodic_task(spacing=CONF.volume_usage_poll_interval)
    def _poll_volume_usage(self, context, start_time=None):
        if CONF.volume_usage_poll_interval == 0:
            return

        if not start_time:
            start_time = utils.last_completed_audit_period()[1]

        compute_host_bdms = self._get_host_volume_bdms(context)
        if not compute_host_bdms:
            return

        LOG.debug("Updating volume usage cache")
        try:
            vol_usages = self.driver.get_all_volume_usage(context,
                                                          compute_host_bdms)
        except NotImplementedError:
            return

        self._update_volume_usage_cache(context, vol_usages)

    @compute_utils.periodic_task_spacing_warn("sync_power_state_interval")
    @periodic_task.periodic_task(spacing=CONF.sync_power_state_interval,
                                 run_immediately=True)
    def _sync_power_states(self, context):
        """Align power states between the database and the hypervisor.

        To sync power state data we make a DB call to get the number of
        virtual machines known by the hypervisor and if the number matches the
        number of virtual machines known by the database, we proceed in a lazy
        loop, one database record at a time, checking if the hypervisor has the
        same power state as is in the database.
        """
        db_instances = objects.InstanceList.get_by_host(context,
                                                             self.host,
                                                             use_slave=True)

        num_vm_instances = self.driver.get_num_instances()
        num_db_instances = len(db_instances)

        if num_vm_instances != num_db_instances:
            LOG.warn(_("Found %(num_db_instances)s in the database and "
                       "%(num_vm_instances)s on the hypervisor."),
                     {'num_db_instances': num_db_instances,
                      'num_vm_instances': num_vm_instances})

        for db_instance in db_instances:
            #NOTE(melwitt): This must be synchronized as we query state from
            #               two separate sources, the driver and the database.
            #               They are set (in stop_instance) and read, in sync.
            @utils.synchronized(db_instance.uuid)
            def query_driver_power_state_and_sync():
                self._query_driver_power_state_and_sync(context, db_instance)

            try:
                query_driver_power_state_and_sync()
            except Exception:
                LOG.exception(_LE("Periodic sync_power_state task had an "
                                  "error while processing an instance."),
                              instance=db_instance)

    def _query_driver_power_state_and_sync(self, context, db_instance):
        if db_instance.task_state is not None:
            LOG.info(_LI("During sync_power_state the instance has a "
                         "pending task (%(task)s). Skip."),
                     {'task': db_instance.task_state}, instance=db_instance)
            return
        # No pending tasks. Now try to figure out the real vm_power_state.
        try:
            vm_instance = self.driver.get_info(db_instance)
            vm_power_state = vm_instance['state']
        except exception.InstanceNotFound:
            vm_power_state = power_state.NOSTATE
        # Note(maoy): the above get_info call might take a long time,
        # for example, because of a broken libvirt driver.
        try:
            self._sync_instance_power_state(context,
                                            db_instance,
                                            vm_power_state,
                                            use_slave=True)
        except exception.InstanceNotFound:
            # NOTE(hanlind): If the instance gets deleted during sync,
            # silently ignore.
            pass

    def _sync_instance_power_state(self, context, db_instance, vm_power_state,
                                   use_slave=False):
        """Align instance power state between the database and hypervisor.

        If the instance is not found on the hypervisor, but is in the database,
        then a stop() API will be called on the instance.
        """

        # We re-query the DB to get the latest instance info to minimize
        # (not eliminate) race condition.
        db_instance.refresh(use_slave=use_slave)
        db_power_state = db_instance.power_state
        vm_state = db_instance.vm_state

        if self.host != db_instance.host:
            # on the sending end of nova-compute _sync_power_state
            # may have yielded to the greenthread performing a live
            # migration; this in turn has changed the resident-host
            # for the VM; However, the instance is still active, it
            # is just in the process of migrating to another host.
            # This implies that the compute source must relinquish
            # control to the compute destination.
            LOG.info(_("During the sync_power process the "
                       "instance has moved from "
                       "host %(src)s to host %(dst)s") %
                       {'src': self.host,
                        'dst': db_instance.host},
                     instance=db_instance)
            return
        elif db_instance.task_state is not None:
            # on the receiving end of nova-compute, it could happen
            # that the DB instance already report the new resident
            # but the actual VM has not showed up on the hypervisor
            # yet. In this case, let's allow the loop to continue
            # and run the state sync in a later round
            LOG.info(_("During sync_power_state the instance has a "
                       "pending task (%(task)s). Skip."),
                     {'task': db_instance.task_state},
                     instance=db_instance)
            return

        if vm_power_state != db_power_state:
            # power_state is always updated from hypervisor to db
            db_instance.power_state = vm_power_state
            db_instance.save()
            db_power_state = vm_power_state

        # Note(maoy): Now resolve the discrepancy between vm_state and
        # vm_power_state. We go through all possible vm_states.
        if vm_state in (vm_states.BUILDING,
                        vm_states.RESCUED,
                        vm_states.RESIZED,
                        vm_states.SUSPENDED,
                        vm_states.ERROR):
            # TODO(maoy): we ignore these vm_state for now.
            pass
        elif vm_state == vm_states.ACTIVE:
            # The only rational power state should be RUNNING
            if vm_power_state in (power_state.SHUTDOWN,
                                  power_state.CRASHED):
                LOG.warn(_("Instance shutdown by itself. Calling "
                           "the stop API."), instance=db_instance)
                try:
                    # Note(maoy): here we call the API instead of
                    # brutally updating the vm_state in the database
                    # to allow all the hooks and checks to be performed.
                    self.compute_api.stop(context, db_instance)
                except Exception:
                    # Note(maoy): there is no need to propagate the error
                    # because the same power_state will be retrieved next
                    # time and retried.
                    # For example, there might be another task scheduled.
                    LOG.exception(_("error during stop() in "
                                    "sync_power_state."),
                                  instance=db_instance)
            elif vm_power_state == power_state.SUSPENDED:
                LOG.warn(_("Instance is suspended unexpectedly. Calling "
                           "the stop API."), instance=db_instance)
                try:
                    self.compute_api.stop(context, db_instance)
                except Exception:
                    LOG.exception(_("error during stop() in "
                                    "sync_power_state."),
                                  instance=db_instance)
            elif vm_power_state == power_state.PAUSED:
                # Note(maoy): a VM may get into the paused state not only
                # because the user request via API calls, but also
                # due to (temporary) external instrumentations.
                # Before the virt layer can reliably report the reason,
                # we simply ignore the state discrepancy. In many cases,
                # the VM state will go back to running after the external
                # instrumentation is done. See bug 1097806 for details.
                LOG.warn(_("Instance is paused unexpectedly. Ignore."),
                         instance=db_instance)
            elif vm_power_state == power_state.NOSTATE:
                # Occasionally, depending on the status of the hypervisor,
                # which could be restarting for example, an instance may
                # not be found.  Therefore just log the condition.
                LOG.warn(_("Instance is unexpectedly not found. Ignore."),
                         instance=db_instance)
        elif vm_state == vm_states.STOPPED:
            if vm_power_state not in (power_state.NOSTATE,
                                      power_state.SHUTDOWN,
                                      power_state.CRASHED):
                LOG.warn(_("Instance is not stopped. Calling "
                           "the stop API."), instance=db_instance)
                try:
                    # NOTE(russellb) Force the stop, because normally the
                    # compute API would not allow an attempt to stop a stopped
                    # instance.
                    self.compute_api.force_stop(context, db_instance)
                except Exception:
                    LOG.exception(_("error during stop() in "
                                    "sync_power_state."),
                                  instance=db_instance)
        elif vm_state == vm_states.PAUSED:
            if vm_power_state in (power_state.SHUTDOWN,
                                  power_state.CRASHED):
                LOG.warn(_("Paused instance shutdown by itself. Calling "
                           "the stop API."), instance=db_instance)
                try:
                    self.compute_api.force_stop(context, db_instance)
                except Exception:
                    LOG.exception(_("error during stop() in "
                                    "sync_power_state."),
                                  instance=db_instance)
        elif vm_state in (vm_states.SOFT_DELETED,
                          vm_states.DELETED):
            if vm_power_state not in (power_state.NOSTATE,
                                      power_state.SHUTDOWN):
                # Note(maoy): this should be taken care of periodically in
                # _cleanup_running_deleted_instances().
                LOG.warn(_("Instance is not (soft-)deleted."),
                         instance=db_instance)

    @periodic_task.periodic_task
    def _reclaim_queued_deletes(self, context):
        """Reclaim instances that are queued for deletion."""
        interval = CONF.reclaim_instance_interval
        if interval <= 0:
            LOG.debug("CONF.reclaim_instance_interval <= 0, skipping...")
            return

        # FIXME(comstud): Dummy quota object for now. See bug 1296414.
        # We have potential for inconsistency if we decide here to not
        # update quotas. _delete_instance() should determine whether or
        # not to update quotas based on if instance is in a SOFT_DELETED
        # state or not.
        quotas = quotas_obj.Quotas.from_reservations(context, None)

        filters = {'vm_state': vm_states.SOFT_DELETED,
                   'task_state': None,
                   'host': self.host}
        instances = objects.InstanceList.get_by_filters(
            context, filters,
            expected_attrs=instance_obj.INSTANCE_DEFAULT_FIELDS,
            use_slave=True)
        for instance in instances:
            if self._deleted_old_enough(instance, interval):
                bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                        context, instance.uuid)
                LOG.info(_('Reclaiming deleted instance'), instance=instance)
                try:
                    self._delete_instance(context, instance, bdms, quotas)
                except Exception as e:
                    LOG.warning(_("Periodic reclaim failed to delete "
                                  "instance: %s"),
                                unicode(e), instance=instance)

    @periodic_task.periodic_task
    def update_available_resource(self, context):
        """See driver.get_available_resource()

        Periodic process that keeps that the compute host's understanding of
        resource availability and usage in sync with the underlying hypervisor.

        :param context: security context
        """
        new_resource_tracker_dict = {}
        nodenames = set(self.driver.get_available_nodes())
        for nodename in nodenames:
            rt = self._get_resource_tracker(nodename)
            rt.update_available_resource(context)
            new_resource_tracker_dict[nodename] = rt

        # Delete orphan compute node not reported by driver but still in db
        compute_nodes_in_db = self._get_compute_nodes_in_db(context)

        for cn in compute_nodes_in_db:
            if cn.hypervisor_hostname not in nodenames:
                LOG.audit(_("Deleting orphan compute node %s") % cn.id)
                cn.destroy()

        self._resource_tracker_dict = new_resource_tracker_dict

    def _get_compute_nodes_in_db(self, context):
        service = objects.Service.get_by_compute_host(context, self.host)
        if not service:
            LOG.error(_("No service record for host %s"), self.host)
            return []
        return objects.ComputeNodeList.get_by_service(context, service)

    @periodic_task.periodic_task(
        spacing=CONF.running_deleted_instance_poll_interval)
    def _cleanup_running_deleted_instances(self, context):
        """Cleanup any instances which are erroneously still running after
        having been deleted.

        Valid actions to take are:

            1. noop - do nothing
            2. log - log which instances are erroneously running
            3. reap - shutdown and cleanup any erroneously running instances
            4. shutdown - power off *and disable* any erroneously running
                          instances

        The use-case for this cleanup task is: for various reasons, it may be
        possible for the database to show an instance as deleted but for that
        instance to still be running on a host machine (see bug
        https://bugs.launchpad.net/nova/+bug/911366).

        This cleanup task is a cross-hypervisor utility for finding these
        zombied instances and either logging the discrepancy (likely what you
        should do in production), or automatically reaping the instances (more
        appropriate for dev environments).
        """
        action = CONF.running_deleted_instance_action

        if action == "noop":
            return

        # NOTE(sirp): admin contexts don't ordinarily return deleted records
        with utils.temporary_mutation(context, read_deleted="yes"):
            for instance in self._running_deleted_instances(context):
                bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                        context, instance.uuid, use_slave=True)

                if action == "log":
                    LOG.warning(_("Detected instance with name label "
                                  "'%s' which is marked as "
                                  "DELETED but still present on host."),
                                instance['name'], instance=instance)

                elif action == 'shutdown':
                    LOG.info(_("Powering off instance with name label "
                               "'%s' which is marked as "
                               "DELETED but still present on host."),
                               instance['name'], instance=instance)
                    try:
                        try:
                            # disable starting the instance
                            self.driver.set_bootable(instance, False)
                        except NotImplementedError:
                            LOG.warn(_("set_bootable is not implemented for "
                                       "the current driver"))
                        # and power it off
                        self.driver.power_off(instance)
                    except Exception:
                        msg = _("Failed to power off instance")
                        LOG.warn(msg, instance=instance, exc_info=True)

                elif action == 'reap':
                    LOG.info(_("Destroying instance with name label "
                               "'%s' which is marked as "
                               "DELETED but still present on host."),
                             instance['name'], instance=instance)
                    self.instance_events.clear_events_for_instance(instance)
                    try:
                        self._shutdown_instance(context, instance, bdms,
                                                notify=False)
                        self._cleanup_volumes(context, instance['uuid'], bdms)
                    except Exception as e:
                        LOG.warning(_("Periodic cleanup failed to delete "
                                      "instance: %s"),
                                    unicode(e), instance=instance)
                else:
                    raise Exception(_("Unrecognized value '%s'"
                                      " for CONF.running_deleted_"
                                      "instance_action") % action)

    def _running_deleted_instances(self, context):
        """Returns a list of instances nova thinks is deleted,
        but the hypervisor thinks is still running.
        """
        timeout = CONF.running_deleted_instance_timeout
        filters = {'deleted': True,
                   'soft_deleted': False,
                   'host': self.host}
        instances = self._get_instances_on_driver(context, filters)
        return [i for i in instances if self._deleted_old_enough(i, timeout)]

    def _deleted_old_enough(self, instance, timeout):
        deleted_at = instance['deleted_at']
        if isinstance(instance, obj_base.NovaObject) and deleted_at:
            deleted_at = deleted_at.replace(tzinfo=None)
        return (not deleted_at or timeutils.is_older_than(deleted_at, timeout))

    @contextlib.contextmanager
    def _error_out_instance_on_exception(self, context, instance,
                                         quotas=None,
                                         instance_state=vm_states.ACTIVE):
        instance_uuid = instance['uuid']
        try:
            yield
        except NotImplementedError as error:
            with excutils.save_and_reraise_exception():
                if quotas:
                    quotas.rollback()
                LOG.info(_("Setting instance back to %(state)s after: "
                           "%(error)s") %
                         {'state': instance_state, 'error': error},
                         instance_uuid=instance_uuid)
                self._instance_update(context, instance_uuid,
                                      vm_state=instance_state,
                                      task_state=None)
        except exception.InstanceFaultRollback as error:
            if quotas:
                quotas.rollback()
            LOG.info(_("Setting instance back to ACTIVE after: %s"),
                     error, instance_uuid=instance_uuid)
            self._instance_update(context, instance_uuid,
                                  vm_state=vm_states.ACTIVE,
                                  task_state=None)
            raise error.inner_exception
        except Exception:
            LOG.exception(_('Setting instance vm_state to ERROR'),
                          instance_uuid=instance_uuid)
            with excutils.save_and_reraise_exception():
                if quotas:
                    quotas.rollback()
                self._set_instance_error_state(context, instance)

    @aggregate_object_compat
    @wrap_exception()
    def add_aggregate_host(self, context, aggregate, host, slave_info):
        """Notify hypervisor of change (for hypervisor pools)."""
        try:
            self.driver.add_to_aggregate(context, aggregate, host,
                                         slave_info=slave_info)
        except NotImplementedError:
            LOG.debug('Hypervisor driver does not support '
                      'add_aggregate_host')
        except exception.AggregateError:
            with excutils.save_and_reraise_exception():
                self.driver.undo_aggregate_operation(
                                    context,
                                    aggregate.delete_host,
                                    aggregate, host)

    @aggregate_object_compat
    @wrap_exception()
    def remove_aggregate_host(self, context, host, slave_info, aggregate):
        """Removes a host from a physical hypervisor pool."""
        try:
            self.driver.remove_from_aggregate(context, aggregate, host,
                                              slave_info=slave_info)
        except NotImplementedError:
            LOG.debug('Hypervisor driver does not support '
                      'remove_aggregate_host')
        except (exception.AggregateError,
                exception.InvalidAggregateAction) as e:
            with excutils.save_and_reraise_exception():
                self.driver.undo_aggregate_operation(
                                    context,
                                    aggregate.add_host,
                                    aggregate, host,
                                    isinstance(e, exception.AggregateError))

    def _process_instance_event(self, instance, event):
        _event = self.instance_events.pop_instance_event(instance, event)
        if _event:
            LOG.debug('Processing event %(event)s',
                      {'event': event.key}, instance=instance)
            _event.send(event)

    @wrap_exception()
    def external_instance_event(self, context, instances, events):
        # NOTE(danms): Some event types are handled by the manager, such
        # as when we're asked to update the instance's info_cache. If it's
        # not one of those, look for some thread(s) waiting for the event and
        # unblock them if so.
        for event in events:
            instance = [inst for inst in instances
                        if inst.uuid == event.instance_uuid][0]
            if event.name == 'network-changed':
                self.network_api.get_instance_nw_info(context, instance)
            else:
                self._process_instance_event(instance, event)

    @compute_utils.periodic_task_spacing_warn("image_cache_manager_interval")
    @periodic_task.periodic_task(spacing=CONF.image_cache_manager_interval,
                                 external_process_ok=True)
    def _run_image_cache_manager_pass(self, context):
        """Run a single pass of the image cache manager."""

        if not self.driver.capabilities["has_imagecache"]:
            return
        if CONF.image_cache_manager_interval == 0:
            return

        # Determine what other nodes use this storage
        storage_users.register_storage_use(CONF.instances_path, CONF.host)
        nodes = storage_users.get_storage_users(CONF.instances_path)

        # Filter all_instances to only include those nodes which share this
        # storage path.
        # TODO(mikal): this should be further refactored so that the cache
        # cleanup code doesn't know what those instances are, just a remote
        # count, and then this logic should be pushed up the stack.
        filters = {'deleted': False,
                   'soft_deleted': True,
                   'host': nodes}
        filtered_instances = objects.InstanceList.get_by_filters(context,
                                 filters, expected_attrs=[], use_slave=True)

        self.driver.manage_image_cache(context, filtered_instances)

    @periodic_task.periodic_task(spacing=CONF.instance_delete_interval)
    def _run_pending_deletes(self, context):
        """Retry any pending instance file deletes."""
        if CONF.instance_delete_interval == 0:
            return

        LOG.debug('Cleaning up deleted instances')
        filters = {'deleted': True,
                   'soft_deleted': False,
                   'host': CONF.host,
                   'cleaned': False}
        attrs = ['info_cache', 'security_groups', 'system_metadata']
        with utils.temporary_mutation(context, read_deleted='yes'):
            instances = objects.InstanceList.get_by_filters(
                context, filters, expected_attrs=attrs)
        LOG.debug('There are %d instances to clean', len(instances))

        for instance in instances:
            attempts = int(instance.system_metadata.get('clean_attempts', '0'))
            LOG.debug('Instance has had %(attempts)s of %(max)s '
                      'cleanup attempts',
                      {'attempts': attempts,
                       'max': CONF.maximum_instance_delete_attempts},
                      instance=instance)
            if attempts < CONF.maximum_instance_delete_attempts:
                success = self.driver.delete_instance_files(instance)

                instance.system_metadata['clean_attempts'] = str(attempts + 1)
                if success:
                    instance.cleaned = True
                with utils.temporary_mutation(context, read_deleted='yes'):
                    instance.save(context)