# vim: tabstop=4 shiftwidth=4 softtabstop=4

# 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.

**Related Flags**

:instances_path:  Where instances are kept on disk
:compute_driver:  Name of class that is used to handle virtualization, loaded
                  by :func:`nova.utils.import_object`
:volume_manager:  Name of class that handles persistent storage, loaded by
                  :func:`nova.utils.import_object`

"""

import datetime
import os
import random
import string
import socket
import sys
import tempfile
import functools

from eventlet import greenthread

from nova import exception
from nova import flags
from nova import log as logging
from nova import manager
from nova import rpc
from nova import utils
from nova import volume
from nova.compute import power_state
from nova.virt import driver


FLAGS = flags.FLAGS
flags.DEFINE_string('instances_path', '$state_path/instances',
                    'where instances are stored on disk')
flags.DEFINE_string('compute_driver', 'nova.virt.connection.get_connection',
                    'Driver to use for controlling virtualization')
flags.DEFINE_string('stub_network', False,
                    'Stub network related code')
flags.DEFINE_integer('password_length', 12,
                    'Length of generated admin passwords')
flags.DEFINE_string('console_host', socket.gethostname(),
                    'Console proxy host to use to connect to instances on'
                    'this host.')
flags.DEFINE_integer('live_migration_retry_count', 30,
                     "Retry count needed in live_migration."
                     " sleep 1 sec for each count")
flags.DEFINE_integer("rescue_timeout", 0,
                     "Automatically unrescue an instance after N seconds."
                     " Set to 0 to disable.")


LOG = logging.getLogger('nova.compute.manager')


def checks_instance_lock(function):
    """Decorator to prevent action against locked instances for non-admins."""
    @functools.wraps(function)
    def decorated_function(self, context, instance_id, *args, **kwargs):
        LOG.info(_("check_instance_lock: decorating: |%s|"), function,
                 context=context)
        LOG.info(_("check_instance_lock: arguments: |%(self)s| |%(context)s|"
                " |%(instance_id)s|") % locals(), context=context)
        locked = self.get_lock(context, instance_id)
        admin = context.is_admin
        LOG.info(_("check_instance_lock: locked: |%s|"), locked,
                 context=context)
        LOG.info(_("check_instance_lock: admin: |%s|"), admin,
                 context=context)

        # if admin or unlocked call function otherwise log error
        if admin or not locked:
            LOG.info(_("check_instance_lock: executing: |%s|"), function,
                     context=context)
            function(self, context, instance_id, *args, **kwargs)
        else:
            LOG.error(_("check_instance_lock: not executing |%s|"),
                      function, context=context)
            return False

    return decorated_function


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

    def __init__(self, compute_driver=None, *args, **kwargs):
        """Load configuration options and connect to the hypervisor."""
        # TODO(vish): sync driver creation logic with the rest of the system
        #             and redocument the module docstring
        if not compute_driver:
            compute_driver = FLAGS.compute_driver

        try:
            self.driver = utils.check_isinstance(
                                        utils.import_object(compute_driver),
                                        driver.ComputeDriver)
        except ImportError as e:
            LOG.error(_("Unable to load the virtualization driver: %s") % (e))
            sys.exit(1)

        self.network_manager = utils.import_object(FLAGS.network_manager)
        self.volume_manager = utils.import_object(FLAGS.volume_manager)
        super(ComputeManager, self).__init__(service_name="compute",
                                             *args, **kwargs)

    def init_host(self):
        """Initialization for a standalone compute service."""
        self.driver.init_host(host=self.host)

    def _update_state(self, context, instance_id):
        """Update the state of an instance from the driver info."""
        # FIXME(ja): include other fields from state?
        instance_ref = self.db.instance_get(context, instance_id)
        try:
            info = self.driver.get_info(instance_ref['name'])
            state = info['state']
        except exception.NotFound:
            state = power_state.FAILED
        self.db.instance_set_state(context, instance_id, state)

    def get_console_topic(self, context, **kwargs):
        """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 self.db.queue_get_for(context,
                                     FLAGS.console_topic,
                                     FLAGS.console_host)

    def get_network_topic(self, context, **kwargs):
        """Retrieves the network host for a project on this host."""
        # TODO(vish): This method should be memoized. This will make
        #             the call to get_network_host cheaper, so that
        #             it can pas messages instead of checking the db
        #             locally.
        if FLAGS.stub_network:
            host = FLAGS.network_host
        else:
            host = self.network_manager.get_network_host(context)
        return self.db.queue_get_for(context,
                                     FLAGS.network_topic,
                                     host)

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

    @exception.wrap_exception
    def refresh_security_group_rules(self, context, security_group_id,
                                     **kwargs):
        """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)

    @exception.wrap_exception
    def refresh_security_group_members(self, context,
                                       security_group_id, **kwargs):
        """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)

    @exception.wrap_exception
    def run_instance(self, context, instance_id, **kwargs):
        """Launch a new instance with specified options."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        instance_ref.injected_files = kwargs.get('injected_files', [])
        if instance_ref['name'] in self.driver.list_instances():
            raise exception.Error(_("Instance has already been created"))
        LOG.audit(_("instance %s: starting..."), instance_id,
                  context=context)
        self.db.instance_update(context,
                                instance_id,
                                {'host': self.host, 'launched_on': self.host})

        self.db.instance_set_state(context,
                                   instance_id,
                                   power_state.NOSTATE,
                                   'networking')

        is_vpn = instance_ref['image_id'] == str(FLAGS.vpn_image_id)
        # NOTE(vish): This could be a cast because we don't do anything
        #             with the address currently, but I'm leaving it as
        #             a call to ensure that network setup completes.  We
        #             will eventually also need to save the address here.
        if not FLAGS.stub_network:
            address = rpc.call(context,
                               self.get_network_topic(context),
                               {"method": "allocate_fixed_ip",
                                "args": {"instance_id": instance_id,
                                         "vpn": is_vpn}})

            self.network_manager.setup_compute_network(context,
                                                       instance_id)

        # TODO(vish) check to make sure the availability zone matches
        self.db.instance_set_state(context,
                                   instance_id,
                                   power_state.NOSTATE,
                                   'spawning')

        try:
            self.driver.spawn(instance_ref)
            now = datetime.datetime.utcnow()
            self.db.instance_update(context,
                                    instance_id,
                                    {'launched_at': now})
        except Exception:  # pylint: disable=W0702
            LOG.exception(_("Instance '%s' failed to spawn. Is virtualization"
                            " enabled in the BIOS?"), instance_id,
                                                     context=context)
            self.db.instance_set_state(context,
                                       instance_id,
                                       power_state.SHUTDOWN)

        self._update_state(context, instance_id)

    @exception.wrap_exception
    @checks_instance_lock
    def terminate_instance(self, context, instance_id):
        """Terminate an instance on this host."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        LOG.audit(_("Terminating instance %s"), instance_id, context=context)

        fixed_ip = instance_ref.get('fixed_ip')
        if not FLAGS.stub_network and fixed_ip:
            floating_ips = fixed_ip.get('floating_ips') or []
            for floating_ip in floating_ips:
                address = floating_ip['address']
                LOG.debug("Disassociating address %s", address,
                          context=context)
                # NOTE(vish): Right now we don't really care if the ip is
                #             disassociated.  We may need to worry about
                #             checking this later.
                network_topic = self.db.queue_get_for(context,
                                                      FLAGS.network_topic,
                                                      floating_ip['host'])
                rpc.cast(context,
                         network_topic,
                         {"method": "disassociate_floating_ip",
                          "args": {"floating_address": address}})

            address = fixed_ip['address']
            if address:
                LOG.debug(_("Deallocating address %s"), address,
                          context=context)
                # NOTE(vish): Currently, nothing needs to be done on the
                #             network node until release. If this changes,
                #             we will need to cast here.
                self.network_manager.deallocate_fixed_ip(context.elevated(),
                                                         address)

        volumes = instance_ref.get('volumes') or []
        for volume in volumes:
            self.detach_volume(context, instance_id, volume['id'])
        if instance_ref['state'] == power_state.SHUTOFF:
            self.db.instance_destroy(context, instance_id)
            raise exception.Error(_('trying to destroy already destroyed'
                                    ' instance: %s') % instance_id)
        self.driver.destroy(instance_ref)

        # TODO(ja): should we keep it in a terminated state for a bit?
        self.db.instance_destroy(context, instance_id)

    @exception.wrap_exception
    @checks_instance_lock
    def reboot_instance(self, context, instance_id):
        """Reboot an instance on this host."""
        context = context.elevated()
        self._update_state(context, instance_id)
        instance_ref = self.db.instance_get(context, instance_id)
        LOG.audit(_("Rebooting instance %s"), instance_id, context=context)

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

        self.db.instance_set_state(context,
                                   instance_id,
                                   power_state.NOSTATE,
                                   'rebooting')
        self.network_manager.setup_compute_network(context, instance_id)
        self.driver.reboot(instance_ref)
        self._update_state(context, instance_id)

    @exception.wrap_exception
    def snapshot_instance(self, context, instance_id, image_id):
        """Snapshot an instance on this host."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)

        #NOTE(sirp): update_state currently only refreshes the state field
        # if we add is_snapshotting, we will need this refreshed too,
        # potentially?
        self._update_state(context, instance_id)

        LOG.audit(_('instance %s: snapshotting'), instance_id,
                  context=context)
        if instance_ref['state'] != power_state.RUNNING:
            state = instance_ref['state']
            running = power_state.RUNNING
            LOG.warn(_('trying to snapshot a non-running '
                       'instance: %(instance_id)s (state: %(state)s '
                       'expected: %(running)s)') % locals())

        self.driver.snapshot(instance_ref, image_id)

    @exception.wrap_exception
    @checks_instance_lock
    def set_admin_password(self, context, instance_id, new_pass=None):
        """Set the root/admin password for an instance on this host."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        instance_id = instance_ref['id']
        instance_state = instance_ref['state']
        expected_state = power_state.RUNNING
        if instance_state != expected_state:
            LOG.warn(_('trying to reset the password on a non-running '
                    'instance: %(instance_id)s (state: %(instance_state)s '
                    'expected: %(expected_state)s)') % locals())
        LOG.audit(_('instance %s: setting admin password'),
                instance_ref['name'])
        if new_pass is None:
            # Generate a random password
            new_pass = utils.generate_password(FLAGS.password_length)
        self.driver.set_admin_password(instance_ref, new_pass)
        self._update_state(context, instance_id)

    @exception.wrap_exception
    @checks_instance_lock
    def inject_file(self, context, instance_id, path, file_contents):
        """Write a file to the specified path in an instance on this host."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        instance_id = instance_ref['id']
        instance_state = instance_ref['state']
        expected_state = power_state.RUNNING
        if instance_state != expected_state:
            LOG.warn(_('trying to inject a file into a non-running '
                    'instance: %(instance_id)s (state: %(instance_state)s '
                    'expected: %(expected_state)s)') % locals())
        nm = instance_ref['name']
        msg = _('instance %(nm)s: injecting file to %(path)s') % locals()
        LOG.audit(msg)
        self.driver.inject_file(instance_ref, path, file_contents)

    @exception.wrap_exception
    @checks_instance_lock
    def rescue_instance(self, context, instance_id):
        """Rescue an instance on this host."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        LOG.audit(_('instance %s: rescuing'), instance_id, context=context)
        self.db.instance_set_state(context,
                                   instance_id,
                                   power_state.NOSTATE,
                                   'rescuing')
        self.network_manager.setup_compute_network(context, instance_id)
        _update_state = lambda result: self._update_state_callback(
                self, context, instance_id, result)
        self.driver.rescue(instance_ref, _update_state)
        self._update_state(context, instance_id)

    @exception.wrap_exception
    @checks_instance_lock
    def unrescue_instance(self, context, instance_id):
        """Rescue an instance on this host."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        LOG.audit(_('instance %s: unrescuing'), instance_id, context=context)
        self.db.instance_set_state(context,
                                   instance_id,
                                   power_state.NOSTATE,
                                   'unrescuing')
        _update_state = lambda result: self._update_state_callback(
                self, context, instance_id, result)
        self.driver.unrescue(instance_ref, _update_state)
        self._update_state(context, instance_id)

    @staticmethod
    def _update_state_callback(self, context, instance_id, result):
        """Update instance state when async task completes."""
        self._update_state(context, instance_id)

    @exception.wrap_exception
    @checks_instance_lock
    def confirm_resize(self, context, instance_id, migration_id):
        """Destroys the source instance."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        self.driver.destroy(instance_ref)

    @exception.wrap_exception
    @checks_instance_lock
    def revert_resize(self, context, instance_id, migration_id):
        """Destroys the new instance on the destination machine.

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

        """
        instance_ref = self.db.instance_get(context, instance_id)
        migration_ref = self.db.migration_get(context, migration_id)

        self.driver.destroy(instance_ref)
        topic = self.db.queue_get_for(context, FLAGS.compute_topic,
                instance_ref['host'])
        rpc.cast(context, topic,
                {'method': 'finish_revert_resize',
                 'args': {
                       'migration_id': migration_ref['id'],
                       'instance_id': instance_id, },
                })

    @exception.wrap_exception
    @checks_instance_lock
    def finish_revert_resize(self, context, instance_id, migration_id):
        """Finishes the second half of reverting a resize.

        Power back on the source instance and revert the resized attributes
        in the database.

        """
        instance_ref = self.db.instance_get(context, instance_id)
        migration_ref = self.db.migration_get(context, migration_id)
        instance_type = self.db.instance_type_get_by_flavor_id(context,
                migration_ref['old_flavor_id'])

        # Just roll back the record. There's no need to resize down since
        # the 'old' VM already has the preferred attributes
        self.db.instance_update(context, instance_id,
           dict(memory_mb=instance_type['memory_mb'],
                vcpus=instance_type['vcpus'],
                local_gb=instance_type['local_gb']))

        self.driver.revert_resize(instance_ref)
        self.db.migration_update(context, migration_id,
                {'status': 'reverted'})

    @exception.wrap_exception
    @checks_instance_lock
    def prep_resize(self, context, instance_id, flavor_id):
        """Initiates the process of moving a running instance to another host.

        Possibly changes the RAM and disk size in the process.

        """
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        if instance_ref['host'] == FLAGS.host:
            raise exception.Error(_(
                    'Migration error: destination same as source!'))

        instance_type = self.db.instance_type_get_by_flavor_id(context,
                flavor_id)
        migration_ref = self.db.migration_create(context,
                {'instance_id': instance_id,
                 'source_compute': instance_ref['host'],
                 'dest_compute': FLAGS.host,
                 'dest_host':   self.driver.get_host_ip_addr(),
                 'old_flavor_id': instance_type['flavorid'],
                 'new_flavor_id': flavor_id,
                 'status':      'pre-migrating'})

        LOG.audit(_('instance %s: migrating to '), instance_id,
                context=context)
        topic = self.db.queue_get_for(context, FLAGS.compute_topic,
                instance_ref['host'])
        rpc.cast(context, topic,
                {'method': 'resize_instance',
                 'args': {
                       'migration_id': migration_ref['id'],
                       'instance_id': instance_id, },
                })

    @exception.wrap_exception
    @checks_instance_lock
    def resize_instance(self, context, instance_id, migration_id):
        """Starts the migration of a running instance to another host."""
        migration_ref = self.db.migration_get(context, migration_id)
        instance_ref = self.db.instance_get(context, instance_id)
        self.db.migration_update(context,
                                 migration_id,
                                 {'status': 'migrating'})

        disk_info = self.driver.migrate_disk_and_power_off(
                instance_ref, migration_ref['dest_host'])
        self.db.migration_update(context,
                                 migration_id,
                                 {'status': 'post-migrating'})

        service = self.db.service_get_by_host_and_topic(
                context, migration_ref['dest_compute'], FLAGS.compute_topic)
        topic = self.db.queue_get_for(context,
                                      FLAGS.compute_topic,
                                      migration_ref['dest_compute'])
        rpc.cast(context, topic, {'method': 'finish_resize',
                                  'args': {'migration_id': migration_id,
                                           'instance_id': instance_id,
                                           'disk_info': disk_info}})

    @exception.wrap_exception
    @checks_instance_lock
    def finish_resize(self, context, instance_id, migration_id, disk_info):
        """Completes the migration process.

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

        """
        migration_ref = self.db.migration_get(context, migration_id)
        instance_ref = self.db.instance_get(context,
                migration_ref['instance_id'])
        # TODO(mdietz): apply the rest of the instance_type attributes going
        # after they're supported
        instance_type = self.db.instance_type_get_by_flavor_id(context,
                migration_ref['new_flavor_id'])
        self.db.instance_update(context, instance_id,
               dict(instance_type=instance_type['name'],
                    memory_mb=instance_type['memory_mb'],
                    vcpus=instance_type['vcpus'],
                    local_gb=instance_type['local_gb']))

        # reload the updated instance ref
        # FIXME(mdietz): is there reload functionality?
        instance_ref = self.db.instance_get(context, instance_id)
        self.driver.finish_resize(instance_ref, disk_info)

        self.db.migration_update(context, migration_id,
                {'status': 'finished', })

    @exception.wrap_exception
    @checks_instance_lock
    def pause_instance(self, context, instance_id):
        """Pause an instance on this host."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        LOG.audit(_('instance %s: pausing'), instance_id, context=context)
        self.db.instance_set_state(context,
                                   instance_id,
                                   power_state.NOSTATE,
                                   'pausing')
        self.driver.pause(instance_ref,
            lambda result: self._update_state_callback(self,
                                                       context,
                                                       instance_id,
                                                       result))

    @exception.wrap_exception
    @checks_instance_lock
    def unpause_instance(self, context, instance_id):
        """Unpause a paused instance on this host."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        LOG.audit(_('instance %s: unpausing'), instance_id, context=context)
        self.db.instance_set_state(context,
                                   instance_id,
                                   power_state.NOSTATE,
                                   'unpausing')
        self.driver.unpause(instance_ref,
            lambda result: self._update_state_callback(self,
                                                       context,
                                                       instance_id,
                                                       result))

    @exception.wrap_exception
    def get_diagnostics(self, context, instance_id):
        """Retrieve diagnostics for an instance on this host."""
        instance_ref = self.db.instance_get(context, instance_id)

        if instance_ref["state"] == power_state.RUNNING:
            LOG.audit(_("instance %s: retrieving diagnostics"), instance_id,
                      context=context)
            return self.driver.get_diagnostics(instance_ref)

    @exception.wrap_exception
    @checks_instance_lock
    def suspend_instance(self, context, instance_id):
        """Suspend the given instance."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        LOG.audit(_('instance %s: suspending'), instance_id, context=context)
        self.db.instance_set_state(context, instance_id,
                                            power_state.NOSTATE,
                                            'suspending')
        self.driver.suspend(instance_ref,
            lambda result: self._update_state_callback(self,
                                                       context,
                                                       instance_id,
                                                       result))

    @exception.wrap_exception
    @checks_instance_lock
    def resume_instance(self, context, instance_id):
        """Resume the given suspended instance."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        LOG.audit(_('instance %s: resuming'), instance_id, context=context)
        self.db.instance_set_state(context, instance_id,
                                            power_state.NOSTATE,
                                            'resuming')
        self.driver.resume(instance_ref,
            lambda result: self._update_state_callback(self,
                                                       context,
                                                       instance_id,
                                                       result))

    @exception.wrap_exception
    def lock_instance(self, context, instance_id):
        """Lock the given instance."""
        context = context.elevated()

        LOG.debug(_('instance %s: locking'), instance_id, context=context)
        self.db.instance_update(context, instance_id, {'locked': True})

    @exception.wrap_exception
    def unlock_instance(self, context, instance_id):
        """Unlock the given instance."""
        context = context.elevated()

        LOG.debug(_('instance %s: unlocking'), instance_id, context=context)
        self.db.instance_update(context, instance_id, {'locked': False})

    @exception.wrap_exception
    def get_lock(self, context, instance_id):
        """Return the boolean state of the given instance's lock."""
        context = context.elevated()
        LOG.debug(_('instance %s: getting locked state'), instance_id,
                  context=context)
        instance_ref = self.db.instance_get(context, instance_id)
        return instance_ref['locked']

    @checks_instance_lock
    def reset_network(self, context, instance_id):
        """Reset networking on the given instance."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        LOG.debug(_('instance %s: reset network'), instance_id,
                                                   context=context)
        self.driver.reset_network(instance_ref)

    @checks_instance_lock
    def inject_network_info(self, context, instance_id):
        """Inject network info for the given instance."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        LOG.debug(_('instance %s: inject network info'), instance_id,
                                                         context=context)
        self.driver.inject_network_info(instance_ref)

    @exception.wrap_exception
    def get_console_output(self, context, instance_id):
        """Send the console output for the given instance."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        LOG.audit(_("Get console output for instance %s"), instance_id,
                  context=context)
        return self.driver.get_console_output(instance_ref)

    @exception.wrap_exception
    def get_ajax_console(self, context, instance_id):
        """Return connection information for an ajax console."""
        context = context.elevated()
        LOG.debug(_("instance %s: getting ajax console"), instance_id)
        instance_ref = self.db.instance_get(context, instance_id)
        return self.driver.get_ajax_console(instance_ref)

    @exception.wrap_exception
    def get_vnc_console(self, context, instance_id):
        """Return connection information for a vnc console."""
        context = context.elevated()
        LOG.debug(_("instance %s: getting vnc console"), instance_id)
        instance_ref = self.db.instance_get(context, instance_id)
        return self.driver.get_vnc_console(instance_ref)

    @checks_instance_lock
    def attach_volume(self, context, instance_id, volume_id, mountpoint):
        """Attach a volume to an instance."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        LOG.audit(_("instance %(instance_id)s: attaching volume %(volume_id)s"
                " to %(mountpoint)s") % locals(), context=context)
        dev_path = self.volume_manager.setup_compute_volume(context,
                                                            volume_id)
        try:
            self.driver.attach_volume(instance_ref['name'],
                                      dev_path,
                                      mountpoint)
            self.db.volume_attached(context,
                                    volume_id,
                                    instance_id,
                                    mountpoint)
        except Exception as exc:  # pylint: disable=W0702
            # NOTE(vish): The inline callback eats the exception info so we
            #             log the traceback here and reraise the same
            #             ecxception below.
            LOG.exception(_("instance %(instance_id)s: attach failed"
                    " %(mountpoint)s, removing") % locals(), context=context)
            self.volume_manager.remove_compute_volume(context,
                                                      volume_id)
            raise exc

        return True

    @exception.wrap_exception
    @checks_instance_lock
    def detach_volume(self, context, instance_id, volume_id):
        """Detach a volume from an instance."""
        context = context.elevated()
        instance_ref = self.db.instance_get(context, instance_id)
        volume_ref = self.db.volume_get(context, volume_id)
        mp = volume_ref['mountpoint']
        LOG.audit(_("Detach volume %(volume_id)s from mountpoint %(mp)s"
                " on instance %(instance_id)s") % locals(), context=context)
        if instance_ref['name'] not in self.driver.list_instances():
            LOG.warn(_("Detaching volume from unknown instance %s"),
                     instance_id, context=context)
        else:
            self.driver.detach_volume(instance_ref['name'],
                                      volume_ref['mountpoint'])
        self.volume_manager.remove_compute_volume(context, volume_id)
        self.db.volume_detached(context, volume_id)
        return True

    def remove_volume(self, context, volume_id):
        """Remove volume on compute host.

        :param context: security context
        :param volume_id: volume ID
        """
        self.volume_manager.remove_compute_volume(context, volume_id)

    @exception.wrap_exception
    def compare_cpu(self, context, cpu_info):
        """Checks that the host cpu is compatible with a cpu given by xml.

        :param context: security context
        :param cpu_info: json string obtained from virConnect.getCapabilities
        :returns: See driver.compare_cpu

        """
        return self.driver.compare_cpu(cpu_info)

    @exception.wrap_exception
    def create_shared_storage_test_file(self, context):
        """Makes tmpfile under FLAGS.instance_path.

        This method enables compute nodes to recognize that they mounts
        same shared storage. (create|check|creanup)_shared_storage_test_file()
        is a pair.

        :param context: security context
        :returns: tmpfile name(basename)

        """
        dirpath = FLAGS.instances_path
        fd, tmp_file = tempfile.mkstemp(dir=dirpath)
        LOG.debug(_("Creating tmpfile %s to notify to other "
                    "compute nodes that they should mount "
                    "the same storage.") % tmp_file)
        os.close(fd)
        return os.path.basename(tmp_file)

    @exception.wrap_exception
    def check_shared_storage_test_file(self, context, filename):
        """Confirms existence of the tmpfile under FLAGS.instances_path.

        :param context: security context
        :param filename: confirm existence of FLAGS.instances_path/thisfile

        """
        tmp_file = os.path.join(FLAGS.instances_path, filename)
        if not os.path.exists(tmp_file):
            raise exception.NotFound(_('%s not found') % tmp_file)

    @exception.wrap_exception
    def cleanup_shared_storage_test_file(self, context, filename):
        """Removes existence of the tmpfile under FLAGS.instances_path.

        :param context: security context
        :param filename: remove existence of FLAGS.instances_path/thisfile

        """
        tmp_file = os.path.join(FLAGS.instances_path, filename)
        os.remove(tmp_file)

    @exception.wrap_exception
    def update_available_resource(self, context):
        """See comments update_resource_info.

        :param context: security context
        :returns: See driver.update_available_resource()

        """
        return self.driver.update_available_resource(context, self.host)

    def pre_live_migration(self, context, instance_id, time=None):
        """Preparations for live migration at dest host.

        :param context: security context
        :param instance_id: nova.db.sqlalchemy.models.Instance.Id

        """
        if not time:
            time = greenthread

        # Getting instance info
        instance_ref = self.db.instance_get(context, instance_id)
        ec2_id = instance_ref['hostname']

        # Getting fixed ips
        fixed_ip = self.db.instance_get_fixed_address(context, instance_id)
        if not fixed_ip:
            msg = _("%(instance_id)s(%(ec2_id)s) does not have fixed_ip.")
            raise exception.NotFound(msg % locals())

        # If any volume is mounted, prepare here.
        if not instance_ref['volumes']:
            LOG.info(_("%s has no volume."), ec2_id)
        else:
            for v in instance_ref['volumes']:
                self.volume_manager.setup_compute_volume(context, v['id'])

        # Bridge settings.
        # Call this method prior to ensure_filtering_rules_for_instance,
        # since bridge is not set up, ensure_filtering_rules_for instance
        # fails.
        #
        # Retry operation is necessary because continuously request comes,
        # concorrent request occurs to iptables, then it complains.
        max_retry = FLAGS.live_migration_retry_count
        for cnt in range(max_retry):
            try:
                self.network_manager.setup_compute_network(context,
                                                           instance_id)
                break
            except exception.ProcessExecutionError:
                if cnt == max_retry - 1:
                    raise
                else:
                    LOG.warn(_("setup_compute_network() failed %(cnt)d."
                               "Retry up to %(max_retry)d for %(ec2_id)s.")
                               % locals())
                    time.sleep(1)

        # 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_ref)

    def live_migration(self, context, instance_id, dest):
        """Executing live migration.

        :param context: security context
        :param instance_id: nova.db.sqlalchemy.models.Instance.Id
        :param dest: destination host

        """
        # Get instance for error handling.
        instance_ref = self.db.instance_get(context, instance_id)
        i_name = instance_ref.name

        try:
            # Checking volume node is working correctly when any volumes
            # are attached to instances.
            if instance_ref['volumes']:
                rpc.call(context,
                          FLAGS.volume_topic,
                          {"method": "check_for_export",
                           "args": {'instance_id': instance_id}})

            # Asking dest host to preparing live migration.
            rpc.call(context,
                     self.db.queue_get_for(context, FLAGS.compute_topic, dest),
                     {"method": "pre_live_migration",
                      "args": {'instance_id': instance_id}})

        except Exception:
            msg = _("Pre live migration for %(i_name)s failed at %(dest)s")
            LOG.error(msg % locals())
            self.recover_live_migration(context, instance_ref)
            raise

        # Executing live migration
        # live_migration might raises exceptions, but
        # nothing must be recovered in this version.
        self.driver.live_migration(context, instance_ref, dest,
                                   self.post_live_migration,
                                   self.recover_live_migration)

    def post_live_migration(self, ctxt, instance_ref, dest):
        """Post operations for live migration.

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

        :param ctxt: security context
        :param instance_id: nova.db.sqlalchemy.models.Instance.Id
        :param dest: destination host

        """

        LOG.info(_('post_live_migration() is started..'))
        instance_id = instance_ref['id']

        # Detaching volumes.
        try:
            for vol in self.db.volume_get_all_by_instance(ctxt, instance_id):
                self.volume_manager.remove_compute_volume(ctxt, vol['id'])
        except exception.NotFound:
            pass

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

        # Releasing security group ingress rule.
        self.driver.unfilter_instance(instance_ref)

        # Database updating.
        i_name = instance_ref.name
        try:
            # Not return if floating_ip is not found, otherwise,
            # instance never be accessible..
            floating_ip = self.db.instance_get_floating_address(ctxt,
                                                         instance_id)
            if not floating_ip:
                LOG.info(_('No floating_ip is found for %s.'), i_name)
            else:
                floating_ip_ref = self.db.floating_ip_get_by_address(ctxt,
                                                              floating_ip)
                self.db.floating_ip_update(ctxt,
                                           floating_ip_ref['address'],
                                           {'host': dest})
        except exception.NotFound:
            LOG.info(_('No floating_ip is found for %s.'), i_name)
        except:
            LOG.error(_("Live migration: Unexpected error:"
                        "%s cannot inherit floating ip..") % i_name)

        # Restore instance/volume state
        self.recover_live_migration(ctxt, instance_ref, dest)

        LOG.info(_('Migrating %(i_name)s to %(dest)s finished successfully.')
                 % locals())
        LOG.info(_("You may see the error \"libvirt: QEMU error: "
                   "Domain not found: no domain with matching name.\" "
                   "This error can be safely ignored."))

    def recover_live_migration(self, ctxt, instance_ref, host=None, dest=None):
        """Recovers Instance/volume state from migrating -> running.

        :param ctxt: security context
        :param instance_id: nova.db.sqlalchemy.models.Instance.Id
        :param host: DB column value is updated by this hostname.
                     If none, the host instance currently running is selected.

        """
        if not host:
            host = instance_ref['host']

        self.db.instance_update(ctxt,
                                instance_ref['id'],
                                {'state_description': 'running',
                                 'state': power_state.RUNNING,
                                 'host': host})

        if dest:
            volume_api = volume.API()
        for volume_ref in instance_ref['volumes']:
            volume_id = volume_ref['id']
            self.db.volume_update(ctxt, volume_id, {'status': 'in-use'})
            if dest:
                volume_api.remove_from_compute(ctxt, volume_id, dest)

    def periodic_tasks(self, context=None):
        """Tasks to be run at a periodic interval."""
        error_list = super(ComputeManager, self).periodic_tasks(context)
        if error_list is None:
            error_list = []

        try:
            if FLAGS.rescue_timeout > 0:
                self.driver.poll_rescued_instances(FLAGS.rescue_timeout)
        except Exception as ex:
            LOG.warning(_("Error during poll_rescued_instances: %s"),
                        unicode(ex))
            error_list.append(ex)

        try:
            self._poll_instance_states(context)
        except Exception as ex:
            LOG.warning(_("Error during instance poll: %s"),
                        unicode(ex))
            error_list.append(ex)

        return error_list

    def _poll_instance_states(self, context):
        vm_instances = self.driver.list_instances_detail()
        vm_instances = dict((vm.name, vm) for vm in vm_instances)

        # Keep a list of VMs not in the DB, cross them off as we find them
        vms_not_found_in_db = list(vm_instances.keys())

        db_instances = self.db.instance_get_all_by_host(context, self.host)

        for db_instance in db_instances:
            name = db_instance['name']
            db_state = db_instance['state']
            vm_instance = vm_instances.get(name)

            if vm_instance is None:
                # NOTE(justinsb): We have to be very careful here, because a
                # concurrent operation could be in progress (e.g. a spawn)
                if db_state == power_state.NOSTATE:
                    # Assume that NOSTATE => spawning
                    # TODO(justinsb): This does mean that if we crash during a
                    # spawn, the machine will never leave the spawning state,
                    # but this is just the way nova is; this function isn't
                    # trying to correct that problem.
                    # We could have a separate task to correct this error.
                    # TODO(justinsb): What happens during a live migration?
                    LOG.info(_("Found instance '%(name)s' in DB but no VM. "
                               "State=%(db_state)s, so assuming spawn is in "
                               "progress.") % locals())
                    vm_state = db_state
                else:
                    LOG.info(_("Found instance '%(name)s' in DB but no VM. "
                               "State=%(db_state)s, so setting state to "
                               "shutoff.") % locals())
                    vm_state = power_state.SHUTOFF
            else:
                vm_state = vm_instance.state
                vms_not_found_in_db.remove(name)

            if db_instance['state_description'] == 'migrating':
                # A situation which db record exists, but no instance"
                # sometimes occurs while live-migration at src compute,
                # this case should be ignored.
                LOG.debug(_("Ignoring %(name)s, as it's currently being "
                           "migrated.") % locals())
                continue

            if vm_state != db_state:
                LOG.info(_("DB/VM state mismatch. Changing state from "
                           "'%(db_state)s' to '%(vm_state)s'") % locals())
                self.db.instance_set_state(context,
                                           db_instance['id'],
                                           vm_state)

            # NOTE(justinsb): We no longer auto-remove SHUTOFF instances
            # It's quite hard to get them back when we do.

        # Are there VMs not in the DB?
        for vm_not_found_in_db in vms_not_found_in_db:
            name = vm_not_found_in_db

            # We only care about instances that compute *should* know about
            if name.startswith("instance-"):
                # TODO(justinsb): What to do here?  Adopt it?  Shut it down?
                LOG.warning(_("Found VM not in DB: '%(name)s'.  Ignoring")
                            % locals())
