text: # Copyright (c) 2013 OpenStack Foundation
  # 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.
  
  from eventlet import greenthread
  import netaddr
  from netaddr.strategy import eui48
  from neutron_lib.agent import constants as agent_consts
  from neutron_lib.agent import topics
  from neutron_lib.api.definitions import address_scope
  from neutron_lib.api.definitions import agent as agent_apidef
  from neutron_lib.api.definitions import agent_resources_synced
  from neutron_lib.api.definitions import allowedaddresspairs as addr_apidef
  from neutron_lib.api.definitions import availability_zone as az_def
  from neutron_lib.api.definitions import availability_zone_filter
  from neutron_lib.api.definitions import default_subnetpools
  from neutron_lib.api.definitions import dhcpagentscheduler
  from neutron_lib.api.definitions import empty_string_filtering
  from neutron_lib.api.definitions import external_net
  from neutron_lib.api.definitions import extra_dhcp_opt as edo_ext
  from neutron_lib.api.definitions import filter_validation as filter_apidef
  from neutron_lib.api.definitions import ip_allocation as ipalloc_apidef
  from neutron_lib.api.definitions import ip_substring_port_filtering
  from neutron_lib.api.definitions import multiprovidernet
  from neutron_lib.api.definitions import network as net_def
  from neutron_lib.api.definitions import network_availability_zone
  from neutron_lib.api.definitions import network_mtu as mtu_apidef
  from neutron_lib.api.definitions import network_mtu_writable as mtuw_apidef
  from neutron_lib.api.definitions import port as port_def
  from neutron_lib.api.definitions import port_mac_address_regenerate
  from neutron_lib.api.definitions import port_security as psec
  from neutron_lib.api.definitions import portbindings
  from neutron_lib.api.definitions import portbindings_extended as pbe_ext
  from neutron_lib.api.definitions import provider_net
  from neutron_lib.api.definitions import rbac_security_groups as rbac_sg_apidef
  from neutron_lib.api.definitions import security_groups_port_filtering
  from neutron_lib.api.definitions import subnet as subnet_def
  from neutron_lib.api.definitions import subnet_onboard as subnet_onboard_def
  from neutron_lib.api.definitions import vlantransparent as vlan_apidef
  from neutron_lib.api import extensions
  from neutron_lib.api import validators
  from neutron_lib.api.validators import availability_zone as az_validator
  from neutron_lib.callbacks import events
  from neutron_lib.callbacks import exceptions
  from neutron_lib.callbacks import registry
  from neutron_lib.callbacks import resources
  from neutron_lib import constants as const
  from neutron_lib.db import api as db_api
  from neutron_lib.db import model_query
  from neutron_lib.db import resource_extend
  from neutron_lib.db import utils as db_utils
  from neutron_lib import exceptions as exc
  from neutron_lib.exceptions import allowedaddresspairs as addr_exc
  from neutron_lib.exceptions import port_security as psec_exc
  from neutron_lib.plugins import constants as plugin_constants
  from neutron_lib.plugins import directory
  from neutron_lib.plugins.ml2 import api
  from neutron_lib.plugins import utils as p_utils
  from neutron_lib import rpc as n_rpc
  from neutron_lib.services.qos import constants as qos_consts
  from oslo_config import cfg
  from oslo_db import exception as os_db_exception
  from oslo_log import helpers as log_helpers
  from oslo_log import log
  from oslo_serialization import jsonutils
  from oslo_utils import excutils
  from oslo_utils import importutils
  from oslo_utils import uuidutils
  import sqlalchemy
  from sqlalchemy import or_
  from sqlalchemy.orm import exc as sa_exc
  
  from neutron._i18n import _
  from neutron.agent import securitygroups_rpc as sg_rpc
  from neutron.api.rpc.agentnotifiers import dhcp_rpc_agent_api
  from neutron.api.rpc.handlers import dhcp_rpc
  from neutron.api.rpc.handlers import dvr_rpc
  from neutron.api.rpc.handlers import metadata_rpc
  from neutron.api.rpc.handlers import resources_rpc
  from neutron.api.rpc.handlers import securitygroups_rpc
  from neutron.common import constants as n_const
  from neutron.common import utils
  from neutron.db import address_scope_db
  from neutron.db import agents_db
  from neutron.db import agentschedulers_db
  from neutron.db import allowedaddresspairs_db as addr_pair_db
  from neutron.db import db_base_plugin_v2
  from neutron.db import dvr_mac_db
  from neutron.db import external_net_db
  from neutron.db import extradhcpopt_db
  from neutron.db.models import securitygroup as sg_models
  from neutron.db import models_v2
  from neutron.db import provisioning_blocks
  from neutron.db.quota import driver  # noqa
  from neutron.db import securitygroups_rpc_base as sg_db_rpc
  from neutron.db import segments_db
  from neutron.db import subnet_service_type_mixin
  from neutron.db import vlantransparent_db
  from neutron.extensions import filter_validation
  from neutron.extensions import vlantransparent
  from neutron.ipam import exceptions as ipam_exc
  from neutron.objects import base as base_obj
  from neutron.objects import ports as ports_obj
  from neutron.plugins.ml2.common import exceptions as ml2_exc
  from neutron.plugins.ml2 import db
  from neutron.plugins.ml2 import driver_context
  from neutron.plugins.ml2.extensions import qos as qos_ext
  from neutron.plugins.ml2 import managers
  from neutron.plugins.ml2 import models
  from neutron.plugins.ml2 import ovo_rpc
  from neutron.plugins.ml2 import rpc
  from neutron.quota import resource_registry
  from neutron.services.segments import plugin as segments_plugin
  
  LOG = log.getLogger(__name__)
  
  MAX_BIND_TRIES = 10
  
  
  SERVICE_PLUGINS_REQUIRED_DRIVERS = {
      'qos': [qos_ext.QOS_EXT_DRIVER_ALIAS]
  }
  
  
  def _ml2_port_result_filter_hook(query, filters):
      values = filters and filters.get(portbindings.HOST_ID, [])
      if not values:
          return query
      bind_criteria = models.PortBinding.host.in_(values)
      return query.filter(models_v2.Port.port_bindings.any(bind_criteria))
  
  
  @resource_extend.has_resource_extenders
  @registry.has_registry_receivers
  class Ml2Plugin(db_base_plugin_v2.NeutronDbPluginV2,
                  dvr_mac_db.DVRDbMixin,
                  external_net_db.External_net_db_mixin,
                  sg_db_rpc.SecurityGroupServerRpcMixin,
                  agentschedulers_db.AZDhcpAgentSchedulerDbMixin,
                  addr_pair_db.AllowedAddressPairsMixin,
                  vlantransparent_db.Vlantransparent_db_mixin,
                  extradhcpopt_db.ExtraDhcpOptMixin,
                  address_scope_db.AddressScopeDbMixin,
                  subnet_service_type_mixin.SubnetServiceTypeMixin):
  
      """Implement the Neutron L2 abstractions using modules.
  
      Ml2Plugin is a Neutron plugin based on separately extensible sets
      of network types and mechanisms for connecting to networks of
      those types. The network types and mechanisms are implemented as
      drivers loaded via Python entry points. Networks can be made up of
      multiple segments (not yet fully implemented).
      """
  
      # This attribute specifies whether the plugin supports or not
      # bulk/pagination/sorting operations. Name mangling is used in
      # order to ensure it is qualified by class
      __native_bulk_support = True
      __native_pagination_support = True
      __native_sorting_support = True
      # This attribute specifies whether the plugin supports or not
      # filter validations. Name mangling is used in
      # order to ensure it is qualified by class
      __filter_validation_support = True
  
      # List of supported extensions
      _supported_extension_aliases = [provider_net.ALIAS,
                                      external_net.ALIAS, portbindings.ALIAS,
                                      "quotas", "security-group",
                                      rbac_sg_apidef.ALIAS,
                                      agent_apidef.ALIAS,
                                      dhcpagentscheduler.ALIAS,
                                      multiprovidernet.ALIAS,
                                      addr_apidef.ALIAS,
                                      edo_ext.ALIAS, "subnet_allocation",
                                      mtu_apidef.ALIAS,
                                      mtuw_apidef.ALIAS,
                                      vlan_apidef.ALIAS,
                                      address_scope.ALIAS,
                                      az_def.ALIAS,
                                      network_availability_zone.ALIAS,
                                      availability_zone_filter.ALIAS,
                                      default_subnetpools.ALIAS,
                                      "subnet-service-types",
                                      ip_substring_port_filtering.ALIAS,
                                      security_groups_port_filtering.ALIAS,
                                      empty_string_filtering.ALIAS,
                                      filter_apidef.ALIAS,
                                      port_mac_address_regenerate.ALIAS,
                                      pbe_ext.ALIAS,
                                      agent_resources_synced.ALIAS,
                                      subnet_onboard_def.ALIAS]
  
      # List of agent types for which all binding_failed ports should try to be
      # rebound when agent revive
      _rebind_on_revive_agent_types = [const.AGENT_TYPE_OVS]
  
      @property
      def supported_extension_aliases(self):
          if not hasattr(self, '_aliases'):
              aliases = self._supported_extension_aliases[:]
              aliases += self.extension_manager.extension_aliases()
              sg_rpc.disable_security_group_extension_by_config(aliases)
              vlantransparent._disable_extension_by_config(aliases)
              filter_validation._disable_extension_by_config(aliases)
              self._aliases = aliases
          return self._aliases
  
      def __new__(cls, *args, **kwargs):
          model_query.register_hook(
              models_v2.Port,
              "ml2_port_bindings",
              query_hook=None,
              filter_hook=None,
              result_filters=_ml2_port_result_filter_hook)
          return super(Ml2Plugin, cls).__new__(cls, *args, **kwargs)
  
      @resource_registry.tracked_resources(
          network=models_v2.Network,
          port=models_v2.Port,
          subnet=models_v2.Subnet,
          subnetpool=models_v2.SubnetPool,
          security_group=sg_models.SecurityGroup,
          security_group_rule=sg_models.SecurityGroupRule)
      def __init__(self):
          # First load drivers, then initialize DB, then initialize drivers
          self.type_manager = managers.TypeManager()
          self.extension_manager = managers.ExtensionManager()
          self.mechanism_manager = managers.MechanismManager()
          super(Ml2Plugin, self).__init__()
          self.type_manager.initialize()
          self.extension_manager.initialize()
          self.mechanism_manager.initialize()
          self._setup_dhcp()
          self._start_rpc_notifiers()
          self.add_agent_status_check_worker(self.agent_health_check)
          self.add_workers(self.mechanism_manager.get_workers())
          self._verify_service_plugins_requirements()
          LOG.info("Modular L2 Plugin initialization complete")
  
      def _setup_rpc(self):
          """Initialize components to support agent communication."""
          self.endpoints = [
              rpc.RpcCallbacks(self.notifier, self.type_manager),
              securitygroups_rpc.SecurityGroupServerRpcCallback(),
              dvr_rpc.DVRServerRpcCallback(),
              dhcp_rpc.DhcpRpcCallback(),
              agents_db.AgentExtRpcCallback(),
              metadata_rpc.MetadataRpcCallback(),
              resources_rpc.ResourcesPullRpcCallback()
          ]
  
      def _setup_dhcp(self):
          """Initialize components to support DHCP."""
          self.network_scheduler = importutils.import_object(
              cfg.CONF.network_scheduler_driver
          )
          self.add_periodic_dhcp_agent_status_check()
  
      def _verify_service_plugins_requirements(self):
          for service_plugin in cfg.CONF.service_plugins:
              extension_drivers = SERVICE_PLUGINS_REQUIRED_DRIVERS.get(
                  service_plugin, []
              )
              for extension_driver in extension_drivers:
                  if extension_driver not in self.extension_manager.names():
                      raise ml2_exc.ExtensionDriverNotFound(
                          driver=extension_driver, service_plugin=service_plugin
                      )
  
      @registry.receives(resources.PORT,
                         [provisioning_blocks.PROVISIONING_COMPLETE])
      def _port_provisioned(self, rtype, event, trigger, context, object_id,
                            **kwargs):
          port_id = object_id
          port = db.get_port(context, port_id)
          port_binding = p_utils.get_port_binding_by_status_and_host(
              getattr(port, 'port_bindings', []), const.ACTIVE)
          if not port or not port_binding:
              LOG.debug("Port %s was deleted so its status cannot be updated.",
                        port_id)
              return
          if port_binding.vif_type in (portbindings.VIF_TYPE_BINDING_FAILED,
                                       portbindings.VIF_TYPE_UNBOUND):
              # NOTE(kevinbenton): we hit here when a port is created without
              # a host ID and the dhcp agent notifies that its wiring is done
              LOG.debug("Port %s cannot update to ACTIVE because it "
                        "is not bound.", port_id)
              return
          else:
              # port is bound, but we have to check for new provisioning blocks
              # one last time to detect the case where we were triggered by an
              # unbound port and the port became bound with new provisioning
              # blocks before 'get_port' was called above
              if provisioning_blocks.is_object_blocked(context, port_id,
                                                       resources.PORT):
                  LOG.debug("Port %s had new provisioning blocks added so it "
                            "will not transition to active.", port_id)
                  return
          if not port.admin_state_up:
              LOG.debug("Port %s is administratively disabled so it will "
                        "not transition to active.", port_id)
              return
          self.update_port_status(context, port_id, const.PORT_STATUS_ACTIVE)
  
      @log_helpers.log_method_call
      def _start_rpc_notifiers(self):
          """Initialize RPC notifiers for agents."""
          self.ovo_notifier = ovo_rpc.OVOServerRpcInterface()
          self.notifier = rpc.AgentNotifierApi(topics.AGENT)
          self.agent_notifiers[const.AGENT_TYPE_DHCP] = (
              dhcp_rpc_agent_api.DhcpAgentNotifyAPI()
          )
  
      @log_helpers.log_method_call
      def start_rpc_listeners(self):
          """Start the RPC loop to let the plugin communicate with agents."""
          self._setup_rpc()
          self.topic = topics.PLUGIN
          self.conn = n_rpc.Connection()
          self.conn.create_consumer(self.topic, self.endpoints, fanout=False)
          self.conn.create_consumer(
              topics.SERVER_RESOURCE_VERSIONS,
              [resources_rpc.ResourcesPushToServerRpcCallback()],
              fanout=True)
          # process state reports despite dedicated rpc workers
          self.conn.create_consumer(topics.REPORTS,
                                    [agents_db.AgentExtRpcCallback()],
                                    fanout=False)
          return self.conn.consume_in_threads()
  
      def start_rpc_state_reports_listener(self):
          self.conn_reports = n_rpc.Connection()
          self.conn_reports.create_consumer(topics.REPORTS,
                                            [agents_db.AgentExtRpcCallback()],
                                            fanout=False)
          return self.conn_reports.consume_in_threads()
  
      def _filter_nets_provider(self, context, networks, filters):
          return [network
                  for network in networks
                  if self.type_manager.network_matches_filters(network, filters)
                  ]
  
      def _check_mac_update_allowed(self, orig_port, port, binding):
          unplugged_types = (portbindings.VIF_TYPE_BINDING_FAILED,
                             portbindings.VIF_TYPE_UNBOUND)
          new_mac = port.get('mac_address')
          mac_change = (new_mac is not None and
                        orig_port['mac_address'] != new_mac)
          if (mac_change and binding.vif_type not in unplugged_types):
              raise exc.PortBound(port_id=orig_port['id'],
                                  vif_type=binding.vif_type,
                                  old_mac=orig_port['mac_address'],
                                  new_mac=port['mac_address'])
          return mac_change
  
      @registry.receives(resources.AGENT, [events.AFTER_UPDATE])
      def _retry_binding_revived_agents(self, resource, event, trigger,
                                        payload=None):
          context = payload.context
          host = payload.metadata.get('host')
          agent = payload.desired_state
          agent_status = agent.get('agent_status')
  
          agent_type = agent.get('agent_type')
  
          if (agent_status != agent_consts.AGENT_REVIVED or
                  not agent.get('admin_state_up') or
                  agent_type not in self._rebind_on_revive_agent_types):
              return
  
          ports = ports_obj.Port.get_ports_by_binding_type_and_host(
              context, portbindings.VIF_TYPE_BINDING_FAILED, host)
          for port in ports:
              binding = self._get_binding_for_host(port.bindings, host)
              if not binding:
                  LOG.debug('No bindings found for port %(port_id)s '
                            'on host %(host)s',
                            {'port_id': port.id, 'host': host})
                  continue
              port_dict = self._make_port_dict(port.db_obj)
              network = self.get_network(context, port.network_id)
              try:
                  levels = db.get_binding_level_objs(
                      context, port.id, binding.host)
                  # TODO(slaweq): use binding OVO instead of binding.db_obj when
                  # ML2 plugin will switch to use Port Binding OVO everywhere
                  mech_context = driver_context.PortContext(
                      self, context, port_dict, network, binding.db_obj, levels)
                  self._bind_port_if_needed(mech_context)
              except Exception as e:
                  LOG.warning('Attempt to bind port %(port_id)s after agent '
                              '%(agent_type)s on host %(host)s revived failed. '
                              'Error: %(error)s',
                              {'port_id': port.id,
                               'agent_type': agent_type,
                               'host': host,
                               'error': e})
  
      def _clear_port_binding(self, mech_context, binding, port, original_host):
          binding.vif_type = portbindings.VIF_TYPE_UNBOUND
          binding.vif_details = ''
          db.clear_binding_levels(mech_context._plugin_context, port['id'],
                                  original_host)
          mech_context._clear_binding_levels()
  
      def _process_port_binding_attributes(self, binding, attrs):
          changes = False
          host = const.ATTR_NOT_SPECIFIED
          if attrs and portbindings.HOST_ID in attrs:
              host = attrs.get(portbindings.HOST_ID) or ''
  
          original_host = binding.host
          if validators.is_attr_set(host) and original_host != host:
              binding.host = host
              changes = True
  
          vnic_type = attrs and attrs.get(portbindings.VNIC_TYPE)
          if (validators.is_attr_set(vnic_type) and
                  binding.vnic_type != vnic_type):
              binding.vnic_type = vnic_type
              changes = True
  
          # treat None as clear of profile.
          profile = None
          if attrs and portbindings.PROFILE in attrs:
              profile = attrs.get(portbindings.PROFILE) or {}
  
          if profile not in (None, const.ATTR_NOT_SPECIFIED,
                             self._get_profile(binding)):
              binding.profile = jsonutils.dumps(profile)
              if len(binding.profile) > models.BINDING_PROFILE_LEN:
                  msg = _("binding:profile value too large")
                  raise exc.InvalidInput(error_message=msg)
              changes = True
          return changes, original_host
  
      def _process_port_binding(self, mech_context, attrs):
          plugin_context = mech_context._plugin_context
          binding = mech_context._binding
          port = mech_context.current
          changes, original_host = self._process_port_binding_attributes(binding,
                                                                         attrs)
  
          # Unbind the port if needed.
          if changes:
              self._clear_port_binding(mech_context, binding, port,
                                       original_host)
              port['status'] = const.PORT_STATUS_DOWN
              super(Ml2Plugin, self).update_port(
                  mech_context._plugin_context, port['id'],
                  {port_def.RESOURCE_NAME:
                      {'status': const.PORT_STATUS_DOWN}})
  
          if port['device_owner'] == const.DEVICE_OWNER_DVR_INTERFACE:
              self._clear_port_binding(mech_context, binding, port,
                                       original_host)
              binding.host = ''
  
          self._update_port_dict_binding(port, binding)
          binding.persist_state_to_session(plugin_context.session)
          return changes
  
      @db_api.retry_db_errors
      def _bind_port_if_needed(self, context, allow_notify=False,
                               need_notify=False, allow_commit=True):
          if not context.network.network_segments:
              LOG.debug("Network %s has no segments, skipping binding",
                        context.network.current['id'])
              return context
          for count in range(1, MAX_BIND_TRIES + 1):
              if count > 1:
                  # yield for binding retries so that we give other threads a
                  # chance to do their work
                  greenthread.sleep(0)
  
                  # multiple attempts shouldn't happen very often so we log each
                  # attempt after the 1st.
                  LOG.info("Attempt %(count)s to bind port %(port)s",
                           {'count': count, 'port': context.current['id']})
  
              bind_context, need_notify, try_again = self._attempt_binding(
                  context, need_notify)
  
              if count == MAX_BIND_TRIES or not try_again:
                  if self._should_bind_port(context) and allow_commit:
                      # At this point, we attempted to bind a port and reached
                      # its final binding state. Binding either succeeded or
                      # exhausted all attempts, thus no need to try again.
                      # Now, the port and its binding state should be committed.
                      context, need_notify, try_again = (
                          self._commit_port_binding(context, bind_context,
                                                    need_notify, try_again))
                  else:
                      context = bind_context
  
              if not try_again:
                  if allow_notify and need_notify:
                      self._notify_port_updated(context)
                  return context
  
          LOG.error("Failed to commit binding results for %(port)s "
                    "after %(max)s tries",
                    {'port': context.current['id'], 'max': MAX_BIND_TRIES})
          return context
  
      def _should_bind_port(self, context):
          return (context._binding.host and context._binding.vif_type
                  in (portbindings.VIF_TYPE_UNBOUND,
                      portbindings.VIF_TYPE_BINDING_FAILED))
  
      def _attempt_binding(self, context, need_notify):
          try_again = False
  
          if self._should_bind_port(context):
              bind_context = self._bind_port(context)
  
              if bind_context.vif_type != portbindings.VIF_TYPE_BINDING_FAILED:
                  # Binding succeeded. Suggest notifying of successful binding.
                  need_notify = True
              else:
                  # Current attempt binding failed, try to bind again.
                  try_again = True
              context = bind_context
  
          return context, need_notify, try_again
  
      def _bind_port(self, orig_context):
          # Construct a new PortContext from the one from the previous
          # transaction.
          port = orig_context.current
          orig_binding = orig_context._binding
          new_binding = models.PortBinding(
              host=orig_binding.host,
              vnic_type=orig_binding.vnic_type,
              profile=orig_binding.profile,
              vif_type=portbindings.VIF_TYPE_UNBOUND,
              vif_details=''
          )
          self._update_port_dict_binding(port, new_binding)
          new_context = driver_context.PortContext(
              self, orig_context._plugin_context, port,
              orig_context.network.current, new_binding, None,
              original_port=orig_context.original)
  
          # Attempt to bind the port and return the context with the
          # result.
          self.mechanism_manager.bind_port(new_context)
          return new_context
  
      def _commit_port_binding(self, orig_context, bind_context,
                               need_notify, try_again,
                               update_binding_levels=True):
          port_id = orig_context.current['id']
          plugin_context = orig_context._plugin_context
          orig_binding = orig_context._binding
          new_binding = bind_context._binding
  
          # TODO(yamahata): revise what to be passed or new resource
          # like PORTBINDING should be introduced?
          # It would be addressed during EventPayload conversion.
          registry.notify(resources.PORT, events.BEFORE_UPDATE, self,
                          context=plugin_context, port=orig_context.current,
                          original_port=orig_context.current,
                          orig_binding=orig_binding, new_binding=new_binding)
  
          # After we've attempted to bind the port, we begin a
          # transaction, get the current port state, and decide whether
          # to commit the binding results.
          with db_api.CONTEXT_WRITER.using(plugin_context):
              # Get the current port state and build a new PortContext
              # reflecting this state as original state for subsequent
              # mechanism driver update_port_*commit() calls.
              try:
                  port_db = self._get_port(plugin_context, port_id)
                  cur_binding = p_utils.get_port_binding_by_status_and_host(
                      port_db.port_bindings, const.ACTIVE)
              except exc.PortNotFound:
                  port_db, cur_binding = None, None
              if not port_db or not cur_binding:
                  # The port has been deleted concurrently, so just
                  # return the unbound result from the initial
                  # transaction that completed before the deletion.
                  LOG.debug("Port %s has been deleted concurrently", port_id)
                  return orig_context, False, False
              # Since the mechanism driver bind_port() calls must be made
              # outside a DB transaction locking the port state, it is
              # possible (but unlikely) that the port's state could change
              # concurrently while these calls are being made. If another
              # thread or process succeeds in binding the port before this
              # thread commits its results, the already committed results are
              # used. If attributes such as binding:host_id, binding:profile,
              # or binding:vnic_type are updated concurrently, the try_again
              # flag is returned to indicate that the commit was unsuccessful.
              oport = self._make_port_dict(port_db)
              port = self._make_port_dict(port_db)
              network = bind_context.network.current
              if port['device_owner'] == const.DEVICE_OWNER_DVR_INTERFACE:
                  # REVISIT(rkukura): The PortBinding instance from the
                  # ml2_port_bindings table, returned as cur_binding
                  # from port_db.port_binding above, is
                  # currently not used for DVR distributed ports, and is
                  # replaced here with the DistributedPortBinding instance from
                  # the ml2_distributed_port_bindings table specific to the host
                  # on which the distributed port is being bound. It
                  # would be possible to optimize this code to avoid
                  # fetching the PortBinding instance in the DVR case,
                  # and even to avoid creating the unused entry in the
                  # ml2_port_bindings table. But the upcoming resolution
                  # for bug 1367391 will eliminate the
                  # ml2_distributed_port_bindings table, use the
                  # ml2_port_bindings table to store non-host-specific
                  # fields for both distributed and non-distributed
                  # ports, and introduce a new ml2_port_binding_hosts
                  # table for the fields that need to be host-specific
                  # in the distributed case. Since the PortBinding
                  # instance will then be needed, it does not make sense
                  # to optimize this code to avoid fetching it.
                  cur_binding = db.get_distributed_port_binding_by_host(
                      plugin_context, port_id, orig_binding.host)
              cur_context_binding = cur_binding
              if new_binding.status == const.INACTIVE:
                  cur_context_binding = (
                      p_utils.get_port_binding_by_status_and_host(
                          port_db.port_bindings, const.INACTIVE,
                          host=new_binding.host))
              cur_context = driver_context.PortContext(
                  self, plugin_context, port, network, cur_context_binding, None,
                  original_port=oport)
  
              # Commit our binding results only if port has not been
              # successfully bound concurrently by another thread or
              # process and no binding inputs have been changed.
              commit = ((cur_binding.vif_type in
                         [portbindings.VIF_TYPE_UNBOUND,
                          portbindings.VIF_TYPE_BINDING_FAILED]) and
                        orig_binding.host == cur_binding.host and
                        orig_binding.vnic_type == cur_binding.vnic_type and
                        orig_binding.profile == cur_binding.profile)
  
              if commit:
                  # Update the port's binding state with our binding
                  # results.
                  if new_binding.status == const.INACTIVE:
                      cur_context_binding.status = const.ACTIVE
                      cur_binding.status = const.INACTIVE
                  else:
                      cur_context_binding.vif_type = new_binding.vif_type
                      cur_context_binding.vif_details = new_binding.vif_details
                  if update_binding_levels:
                      db.clear_binding_levels(plugin_context, port_id,
                                              cur_binding.host)
                      db.set_binding_levels(plugin_context,
                                            bind_context._binding_levels)
                  # refresh context with a snapshot of updated state
                  cur_context._binding = driver_context.InstanceSnapshot(
                      cur_context_binding)
                  cur_context._binding_levels = bind_context._binding_levels
  
                  # Update PortContext's port dictionary to reflect the
                  # updated binding state.
                  self._update_port_dict_binding(port, cur_context_binding)
  
                  # Update the port status if requested by the bound driver.
                  if (bind_context._binding_levels and
                          bind_context._new_port_status):
                      port_db.status = bind_context._new_port_status
                      port['status'] = bind_context._new_port_status
  
                  # Call the mechanism driver precommit methods, commit
                  # the results, and call the postcommit methods.
                  self.mechanism_manager.update_port_precommit(cur_context)
          if commit:
              # Continue, using the port state as of the transaction that
              # just finished, whether that transaction committed new
              # results or discovered concurrent port state changes.
              # Also, Trigger notification for successful binding commit.
              kwargs = {
                  'context': plugin_context,
                  'port': self._make_port_dict(port_db),  # ensure latest state
                  'mac_address_updated': False,
                  'original_port': oport,
              }
              registry.notify(resources.PORT, events.AFTER_UPDATE,
                              self, **kwargs)
              self.mechanism_manager.update_port_postcommit(cur_context)
              need_notify = True
              try_again = False
          else:
              try_again = True
  
          return cur_context, need_notify, try_again
  
      def _update_port_dict_binding(self, port, binding):
          port[portbindings.VNIC_TYPE] = binding.vnic_type
          port[portbindings.PROFILE] = self._get_profile(binding)
          if port['device_owner'] == const.DEVICE_OWNER_DVR_INTERFACE:
              port[portbindings.HOST_ID] = ''
              port[portbindings.VIF_TYPE] = portbindings.VIF_TYPE_DISTRIBUTED
              port[portbindings.VIF_DETAILS] = {}
          else:
              port[portbindings.HOST_ID] = binding.host
              port[portbindings.VIF_TYPE] = binding.vif_type
              port[portbindings.VIF_DETAILS] = self._get_vif_details(binding)
  
      def _get_vif_details(self, binding):
          if binding.vif_details:
              try:
                  return jsonutils.loads(binding.vif_details)
              except Exception:
                  LOG.error("Serialized vif_details DB value '%(value)s' "
                            "for port %(port)s is invalid",
                            {'value': binding.vif_details,
                             'port': binding.port_id})
          return {}
  
      def _get_profile(self, binding):
          if binding.profile:
              try:
                  return jsonutils.loads(binding.profile)
              except Exception:
                  LOG.error("Serialized profile DB value '%(value)s' for "
                            "port %(port)s is invalid",
                            {'value': binding.profile,
                             'port': binding.port_id})
          return {}
  
      @staticmethod
      @resource_extend.extends([port_def.COLLECTION_NAME])
      def _ml2_extend_port_dict_binding(port_res, port_db):
          plugin = directory.get_plugin()
          if isinstance(port_db, ports_obj.Port):
              bindings = port_db.bindings
          else:
              bindings = port_db.port_bindings
          port_binding = p_utils.get_port_binding_by_status_and_host(
              bindings, const.ACTIVE)
          # None when called during unit tests for other plugins.
          if port_binding:
              plugin._update_port_dict_binding(port_res, port_binding)
  
      # ML2's resource extend functions allow extension drivers that extend
      # attributes for the resources to add those attributes to the result.
  
      @staticmethod
      @resource_extend.extends([net_def.COLLECTION_NAME])
      def _ml2_md_extend_network_dict(result, netdb):
          plugin = directory.get_plugin()
          session = plugin._object_session_or_new_session(netdb)
          plugin.extension_manager.extend_network_dict(session, netdb, result)
  
      @staticmethod
      @resource_extend.extends([port_def.COLLECTION_NAME])
      def _ml2_md_extend_port_dict(result, portdb):
          plugin = directory.get_plugin()
          session = plugin._object_session_or_new_session(portdb)
          plugin.extension_manager.extend_port_dict(session, portdb, result)
  
      @staticmethod
      @resource_extend.extends([subnet_def.COLLECTION_NAME])
      def _ml2_md_extend_subnet_dict(result, subnetdb):
          plugin = directory.get_plugin()
          session = plugin._object_session_or_new_session(subnetdb)
          plugin.extension_manager.extend_subnet_dict(session, subnetdb, result)
  
      @staticmethod
      def _object_session_or_new_session(sql_obj):
          session = sqlalchemy.inspect(sql_obj).session
          if not session:
              session = db_api.get_reader_session()
          return session
  
      def _notify_port_updated(self, mech_context):
          port = mech_context.current
          segment = mech_context.bottom_bound_segment
          if not segment:
              # REVISIT(rkukura): This should notify agent to unplug port
              network = mech_context.network.current
              LOG.debug("In _notify_port_updated(), no bound segment for "
                        "port %(port_id)s on network %(network_id)s",
                        {'port_id': port['id'], 'network_id': network['id']})
              return
          self.notifier.port_update(mech_context._plugin_context, port,
                                    segment[api.NETWORK_TYPE],
                                    segment[api.SEGMENTATION_ID],
                                    segment[api.PHYSICAL_NETWORK])
  
      def _update_provider_network_attributes(self, context, network, net_data):
          """Raise exception if provider network attrs update are not supported.
  
          This function will raise an exception if the provider network attribute
          update is not supported.
          """
          provider_net_attrs = set(provider_net.ATTRIBUTES)
          requested_provider_net_attrs = set(net_data) & provider_net_attrs
          for attr in requested_provider_net_attrs:
              if (validators.is_attr_set(net_data.get(attr)) and
                      net_data.get(attr) != network[attr]):
                  msg = (_('Plugin does not support updating the following '
                           'provider network attributes: %s') %
                         ', '.join(provider_net_attrs))
                  raise exc.InvalidInput(error_message=msg)
  
      def _delete_objects(self, context, resource, objects):
          delete_op = getattr(self, 'delete_%s' % resource)
          for obj in objects:
              try:
                  delete_op(context, obj['result']['id'])
              except KeyError:
                  LOG.exception("Could not find %s to delete.",
                                resource)
              except Exception:
                  LOG.exception("Could not delete %(res)s %(id)s.",
                                {'res': resource,
                                 'id': obj['result']['id']})
  
      def _create_bulk_ml2(self, resource, context, request_items):
          objects = []
          collection = "%ss" % resource
          items = request_items[collection]
          obj_before_create = getattr(self, '_before_create_%s' % resource)
          for item in items:
              obj_before_create(context, item)
          with db_api.CONTEXT_WRITER.using(context):
              obj_creator = getattr(self, '_create_%s_db' % resource)
              for item in items:
                  try:
                      attrs = item[resource]
                      result, mech_context = obj_creator(context, item)
                      objects.append({'mech_context': mech_context,
                                      'result': result,
                                      'attributes': attrs})
  
                  except Exception as e:
                      with excutils.save_and_reraise_exception():
                          utils.attach_exc_details(
                              e, ("An exception occurred while creating "
                                  "the %(resource)s:%(item)s"),
                              {'resource': resource, 'item': item})
  
          postcommit_op = getattr(self, '_after_create_%s' % resource)
          for obj in objects:
              try:
                  postcommit_op(context, obj['result'], obj['mech_context'])
              except Exception:
                  with excutils.save_and_reraise_exception():
                      resource_ids = [res['result']['id'] for res in objects]
                      LOG.exception("ML2 _after_create_%(res)s "
                                    "failed for %(res)s: "
                                    "'%(failed_id)s'. Deleting "
                                    "%(res)ss %(resource_ids)s",
                                    {'res': resource,
                                     'failed_id': obj['result']['id'],
                                     'resource_ids': ', '.join(resource_ids)})
                      # _after_handler will have deleted the object that threw
                      to_delete = [o for o in objects if o != obj]
                      self._delete_objects(context, resource, to_delete)
          return objects
  
      def _get_network_mtu(self, network_db, validate=True):
          mtus = []
          try:
              segments = network_db['segments']
          except KeyError:
              segments = [network_db]
          for s in segments:
              segment_type = s.get('network_type')
              if segment_type is None:
                  continue
              try:
                  type_driver = self.type_manager.drivers[segment_type].obj
              except KeyError:
                  # NOTE(ihrachys) This can happen when type driver is not loaded
                  # for an existing segment, or simply when the network has no
                  # segments at the specific time this is computed.
                  # In the former case, while it's probably an indication of
                  # a bad setup, it's better to be safe than sorry here. Also,
                  # several unit tests use non-existent driver types that may
                  # trigger the exception here.
                  if segment_type and s['segmentation_id']:
                      LOG.warning(
                          "Failed to determine MTU for segment "
                          "%(segment_type)s:%(segment_id)s; network "
                          "%(network_id)s MTU calculation may be not "
                          "accurate",
                          {
                              'segment_type': segment_type,
                              'segment_id': s['segmentation_id'],
                              'network_id': network_db['id'],
                          }
                      )
              else:
                  mtu = type_driver.get_mtu(s['physical_network'])
                  # Some drivers, like 'local', may return None; the assumption
                  # then is that for the segment type, MTU has no meaning or
                  # unlimited, and so we should then ignore those values.
                  if mtu:
                      mtus.append(mtu)
  
          max_mtu = min(mtus) if mtus else p_utils.get_deployment_physnet_mtu()
          net_mtu = network_db.get('mtu')
  
          if validate:
              # validate that requested mtu conforms to allocated segments
              if net_mtu and max_mtu and max_mtu < net_mtu:
                  msg = _("Requested MTU is too big, maximum is %d") % max_mtu
                  raise exc.InvalidInput(error_message=msg)
  
          # if mtu is not set in database, use the maximum possible
          return net_mtu or max_mtu
  
      def _before_create_network(self, context, network):
          net_data = network[net_def.RESOURCE_NAME]
          registry.notify(resources.NETWORK, events.BEFORE_CREATE, self,
                          context=context, network=net_data)
  
      def _create_network_db(self, context, network):
          net_data = network[net_def.RESOURCE_NAME]
          tenant_id = net_data['tenant_id']
          with db_api.CONTEXT_WRITER.using(context):
              net_db = self.create_network_db(context, network)
              net_data['id'] = net_db.id
              self.type_manager.create_network_segments(context, net_data,
                                                        tenant_id)
              net_db.mtu = self._get_network_mtu(net_db)
  
              result = self._make_network_dict(net_db, process_extensions=False,
                                               context=context)
  
              self.extension_manager.process_create_network(
                  context,
                  # NOTE(ihrachys) extensions expect no id in the dict
                  {k: v for k, v in net_data.items() if k != 'id'},
                  result)
  
              self._process_l3_create(context, result, net_data)
              self.type_manager.extend_network_dict_provider(context, result)
  
              # Update the transparent vlan if configured
              if extensions.is_extension_supported(self, 'vlan-transparent'):
                  vlt = vlan_apidef.get_vlan_transparent(net_data)
                  net_db['vlan_transparent'] = vlt
                  result['vlan_transparent'] = vlt
  
              if az_def.AZ_HINTS in net_data:
                  self.validate_availability_zones(context, 'network',
                                                   net_data[az_def.AZ_HINTS])
                  az_hints = az_validator.convert_az_list_to_string(
                                                  net_data[az_def.AZ_HINTS])
                  net_db[az_def.AZ_HINTS] = az_hints
                  result[az_def.AZ_HINTS] = az_hints
              registry.notify(resources.NETWORK, events.PRECOMMIT_CREATE, self,
                              context=context, request=net_data, network=result)
  
              resource_extend.apply_funcs('networks', result, net_db)
              mech_context = driver_context.NetworkContext(self, context,
                                                           result)
              self.mechanism_manager.create_network_precommit(mech_context)
          return result, mech_context
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def create_network(self, context, network):
          self._before_create_network(context, network)
          result, mech_context = self._create_network_db(context, network)
          return self._after_create_network(context, result, mech_context)
  
      def _after_create_network(self, context, result, mech_context):
          kwargs = {'context': context, 'network': result}
          registry.notify(resources.NETWORK, events.AFTER_CREATE, self, **kwargs)
          try:
              self.mechanism_manager.create_network_postcommit(mech_context)
          except ml2_exc.MechanismDriverError:
              with excutils.save_and_reraise_exception():
                  LOG.error("mechanism_manager.create_network_postcommit "
                            "failed, deleting network '%s'", result['id'])
                  self.delete_network(context, result['id'])
  
          return result
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def create_network_bulk(self, context, networks):
          objects = self._create_bulk_ml2(
              net_def.RESOURCE_NAME, context, networks)
          return [obj['result'] for obj in objects]
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def update_network(self, context, id, network):
          net_data = network[net_def.RESOURCE_NAME]
          need_network_update_notify = False
  
          with db_api.CONTEXT_WRITER.using(context):
              original_network = self.get_network(context, id)
              self._update_provider_network_attributes(
                  context, original_network, net_data)
              updated_network = super(Ml2Plugin, self).update_network(context,
                                                                      id,
                                                                      network)
              self.extension_manager.process_update_network(context, net_data,
                                                            updated_network)
              self._process_l3_update(context, updated_network, net_data)
  
              # ToDO(QoS): This would change once EngineFacade moves out
              db_network = self._get_network(context, id)
              # Expire the db_network in current transaction, so that the join
              # relationship can be updated.
              context.session.expire(db_network)
  
              if (mtuw_apidef.MTU in net_data or
                  # NOTE(ihrachys) mtu may be null for existing networks,
                  # calculate and update it as needed; the conditional can be
                  # removed in Queens when we populate all mtu attributes and
                  # enforce it's not nullable on database level
                      db_network.mtu is None):
                  db_network.mtu = self._get_network_mtu(db_network,
                                                         validate=False)
                  # agents should now update all ports to reflect new MTU
                  need_network_update_notify = True
  
              updated_network = self._make_network_dict(
                  db_network, context=context)
              self.type_manager.extend_network_dict_provider(
                  context, updated_network)
  
              registry.publish(resources.NETWORK, events.PRECOMMIT_UPDATE, self,
                               payload=events.DBEventPayload(
                                   context, request_body=net_data,
                                   states=(original_network,),
                                   resource_id=id,
                                   desired_state=updated_network))
  
              # TODO(QoS): Move out to the extension framework somehow.
              need_network_update_notify |= (
                  qos_consts.QOS_POLICY_ID in net_data and
                  original_network[qos_consts.QOS_POLICY_ID] !=
                  updated_network[qos_consts.QOS_POLICY_ID])
  
              mech_context = driver_context.NetworkContext(
                  self, context, updated_network,
                  original_network=original_network)
              self.mechanism_manager.update_network_precommit(mech_context)
  
          # TODO(apech) - handle errors raised by update_network, potentially
          # by re-calling update_network with the previous attributes. For
          # now the error is propagated to the caller, which is expected to
          # either undo/retry the operation or delete the resource.
          kwargs = {'context': context, 'network': updated_network,
                    'original_network': original_network}
          registry.notify(resources.NETWORK, events.AFTER_UPDATE, self, **kwargs)
          self.mechanism_manager.update_network_postcommit(mech_context)
          if need_network_update_notify:
              self.notifier.network_update(context, updated_network)
          return updated_network
  
      @db_api.retry_if_session_inactive()
      def get_network(self, context, id, fields=None):
          # NOTE(ihrachys) use writer manager to be able to update mtu
          # TODO(ihrachys) remove in Queens+ when mtu is not nullable
          with db_api.CONTEXT_WRITER.using(context):
              net_db = self._get_network(context, id)
  
              # NOTE(ihrachys) pre Pike networks may have null mtus; update them
              # in database if needed
              # TODO(ihrachys) remove in Queens+ when mtu is not nullable
              if net_db.mtu is None:
                  net_db.mtu = self._get_network_mtu(net_db, validate=False)
  
              net_data = self._make_network_dict(net_db, context=context)
              self.type_manager.extend_network_dict_provider(context, net_data)
  
          return db_utils.resource_fields(net_data, fields)
  
      @db_api.retry_if_session_inactive()
      def get_networks(self, context, filters=None, fields=None,
                       sorts=None, limit=None, marker=None, page_reverse=False):
          # NOTE(ihrachys) use writer manager to be able to update mtu
          # TODO(ihrachys) remove in Queens when mtu is not nullable
          with db_api.CONTEXT_WRITER.using(context):
              nets_db = super(Ml2Plugin, self)._get_networks(
                  context, filters, None, sorts, limit, marker, page_reverse)
  
              # NOTE(ihrachys) pre Pike networks may have null mtus; update them
              # in database if needed
              # TODO(ihrachys) remove in Queens+ when mtu is not nullable
              net_data = []
              for net in nets_db:
                  if net.mtu is None:
                      net.mtu = self._get_network_mtu(net, validate=False)
                  net_data.append(self._make_network_dict(net, context=context))
  
              self.type_manager.extend_networks_dict_provider(context, net_data)
              nets = self._filter_nets_provider(context, net_data, filters)
          return [db_utils.resource_fields(net, fields) for net in nets]
  
      def get_network_contexts(self, context, network_ids):
          """Return a map of network_id to NetworkContext for network_ids."""
          net_filters = {'id': list(set(network_ids))}
          nets_by_netid = {
              n['id']: n for n in self.get_networks(context,
                                                    filters=net_filters)
          }
          segments_by_netid = segments_db.get_networks_segments(
              context, list(nets_by_netid.keys()))
          netctxs_by_netid = {
              net_id: driver_context.NetworkContext(
                  self, context, nets_by_netid[net_id],
                  segments=segments_by_netid[net_id])
              for net_id in nets_by_netid.keys()
          }
          return netctxs_by_netid
  
      @utils.transaction_guard
      def delete_network(self, context, id):
          # the only purpose of this override is to protect this from being
          # called inside of a transaction.
          return super(Ml2Plugin, self).delete_network(context, id)
  
      @registry.receives(resources.NETWORK, [events.PRECOMMIT_DELETE])
      def _network_delete_precommit_handler(self, rtype, event, trigger,
                                            context, network_id, **kwargs):
          network = self.get_network(context, network_id)
          mech_context = driver_context.NetworkContext(self,
                                                       context,
                                                       network)
          # TODO(kevinbenton): move this mech context into something like
          # a 'delete context' so it's not polluting the real context object
          setattr(context, '_mech_context', mech_context)
          self.mechanism_manager.delete_network_precommit(
              mech_context)
  
      @registry.receives(resources.NETWORK, [events.AFTER_DELETE])
      def _network_delete_after_delete_handler(self, rtype, event, trigger,
                                               context, network, **kwargs):
          try:
              self.mechanism_manager.delete_network_postcommit(
                  context._mech_context)
          except ml2_exc.MechanismDriverError:
              # TODO(apech) - One or more mechanism driver failed to
              # delete the network.  Ideally we'd notify the caller of
              # the fact that an error occurred.
              LOG.error("mechanism_manager.delete_network_postcommit"
                        " failed")
          self.notifier.network_delete(context, network['id'])
  
      def _before_create_subnet(self, context, subnet):
          subnet_data = subnet[subnet_def.RESOURCE_NAME]
          registry.notify(resources.SUBNET, events.BEFORE_CREATE, self,
                          context=context, subnet=subnet_data)
  
      def _create_subnet_db(self, context, subnet):
          with db_api.CONTEXT_WRITER.using(context):
              result, net_db, ipam_sub = self._create_subnet_precommit(
                  context, subnet)
  
              # NOTE(ihrachys) pre Pike networks may have null mtus; update them
              # in database if needed
              # TODO(ihrachys) remove in Queens+ when mtu is not nullable
              if net_db['mtu'] is None:
                  net_db['mtu'] = self._get_network_mtu(net_db, validate=False)
  
              self.extension_manager.process_create_subnet(
                  context, subnet[subnet_def.RESOURCE_NAME], result)
              network = self._make_network_dict(net_db, context=context)
              self.type_manager.extend_network_dict_provider(context, network)
              mech_context = driver_context.SubnetContext(self, context,
                                                          result, network)
              self.mechanism_manager.create_subnet_precommit(mech_context)
  
          # TODO(kevinbenton): move this to '_after_subnet_create'
          # db base plugin post commit ops
          self._create_subnet_postcommit(context, result, net_db, ipam_sub)
  
          return result, mech_context
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def create_subnet(self, context, subnet):
          self._before_create_subnet(context, subnet)
          result, mech_context = self._create_subnet_db(context, subnet)
          return self._after_create_subnet(context, result, mech_context)
  
      def _after_create_subnet(self, context, result, mech_context):
          kwargs = {'context': context, 'subnet': result}
          registry.notify(resources.SUBNET, events.AFTER_CREATE, self, **kwargs)
          try:
              self.mechanism_manager.create_subnet_postcommit(mech_context)
          except ml2_exc.MechanismDriverError:
              with excutils.save_and_reraise_exception():
                  LOG.error("mechanism_manager.create_subnet_postcommit "
                            "failed, deleting subnet '%s'", result['id'])
                  self.delete_subnet(context, result['id'])
          return result
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def create_subnet_bulk(self, context, subnets):
          objects = self._create_bulk_ml2(
              subnet_def.RESOURCE_NAME, context, subnets)
          return [obj['result'] for obj in objects]
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def update_subnet(self, context, id, subnet):
          with db_api.CONTEXT_WRITER.using(context):
              updated_subnet, original_subnet = self._update_subnet_precommit(
                  context, id, subnet)
              self.extension_manager.process_update_subnet(
                  context, subnet[subnet_def.RESOURCE_NAME], updated_subnet)
              updated_subnet = self.get_subnet(context, id)
              mech_context = driver_context.SubnetContext(
                  self, context, updated_subnet, network=None,
                  original_subnet=original_subnet)
              self.mechanism_manager.update_subnet_precommit(mech_context)
  
          self._update_subnet_postcommit(context, original_subnet,
                                         updated_subnet)
          # TODO(apech) - handle errors raised by update_subnet, potentially
          # by re-calling update_subnet with the previous attributes. For
          # now the error is propagated to the caller, which is expected to
          # either undo/retry the operation or delete the resource.
          self.mechanism_manager.update_subnet_postcommit(mech_context)
          return updated_subnet
  
      @utils.transaction_guard
      def delete_subnet(self, context, id):
          # the only purpose of this override is to protect this from being
          # called inside of a transaction.
          return super(Ml2Plugin, self).delete_subnet(context, id)
  
      @registry.receives(resources.SUBNET, [events.PRECOMMIT_DELETE])
      def _subnet_delete_precommit_handler(self, rtype, event, trigger,
                                           context, subnet_id, **kwargs):
          subnet_obj = self._get_subnet_object(context, subnet_id)
          subnet = self._make_subnet_dict(subnet_obj, context=context)
          network = self.get_network(context, subnet['network_id'])
          mech_context = driver_context.SubnetContext(self, context,
                                                      subnet, network)
          # TODO(kevinbenton): move this mech context into something like
          # a 'delete context' so it's not polluting the real context object
          setattr(context, '_mech_context', mech_context)
          self.mechanism_manager.delete_subnet_precommit(mech_context)
  
      @registry.receives(resources.SUBNET, [events.AFTER_DELETE])
      def _subnet_delete_after_delete_handler(self, rtype, event, trigger,
                                              context, subnet, **kwargs):
          try:
              self.mechanism_manager.delete_subnet_postcommit(
                  context._mech_context)
          except ml2_exc.MechanismDriverError:
              # TODO(apech) - One or more mechanism driver failed to
              # delete the subnet.  Ideally we'd notify the caller of
              # the fact that an error occurred.
              LOG.error("mechanism_manager.delete_subnet_postcommit failed")
  
      # TODO(yalei) - will be simplified after security group and address pair be
      # converted to ext driver too.
      def _portsec_ext_port_create_processing(self, context, port_data, port):
          attrs = port[port_def.RESOURCE_NAME]
          port_security = ((port_data.get(psec.PORTSECURITY) is None) or
                           port_data[psec.PORTSECURITY])
  
          # allowed address pair checks
          if self._check_update_has_allowed_address_pairs(port):
              if not port_security:
                  raise addr_exc.AddressPairAndPortSecurityRequired()
          else:
              # remove ATTR_NOT_SPECIFIED
              attrs[addr_apidef.ADDRESS_PAIRS] = []
  
          if port_security:
              self._ensure_default_security_group_on_port(context, port)
          elif self._check_update_has_security_groups(port):
              raise psec_exc.PortSecurityAndIPRequiredForSecurityGroups()
  
      def _setup_dhcp_agent_provisioning_component(self, context, port):
          subnet_ids = [f['subnet_id'] for f in port['fixed_ips']]
          if (db.is_dhcp_active_on_any_subnet(context, subnet_ids) and
              len(self.get_dhcp_agents_hosting_networks(context,
                                                        [port['network_id']]))):
              # the agents will tell us when the dhcp config is ready so we setup
              # a provisioning component to prevent the port from going ACTIVE
              # until a dhcp_ready_on_port notification is received.
              provisioning_blocks.add_provisioning_component(
                  context, port['id'], resources.PORT,
                  provisioning_blocks.DHCP_ENTITY)
          else:
              provisioning_blocks.remove_provisioning_component(
                  context, port['id'], resources.PORT,
                  provisioning_blocks.DHCP_ENTITY)
  
      def _before_create_port(self, context, port):
          attrs = port[port_def.RESOURCE_NAME]
          if not attrs.get('status'):
              attrs['status'] = const.PORT_STATUS_DOWN
  
          registry.notify(resources.PORT, events.BEFORE_CREATE, self,
                          context=context, port=attrs)
          # NOTE(kevinbenton): triggered outside of transaction since it
          # emits 'AFTER' events if it creates.
          self._ensure_default_security_group(context, attrs['tenant_id'])
  
      def _create_port_db(self, context, port):
          attrs = port[port_def.RESOURCE_NAME]
          with db_api.CONTEXT_WRITER.using(context):
              dhcp_opts = attrs.get(edo_ext.EXTRADHCPOPTS, [])
              port_db = self.create_port_db(context, port)
              result = self._make_port_dict(port_db, process_extensions=False)
              self.extension_manager.process_create_port(context, attrs, result)
              self._portsec_ext_port_create_processing(context, result, port)
  
              # sgids must be got after portsec checked with security group
              sgids = self._get_security_groups_on_port(context, port)
              self._process_port_create_security_group(context, result, sgids)
              network = self.get_network(context, result['network_id'])
              binding = db.add_port_binding(context, result['id'])
              mech_context = driver_context.PortContext(self, context, result,
                                                        network, binding, None)
              self._process_port_binding(mech_context, attrs)
  
              result[addr_apidef.ADDRESS_PAIRS] = (
                  self._process_create_allowed_address_pairs(
                      context, result,
                      attrs.get(addr_apidef.ADDRESS_PAIRS)))
              self._process_port_create_extra_dhcp_opts(context, result,
                                                        dhcp_opts)
              kwargs = {'context': context, 'port': result}
              registry.notify(
                  resources.PORT, events.PRECOMMIT_CREATE, self, **kwargs)
              self.mechanism_manager.create_port_precommit(mech_context)
              self._setup_dhcp_agent_provisioning_component(context, result)
  
          resource_extend.apply_funcs('ports', result, port_db)
          return result, mech_context
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def create_port(self, context, port):
          self._before_create_port(context, port)
          result, mech_context = self._create_port_db(context, port)
          return self._after_create_port(context, result, mech_context)
  
      def _after_create_port(self, context, result, mech_context):
          # notify any plugin that is interested in port create events
          kwargs = {'context': context, 'port': result}
          registry.notify(resources.PORT, events.AFTER_CREATE, self, **kwargs)
  
          try:
              self.mechanism_manager.create_port_postcommit(mech_context)
          except ml2_exc.MechanismDriverError:
              with excutils.save_and_reraise_exception():
                  LOG.error("mechanism_manager.create_port_postcommit "
                            "failed, deleting port '%s'", result['id'])
                  self.delete_port(context, result['id'], l3_port_check=False)
          try:
              bound_context = self._bind_port_if_needed(mech_context)
          except ml2_exc.MechanismDriverError:
              with excutils.save_and_reraise_exception():
                  LOG.error("_bind_port_if_needed "
                            "failed, deleting port '%s'", result['id'])
                  self.delete_port(context, result['id'], l3_port_check=False)
  
          return bound_context.current
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def create_port_bulk(self, context, ports):
          # TODO(njohnston): Break this up into smaller functions.
          port_list = ports.get('ports')
          for port in port_list:
              self._before_create_port(context, port)
  
          port_data = []
          network_cache = dict()
          macs = self._generate_macs(len(port_list))
          with db_api.CONTEXT_WRITER.using(context):
              for port in port_list:
                  # Set up the port request dict
                  pdata = port.get('port')
                  if pdata.get('device_owner'):
                      self._enforce_device_owner_not_router_intf_or_device_id(
                          context, pdata.get('device_owner'),
                          pdata.get('device_id'), pdata.get('tenant_id'))
                  bulk_port_data = dict(project_id=pdata.get('project_id'),
                      name=pdata.get('name'),
                      network_id=pdata.get('network_id'),
                      admin_state_up=pdata.get('admin_state_up'),
                      status=pdata.get('status',
                          const.PORT_STATUS_ACTIVE),
                      device_id=pdata.get('device_id'),
                      device_owner=pdata.get('device_owner'),
                      security_groups=pdata.get('security_groups'),
                      description=pdata.get('description'))
  
                  # Ensure that the networks exist.
                  network_id = pdata.get('network_id')
                  if network_id not in network_cache:
                      network = self.get_network(context, network_id)
                      network_cache[network_id] = network
                  else:
                      network = network_cache[network_id]
  
                  # Determine the MAC address
                  raw_mac_address = pdata.get('mac_address',
                      const.ATTR_NOT_SPECIFIED)
                  if raw_mac_address is const.ATTR_NOT_SPECIFIED:
                      raw_mac_address = macs.pop()
                  elif self._is_mac_in_use(context, network_id, raw_mac_address):
                      raise exc.MacAddressInUse(net_id=network_id,
                                                mac=raw_mac_address)
                  eui_mac_address = netaddr.EUI(raw_mac_address,
                                                dialect=eui48.mac_unix_expanded)
  
                  # Create the Port object
                  db_port_obj = ports_obj.Port(context,
                                              mac_address=eui_mac_address,
                                              id=uuidutils.generate_uuid(),
                                              **bulk_port_data)
                  db_port_obj.create()
                  port_dict = self._make_port_dict(db_port_obj,
                                                   process_extensions=False)
                  port_compat = {'port': port_dict}
  
                  # Call IPAM to allocate IP addresses
                  try:
                      # TODO(njohnston): IPAM allocation needs to be revamped to
                      # be bulk-friendly.
                      self.ipam.allocate_ips_for_port_and_store(
                          context, db_port_obj, db_port_obj['id'])
                      db_port_obj['ip_allocation'] = (ipalloc_apidef.
                                                  IP_ALLOCATION_IMMEDIATE)
                  except ipam_exc.DeferIpam:
                      db_port_obj['ip_allocation'] = (ipalloc_apidef.
                                                  IP_ALLOCATION_DEFERRED)
                  fixed_ips = pdata.get('fixed_ips')
                  if validators.is_attr_set(fixed_ips) and not fixed_ips:
                      # [] was passed explicitly as fixed_ips: unaddressed port.
                      db_port_obj['ip_allocation'] = (ipalloc_apidef.
                                                      IP_ALLOCATION_NONE)
  
                  # Activities immediately post-port-creation
                  self.extension_manager.process_create_port(context, port_dict,
                                                             db_port_obj)
                  self._portsec_ext_port_create_processing(context, port_dict,
                                                           port_compat)
  
                  # sgids must be got after portsec checked with security group
                  sgids = self._get_security_groups_on_port(context, port_compat)
                  self._process_port_create_security_group(context, port_dict,
                                                           sgids)
  
                  # process port binding
                  binding = db.add_port_binding(context, port_dict['id'])
                  mech_context = driver_context.PortContext(self, context,
                                                            port_dict, network,
                                                            binding, None)
                  self._process_port_binding(mech_context, port_dict)
  
                  # process allowed address pairs
                  db_port_obj[addr_apidef.ADDRESS_PAIRS] = (
                      self._process_create_allowed_address_pairs(
                          context, port_compat,
                          port_dict.get(addr_apidef.ADDRESS_PAIRS)))
  
                  # handle DHCP setup
                  dhcp_opts = port_dict.get(edo_ext.EXTRADHCPOPTS, [])
                  self._process_port_create_extra_dhcp_opts(context, port_dict,
                                                            dhcp_opts)
                  # send PRECOMMIT_CREATE notification
                  kwargs = {'context': context, 'port': db_port_obj}
                  registry.notify(
                      resources.PORT, events.PRECOMMIT_CREATE, self, **kwargs)
                  self.mechanism_manager.create_port_precommit(mech_context)
  
                  # handle DHCP agent provisioning
                  self._setup_dhcp_agent_provisioning_component(context,
                                                                port_dict)
  
                  port_data.append(
                          {
                              'id': db_port_obj['id'],
                              'port_obj': db_port_obj,
                              'mech_context': mech_context,
                              'port_dict': port_dict
                          })
  
          # Perform actions after the transaction is committed
          completed_ports = []
          for port in port_data:
              resource_extend.apply_funcs('ports',
                                          port['port_dict'],
                                          port['port_obj'].db_obj)
              completed_ports.append(
                      self._after_create_port(context,
                                              port['port_dict'],
                                              port['mech_context']))
          return completed_ports
  
      # TODO(yalei) - will be simplified after security group and address pair be
      # converted to ext driver too.
      def _portsec_ext_port_update_processing(self, updated_port, context, port,
                                              id):
          port_security = ((updated_port.get(psec.PORTSECURITY) is None) or
                           updated_port[psec.PORTSECURITY])
  
          if port_security:
              return
  
          # check the address-pairs
          if self._check_update_has_allowed_address_pairs(port):
              #  has address pairs in request
              raise addr_exc.AddressPairAndPortSecurityRequired()
          elif not self._check_update_deletes_allowed_address_pairs(port):
              # not a request for deleting the address-pairs
              updated_port[addr_apidef.ADDRESS_PAIRS] = (
                      self.get_allowed_address_pairs(context, id))
  
              # check if address pairs has been in db, if address pairs could
              # be put in extension driver, we can refine here.
              if updated_port[addr_apidef.ADDRESS_PAIRS]:
                  raise addr_exc.AddressPairAndPortSecurityRequired()
  
          # checks if security groups were updated adding/modifying
          # security groups, port security is set
          if self._check_update_has_security_groups(port):
              raise psec_exc.PortSecurityAndIPRequiredForSecurityGroups()
          elif not self._check_update_deletes_security_groups(port):
              if not extensions.is_extension_supported(self, 'security-group'):
                  return
              # Update did not have security groups passed in. Check
              # that port does not have any security groups already on it.
              filters = {'port_id': [id]}
              security_groups = (
                  super(Ml2Plugin, self)._get_port_security_group_bindings(
                          context, filters)
                       )
              if security_groups:
                  raise psec_exc.PortSecurityPortHasSecurityGroup()
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def update_port(self, context, id, port):
          attrs = port[port_def.RESOURCE_NAME]
          need_port_update_notify = False
          bound_mech_contexts = []
          original_port = self.get_port(context, id)
          registry.notify(resources.PORT, events.BEFORE_UPDATE, self,
                          context=context, port=attrs,
                          original_port=original_port)
          with db_api.CONTEXT_WRITER.using(context):
              port_db = self._get_port(context, id)
              binding = p_utils.get_port_binding_by_status_and_host(
                  port_db.port_bindings, const.ACTIVE)
              if not binding:
                  raise exc.PortNotFound(port_id=id)
              mac_address_updated = self._check_mac_update_allowed(
                  port_db, attrs, binding)
              need_port_update_notify |= mac_address_updated
              original_port = self._make_port_dict(port_db)
              updated_port = super(Ml2Plugin, self).update_port(context, id,
                                                                port)
              self.extension_manager.process_update_port(context, attrs,
                                                         updated_port)
              self._portsec_ext_port_update_processing(updated_port, context,
                                                       port, id)
  
              if (psec.PORTSECURITY in attrs) and (
                          original_port[psec.PORTSECURITY] !=
                          updated_port[psec.PORTSECURITY]):
                  need_port_update_notify = True
              # TODO(QoS): Move out to the extension framework somehow.
              # Follow https://review.openstack.org/#/c/169223 for a solution.
              if (qos_consts.QOS_POLICY_ID in attrs and
                      original_port[qos_consts.QOS_POLICY_ID] !=
                      updated_port[qos_consts.QOS_POLICY_ID]):
                  need_port_update_notify = True
  
              if addr_apidef.ADDRESS_PAIRS in attrs:
                  need_port_update_notify |= (
                      self.update_address_pairs_on_port(context, id, port,
                                                        original_port,
                                                        updated_port))
              need_port_update_notify |= self.update_security_group_on_port(
                  context, id, port, original_port, updated_port)
              network = self.get_network(context, original_port['network_id'])
              need_port_update_notify |= self._update_extra_dhcp_opts_on_port(
                  context, id, port, updated_port)
              levels = db.get_binding_level_objs(context, id, binding.host)
              # one of the operations above may have altered the model call
              # _make_port_dict again to ensure latest state is reflected so mech
              # drivers, callback handlers, and the API caller see latest state.
              # We expire here to reflect changed relationships on the obj.
              # Repeatable read will ensure we still get the state from this
              # transaction in spite of concurrent updates/deletes.
              context.session.expire(port_db)
              updated_port.update(self._make_port_dict(port_db))
              mech_context = driver_context.PortContext(
                  self, context, updated_port, network, binding, levels,
                  original_port=original_port)
              need_port_update_notify |= self._process_port_binding(
                  mech_context, attrs)
  
              registry.publish(
                  resources.PORT, events.PRECOMMIT_UPDATE, self,
                  payload=events.DBEventPayload(
                      context, request_body=attrs, states=(original_port,),
                      resource_id=id, desired_state=updated_port))
  
              # For DVR router interface ports we need to retrieve the
              # DVRPortbinding context instead of the normal port context.
              # The normal Portbinding context does not have the status
              # of the ports that are required by the l2pop to process the
              # postcommit events.
  
              # NOTE:Sometimes during the update_port call, the DVR router
              # interface port may not have the port binding, so we cannot
              # create a generic bindinglist that will address both the
              # DVR and non-DVR cases here.
              # TODO(Swami): This code need to be revisited.
              if port_db['device_owner'] == const.DEVICE_OWNER_DVR_INTERFACE:
                  dist_binding_list = db.get_distributed_port_bindings(context,
                                                                       id)
                  for dist_binding in dist_binding_list:
                      levels = db.get_binding_level_objs(context, id,
                                                         dist_binding.host)
                      dist_mech_context = driver_context.PortContext(
                          self, context, updated_port, network,
                          dist_binding, levels, original_port=original_port)
                      self.mechanism_manager.update_port_precommit(
                          dist_mech_context)
                      bound_mech_contexts.append(dist_mech_context)
              else:
                  self.mechanism_manager.update_port_precommit(mech_context)
                  if any(updated_port[k] != original_port[k]
                         for k in ('fixed_ips', 'mac_address')):
                      # only add block if fixed_ips or mac_address changed
                      self._setup_dhcp_agent_provisioning_component(
                          context, updated_port)
                  bound_mech_contexts.append(mech_context)
  
          # Notifications must be sent after the above transaction is complete
          kwargs = {
              'context': context,
              'port': updated_port,
              'mac_address_updated': mac_address_updated,
              'original_port': original_port,
          }
          registry.notify(resources.PORT, events.AFTER_UPDATE, self, **kwargs)
  
          # Note that DVR Interface ports will have bindings on
          # multiple hosts, and so will have multiple mech_contexts,
          # while other ports typically have just one.
          # Since bound_mech_contexts has both the DVR and non-DVR
          # contexts we can manage just with a single for loop.
          try:
              for mech_context in bound_mech_contexts:
                  self.mechanism_manager.update_port_postcommit(
                      mech_context)
          except ml2_exc.MechanismDriverError:
              LOG.error("mechanism_manager.update_port_postcommit "
                        "failed for port %s", id)
  
          need_port_update_notify |= self.is_security_group_member_updated(
              context, original_port, updated_port)
  
          if original_port['admin_state_up'] != updated_port['admin_state_up']:
              need_port_update_notify = True
          if original_port['status'] != updated_port['status']:
              need_port_update_notify = True
          # NOTE: In the case of DVR ports, the port-binding is done after
          # router scheduling when sync_routers is called and so this call
          # below may not be required for DVR routed interfaces. But still
          # since we don't have the mech_context for the DVR router interfaces
          # at certain times, we just pass the port-context and return it, so
          # that we don't disturb other methods that are expecting a return
          # value.
          bound_context = self._bind_port_if_needed(
              mech_context,
              allow_notify=True,
              need_notify=need_port_update_notify)
          return bound_context.current
  
      def _process_distributed_port_binding(self, mech_context, context, attrs):
          plugin_context = mech_context._plugin_context
          binding = mech_context._binding
          port = mech_context.current
          port_id = port['id']
  
          if binding.vif_type != portbindings.VIF_TYPE_UNBOUND:
              binding.vif_details = ''
              binding.vif_type = portbindings.VIF_TYPE_UNBOUND
              if binding.host:
                  db.clear_binding_levels(plugin_context, port_id, binding.host)
              binding.host = ''
  
          self._update_port_dict_binding(port, binding)
          binding.host = attrs and attrs.get(portbindings.HOST_ID)
          binding.router_id = attrs and attrs.get('device_id')
          # merge into session to reflect changes
          binding.persist_state_to_session(plugin_context.session)
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def update_distributed_port_binding(self, context, id, port):
          attrs = port[port_def.RESOURCE_NAME]
  
          host = attrs and attrs.get(portbindings.HOST_ID)
          host_set = validators.is_attr_set(host)
  
          if not host_set:
              LOG.error("No Host supplied to bind DVR Port %s", id)
              return
  
          binding = db.get_distributed_port_binding_by_host(context,
                                                            id, host)
          device_id = attrs and attrs.get('device_id')
          router_id = binding and binding.get('router_id')
          update_required = (
              not binding or
              binding.vif_type == portbindings.VIF_TYPE_BINDING_FAILED or
              router_id != device_id)
          if update_required:
              try:
                  with db_api.CONTEXT_WRITER.using(context):
                      orig_port = self.get_port(context, id)
                      if not binding:
                          binding = db.ensure_distributed_port_binding(
                              context, id, host, router_id=device_id)
                      network = self.get_network(context,
                                                 orig_port['network_id'])
                      levels = db.get_binding_level_objs(context, id, host)
                      mech_context = driver_context.PortContext(
                          self, context, orig_port, network,
                          binding, levels, original_port=orig_port)
                      self._process_distributed_port_binding(
                          mech_context, context, attrs)
              except (os_db_exception.DBReferenceError, exc.PortNotFound):
                  LOG.debug("DVR Port %s has been deleted concurrently", id)
                  return
              self._bind_port_if_needed(mech_context)
  
      def _pre_delete_port(self, context, port_id, port_check):
          """Do some preliminary operations before deleting the port."""
          LOG.debug("Deleting port %s", port_id)
          try:
              # notify interested parties of imminent port deletion;
              # a failure here prevents the operation from happening
              registry.publish(
                  resources.PORT, events.BEFORE_DELETE, self,
                  payload=events.DBEventPayload(
                      context, metadata={'port_check': port_check},
                      resource_id=port_id))
          except exceptions.CallbackFailure as e:
              # NOTE(armax): preserve old check's behavior
              if len(e.errors) == 1:
                  raise e.errors[0].error
              raise exc.ServicePortInUse(port_id=port_id, reason=e)
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def delete_port(self, context, id, l3_port_check=True):
          self._pre_delete_port(context, id, l3_port_check)
          # TODO(armax): get rid of the l3 dependency in the with block
          router_ids = []
          l3plugin = directory.get_plugin(plugin_constants.L3)
  
          with db_api.CONTEXT_WRITER.using(context):
              try:
                  port_db = self._get_port(context, id)
                  binding = p_utils.get_port_binding_by_status_and_host(
                      port_db.port_bindings, const.ACTIVE,
                      raise_if_not_found=True, port_id=id)
              except exc.PortNotFound:
                  LOG.debug("The port '%s' was deleted", id)
                  return
              port = self._make_port_dict(port_db)
  
              network = self.get_network(context, port['network_id'])
              bound_mech_contexts = []
              kwargs = {
                  'context': context,
                  'id': id,
                  'network': network,
                  'port': port,
                  'port_db': port_db,
                  'bindings': binding,
              }
              device_owner = port['device_owner']
              if device_owner == const.DEVICE_OWNER_DVR_INTERFACE:
                  bindings = db.get_distributed_port_bindings(context,
                                                              id)
                  for bind in bindings:
                      levels = db.get_binding_level_objs(context, id, bind.host)
                      kwargs['bind'] = bind
                      kwargs['levels'] = levels
                      registry.notify(resources.PORT, events.PRECOMMIT_DELETE,
                                      self, **kwargs)
                      mech_context = driver_context.PortContext(
                          self, context, port, network, bind, levels)
                      self.mechanism_manager.delete_port_precommit(mech_context)
                      bound_mech_contexts.append(mech_context)
              else:
                  levels = db.get_binding_level_objs(context, id, binding.host)
                  kwargs['bind'] = None
                  kwargs['levels'] = levels
                  registry.notify(resources.PORT, events.PRECOMMIT_DELETE,
                                  self, **kwargs)
                  mech_context = driver_context.PortContext(
                      self, context, port, network, binding, levels)
                  self.mechanism_manager.delete_port_precommit(mech_context)
                  bound_mech_contexts.append(mech_context)
              if l3plugin:
                  router_ids = l3plugin.disassociate_floatingips(
                      context, id, do_notify=False)
  
              LOG.debug("Calling delete_port for %(port_id)s owned by %(owner)s",
                        {"port_id": id, "owner": device_owner})
              super(Ml2Plugin, self).delete_port(context, id)
  
          self._post_delete_port(
              context, port, router_ids, bound_mech_contexts)
  
      def _post_delete_port(
          self, context, port, router_ids, bound_mech_contexts):
          kwargs = {
              'context': context,
              'port': port,
              'router_ids': router_ids,
          }
          registry.notify(resources.PORT, events.AFTER_DELETE, self, **kwargs)
          try:
              # Note that DVR Interface ports will have bindings on
              # multiple hosts, and so will have multiple mech_contexts,
              # while other ports typically have just one.
              for mech_context in bound_mech_contexts:
                  self.mechanism_manager.delete_port_postcommit(mech_context)
          except ml2_exc.MechanismDriverError:
              # TODO(apech) - One or more mechanism driver failed to
              # delete the port.  Ideally we'd notify the caller of the
              # fact that an error occurred.
              LOG.error("mechanism_manager.delete_port_postcommit failed for"
                        " port %s", port['id'])
          self.notifier.port_delete(context, port['id'])
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive(context_var_name='plugin_context')
      def get_bound_port_context(self, plugin_context, port_id, host=None,
                                 cached_networks=None):
          # NOTE(ihrachys) use writer manager to be able to update mtu when
          # fetching network
          # TODO(ihrachys) remove in Queens+ when mtu is not nullable
          with db_api.CONTEXT_WRITER.using(plugin_context) as session:
              try:
                  port_db = (session.query(models_v2.Port).
                             enable_eagerloads(False).
                             filter(models_v2.Port.id.startswith(port_id)).
                             one())
              except sa_exc.NoResultFound:
                  LOG.info("No ports have port_id starting with %s",
                           port_id)
                  return
              except sa_exc.MultipleResultsFound:
                  LOG.error("Multiple ports have port_id starting with %s",
                            port_id)
                  return
              port = self._make_port_dict(port_db)
              network = (cached_networks or {}).get(port['network_id'])
  
              if not network:
                  network = self.get_network(plugin_context, port['network_id'])
  
              if port['device_owner'] == const.DEVICE_OWNER_DVR_INTERFACE:
                  binding = db.get_distributed_port_binding_by_host(
                      plugin_context, port['id'], host)
                  if not binding:
                      LOG.error("Binding info for DVR port %s not found",
                                port_id)
                      return None
                  levels = db.get_binding_level_objs(
                      plugin_context, port_db.id, host)
                  port_context = driver_context.PortContext(
                      self, plugin_context, port, network, binding, levels)
              else:
                  # since eager loads are disabled in port_db query
                  # related attribute port_binding could disappear in
                  # concurrent port deletion.
                  # It's not an error condition.
                  binding = p_utils.get_port_binding_by_status_and_host(
                      port_db.port_bindings, const.ACTIVE)
                  if not binding:
                      LOG.info("Binding info for port %s was not found, "
                               "it might have been deleted already.",
                               port_id)
                      return
                  levels = db.get_binding_level_objs(
                      plugin_context, port_db.id, binding.host)
                  port_context = driver_context.PortContext(
                      self, plugin_context, port, network, binding, levels)
  
          return self._bind_port_if_needed(port_context)
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive(context_var_name='plugin_context')
      def get_bound_ports_contexts(self, plugin_context, dev_ids, host=None):
          result = {}
          # NOTE(ihrachys) use writer manager to be able to update mtu when
          # fetching network
          # TODO(ihrachys) remove in Queens+ when mtu is not nullable
          with db_api.CONTEXT_WRITER.using(plugin_context):
              dev_to_full_pids = db.partial_port_ids_to_full_ids(
                  plugin_context, dev_ids)
              # get all port objects for IDs
              port_dbs_by_id = db.get_port_db_objects(
                  plugin_context, dev_to_full_pids.values())
              # get all networks for PortContext construction
              netctxs_by_netid = self.get_network_contexts(
                  plugin_context,
                  {p.network_id for p in port_dbs_by_id.values()})
              for dev_id in dev_ids:
                  port_id = dev_to_full_pids.get(dev_id)
                  port_db = port_dbs_by_id.get(port_id)
                  if (not port_id or not port_db or
                          port_db.network_id not in netctxs_by_netid):
                      result[dev_id] = None
                      continue
                  port = self._make_port_dict(port_db)
                  if port['device_owner'] == const.DEVICE_OWNER_DVR_INTERFACE:
                      binding = db.get_distributed_port_binding_by_host(
                          plugin_context, port['id'], host)
                      bindlevelhost_match = host
                  else:
                      binding = p_utils.get_port_binding_by_status_and_host(
                          port_db.port_bindings, const.ACTIVE)
                      bindlevelhost_match = binding.host if binding else None
                  if not binding:
                      LOG.info("Binding info for port %s was not found, "
                               "it might have been deleted already.",
                               port_id)
                      result[dev_id] = None
                      continue
                  levels = [l for l in port_db.binding_levels
                            if l.host == bindlevelhost_match]
                  levels = sorted(levels, key=lambda l: l.level)
                  network_ctx = netctxs_by_netid.get(port_db.network_id)
                  port_context = driver_context.PortContext(
                      self, plugin_context, port, network_ctx, binding, levels)
                  result[dev_id] = port_context
  
          return {d: self._bind_port_if_needed(pctx) if pctx else None
                  for d, pctx in result.items()}
  
      def update_port_status(self, context, port_id, status, host=None,
                             network=None):
          """Update port status
  
          Returns port_id (non-truncated uuid) if the port exists.
          Otherwise returns None.
          'network' is deprecated and has no effect
          """
          full = db.partial_port_ids_to_full_ids(context, [port_id])
          if port_id not in full:
              return None
          port_id = full[port_id]
          return self.update_port_statuses(
              context, {port_id: status}, host)[port_id]
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def update_port_statuses(self, context, port_id_to_status, host=None):
          result = {}
          port_ids = port_id_to_status.keys()
          port_dbs_by_id = db.get_port_db_objects(context, port_ids)
          for port_id, status in port_id_to_status.items():
              if not port_dbs_by_id.get(port_id):
                  LOG.debug("Port %(port)s update to %(val)s by agent not found",
                            {'port': port_id, 'val': status})
                  result[port_id] = None
                  continue
              result[port_id] = self._safe_update_individual_port_db_status(
                  context, port_dbs_by_id[port_id], status, host)
          return result
  
      def _safe_update_individual_port_db_status(self, context, port,
                                                 status, host):
          port_id = port.id
          try:
              return self._update_individual_port_db_status(
                  context, port, status, host)
          except Exception:
              with excutils.save_and_reraise_exception() as ectx:
                  # don't reraise if port doesn't exist anymore
                  ectx.reraise = bool(db.get_port(context, port_id))
  
      def _update_individual_port_db_status(self, context, port, status, host):
          updated = False
          network = None
          port_id = port.id
          if ((port.status != status and
                  port['device_owner'] != const.DEVICE_OWNER_DVR_INTERFACE) or
                  port['device_owner'] == const.DEVICE_OWNER_DVR_INTERFACE):
              attr = {
                  'id': port.id,
                  portbindings.HOST_ID: host,
                  'status': status
              }
              registry.notify(resources.PORT, events.BEFORE_UPDATE, self,
                              original_port=port,
                              context=context, port=attr)
          with db_api.CONTEXT_WRITER.using(context):
              context.session.add(port)  # bring port into writer session
              if (port.status != status and
                      port['device_owner'] != const.DEVICE_OWNER_DVR_INTERFACE):
                  original_port = self._make_port_dict(port)
                  port.status = status
                  # explicit flush before _make_port_dict to ensure extensions
                  # listening for db events can modify the port if necessary
                  context.session.flush()
                  updated_port = self._make_port_dict(port)
                  binding = p_utils.get_port_binding_by_status_and_host(
                      port.port_bindings, const.ACTIVE, raise_if_not_found=True,
                      port_id=port_id)
                  levels = db.get_binding_level_objs(
                      context, port.id, binding.host)
                  mech_context = driver_context.PortContext(
                      self, context, updated_port, network, binding, levels,
                      original_port=original_port)
                  self.mechanism_manager.update_port_precommit(mech_context)
                  updated = True
              elif port['device_owner'] == const.DEVICE_OWNER_DVR_INTERFACE:
                  binding = db.get_distributed_port_binding_by_host(
                      context, port['id'], host)
                  if not binding:
                      return
                  if binding.status != status:
                      binding.status = status
                      updated = True
  
          if (updated and
                  port['device_owner'] == const.DEVICE_OWNER_DVR_INTERFACE):
              with db_api.CONTEXT_WRITER.using(context):
                  port = db.get_port(context, port_id)
                  if not port:
                      LOG.warning("Port %s not found during update",
                                  port_id)
                      return
                  original_port = self._make_port_dict(port)
                  network = network or self.get_network(
                      context, original_port['network_id'])
                  port.status = db.generate_distributed_port_status(context,
                                                                    port['id'])
                  updated_port = self._make_port_dict(port)
                  levels = db.get_binding_level_objs(context, port_id, host)
                  mech_context = (driver_context.PortContext(
                      self, context, updated_port, network,
                      binding, levels, original_port=original_port))
                  self.mechanism_manager.update_port_precommit(mech_context)
  
          if updated:
              self.mechanism_manager.update_port_postcommit(mech_context)
              kwargs = {'context': context, 'port': mech_context.current,
                        'original_port': original_port}
              if status == const.PORT_STATUS_ACTIVE:
                  # NOTE(kevinbenton): this kwarg was carried over from
                  # the RPC handler that used to call this. it's not clear
                  # who uses it so maybe it can be removed. added in commit
                  # 3f3874717c07e2b469ea6c6fd52bcb4da7b380c7
                  kwargs['update_device_up'] = True
              registry.notify(resources.PORT, events.AFTER_UPDATE, self,
                              **kwargs)
  
          if port['device_owner'] == const.DEVICE_OWNER_DVR_INTERFACE:
              db.delete_distributed_port_binding_if_stale(context, binding)
  
          return port['id']
  
      @db_api.retry_if_session_inactive()
      def port_bound_to_host(self, context, port_id, host):
          if not host:
              return
          port = db.get_port(context, port_id)
          if not port:
              LOG.debug("No Port match for: %s", port_id)
              return
          if port['device_owner'] == const.DEVICE_OWNER_DVR_INTERFACE:
              bindings = db.get_distributed_port_bindings(context,
                                                          port_id)
              for b in bindings:
                  if b.host == host:
                      return port
              LOG.debug("No binding found for DVR port %s", port['id'])
              return
          else:
              port_host = db.get_port_binding_host(context, port_id)
              return port if (port_host == host) else None
  
      @db_api.retry_if_session_inactive()
      def get_ports_from_devices(self, context, devices):
          port_ids_to_devices = dict(
              (self._device_to_port_id(context, device), device)
              for device in devices)
          port_ids = list(port_ids_to_devices.keys())
          ports = db.get_ports_and_sgs(context, port_ids)
          for port in ports:
              # map back to original requested id
              port_id = next((port_id for port_id in port_ids
                             if port['id'].startswith(port_id)), None)
              port['device'] = port_ids_to_devices.get(port_id)
  
          return ports
  
      @staticmethod
      def _device_to_port_id(context, device):
          # REVISIT(rkukura): Consider calling into MechanismDrivers to
          # process device names, or having MechanismDrivers supply list
          # of device prefixes to strip.
          for prefix in n_const.INTERFACE_PREFIXES:
              if device.startswith(prefix):
                  return device[len(prefix):]
          # REVISIT(irenab): Consider calling into bound MD to
          # handle the get_device_details RPC
          if not uuidutils.is_uuid_like(device):
              port = db.get_port_from_device_mac(context, device)
              if port:
                  return port.id
          return device
  
      def _get_ports_query(self, context, filters=None, *args, **kwargs):
          filters = filters or {}
          security_groups = filters.pop("security_groups", None)
          if security_groups:
              port_bindings = self._get_port_security_group_bindings(
                  context, filters={'security_group_id':
                                    security_groups})
              if 'id' in filters:
                  filters['id'] = [entry['port_id'] for
                                   entry in port_bindings
                                   if entry['port_id'] in filters['id']]
              else:
                  filters['id'] = [entry['port_id'] for entry in port_bindings]
          fixed_ips = filters.get('fixed_ips', {})
          ip_addresses_s = fixed_ips.get('ip_address_substr')
          query = super(Ml2Plugin, self)._get_ports_query(context, filters,
                                                          *args, **kwargs)
          if ip_addresses_s:
              substr_filter = or_(*[models_v2.Port.fixed_ips.any(
                  models_v2.IPAllocation.ip_address.like('%%%s%%' % ip))
                  for ip in ip_addresses_s])
              query = query.filter(substr_filter)
          return query
  
      def filter_hosts_with_network_access(
              self, context, network_id, candidate_hosts):
          segments = segments_db.get_network_segments(context, network_id)
          return self.mechanism_manager.filter_hosts_with_segment_access(
              context, segments, candidate_hosts, self.get_agents)
  
      def check_segment_for_agent(self, segment, agent):
          for mech_driver in self.mechanism_manager.ordered_mech_drivers:
              driver_agent_type = getattr(mech_driver.obj, 'agent_type', None)
              if driver_agent_type and driver_agent_type == agent['agent_type']:
                  if mech_driver.obj.check_segment_for_agent(segment, agent):
                      return True
          return False
  
      @registry.receives(resources.SEGMENT, [events.AFTER_DELETE])
      def _handle_after_delete_segment_change(
              self, rtype, event, trigger, payload=None):
          # TODO(boden); refactor into _handle_segment_change once all
          # event types use payloads
          return self._handle_segment_change(
              rtype, event, trigger, payload.context, payload.latest_state)
  
      @registry.receives(resources.SEGMENT, (events.PRECOMMIT_CREATE,
                                             events.PRECOMMIT_DELETE,
                                             events.AFTER_CREATE))
      def _handle_segment_change(self, rtype, event, trigger, context, segment):
          if (event == events.PRECOMMIT_CREATE and
                  not isinstance(trigger, segments_plugin.Plugin)):
              # TODO(xiaohhui): Now, when create network, ml2 will reserve
              # segment and trigger this event handler. This event handler
              # will reserve segment again, which will lead to error as the
              # segment has already been reserved. This check could be removed
              # by unifying segment creation procedure.
              return
  
          network_id = segment.get('network_id')
  
          if event == events.PRECOMMIT_CREATE:
              updated_segment = self.type_manager.reserve_network_segment(
                  context, segment)
              # The segmentation id might be from ML2 type driver, update it
              # in the original segment.
              segment[api.SEGMENTATION_ID] = updated_segment[api.SEGMENTATION_ID]
          elif event == events.PRECOMMIT_DELETE:
              self.type_manager.release_network_segment(context, segment)
  
          # change in segments could affect resulting network mtu, so let's
          # recalculate it
          network_db = self._get_network(context, network_id)
          network_db.mtu = self._get_network_mtu(
              network_db,
              validate=(event != events.PRECOMMIT_DELETE))
          network_db.save(session=context.session)
  
          try:
              self._notify_mechanism_driver_for_segment_change(
                  event, context, network_id)
          except ml2_exc.MechanismDriverError:
              with excutils.save_and_reraise_exception():
                  LOG.error("mechanism_manager error occurred when "
                            "handle event %(event)s for segment "
                            "'%(segment)s'",
                            {'event': event, 'segment': segment['id']})
  
      def _notify_mechanism_driver_for_segment_change(self, event,
                                                      context, network_id):
          network_with_segments = self.get_network(context, network_id)
          mech_context = driver_context.NetworkContext(
              self, context, network_with_segments,
              original_network=network_with_segments)
          if event in [events.PRECOMMIT_CREATE, events.PRECOMMIT_DELETE]:
              self.mechanism_manager.update_network_precommit(mech_context)
          elif event in [events.AFTER_CREATE, events.AFTER_DELETE]:
              self.mechanism_manager.update_network_postcommit(mech_context)
  
      @staticmethod
      def _validate_compute_port(port):
          if not port['device_owner'].startswith(
                  const.DEVICE_OWNER_COMPUTE_PREFIX):
              msg = _('Invalid port %s. Operation only valid on compute '
                      'ports') % port['id']
              raise exc.BadRequest(resource='port', msg=msg)
  
      def _make_port_binding_dict(self, binding, fields=None):
          res = {key: binding[key] for key in (
                      pbe_ext.HOST, pbe_ext.VIF_TYPE, pbe_ext.VNIC_TYPE,
                      pbe_ext.STATUS)}
          if isinstance(binding, ports_obj.PortBinding):
              res[pbe_ext.PROFILE] = binding.profile or {}
              res[pbe_ext.VIF_DETAILS] = binding.vif_details or {}
          else:
              res[pbe_ext.PROFILE] = self._get_profile(binding)
              res[pbe_ext.VIF_DETAILS] = self._get_vif_details(binding)
          return db_utils.resource_fields(res, fields)
  
      def _get_port_binding_attrs(self, binding, host=None):
          return {portbindings.VNIC_TYPE: binding.get(pbe_ext.VNIC_TYPE),
                  portbindings.HOST_ID: binding.get(pbe_ext.HOST) or host,
                  portbindings.PROFILE: binding.get(pbe_ext.PROFILE, {})}
  
      def _process_active_binding_change(self, changes, mech_context, port_dict,
                                         original_host):
          if changes:
              self._clear_port_binding(mech_context,
                                       mech_context._binding, port_dict,
                                       original_host)
              port_dict['status'] = const.PORT_STATUS_DOWN
              super(Ml2Plugin, self).update_port(
                  mech_context._plugin_context, port_dict['id'],
                  {port_def.RESOURCE_NAME:
                      {'status': const.PORT_STATUS_DOWN}})
          self._update_port_dict_binding(port_dict,
                                         mech_context._binding)
          mech_context._binding.persist_state_to_session(
              mech_context._plugin_context.session)
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def create_port_binding(self, context, port_id, binding):
          attrs = binding[pbe_ext.RESOURCE_NAME]
          with db_api.CONTEXT_WRITER.using(context):
              port_db = self._get_port(context, port_id)
              self._validate_compute_port(port_db)
              if self._get_binding_for_host(port_db.port_bindings,
                                            attrs[pbe_ext.HOST]):
                  raise exc.PortBindingAlreadyExists(
                      port_id=port_id, host=attrs[pbe_ext.HOST])
              status = const.ACTIVE
              is_active_binding = True
              active_binding = p_utils.get_port_binding_by_status_and_host(
                  port_db.port_bindings, const.ACTIVE)
              if active_binding:
                  status = const.INACTIVE
                  is_active_binding = False
              network = self.get_network(context, port_db['network_id'])
              port_dict = self._make_port_dict(port_db)
              new_binding = models.PortBinding(
                  port_id=port_id,
                  vif_type=portbindings.VIF_TYPE_UNBOUND,
                  status=status)
              mech_context = driver_context.PortContext(self, context, port_dict,
                                                        network, new_binding,
                                                        None)
              changes, original_host = self._process_port_binding_attributes(
                  mech_context._binding, self._get_port_binding_attrs(attrs))
              if is_active_binding:
                  self._process_active_binding_change(changes, mech_context,
                                                      port_dict, original_host)
          bind_context = self._bind_port_if_needed(
              mech_context, allow_commit=is_active_binding)
          if (bind_context._binding.vif_type ==
                  portbindings.VIF_TYPE_BINDING_FAILED):
              raise exc.PortBindingError(port_id=port_id,
                                         host=attrs[pbe_ext.HOST])
          bind_context._binding.port_id = port_id
          bind_context._binding.status = status
          if not is_active_binding:
              with db_api.CONTEXT_WRITER.using(context):
                  bind_context._binding.persist_state_to_session(context.session)
                  db.set_binding_levels(context, bind_context._binding_levels)
          return self._make_port_binding_dict(bind_context._binding)
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def get_port_bindings(self, context, port_id, filters=None, fields=None,
                            sorts=None, limit=None, marker=None,
                            page_reverse=False):
          port = ports_obj.Port.get_object(context, id=port_id)
          if not port:
              raise exc.PortNotFound(port_id=port_id)
          self._validate_compute_port(port)
          filters = filters or {}
          pager = base_obj.Pager(sorts, limit, page_reverse, marker)
          bindings = ports_obj.PortBinding.get_objects(
              context, _pager=pager, port_id=port_id, **filters)
  
          return [self._make_port_binding_dict(binding, fields)
                  for binding in bindings]
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def get_port_binding(self, context, host, port_id, fields=None):
          port = ports_obj.Port.get_object(context, id=port_id)
          if not port:
              raise exc.PortNotFound(port_id=port_id)
          self._validate_compute_port(port)
          binding = ports_obj.PortBinding.get_object(context, host=host,
                                                     port_id=port_id)
          if not binding:
              raise exc.PortBindingNotFound(port_id=port_id, host=host)
          return self._make_port_binding_dict(binding, fields)
  
      def _get_binding_for_host(self, bindings, host):
          for binding in bindings:
              if binding.host == host:
                  return binding
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def update_port_binding(self, context, host, port_id, binding):
          attrs = binding[pbe_ext.RESOURCE_NAME]
          with db_api.CONTEXT_WRITER.using(context):
              port_db = self._get_port(context, port_id)
              self._validate_compute_port(port_db)
              original_binding = self._get_binding_for_host(
                  port_db.port_bindings, host)
              if not original_binding:
                  raise exc.PortBindingNotFound(port_id=port_id, host=host)
              is_active_binding = (original_binding.status == const.ACTIVE)
              network = self.get_network(context, port_db['network_id'])
              port_dict = self._make_port_dict(port_db)
              mech_context = driver_context.PortContext(self, context, port_dict,
                                                        network,
                                                        original_binding, None)
              changes, original_host = self._process_port_binding_attributes(
                  mech_context._binding, self._get_port_binding_attrs(attrs,
                                                                      host=host))
              if is_active_binding:
                  self._process_active_binding_change(changes, mech_context,
                                                      port_dict, original_host)
          bind_context = self._bind_port_if_needed(
              mech_context, allow_commit=is_active_binding)
          if (bind_context._binding.vif_type ==
                  portbindings.VIF_TYPE_BINDING_FAILED):
              raise exc.PortBindingError(port_id=port_id, host=host)
          if not is_active_binding:
              with db_api.CONTEXT_WRITER.using(context):
                  bind_context._binding.persist_state_to_session(context.session)
                  db.set_binding_levels(context, bind_context._binding_levels)
          return self._make_port_binding_dict(bind_context._binding)
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def activate(self, context, host, port_id):
          with db_api.CONTEXT_WRITER.using(context):
              # TODO(mlavalle) Next two lines can be removed when bug #1770267 is
              # fixed
              if isinstance(port_id, dict):
                  port_id = port_id['port_id']
              port_db = self._get_port(context, port_id)
              self._validate_compute_port(port_db)
              active_binding = p_utils.get_port_binding_by_status_and_host(
                  port_db.port_bindings, const.ACTIVE)
              if host == (active_binding and active_binding.host):
                  raise exc.PortBindingAlreadyActive(port_id=port_id,
                                                     host=host)
              inactive_binding = p_utils.get_port_binding_by_status_and_host(
                  port_db.port_bindings, const.INACTIVE, host=host)
              if not inactive_binding or inactive_binding.host != host:
                  raise exc.PortBindingNotFound(port_id=port_id, host=host)
              network = self.get_network(context, port_db['network_id'])
              port_dict = self._make_port_dict(port_db)
              levels = db.get_binding_level_objs(context, port_id,
                                                 active_binding.host)
              original_context = driver_context.PortContext(self, context,
                                                            port_dict, network,
                                                            active_binding,
                                                            levels)
              self._clear_port_binding(original_context, active_binding,
                                       port_dict, active_binding.host)
              port_dict['status'] = const.PORT_STATUS_DOWN
              super(Ml2Plugin, self).update_port(
                  context, port_dict['id'],
                  {port_def.RESOURCE_NAME:
                      {'status': const.PORT_STATUS_DOWN}})
              levels = db.get_binding_level_objs(context, port_id,
                                                 inactive_binding.host)
              bind_context = driver_context.PortContext(self, context, port_dict,
                                                        network,
                                                        inactive_binding, levels)
          for count in range(MAX_BIND_TRIES):
              cur_context, _, try_again = self._commit_port_binding(
                  original_context, bind_context, need_notify=True,
                  try_again=True, update_binding_levels=False)
              if not try_again:
                  self.notifier.binding_deactivate(context, port_id,
                                                   active_binding.host,
                                                   network['id'])
                  self.notifier.binding_activate(context, port_id,
                                                 inactive_binding.host)
                  return self._make_port_binding_dict(cur_context._binding)
          raise exc.PortBindingError(port_id=port_id, host=host)
  
      @utils.transaction_guard
      @db_api.retry_if_session_inactive()
      def delete_port_binding(self, context, host, port_id):
          ports_obj.PortBinding.delete_objects(context,
                                               host=host,
                                               port_id=port_id)
          db.clear_binding_levels(context,
                                  port_id=port_id,
                                  host=host)
  