neutron-lib/neutron_lib/plugins/ml2/api.py

# 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.

import abc

import six


# The following keys are used in the segment dictionaries passed via
# the driver API.
ID = 'id'
NETWORK_TYPE = 'network_type'
PHYSICAL_NETWORK = 'physical_network'
SEGMENTATION_ID = 'segmentation_id'
MTU = 'mtu'
NETWORK_ID = 'network_id'

# The following keys are used in the binding level dictionaries
# available via the binding_levels and original_binding_levels
# PortContext properties.
BOUND_DRIVER = 'bound_driver'
BOUND_SEGMENT = 'bound_segment'


@six.add_metaclass(abc.ABCMeta)
class MechanismDriver(object):
    """Define stable abstract interface for ML2 mechanism drivers.

    A mechanism driver is called on the creation, update, and deletion
    of networks and ports. For every event, there are two methods that
    get called - one within the database transaction (method suffix of
    _precommit), one right afterwards (method suffix of _postcommit).

    Exceptions raised by methods called inside the transaction can
    rollback, but should not make any blocking calls (for example,
    REST requests to an outside controller). Methods called after
    transaction commits can make blocking external calls, though these
    will block the entire process. Exceptions raised in calls after
    the transaction commits may cause the associated resource to be
    deleted.

    Because rollback outside of the transaction is not done in the
    update network/port case, all data validation must be done within
    methods that are part of the database transaction.
    """

    # Used in generating resource provider UUIDs for physical network
    # interfaces. Each mechanism driver supporting Placement should have its
    # own UUID v5 namespace (which is a UUID v1 in turn). When set to a
    # concrete value use a uuid.UUID() object, not the string format.
    # It will be used when hashing RP UUIDs from:
    #     (mech driver namespace, hostname, physical bridge/interface name)
    # When needed generate new namespace UUIDs by:
    #     python -c 'import uuid ; print uuid.uuid1()'
    # See also:
    #     https://tools.ietf.org/html/rfc4122
    #     https://stackoverflow.com/a/7816117
    resource_provider_uuid5_namespace = None

    @abc.abstractmethod
    def initialize(self):
        """Perform driver initialization.

        Called after all drivers have been loaded and the database has
        been initialized. No abstract methods defined below will be
        called prior to this method being called.
        """
        pass

    def create_network_precommit(self, context):
        """Allocate resources for a new network.

        :param context: NetworkContext instance describing the new
            network.

        Create a new network, allocating resources as necessary in the
        database. Called inside transaction context on session. Call
        cannot block.  Raising an exception will result in a rollback
        of the current transaction.
        """
        pass

    def create_network_postcommit(self, context):
        """Create a network.

        :param context: NetworkContext instance describing the new
            network.

        Called after the transaction commits. Call can block, though
        will block the entire process so care should be taken to not
        drastically affect performance. Raising an exception will
        cause the deletion of the resource.
        """
        pass

    def update_network_precommit(self, context):
        """Update resources of a network.

        :param context: NetworkContext instance describing the new
            state of the network, as well as the original state prior
            to the update_network call.

        Update values of a network, updating the associated resources
        in the database. Called inside transaction context on session.
        Raising an exception will result in rollback of the
        transaction.

        update_network_precommit is called for all changes to the
        network state. It is up to the mechanism driver to ignore
        state or state changes that it does not know or care about.
        """
        pass

    def update_network_postcommit(self, context):
        """Update a network.

        :param context: NetworkContext instance describing the new
            state of the network, as well as the original state prior
            to the update_network call.

        Called after the transaction commits. Call can block, though
        will block the entire process so care should be taken to not
        drastically affect performance. Raising an exception will
        cause the deletion of the resource.

        update_network_postcommit is called for all changes to the
        network state.  It is up to the mechanism driver to ignore
        state or state changes that it does not know or care about.
        """
        pass

    def delete_network_precommit(self, context):
        """Delete resources for a network.

        :param context: NetworkContext instance describing the current
            state of the network, prior to the call to delete it.

        Delete network resources previously allocated by this
        mechanism driver for a network. Called inside transaction
        context on session. Runtime errors are not expected, but
        raising an exception will result in rollback of the
        transaction.
        """
        pass

    def delete_network_postcommit(self, context):
        """Delete a network.

        :param context: NetworkContext instance describing the current
            state of the network, prior to the call to delete it.

        Called after the transaction commits. Call can block, though
        will block the entire process so care should be taken to not
        drastically affect performance. Runtime errors are not
        expected, and will not prevent the resource from being
        deleted.
        """
        pass

    def create_subnet_precommit(self, context):
        """Allocate resources for a new subnet.

        :param context: SubnetContext instance describing the new
            subnet.

        Create a new subnet, allocating resources as necessary in the
        database. Called inside transaction context on session. Call
        cannot block.  Raising an exception will result in a rollback
        of the current transaction.
        """
        pass

    def create_subnet_postcommit(self, context):
        """Create a subnet.

        :param context: SubnetContext instance describing the new
            subnet.

        Called after the transaction commits. Call can block, though
        will block the entire process so care should be taken to not
        drastically affect performance. Raising an exception will
        cause the deletion of the resource.
        """
        pass

    def update_subnet_precommit(self, context):
        """Update resources of a subnet.

        :param context: SubnetContext instance describing the new
            state of the subnet, as well as the original state prior
            to the update_subnet call.

        Update values of a subnet, updating the associated resources
        in the database. Called inside transaction context on session.
        Raising an exception will result in rollback of the
        transaction.

        update_subnet_precommit is called for all changes to the
        subnet state. It is up to the mechanism driver to ignore
        state or state changes that it does not know or care about.
        """
        pass

    def update_subnet_postcommit(self, context):
        """Update a subnet.

        :param context: SubnetContext instance describing the new
            state of the subnet, as well as the original state prior
            to the update_subnet call.

        Called after the transaction commits. Call can block, though
        will block the entire process so care should be taken to not
        drastically affect performance. Raising an exception will
        cause the deletion of the resource.

        update_subnet_postcommit is called for all changes to the
        subnet state.  It is up to the mechanism driver to ignore
        state or state changes that it does not know or care about.
        """
        pass

    def delete_subnet_precommit(self, context):
        """Delete resources for a subnet.

        :param context: SubnetContext instance describing the current
            state of the subnet, prior to the call to delete it.

        Delete subnet resources previously allocated by this
        mechanism driver for a subnet. Called inside transaction
        context on session. Runtime errors are not expected, but
        raising an exception will result in rollback of the
        transaction.
        """
        pass

    def delete_subnet_postcommit(self, context):
        """Delete a subnet.

        :param context: SubnetContext instance describing the current
            state of the subnet, prior to the call to delete it.

        Called after the transaction commits. Call can block, though
        will block the entire process so care should be taken to not
        drastically affect performance. Runtime errors are not
        expected, and will not prevent the resource from being
        deleted.
        """
        pass

    def create_port_precommit(self, context):
        """Allocate resources for a new port.

        :param context: PortContext instance describing the port.

        Create a new port, allocating resources as necessary in the
        database. Called inside transaction context on session. Call
        cannot block.  Raising an exception will result in a rollback
        of the current transaction.
        """
        pass

    def create_port_postcommit(self, context):
        """Create a port.

        :param context: PortContext instance describing the port.

        Called after the transaction completes. Call can block, though
        will block the entire process so care should be taken to not
        drastically affect performance.  Raising an exception will
        result in the deletion of the resource.
        """
        pass

    def update_port_precommit(self, context):
        """Update resources of a port.

        :param context: PortContext instance describing the new
            state of the port, as well as the original state prior
            to the update_port call.

        Called inside transaction context on session to complete a
        port update as defined by this mechanism driver. Raising an
        exception will result in rollback of the transaction.

        update_port_precommit is called for all changes to the port
        state. It is up to the mechanism driver to ignore state or
        state changes that it does not know or care about.
        """
        pass

    def update_port_postcommit(self, context):
        """Update a port.

        :param context: PortContext instance describing the new
            state of the port, as well as the original state prior
            to the update_port call.

        Called after the transaction completes. Call can block, though
        will block the entire process so care should be taken to not
        drastically affect performance.  Raising an exception will
        result in the deletion of the resource.

        update_port_postcommit is called for all changes to the port
        state. It is up to the mechanism driver to ignore state or
        state changes that it does not know or care about.
        """
        pass

    def delete_port_precommit(self, context):
        """Delete resources of a port.

        :param context: PortContext instance describing the current
            state of the port, prior to the call to delete it.

        Called inside transaction context on session. Runtime errors
        are not expected, but raising an exception will result in
        rollback of the transaction.
        """
        pass

    def delete_port_postcommit(self, context):
        """Delete a port.

        :param context: PortContext instance describing the current
            state of the port, prior to the call to delete it.

        Called after the transaction completes. Call can block, though
        will block the entire process so care should be taken to not
        drastically affect performance.  Runtime errors are not
        expected, and will not prevent the resource from being
        deleted.
        """
        pass

    def bind_port(self, context):
        """Attempt to bind a port.

        :param context: PortContext instance describing the port

        This method is called outside any transaction to attempt to
        establish a port binding using this mechanism driver. Bindings
        may be created at each of multiple levels of a hierarchical
        network, and are established from the top level downward. At
        each level, the mechanism driver determines whether it can
        bind to any of the network segments in the
        context.segments_to_bind property, based on the value of the
        context.host property, any relevant port or network
        attributes, and its own knowledge of the network topology. At
        the top level, context.segments_to_bind contains the static
        segments of the port's network. At each lower level of
        binding, it contains static or dynamic segments supplied by
        the driver that bound at the level above. If the driver is
        able to complete the binding of the port to any segment in
        context.segments_to_bind, it must call context.set_binding
        with the binding details. If it can partially bind the port,
        it must call context.continue_binding with the network
        segments to be used to bind at the next lower level.

        If the binding results are committed after bind_port returns,
        they will be seen by all mechanism drivers as
        update_port_precommit and update_port_postcommit calls. But if
        some other thread or process concurrently binds or updates the
        port, these binding results will not be committed, and
        update_port_precommit and update_port_postcommit will not be
        called on the mechanism drivers with these results. Because
        binding results can be discarded rather than committed,
        drivers should avoid making persistent state changes in
        bind_port, or else must ensure that such state changes are
        eventually cleaned up.

        Implementing this method explicitly declares the mechanism
        driver as having the intention to bind ports. This is inspected
        by the QoS service to identify the available QoS rules you
        can use with ports.
        """
        pass

    @property
    def _supports_port_binding(self):
        return self.__class__.bind_port != MechanismDriver.bind_port

    def check_vlan_transparency(self, context):
        """Check if the network supports vlan transparency.

        :param context: NetworkContext instance describing the network.

        Check if the network supports vlan transparency or not.
        """
        pass

    def get_workers(self):
        """Get any NeutronWorker instances that should have their own process

        Any driver that needs to run processes separate from the API or RPC
        workers, can return a sequence of NeutronWorker instances.
        """
        return ()

    @classmethod
    def is_host_filtering_supported(cls):
        return (cls.filter_hosts_with_segment_access !=
                MechanismDriver.filter_hosts_with_segment_access)

    def filter_hosts_with_segment_access(
            self, context, segments, candidate_hosts, agent_getter):
        """Filter hosts with access to at least one segment.

        :returns: a set with a subset of candidate_hosts.

        A driver can overload this method to return a subset of candidate_hosts
        with the ones with access to at least one segment.

        Default implementation returns all hosts to disable filtering
        (backward compatibility).
        """
        return candidate_hosts

    def responsible_for_ports_allocation(self, context):
        """Is responsible for a port's resource provider?

        :param context: PortContext instance describing the port
        :returns: True for responsible, False for not responsible

        For ports having an allocation in Placement (as expressed
        in the port's binding:profile.allocation) decide while
        binding if this mechanism driver is responsible for the
        physical network interface represented by the resource
        provider in Placement. Find the resource provider UUID in
        context.current['binding:profile']['allocation'].

        Drivers wanting to support resource allocations for ports in
        Placement (eg. wanting to guarantee some minimum bandwidth)
        must implement this method.

        Default implementation returns False (backward compatibility).
        """
        return False


@six.add_metaclass(abc.ABCMeta)
class _TypeDriverBase(object):

    @abc.abstractmethod
    def get_type(self):
        """Get driver's network type.

        :returns: network_type value handled by this driver
        """
        pass

    @abc.abstractmethod
    def initialize(self):
        """Perform driver initialization.

        Called after all drivers have been loaded and the database has
        been initialized. No abstract methods defined below will be
        called prior to this method being called.
        """
        pass

    @abc.abstractmethod
    def is_partial_segment(self, segment):
        """Return True if segment is a partially specified segment.

        :param segment: segment dictionary
        :returns: boolean
        """

    @abc.abstractmethod
    def validate_provider_segment(self, segment):
        """Validate attributes of a provider network segment.

        :param segment: segment dictionary using keys defined above
        :raises: neutron_lib.exceptions.InvalidInput if invalid

        Called outside transaction context to validate the provider
        attributes for a provider network segment. Raise InvalidInput
        if:

         - any required attribute is missing
         - any prohibited or unrecognized attribute is present
         - any attribute value is not valid

        The network_type attribute is present in segment, but
        need not be validated.
        """
        pass

    @abc.abstractmethod
    def get_mtu(self, physical):
        """Get driver's network MTU.

        :returns: mtu maximum transmission unit

        Returns the mtu for the network based on the config values and
        the network type.
        """
        pass


@six.add_metaclass(abc.ABCMeta)
class TypeDriver(_TypeDriverBase):
    """Define abstract interface for ML2 type drivers.

    ML2 type drivers each support a specific network_type for provider
    and/or tenant network segments. Type drivers must implement this
    abstract interface, which defines the API by which the plugin uses
    the driver to manage the persistent type-specific resource
    allocation state associated with network segments of that type.

    Network segments are represented by segment dictionaries using the
    NETWORK_TYPE, PHYSICAL_NETWORK, and SEGMENTATION_ID keys defined
    above, corresponding to the provider attributes.  Future revisions
    of the TypeDriver API may add additional segment dictionary
    keys. Attributes not applicable for a particular network_type may
    either be excluded or stored as None.

    TypeDriver passes session as argument for:
    - reserve_provider_segment
    - allocate_tenant_segment
    - release_segment
    - get_allocation
    """

    @abc.abstractmethod
    def reserve_provider_segment(self, session, segment):
        """Reserve resource associated with a provider network segment.

        :param session: database session
        :param segment: segment dictionary
        :returns: segment dictionary

        Called inside transaction context on session to reserve the
        type-specific resource for a provider network segment. The
        segment dictionary passed in was returned by a previous
        validate_provider_segment() call.
        """
        pass

    @abc.abstractmethod
    def allocate_tenant_segment(self, session):
        """Allocate resource for a new tenant network segment.

        :param session: database session
        :returns: segment dictionary using keys defined above

        Called inside transaction context on session to allocate a new
        tenant network, typically from a type-specific resource
        pool. If successful, return a segment dictionary describing
        the segment. If tenant network segment cannot be allocated
        (i.e. tenant networks not supported or resource pool is
        exhausted), return None.
        """
        pass

    @abc.abstractmethod
    def release_segment(self, session, segment):
        """Release network segment.

        :param session: database session
        :param segment: segment dictionary using keys defined above

        Called inside transaction context on session to release a
        tenant or provider network's type-specific resource. Runtime
        errors are not expected, but raising an exception will result
        in rollback of the transaction.
        """
        pass


@six.add_metaclass(abc.ABCMeta)
class ML2TypeDriver(_TypeDriverBase):
    """Define abstract interface for ML2 type drivers.

    ML2 type drivers each support a specific network_type for provider
    and/or tenant network segments. Type drivers must implement this
    abstract interface, which defines the API by which the plugin uses
    the driver to manage the persistent type-specific resource
    allocation state associated with network segments of that type.

    Network segments are represented by segment dictionaries using the
    NETWORK_TYPE, PHYSICAL_NETWORK, and SEGMENTATION_ID keys defined
    above, corresponding to the provider attributes.  Future revisions
    of the TypeDriver API may add additional segment dictionary
    keys. Attributes not applicable for a particular network_type may
    either be excluded or stored as None.

    ML2TypeDriver passes context as argument for:
    - reserve_provider_segment
    - allocate_tenant_segment
    - release_segment
    - get_allocation
    """

    @abc.abstractmethod
    def reserve_provider_segment(self, context, segment):
        """Reserve resource associated with a provider network segment.

        :param context: instance of neutron context with DB session
        :param segment: segment dictionary
        :returns: segment dictionary

        Called inside transaction context on session to reserve the
        type-specific resource for a provider network segment. The
        segment dictionary passed in was returned by a previous
        validate_provider_segment() call.
        """
        pass

    @abc.abstractmethod
    def allocate_tenant_segment(self, context):
        """Allocate resource for a new tenant network segment.

        :param context: instance of neutron context with DB session
        :returns: segment dictionary using keys defined above

        Called inside transaction context on session to allocate a new
        tenant network, typically from a type-specific resource
        pool. If successful, return a segment dictionary describing
        the segment. If tenant network segment cannot be allocated
        (i.e. tenant networks not supported or resource pool is
        exhausted), return None.
        """
        pass

    @abc.abstractmethod
    def release_segment(self, context, segment):
        """Release network segment.

        :param context: instance of neutron context with DB session
        :param segment: segment dictionary using keys defined above

        Called inside transaction context on session to release a
        tenant or provider network's type-specific resource. Runtime
        errors are not expected, but raising an exception will result
        in rollback of the transaction.
        """
        pass


@six.add_metaclass(abc.ABCMeta)
class NetworkContext(object):
    """Context passed to MechanismDrivers for changes to network resources.

    A NetworkContext instance wraps a network resource. It provides
    helper methods for accessing other relevant information. Results
    from expensive operations are cached so that other
    MechanismDrivers can freely access the same information.
    """

    @abc.abstractproperty
    def current(self):
        """Return the network in its current configuration.

        Return the network, as defined by NeutronPluginBaseV2.
        create_network and all extensions in the ml2 plugin, with
        all its properties 'current' at the time the context was
        established.
        """
        pass

    @abc.abstractproperty
    def original(self):
        """Return the network in its original configuration.

        Return the network, with all its properties set to their
        original values prior to a call to update_network. Method is
        only valid within calls to update_network_precommit and
        update_network_postcommit.
        """
        pass

    @abc.abstractproperty
    def network_segments(self):
        """Return the segments associated with this network resource."""
        pass


@six.add_metaclass(abc.ABCMeta)
class SubnetContext(object):
    """Context passed to MechanismDrivers for changes to subnet resources.

    A SubnetContext instance wraps a subnet resource. It provides
    helper methods for accessing other relevant information. Results
    from expensive operations are cached so that other
    MechanismDrivers can freely access the same information.
    """

    @abc.abstractproperty
    def current(self):
        """Return the subnet in its current configuration.

        Return the subnet, as defined by NeutronPluginBaseV2.
        create_subnet and all extensions in the ml2 plugin, with
        all its properties 'current' at the time the context was
        established.
        """
        pass

    @abc.abstractproperty
    def original(self):
        """Return the subnet in its original configuration.

        Return the subnet, with all its properties set to their
        original values prior to a call to update_subnet. Method is
        only valid within calls to update_subnet_precommit and
        update_subnet_postcommit.
        """
        pass


@six.add_metaclass(abc.ABCMeta)
class PortContext(object):
    """Context passed to MechanismDrivers for changes to port resources.

    A PortContext instance wraps a port resource. It provides helper
    methods for accessing other relevant information. Results from
    expensive operations are cached so that other MechanismDrivers can
    freely access the same information.
    """

    @abc.abstractproperty
    def current(self):
        """Return the port in its current configuration.

        Return the port, as defined by NeutronPluginBaseV2.
        create_port and all extensions in the ml2 plugin, with
        all its properties 'current' at the time the context was
        established.
        """
        pass

    @abc.abstractproperty
    def original(self):
        """Return the port in its original configuration.

        Return the port, with all its properties set to their
        original values prior to a call to update_port. Method is
        only valid within calls to update_port_precommit and
        update_port_postcommit.
        """
        pass

    @abc.abstractproperty
    def status(self):
        """Return the status of the current port."""
        pass

    @abc.abstractproperty
    def original_status(self):
        """Return the status of the original port.

        The method is only valid within calls to update_port_precommit and
        update_port_postcommit.
        """
        pass

    @abc.abstractproperty
    def network(self):
        """Return the NetworkContext associated with this port."""
        pass

    @abc.abstractproperty
    def binding_levels(self):
        """Return dictionaries describing the current binding levels.

        This property returns a list of dictionaries describing each
        binding level if the port is bound or partially bound, or None
        if the port is unbound. Each returned dictionary contains the
        name of the bound driver under the BOUND_DRIVER key, and the
        bound segment dictionary under the BOUND_SEGMENT key.

        The first entry (index 0) describes the top-level binding,
        which always involves one of the port's network's static
        segments. In the case of a hierarchical binding, subsequent
        entries describe the lower-level bindings in descending order,
        which may involve dynamic segments. Adjacent levels where
        different drivers bind the same static or dynamic segment are
        possible. The last entry (index -1) describes the bottom-level
        binding that supplied the port's binding:vif_type and
        binding:vif_details attribute values.

        Within calls to MechanismDriver.bind_port, descriptions of the
        levels above the level currently being bound are returned.
        """
        pass

    @abc.abstractproperty
    def original_binding_levels(self):
        """Return dictionaries describing the original binding levels.

        This property returns a list of dictionaries describing each
        original binding level if the port was previously bound, or
        None if the port was unbound. The content is as described for
        the binding_levels property.

        This property is only valid within calls to
        update_port_precommit and update_port_postcommit. It returns
        None otherwise.
        """
        pass

    @abc.abstractproperty
    def top_bound_segment(self):
        """Return the current top-level bound segment dictionary.

        This property returns the current top-level bound segment
        dictionary, or None if the port is unbound. For a bound port,
        top_bound_segment is equivalent to
        binding_levels[0][BOUND_SEGMENT], and returns one of the
        port's network's static segments.
        """
        pass

    @abc.abstractproperty
    def original_top_bound_segment(self):
        """Return the original top-level bound segment dictionary.

        This property returns the original top-level bound segment
        dictionary, or None if the port was previously unbound. For a
        previously bound port, original_top_bound_segment is
        equivalent to original_binding_levels[0][BOUND_SEGMENT], and
        returns one of the port's network's static segments.

        This property is only valid within calls to
        update_port_precommit and update_port_postcommit. It returns
        None otherwise.
        """
        pass

    @abc.abstractproperty
    def bottom_bound_segment(self):
        """Return the current bottom-level bound segment dictionary.

        This property returns the current bottom-level bound segment
        dictionary, or None if the port is unbound. For a bound port,
        bottom_bound_segment is equivalent to
        binding_levels[-1][BOUND_SEGMENT], and returns the segment
        whose binding supplied the port's binding:vif_type and
        binding:vif_details attribute values.
        """
        pass

    @abc.abstractproperty
    def original_bottom_bound_segment(self):
        """Return the original bottom-level bound segment dictionary.

        This property returns the original bottom-level bound segment
        dictionary, or None if the port was previously unbound. For a
        previously bound port, original_bottom_bound_segment is
        equivalent to original_binding_levels[-1][BOUND_SEGMENT], and
        returns the segment whose binding supplied the port's previous
        binding:vif_type and binding:vif_details attribute values.

        This property is only valid within calls to
        update_port_precommit and update_port_postcommit. It returns
        None otherwise.
        """
        pass

    @abc.abstractproperty
    def host(self):
        """Return the host with which the port is associated.

        In the context of a host-specific operation on a distributed
        port, the host property indicates the host for which the port
        operation is being performed. Otherwise, it is the same value
        as current['binding:host_id'].
        """
        pass

    @abc.abstractproperty
    def original_host(self):
        """Return the original host with which the port was associated.

        In the context of a host-specific operation on a distributed
        port, the original_host property indicates the host for which
        the port operation is being performed. Otherwise, it is the
        same value as original['binding:host_id'].

        This property is only valid within calls to
        update_port_precommit and update_port_postcommit. It returns
        None otherwise.
        """
        pass

    @abc.abstractproperty
    def vif_type(self):
        """Return the vif_type indicating the binding state of the port.

        In the context of a host-specific operation on a distributed
        port, the vif_type property indicates the binding state for
        the host for which the port operation is being
        performed. Otherwise, it is the same value as
        current['binding:vif_type'].
        """
        pass

    @abc.abstractproperty
    def original_vif_type(self):
        """Return the original vif_type of the port.

        In the context of a host-specific operation on a distributed
        port, the original_vif_type property indicates original
        binding state for the host for which the port operation is
        being performed. Otherwise, it is the same value as
        original['binding:vif_type'].

        This property is only valid within calls to
        update_port_precommit and update_port_postcommit. It returns
        None otherwise.
        """
        pass

    @abc.abstractproperty
    def vif_details(self):
        """Return the vif_details describing the binding of the port.

        In the context of a host-specific operation on a distributed
        port, the vif_details property describes the binding for the
        host for which the port operation is being
        performed. Otherwise, it is the same value as
        current['binding:vif_details'].
        """
        pass

    @abc.abstractproperty
    def original_vif_details(self):
        """Return the original vif_details of the port.

        In the context of a host-specific operation on a distributed
        port, the original_vif_details property describes the original
        binding for the host for which the port operation is being
        performed. Otherwise, it is the same value as
        original['binding:vif_details'].

        This property is only valid within calls to
        update_port_precommit and update_port_postcommit. It returns
        None otherwise.
        """
        pass

    @abc.abstractproperty
    def segments_to_bind(self):
        """Return the list of segments with which to bind the port.

        This property returns the list of segment dictionaries with
        which the mechanism driver may bind the port. When
        establishing a top-level binding, these will be the port's
        network's static segments. For each subsequent level, these
        will be the segments passed to continue_binding by the
        mechanism driver that bound the level above.

        This property is only valid within calls to
        MechanismDriver.bind_port. It returns None otherwise.
        """
        pass

    @abc.abstractmethod
    def host_agents(self, agent_type):
        """Get agents of the specified type on port's host.

        :param agent_type: Agent type identifier
        :returns: List of neutron.db.models.agent.Agent records
        """
        pass

    @abc.abstractmethod
    def set_binding(self, segment_id, vif_type, vif_details,
                    status=None):
        """Set the bottom-level binding for the port.

        :param segment_id: Network segment bound for the port.
        :param vif_type: The VIF type for the bound port.
        :param vif_details: Dictionary with details for VIF driver.
        :param status: Port status to set if not None.

        This method is called by MechanismDriver.bind_port to indicate
        success and specify binding details to use for port. The
        segment_id must identify an item in the current value of the
        segments_to_bind property.
        """
        pass

    @abc.abstractmethod
    def continue_binding(self, segment_id, next_segments_to_bind):
        """Continue binding the port with different segments.

        :param segment_id: Network segment partially bound for the port.
        :param next_segments_to_bind: Segments to continue binding with.

        This method is called by MechanismDriver.bind_port to indicate
        it was able to partially bind the port, but that one or more
        additional mechanism drivers are required to complete the
        binding. The segment_id must identify an item in the current
        value of the segments_to_bind property. The list of segments
        IDs passed as next_segments_to_bind identify dynamic (or
        static) segments of the port's network that will be used to
        populate segments_to_bind for the next lower level of a
        hierarchical binding.
        """
        pass

    @abc.abstractmethod
    def allocate_dynamic_segment(self, segment):
        """Allocate a dynamic segment.

        :param segment: A partially or fully specified segment dictionary

        Called by the MechanismDriver.bind_port, create_port or update_port
        to dynamically allocate a segment for the port using the partial
        segment specified. The segment dictionary can be a fully or partially
        specified segment. At a minimum it needs the network_type populated to
        call on the appropriate type driver.
        """
        pass

    @abc.abstractmethod
    def release_dynamic_segment(self, segment_id):
        """Release an allocated dynamic segment.

        :param segment_id: UUID of the dynamic network segment.

        Called by the MechanismDriver.delete_port or update_port to release
        the dynamic segment allocated for this port.
        """
        pass


@six.add_metaclass(abc.ABCMeta)
class ExtensionDriver(object):
    """Define stable abstract interface for ML2 extension drivers.

    An extension driver extends the core resources implemented by the
    ML2 plugin with additional attributes. Methods that process create
    and update operations for these resources validate and persist
    values for extended attributes supplied through the API. Other
    methods extend the resource dictionaries returned from the API
    operations with the values of the extended attributes.
    """

    @abc.abstractmethod
    def initialize(self):
        """Perform driver initialization.

        Called after all drivers have been loaded and the database has
        been initialized. No abstract methods defined below will be
        called prior to this method being called.
        """
        pass

    @property
    def extension_alias(self):
        """Supported extension alias.

        Return the alias identifying the core API extension supported
        by this driver. Do not declare if API extension handling will
        be left to a service plugin, and we just need to provide
        core resource extension and updates.
        """
        pass

    @property
    def extension_aliases(self):
        """List of extension aliases supported by the driver.

        Return a list of aliases identifying the core API extensions
        supported by the driver. By default this just returns the
        extension_alias property for backwards compatibility.
        """
        return [self.extension_alias]

    def process_create_network(self, plugin_context, data, result):
        """Process extended attributes for create network.

        :param plugin_context: plugin request context
        :param data: dictionary of incoming network data
        :param result: network dictionary to extend

        Called inside transaction context on plugin_context.session to
        validate and persist any extended network attributes defined by this
        driver. Extended attribute values must also be added to
        result.
        """
        pass

    def process_create_subnet(self, plugin_context, data, result):
        """Process extended attributes for create subnet.

        :param plugin_context: plugin request context
        :param data: dictionary of incoming subnet data
        :param result: subnet dictionary to extend

        Called inside transaction context on plugin_context.session to
        validate and persist any extended subnet attributes defined by this
        driver. Extended attribute values must also be added to
        result.
        """
        pass

    def process_create_port(self, plugin_context, data, result):
        """Process extended attributes for create port.

        :param plugin_context: plugin request context
        :param data: dictionary of incoming port data
        :param result: port dictionary to extend

        Called inside transaction context on plugin_context.session to
        validate and persist any extended port attributes defined by this
        driver. Extended attribute values must also be added to
        result.
        """
        pass

    def process_update_network(self, plugin_context, data, result):
        """Process extended attributes for update network.

        :param plugin_context: plugin request context
        :param data: dictionary of incoming network data
        :param result: network dictionary to extend

        Called inside transaction context on plugin_context.session to
        validate and update any extended network attributes defined by this
        driver. Extended attribute values, whether updated or not,
        must also be added to result.
        """
        pass

    def process_update_subnet(self, plugin_context, data, result):
        """Process extended attributes for update subnet.

        :param plugin_context: plugin request context
        :param data: dictionary of incoming subnet data
        :param result: subnet dictionary to extend

        Called inside transaction context on plugin_context.session to
        validate and update any extended subnet attributes defined by this
        driver. Extended attribute values, whether updated or not,
        must also be added to result.
        """
        pass

    def process_update_port(self, plugin_context, data, result):
        """Process extended attributes for update port.

        :param plugin_context: plugin request context
        :param data: dictionary of incoming port data
        :param result: port dictionary to extend

        Called inside transaction context on plugin_context.session to
        validate and update any extended port attributes defined by this
        driver. Extended attribute values, whether updated or not,
        must also be added to result.
        """
        pass

    def extend_network_dict(self, session, base_model, result):
        """Add extended attributes to network dictionary.

        :param session: database session
        :param base_model: network model data
        :param result: network dictionary to extend

        Called inside transaction context on session to add any
        extended attributes defined by this driver to a network
        dictionary to be used for mechanism driver calls and/or
        returned as the result of a network operation.
        """
        pass

    def extend_subnet_dict(self, session, base_model, result):
        """Add extended attributes to subnet dictionary.

        :param session: database session
        :param base_model: subnet model data
        :param result: subnet dictionary to extend

        Called inside transaction context on session to add any
        extended attributes defined by this driver to a subnet
        dictionary to be used for mechanism driver calls and/or
        returned as the result of a subnet operation.
        """
        pass

    def extend_port_dict(self, session, base_model, result):
        """Add extended attributes to port dictionary.

        :param session: database session
        :param base_model: port model data
        :param result: port dictionary to extend

        Called inside transaction context on session to add any
        extended attributes defined by this driver to a port
        dictionary to be used for mechanism driver calls
        and/or returned as the result of a port operation.
        """
        pass