neutron中的QOS实现源码-core_extensions类中的实现

core_extensions类中主要实现了一些核心的扩展方法

base.py

主要定义了一个基类CoreResourceExtension，定义了两个抽象接口，process_fields和extract_fields，传入的参数包括network、port类型以及扩展域，对于qos来说， 这个扩展域可以理解为qos的policy。

"""资源类型主要包括network和port信息 """

NETWORK = 'network'
PORT = 'port'



CORE_RESOURCES = [NETWORK, PORT]


@six.add_metaclass(abc.ABCMeta)
class CoreResourceExtension(object):
    # 抽象方法，
    @abc.abstractmethod
    def process_fields(self, context, resource_type,
                       requested_resource, actual_resource):
        """Process extension fields.

        :param context: neutron api request context
        :param resource_type: core resource type (one of CORE_RESOURCES)
        :param requested_resource: resource dict that contains extension fields
        :param actual_resource: actual resource dict known to plugin
        """

    @abc.abstractmethod
    def extract_fields(self, resource_type, resource):
        """Extract extension fields.

        :param resource_type: core resource type (one of CORE_RESOURCES)
        :param resource: resource dict that contains extension fields
        """

qos.py

现在来具体看qos是如何对抽象方法进行实现的，主要实现了QosCoreResourceExtension类，该类是继承基类CoreResourceExtension，里面具体实现了process_fields和extract_fields。

    # @property将定义的方法装饰为属性，直接进行调用
    """
    判断qos的plugin是否已经加载，如果没有就调用NeutronManager的get_service_plugins()进行加载，
    常量plugin_constants.QOS用于遍历，返回结果
    """
    @property
    def plugin_loaded(self):
        if not hasattr(self, '_plugin_loaded'):
            service_plugins = manager.NeutronManager.get_service_plugins()
            self._plugin_loaded = plugin_constants.QOS in service_plugins
        return self._plugin_loaded

下面来看两个内部方法，_get_policy_obj和_update_port_policy

对于_get_policy_obj来说，类QosPolicy位于neutron.objects.qos.policy中，通过传入的policy_id得到有关qos的policy对象 对于_update_port_policy来说，根据port的ID来找出对应qos的policy，detach_port方法直接将找出的old_policy进行删除；接着在需要更新policy的port上找到 qos_policy_id，然后获得policy对象，将更新policy的port信息加到数据库中去。

    def _get_policy_obj(self, context, policy_id):
        obj = policy_object.QosPolicy.get_by_id(context, policy_id)
        if obj is None:
            raise n_exc.QosPolicyNotFound(policy_id=policy_id)
        return obj

    def _update_port_policy(self, context, port, port_changes):
        old_policy = policy_object.QosPolicy.get_port_policy(
            context, port['id'])
        if old_policy:
            old_policy.detach_port(port['id'])

        qos_policy_id = port_changes.get(qos_consts.QOS_POLICY_ID)
        if qos_policy_id is not None:
            policy = self._get_policy_obj(context, qos_policy_id)
            policy.attach_port(port['id'])
        port[qos_consts.QOS_POLICY_ID] = qos_policy_id

detach_port方法在类QosPolicy进行实现，直接在数据库中删除有关old_qos_policy的数据。

    def detach_port(self, port_id):
        qos_db_api.delete_policy_port_binding(self._context,
                                              policy_id=self.id,
                                              port_id=port_id)

attach_port方法在类QosPolicy进行实现，直接在数据库中添加有关qos_policy的数据。

    def attach_port(self, port_id):
        qos_db_api.create_policy_port_binding(self._context,
                                              policy_id=self.id,
                                              port_id=port_id)

_update_network_policy方法主要实现network的policy的操作，实现原理和port一致。

    def _update_network_policy(self, context, network, network_changes):
        old_policy = policy_object.QosPolicy.get_network_policy(
            context, network['id'])
        if old_policy:
            old_policy.detach_network(network['id'])

        qos_policy_id = network_changes.get(qos_consts.QOS_POLICY_ID)
        if qos_policy_id is not None:
            policy = self._get_policy_obj(context, qos_policy_id)
            policy.attach_network(network['id'])
        network[qos_consts.QOS_POLICY_ID] = qos_policy_id

上述有关port和network的操作，就是对应的resource_type

既然是继承自CoreResourceExtension，就要实现里面的抽象接口。

    def process_fields(self, context, resource_type,
                       requested_resource, actual_resource):
        if (qos_consts.QOS_POLICY_ID in requested_resource and
            self.plugin_loaded):
            self._exec('_update_%s_policy' % resource_type, context,
                       {resource_type: actual_resource,
                        "%s_changes" % resource_type: requested_resource})

    def extract_fields(self, resource_type, resource):
        if not self.plugin_loaded:
            return {}

        binding = resource['qos_policy_binding']
        qos_policy_id = binding['policy_id'] if binding else None
        return {qos_consts.QOS_POLICY_ID: qos_policy_id}

_exec方法

    def _exec(self, method_name, context, kwargs):
        with db_api.autonested_transaction(context.session):
            return getattr(self, method_name)(context=context, **kwargs)

db_api.autonested_transaction是neutron.db.api中定义的方法，防止被传入的参数嵌套。

@contextlib.contextmanager
def autonested_transaction(sess):
    """This is a convenience method to not bother with 'nested' parameter."""
    try:
        session_context = sess.begin_nested()
    except exc.InvalidRequestError:
        session_context = sess.begin(subtransactions=True)
    finally:
        with session_context as tx:
            yield tx