创建资源后如何通知agent

当一个subnet创建后，需要通知dhcp-agent等,比如subnet_delete，subnet_create等，这个notify是什么时候发的呢，原来在API的Controller里

[python]
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def delete(self, request, id, **kwargs):
    """Deletes the specified entity."""
    notifier_api.notify(request.context,
                        self._publisher_id,
                        self._resource + '.delete.start',
                        notifier_api.CONF.default_notification_level,
                        {self._resource + '_id': id})
    action = self._plugin_handlers[self.DELETE]

    # Check authz
    parent_id = kwargs.get(self._parent_id_name)
    obj = self._item(request, id, parent_id=parent_id)
    try:
        policy.enforce(request.context,
                       action,
                       obj,
                       resource=id)
    except exceptions.PolicyNotAuthorized as err:
        # To avoid giving away information, pretend that it
        # doesn't exist
        raise webob.exc.HTTPForbidden(explanation=err.msg)

    obj_deleter = getattr(self._plugin, action)
    obj_deleter(request.context, id, **kwargs)
    notifier_method = self._resource + '.delete.end'
    notifier_api.notify(request.context,
                        self._publisher_id,
                        notifier_method,
                        notifier_api.CONF.default_notification_level,
                        {self._resource + '_id': id})
    result = {self._resource: self._view(request.context, obj)}
    self._nova_notifier.send_network_change(action, {}, result)
    self._send_dhcp_notification(request.context,
                                 result,
                                 notifier_method)  <----------

代码里经常看到
create_XXX_precommit
create_XXX_postcommit
这样的函数，我以为是通知agent的呢，但看了子网的这2个家伙，发现只是通知driver而已，通知agent是由上面的notifyer完成的，可以看下面的log

<% codeblock %>
2016-06-27 12:00:55.725 14997 ERROR neutron.plugins.ml2.managers [req-1df986e6-3df2-4125-b555-e29ab7df384c None] #######3:<stevedore.extension.Extension object at 0x4b85c90>
2016-06-27 12:00:55.736 14997 ERROR neutron.plugins.ml2.managers [req-1df986e6-3df2-4125-b555-e29ab7df384c None] #######4:
2016-06-27 12:00:55.736 14997 ERROR neutron.plugins.ml2.managers [req-1df986e6-3df2-4125-b555-e29ab7df384c None] #######5:(<bound method BareMetalMechanismDriver.delete_subnet_postc
ommit of <neutron.plugins.ml2.drivers.mech_baremetal.BareMetalMechanismDriver object at 0x3a42610>>,)
2016-06-27 12:00:55.737 14997 ERROR neutron.plugins.ml2.managers [req-1df986e6-3df2-4125-b555-e29ab7df384c None] #######6:
2016-06-27 12:00:55.738 14997 ERROR neutron.plugins.ml2.managers [req-1df986e6-3df2-4125-b555-e29ab7df384c None] #######3:<stevedore.extension.Extension object at 0x492fc50>
2016-06-27 12:00:55.749 14997 ERROR neutron.plugins.ml2.managers [req-1df986e6-3df2-4125-b555-e29ab7df384c None] #######4:
2016-06-27 12:00:55.750 14997 ERROR neutron.plugins.ml2.managers [req-1df986e6-3df2-4125-b555-e29ab7df384c None] #######5:(<bound method OpenvswitchMechanismDriver.delete_subnet_pos
tcommit of <neutron.plugins.ml2.drivers.mech_openvswitch.OpenvswitchMechanismDriver object at 0x3a42d50>>,)
2016-06-27 12:00:55.750 14997 ERROR neutron.plugins.ml2.managers [req-1df986e6-3df2-4125-b555-e29ab7df384c None] #######6:
2016-06-27 12:00:55.751 14997 ERROR neutron.plugins.ml2.managers [req-1df986e6-3df2-4125-b555-e29ab7df384c None] #######3:<stevedore.extension.Extension object at 0x492fc50>
2016-06-27 12:00:55.762 14997 ERROR neutron.plugins.ml2.managers [req-1df986e6-3df2-4125-b555-e29ab7df384c None] #######4:
2016-06-27 12:00:55.763 14997 ERROR neutron.plugins.ml2.managers [req-1df986e6-3df2-4125-b555-e29ab7df384c None] #######5:(<bound method L2populationMechanismDriver.delete_subnet_po
stcommit of <neutron.plugins.ml2.drivers.l2pop.mech_driver.L2populationMechanismDriver object at 0x3a429d0>>,)
2016-06-27 12:00:55.763 14997 ERROR neutron.plugins.ml2.managers [req-1df986e6-3df2-4125-b555-e29ab7df384c None] #######6:

<% endcodeblock %>

另外一个有意思的细节是network什么时候schedule的呢，就是第一个create_port的时候，
Controller在收到发送port_create_end消息的时候，会调用DhcpAgentNotifyAPI的notify
这里的notify就很特殊处理了，不会傻乎乎的直接notify
如果是port_create_end消息，先做schedule，然后才发送消息。
也就是之前虽然有network_create_end, subnet_create_end之类的消息，基本没啥用

<% codeblock %>

# schedule the network first, if needed
schedule_required = method == 'port_create_end'
if schedule_required:
    agents = self._schedule_network(admin_ctx, network, agents)

enabled_agents = self._get_enabled_agents(
    context, network, agents, method, payload)
for agent in enabled_agents:
    self._cast_message(
        context, method, payload, agent.host, agent.topic)

<% endcodeblock %>