openstack plugin 之（七）怎怎样写 OpenStack Neutron 的 Extension

上文说到需要在 /neutronclient/v2_0/myextension/extension.py 中分别定义五个 class：List/Show/Create/Delete/UpdateExtension。具体形式如下：

import argparseimport loggingfrom neutronclient.neutron import v2_0 as neutronV20from neutronclient.openstack.common.gettextutils import _
RESOURCE = 'myextension'
class ListExtension(neutronV20.ListCommand):    """List extensions"""    resource = RESOURCE    log = logging.getLogger(__name__ + '.ListExtension')    list_columns = ['id', 'name']    class ShowExtension(neutronV20.ShowCommand):    """Show information of a given extension."""    resource = RESOURCE    log = logging.getLogger(__name__ + '.ShowExtension')    class CreatePhysicalGateway(neutronV20.CreateCommand):    """Create an extension."""    resource = RESOURCE    log = logging.getLogger(__name__ + '.CreateExtension')    def add_known_arguments(self, parser):        parser.add_argument(            'name', metavar='NAME',            help=_('Name of extension to create'))           def args2body(self, parsed_args):        body = {self.resource: {            'name': parsed_args.name}}        return body 

class UpdateExtension(neutronV20.UpdateCommand):    """update a given extension."""    resource = RESOURCE    log = logging.getLogger(__name__ + '.UpdateExtension')      

class DeleteExtension(neutronV20.DeleteCommand):    """Delete a given extension."""    resource = RESOURCE    log = logging.getLogger(__name__ + '.DeleteExtension')       

这些 class 处在接受 CLI 命令的第一线，负责将命令转化成 API call。需要特别注意的是 CreateExtension 这个类，它有两个方法 add_known_arguments 和 args2body。前者定义了 CLI 命令接受哪些参数，后者规定如何将收到的参数打包起来。

这些参数打包之后就会发给 neutron 后台中我们自己定义的 plugin controller，但是如何发送这些参数还需要我们去 /neutronclient/v2_0/client.py 的 Client 类中设置：

首先是 uri 路径：

    myextensions_path = "/myextensions"    myextension_path = "/myextensions/%s"

然后是每个操作所对应的传递方法：

　　 @APIParamsCall    def list_myextensions(self, retrieve_all=True, **_params):        """Fetches a list of all myextensions for a tenant."""        return self.list('myextensions', self.myextensions_path, retrieve_all,                         **_params)                             @APIParamsCall    def show_myextension(self, myextension, **_params):        """Fetches information of a certain entry in myextension."""        return self.get(self.myextension_path % (myextension), params=_params)            @APIParamsCall    def create_myextension(self, body=None):        """Creates a new myextension entry."""        return self.post(self.myextensions_path, body=body)            @APIParamsCall    def delete_myextension(self, myextension):        """Deletes the specified myextension."""        return self.delete(self.myextension_path % (myextension))　　 @APIParamsCall    def update_myextension(self, myextension, body=None):        """Updates a myextension."""        return self.put(self.myextension_path % (myextension), body=body)

如此一来，我们自己实现的 neutron plugin 就能够收到 CLI 发送过来的命令啦。

下一章再来说说怎么修改 OpenStack 的 Dashboard 来显示我们在 extension 中添加的新元素。