nova update

update的入口代码在nova/api/openstack/compute/servers.py，方法是update()，如下    def update(self, req, id, body):        """Update server then pass on to version-specific controller."""        ctxt = req.environ['nova.context']//update_dict 表示要更新的字典        update_dict = {}//根据id找到要更新的instance        instance = self._get_server(ctxt, req, id, is_detail=True)//判断是否有权限权限更新instance        ctxt.can(server_policies.SERVERS % 'update',                 target={'user_id': instance.user_id,                         'project_id': instance.project_id})        server = body['server']//更新display_name        if 'name' in server:            update_dict['display_name'] = common.normalize_name(                server['name'])//更新description        if 'description' in server:            # This is allowed to be None (remove description)            update_dict['display_description'] = server['description']        helpers.translate_attributes(helpers.UPDATE, server, update_dict)        try:            instance = self.compute_api.update_instance(ctxt, instance,                                                        update_dict)            return self._view_builder.show(req, instance,                                           extend_address=False)        except exception.InstanceNotFound:            msg = _("Instance could not be found")            raise exc.HTTPNotFound(explanation=msg)在__init__ 函数中self.compute_api = compute.API()，因此这里就转到    def update_instance(self, context, instance, updates):        """Updates a single Instance object with some updates dict.        Returns the updated instance.       """    //如果instance设置了id的话，则直接调用instance.update 来更新，最后调用instance.save()来保存更新。        if instance.obj_attr_is_set('id'):            instance.update(updates)             inst_map = self._get_instance_map_or_none(context, instance.uuid)            if inst_map and (inst_map.cell_mapping is not None):                with nova_context.target_cell(context, inst_map.cell_mapping):                    instance.save()            else:                # If inst_map.cell_mapping does not point at a cell then cell                # migration has not happened yet.                # TODO(alaski): Make this a failure case after we put in                # a block that requires migrating to cellsv2.                instance.save()        else:    //如果这个instance没有设置id的话，则从更具instance的uuid找到这个instance，同样通过instance.update(updates)更新后，通过build_req.save()来保存            try:                build_req = objects.BuildRequest.get_by_instance_uuid(                    context, instance.uuid)                instance = build_req.instance                instance.update(updates)                       build_req.save()            except exception.BuildRequestNotFound:                    return instance总结一下nova的update函数从nova/api/openstack/compute/servers.py 中开始到nova/compute/api.py中结束。看起来这个函数只会更新instance的display_name和description 这两个字符串