Openstack nova代码部分注释一

做个一个没怎么学过python的菜鸟，看源码是最好的学习方式了，现在就从nova入手，主要注释一下 nova/compute/api.py 中的 create_instance函数

   def _create_instance(self, context, instance_type,               image_href, kernel_id, ramdisk_id,               min_count, max_count,               display_name, display_description,               key_name, key_data, security_group,               availability_zone, user_data, metadata,               injected_files, admin_password,               access_ip_v4, access_ip_v6,               requested_networks, config_drive,               block_device_mapping, auto_disk_config,               reservation_id=None, create_instance_here=False,               scheduler_hints=None):        """Verify all the input parameters regardless of the provisioning        strategy being performed and schedule the instance(s) for        creation."""        if not metadata:            metadata = {}        if not display_description:            display_description = ''        if not security_group:            security_group = 'default'        if not instance_type:            instance_type = instance_types.get_default_instance_type()        if not min_count:            min_count = 1        if not max_count:            max_count = min_count        if not metadata:            metadata = {}        block_device_mapping = block_device_mapping or []#从quota得到具体的实例限制        num_instances = quota.allowed_instances(context, max_count,                                                instance_type)        if num_instances < min_count:            pid = context.project_id            if num_instances <= 0:                msg = _("Cannot run any more instances of this type.")            else:                msg = (_("Can only run %s more instances of this type.") %                       num_instances)            LOG.warn(_("Quota exceeded for %(pid)s,"                  " tried to run %(min_count)s instances. " + msg) % locals())            raise exception.QuotaError(code="InstanceLimitExceeded")#检查元数据、注入文件、网络        self._check_metadata_properties_quota(context, metadata)        self._check_injected_file_quota(context, injected_files)        self._check_requested_networks(context, requested_networks)        (image_service, image_id) = nova.image.get_image_service(context,                                                                 image_href)#通过镜像id，访问镜像的具体服务。得到一个image字典。        image = image_service.show(context, image_id)#iamge 是一个字典，返回key='min_ram'对应的值， get是字典的一个方法。#memory_mb：是虚拟机所属内存。        if instance_type['memory_mb'] < int(image.get('min_ram') or 0):            raise exception.InstanceTypeMemoryTooSmall()#root_gb ：虚拟机根硬盘大小；instance_type代表了创建虚拟机的需求或者说配置，image则是实际上存在镜像的一个东西。        if instance_type['root_gb'] < int(image.get('min_disk') or 0):            raise exception.InstanceTypeDiskTooSmall()        config_drive_id = None        if config_drive and config_drive is not True:            # config_drive is volume id            config_drive, config_drive_id = None, config_drive        os_type = None#properties是字典image的一个属性，image[properties]又是一个字典。        if 'properties' in image and 'os_type' in image['properties']:            os_type = image['properties']['os_type']        architecture = None        if 'properties' in image and 'arch' in image['properties']:            architecture = image['properties']['arch']        vm_mode = None        if 'properties' in image and 'vm_mode' in image['properties']:            vm_mode = image['properties']['vm_mode']        # If instance doesn't have auto_disk_config overridden by request, use        # whatever the image indicates        if auto_disk_config is None:            if ('properties' in image and                'auto_disk_config' in image['properties']):#bool_from_str:将字符串转化为数组                auto_disk_config = utils.bool_from_str(                    image['properties']['auto_disk_config'])        if kernel_id is None:            kernel_id = image['properties'].get('kernel_id', None)        if ramdisk_id is None:            ramdisk_id = image['properties'].get('ramdisk_id', None)        # FIXME(sirp): is there a way we can remove null_kernel?        # No kernel and ramdisk for raw images        if kernel_id == str(FLAGS.null_kernel):            kernel_id = None            ramdisk_id = None            LOG.debug(_("Creating a raw instance"))        # Make sure we have access to kernel and ramdisk (if not raw)#locals() 返回一个名字/值对的字典        LOG.debug(_("Using Kernel=%(kernel_id)s, Ramdisk=%(ramdisk_id)s")                  % locals())    #show具体是干嘛的？？？？        if kernel_id:            image_service.show(context, kernel_id)        if ramdisk_id:            image_service.show(context, ramdisk_id)        if config_drive_id:            image_service.show(context, config_drive_id)#检查是否具有安全防火墙，如果不具有就创建一个默认的安全组。        self.ensure_default_security_group(context)#ssh 密钥文件名存在，但是数据不存在。        if key_data is None and key_name:            key_pair = self.db.key_pair_get(context, context.user_id, key_name)            key_data = key_pair['public_key']        if reservation_id is None:            reservation_id = utils.generate_uid('r')#根设备名        root_device_name = block_device.properties_root_device_name(            image['properties'])        # NOTE(vish): We have a legacy hack to allow admins to specify hosts        #             via az using az:host. It might be nice to expose an        #             api to specify specific hosts to force onto, but for        #             now it just supports this legacy hack.        host = None#parition 函数进行分割字符串，如果分割成功，返回tuple,中间的为分隔符；如果找不到，返回1个有用字符串#剩余两个元素为空。#下边主要功能是设置调度集群。        if availability_zone:            availability_zone, _x, host = availability_zone.partition(':')        if not availability_zone:            availability_zone = FLAGS.default_schedule_zone        if context.is_admin and host:            filter_properties = {'force_hosts': [host]}        else:            filter_properties = {}        filter_properties['scheduler_hints'] = scheduler_hints        base_options = {            'reservation_id': reservation_id,            'image_ref': image_href,            'kernel_id': kernel_id or '',            'ramdisk_id': ramdisk_id or '',            'power_state': power_state.NOSTATE,            'vm_state': vm_states.BUILDING, #注意刚开始是创建中状态。            'config_drive_id': config_drive_id or '',            'config_drive': config_drive or '',            'user_id': context.user_id,            'project_id': context.project_id,            'launch_time': time.strftime('%Y-%m-%dT%H:%M:%SZ', time.gmtime()),#格式化一个时间字符串。            'instance_type_id': instance_type['id'],#虚拟机的套餐类型。            'memory_mb': instance_type['memory_mb'],#虚拟机的内存            'vcpus': instance_type['vcpus'],#虚拟机的cpu核数。            'root_gb': instance_type['root_gb'],#虚机根硬盘大小            'ephemeral_gb': instance_type['ephemeral_gb'],            'display_name': display_name,            'display_description': display_description,            'user_data': user_data or '',            'key_name': key_name,#密钥文件名            'key_data': key_data,#密钥数据            'locked': False,            'metadata': metadata,            'access_ip_v4': access_ip_v4,            'access_ip_v6': access_ip_v6,            'availability_zone': availability_zone,            'os_type': os_type,#操作系统类型。            'architecture': architecture,            'vm_mode': vm_mode,#虚机状态。            'root_device_name': root_device_name,#根设备名称。            'progress': 0,            'auto_disk_config': auto_disk_config}        LOG.debug(_("Going to run %s instances...") % num_instances)        if create_instance_here:            instance = self.create_db_entry_for_new_instance(                    context, instance_type, image, base_options,                    security_group, block_device_mapping)            # Tells scheduler we created the instance already.            base_options['uuid'] = instance['uuid']#cast是单向的不需要等待对方回复即可返回。            rpc_method = rpc.cast        else:            # We need to wait for the scheduler to create the instance            # DB entries, because the instance *could* be # created in            # a child zone.#我的理解：该实例不一定在这个集群创建，可能去子集群，因为可能有很多个吧#因此需要等待他的创建完成。            rpc_method = rpc.call        # TODO(comstud): We should use rpc.multicall when we can        # retrieve the full instance dictionary from the scheduler.        # Otherwise, we could exceed the AMQP max message size limit.        # This would require the schedulers' schedule_run_instances        # methods to return an iterator vs a list.#这里应该是调度器发消息了，让调度器去通知具体节点的nova-compute进程去创建虚机。        instances = self._schedule_run_instance(                rpc_method,                context, base_options,                instance_type,                availability_zone, injected_files,                admin_password, image,                num_instances, requested_networks,                block_device_mapping, security_group,                filter_properties)#这里创建完毕，返回instance实例。        if create_instance_here:            return ([instance], reservation_id)        return (instances, reservation_id)

下边这个是给调度器发送instance创建消息的函数：_schedule_run_instance

#create_instance 调用，发送消息给调度器    def _schedule_run_instance(self,            rpc_method,            context, base_options,            instance_type,            availability_zone, injected_files,            admin_password, image,            num_instances,            requested_networks,            block_device_mapping,            security_group,            filter_properties):        """Send a run_instance request to the schedulers for processing."""#pid不是进程id，是项目id.....        pid = context.project_id        uid = context.user_id        LOG.debug(_("Sending create to scheduler for %(pid)s/%(uid)s's") %                locals())        request_spec = {            'image': utils.to_primitive(image),            'instance_properties': base_options,            'instance_type': instance_type,            'num_instances': num_instances,            'block_device_mapping': block_device_mapping,            'security_group': security_group,        }        return rpc_method(context,                FLAGS.scheduler_topic,                {"method": "run_instance",                 "args": {"topic": FLAGS.compute_topic,                          "request_spec": request_spec,                          "admin_password": admin_password,                          "injected_files": injected_files,                          "requested_networks": requested_networks,                          "is_first_time": True,                          "filter_properties": filter_properties}})

这个代码是我个人的理解。最进学习openstack感觉一头雾水，边看《云计算与openstack》边写一些东西出来，也是一种体验吧。加油！！！！