链路层收包

 

 

 

//当底层设备驱动程序接收一个报文时，就会通过调用netif_receive_skb将报文的SKB上传至网络层。
/*
在netif_rx函数中会调用netif_rx_schedule, 然后该函数又会去调用__netif_rx_schedule
在函数__netif_rx_schedule中会去触发软中断NET_RX_SOFTIRQ, 也即是去调用net_rx_action.
然后在net_rx_action函数中会去调用设备的poll函数, 它是设备自己注册的.
在设备的poll函数中, 会去调用netif_receive_skb函数,  在该函数中有下面一条语句 pt_prev->func, 此处的func为一个函数指针,
因此, 就完成了从链路层上传到网络层的这一个过程了.
*/

/*非NAPI方式，从驱动硬件中断中调用这个netif_rx函数，

而NAPI方式从硬件中断中调用____napi_schedule激活软中断,
*/
/*
            非NAPI方式                                              NAPI方式NAPI方式(NAPI的napi_struct是自己构造的，该结构上的poll钩子函数也是自己定义的。

                                        IRQ
                                         |
                  _______________________|_____________________________
                  |                                                     |
             netif_rx(netif_rx_internal)                napi_schedule
 上半部           |                                                     |
             enqueue_to_backlog                                  __napi_schedule
                  |                                                     |           
            skb加入input_pkt_queuem中                           napi_struct加入poll_list中
       　　__napi_schedule    

　　 　softnet_data->backlog加入poll_list中                                      |
                   |____________________________________________________|
                                             |
                                        net_rx_action
下半部                                       |
                      _______________________|_____________________________
                      |                                                     |
            process_backlog->__netif_receive_skb                驱动poll方法->napi_gro_receive->netif_receive_skb->__netif_receive_skb

*/

 

?

static int netif_rx_internal(struct sk_buff *skb)

{

    int ret;

 

    net_timestamp_check(netdev_tstamp_prequeue, skb);

 

    trace_netif_rx(skb);

#ifdef CONFIG_RPS

    if (static_key_false(&rps_needed)) {

        struct rps_dev_flow voidflow, *rflow = &voidflow;

        int cpu;

 

        preempt_disable();

        rcu_read_lock();

 

        cpu = get_rps_cpu(skb->dev, skb, &rflow);

        if (cpu < 0)

            cpu = smp_processor_id();

 

        ret = enqueue_to_backlog(skb, cpu, &rflow->last_qtail);//这里面的数据在process_backlog

 

        rcu_read_unlock();

        preempt_enable();

    } else

#endif

    {

        unsigned int qtail;

        ret = enqueue_to_backlog(skb, get_cpu(), &qtail);

        put_cpu();

    }

    return ret;

}

 /* 队列中.在中断轮询的时候,软中断总函数do_softirq()直接到达网卡的接收软中断函数net_rx_action()，
   在此函数中调用queue->backlog_dev.poll=process_backlog;即process_backlog()函数，它将queue->input_pkt_queue
   队列中的数据向上层协议传输，比如网络层的ip协议等。
*/
/*
            非NAPI方式                                              NAPI方式NAPI方式(NAPI的napi_struct是自己构造的，该结构上的poll钩子函数也是自己定义的

                                        IRQ
                                         |
                  _______________________|_____________________________
                  |                                                     　　|
             netif_rx                                            napi_schedule
 上半部      |                                                       　  |
             enqueue_to_backlog

　　　　　____napi_schedule                                 __napi_schedule
                  |                                                    　　 |           
            skb加入input_pkt_queuem中                           napi_struct加入poll_list中
            softnet_data->backlog加入poll_list中                                      |
                   |____________________________________________________|
                                             |
                                        net_rx_action
下半部                                       |
                      _______________________|_____________________________
                      |                                                     |
            porcess_backlog->__netif_receive_skb                驱动poll方法->napi_gro_receive->netif_receive_skb->__netif_receive_skb

*/

?

static int enqueue_to_backlog(struct sk_buff *skb, int cpu,

                  unsigned int *qtail)

{

    struct softnet_data *sd;

    unsigned long flags;

    unsigned int qlen;

 

    sd = &per_cpu(softnet_data, cpu);//获取cpu接口缓存队列（每cpu变量下次写内核同步介绍）

 

    local_irq_save(flags);//关中断，当该SKB添加到输入队列input_pkt_queue后打开中断，继续从硬件中断中接收输入然后放入该接收队列中

 

    rps_lock(sd);

    if (!netif_running(skb->dev))

        goto drop;

    qlen = skb_queue_len(&sd->input_pkt_queue);

    if (qlen <= netdev_max_backlog && !skb_flow_limit(skb, qlen)) {如果链路层缓存队列还没有满，则加入队列，否者上层处理严重阻塞，丢失，drop++

        if (qlen) { 队列不为空，说明已经有数据，只需加入队列，等待下次软中断处理

enqueue:

            __skb_queue_tail(&sd->input_pkt_queue, skb);/* 挂softnet_data输入队列 */ //net_rx_action中会对包的个数，以及软中断处理时间进行限制

            input_queue_tail_incr_save(sd, qtail);

            rps_unlock(sd);

            local_irq_restore(flags);//打开中断，当该SKB添加到输入队列input_pkt_queue后打开中断，继续从硬件中断中接收输入然后放入该接收队列中

            return NET_RX_SUCCESS;

        }

 

        /* Schedule NAPI for backlog device

         * We can use non atomic operation since we own the queue lock

         */ /* &sd->backlog加入napi->poll_list，backlog即函数process_backlog */

        if (!__test_and_set_bit(NAPI_STATE_SCHED, &sd->backlog.state)) {

            if (!rps_ipi_queued(sd))//这里就会调用net_dev_init中的->backlog_dev.poll=process_backlog从而到process_backlog中执行　　　　　　　　　　　　　　　　　　for_each_possible_cpu(i) {

        struct softnet_data *sd = &per_cpu(softnet_data, i);

 

        skb_queue_head_init(&sd->input_pkt_queue);

        skb_queue_head_init(&sd->process_queue);

        INIT_LIST_HEAD(&sd->poll_list);

        sd->output_queue_tailp = &sd->output_queue;

#ifdef CONFIG_RPS

        sd->csd.func = rps_trigger_softirq;

        sd->csd.info = sd;

        sd->cpu = i;

#endif

 

        sd->backlog.poll = process_backlog;

        sd->backlog.weight = weight_p;

    }

 

    dev_boot_phase = 0;

 

    /* The loopback device is special if any other network devices

     * is present in a network namespace the loopback device must

     * be present. Since we now dynamically allocate and free the

     * loopback device ensure this invariant is maintained by

     * keeping the loopback device as the first device on the

     * list of network devices.  Ensuring the loopback devices

     * is the first device that appears and the last network device

     * that disappears.

     */

    if (register_pernet_device(&loopback_net_ops))

        goto out;

 

    if (register_pernet_device(&default_device_ops))

        goto out;

 

    open_softirq(NET_TX_SOFTIRQ, net_tx_action);

    open_softirq(NET_RX_SOFTIRQ, net_rx_action);/* Called with irq disabled */

static inline void ____napi_schedule(struct softnet_data *sd,

                     struct napi_struct *napi)

{

    list_add_tail(&napi->poll_list, &sd->poll_list);

    __raise_softirq_irqoff(NET_RX_SOFTIRQ);

}       }

        goto enqueue;

    }

 

drop:

    sd->dropped++;

    rps_unlock(sd);

 

    local_irq_restore(flags);

 

    atomic_long_inc(&skb->dev->rx_dropped);

    kfree_skb(skb);

    return NET_RX_DROP;

}

 　　　　　　　　　　　　　　____napi_schedule(sd, &sd->backlog);//加入list 并激活软中断  ---等待被”调度“到执行

/*NAPI方式，把dev设备添加到了poll_list链表中。
每个网络设备（MAC层）都有自己的net_device数据结构，这个结构上有napi_struct。每当收到数据包时，网络设备驱动会把自己的napi_struct挂到CPU私有变量上。
这样在软中断时，net_rx_action会遍历cpu私有变量的poll_list，执行上面所挂的napi_struct结构的poll钩子函数,将数据包从驱动传到网络协议栈。

NAPI的napi_struct是自己构造的，该结构上的poll钩子函数也是自己定义的。
非NAPI的napi_struct结构是默认的，也就是per cpu的softnet_data>backlog，起poll钩子函数为process_backlog
*/