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链路层收包

分析网络数据包怎样从中断(链路层)中拷贝到上层 netif_rx_internal


 

链路层收包_软中断

 

 

//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

链路层收包_钩子函数_02链路层收包_软中断_03

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);

View Code

               ____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
*/

链路层收包_钩子函数_02链路层收包_软中断_03

/* 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);
}

View Code

 

}
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;
}

 

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