首页 > 代码库 > Linux内核--网络栈实现分析(十一)--驱动程序层(下)
Linux内核--网络栈实现分析(十一)--驱动程序层(下)
本文分析基于Linux Kernel 1.2.13
原创作品,转载请标明http://blog.csdn.net/yming0221/article/details/7555870
更多请查看专栏,地址http://blog.csdn.net/column/details/linux-kernel-net.html
作者:闫明
注:标题中的”(上)“,”(下)“表示分析过程基于数据包的传递方向:”(上)“表示分析是从底层向上分析、”(下)“表示分析是从上向下分析。
在博文Linux内核--网络栈实现分析(三)--驱动程序层(链路层)(上)中对网络设备结构,网络设备初始化等函数有了初步认识,并列出了设备的发送和接收函数。
设备接口层会调用函数设备驱动层ei_start_xmit()函数发送数据,这里没有详细分析。
[cpp] view plaincopy
- static int ei_start_xmit(struct sk_buff *skb, struct device *dev)
- {
- int e8390_base = dev->base_addr;
- struct ei_device *ei_local = (struct ei_device *) dev->priv;//取出网卡设备的私有数据,和具体的网卡型号有关,在ethdev_init()函数中已经分配空间
- int length, send_length;
- unsigned long flags;
- /*
- * We normally shouldn‘t be called if dev->tbusy is set, but the
- * existing code does anyway. If it has been too long since the
- * last Tx, we assume the board has died and kick it.
- */
- if (dev->tbusy) { /* Do timeouts, just like the 8003 driver. */
- ........................................
- ........................................
- }
- /* Sending a NULL skb means some higher layer thinks we‘ve missed an
- tx-done interrupt. Caution: dev_tint() handles the cli()/sti()
- itself. */
- if (skb == NULL) {//该条件似乎不会发生,这用于处理内核中的BUG
- dev_tint(dev);//发送设备中的所有缓存的数据包
- return 0;
- }
- length = skb->len;
- if (skb->len <= 0)
- return 0;
- save_flags(flags);
- cli();
- /* Block a timer-based transmit from overlapping. */
- if ((set_bit(0, (void*)&dev->tbusy) != 0) || ei_local->irqlock) {
- printk("%s: Tx access conflict. irq=%d lock=%d tx1=%d tx2=%d last=%d\n",
- dev->name, dev->interrupt, ei_local->irqlock, ei_local->tx1,
- ei_local->tx2, ei_local->lasttx);
- restore_flags(flags);
- return 1;
- }
- /* Mask interrupts from the ethercard. */
- outb(0x00, e8390_base + EN0_IMR);
- ei_local->irqlock = 1;
- restore_flags(flags);
- send_length = ETH_ZLEN < length ? length : ETH_ZLEN;
- if (ei_local->pingpong) {
- int output_page;
- if (ei_local->tx1 == 0) {
- output_page = ei_local->tx_start_page;
- ei_local->tx1 = send_length;
- if (ei_debug && ei_local->tx2 > 0)
- printk("%s: idle transmitter tx2=%d, lasttx=%d, txing=%d.\n",
- dev->name, ei_local->tx2, ei_local->lasttx,
- ei_local->txing);
- } else if (ei_local->tx2 == 0) {
- output_page = ei_local->tx_start_page + 6;
- ei_local->tx2 = send_length;
- if (ei_debug && ei_local->tx1 > 0)
- printk("%s: idle transmitter, tx1=%d, lasttx=%d, txing=%d.\n",
- dev->name, ei_local->tx1, ei_local->lasttx,
- ei_local->txing);
- } else { /* We should never get here. */
- if (ei_debug)
- printk("%s: No Tx buffers free. irq=%d tx1=%d tx2=%d last=%d\n",
- dev->name, dev->interrupt, ei_local->tx1,
- ei_local->tx2, ei_local->lasttx);
- ei_local->irqlock = 0;
- dev->tbusy = 1;
- outb_p(ENISR_ALL, e8390_base + EN0_IMR);
- return 1;
- }
- ei_block_output(dev, length, skb->data, output_page);
- if (! ei_local->txing) {
- ei_local->txing = 1;
- NS8390_trigger_send(dev, send_length, output_page);
- dev->trans_start = jiffies;
- if (output_page == ei_local->tx_start_page)
- ei_local->tx1 = -1, ei_local->lasttx = -1;
- else
- ei_local->tx2 = -1, ei_local->lasttx = -2;
- } else
- ei_local->txqueue++;
- dev->tbusy = (ei_local->tx1 && ei_local->tx2);
- } else { /* No pingpong, just a single Tx buffer. */
- ei_block_output(dev, length, skb->data, ei_local->tx_start_page);
- ei_local->txing = 1;
- NS8390_trigger_send(dev, send_length, ei_local->tx_start_page);
- dev->trans_start = jiffies;
- dev->tbusy = 1;
- }
- /* Turn 8390 interrupts back on. */
- ei_local->irqlock = 0;
- outb_p(ENISR_ALL, e8390_base + EN0_IMR);
- dev_kfree_skb (skb, FREE_WRITE);
- return 0;
其中的dev_tint()函数是将设备的所有缓存队列中的数据全部调用dev_queue_xmit()发送全部数据包。
[cpp] view plaincopy
- /*
- * This routine is called when an device driver (i.e. an
- * interface) is ready to transmit a packet.
- */
- //该函数功能:遍历设备的缓冲队列,对所有的数据包调用dev_queue_xmit()函数发送数据
- void dev_tint(struct device *dev)
- {
- int i;
- struct sk_buff *skb;
- unsigned long flags;
- save_flags(flags);
- /*
- * Work the queues in priority order
- */
- for(i = 0;i < DEV_NUMBUFFS; i++)
- {
- /*
- * Pull packets from the queue
- */
- cli();
- while((skb=skb_dequeue(&dev->buffs[i]))!=NULL)
- {
- /*
- * Stop anyone freeing the buffer while we retransmit it
- */
- skb_device_lock(skb);
- restore_flags(flags);
- /*
- * Feed them to the output stage and if it fails
- * indicate they re-queue at the front.
- */
- dev_queue_xmit(skb,dev,-i - 1);//注意优先级的计算方式,在函数dev_queue_xmit()中优先级若<0则计算pri=-pri-1=-(-i-1)-1=i,
- //这样做的目的就是为了得到正确的where值,函数(dev_queue_xmit())中
- /*
- * If we can take no more then stop here.
- */
- if (dev->tbusy)
- return;
- cli();
- }
- }
- restore_flags(flags);
- }
驱动层严格的说不属于内核网络栈的内容,和硬件关系密切,何况这种网卡硬件设备可能已经不用了,这里就没有详细分析,如果对网卡驱动有兴趣可以看一下之前的分析的ARM-Linux下的DM9000网卡驱动的分析,链接如下:
- ARM-Linux驱动--DM9000网卡驱动分析(一)
- ARM-Linux驱动--DM9000网卡驱动分析(二)
- ARM-Linux驱动--DM9000网卡驱动分析(三)
- ARM-Linux驱动--DM9000网卡驱动分析(四)
Linux内核--网络栈实现分析(十一)--驱动程序层(下)
声明:以上内容来自用户投稿及互联网公开渠道收集整理发布,本网站不拥有所有权,未作人工编辑处理,也不承担相关法律责任,若内容有误或涉及侵权可进行投诉: 投诉/举报 工作人员会在5个工作日内联系你,一经查实,本站将立刻删除涉嫌侵权内容。