网卡驱动设计---架构分析加回环网卡驱动设计（网卡驱动上）

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网卡驱动架构分析：

1. Linux网络子系统

2. 重要数据结构

总结一下三个重要的数据结构：

    2.1. net_device

    2.2. net_device_ops

    2.3. sk_buff

3. 网卡驱动架构分析

CS8900.c //早期2410使用的网卡芯片 

3.1. 网卡初始化

首先找到驱动程序的入口：

早期的驱动入口并不是module_init()函数，而是init_module，所以找到这个函数

int __init init_module(void)
{
	struct net_device *dev = alloc_etherdev(sizeof(struct net_local));
	struct net_local *lp;
	int ret = 0;

#if DEBUGGING
	net_debug = debug;
#else
	debug = 0;
#endif
	if (!dev)
		return -ENOMEM;

	dev->irq = irq;
	dev->base_addr = io;
	lp = netdev_priv(dev);

#if ALLOW_DMA
	if (use_dma) {
		lp->use_dma = use_dma;
		lp->dma = dma;
		lp->dmasize = dmasize;
	}
#endif

	spin_lock_init(&lp->lock);

        /* boy, they'd better get these right */
        if (!strcmp(media, "rj45"))
		lp->adapter_cnf = A_CNF_MEDIA_10B_T | A_CNF_10B_T;
	else if (!strcmp(media, "aui"))
		lp->adapter_cnf = A_CNF_MEDIA_AUI   | A_CNF_AUI;
	else if (!strcmp(media, "bnc"))
		lp->adapter_cnf = A_CNF_MEDIA_10B_2 | A_CNF_10B_2;
	else
		lp->adapter_cnf = A_CNF_MEDIA_10B_T | A_CNF_10B_T;

        if (duplex==-1)
		lp->auto_neg_cnf = AUTO_NEG_ENABLE;

        if (io == 0) {
                printk(KERN_ERR "cs89x0.c: Module autoprobing not allowed.\n");
                printk(KERN_ERR "cs89x0.c: Append io=0xNNN\n");
                ret = -EPERM;
		goto out;
        } else if (io <= 0x1ff) {
		ret = -ENXIO;
		goto out;
	}

第一步：分配net_device结构，

第二步：初始化net_device结构，

       dev->irq = irq;//分配中断号
	dev->base_addr = io;//设备基地址
	lp = netdev_priv(dev);

ret = cs89x0_probe1(dev, io, 1);\\这一步其实也是初始化硬件的！还有一部分是对device结构进行一些初始化

dev->netdev_ops = &net_ops; \\这个是对netdev_ops成员进行初始化

最后一步注册网卡驱动！上图中第二个红色箭头所指向的地方！

总结一下上图：

3.2. 网卡数据的发送

这个结合前面的经验，找到网卡的函数操作集结构：

可以看到这个成员函数的名字叫做：net_send_packet

static netdev_tx_t net_send_packet(struct sk_buff *skb,struct net_device *dev)
{
	struct net_local *lp = netdev_priv(dev);
	unsigned long flags;

	if (net_debug > 3) {
		printk("%s: sent %d byte packet of type %x\n",
			dev->name, skb->len,
			(skb->data[ETH_ALEN+ETH_ALEN] << 8) | skb->data[ETH_ALEN+ETH_ALEN+1]);
	}

	/* keep the upload from being interrupted, since we
                  ask the chip to start transmitting before the
                  whole packet has been completely uploaded. */

	spin_lock_irqsave(&lp->lock, flags);
	netif_stop_queue(dev);//1. 网卡驱动在向上层发送数据的时候暂时停止接收上层发来的数据

	/* initiate a transmit sequence */
	writeword(dev->base_addr, TX_CMD_PORT, lp->send_cmd);//2. 将skb中的数据写入寄存器
	writeword(dev->base_addr, TX_LEN_PORT, skb->len);

	/* Test to see if the chip has allocated memory for the packet */
	if ((readreg(dev, PP_BusST) & READY_FOR_TX_NOW) == 0) {
		/*
		 * Gasp!  It hasn't.  But that shouldn't happen since
		 * we're waiting for TxOk, so return 1 and requeue this packet.
		 */

		spin_unlock_irqrestore(&lp->lock, flags);
		if (net_debug) printk("cs89x0: Tx buffer not free!\n");
		return NETDEV_TX_BUSY;
	}
	/* Write the contents of the packet */
	writewords(dev->base_addr, TX_FRAME_PORT,skb->data,(skb->len+1) >>1);
	spin_unlock_irqrestore(&lp->lock, flags);
	dev->stats.tx_bytes += skb->len;
	dev_kfree_skb (skb);//3. 释放skb结构

        //发送数据完后，网卡会产生一个中断
	return NETDEV_TX_OK;
}

ret = request_irq(dev->irq, net_interrupt, 0, dev->name, dev);</span>

可以看到这里调用了net_initerupt函数，网卡发送和接收中断！

一个是发送中断，一个是接收中断，

netif_wake_queue(dev);/* Inform upper layers. */   // 这行代码表示在发送中断处理过程中，通知上层协议，可以再次向网卡传输数据。

3.3. 网卡数据的接收

网卡数据的接收入口是在中断中完成的，这个是从中断函数中可以看到net_interrupt

接收中断处理函数net_rx(dev)

/* We have a good packet(s), get it/them out of the buffers. */
static void
net_rx(struct net_device *dev)
{
	struct sk_buff *skb;
	int status, length;

	int ioaddr = dev->base_addr;
	status = readword(ioaddr, RX_FRAME_PORT);//读取寄存器，网卡接收状态
	length = readword(ioaddr, RX_FRAME_PORT);//网卡接收字节长度

	if ((status & RX_OK) == 0) {
		count_rx_errors(status, dev);
		return;
	}

	/* Malloc up new buffer. */
	skb = dev_alloc_skb(length + 2);//分配skb结构 +2字节空间是为头预留的
	if (skb == NULL) {
#if 0		/* Again, this seems a cruel thing to do */
		printk(KERN_WARNING "%s: Memory squeeze, dropping packet.\n", dev->name);
#endif
		dev->stats.rx_dropped++;
		return;
	}
	skb_reserve(skb, 2);	/* longword align L3 header */

	readwords(ioaddr, RX_FRAME_PORT, skb_put(skb, length), length >> 1);//将收到的数据填充入skb
	if (length & 1)
		skb->data[length-1] = readword(ioaddr, RX_FRAME_PORT);

	if (net_debug > 3) {
		printk(	"%s: received %d byte packet of type %x\n",
			dev->name, length,
			(skb->data[ETH_ALEN+ETH_ALEN] << 8) | skb->data[ETH_ALEN+ETH_ALEN+1]);
	}

        skb->protocol=eth_type_trans(skb,dev);
	netif_rx(skb);//将skb提交到协议栈
	dev->stats.rx_packets++;
	dev->stats.rx_bytes += length;
}

回环网卡驱动设计：

使用ifocnfig,可以看到除了eth0还有一个l0， eth0代表的是一个物理网卡，l0代表的就是回环网卡，从上面的打印信息可以看到l0的IP地址是127.0.0.1，可以看到当ping 127.0.0.x的时候能ping通，其实l0就是网卡的tx和rx在软件层的短接！所以才叫做回环网卡！

其实内核代码中也可以找到回环网卡的驱动！Lookback.c

这个文件中的代码部分其实不是内核模块，而是由其它部分的调用的！

删掉内核代码中的原有的loopback.c，结合上面的的分析和原有源码的分析重写编写loopback.c，

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/if_ether.h>	/* For the statistics structure. */


unsigned long bytes = 0;
unsigned long packets = 0;//skb包


static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)//数据发送
{

	skb->protocol = eth_type_trans(skb,dev);//表明skb包的协议 以太网协议


	bytes += skb->len;//发送的数据量
	packets++; //发送的数据包也要加一

	netif_rx(skb);//将skb向回送， 回环网卡驱动就是这实现的，这是很关键的一步

	return 0;
}

static struct net_device_stats *loopback_get_stats(struct net_device *dev)//获取网卡状态
{
	struct net_device_stats *stats = &dev->stats;//首先把state这个成员取出来
	
	stats->rx_packets = packets;//表示网卡收到了多少个包
	stats->tx_packets = packets;//表示网卡发送了多少个包
	stats->rx_bytes = bytes;//表示网卡接收到了多少个字节
	stats->tx_bytes = bytes;
	return stats;//返回状态
}

static const struct net_device_ops loopback_ops = {//定义一个net_device_ops 结构
	.ndo_start_xmit= loopback_xmit,//发送指针
	.ndo_get_stats = loopback_get_stats,//获取网卡状态的函数
};


static void loopback_setup(struct net_device *dev)//初始化设置操作
{
	dev->mtu	= (16 * 1024) + 20 + 20 + 12;//网卡最大接收包的尺寸：16K + TCP头 + IP头 + 以太网头
	dev->flags		= IFF_LOOPBACK;//回环网卡专有标志 这是一个宏内核代码可查
	dev->header_ops		= ð_header_ops;//这个是网络包的函数操作集，内核可以看这个成员的数据结构
	dev->netdev_ops		= &loopback_ops;//网卡所支持操作的集合

}


static __net_init int loopback_net_init(struct net *net)
{
	struct net_device *dev;
	int err;
	err = -ENOMEM;
	dev = alloc_netdev(0, "lo", loopback_setup);//分配一个net_device结构，loopback为一个初始化函数
	if (!dev)
		goto out;

	err = register_netdev(dev);//注册网卡驱动程序
	if (err)
		goto out_free_netdev;

	net->loopback_dev = dev;
	return 0;


out_free_netdev:
	free_netdev(dev);
out:
	if (net == &init_net)
		panic("loopback: Failed to register netdevice: %d\n", err);
	return err;
}

static __net_exit void loopback_net_exit(struct net *net)
{
	struct net_device *dev = net->loopback_dev;

	unregister_netdev(dev);//注销网卡驱动程序
}

/* Registered in net/core/dev.c */
struct pernet_operations __net_initdata loopback_net_ops = {
       .init = loopback_net_init,
       .exit = loopback_net_exit,
};
</span>

上面的回环网卡驱动有点问题，ping不同！

这是能ping通的内核自带的源码：

#include <linux/kernel.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/errno.h>
#include <linux/fcntl.h>
#include <linux/in.h>
#include <linux/init.h>

#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/io.h>

#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/ethtool.h>
#include <net/sock.h>
#include <net/checksum.h>
#include <linux/if_ether.h>	/* For the statistics structure. */
#include <linux/if_arp.h>	/* For ARPHRD_ETHER */
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/percpu.h>
#include <net/net_namespace.h>
#include <linux/u64_stats_sync.h>

struct pcpu_lstats {
	u64			packets;
	u64			bytes;
	struct u64_stats_sync	syncp;
};

/*
 * The higher levels take care of making this non-reentrant (it's
 * called with bh's disabled).
 */
static netdev_tx_t loopback_xmit(struct sk_buff *skb,
				 struct net_device *dev)
{
	struct pcpu_lstats *lb_stats;
	int len;

	skb_orphan(skb);

	skb->protocol = eth_type_trans(skb, dev);

	/* it's OK to use per_cpu_ptr() because BHs are off */
	lb_stats = this_cpu_ptr(dev->lstats);

	len = skb->len;
	if (likely(netif_rx(skb) == NET_RX_SUCCESS)) {
		u64_stats_update_begin(&lb_stats->syncp);
		lb_stats->bytes += len;
		lb_stats->packets++;
		u64_stats_update_end(&lb_stats->syncp);
	}

	return NETDEV_TX_OK;
}

static struct rtnl_link_stats64 *loopback_get_stats64(struct net_device *dev,
						      struct rtnl_link_stats64 *stats)
{
	u64 bytes = 0;
	u64 packets = 0;
	int i;

	for_each_possible_cpu(i) {
		const struct pcpu_lstats *lb_stats;
		u64 tbytes, tpackets;
		unsigned int start;

		lb_stats = per_cpu_ptr(dev->lstats, i);
		do {
			start = u64_stats_fetch_begin(&lb_stats->syncp);
			tbytes = lb_stats->bytes;
			tpackets = lb_stats->packets;
		} while (u64_stats_fetch_retry(&lb_stats->syncp, start));
		bytes   += tbytes;
		packets += tpackets;
	}
	stats->rx_packets = packets;
	stats->tx_packets = packets;
	stats->rx_bytes   = bytes;
	stats->tx_bytes   = bytes;
	return stats;
}

static u32 always_on(struct net_device *dev)
{
	return 1;
}

static const struct ethtool_ops loopback_ethtool_ops = {
	.get_link		= always_on,
};

static int loopback_dev_init(struct net_device *dev)
{
	dev->lstats = alloc_percpu(struct pcpu_lstats);
	if (!dev->lstats)
		return -ENOMEM;

	return 0;
}

static void loopback_dev_free(struct net_device *dev)
{
	free_percpu(dev->lstats);
	free_netdev(dev);
}

static const struct net_device_ops loopback_ops = {
	.ndo_init      = loopback_dev_init,
	.ndo_start_xmit= loopback_xmit,
	.ndo_get_stats64 = loopback_get_stats64,
};

/*
 * The loopback device is special. There is only one instance
 * per network namespace.
 */
static void loopback_setup(struct net_device *dev)
{
	dev->mtu		= (16 * 1024) + 20 + 20 + 12;
	dev->hard_header_len	= ETH_HLEN;	/* 14	*/
	dev->addr_len		= ETH_ALEN;	/* 6	*/
	dev->tx_queue_len	= 0;
	dev->type		= ARPHRD_LOOPBACK;	/* 0x0001*/
	dev->flags		= IFF_LOOPBACK;
	dev->priv_flags	       &= ~IFF_XMIT_DST_RELEASE;
	dev->hw_features	= NETIF_F_ALL_TSO | NETIF_F_UFO;
	dev->features 		= NETIF_F_SG | NETIF_F_FRAGLIST
		| NETIF_F_ALL_TSO
		| NETIF_F_UFO
		| NETIF_F_NO_CSUM
		| NETIF_F_RXCSUM
		| NETIF_F_HIGHDMA
		| NETIF_F_LLTX
		| NETIF_F_NETNS_LOCAL
		| NETIF_F_VLAN_CHALLENGED
		| NETIF_F_LOOPBACK;
	dev->ethtool_ops	= &loopback_ethtool_ops;
	dev->header_ops		= ð_header_ops;
	dev->netdev_ops		= &loopback_ops;
	dev->destructor		= loopback_dev_free;
}

/* Setup and register the loopback device. */
static __net_init int loopback_net_init(struct net *net)
{
	struct net_device *dev;
	int err;

	err = -ENOMEM;
	dev = alloc_netdev(0, "lo", loopback_setup);
	if (!dev)
		goto out;

	dev_net_set(dev, net);
	err = register_netdev(dev);
	if (err)
		goto out_free_netdev;

	net->loopback_dev = dev;
	return 0;


out_free_netdev:
	free_netdev(dev);
out:
	if (net_eq(net, &init_net))
		panic("loopback: Failed to register netdevice: %d\n", err);
	return err;
}

/* Registered in net/core/dev.c */
struct pernet_operations __net_initdata loopback_net_ops = {
       .init = loopback_net_init,
};

自己将两份源码对照着看了，暂时还没找出原因，这里先上一张错误的截图以及我认为出错的原因

网卡驱动设计---架构分析加回环网卡驱动设计（网卡驱动上）

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原文地址：http://blog.csdn.net/coding__madman/article/details/51520052