snull网络驱动程序（参考《Linux设备驱动程序第三版》）

snull网络设备驱动程序

头文件

/*
 * snull.h -- definitions for the network module
 *
 *
 */

#ifndef __SNULL_H__
#define __SNULL_H__


#define SNULL_RX_INTR 0x0001
#define SNULL_TX_INTR 0x0002
#define SNULL_TIMEOUT 5

struct snull_priv {
    struct net_device_stats stats;
    int status;
    int rx_packetlen;
    u8 *rx_packetdata;
    int tx_packetlen;
    u8 *tx_packetdata;
    struct sk_buff *skb;
    spinlock_t lock;
    struct net_device *dev;
};


#endif

驱动源码

/*
 * name:snull.c
 * function:the Simple Network Utility
 * time:2012-2-22
 *
 * author:txgcwm
 * mail:[e-mail]
 * reference:Linux设备驱动程序(第三版)
 */
#ifndef __KERNEL__
#  define __KERNEL__
#endif
#ifndef MODULE
#  define MODULE
#endif

#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/interrupt.h>
#include <linux/in.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/skbuff.h>
#include <linux/in6.h>
#include <asm/checksum.h>
#include "snull.h"


static int lockup = 0;
module_param(lockup,int,0);
static int timeout = SNULL_TIMEOUT;
module_param(timeout,int,0);
struct net_device *snull_devs[2];

void snull_tx_timeout(struct net_device *dev);



int snull_open(struct net_device *dev)
{
    /*在接口能够和外界通讯之前，要将硬件（MAC）从硬件设备复制到dev->dev_addr。硬件地址可在打开期间拷贝到设备中。snull软件接口在open时赋予硬件地址--它其实使用了一个长度为ETH_ALEN的ASCII字符串作为假的硬件地址，其中ETH_ALEN是以太网硬件地址的长度*/
    memcpy(dev->dev_addr, "\0SNUL0", ETH_ALEN);
    if(dev == snull_devs[1])
        dev->dev_addr[ETH_ALEN-1] ++;
    netif_start_queue(dev);    //一旦准备好开始发送数据后，open方法还应该启动接口的传输队列，允许接口接受传输包。

    return 0;
}

int snull_release(struct net_device *dev)
{
    netif_stop_queue(dev);    //在接口被关闭时，必须调用该函数，但该函数也可以用来临时停止传输。

    return 0;
}

int snull_config(struct net_device *dev, struct ifmap *map)
{
    if (dev->flags & IFF_UP)
        return -EBUSY;

    if (map->base_addr != dev->base_addr)
    {
        printk(KERN_WARNING "snull: Can't change I/O address\n");
        return -EOPNOTSUPP;
    }

    if (map->irq != dev->irq)
    {
        dev->irq = map->irq;
    }

    return 0;
}

void snull_rx(struct net_device *dev, int len, unsigned char *buf)
{
    struct sk_buff *skb;
    struct snull_priv *priv = netdev_priv(dev);

    skb = dev_alloc_skb(len+2);    //分配一个保存数据包的缓冲区
    if (!skb)
    {
        printk("snull rx: low on mem - packet dropped\n");
        priv->stats.rx_dropped++;
        return;
    }
    skb_reserve(skb, 2);
    memcpy(skb_put(skb, len), buf, len);    //skb_put函数刷新缓冲区内的数据末尾指针，并且返回新创建数据区的指针

    skb->dev = dev;
    skb->protocol = eth_type_trans(skb, dev);
    skb->ip_summed = CHECKSUM_UNNECESSARY;
    priv->stats.rx_packets++;
    priv->stats.rx_bytes += len;
    netif_rx(skb);    //将套接字缓冲区传递给上层软件处理

    return;
}

void snull_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
    int statusword;
    struct net_device *dev = (struct net_device *)dev_id;
    struct snull_priv *priv = netdev_priv(dev);

    if (!dev)
        return;

    spin_lock(&priv->lock);
    statusword = priv->status;
    priv->status = 0;
    if (statusword & SNULL_RX_INTR)
    {
        snull_rx(dev, priv->rx_packetlen, priv->rx_packetdata);
    }
    if (statusword & SNULL_TX_INTR)
    {
        priv->stats.tx_packets++;
        priv->stats.tx_bytes += priv->tx_packetlen;
        dev_kfree_skb(priv->skb);
    }
    spin_unlock(&priv->lock);

    return;
}

void snull_hw_tx(char *buf, int len, struct net_device *dev)
{
    struct iphdr *ih;
    struct net_device *dest;
    struct snull_priv *priv = netdev_priv(dev);
    u32 *saddr, *daddr;

    if (len < sizeof(struct ethhdr) + sizeof(struct iphdr))
    {
        printk("snull: Hmm... packet too short (%i octets)\n",len);
        return;
    }

    ih = (struct iphdr *)(buf+sizeof(struct ethhdr));
    saddr = &ih->saddr;
    daddr = &ih->daddr;
    ((u8 *)saddr)[2] ^= 1;
    ((u8 *)daddr)[2] ^= 1;
    ih->check = 0;
    ih->check = ip_fast_csum((unsigned char *)ih,ih->ihl);

    if (dev == snull_devs[0])
        printk(KERN_INFO"%08x:%05i --> %08x:%05i\n",
               ntohl(ih->saddr),ntohs(((struct tcphdr *)(ih+1))->source),
               ntohl(ih->daddr),ntohs(((struct tcphdr *)(ih+1))->dest));
    else
        printk(KERN_INFO"%08x:%05i <-- %08x:%05i\n",
               ntohl(ih->daddr),ntohs(((struct tcphdr *)(ih+1))->dest),
               ntohl(ih->saddr),ntohs(((struct tcphdr *)(ih+1))->source));

    dest = snull_devs[0] + (dev==snull_devs[0] ? 1 : 0);
    priv->status = SNULL_RX_INTR;
    priv->rx_packetlen = len;
    priv->rx_packetdata = buf;
    snull_interrupt(0, dest, NULL);

    priv->status = SNULL_TX_INTR;
    priv->tx_packetlen = len;
    priv->tx_packetdata = buf;
    if (lockup && ((priv->stats.tx_packets + 1) % lockup) == 0)
    {
        netif_stop_queue(dev);
        printk(KERN_INFO"Simulate lockup at %ld, txp %ld\n", jiffies,(unsigned long) priv->stats.tx_packets);
    }
    else
        snull_interrupt(0, dev, NULL);

    return;
}

int snull_tx(struct sk_buff *skb, struct net_device *dev)
{
    int len;
    char *data;
    struct snull_priv *priv = netdev_priv(dev);

    len = skb->len < ETH_ZLEN ? ETH_ZLEN : skb->len;    //当所需传输的数据包长度小于介质所支持的最小长度时，需要小心处理。
    data = skb->data;
    dev->trans_start = jiffies;
    priv->skb = skb;

    snull_hw_tx(data, len, dev);

    return 0;
}

void snull_tx_timeout (struct net_device *dev)
{
    struct snull_priv *priv = netdev_priv(dev);
    printk(KERN_INFO"Transmit timeout at %ld, latency %ld\n", jiffies,jiffies - dev->trans_start);

    priv->status = SNULL_TX_INTR;
    snull_interrupt(0, dev, NULL);
    priv->stats.tx_errors++;
    netif_wake_queue(dev);

    return;
}

int snull_ioctl(struct net_device *dev, struct ifreq *rq, int cmd)
{
    return 0;
}

struct net_device_stats *snull_stats(struct net_device *dev)
{
    struct snull_priv *priv = netdev_priv(dev);

    return &priv->stats;
}

int snull_rebuild_header(struct sk_buff *skb)
{
    struct ethhdr *eth = (struct ethhdr *) skb->data;
    struct net_device *dev = skb->dev;

    memcpy(eth->h_source, dev->dev_addr, dev->addr_len);
    memcpy(eth->h_dest, dev->dev_addr, dev->addr_len);
    eth->h_dest[ETH_ALEN-1]  ^= 0x01;

    return 0;
}

int snull_header(struct sk_buff *skb, struct net_device *dev,
                unsigned short type, const void *daddr, const void *saddr,
                unsigned int len)
{
    struct ethhdr *eth = (struct ethhdr *)skb_push(skb,ETH_HLEN);

    eth->h_proto = htons(type);
    memcpy(eth->h_source, saddr ? saddr : dev->dev_addr, dev->addr_len);
    memcpy(eth->h_dest,   daddr ? daddr : dev->dev_addr, dev->addr_len);
    eth->h_dest[ETH_ALEN-1]   ^= 0x01;

    return (dev->hard_header_len);
}

int snull_change_mtu(struct net_device *dev, int new_mtu)
{
    unsigned long flags;
    struct snull_priv *priv = netdev_priv(dev);
    spinlock_t *lock = &((struct snull_priv *)priv)->lock;

    if ((new_mtu < 68) || (new_mtu > 1500))    //以太网的MTU是1500个octet（ETH_DATA_LEN）
        return -EINVAL;

    spin_lock_irqsave(lock, flags);
    dev->mtu = new_mtu;
    spin_unlock_irqrestore(lock, flags);

    return 0;
}

//以下两个结构是相关接口函数的初始化
static const struct net_device_ops snull_dev_ops = {
    .ndo_open  = snull_open,
    .ndo_stop  = snull_release,
    .ndo_set_config = snull_config,
    .ndo_start_xmit = snull_tx,
    .ndo_do_ioctl = snull_ioctl,
    .ndo_get_stats = snull_stats,
    .ndo_change_mtu = snull_change_mtu,
    .ndo_tx_timeout = snull_tx_timeout,
};

static const struct header_ops snull_header_ops= {
    .create    = snull_header,
    .rebuild = snull_rebuild_header,
    .cache = NULL,
};

void snull_init(struct net_device *dev)
{
    struct snull_priv *priv = NULL;

    ether_setup(dev); //对某些成员作一些初始化

    dev->netdev_ops = &snull_dev_ops;
    dev->header_ops = &snull_header_ops;
    dev->watchdog_timeo = timeout;
    dev->flags |= IFF_NOARP;    //禁止ARP
      dev->features |= NETIF_F_NO_CSUM;

    priv = netdev_priv(dev);    //priv是net_device中的一个成员，它与net_device一起被分配，当需要访问私有成员priv时使用该函数
    memset(priv, 0, sizeof(struct snull_priv));
    priv->dev = dev;
    spin_lock_init(&((struct snull_priv *)priv)->lock);

    return;
}

static __init int snull_init_module(void)
{
    int result, i, device_present = 0;

    /*alloc_netdev用来动态分配struct net_device内核数据结构，第一个参数为驱动程序的“私有数据“，第二个是接口的名字，第三个是用来设置net_device结构的初始化函数。对于设备名称，如果驱动程序设置的名称中包含%d格式化字符串，register_netdev将使用一个数字代替它，使之成为唯一的名字，分配的编号从零开始。*/
    snull_devs[0] = alloc_netdev(sizeof(struct snull_priv),"sn%d",snull_init);
    snull_devs[1] = alloc_netdev(sizeof(struct snull_priv),"sn%d",snull_init);
    if(snull_devs[0] == NULL || snull_devs[1] == NULL)
        goto fail;

    for (i=0;i<2;i++)
    {
        //注册设备，必须在初始化一切事情后再注册
        if((result = register_netdev(snull_devs[i])))
            printk("snull: error %i registering device \"%s\"\n",result, snull_devs[i]->name);
        else
            device_present++;
    }

  fail:
    return device_present ? 0 : -ENODEV;
}

static __exit void snull_cleanup(void)
{
    int i;

    for (i=0; i<2;i++)
    {
        if(snull_devs[i])
        {
            unregister_netdev(snull_devs[i]);    //从系统中删除接口
            free_netdev(snull_devs[i]);    //将net_device结构返还给系统
        }
    }
    return;
}


module_init(snull_init_module);
module_exit(snull_cleanup);

MODULE_AUTHOR("txgcwm");
MODULE_VERSION("snull_v1.0");
MODULE_LICENSE("GPL");

Makefile

ifneq ($(KERNELRELEASE),)
    obj-m := snull.o
else
    KERNELDIR ?= /lib/modules/$(shell uname -r)/build
    PWD := $(shell pwd)
all:
    make -C $(KERNELDIR) M=$(PWD) modules
clean:
    rm -f *.ko *.o *.mod.o *.mod.c *.symvers *.order
endif

加载文件

#!/bin/sh

export PATH=/sbin:/bin

# Use a pathname, as new modutils don't look in the current dir by default
insmod ./snull.ko $*
ifconfig sn0 local0
ifconfig sn1 local1

# The route commands are needed for 2.0, not for later kernels
case "`uname -r`" in
    2.0.*)
        route add -net snullnet0 sn0
        route add -net snullnet1 sn1
        ;;
esac

卸载文件

#!/bin/sh

/sbin/ifconfig sn0 down
/sbin/ifconfig sn1 down
/sbin/rmmod snull

附件：     snull.rar