a software switch written with the netfilter framework

Makefile

obj-m += switch.o
 
all:
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
 
clean:
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clear

switch.c

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/ip.h>
#include <linux/netdevice.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/skbuff.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/string.h>
#include <linux/ipv6.h>
#include <linux/inet.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("lijin liu<llj098@gmail.com>");
MODULE_DESCRIPTION("Software switch");

static struct nf_hook_ops netfilter_ops_in;/* IP PRE ROUTING */
struct tcphdr *tcp_header;
struct sk_buff *sock_buff;
struct iphdr *ip_header;
int sadd,dadd,bit1,bit2,bit3,bit4;
struct net_device *dev;
char *in_face = "eth0";
char *out_face = "eth1";

void log_ip(int sadd,int dadd)
{
	int b1,b2,b3,b4;
	b1 = 255 & sadd;
	b2 = (0xff00 & sadd) >> 8;
	b3 = (0xff0000 & sadd) >> 16;
	b4 = (0xff000000 &sadd) >>24;

	printk("sw:Source IP: %d.%d.%d.%d",b1,b2,b3,b4);

	b1 = 255 & dadd;
	b2 = (0xff00 & dadd) >> 8;
	b3 = (0xff0000 & dadd) >> 16;
	b4 = (0xff000000 & dadd) >>24;

	printk(" sw: Destination IP: %d.%d.%d.%d",b1,b2,b3,b4);
}

unsigned int main_hook(unsigned int hooknum,
		const struct sk_buff *skb,
		const struct net_device *in,
		const struct net_device *out,
		int(*okfn)(struct sk_buff*))
{
	printk("sw:----------------------------------\n");

	sock_buff = skb_copy(skb,GFP_ATOMIC);
	ip_header = (struct iphdr*)(sock_buff->network_header);
	log_ip(ip_header->saddr,ip_header->daddr);
	
	printk("sw: dev->name is %s\n",sock_buff->dev);

	for_each_netdev(&init_net,dev){
		if(strcmp(dev->name,in_face) == 0){

			printk("sw: in face\n");
			sock_buff->dev = out_face;
			break;
		}
		else if(strcmp(dev->name,out_face) ==0){
			printk("sw: out face\n");
			sock_buff->dev = in_face;
			break;
		}
	}

	printk("sw:----------------------------------\n");
	return NF_ACCEPT;
}

/*check the package wether should pass though*/
int package_passthough(struct sk_buff *skbuff)
{
	return 1;
}

int init_module(void)
{
	netfilter_ops_in.hook = main_hook;
	netfilter_ops_in.pf = PF_INET;
	netfilter_ops_in.hooknum= NF_INET_PRE_ROUTING;
	netfilter_ops_in.priority=NF_IP_PRI_FIRST;

	nf_register_hook(&netfilter_ops_in);

	printk(KERN_INFO "sw: init_module() called\n");
	return 0;
}
 
void cleanup_module(void)
{
	printk(KERN_INFO "sw: cleanup_module() called\n");
	nf_unregister_hook(&netfilter_ops_in);
	printk(KERN_INFO "sw: hook unregisted, quit called\n");
}