内核函数之fib_add_ifaddr()

在通过ifconfig eth0 xxx 修改ip地址的时候内核流程为:

fib_inetaddr_notifier{}:fib_inetaddr_event->fib_add_ifaddr()

在此我们已ifconfig eth0 192.168.11.103为例子看一下fib_add_ifaddr的执行过程

//ifconfig eth0 192.168.11.103
void fib_add_ifaddr(struct in_ifaddr *ifa)
{
	struct in_device *in_dev = ifa->ifa_dev;
	struct net_device *dev = in_dev->dev;
	struct in_ifaddr *prim = ifa;
	__be32 mask = ifa->ifa_mask;//00ffffff
	__be32 addr = ifa->ifa_local;//670ba8c0 =ifa_address
	__be32 prefix = ifa->ifa_address&mask;//00ffffff & 670ba8c0=000ba8c0

    //如果flag参数指定了配置IP对象为从属设备或者临时设备
	if (ifa->ifa_flags&IFA_F_SECONDARY) 
	{
		//但是根据索引找不到该设备，返回错误 
		prim = inet_ifa_byprefix(in_dev, prefix, mask);
		if (prim == NULL) 
		{
			printk(KERN_WARNING "fib_add_ifaddr: bug: prim == NULL\n");
			return;
		}
	}
    //通过ifconfig eth0 192.168.11.103  将192.168.11.103加入local表中
	//在local表中添加路由表项
	fib_magic(RTM_NEWROUTE, RTN_LOCAL, addr, 32, prim);

	//设备是否在运行
	if (!(dev->flags & IFF_UP))
		return;

	/* Add broadcast address, if it is explicitly assigned. */
	//通过ifconfig eth0 192.168.11.103
	//广播地址为ifa->ifa_broadcast=ff0ba8c0
	if (ifa->ifa_broadcast && ifa->ifa_broadcast != htonl(0xFFFFFFFF))
		fib_magic(RTM_NEWROUTE, RTN_BROADCAST, ifa->ifa_broadcast, 32, prim);

    //htonl(0xff000000) & 000ba8c0 == 0为假
	if (!ipv4_is_zeronet(prefix) && !(ifa->ifa_flags&IFA_F_SECONDARY) &&
	    (prefix != addr || ifa->ifa_prefixlen < 32)) 
	{  
	    //将192.168.11.0/24加入到MAIN表中
		fib_magic(RTM_NEWROUTE, 
			      dev->flags&IFF_LOOPBACK ? RTN_LOCAL: RTN_UNICAST , //RTN_UNICAST
			      prefix, //192.168.11.0
			      ifa->ifa_prefixlen, //24
			      prim);

		/* Add network specific broadcasts, when it takes a sense */
        //ifconfig eth0 192.168.11.103 掩码长度24
		if (ifa->ifa_prefixlen < 31) 
		{
			fib_magic(RTM_NEWROUTE, RTN_BROADCAST, prefix, 32, prim);//192.168.11.0 加入到local表
			fib_magic(RTM_NEWROUTE, RTN_BROADCAST, prefix|~mask, 32, prim);
		}                                          // 000ba8c0 | 11000000 =192.168.11.255加入到local表
	}
}

 fib_add_ifaddr()调用之前main表和local表

 

执行ifconfig eth1 192.168.1.2后路由表main表和local表的变化内核通过fib_add_ifaddr()将路由项加入路由表中