网络子系统63_路由子系统处理netlink事件

//	路由子系统netlink控制块
//		在ip_rt_init->devinet_init中注册。
1.1 static struct rtnetlink_link inet_rtnetlink_table[RTM_MAX - RTM_BASE + 1] = {
	 [4] = { .doit	 = inet_rtm_newaddr,  },
	 [5] = { .doit	 = inet_rtm_deladdr,  },
	 [6] = { .dumpit = inet_dump_ifaddr,  },
	 [8] = { .doit	 = inet_rtm_newroute, },
	 [9] = { .doit	 = inet_rtm_delroute, },
	[10] = { .doit	 = inet_rtm_getroute, .dumpit = inet_dump_fib, },
#ifdef CONFIG_IP_MULTIPLE_TABLES
	[16] = { .doit	 = inet_rtm_newrule, },
	[17] = { .doit	 = inet_rtm_delrule, },
	[18] = { .dumpit = inet_dump_rules,  },
#endif
};

//	为设备配置ip地址
//	函数主要任务：
//		1.检查有效性
//			1.1 网络部分<=32，提供了ip地址
//		2.分配in_ifaddr并填充信息
//		3.将in_ifaddr插入到in_device中

1.2 static int inet_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
{
	struct rtattr **rta = arg;
	struct net_device *dev;
	struct in_device *in_dev;
	struct ifaddrmsg *ifm = NLMSG_DATA(nlh);
	struct in_ifaddr *ifa;
	int rc = -EINVAL;
	// 有效性检查
	//	网路地址部分 <= 32
	if (ifm->ifa_prefixlen > 32 || !rta[IFA_LOCAL - 1])
		goto out;

	rc = -ENODEV;
	//通过设备index获取设备描述符
	if ((dev = __dev_get_by_index(ifm->ifa_index)) == NULL)
		goto out;

	rc = -ENOBUFS;
	//获取设备配置信息
	if ((in_dev = __in_dev_get(dev)) == NULL) {
		//第一次配置设备，则创建配置信息
		in_dev = inetdev_init(dev);
	}
	//分配ip地址
	if ((ifa = inet_alloc_ifa()) == NULL)
		goto out;
	//如果地址指派给隧道接口：
	//	ifa->ifa_local为隧道的本地地址，ifa->ifa_address为远程地址
	//否则：
	// ifa->ifa_local, ifa->ifa_address均为本地地址
	if (!rta[IFA_ADDRESS - 1])
		rta[IFA_ADDRESS - 1] = rta[IFA_LOCAL - 1];
	memcpy(&ifa->ifa_local, RTA_DATA(rta[IFA_LOCAL - 1]), 4);
	memcpy(&ifa->ifa_address, RTA_DATA(rta[IFA_ADDRESS - 1]), 4);
	//网络地址部分
	ifa->ifa_prefixlen = ifm->ifa_prefixlen;
	//掩码
	ifa->ifa_mask = inet_make_mask(ifm->ifa_prefixlen);
	//广播地址
	if (rta[IFA_BROADCAST - 1])
		memcpy(&ifa->ifa_broadcast,
		       RTA_DATA(rta[IFA_BROADCAST - 1]), 4);
	//选播地址
	if (rta[IFA_ANYCAST - 1])
		memcpy(&ifa->ifa_anycast, RTA_DATA(rta[IFA_ANYCAST - 1]), 4);
	//ifa_flags标示主辅地址
	ifa->ifa_flags = ifm->ifa_flags;
	ifa->ifa_scope = ifm->ifa_scope;
	in_dev_hold(in_dev);
	ifa->ifa_dev   = in_dev;
	//设备别名
	if (rta[IFA_LABEL - 1])
		rtattr_strlcpy(ifa->ifa_label, rta[IFA_LABEL - 1], IFNAMSIZ);
	else
		memcpy(ifa->ifa_label, dev->name, IFNAMSIZ);
	//将新地址插入到in_device中
	rc = inet_insert_ifa(ifa);
out:
	return rc;
}

//	删除设备ip地址
//	函数主要任务：
//		1.获取设备的配置描述符in_device
//		2.从配置描述符中删除ip信息
1.3 static int inet_rtm_deladdr(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
{
	struct rtattr **rta = arg;
	struct in_device *in_dev;
	struct ifaddrmsg *ifm = NLMSG_DATA(nlh);
	struct in_ifaddr *ifa, **ifap;
	//获取设备描述
	if ((in_dev = inetdev_by_index(ifm->ifa_index)) == NULL)
		goto out;
	__in_dev_put(in_dev);

	for (ifap = &in_dev->ifa_list; (ifa = *ifap) != NULL;
	     ifap = &ifa->ifa_next) {
		if ((rta[IFA_LOCAL - 1] &&
		     memcmp(RTA_DATA(rta[IFA_LOCAL - 1]),
			    &ifa->ifa_local, 4)) ||
		    (rta[IFA_LABEL - 1] &&
		     rtattr_strcmp(rta[IFA_LABEL - 1], ifa->ifa_label)) ||
		    (rta[IFA_ADDRESS - 1] &&
		     (ifm->ifa_prefixlen != ifa->ifa_prefixlen ||
		      !inet_ifa_match(*(u32*)RTA_DATA(rta[IFA_ADDRESS - 1]),
			      	      ifa))))
			continue;
		//从in_device 删除配置的ip地址
		inet_del_ifa(in_dev, ifap, 1);
		return 0;
	}
out:
	return -EADDRNOTAVAIL;
}

//	添加路由
//		通过id选择路由表，通过特定于路由表的回调函数添加路由项
1.4 int inet_rtm_newroute(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
{
	struct fib_table * tb;
	struct rtattr **rta = arg;
	struct rtmsg *r = NLMSG_DATA(nlh);

	if (inet_check_attr(r, rta))
		return -EINVAL;
	//根据指定的id，选择路由表
	tb = fib_new_table(r->rtm_table);
	if (tb)	//有路由表的回调函数添加一条新路由
		return tb->tb_insert(tb, r, (struct kern_rta*)rta, nlh, &NETLINK_CB(skb));
	return -ENOBUFS;
}

//	获取路由信息
//	函数主要任务：
//		1.指定了入口设备，通过ip_route_input路由数据包，获取路由信息
//		2.否则通过出口路由，获取路由信息
//		3.将获取的路由信息通过netlink应答
1.5 int inet_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr* nlh, void *arg)
{
	struct rtattr **rta = arg;
	struct rtmsg *rtm = NLMSG_DATA(nlh);
	struct rtable *rt = NULL;
	u32 dst = 0;
	u32 src = 0;
	int iif = 0;
	int err = -ENOBUFS;
	struct sk_buff *skb;

	skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
	if (!skb)
		goto out;

	skb->mac.raw = skb->data;
	skb_reserve(skb, MAX_HEADER + sizeof(struct iphdr));

	if (rta[RTA_SRC - 1])
		memcpy(&src, RTA_DATA(rta[RTA_SRC - 1]), 4);
	if (rta[RTA_DST - 1])
		memcpy(&dst, RTA_DATA(rta[RTA_DST - 1]), 4);
	if (rta[RTA_IIF - 1])
		memcpy(&iif, RTA_DATA(rta[RTA_IIF - 1]), sizeof(int));
	//入口路由
	if (iif) {
		struct net_device *dev = __dev_get_by_index(iif);
		err = -ENODEV;
		if (!dev)
			goto out_free;
		skb->protocol	= htons(ETH_P_IP);
		skb->dev	= dev;
		local_bh_disable();
		//路由此skb，获取路由信息
		err = ip_route_input(skb, dst, src, rtm->rtm_tos, dev);
		local_bh_enable();
		rt = (struct rtable*)skb->dst;
		if (!err && rt->u.dst.error)
			err = -rt->u.dst.error;
	//出口路由
	} else {
		//构造查找关键字
		struct flowi fl = { .nl_u = { .ip4_u = { .daddr = dst,
							 .saddr = src,
							 .tos = rtm->rtm_tos } } };
		int oif = 0;
		//出口设备
		if (rta[RTA_OIF - 1])
			memcpy(&oif, RTA_DATA(rta[RTA_OIF - 1]), sizeof(int));
		fl.oif = oif;
		//出口路由
		err = ip_route_output_key(&rt, &fl);
	}
	if (err)
		goto out_free;

	skb->dst = &rt->u.dst;
	if (rtm->rtm_flags & RTM_F_NOTIFY)
		rt->rt_flags |= RTCF_NOTIFY;
	//netlink控制块
	NETLINK_CB(skb).dst_pid = NETLINK_CB(in_skb).pid;

	err = rt_fill_info(skb, NETLINK_CB(in_skb).pid, nlh->nlmsg_seq,
				RTM_NEWROUTE, 0);
	//通过netlink应答
	err = netlink_unicast(rtnl, skb, NETLINK_CB(in_skb).pid, MSG_DONTWAIT);
	if (err > 0)
		err = 0;
out:	return err;

out_free:
	kfree_skb(skb);
	goto out;
}