lvs源代码分析

/* After packet filtering, forward packet through VS/DR, VS/TUN,
   or VS/NAT(change destination), so that filtering rules can be
   applied to IPVS. */	
static struct nf_hook_ops ip_vs_in_ops = {
	.hook		= ip_vs_in,
	.owner		= THIS_MODULE,
	.pf		= PF_INET,
	.hooknum        = NF_IP_LOCAL_IN,
	.priority       = 100,
};

/* After packet filtering, change source only for VS/NAT */
static struct nf_hook_ops ip_vs_out_ops = {
	.hook		= ip_vs_out,
	.owner		= THIS_MODULE,
	.pf		= PF_INET,
	.hooknum        = NF_IP_FORWARD,
	.priority       = 100,
};

/* After packet filtering (but before ip_vs_out_icmp), catch icmp
   destined for 0.0.0.0/0, which is for incoming IPVS connections */
static struct nf_hook_ops ip_vs_forward_icmp_ops = {
	.hook		= ip_vs_forward_icmp,
	.owner		= THIS_MODULE,
	.pf		= PF_INET,
	.hooknum        = NF_IP_FORWARD,
	.priority       = 99,
};

/* Before the netfilter connection tracking, exit from POST_ROUTING */
static struct nf_hook_ops ip_vs_post_routing_ops = {
	.hook		= ip_vs_post_routing,
	.owner		= THIS_MODULE,
	.pf		= PF_INET,
	.hooknum        = NF_IP_POST_ROUTING,
	.priority       = NF_IP_PRI_NAT_SRC-1,
};

/*
 *	Check if it‘s for virtual services, look it up,
 *	and send it on its way...
 */
static unsigned int
ip_vs_in(unsigned int hooknum, struct sk_buff **pskb,
	 const struct net_device *in, const struct net_device *out,
	 int (*okfn)(struct sk_buff *))
{
	struct sk_buff	*skb = *pskb;
	struct iphdr	*iph;
	struct ip_vs_protocol *pp;
	struct ip_vs_conn *cp;
	int ret, restart;
	int ihl;

	/*
	 *	Big tappo: only PACKET_HOST (neither loopback nor mcasts)
	 *	... don‘t know why 1st test DOES NOT include 2nd (?)
	 */
        PACKET_HOST代表什么?
	PACKET_HOST代表本地的报文,即mac地址为本机网卡mac地址
	if (unlikely(skb->pkt_type != PACKET_HOST
		     || skb->dev == &loopback_dev || skb->sk)) {
		IP_VS_DBG(12, "packet type=%d proto=%d daddr=%d.%d.%d.%d ignored\n",
			  skb->pkt_type,
			  skb->nh.iph->protocol,
			  NIPQUAD(skb->nh.iph->daddr));
		return NF_ACCEPT;
	}

	iph = skb->nh.iph;
	if (unlikely(iph->protocol == IPPROTO_ICMP)) {
		int related, verdict = ip_vs_in_icmp(pskb, &related, hooknum);

		if (related)
			return verdict;
		skb = *pskb;
		iph = skb->nh.iph;
	}
        //此处为ip_vs_protol_init时注册的协议
	/* Protocol supported? */
	pp = ip_vs_proto_get(iph->protocol);
	if (unlikely(!pp))
		return NF_ACCEPT;

	ihl = iph->ihl << 2;

	/*
	 * Check if the packet belongs to an existing connection entry
	 */
       根据目的ip,查找此连接是否已经存在,或没有查找到则说明之前此连接并未建立过,需要为这个连接通过conn_schedule选择rserver.并将此连接信息存入ip_vs_conn_tab数组中.
	cp = pp->conn_in_get(skb, pp, iph, ihl, 0);
	if (unlikely(!cp)) {
		int v;
		if (!pp->conn_schedule(skb, pp, &v, &cp))
			return v;
	}

	if (unlikely(!cp)) {
		/* sorry, all this trouble for a no-hit :) */
		IP_VS_DBG_PKT(12, pp, skb, 0,
			      "packet continues traversal as normal");
		return NF_ACCEPT;
	}

	IP_VS_DBG_PKT(11, pp, skb, 0, "Incoming packet");

　　如果rserver状态异常则将连接删除(expire?),并将此报文丢弃.
	/* Check the server status */
	if (cp->dest && !(cp->dest->flags & IP_VS_DEST_F_AVAILABLE)) {
		/* the destination server is not available */

		if (sysctl_ip_vs_expire_nodest_conn) {
			/* try to expire the connection immediately */
			ip_vs_conn_expire_now(cp);
		}
		/* don‘t restart its timer, and silently
		   drop the packet. */
		__ip_vs_conn_put(cp);
		return NF_DROP;
	}

	ip_vs_in_stats(cp, skb);
	restart = ip_vs_set_state(cp, IP_VS_DIR_INPUT, skb, pp);
	//关键:根据不同的lvs模式(DR NAT等)将报文做不同的发送处理(ip_vs_conn_new->ip_vs_bind_xmit)
　　//例:DR模式调用ip_vs_dr_xmit,其中查询路由完成之后调用IP_VS_XMIT,走NF_IP_LOCAL_OUT进入netfilter框架处理.
	if (cp->packet_xmit)
		ret = cp->packet_xmit(skb, cp, pp);
		/* do not touch skb anymore */
	else {
		IP_VS_DBG_RL("warning: packet_xmit is null");
		ret = NF_ACCEPT;
	}

	/* increase its packet counter and check if it is needed
	   to be synchronized */
	atomic_inc(&cp->in_pkts);
	if ((ip_vs_sync_state & IP_VS_STATE_MASTER) &&
	    (cp->protocol != IPPROTO_TCP ||
	     cp->state == IP_VS_TCP_S_ESTABLISHED) &&
	    (atomic_read(&cp->in_pkts) % sysctl_ip_vs_sync_threshold[1]
	     == sysctl_ip_vs_sync_threshold[0]))
		ip_vs_sync_conn(cp);

	ip_vs_conn_put(cp);
	return ret;
}