TCP listen socket inet_lookup_listener

 netstat -atnp |grep 8080
tcp        0      0 192.168.1.208:8080      0.0.0.0:*               LISTEN      109094/server       
tcp6       0      0 :::8080                 :::*                    LISTEN      109094/server  

在linux 3.9 后引入reuseport 就引入如上问题。sk_A和sk_B同时侦听8080端口；有时tcp syn进入去查找listen socket时，希望匹配到192.168.1.208:8080的sock；

但是由于当前使用的是port进行hash；最后不是自己想要的！

所以必须对内核lookup listener 进行改造，当时使用的是ip+port进行hask；可以解决上述问题。

今天来看新内核linux 5.10 是怎样处理的

根据代码可知：直接hashtable中进行查找，但是使用ip+port进行hash，在匹配时；ip不对就直接返回

struct sock *__inet_lookup_listener(struct net *net,
                    struct inet_hashinfo *hashinfo,
                    struct sk_buff *skb, int doff,
                    const __be32 saddr, __be16 sport,
                    const __be32 daddr, const unsigned short hnum,
                    const int dif, const int sdif)
{
    struct inet_listen_hashbucket *ilb2;
    struct sock *result = NULL;
    unsigned int hash2;

    /* Lookup redirect from BPF */
    if (static_branch_unlikely(&bpf_sk_lookup_enabled)) {
        result = inet_lookup_run_bpf(net, hashinfo, skb, doff,
                         saddr, sport, daddr, hnum);
        if (result)
            goto done;
    }

    hash2 = ipv4_portaddr_hash(net, daddr, hnum);
    ilb2 = inet_lhash2_bucket(hashinfo, hash2);

    result = inet_lhash2_lookup(net, ilb2, skb, doff,
                    saddr, sport, daddr, hnum,
                    dif, sdif);
    if (result)
        goto done;

    /* Lookup lhash2 with INADDR_ANY */
    hash2 = ipv4_portaddr_hash(net, htonl(INADDR_ANY), hnum);
    ilb2 = inet_lhash2_bucket(hashinfo, hash2);

    result = inet_lhash2_lookup(net, ilb2, skb, doff,
                    saddr, sport, htonl(INADDR_ANY), hnum,
                    dif, sdif);
done:
    if (IS_ERR(result))
        return NULL;
    return result;
}

inet: Add a 2nd listener hashtable (port+addr) inet_connection_sock.h
inet: Add a 2nd listener hashtable (port+addr) inet_hashtables.h
inet: Add a 2nd listener hashtable (port+addr) inet_hashtables.c
net: tcp: prefer listeners bound to an address inet_hashtables.c