taglinefilesource code
link346include/linux/skbuff.hstruct sk_buff    * volatile link3;  /* Link for IP protocol level buffer chains   */
link3541net/core/skbuff.cskb->link3 = NULL;
link3611net/core/skbuff.cn->link3=NULL;
link3352net/ipv4/af_inet.cskb2 = skb->link3;
link31682net/ipv4/ip.cnewskb->link3=NULL;
link31832net/ipv4/ip.cif (skb->link3 != NULL)
link31835net/ipv4/ip.cskb->link3 = NULL;
link31844net/ipv4/ip.csk->send_tail->link3 = skb;
link3541net/ipv4/tcp.cskb = skb->link3;
link33181net/ipv4/tcp.cskb2 = skb->link3;
link33182net/ipv4/tcp.cskb->link3 = NULL;
link33208net/ipv4/tcp.csk->send_tail->link3 = skb;
link33211net/ipv4/tcp.cskb->link3 = NULL;
link33317net/ipv4/tcp.cif (sk->send_head->link3 &&
link33318net/ipv4/tcp.cafter(sk->send_head->h.seq, sk->send_head->link3->h.seq)) 
link33344net/ipv4/tcp.cif (sk->send_head->link3)  /* Any more queued retransmits? */
link33412net/ipv4/tcp.csk->send_head = oskb->link3;