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;
link3353net/ipv4/af_inet.cskb2 = skb->link3;
link31758net/ipv4/ip.cnewskb->link3=NULL;
link31912net/ipv4/ip.cif (skb->link3 != NULL)
link31915net/ipv4/ip.cskb->link3 = NULL;
link31924net/ipv4/ip.csk->send_tail->link3 = skb;
link3769net/ipv4/tcp.cskb = skb->link3;
link33414net/ipv4/tcp.cskb2 = skb->link3;
link33415net/ipv4/tcp.cskb->link3 = NULL;
link33441net/ipv4/tcp.csk->send_tail->link3 = skb;
link33444net/ipv4/tcp.cskb->link3 = NULL;
link33550net/ipv4/tcp.cif (sk->send_head->link3 &&
link33551net/ipv4/tcp.cafter(sk->send_head->h.seq, sk->send_head->link3->h.seq)) 
link33577net/ipv4/tcp.cif (sk->send_head->link3)  /* Any more queued retransmits? */
link33645net/ipv4/tcp.csk->send_head = oskb->link3;