Function tcp_close

freebsd/netinet/tcp_subr.c:2099–2139

* Attempt to close a TCP control block, marking it as dropped, and freeing * the socket if we hold the only reference. */

 * the socket if we hold the only reference.
 */
struct tcpcb *
tcp_close(struct tcpcb *tp)
{
	struct inpcb *inp = tp->t_inpcb;
	struct socket *so;

	INP_INFO_LOCK_ASSERT(&V_tcbinfo);
	INP_WLOCK_ASSERT(inp);

#ifdef TCP_OFFLOAD
	if (tp->t_state == TCPS_LISTEN)
		tcp_offload_listen_stop(tp);
#endif
	/*
	 * This releases the TFO pending counter resource for TFO listen
	 * sockets as well as passively-created TFO sockets that transition
	 * from SYN_RECEIVED to CLOSED.
	 */
	if (tp->t_tfo_pending) {
		tcp_fastopen_decrement_counter(tp->t_tfo_pending);
		tp->t_tfo_pending = NULL;
	}
	in_pcbdrop(inp);
	TCPSTAT_INC(tcps_closed);
	if (tp->t_state != TCPS_CLOSED)
		tcp_state_change(tp, TCPS_CLOSED);
	KASSERT(inp->inp_socket != NULL, ("tcp_close: inp_socket NULL"));
	so = inp->inp_socket;
	soisdisconnected(so);
	if (inp->inp_flags & INP_SOCKREF) {
		KASSERT(so->so_state & SS_PROTOREF,
		    ("tcp_close: !SS_PROTOREF"));
		inp->inp_flags &= ~INP_SOCKREF;
		INP_WUNLOCK(inp);
		SOCK_LOCK(so);
		so->so_state &= ~SS_PROTOREF;
		sofree(so);
		return (NULL);
	}
	return (tp);
}

void
tcp_drain(void)