IABSD.fr/src/sys/netinet/tcp_input.c

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• Author : jsg
  Date : 2025-07-08 00:47:41
  Hash : 148caabb
  Message : remove unneeded includes; ok bluhm@

• sys/netinet/tcp_input.c

• /*	$OpenBSD: tcp_input.c,v 1.456 2025/07/08 00:47:41 jsg Exp $	*/
  /*	$NetBSD: tcp_input.c,v 1.23 1996/02/13 23:43:44 christos Exp $	*/
  
  /*
   * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994
   *	The Regents of the University of California.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. Neither the name of the University nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   *	@(#)COPYRIGHT	1.1 (NRL) 17 January 1995
   *
   * NRL grants permission for redistribution and use in source and binary
   * forms, with or without modification, of the software and documentation
   * created at NRL provided that the following conditions are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. All advertising materials mentioning features or use of this software
   *    must display the following acknowledgements:
   *	This product includes software developed by the University of
   *	California, Berkeley and its contributors.
   *	This product includes software developed at the Information
   *	Technology Division, US Naval Research Laboratory.
   * 4. Neither the name of the NRL nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL AND CONTRIBUTORS ``AS
   * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
   * PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL NRL OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * The views and conclusions contained in the software and documentation
   * are those of the authors and should not be interpreted as representing
   * official policies, either expressed or implied, of the US Naval
   * Research Laboratory (NRL).
   */
  
  #include "pf.h"
  
  #include <sys/param.h>
  #include <sys/systm.h>
  #include <sys/mbuf.h>
  #include <sys/protosw.h>
  #include <sys/socket.h>
  #include <sys/timeout.h>
  #include <sys/kernel.h>
  #include <sys/pool.h>
  
  #include <net/if.h>
  #include <net/if_var.h>
  #include <net/route.h>
  
  #include <netinet/if_ether.h>
  #include <netinet/in.h>
  #include <netinet/ip.h>
  #include <netinet/in_pcb.h>
  #include <netinet/ip_var.h>
  #include <netinet6/ip6_var.h>
  #include <netinet/tcp.h>
  #include <netinet/tcp_fsm.h>
  #include <netinet/tcp_seq.h>
  #include <netinet/tcp_timer.h>
  #include <netinet/tcp_var.h>
  #include <netinet/tcp_debug.h>
  
  #if NPF > 0
  #include <net/pfvar.h>
  #endif
  
  #ifdef INET6
  #include <netinet6/in6_var.h>
  #include <netinet6/nd6.h>
  #endif /* INET6 */
  
  const int tcprexmtthresh = 3;
  
  int tcp_rst_ppslim = 100;		/* 100pps */
  int tcp_rst_ppslim_count = 0;
  struct timeval tcp_rst_ppslim_last;
  
  int tcp_ackdrop_ppslim = 100;		/* 100pps */
  int tcp_ackdrop_ppslim_count = 0;
  struct timeval tcp_ackdrop_ppslim_last;
  
  #define TCP_PAWS_IDLE	TCP_TIME(24 * 24 * 60 * 60)
  
  /* for modulo comparisons of timestamps */
  #define TSTMP_LT(a,b)	((int32_t)((a)-(b)) < 0)
  #define TSTMP_GEQ(a,b)	((int32_t)((a)-(b)) >= 0)
  
  /* for TCP SACK comparisons */
  #define	SEQ_MIN(a,b)	(SEQ_LT(a,b) ? (a) : (b))
  #define	SEQ_MAX(a,b)	(SEQ_GT(a,b) ? (a) : (b))
  
  /*
   * Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint.
   */
  #ifdef INET6
  #define ND6_HINT(tp) \
  do { \
  	if (tp && tp->t_inpcb &&					\
  	    ISSET(tp->t_inpcb->inp_flags, INP_IPV6) &&			\
  	    rtisvalid(tp->t_inpcb->inp_route.ro_rt)) {			\
  		nd6_nud_hint(tp->t_inpcb->inp_route.ro_rt);		\
  	} \
  } while (0)
  #else
  #define ND6_HINT(tp)
  #endif
  
  #ifdef TCP_ECN
  /*
   * ECN (Explicit Congestion Notification) support based on RFC3168
   * implementation note:
   *   snd_last is used to track a recovery phase.
   *   when cwnd is reduced, snd_last is set to snd_max.
   *   while snd_last > snd_una, the sender is in a recovery phase and
   *   its cwnd should not be reduced again.
   *   snd_last follows snd_una when not in a recovery phase.
   */
  #endif
  
  /*
   * Macro to compute ACK transmission behavior.  Delay the ACK unless
   * we have already delayed an ACK (must send an ACK every two segments).
   * We also ACK immediately if we received a PUSH and the ACK-on-PUSH
   * option is enabled or when the packet is coming from a loopback
   * interface.
   */
  #define	TCP_SETUP_ACK(tp, tiflags, m) \
  do { \
  	struct ifnet *ifp = NULL; \
  	if (m && (m->m_flags & M_PKTHDR)) \
  		ifp = if_get(m->m_pkthdr.ph_ifidx); \
  	if (TCP_TIMER_ISARMED(tp, TCPT_DELACK) || \
  	    (atomic_load_int(&tcp_ack_on_push) && (tiflags) & TH_PUSH) || \
  	    (ifp && (ifp->if_flags & IFF_LOOPBACK))) \
  		tp->t_flags |= TF_ACKNOW; \
  	else \
  		TCP_TIMER_ARM(tp, TCPT_DELACK, tcp_delack_msecs); \
  	if_put(ifp); \
  } while (0)
  
  int	 tcp_input_solocked(struct mbuf **, int *, int, int, struct socket **);
  int	 tcp_mss_adv(struct rtentry *, int);
  int	 tcp_flush_queue(struct tcpcb *);
  void	 tcp_sack_partialack(struct tcpcb *, struct tcphdr *);
  void	 tcp_newreno_partialack(struct tcpcb *, struct tcphdr *);
  
  void	 syn_cache_put(struct syn_cache *);
  void	 syn_cache_rm(struct syn_cache *);
  int	 syn_cache_respond(struct syn_cache *, struct mbuf *, uint64_t, int);
  void	 syn_cache_timer(void *);
  void	 syn_cache_insert(struct syn_cache *, struct tcpcb *);
  void	 syn_cache_reset(struct sockaddr *, struct sockaddr *,
  		struct tcphdr *, u_int);
  int	 syn_cache_add(struct sockaddr *, struct sockaddr *, struct tcphdr *,
  		unsigned int, struct socket *, struct mbuf *, u_char *, int,
  		struct tcp_opt_info *, tcp_seq *, uint64_t, int);
  struct socket *syn_cache_get(struct sockaddr *, struct sockaddr *,
  		struct tcphdr *, unsigned int, unsigned int, struct socket *,
  		struct mbuf *, uint64_t, int);
  struct syn_cache *syn_cache_lookup(const struct sockaddr *,
  		const struct sockaddr *, struct syn_cache_head **, u_int);
  
  /*
   * Insert segment ti into reassembly queue of tcp with
   * control block tp.  Return TH_FIN if reassembly now includes
   * a segment with FIN.  The macro form does the common case inline
   * (segment is the next to be received on an established connection,
   * and the queue is empty), avoiding linkage into and removal
   * from the queue and repetition of various conversions.
   * Set DELACK for segments received in order, but ack immediately
   * when segments are out of order (so fast retransmit can work).
   */
  
  int
  tcp_reass(struct tcpcb *tp, struct tcphdr *th, struct mbuf *m, int *tlen)
  {
  	struct tcpqent *p, *q, *nq, *tiqe;
  
  	/*
  	 * Allocate a new queue entry, before we throw away any data.
  	 * If we can't, just drop the packet.  XXX
  	 */
  	tiqe = pool_get(&tcpqe_pool, PR_NOWAIT);
  	if (tiqe == NULL) {
  		tiqe = TAILQ_LAST(&tp->t_segq, tcpqehead);
  		if (tiqe != NULL && th->th_seq == tp->rcv_nxt) {
  			/* Reuse last entry since new segment fills a hole */
  			m_freem(tiqe->tcpqe_m);
  			TAILQ_REMOVE(&tp->t_segq, tiqe, tcpqe_q);
  		}
  		if (tiqe == NULL || th->th_seq != tp->rcv_nxt) {
  			/* Flush segment queue for this connection */
  			tcp_freeq(tp);
  			tcpstat_inc(tcps_rcvmemdrop);
  			m_freem(m);
  			return (0);
  		}
  	}
  
  	/*
  	 * Find a segment which begins after this one does.
  	 */
  	for (p = NULL, q = TAILQ_FIRST(&tp->t_segq); q != NULL;
  	    p = q, q = TAILQ_NEXT(q, tcpqe_q))
  		if (SEQ_GT(q->tcpqe_tcp->th_seq, th->th_seq))
  			break;
  
  	/*
  	 * If there is a preceding segment, it may provide some of
  	 * our data already.  If so, drop the data from the incoming
  	 * segment.  If it provides all of our data, drop us.
  	 */
  	if (p != NULL) {
  		struct tcphdr *phdr = p->tcpqe_tcp;
  		int i;
  
  		/* conversion to int (in i) handles seq wraparound */
  		i = phdr->th_seq + phdr->th_reseqlen - th->th_seq;
  		if (i > 0) {
  			if (i >= *tlen) {
  				tcpstat_pkt(tcps_rcvduppack, tcps_rcvdupbyte,
  				    *tlen);
  				m_freem(m);
  				pool_put(&tcpqe_pool, tiqe);
  				return (0);
  			}
  			m_adj(m, i);
  			*tlen -= i;
  			th->th_seq += i;
  		}
  	}
  	tcpstat_pkt(tcps_rcvoopack, tcps_rcvoobyte, *tlen);
  	tp->t_rcvoopack++;
  
  	/*
  	 * While we overlap succeeding segments trim them or,
  	 * if they are completely covered, dequeue them.
  	 */
  	for (; q != NULL; q = nq) {
  		struct tcphdr *qhdr = q->tcpqe_tcp;
  		int i = (th->th_seq + *tlen) - qhdr->th_seq;
  
  		if (i <= 0)
  			break;
  		if (i < qhdr->th_reseqlen) {
  			qhdr->th_seq += i;
  			qhdr->th_reseqlen -= i;
  			m_adj(q->tcpqe_m, i);
  			break;
  		}
  		nq = TAILQ_NEXT(q, tcpqe_q);
  		m_freem(q->tcpqe_m);
  		TAILQ_REMOVE(&tp->t_segq, q, tcpqe_q);
  		pool_put(&tcpqe_pool, q);
  	}
  
  	/* Insert the new segment queue entry into place. */
  	tiqe->tcpqe_m = m;
  	th->th_reseqlen = *tlen;
  	tiqe->tcpqe_tcp = th;
  	if (p == NULL) {
  		TAILQ_INSERT_HEAD(&tp->t_segq, tiqe, tcpqe_q);
  	} else {
  		TAILQ_INSERT_AFTER(&tp->t_segq, p, tiqe, tcpqe_q);
  	}
  
  	if (th->th_seq != tp->rcv_nxt)
  		return (0);
  
  	return (tcp_flush_queue(tp));
  }
  
  int
  tcp_flush_queue(struct tcpcb *tp)
  {
  	struct socket *so = tp->t_inpcb->inp_socket;
  	struct tcpqent *q, *nq;
  	int flags;
  
  	/*
  	 * Present data to user, advancing rcv_nxt through
  	 * completed sequence space.
  	 */
  	if (TCPS_HAVEESTABLISHED(tp->t_state) == 0)
  		return (0);
  	q = TAILQ_FIRST(&tp->t_segq);
  	if (q == NULL || q->tcpqe_tcp->th_seq != tp->rcv_nxt)
  		return (0);
  	if (tp->t_state == TCPS_SYN_RECEIVED && q->tcpqe_tcp->th_reseqlen)
  		return (0);
  	do {
  		tp->rcv_nxt += q->tcpqe_tcp->th_reseqlen;
  		flags = q->tcpqe_tcp->th_flags & TH_FIN;
  
  		nq = TAILQ_NEXT(q, tcpqe_q);
  		TAILQ_REMOVE(&tp->t_segq, q, tcpqe_q);
  		ND6_HINT(tp);
  		if (so->so_rcv.sb_state & SS_CANTRCVMORE)
  			m_freem(q->tcpqe_m);
  		else {
  			mtx_enter(&so->so_rcv.sb_mtx);
  			sbappendstream(&so->so_rcv, q->tcpqe_m);
  			mtx_leave(&so->so_rcv.sb_mtx);
  		}
  		pool_put(&tcpqe_pool, q);
  		q = nq;
  	} while (q != NULL && q->tcpqe_tcp->th_seq == tp->rcv_nxt);
  	tp->t_flags |= TF_BLOCKOUTPUT;
  	sorwakeup(so);
  	tp->t_flags &= ~TF_BLOCKOUTPUT;
  	return (flags);
  }
  
  int
  tcp_input(struct mbuf **mp, int *offp, int proto, int af, struct netstack *ns)
  {
  	if (ns == NULL)
  		return tcp_input_solocked(mp, offp, proto, af, NULL);
  	(*mp)->m_pkthdr.ph_cookie = (void *)(long)(*offp);
  	switch (af) {
  	case AF_INET:
  		ml_enqueue(&ns->ns_tcp_ml, *mp);
  		break;
  #ifdef INET6
  	case AF_INET6:
  		ml_enqueue(&ns->ns_tcp6_ml, *mp);
  		break;
  #endif
  	default:
  		m_freemp(mp);
  	}
  	*mp = NULL;
  	return IPPROTO_DONE;
  }
  
  void
  tcp_input_mlist(struct mbuf_list *ml, int af)
  {
  	struct socket *so = NULL;
  	struct mbuf *m;
  
  	while ((m = ml_dequeue(ml)) != NULL) {
  		int off, nxt;
  
  		off = (long)m->m_pkthdr.ph_cookie;
  		m->m_pkthdr.ph_cookie = NULL;
  		nxt = tcp_input_solocked(&m, &off, IPPROTO_TCP, af, &so);
  		KASSERT(nxt == IPPROTO_DONE);
  	}
  
  	in_pcbsounlock(NULL, so);
  }
  
  /*
   * TCP input routine, follows pages 65-76 of the
   * protocol specification dated September, 1981 very closely.
   */
  int
  tcp_input_solocked(struct mbuf **mp, int *offp, int proto, int af,
      struct socket **solocked)
  {
  	struct mbuf *m = *mp;
  	int iphlen = *offp;
  	struct ip *ip = NULL;
  	struct inpcb *inp = NULL;
  	u_int8_t *optp = NULL;
  	int optlen = 0;
  	int tlen, off;
  	struct tcpcb *otp = NULL, *tp = NULL;
  	int tiflags;
  	struct socket *so = NULL;
  	int todrop, acked, ourfinisacked;
  	int hdroptlen = 0;
  	short ostate;
  	union {
  		struct	tcpiphdr tcpip;
  #ifdef INET6
  		struct  tcpipv6hdr tcpip6;
  #endif
  		char	caddr;
  	} saveti;
  	tcp_seq iss, *reuse = NULL;
  	uint64_t now;
  	u_long tiwin;
  	struct tcp_opt_info opti;
  	struct tcphdr *th;
  #ifdef INET6
  	struct ip6_hdr *ip6 = NULL;
  #endif /* INET6 */
  	int do_ecn = 0;
  #ifdef TCP_ECN
  	u_char iptos;
  #endif
  
  	tcpstat_inc(tcps_rcvtotal);
  
  	opti.ts_present = 0;
  	opti.maxseg = 0;
  	now = tcp_now();
  #ifdef TCP_ECN
  	do_ecn = atomic_load_int(&tcp_do_ecn);
  #endif
  
  	/*
  	 * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
  	 */
  	if (m->m_flags & (M_BCAST|M_MCAST))
  		goto drop;
  
  	/*
  	 * Get IP and TCP header together in first mbuf.
  	 * Note: IP leaves IP header in first mbuf.
  	 */
  	th = ip6_exthdr_get(mp, iphlen, sizeof(*th));
  	if (th == NULL) {
  		tcpstat_inc(tcps_rcvshort);
  		return IPPROTO_DONE;
  	}
  
  	tlen = m->m_pkthdr.len - iphlen;
  	switch (af) {
  	case AF_INET:
  		ip = mtod(m, struct ip *);
  #ifdef TCP_ECN
  		/* save ip_tos before clearing it for checksum */
  		iptos = ip->ip_tos;
  #endif
  		break;
  #ifdef INET6
  	case AF_INET6:
  		ip6 = mtod(m, struct ip6_hdr *);
  #ifdef TCP_ECN
  		iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
  #endif
  
  		/*
  		 * Be proactive about unspecified IPv6 address in source.
  		 * As we use all-zero to indicate unbounded/unconnected pcb,
  		 * unspecified IPv6 address can be used to confuse us.
  		 *
  		 * Note that packets with unspecified IPv6 destination is
  		 * already dropped in ip6_input.
  		 */
  		if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
  			/* XXX stat */
  			goto drop;
  		}
  
  		/* Discard packets to multicast */
  		if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst)) {
  			/* XXX stat */
  			goto drop;
  		}
  		break;
  #endif
  	default:
  		unhandled_af(af);
  	}
  
  	/*
  	 * Checksum extended TCP header and data.
  	 */
  	if ((m->m_pkthdr.csum_flags & M_TCP_CSUM_IN_OK) == 0) {
  		int sum;
  
  		if (m->m_pkthdr.csum_flags & M_TCP_CSUM_IN_BAD) {
  			tcpstat_inc(tcps_rcvbadsum);
  			goto drop;
  		}
  		tcpstat_inc(tcps_inswcsum);
  		switch (af) {
  		case AF_INET:
  			sum = in4_cksum(m, IPPROTO_TCP, iphlen, tlen);
  			break;
  #ifdef INET6
  		case AF_INET6:
  			sum = in6_cksum(m, IPPROTO_TCP, iphlen, tlen);
  			break;
  #endif
  		}
  		if (sum != 0) {
  			tcpstat_inc(tcps_rcvbadsum);
  			goto drop;
  		}
  	}
  
  	/*
  	 * Check that TCP offset makes sense,
  	 * pull out TCP options and adjust length.		XXX
  	 */
  	off = th->th_off << 2;
  	if (off < sizeof(struct tcphdr) || off > tlen) {
  		tcpstat_inc(tcps_rcvbadoff);
  		goto drop;
  	}
  	tlen -= off;
  	if (off > sizeof(struct tcphdr)) {
  		th = ip6_exthdr_get(mp, iphlen, off);
  		if (th == NULL) {
  			tcpstat_inc(tcps_rcvshort);
  			return IPPROTO_DONE;
  		}
  		optlen = off - sizeof(struct tcphdr);
  		optp = (u_int8_t *)(th + 1);
  		/*
  		 * Do quick retrieval of timestamp options ("options
  		 * prediction?").  If timestamp is the only option and it's
  		 * formatted as recommended in RFC 1323 appendix A, we
  		 * quickly get the values now and not bother calling
  		 * tcp_dooptions(), etc.
  		 */
  		if ((optlen == TCPOLEN_TSTAMP_APPA ||
  		     (optlen > TCPOLEN_TSTAMP_APPA &&
  		      optp[TCPOLEN_TSTAMP_APPA] == TCPOPT_EOL)) &&
  		     *(u_int32_t *)optp == htonl(TCPOPT_TSTAMP_HDR) &&
  		     (th->th_flags & TH_SYN) == 0) {
  			opti.ts_present = 1;
  			opti.ts_val = ntohl(*(u_int32_t *)(optp + 4));
  			opti.ts_ecr = ntohl(*(u_int32_t *)(optp + 8));
  			optp = NULL;	/* we've parsed the options */
  		}
  	}
  	tiflags = th->th_flags;
  
  	/*
  	 * Convert TCP protocol specific fields to host format.
  	 */
  	th->th_seq = ntohl(th->th_seq);
  	th->th_ack = ntohl(th->th_ack);
  	th->th_win = ntohs(th->th_win);
  	th->th_urp = ntohs(th->th_urp);
  
  	if (th->th_dport == 0) {
  		tcpstat_inc(tcps_noport);
  		goto dropwithreset_ratelim;
  	}
  
  	/*
  	 * Locate pcb for segment.
  	 */
  #if NPF > 0
  	inp = pf_inp_lookup(m);
  #endif
  findpcb:
  	if (inp == NULL) {
  		switch (af) {
  #ifdef INET6
  		case AF_INET6:
  			inp = in6_pcblookup(&tcb6table, &ip6->ip6_src,
  			    th->th_sport, &ip6->ip6_dst, th->th_dport,
  			    m->m_pkthdr.ph_rtableid);
  			break;
  #endif
  		case AF_INET:
  			inp = in_pcblookup(&tcbtable, ip->ip_src,
  			    th->th_sport, ip->ip_dst, th->th_dport,
  			    m->m_pkthdr.ph_rtableid);
  			break;
  		}
  	}
  	if (inp == NULL) {
  		tcpstat_inc(tcps_pcbhashmiss);
  		switch (af) {
  #ifdef INET6
  		case AF_INET6:
  			inp = in6_pcblookup_listen(&tcb6table, &ip6->ip6_dst,
  			    th->th_dport, m, m->m_pkthdr.ph_rtableid);
  			break;
  #endif
  		case AF_INET:
  			inp = in_pcblookup_listen(&tcbtable, ip->ip_dst,
  			    th->th_dport, m, m->m_pkthdr.ph_rtableid);
  			break;
  		}
  		/*
  		 * If the state is CLOSED (i.e., TCB does not exist) then
  		 * all data in the incoming segment is discarded.
  		 * If the TCB exists but is in CLOSED state, it is embryonic,
  		 * but should either do a listen or a connect soon.
  		 */
  	}
  #ifdef IPSEC
  	if (ipsec_in_use) {
  		struct m_tag *mtag;
  		struct tdb *tdb = NULL;
  		int error;
  
  		/* Find most recent IPsec tag */
  		mtag = m_tag_find(m, PACKET_TAG_IPSEC_IN_DONE, NULL);
  		if (mtag != NULL) {
  			struct tdb_ident *tdbi;
  
  			tdbi = (struct tdb_ident *)(mtag + 1);
  			tdb = gettdb(tdbi->rdomain, tdbi->spi,
  			    &tdbi->dst, tdbi->proto);
  		}
  		error = ipsp_spd_lookup(m, af, iphlen, IPSP_DIRECTION_IN,
  		    tdb, inp ? &inp->inp_seclevel : NULL, NULL, NULL);
  		tdb_unref(tdb);
  		if (error) {
  			tcpstat_inc(tcps_rcvnosec);
  			goto drop;
  		}
  	}
  #endif /* IPSEC */
  
  	if (inp == NULL) {
  		tcpstat_inc(tcps_noport);
  		goto dropwithreset_ratelim;
  	}
  	/*
  	 * Avoid needless lock and unlock operation when handling multiple
  	 * TCP packets from the same stream consecutively.
  	 */
  	if (solocked != NULL && *solocked != NULL &&
  	    sotoinpcb(*solocked) == inp) {
  		so = *solocked;
  		*solocked = NULL;
  	} else {
  		if (solocked != NULL && *solocked != NULL) {
  			in_pcbsounlock(NULL, *solocked);
  			*solocked = NULL;
  		}
  		so = in_pcbsolock(inp);
  	}
  	if (so == NULL) {
  		tcpstat_inc(tcps_closing);
  		goto dropwithreset_ratelim;
  	}
  	KASSERT(sotoinpcb(inp->inp_socket) == inp);
  	KASSERT(intotcpcb(inp) == NULL || intotcpcb(inp)->t_inpcb == inp);
  	soassertlocked(inp->inp_socket);
  
  	/* Check the minimum TTL for socket. */
  	switch (af) {
  	case AF_INET:
  		if (inp->inp_ip_minttl && inp->inp_ip_minttl > ip->ip_ttl)
  			goto drop;
  		break;
  #ifdef INET6
  	case AF_INET6:
  		if (inp->inp_ip6_minhlim &&
  		    inp->inp_ip6_minhlim > ip6->ip6_hlim)
  			goto drop;
  		break;
  #endif
  	}
  
  	tp = intotcpcb(inp);
  	if (tp == NULL)
  		goto dropwithreset_ratelim;
  	if (tp->t_state == TCPS_CLOSED)
  		goto drop;
  
  	/* Unscale the window into a 32-bit value. */
  	if ((tiflags & TH_SYN) == 0)
  		tiwin = th->th_win << tp->snd_scale;
  	else
  		tiwin = th->th_win;
  
  	if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
  		union syn_cache_sa src;
  		union syn_cache_sa dst;
  
  		bzero(&src, sizeof(src));
  		bzero(&dst, sizeof(dst));
  		switch (af) {
  		case AF_INET:
  			src.sin.sin_len = sizeof(struct sockaddr_in);
  			src.sin.sin_family = AF_INET;
  			src.sin.sin_addr = ip->ip_src;
  			src.sin.sin_port = th->th_sport;
  
  			dst.sin.sin_len = sizeof(struct sockaddr_in);
  			dst.sin.sin_family = AF_INET;
  			dst.sin.sin_addr = ip->ip_dst;
  			dst.sin.sin_port = th->th_dport;
  			break;
  #ifdef INET6
  		case AF_INET6:
  			src.sin6.sin6_len = sizeof(struct sockaddr_in6);
  			src.sin6.sin6_family = AF_INET6;
  			src.sin6.sin6_addr = ip6->ip6_src;
  			src.sin6.sin6_port = th->th_sport;
  
  			dst.sin6.sin6_len = sizeof(struct sockaddr_in6);
  			dst.sin6.sin6_family = AF_INET6;
  			dst.sin6.sin6_addr = ip6->ip6_dst;
  			dst.sin6.sin6_port = th->th_dport;
  			break;
  #endif /* INET6 */
  		}
  
  		if (so->so_options & SO_DEBUG) {
  			otp = tp;
  			ostate = tp->t_state;
  			switch (af) {
  #ifdef INET6
  			case AF_INET6:
  				saveti.tcpip6.ti6_i = *ip6;
  				saveti.tcpip6.ti6_t = *th;
  				break;
  #endif
  			case AF_INET:
  				memcpy(&saveti.tcpip.ti_i, ip, sizeof(*ip));
  				saveti.tcpip.ti_t = *th;
  				break;
  			}
  		}
  		if (so->so_options & SO_ACCEPTCONN) {
  			switch (tiflags & (TH_RST|TH_SYN|TH_ACK)) {
  
  			case TH_SYN|TH_ACK|TH_RST:
  			case TH_SYN|TH_RST:
  			case TH_ACK|TH_RST:
  			case TH_RST:
  				syn_cache_reset(&src.sa, &dst.sa, th,
  				    inp->inp_rtableid);
  				goto drop;
  
  			case TH_SYN|TH_ACK:
  				/*
  				 * Received a SYN,ACK.  This should
  				 * never happen while we are in
  				 * LISTEN.  Send an RST.
  				 */
  				goto badsyn;
  
  			case TH_ACK:
  				so = syn_cache_get(&src.sa, &dst.sa,
  				    th, iphlen, tlen, so, m, now, do_ecn);
  				if (so == NULL) {
  					/*
  					 * We don't have a SYN for
  					 * this ACK; send an RST.
  					 */
  					goto badsyn;
  				} else if (so == (struct socket *)(-1)) {
  					/*
  					 * We were unable to create
  					 * the connection.  If the
  					 * 3-way handshake was
  					 * completed, and RST has
  					 * been sent to the peer.
  					 * Since the mbuf might be
  					 * in use for the reply,
  					 * do not free it.
  					 */
  					so = NULL;
  					m = *mp = NULL;
  					goto drop;
  				} else {
  					/*
  					 * We have created a
  					 * full-blown connection.
  					 */
  					in_pcbunref(inp);
  					/* syn_cache_get() has refcounted inp */
  					inp = sotoinpcb(so);
  					tp = intotcpcb(inp);
  					if (tp == NULL)
  						goto badsyn;	/*XXX*/
  				}
  				break;
  
  			default:
  				/*
  				 * None of RST, SYN or ACK was set.
  				 * This is an invalid packet for a
  				 * TCB in LISTEN state.  Send a RST.
  				 */
  				goto badsyn;
  
  			case TH_SYN:
  				/*
  				 * Received a SYN.
  				 */
  #ifdef INET6
  				/*
  				 * If deprecated address is forbidden, we do
  				 * not accept SYN to deprecated interface
  				 * address to prevent any new inbound
  				 * connection from getting established.
  				 * When we do not accept SYN, we send a TCP
  				 * RST, with deprecated source address (instead
  				 * of dropping it).  We compromise it as it is
  				 * much better for peer to send a RST, and
  				 * RST will be the final packet for the
  				 * exchange.
  				 *
  				 * If we do not forbid deprecated addresses, we
  				 * accept the SYN packet.  RFC2462 does not
  				 * suggest dropping SYN in this case.
  				 * If we decipher RFC2462 5.5.4, it says like
  				 * this:
  				 * 1. use of deprecated addr with existing
  				 *    communication is okay - "SHOULD continue
  				 *    to be used"
  				 * 2. use of it with new communication:
  				 *   (2a) "SHOULD NOT be used if alternate
  				 *        address with sufficient scope is
  				 *        available"
  				 *   (2b) nothing mentioned otherwise.
  				 * Here we fall into (2b) case as we have no
  				 * choice in our source address selection - we
  				 * must obey the peer.
  				 *
  				 * The wording in RFC2462 is confusing, and
  				 * there are multiple description text for
  				 * deprecated address handling - worse, they
  				 * are not exactly the same.  I believe 5.5.4
  				 * is the best one, so we follow 5.5.4.
  				 */
  				if (ip6 && !ip6_use_deprecated) {
  					struct in6_ifaddr *ia6;
  					struct ifnet *ifp =
  					    if_get(m->m_pkthdr.ph_ifidx);
  
  					if (ifp &&
  					    (ia6 = in6ifa_ifpwithaddr(ifp,
  					    &ip6->ip6_dst)) &&
  					    (ia6->ia6_flags &
  					    IN6_IFF_DEPRECATED)) {
  						tp = NULL;
  						if_put(ifp);
  						goto dropwithreset;
  					}
  					if_put(ifp);
  				}
  #endif
  
  				/*
  				 * LISTEN socket received a SYN
  				 * from itself?  This can't possibly
  				 * be valid; drop the packet.
  				 */
  				if (th->th_dport == th->th_sport) {
  					switch (af) {
  #ifdef INET6
  					case AF_INET6:
  						if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_src,
  						    &ip6->ip6_dst)) {
  							tcpstat_inc(tcps_badsyn);
  							goto drop;
  						}
  						break;
  #endif /* INET6 */
  					case AF_INET:
  						if (ip->ip_dst.s_addr == ip->ip_src.s_addr) {
  							tcpstat_inc(tcps_badsyn);
  							goto drop;
  						}
  						break;
  					}
  				}
  
  				/*
  				 * SYN looks ok; create compressed TCP
  				 * state for it.
  				 */
  				if (so->so_qlen > so->so_qlimit ||
  				    syn_cache_add(&src.sa, &dst.sa, th, iphlen,
  				    so, m, optp, optlen, &opti, reuse, now,
  				    do_ecn) == -1) {
  					tcpstat_inc(tcps_dropsyn);
  					goto drop;
  				}
  				if (solocked != NULL)
  					*solocked = so;
  				else
  					in_pcbsounlock(inp, so);
  				in_pcbunref(inp);
  				return IPPROTO_DONE;
  			}
  		}
  	}
  
  #ifdef DIAGNOSTIC
  	/*
  	 * Should not happen now that all embryonic connections
  	 * are handled with compressed state.
  	 */
  	if (tp->t_state == TCPS_LISTEN)
  		panic("tcp_input: TCPS_LISTEN");
  #endif
  
  #if NPF > 0
  	pf_inp_link(m, inp);
  #endif
  
  	/*
  	 * Segment received on connection.
  	 * Reset idle time and keep-alive timer.
  	 */
  	tp->t_rcvtime = now;
  	if (TCPS_HAVEESTABLISHED(tp->t_state))
  		TCP_TIMER_ARM(tp, TCPT_KEEP, atomic_load_int(&tcp_keepidle));
  
  	if (tp->sack_enable)
  		tcp_del_sackholes(tp, th); /* Delete stale SACK holes */
  
  	/*
  	 * Process options.
  	 */
  	if (optp
  #ifdef TCP_SIGNATURE
  	    || (tp->t_flags & TF_SIGNATURE)
  #endif
  	    ) {
  		if (tcp_dooptions(tp, optp, optlen, th, m, iphlen, &opti,
  		    m->m_pkthdr.ph_rtableid, now))
  			goto drop;
  	}
  
  	if (opti.ts_present && opti.ts_ecr) {
  		int32_t rtt_test;
  
  		/* subtract out the tcp timestamp modulator */
  		opti.ts_ecr -= tp->ts_modulate;
  
  		/* make sure ts_ecr is sensible */
  		rtt_test = now - opti.ts_ecr;
  		if (rtt_test < 0 || rtt_test > TCP_RTT_MAX)
  			opti.ts_ecr = 0;
  	}
  
  #ifdef TCP_ECN
  	/* if congestion experienced, set ECE bit in subsequent packets. */
  	if ((iptos & IPTOS_ECN_MASK) == IPTOS_ECN_CE) {
  		tp->t_flags |= TF_RCVD_CE;
  		tcpstat_inc(tcps_ecn_rcvce);
  	}
  #endif
  	/*
  	 * Header prediction: check for the two common cases
  	 * of a uni-directional data xfer.  If the packet has
  	 * no control flags, is in-sequence, the window didn't
  	 * change and we're not retransmitting, it's a
  	 * candidate.  If the length is zero and the ack moved
  	 * forward, we're the sender side of the xfer.  Just
  	 * free the data acked & wake any higher level process
  	 * that was blocked waiting for space.  If the length
  	 * is non-zero and the ack didn't move, we're the
  	 * receiver side.  If we're getting packets in-order
  	 * (the reassembly queue is empty), add the data to
  	 * the socket buffer and note that we need a delayed ack.
  	 */
  	if (tp->t_state == TCPS_ESTABLISHED &&
  #ifdef TCP_ECN
  	    (tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ECE|TH_CWR|TH_ACK)) == TH_ACK &&
  #else
  	    (tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
  #endif
  	    (!opti.ts_present || TSTMP_GEQ(opti.ts_val, tp->ts_recent)) &&
  	    th->th_seq == tp->rcv_nxt &&
  	    tiwin && tiwin == tp->snd_wnd &&
  	    tp->snd_nxt == tp->snd_max) {
  
  		/*
  		 * If last ACK falls within this segment's sequence numbers,
  		 *  record the timestamp.
  		 * Fix from Braden, see Stevens p. 870
  		 */
  		if (opti.ts_present && SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
  			tp->ts_recent_age = now;
  			tp->ts_recent = opti.ts_val;
  		}
  
  		if (tlen == 0) {
  			if (SEQ_GT(th->th_ack, tp->snd_una) &&
  			    SEQ_LEQ(th->th_ack, tp->snd_max) &&
  			    tp->snd_cwnd >= tp->snd_wnd &&
  			    tp->t_dupacks == 0) {
  				/*
  				 * this is a pure ack for outstanding data.
  				 */
  				tcpstat_inc(tcps_predack);
  				if (opti.ts_present && opti.ts_ecr)
  					tcp_xmit_timer(tp, now - opti.ts_ecr);
  				else if (tp->t_rtttime &&
  				    SEQ_GT(th->th_ack, tp->t_rtseq))
  					tcp_xmit_timer(tp, now - tp->t_rtttime);
  				acked = th->th_ack - tp->snd_una;
  				tcpstat_pkt(tcps_rcvackpack, tcps_rcvackbyte,
  				    acked);
  				tp->t_rcvacktime = now;
  				ND6_HINT(tp);
  
  				mtx_enter(&so->so_snd.sb_mtx);
  				sbdrop(&so->so_snd, acked);
  				mtx_leave(&so->so_snd.sb_mtx);
  
  				/*
  				 * If we had a pending ICMP message that
  				 * refers to data that have just been
  				 * acknowledged, disregard the recorded ICMP
  				 * message.
  				 */
  				if ((tp->t_flags & TF_PMTUD_PEND) &&
  				    SEQ_GT(th->th_ack, tp->t_pmtud_th_seq))
  					tp->t_flags &= ~TF_PMTUD_PEND;
  
  				/*
  				 * Keep track of the largest chunk of data
  				 * acknowledged since last PMTU update
  				 */
  				if (tp->t_pmtud_mss_acked < acked)
  					tp->t_pmtud_mss_acked = acked;
  
  				tp->snd_una = th->th_ack;
  				/* Pull snd_wl2 up to prevent seq wrap. */
  				tp->snd_wl2 = th->th_ack;
  				/*
  				 * We want snd_last to track snd_una so
  				 * as to avoid sequence wraparound problems
  				 * for very large transfers.
  				 */
  #ifdef TCP_ECN
  				if (SEQ_GT(tp->snd_una, tp->snd_last))
  #endif
  				tp->snd_last = tp->snd_una;
  				m_freem(m);
  
  				/*
  				 * If all outstanding data are acked, stop
  				 * retransmit timer, otherwise restart timer
  				 * using current (possibly backed-off) value.
  				 * If process is waiting for space,
  				 * wakeup/selwakeup/signal.  If data
  				 * are ready to send, let tcp_output
  				 * decide between more output or persist.
  				 */
  				if (tp->snd_una == tp->snd_max)
  					TCP_TIMER_DISARM(tp, TCPT_REXMT);
  				else if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0)
  					TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur);
  
  				tcp_update_sndspace(tp);
  				if (sb_notify(&so->so_snd)) {
  					tp->t_flags |= TF_BLOCKOUTPUT;
  					sowwakeup(so);
  					tp->t_flags &= ~TF_BLOCKOUTPUT;
  				}
  				if (so->so_snd.sb_cc ||
  				    tp->t_flags & TF_NEEDOUTPUT)
  					(void) tcp_output(tp);
  				if (solocked != NULL)
  					*solocked = so;
  				else
  					in_pcbsounlock(inp, so);
  				in_pcbunref(inp);
  				return IPPROTO_DONE;
  			}
  		} else if (th->th_ack == tp->snd_una &&
  		    TAILQ_EMPTY(&tp->t_segq) &&
  		    tlen <= sbspace(&so->so_rcv)) {
  			/*
  			 * This is a pure, in-sequence data packet
  			 * with nothing on the reassembly queue and
  			 * we have enough buffer space to take it.
  			 */
  			/* Clean receiver SACK report if present */
  			if (tp->sack_enable && tp->rcv_numsacks)
  				tcp_clean_sackreport(tp);
  			tcpstat_inc(tcps_preddat);
  			tp->rcv_nxt += tlen;
  			/* Pull snd_wl1 and rcv_up up to prevent seq wrap. */
  			tp->snd_wl1 = th->th_seq;
  			/* Packet has most recent segment, no urgent exists. */
  			tp->rcv_up = tp->rcv_nxt;
  			tcpstat_pkt(tcps_rcvpack, tcps_rcvbyte, tlen);
  			ND6_HINT(tp);
  
  			TCP_SETUP_ACK(tp, tiflags, m);
  			/*
  			 * Drop TCP, IP headers and TCP options then add data
  			 * to socket buffer.
  			 */
  			if (so->so_rcv.sb_state & SS_CANTRCVMORE)
  				m_freem(m);
  			else {
  				if (tp->t_srtt != 0 && tp->rfbuf_ts != 0 &&
  				    now - tp->rfbuf_ts > (tp->t_srtt >>
  				    (TCP_RTT_SHIFT + TCP_RTT_BASE_SHIFT))) {
  					tcp_update_rcvspace(tp);
  					/* Start over with next RTT. */
  					tp->rfbuf_cnt = 0;
  					tp->rfbuf_ts = 0;
  				} else
  					tp->rfbuf_cnt += tlen;
  				m_adj(m, iphlen + off);
  				mtx_enter(&so->so_rcv.sb_mtx);
  				sbappendstream(&so->so_rcv, m);
  				mtx_leave(&so->so_rcv.sb_mtx);
  			}
  			tp->t_flags |= TF_BLOCKOUTPUT;
  			sorwakeup(so);
  			tp->t_flags &= ~TF_BLOCKOUTPUT;
  			if (tp->t_flags & (TF_ACKNOW|TF_NEEDOUTPUT))
  				(void) tcp_output(tp);
  			if (solocked != NULL)
  				*solocked = so;
  			else
  				in_pcbsounlock(inp, so);
  			in_pcbunref(inp);
  			return IPPROTO_DONE;
  		}
  	}
  
  	/*
  	 * Compute mbuf offset to TCP data segment.
  	 */
  	hdroptlen = iphlen + off;
  
  	/*
  	 * Calculate amount of space in receive window,
  	 * and then do TCP input processing.
  	 * Receive window is amount of space in rcv queue,
  	 * but not less than advertised window.
  	 */
  	{
  		int win;
  
  		win = sbspace(&so->so_rcv);
  		if (win < 0)
  			win = 0;
  		tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
  	}
  
  	switch (tp->t_state) {
  
  	/*
  	 * If the state is SYN_RECEIVED:
  	 *	if seg contains SYN/ACK, send an RST.
  	 *	if seg contains an ACK, but not for our SYN/ACK, send an RST
  	 */
  
  	case TCPS_SYN_RECEIVED:
  		if (tiflags & TH_ACK) {
  			if (tiflags & TH_SYN) {
  				tcpstat_inc(tcps_badsyn);
  				goto dropwithreset;
  			}
  			if (SEQ_LEQ(th->th_ack, tp->snd_una) ||
  			    SEQ_GT(th->th_ack, tp->snd_max))
  				goto dropwithreset;
  		}
  		break;
  
  	/*
  	 * If the state is SYN_SENT:
  	 *	if seg contains an ACK, but not for our SYN, drop the input.
  	 *	if seg contains a RST, then drop the connection.
  	 *	if seg does not contain SYN, then drop it.
  	 * Otherwise this is an acceptable SYN segment
  	 *	initialize tp->rcv_nxt and tp->irs
  	 *	if seg contains ack then advance tp->snd_una
  	 *	if SYN has been acked change to ESTABLISHED else SYN_RCVD state
  	 *	arrange for segment to be acked (eventually)
  	 *	continue processing rest of data/controls, beginning with URG
  	 */
  	case TCPS_SYN_SENT:
  		if ((tiflags & TH_ACK) &&
  		    (SEQ_LEQ(th->th_ack, tp->iss) ||
  		     SEQ_GT(th->th_ack, tp->snd_max)))
  			goto dropwithreset;
  		if (tiflags & TH_RST) {
  #ifdef TCP_ECN
  			/* if ECN is enabled, fall back to non-ecn at rexmit */
  			if (do_ecn && !(tp->t_flags & TF_DISABLE_ECN))
  				goto drop;
  #endif
  			if (tiflags & TH_ACK)
  				tp = tcp_drop(tp, ECONNREFUSED);
  			goto drop;
  		}
  		if ((tiflags & TH_SYN) == 0)
  			goto drop;
  		if (tiflags & TH_ACK) {
  			tp->snd_una = th->th_ack;
  			if (SEQ_LT(tp->snd_nxt, tp->snd_una))
  				tp->snd_nxt = tp->snd_una;
  		}
  		TCP_TIMER_DISARM(tp, TCPT_REXMT);
  		tp->irs = th->th_seq;
  		tcp_mss(tp, opti.maxseg);
  		/* Reset initial window to 1 segment for retransmit */
  		if (tp->t_rxtshift > 0)
  			tp->snd_cwnd = tp->t_maxseg;
  		tcp_rcvseqinit(tp);
  		tp->t_flags |= TF_ACKNOW;
  		/*
  		 * If we've sent a SACK_PERMITTED option, and the peer
  		 * also replied with one, then TF_SACK_PERMIT should have
  		 * been set in tcp_dooptions().  If it was not, disable SACKs.
  		 */
  		if (tp->sack_enable)
  			tp->sack_enable = tp->t_flags & TF_SACK_PERMIT;
  #ifdef TCP_ECN
  		/*
  		 * if ECE is set but CWR is not set for SYN-ACK, or
  		 * both ECE and CWR are set for simultaneous open,
  		 * peer is ECN capable.
  		 */
  		if (do_ecn) {
  			switch (tiflags & (TH_ACK|TH_ECE|TH_CWR)) {
  			case TH_ACK|TH_ECE:
  			case TH_ECE|TH_CWR:
  				tp->t_flags |= TF_ECN_PERMIT;
  				tiflags &= ~(TH_ECE|TH_CWR);
  				tcpstat_inc(tcps_ecn_accepts);
  			}
  		}
  #endif
  
  		if (tiflags & TH_ACK && SEQ_GT(tp->snd_una, tp->iss)) {
  			tcpstat_inc(tcps_connects);
  			tp->t_flags |= TF_BLOCKOUTPUT;
  			soisconnected(so);
  			tp->t_flags &= ~TF_BLOCKOUTPUT;
  			tp->t_state = TCPS_ESTABLISHED;
  			TCP_TIMER_ARM(tp, TCPT_KEEP,
  			    atomic_load_int(&tcp_keepidle));
  			/* Do window scaling on this connection? */
  			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
  				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
  				tp->snd_scale = tp->requested_s_scale;
  				tp->rcv_scale = tp->request_r_scale;
  			}
  			tcp_flush_queue(tp);
  
  			/*
  			 * if we didn't have to retransmit the SYN,
  			 * use its rtt as our initial srtt & rtt var.
  			 */
  			if (tp->t_rtttime)
  				tcp_xmit_timer(tp, now - tp->t_rtttime);
  			/*
  			 * Since new data was acked (the SYN), open the
  			 * congestion window by one MSS.  We do this
  			 * here, because we won't go through the normal
  			 * ACK processing below.  And since this is the
  			 * start of the connection, we know we are in
  			 * the exponential phase of slow-start.
  			 */
  			tp->snd_cwnd += tp->t_maxseg;
  		} else
  			tp->t_state = TCPS_SYN_RECEIVED;
  
  #if 0
  trimthenstep6:
  #endif
  		/*
  		 * Advance th->th_seq to correspond to first data byte.
  		 * If data, trim to stay within window,
  		 * dropping FIN if necessary.
  		 */
  		th->th_seq++;
  		if (tlen > tp->rcv_wnd) {
  			todrop = tlen - tp->rcv_wnd;
  			m_adj(m, -todrop);
  			tlen = tp->rcv_wnd;
  			tiflags &= ~TH_FIN;
  			tcpstat_pkt(tcps_rcvpackafterwin, tcps_rcvbyteafterwin,
  			    todrop);
  		}
  		tp->snd_wl1 = th->th_seq - 1;
  		tp->rcv_up = th->th_seq;
  		goto step6;
  	/*
  	 * If a new connection request is received while in TIME_WAIT,
  	 * drop the old connection and start over if the if the
  	 * timestamp or the sequence numbers are above the previous
  	 * ones.
  	 */
  	case TCPS_TIME_WAIT:
  		if (((tiflags & (TH_SYN|TH_ACK)) == TH_SYN) &&
  		    ((opti.ts_present &&
  		    TSTMP_LT(tp->ts_recent, opti.ts_val)) ||
  		    SEQ_GT(th->th_seq, tp->rcv_nxt))) {
  #if NPF > 0
  			/*
  			 * The socket will be recreated but the new state
  			 * has already been linked to the socket.  Remove the
  			 * link between old socket and new state.
  			 */
  			pf_inp_unlink(inp);
  #endif
  			/*
  			* Advance the iss by at least 32768, but
  			* clear the msb in order to make sure
  			* that SEG_LT(snd_nxt, iss).
  			*/
  			iss = tp->snd_nxt +
  			    ((arc4random() & 0x7fffffff) | 0x8000);
  			reuse = &iss;
  			tp = tcp_close(tp);
  			in_pcbsounlock(inp, so);
  			so = NULL;
  			in_pcbunref(inp);
  			inp = NULL;
  			goto findpcb;
  		}
  	}
  
  	/*
  	 * States other than LISTEN or SYN_SENT.
  	 * First check timestamp, if present.
  	 * Then check that at least some bytes of segment are within
  	 * receive window.  If segment begins before rcv_nxt,
  	 * drop leading data (and SYN); if nothing left, just ack.
  	 *
  	 * RFC 1323 PAWS: If we have a timestamp reply on this segment
  	 * and it's less than opti.ts_recent, drop it.
  	 */
  	if (opti.ts_present && (tiflags & TH_RST) == 0 && tp->ts_recent &&
  	    TSTMP_LT(opti.ts_val, tp->ts_recent)) {
  
  		/* Check to see if ts_recent is over 24 days old.  */
  		if (now - tp->ts_recent_age > TCP_PAWS_IDLE) {
  			/*
  			 * Invalidate ts_recent.  If this segment updates
  			 * ts_recent, the age will be reset later and ts_recent
  			 * will get a valid value.  If it does not, setting
  			 * ts_recent to zero will at least satisfy the
  			 * requirement that zero be placed in the timestamp
  			 * echo reply when ts_recent isn't valid.  The
  			 * age isn't reset until we get a valid ts_recent
  			 * because we don't want out-of-order segments to be
  			 * dropped when ts_recent is old.
  			 */
  			tp->ts_recent = 0;
  		} else {
  			tcpstat_pkt(tcps_rcvduppack, tcps_rcvdupbyte, tlen);
  			tcpstat_inc(tcps_pawsdrop);
  			if (tlen)
  				goto dropafterack;
  			goto drop;
  		}
  	}
  
  	todrop = tp->rcv_nxt - th->th_seq;
  	if (todrop > 0) {
  		if (tiflags & TH_SYN) {
  			tiflags &= ~TH_SYN;
  			th->th_seq++;
  			if (th->th_urp > 1)
  				th->th_urp--;
  			else
  				tiflags &= ~TH_URG;
  			todrop--;
  		}
  		if (todrop > tlen ||
  		    (todrop == tlen && (tiflags & TH_FIN) == 0)) {
  			/*
  			 * Any valid FIN must be to the left of the
  			 * window.  At this point, FIN must be a
  			 * duplicate or out-of-sequence, so drop it.
  			 */
  			tiflags &= ~TH_FIN;
  			/*
  			 * Send ACK to resynchronize, and drop any data,
  			 * but keep on processing for RST or ACK.
  			 */
  			tp->t_flags |= TF_ACKNOW;
  			todrop = tlen;
  			tcpstat_pkt(tcps_rcvduppack, tcps_rcvdupbyte, todrop);
  		} else {
  			tcpstat_pkt(tcps_rcvpartduppack, tcps_rcvpartdupbyte,
  			    todrop);
  		}
  		hdroptlen += todrop;	/* drop from head afterwards */
  		th->th_seq += todrop;
  		tlen -= todrop;
  		if (th->th_urp > todrop)
  			th->th_urp -= todrop;
  		else {
  			tiflags &= ~TH_URG;
  			th->th_urp = 0;
  		}
  	}
  
  	/*
  	 * If new data are received on a connection after the
  	 * user processes are gone, then RST the other end.
  	 */
  	if ((so->so_state & SS_NOFDREF) &&
  	    tp->t_state > TCPS_CLOSE_WAIT && tlen) {
  		tp = tcp_close(tp);
  		tcpstat_inc(tcps_rcvafterclose);
  		goto dropwithreset;
  	}
  
  	/*
  	 * If segment ends after window, drop trailing data
  	 * (and PUSH and FIN); if nothing left, just ACK.
  	 */
  	todrop = (th->th_seq + tlen) - (tp->rcv_nxt+tp->rcv_wnd);
  	if (todrop > 0) {
  		tcpstat_inc(tcps_rcvpackafterwin);
  		if (todrop >= tlen) {
  			tcpstat_add(tcps_rcvbyteafterwin, tlen);
  			/*
  			 * If window is closed can only take segments at
  			 * window edge, and have to drop data and PUSH from
  			 * incoming segments.  Continue processing, but
  			 * remember to ack.  Otherwise, drop segment
  			 * and ack.
  			 */
  			if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
  				tp->t_flags |= TF_ACKNOW;
  				tcpstat_inc(tcps_rcvwinprobe);
  			} else
  				goto dropafterack;
  		} else
  			tcpstat_add(tcps_rcvbyteafterwin, todrop);
  		m_adj(m, -todrop);
  		tlen -= todrop;
  		tiflags &= ~(TH_PUSH|TH_FIN);
  	}
  
  	/*
  	 * If last ACK falls within this segment's sequence numbers,
  	 * record its timestamp if it's more recent.
  	 * NOTE that the test is modified according to the latest
  	 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
  	 */
  	if (opti.ts_present && TSTMP_GEQ(opti.ts_val, tp->ts_recent) &&
  	    SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
  		tp->ts_recent_age = now;
  		tp->ts_recent = opti.ts_val;
  	}
  
  	/*
  	 * If the RST bit is set examine the state:
  	 *    SYN_RECEIVED STATE:
  	 *	If passive open, return to LISTEN state.
  	 *	If active open, inform user that connection was refused.
  	 *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES:
  	 *	Inform user that connection was reset, and close tcb.
  	 *    CLOSING, LAST_ACK, TIME_WAIT STATES
  	 *	Close the tcb.
  	 */
  	if (tiflags & TH_RST) {
  		if (th->th_seq != tp->last_ack_sent &&
  		    th->th_seq != tp->rcv_nxt &&
  		    th->th_seq != (tp->rcv_nxt + 1))
  			goto drop;
  
  		switch (tp->t_state) {
  		case TCPS_SYN_RECEIVED:
  #ifdef TCP_ECN
  			/* if ECN is enabled, fall back to non-ecn at rexmit */
  			if (do_ecn && !(tp->t_flags & TF_DISABLE_ECN))
  				goto drop;
  #endif
  			so->so_error = ECONNREFUSED;
  			goto close;
  
  		case TCPS_ESTABLISHED:
  		case TCPS_FIN_WAIT_1:
  		case TCPS_FIN_WAIT_2:
  		case TCPS_CLOSE_WAIT:
  			so->so_error = ECONNRESET;
  		close:
  			tp->t_state = TCPS_CLOSED;
  			tcpstat_inc(tcps_drops);
  			tp = tcp_close(tp);
  			goto drop;
  		case TCPS_CLOSING:
  		case TCPS_LAST_ACK:
  		case TCPS_TIME_WAIT:
  			tp = tcp_close(tp);
  			goto drop;
  		}
  	}
  
  	/*
  	 * If a SYN is in the window, then this is an
  	 * error and we ACK and drop the packet.
  	 */
  	if (tiflags & TH_SYN)
  		goto dropafterack_ratelim;
  
  	/*
  	 * If the ACK bit is off we drop the segment and return.
  	 */
  	if ((tiflags & TH_ACK) == 0) {
  		if (tp->t_flags & TF_ACKNOW)
  			goto dropafterack;
  		else
  			goto drop;
  	}
  
  	/*
  	 * Ack processing.
  	 */
  	switch (tp->t_state) {
  
  	/*
  	 * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
  	 * ESTABLISHED state and continue processing.
  	 * The ACK was checked above.
  	 */
  	case TCPS_SYN_RECEIVED:
  		tcpstat_inc(tcps_connects);
  		tp->t_flags |= TF_BLOCKOUTPUT;
  		soisconnected(so);
  		tp->t_flags &= ~TF_BLOCKOUTPUT;
  		tp->t_state = TCPS_ESTABLISHED;
  		TCP_TIMER_ARM(tp, TCPT_KEEP, atomic_load_int(&tcp_keepidle));
  		/* Do window scaling? */
  		if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
  			(TF_RCVD_SCALE|TF_REQ_SCALE)) {
  			tp->snd_scale = tp->requested_s_scale;
  			tp->rcv_scale = tp->request_r_scale;
  			tiwin = th->th_win << tp->snd_scale;
  		}
  		tcp_flush_queue(tp);
  		tp->snd_wl1 = th->th_seq - 1;
  		/* fall into ... */
  
  	/*
  	 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
  	 * ACKs.  If the ack is in the range
  	 *	tp->snd_una < th->th_ack <= tp->snd_max
  	 * then advance tp->snd_una to th->th_ack and drop
  	 * data from the retransmission queue.  If this ACK reflects
  	 * more up to date window information we update our window information.
  	 */
  	case TCPS_ESTABLISHED:
  	case TCPS_FIN_WAIT_1:
  	case TCPS_FIN_WAIT_2:
  	case TCPS_CLOSE_WAIT:
  	case TCPS_CLOSING:
  	case TCPS_LAST_ACK:
  	case TCPS_TIME_WAIT:
  #ifdef TCP_ECN
  		/*
  		 * if we receive ECE and are not already in recovery phase,
  		 * reduce cwnd by half but don't slow-start.
  		 * advance snd_last to snd_max not to reduce cwnd again
  		 * until all outstanding packets are acked.
  		 */
  		if (do_ecn && (tiflags & TH_ECE)) {
  			if ((tp->t_flags & TF_ECN_PERMIT) &&
  			    SEQ_GEQ(tp->snd_una, tp->snd_last)) {
  				u_int win;
  
  				win = min(tp->snd_wnd, tp->snd_cwnd) / tp->t_maxseg;
  				if (win > 1) {
  					tp->snd_ssthresh = win / 2 * tp->t_maxseg;
  					tp->snd_cwnd = tp->snd_ssthresh;
  					tp->snd_last = tp->snd_max;
  					tp->t_flags |= TF_SEND_CWR;
  					tcpstat_inc(tcps_cwr_ecn);
  				}
  			}
  			tcpstat_inc(tcps_ecn_rcvece);
  		}
  		/*
  		 * if we receive CWR, we know that the peer has reduced
  		 * its congestion window.  stop sending ecn-echo.
  		 */
  		if ((tiflags & TH_CWR)) {
  			tp->t_flags &= ~TF_RCVD_CE;
  			tcpstat_inc(tcps_ecn_rcvcwr);
  		}
  #endif /* TCP_ECN */
  
  		if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
  			/*
  			 * Duplicate/old ACK processing.
  			 * Increments t_dupacks:
  			 *	Pure duplicate (same seq/ack/window, no data)
  			 * Doesn't affect t_dupacks:
  			 *	Data packets.
  			 *	Normal window updates (window opens)
  			 * Resets t_dupacks:
  			 *	New data ACKed.
  			 *	Window shrinks
  			 *	Old ACK
  			 */
  			if (tlen) {
  				/* Drop very old ACKs unless th_seq matches */
  				if (th->th_seq != tp->rcv_nxt &&
  				   SEQ_LT(th->th_ack,
  				   tp->snd_una - tp->max_sndwnd)) {
  					tcpstat_inc(tcps_rcvacktooold);
  					goto drop;
  				}
  				break;
  			}
  			/*
  			 * If we get an old ACK, there is probably packet
  			 * reordering going on.  Be conservative and reset
  			 * t_dupacks so that we are less aggressive in
  			 * doing a fast retransmit.
  			 */
  			if (th->th_ack != tp->snd_una) {
  				tp->t_dupacks = 0;
  				break;
  			}
  			if (tiwin == tp->snd_wnd) {
  				tcpstat_inc(tcps_rcvdupack);
  				/*
  				 * If we have outstanding data (other than
  				 * a window probe), this is a completely
  				 * duplicate ack (ie, window info didn't
  				 * change), the ack is the biggest we've
  				 * seen and we've seen exactly our rexmt
  				 * threshold of them, assume a packet
  				 * has been dropped and retransmit it.
  				 * Kludge snd_nxt & the congestion
  				 * window so we send only this one
  				 * packet.
  				 *
  				 * We know we're losing at the current
  				 * window size so do congestion avoidance
  				 * (set ssthresh to half the current window
  				 * and pull our congestion window back to
  				 * the new ssthresh).
  				 *
  				 * Dup acks mean that packets have left the
  				 * network (they're now cached at the receiver)
  				 * so bump cwnd by the amount in the receiver
  				 * to keep a constant cwnd packets in the
  				 * network.
  				 */
  				if (TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0)
  					tp->t_dupacks = 0;
  				else if (++tp->t_dupacks == tcprexmtthresh) {
  					tcp_seq onxt = tp->snd_nxt;
  					u_long win =
  					    ulmin(tp->snd_wnd, tp->snd_cwnd) /
  						2 / tp->t_maxseg;
  
  					if (SEQ_LT(th->th_ack, tp->snd_last)){
  						/*
  						 * False fast retx after
  						 * timeout.  Do not cut window.
  						 */
  						tp->t_dupacks = 0;
  						goto drop;
  					}
  					if (win < 2)
  						win = 2;
  					tp->snd_ssthresh = win * tp->t_maxseg;
  					tp->snd_last = tp->snd_max;
  					if (tp->sack_enable) {
  						TCP_TIMER_DISARM(tp, TCPT_REXMT);
  						tp->t_rtttime = 0;
  #ifdef TCP_ECN
  						tp->t_flags |= TF_SEND_CWR;
  #endif
  						tcpstat_inc(tcps_cwr_frecovery);
  						tcpstat_inc(tcps_sack_recovery_episode);
  						/*
  						 * tcp_output() will send
  						 * oldest SACK-eligible rtx.
  						 */
  						(void) tcp_output(tp);
  						tp->snd_cwnd = tp->snd_ssthresh+
  						   tp->t_maxseg * tp->t_dupacks;
  						goto drop;
  					}
  					TCP_TIMER_DISARM(tp, TCPT_REXMT);
  					tp->t_rtttime = 0;
  					tp->snd_nxt = th->th_ack;
  					tp->snd_cwnd = tp->t_maxseg;
  #ifdef TCP_ECN
  					tp->t_flags |= TF_SEND_CWR;
  #endif
  					tcpstat_inc(tcps_cwr_frecovery);
  					tcpstat_inc(tcps_sndrexmitfast);
  					(void) tcp_output(tp);
  
  					tp->snd_cwnd = tp->snd_ssthresh +
  					    tp->t_maxseg * tp->t_dupacks;
  					if (SEQ_GT(onxt, tp->snd_nxt))
  						tp->snd_nxt = onxt;
  					goto drop;
  				} else if (tp->t_dupacks > tcprexmtthresh) {
  					tp->snd_cwnd += tp->t_maxseg;
  					(void) tcp_output(tp);
  					goto drop;
  				}
  			} else if (tiwin < tp->snd_wnd) {
  				/*
  				 * The window was retracted!  Previous dup
  				 * ACKs may have been due to packets arriving
  				 * after the shrunken window, not a missing
  				 * packet, so play it safe and reset t_dupacks
  				 */
  				tp->t_dupacks = 0;
  			}
  			break;
  		}
  		/*
  		 * If the congestion window was inflated to account
  		 * for the other side's cached packets, retract it.
  		 */
  		if (tp->t_dupacks >= tcprexmtthresh) {
  			/* Check for a partial ACK */
  			if (SEQ_LT(th->th_ack, tp->snd_last)) {
  				if (tp->sack_enable)
  					tcp_sack_partialack(tp, th);
  				else
  					tcp_newreno_partialack(tp, th);
  			} else {
  				/* Out of fast recovery */
  				tp->snd_cwnd = tp->snd_ssthresh;
  				if (tcp_seq_subtract(tp->snd_max, th->th_ack) <
  				    tp->snd_ssthresh)
  					tp->snd_cwnd =
  					    tcp_seq_subtract(tp->snd_max,
  					    th->th_ack);
  				tp->t_dupacks = 0;
  			}
  		} else {
  			/*
  			 * Reset the duplicate ACK counter if we
  			 * were not in fast recovery.
  			 */
  			tp->t_dupacks = 0;
  		}
  		if (SEQ_GT(th->th_ack, tp->snd_max)) {
  			tcpstat_inc(tcps_rcvacktoomuch);
  			goto dropafterack_ratelim;
  		}
  		acked = th->th_ack - tp->snd_una;
  		tcpstat_pkt(tcps_rcvackpack, tcps_rcvackbyte, acked);
  		tp->t_rcvacktime = now;
  
  		/*
  		 * If we have a timestamp reply, update smoothed
  		 * round trip time.  If no timestamp is present but
  		 * transmit timer is running and timed sequence
  		 * number was acked, update smoothed round trip time.
  		 * Since we now have an rtt measurement, cancel the
  		 * timer backoff (cf., Phil Karn's retransmit alg.).
  		 * Recompute the initial retransmit timer.
  		 */
  		if (opti.ts_present && opti.ts_ecr)
  			tcp_xmit_timer(tp, now - opti.ts_ecr);
  		else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq))
  			tcp_xmit_timer(tp, now - tp->t_rtttime);
  
  		/*
  		 * If all outstanding data is acked, stop retransmit
  		 * timer and remember to restart (more output or persist).
  		 * If there is more data to be acked, restart retransmit
  		 * timer, using current (possibly backed-off) value.
  		 */
  		if (th->th_ack == tp->snd_max) {
  			TCP_TIMER_DISARM(tp, TCPT_REXMT);
  			tp->t_flags |= TF_NEEDOUTPUT;
  		} else if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0)
  			TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur);
  		/*
  		 * When new data is acked, open the congestion window.
  		 * If the window gives us less than ssthresh packets
  		 * in flight, open exponentially (maxseg per packet).
  		 * Otherwise open linearly: maxseg per window
  		 * (maxseg^2 / cwnd per packet).
  		 */
  		{
  		u_int cw = tp->snd_cwnd;
  		u_int incr = tp->t_maxseg;
  
  		if (cw > tp->snd_ssthresh)
  			incr = max(incr * incr / cw, 1);
  		if (tp->t_dupacks < tcprexmtthresh)
  			tp->snd_cwnd = ulmin(cw + incr,
  			    TCP_MAXWIN << tp->snd_scale);
  		}
  		ND6_HINT(tp);
  		if (acked > so->so_snd.sb_cc) {
  			if (tp->snd_wnd > so->so_snd.sb_cc)
  				tp->snd_wnd -= so->so_snd.sb_cc;
  			else
  				tp->snd_wnd = 0;
  			mtx_enter(&so->so_snd.sb_mtx);
  			sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
  			mtx_leave(&so->so_snd.sb_mtx);
  			ourfinisacked = 1;
  		} else {
  			mtx_enter(&so->so_snd.sb_mtx);
  			sbdrop(&so->so_snd, acked);
  			mtx_leave(&so->so_snd.sb_mtx);
  			if (tp->snd_wnd > acked)
  				tp->snd_wnd -= acked;
  			else
  				tp->snd_wnd = 0;
  			ourfinisacked = 0;
  		}
  
  		tcp_update_sndspace(tp);
  		if (sb_notify(&so->so_snd)) {
  			tp->t_flags |= TF_BLOCKOUTPUT;
  			sowwakeup(so);
  			tp->t_flags &= ~TF_BLOCKOUTPUT;
  		}
  
  		/*
  		 * If we had a pending ICMP message that referred to data
  		 * that have just been acknowledged, disregard the recorded
  		 * ICMP message.
  		 */
  		if ((tp->t_flags & TF_PMTUD_PEND) &&
  		    SEQ_GT(th->th_ack, tp->t_pmtud_th_seq))
  			tp->t_flags &= ~TF_PMTUD_PEND;
  
  		/*
  		 * Keep track of the largest chunk of data acknowledged
  		 * since last PMTU update
  		 */
  		if (tp->t_pmtud_mss_acked < acked)
  			tp->t_pmtud_mss_acked = acked;
  
  		tp->snd_una = th->th_ack;
  #ifdef TCP_ECN
  		/* sync snd_last with snd_una */
  		if (SEQ_GT(tp->snd_una, tp->snd_last))
  			tp->snd_last = tp->snd_una;
  #endif
  		if (SEQ_LT(tp->snd_nxt, tp->snd_una))
  			tp->snd_nxt = tp->snd_una;
  
  		switch (tp->t_state) {
  
  		/*
  		 * In FIN_WAIT_1 STATE in addition to the processing
  		 * for the ESTABLISHED state if our FIN is now acknowledged
  		 * then enter FIN_WAIT_2.
  		 */
  		case TCPS_FIN_WAIT_1:
  			if (ourfinisacked) {
  				/*
  				 * If we can't receive any more
  				 * data, then closing user can proceed.
  				 * Starting the timer is contrary to the
  				 * specification, but if we don't get a FIN
  				 * we'll hang forever.
  				 */
  				if (so->so_rcv.sb_state & SS_CANTRCVMORE) {
  					int maxidle;
  
  					tp->t_flags |= TF_BLOCKOUTPUT;
  					soisdisconnected(so);
  					tp->t_flags &= ~TF_BLOCKOUTPUT;
  					maxidle = TCPTV_KEEPCNT *
  					    atomic_load_int(&tcp_keepidle);
  					TCP_TIMER_ARM(tp, TCPT_2MSL, maxidle);
  				}
  				tp->t_state = TCPS_FIN_WAIT_2;
  			}
  			break;
  
  		/*
  		 * In CLOSING STATE in addition to the processing for
  		 * the ESTABLISHED state if the ACK acknowledges our FIN
  		 * then enter the TIME-WAIT state, otherwise ignore
  		 * the segment.
  		 */
  		case TCPS_CLOSING:
  			if (ourfinisacked) {
  				tp->t_state = TCPS_TIME_WAIT;
  				tcp_canceltimers(tp);
  				TCP_TIMER_ARM(tp, TCPT_2MSL, 2 * TCPTV_MSL);
  				tp->t_flags |= TF_BLOCKOUTPUT;
  				soisdisconnected(so);
  				tp->t_flags &= ~TF_BLOCKOUTPUT;
  			}
  			break;
  
  		/*
  		 * In LAST_ACK, we may still be waiting for data to drain
  		 * and/or to be acked, as well as for the ack of our FIN.
  		 * If our FIN is now acknowledged, delete the TCB,
  		 * enter the closed state and return.
  		 */
  		case TCPS_LAST_ACK:
  			if (ourfinisacked) {
  				tp = tcp_close(tp);
  				goto drop;
  			}
  			break;
  
  		/*
  		 * In TIME_WAIT state the only thing that should arrive
  		 * is a retransmission of the remote FIN.  Acknowledge
  		 * it and restart the finack timer.
  		 */
  		case TCPS_TIME_WAIT:
  			TCP_TIMER_ARM(tp, TCPT_2MSL, 2 * TCPTV_MSL);
  			goto dropafterack;
  		}
  	}
  
  step6:
  	/*
  	 * Update window information.
  	 * Don't look at window if no ACK: TAC's send garbage on first SYN.
  	 */
  	if ((tiflags & TH_ACK) &&
  	    (SEQ_LT(tp->snd_wl1, th->th_seq) || (tp->snd_wl1 == th->th_seq &&
  	    (SEQ_LT(tp->snd_wl2, th->th_ack) ||
  	    (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
  		/* keep track of pure window updates */
  		if (tlen == 0 &&
  		    tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
  			tcpstat_inc(tcps_rcvwinupd);
  		tp->snd_wnd = tiwin;
  		tp->snd_wl1 = th->th_seq;
  		tp->snd_wl2 = th->th_ack;
  		if (tp->snd_wnd > tp->max_sndwnd)
  			tp->max_sndwnd = tp->snd_wnd;
  		tp->t_flags |= TF_NEEDOUTPUT;
  	}
  
  	/*
  	 * Process segments with URG.
  	 */
  	if ((tiflags & TH_URG) && th->th_urp &&
  	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
  		u_long urgent;
  
  		/*
  		 * This is a kludge, but if we receive and accept
  		 * random urgent pointers, we'll crash in
  		 * soreceive.  It's hard to imagine someone
  		 * actually wanting to send this much urgent data.
  		 */
  		mtx_enter(&so->so_rcv.sb_mtx);
  		urgent = th->th_urp + so->so_rcv.sb_cc;
  		mtx_leave(&so->so_rcv.sb_mtx);
  
  		if (urgent > sb_max) {
  			th->th_urp = 0;			/* XXX */
  			tiflags &= ~TH_URG;		/* XXX */
  			goto dodata;			/* XXX */
  		}
  		/*
  		 * If this segment advances the known urgent pointer,
  		 * then mark the data stream.  This should not happen
  		 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
  		 * a FIN has been received from the remote side.
  		 * In these states we ignore the URG.
  		 *
  		 * According to RFC961 (Assigned Protocols),
  		 * the urgent pointer points to the last octet
  		 * of urgent data.  We continue, however,
  		 * to consider it to indicate the first octet
  		 * of data past the urgent section as the original
  		 * spec states (in one of two places).
  		 */
  		if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
  			tp->rcv_up = th->th_seq + th->th_urp;
  			mtx_enter(&so->so_rcv.sb_mtx);
  			so->so_oobmark = so->so_rcv.sb_cc +
  			    (tp->rcv_up - tp->rcv_nxt) - 1;
  			if (so->so_oobmark == 0)
  				so->so_rcv.sb_state |= SS_RCVATMARK;
  			mtx_leave(&so->so_rcv.sb_mtx);
  			sohasoutofband(so);
  			tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
  		}
  		/*
  		 * Remove out of band data so doesn't get presented to user.
  		 * This can happen independent of advancing the URG pointer,
  		 * but if two URG's are pending at once, some out-of-band
  		 * data may creep in... ick.
  		 */
  		if (th->th_urp <= (u_int16_t) tlen &&
  		    (so->so_options & SO_OOBINLINE) == 0)
  			tcp_pulloutofband(so, th->th_urp, m, hdroptlen);
  	} else
  		/*
  		 * If no out of band data is expected,
  		 * pull receive urgent pointer along
  		 * with the receive window.
  		 */
  		if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
  			tp->rcv_up = tp->rcv_nxt;
  dodata:							/* XXX */
  
  	/*
  	 * Process the segment text, merging it into the TCP sequencing queue,
  	 * and arranging for acknowledgment of receipt if necessary.
  	 * This process logically involves adjusting tp->rcv_wnd as data
  	 * is presented to the user (this happens in tcp_usrreq.c,
  	 * case PRU_RCVD).  If a FIN has already been received on this
  	 * connection then we just ignore the text.
  	 */
  	if ((tlen || (tiflags & TH_FIN)) &&
  	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
  		tcp_seq laststart = th->th_seq;
  		tcp_seq lastend = th->th_seq + tlen;
  
  		if (th->th_seq == tp->rcv_nxt && TAILQ_EMPTY(&tp->t_segq) &&
  		    tp->t_state == TCPS_ESTABLISHED) {
  			TCP_SETUP_ACK(tp, tiflags, m);
  			tp->rcv_nxt += tlen;
  			tiflags = th->th_flags & TH_FIN;
  			tcpstat_pkt(tcps_rcvpack, tcps_rcvbyte, tlen);
  			ND6_HINT(tp);
  			if (so->so_rcv.sb_state & SS_CANTRCVMORE)
  				m_freem(m);
  			else {
  				m_adj(m, hdroptlen);
  				mtx_enter(&so->so_rcv.sb_mtx);
  				sbappendstream(&so->so_rcv, m);
  				mtx_leave(&so->so_rcv.sb_mtx);
  			}
  			tp->t_flags |= TF_BLOCKOUTPUT;
  			sorwakeup(so);
  			tp->t_flags &= ~TF_BLOCKOUTPUT;
  		} else {
  			m_adj(m, hdroptlen);
  			tiflags = tcp_reass(tp, th, m, &tlen);
  			tp->t_flags |= TF_ACKNOW;
  		}
  		if (tp->sack_enable)
  			tcp_update_sack_list(tp, laststart, lastend);
  
  		/*
  		 * variable len never referenced again in modern BSD,
  		 * so why bother computing it ??
  		 */
  #if 0
  		/*
  		 * Note the amount of data that peer has sent into
  		 * our window, in order to estimate the sender's
  		 * buffer size.
  		 */
  		len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
  #endif /* 0 */
  	} else {
  		m_freem(m);
  		tiflags &= ~TH_FIN;
  	}
  
  	/*
  	 * If FIN is received ACK the FIN and let the user know
  	 * that the connection is closing.  Ignore a FIN received before
  	 * the connection is fully established.
  	 */
  	if ((tiflags & TH_FIN) && TCPS_HAVEESTABLISHED(tp->t_state)) {
  		if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
  			tp->t_flags |= TF_BLOCKOUTPUT;
  			socantrcvmore(so);
  			tp->t_flags &= ~TF_BLOCKOUTPUT;
  			tp->t_flags |= TF_ACKNOW;
  			tp->rcv_nxt++;
  		}
  		switch (tp->t_state) {
  
  		/*
  		 * In ESTABLISHED STATE enter the CLOSE_WAIT state.
  		 */
  		case TCPS_ESTABLISHED:
  			tp->t_state = TCPS_CLOSE_WAIT;
  			break;
  
  		/*
  		 * If still in FIN_WAIT_1 STATE FIN has not been acked so
  		 * enter the CLOSING state.
  		 */
  		case TCPS_FIN_WAIT_1:
  			tp->t_state = TCPS_CLOSING;
  			break;
  
  		/*
  		 * In FIN_WAIT_2 state enter the TIME_WAIT state,
  		 * starting the time-wait timer, turning off the other
  		 * standard timers.
  		 */
  		case TCPS_FIN_WAIT_2:
  			tp->t_state = TCPS_TIME_WAIT;
  			tcp_canceltimers(tp);
  			TCP_TIMER_ARM(tp, TCPT_2MSL, 2 * TCPTV_MSL);
  			tp->t_flags |= TF_BLOCKOUTPUT;
  			soisdisconnected(so);
  			tp->t_flags &= ~TF_BLOCKOUTPUT;
  			break;
  
  		/*
  		 * In TIME_WAIT state restart the 2 MSL time_wait timer.
  		 */
  		case TCPS_TIME_WAIT:
  			TCP_TIMER_ARM(tp, TCPT_2MSL, 2 * TCPTV_MSL);
  			break;
  		}
  	}
  	if (otp)
  		tcp_trace(TA_INPUT, ostate, tp, otp, &saveti.caddr, 0, tlen);
  
  	/*
  	 * Return any desired output.
  	 */
  	if (tp->t_flags & (TF_ACKNOW|TF_NEEDOUTPUT))
  		(void) tcp_output(tp);
  	if (solocked != NULL)
  		*solocked = so;
  	else
  		in_pcbsounlock(inp, so);
  	in_pcbunref(inp);
  	return IPPROTO_DONE;
  
  badsyn:
  	/*
  	 * Received a bad SYN.  Increment counters and dropwithreset.
  	 */
  	tcpstat_inc(tcps_badsyn);
  	tp = NULL;
  	goto dropwithreset;
  
  dropafterack_ratelim:
  	if (ppsratecheck(&tcp_ackdrop_ppslim_last, &tcp_ackdrop_ppslim_count,
  	    tcp_ackdrop_ppslim) == 0) {
  		/* XXX stat */
  		goto drop;
  	}
  	/* ...fall into dropafterack... */
  
  dropafterack:
  	/*
  	 * Generate an ACK dropping incoming segment if it occupies
  	 * sequence space, where the ACK reflects our state.
  	 */
  	if (tiflags & TH_RST)
  		goto drop;
  	m_freem(m);
  	tp->t_flags |= TF_ACKNOW;
  	(void) tcp_output(tp);
  	if (solocked != NULL)
  		*solocked = so;
  	else
  		in_pcbsounlock(inp, so);
  	in_pcbunref(inp);
  	return IPPROTO_DONE;
  
  dropwithreset_ratelim:
  	/*
  	 * We may want to rate-limit RSTs in certain situations,
  	 * particularly if we are sending an RST in response to
  	 * an attempt to connect to or otherwise communicate with
  	 * a port for which we have no socket.
  	 */
  	if (ppsratecheck(&tcp_rst_ppslim_last, &tcp_rst_ppslim_count,
  	    atomic_load_int(&tcp_rst_ppslim)) == 0) {
  		/* XXX stat */
  		goto drop;
  	}
  	/* ...fall into dropwithreset... */
  
  dropwithreset:
  	/*
  	 * Generate a RST, dropping incoming segment.
  	 * Make ACK acceptable to originator of segment.
  	 * Don't bother to respond to RST.
  	 */
  	if (tiflags & TH_RST)
  		goto drop;
  	if (tiflags & TH_ACK) {
  		tcp_respond(tp, mtod(m, caddr_t), th, (tcp_seq)0, th->th_ack,
  		    TH_RST, m->m_pkthdr.ph_rtableid, now);
  	} else {
  		if (tiflags & TH_SYN)
  			tlen++;
  		tcp_respond(tp, mtod(m, caddr_t), th, th->th_seq + tlen,
  		    (tcp_seq)0, TH_RST|TH_ACK, m->m_pkthdr.ph_rtableid, now);
  	}
  	m_freem(m);
  	in_pcbsounlock(inp, so);
  	in_pcbunref(inp);
  	return IPPROTO_DONE;
  
  drop:
  	/*
  	 * Drop space held by incoming segment and return.
  	 */
  	if (otp)
  		tcp_trace(TA_DROP, ostate, tp, otp, &saveti.caddr, 0, tlen);
  
  	m_freem(m);
  	in_pcbsounlock(inp, so);
  	in_pcbunref(inp);
  	return IPPROTO_DONE;
  }
  
  int
  tcp_dooptions(struct tcpcb *tp, u_char *cp, int cnt, struct tcphdr *th,
      struct mbuf *m, int iphlen, struct tcp_opt_info *oi,
      u_int rtableid, uint64_t now)
  {
  	u_int16_t mss = 0;
  	int opt, optlen;
  #ifdef TCP_SIGNATURE
  	caddr_t sigp = NULL;
  	struct tdb *tdb = NULL;
  #endif
  
  	for (; cp && cnt > 0; cnt -= optlen, cp += optlen) {
  		opt = cp[0];
  		if (opt == TCPOPT_EOL)
  			break;
  		if (opt == TCPOPT_NOP)
  			optlen = 1;
  		else {
  			if (cnt < 2)
  				break;
  			optlen = cp[1];
  			if (optlen < 2 || optlen > cnt)
  				break;
  		}
  		switch (opt) {
  
  		default:
  			continue;
  
  		case TCPOPT_MAXSEG:
  			if (optlen != TCPOLEN_MAXSEG)
  				continue;
  			if (!(th->th_flags & TH_SYN))
  				continue;
  			if (TCPS_HAVERCVDSYN(tp->t_state))
  				continue;
  			memcpy(&mss, cp + 2, sizeof(mss));
  			mss = ntohs(mss);
  			oi->maxseg = mss;
  			break;
  
  		case TCPOPT_WINDOW:
  			if (optlen != TCPOLEN_WINDOW)
  				continue;
  			if (!(th->th_flags & TH_SYN))
  				continue;
  			if (TCPS_HAVERCVDSYN(tp->t_state))
  				continue;
  			tp->t_flags |= TF_RCVD_SCALE;
  			tp->requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
  			break;
  
  		case TCPOPT_TIMESTAMP:
  			if (optlen != TCPOLEN_TIMESTAMP)
  				continue;
  			oi->ts_present = 1;
  			memcpy(&oi->ts_val, cp + 2, sizeof(oi->ts_val));
  			oi->ts_val = ntohl(oi->ts_val);
  			memcpy(&oi->ts_ecr, cp + 6, sizeof(oi->ts_ecr));
  			oi->ts_ecr = ntohl(oi->ts_ecr);
  
  			if (!(th->th_flags & TH_SYN))
  				continue;
  			if (TCPS_HAVERCVDSYN(tp->t_state))
  				continue;
  			/*
  			 * A timestamp received in a SYN makes
  			 * it ok to send timestamp requests and replies.
  			 */
  			tp->t_flags |= TF_RCVD_TSTMP;
  			tp->ts_recent = oi->ts_val;
  			tp->ts_recent_age = now;
  			break;
  
  		case TCPOPT_SACK_PERMITTED:
  			if (!tp->sack_enable || optlen!=TCPOLEN_SACK_PERMITTED)
  				continue;
  			if (!(th->th_flags & TH_SYN))
  				continue;
  			if (TCPS_HAVERCVDSYN(tp->t_state))
  				continue;
  			/* MUST only be set on SYN */
  			tp->t_flags |= TF_SACK_PERMIT;
  			break;
  		case TCPOPT_SACK:
  			tcp_sack_option(tp, th, cp, optlen);
  			break;
  #ifdef TCP_SIGNATURE
  		case TCPOPT_SIGNATURE:
  			if (optlen != TCPOLEN_SIGNATURE)
  				continue;
  
  			if (sigp && timingsafe_bcmp(sigp, cp + 2, 16))
  				goto bad;
  
  			sigp = cp + 2;
  			break;
  #endif /* TCP_SIGNATURE */
  		}
  	}
  
  #ifdef TCP_SIGNATURE
  	if (tp->t_flags & TF_SIGNATURE) {
  		union sockaddr_union src, dst;
  
  		memset(&src, 0, sizeof(union sockaddr_union));
  		memset(&dst, 0, sizeof(union sockaddr_union));
  
  		switch (tp->pf) {
  		case 0:
  		case AF_INET:
  			src.sa.sa_len = sizeof(struct sockaddr_in);
  			src.sa.sa_family = AF_INET;
  			src.sin.sin_addr = mtod(m, struct ip *)->ip_src;
  			dst.sa.sa_len = sizeof(struct sockaddr_in);
  			dst.sa.sa_family = AF_INET;
  			dst.sin.sin_addr = mtod(m, struct ip *)->ip_dst;
  			break;
  #ifdef INET6
  		case AF_INET6:
  			src.sa.sa_len = sizeof(struct sockaddr_in6);
  			src.sa.sa_family = AF_INET6;
  			src.sin6.sin6_addr = mtod(m, struct ip6_hdr *)->ip6_src;
  			dst.sa.sa_len = sizeof(struct sockaddr_in6);
  			dst.sa.sa_family = AF_INET6;
  			dst.sin6.sin6_addr = mtod(m, struct ip6_hdr *)->ip6_dst;
  			break;
  #endif /* INET6 */
  		}
  
  		tdb = gettdbbysrcdst(rtable_l2(rtableid),
  		    0, &src, &dst, IPPROTO_TCP);
  
  		/*
  		 * We don't have an SA for this peer, so we turn off
  		 * TF_SIGNATURE on the listen socket
  		 */
  		if (tdb == NULL && tp->t_state == TCPS_LISTEN)
  			tp->t_flags &= ~TF_SIGNATURE;
  
  	}
  
  	if ((sigp ? TF_SIGNATURE : 0) ^ (tp->t_flags & TF_SIGNATURE)) {
  		tcpstat_inc(tcps_rcvbadsig);
  		goto bad;
  	}
  
  	if (sigp) {
  		char sig[16];
  
  		if (tdb == NULL) {
  			tcpstat_inc(tcps_rcvbadsig);
  			goto bad;
  		}
  
  		if (tcp_signature(tdb, tp->pf, m, th, iphlen, 1, sig) < 0)
  			goto bad;
  
  		if (timingsafe_bcmp(sig, sigp, 16)) {
  			tcpstat_inc(tcps_rcvbadsig);
  			goto bad;
  		}
  
  		tcpstat_inc(tcps_rcvgoodsig);
  	}
  
  	tdb_unref(tdb);
  #endif /* TCP_SIGNATURE */
  
  	return (0);
  
  #ifdef TCP_SIGNATURE
   bad:
  	tdb_unref(tdb);
  #endif
  	return (-1);
  }
  
  u_long
  tcp_seq_subtract(u_long a, u_long b)
  {
  	return ((long)(a - b));
  }
  
  /*
   * This function is called upon receipt of new valid data (while not in header
   * prediction mode), and it updates the ordered list of sacks.
   */
  void
  tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_laststart,
      tcp_seq rcv_lastend)
  {
  	/*
  	 * First reported block MUST be the most recent one.  Subsequent
  	 * blocks SHOULD be in the order in which they arrived at the
  	 * receiver.  These two conditions make the implementation fully
  	 * compliant with RFC 2018.
  	 */
  	int i, j = 0, count = 0, lastpos = -1;
  	struct sackblk sack, firstsack, temp[MAX_SACK_BLKS];
  
  	/* First clean up current list of sacks */
  	for (i = 0; i < tp->rcv_numsacks; i++) {
  		sack = tp->sackblks[i];
  		if (sack.start == 0 && sack.end == 0) {
  			count++; /* count = number of blocks to be discarded */
  			continue;
  		}
  		if (SEQ_LEQ(sack.end, tp->rcv_nxt)) {
  			tp->sackblks[i].start = tp->sackblks[i].end = 0;
  			count++;
  		} else {
  			temp[j].start = tp->sackblks[i].start;
  			temp[j++].end = tp->sackblks[i].end;
  		}
  	}
  	tp->rcv_numsacks -= count;
  	if (tp->rcv_numsacks == 0) { /* no sack blocks currently (fast path) */
  		tcp_clean_sackreport(tp);
  		if (SEQ_LT(tp->rcv_nxt, rcv_laststart)) {
  			/* ==> need first sack block */
  			tp->sackblks[0].start = rcv_laststart;
  			tp->sackblks[0].end = rcv_lastend;
  			tp->rcv_numsacks = 1;
  		}
  		return;
  	}
  	/* Otherwise, sack blocks are already present. */
  	for (i = 0; i < tp->rcv_numsacks; i++)
  		tp->sackblks[i] = temp[i]; /* first copy back sack list */
  	if (SEQ_GEQ(tp->rcv_nxt, rcv_lastend))
  		return;     /* sack list remains unchanged */
  	/*
  	 * From here, segment just received should be (part of) the 1st sack.
  	 * Go through list, possibly coalescing sack block entries.
  	 */
  	firstsack.start = rcv_laststart;
  	firstsack.end = rcv_lastend;
  	for (i = 0; i < tp->rcv_numsacks; i++) {
  		sack = tp->sackblks[i];
  		if (SEQ_LT(sack.end, firstsack.start) ||
  		    SEQ_GT(sack.start, firstsack.end))
  			continue; /* no overlap */
  		if (sack.start == firstsack.start && sack.end == firstsack.end){
  			/*
  			 * identical block; delete it here since we will
  			 * move it to the front of the list.
  			 */
  			tp->sackblks[i].start = tp->sackblks[i].end = 0;
  			lastpos = i;    /* last posn with a zero entry */
  			continue;
  		}
  		if (SEQ_LEQ(sack.start, firstsack.start))
  			firstsack.start = sack.start; /* merge blocks */
  		if (SEQ_GEQ(sack.end, firstsack.end))
  			firstsack.end = sack.end;     /* merge blocks */
  		tp->sackblks[i].start = tp->sackblks[i].end = 0;
  		lastpos = i;    /* last posn with a zero entry */
  	}
  	if (lastpos != -1) {    /* at least one merge */
  		for (i = 0, j = 1; i < tp->rcv_numsacks; i++) {
  			sack = tp->sackblks[i];
  			if (sack.start == 0 && sack.end == 0)
  				continue;
  			temp[j++] = sack;
  		}
  		tp->rcv_numsacks = j; /* including first blk (added later) */
  		for (i = 1; i < tp->rcv_numsacks; i++) /* now copy back */
  			tp->sackblks[i] = temp[i];
  	} else {        /* no merges -- shift sacks by 1 */
  		if (tp->rcv_numsacks < MAX_SACK_BLKS)
  			tp->rcv_numsacks++;
  		for (i = tp->rcv_numsacks-1; i > 0; i--)
  			tp->sackblks[i] = tp->sackblks[i-1];
  	}
  	tp->sackblks[0] = firstsack;
  	return;
  }
  
  /*
   * Process the TCP SACK option.  tp->snd_holes is an ordered list
   * of holes (oldest to newest, in terms of the sequence space).
   */
  void
  tcp_sack_option(struct tcpcb *tp, struct tcphdr *th, u_char *cp, int optlen)
  {
  	int tmp_olen;
  	u_char *tmp_cp;
  	struct sackhole *cur, *p, *temp;
  
  	if (!tp->sack_enable)
  		return;
  	/* SACK without ACK doesn't make sense. */
  	if ((th->th_flags & TH_ACK) == 0)
  		return;
  	/* Make sure the ACK on this segment is in [snd_una, snd_max]. */
  	if (SEQ_LT(th->th_ack, tp->snd_una) ||
  	    SEQ_GT(th->th_ack, tp->snd_max))
  		return;
  	/* Note: TCPOLEN_SACK must be 2*sizeof(tcp_seq) */
  	if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
  		return;
  	/* Note: TCPOLEN_SACK must be 2*sizeof(tcp_seq) */
  	tmp_cp = cp + 2;
  	tmp_olen = optlen - 2;
  	tcpstat_inc(tcps_sack_rcv_opts);
  	if (tp->snd_numholes < 0)
  		tp->snd_numholes = 0;
  	if (tp->t_maxseg == 0)
  		panic("tcp_sack_option"); /* Should never happen */
  	while (tmp_olen > 0) {
  		struct sackblk sack;
  
  		memcpy(&sack.start, tmp_cp, sizeof(tcp_seq));
  		sack.start = ntohl(sack.start);
  		memcpy(&sack.end, tmp_cp + sizeof(tcp_seq), sizeof(tcp_seq));
  		sack.end = ntohl(sack.end);
  		tmp_olen -= TCPOLEN_SACK;
  		tmp_cp += TCPOLEN_SACK;
  		if (SEQ_LEQ(sack.end, sack.start))
  			continue; /* bad SACK fields */
  		if (SEQ_LEQ(sack.end, tp->snd_una))
  			continue; /* old block */
  		if (SEQ_GT(th->th_ack, tp->snd_una)) {
  			if (SEQ_LT(sack.start, th->th_ack))
  				continue;
  		}
  		if (SEQ_GT(sack.end, tp->snd_max))
  			continue;
  		if (tp->snd_holes == NULL) { /* first hole */
  			tp->snd_holes = (struct sackhole *)
  			    pool_get(&sackhl_pool, PR_NOWAIT);
  			if (tp->snd_holes == NULL) {
  				/* ENOBUFS, so ignore SACKed block for now */
  				goto dropped;
  			}
  			cur = tp->snd_holes;
  			cur->start = th->th_ack;
  			cur->end = sack.start;
  			cur->rxmit = cur->start;
  			cur->next = NULL;
  			tp->snd_numholes = 1;
  			tp->rcv_lastsack = sack.end;
  			/*
  			 * dups is at least one.  If more data has been
  			 * SACKed, it can be greater than one.
  			 */
  			cur->dups = min(tcprexmtthresh,
  			    ((sack.end - cur->end)/tp->t_maxseg));
  			if (cur->dups < 1)
  				cur->dups = 1;
  			continue; /* with next sack block */
  		}
  		/* Go thru list of holes:  p = previous,  cur = current */
  		p = cur = tp->snd_holes;
  		while (cur) {
  			if (SEQ_LEQ(sack.end, cur->start))
  				/* SACKs data before the current hole */
  				break; /* no use going through more holes */
  			if (SEQ_GEQ(sack.start, cur->end)) {
  				/* SACKs data beyond the current hole */
  				cur->dups++;
  				if (((sack.end - cur->end)/tp->t_maxseg) >=
  				    tcprexmtthresh)
  					cur->dups = tcprexmtthresh;
  				p = cur;
  				cur = cur->next;
  				continue;
  			}
  			if (SEQ_LEQ(sack.start, cur->start)) {
  				/* Data acks at least the beginning of hole */
  				if (SEQ_GEQ(sack.end, cur->end)) {
  					/* Acks entire hole, so delete hole */
  					if (p != cur) {
  						p->next = cur->next;
  						pool_put(&sackhl_pool, cur);
  						cur = p->next;
  					} else {
  						cur = cur->next;
  						pool_put(&sackhl_pool, p);
  						p = cur;
  						tp->snd_holes = p;
  					}
  					tp->snd_numholes--;
  					continue;
  				}
  				/* otherwise, move start of hole forward */
  				cur->start = sack.end;
  				cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
  				p = cur;
  				cur = cur->next;
  				continue;
  			}
  			/* move end of hole backward */
  			if (SEQ_GEQ(sack.end, cur->end)) {
  				cur->end = sack.start;
  				cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
  				cur->dups++;
  				if (((sack.end - cur->end)/tp->t_maxseg) >=
  				    tcprexmtthresh)
  					cur->dups = tcprexmtthresh;
  				p = cur;
  				cur = cur->next;
  				continue;
  			}
  			if (SEQ_LT(cur->start, sack.start) &&
  			    SEQ_GT(cur->end, sack.end)) {
  				/*
  				 * ACKs some data in middle of a hole; need to
  				 * split current hole
  				 */
  				if (tp->snd_numholes >= TCP_SACKHOLE_LIMIT)
  					goto dropped;
  				temp = (struct sackhole *)
  				    pool_get(&sackhl_pool, PR_NOWAIT);
  				if (temp == NULL)
  					goto dropped; /* ENOBUFS */
  				temp->next = cur->next;
  				temp->start = sack.end;
  				temp->end = cur->end;
  				temp->dups = cur->dups;
  				temp->rxmit = SEQ_MAX(cur->rxmit, temp->start);
  				cur->end = sack.start;
  				cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
  				cur->dups++;
  				if (((sack.end - cur->end)/tp->t_maxseg) >=
  					tcprexmtthresh)
  					cur->dups = tcprexmtthresh;
  				cur->next = temp;
  				p = temp;
  				cur = p->next;
  				tp->snd_numholes++;
  			}
  		}
  		/* At this point, p points to the last hole on the list */
  		if (SEQ_LT(tp->rcv_lastsack, sack.start)) {
  			/*
  			 * Need to append new hole at end.
  			 * Last hole is p (and it's not NULL).
  			 */
  			if (tp->snd_numholes >= TCP_SACKHOLE_LIMIT)
  				goto dropped;
  			temp = (struct sackhole *)
  			    pool_get(&sackhl_pool, PR_NOWAIT);
  			if (temp == NULL)
  				goto dropped; /* ENOBUFS */
  			temp->start = tp->rcv_lastsack;
  			temp->end = sack.start;
  			temp->dups = min(tcprexmtthresh,
  			    ((sack.end - sack.start)/tp->t_maxseg));
  			if (temp->dups < 1)
  				temp->dups = 1;
  			temp->rxmit = temp->start;
  			temp->next = 0;
  			p->next = temp;
  			tp->rcv_lastsack = sack.end;
  			tp->snd_numholes++;
  		}
  	}
  	return;
  dropped:
  	tcpstat_inc(tcps_sack_drop_opts);
  }
  
  /*
   * Delete stale (i.e, cumulatively ack'd) holes.  Hole is deleted only if
   * it is completely acked; otherwise, tcp_sack_option(), called from
   * tcp_dooptions(), will fix up the hole.
   */
  void
  tcp_del_sackholes(struct tcpcb *tp, struct tcphdr *th)
  {
  	if (tp->sack_enable && tp->t_state != TCPS_LISTEN) {
  		/* max because this could be an older ack just arrived */
  		tcp_seq lastack = SEQ_GT(th->th_ack, tp->snd_una) ?
  			th->th_ack : tp->snd_una;
  		struct sackhole *cur = tp->snd_holes;
  		struct sackhole *prev;
  		while (cur)
  			if (SEQ_LEQ(cur->end, lastack)) {
  				prev = cur;
  				cur = cur->next;
  				pool_put(&sackhl_pool, prev);
  				tp->snd_numholes--;
  			} else if (SEQ_LT(cur->start, lastack)) {
  				cur->start = lastack;
  				if (SEQ_LT(cur->rxmit, cur->start))
  					cur->rxmit = cur->start;
  				break;
  			} else
  				break;
  		tp->snd_holes = cur;
  	}
  }
  
  /*
   * Delete all receiver-side SACK information.
   */
  void
  tcp_clean_sackreport(struct tcpcb *tp)
  {
  	int i;
  
  	tp->rcv_numsacks = 0;
  	for (i = 0; i < MAX_SACK_BLKS; i++)
  		tp->sackblks[i].start = tp->sackblks[i].end=0;
  
  }
  
  /*
   * Partial ack handling within a sack recovery episode.  When a partial ack
   * arrives, turn off retransmission timer, deflate the window, do not clear
   * tp->t_dupacks.
   */
  void
  tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
  {
  	/* Turn off retx. timer (will start again next segment) */
  	TCP_TIMER_DISARM(tp, TCPT_REXMT);
  	tp->t_rtttime = 0;
  	/*
  	 * Partial window deflation.  This statement relies on the
  	 * fact that tp->snd_una has not been updated yet.
  	 */
  	if (tp->snd_cwnd > (th->th_ack - tp->snd_una)) {
  		tp->snd_cwnd -= th->th_ack - tp->snd_una;
  		tp->snd_cwnd += tp->t_maxseg;
  	} else
  		tp->snd_cwnd = tp->t_maxseg;
  	tp->snd_cwnd += tp->t_maxseg;
  	tp->t_flags |= TF_NEEDOUTPUT;
  }
  
  /*
   * Pull out of band byte out of a segment so
   * it doesn't appear in the user's data queue.
   * It is still reflected in the segment length for
   * sequencing purposes.
   */
  void
  tcp_pulloutofband(struct socket *so, u_int urgent, struct mbuf *m, int off)
  {
  	int cnt = off + urgent - 1;
  
  	while (cnt >= 0) {
  		if (m->m_len > cnt) {
  			char *cp = mtod(m, caddr_t) + cnt;
  			struct tcpcb *tp = sototcpcb(so);
  
  			tp->t_iobc = *cp;
  			tp->t_oobflags |= TCPOOB_HAVEDATA;
  			memmove(cp, cp + 1, m->m_len - cnt - 1);
  			m->m_len--;
  			return;
  		}
  		cnt -= m->m_len;
  		m = m->m_next;
  		if (m == NULL)
  			break;
  	}
  	panic("tcp_pulloutofband");
  }
  
  /*
   * Collect new round-trip time estimate
   * and update averages and current timeout.
   */
  void
  tcp_xmit_timer(struct tcpcb *tp, int32_t rtt)
  {
  	int delta, rttmin;
  
  	if (rtt < 0)
  		rtt = 0;
  	else if (rtt > TCP_RTT_MAX)
  		rtt = TCP_RTT_MAX;
  
  	tcpstat_inc(tcps_rttupdated);
  	if (tp->t_srtt != 0) {
  		/*
  		 * delta is fixed point with 2 (TCP_RTT_BASE_SHIFT) bits
  		 * after the binary point (scaled by 4), whereas
  		 * srtt is stored as fixed point with 5 bits after the
  		 * binary point (i.e., scaled by 32).  The following magic
  		 * is equivalent to the smoothing algorithm in rfc793 with
  		 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
  		 * point).
  		 */
  		delta = (rtt << TCP_RTT_BASE_SHIFT) -
  		    (tp->t_srtt >> TCP_RTT_SHIFT);
  		if ((tp->t_srtt += delta) <= 0)
  			tp->t_srtt = 1 << TCP_RTT_BASE_SHIFT;
  		/*
  		 * We accumulate a smoothed rtt variance (actually, a
  		 * smoothed mean difference), then set the retransmit
  		 * timer to smoothed rtt + 4 times the smoothed variance.
  		 * rttvar is stored as fixed point with 4 bits after the
  		 * binary point (scaled by 16).  The following is
  		 * equivalent to rfc793 smoothing with an alpha of .75
  		 * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
  		 * rfc793's wired-in beta.
  		 */
  		if (delta < 0)
  			delta = -delta;
  		delta -= (tp->t_rttvar >> TCP_RTTVAR_SHIFT);
  		if ((tp->t_rttvar += delta) <= 0)
  			tp->t_rttvar = 1 << TCP_RTT_BASE_SHIFT;
  	} else {
  		/*
  		 * No rtt measurement yet - use the unsmoothed rtt.
  		 * Set the variance to half the rtt (so our first
  		 * retransmit happens at 3*rtt).
  		 */
  		tp->t_srtt = (rtt + 1) << (TCP_RTT_SHIFT + TCP_RTT_BASE_SHIFT);
  		tp->t_rttvar = (rtt + 1) <<
  		    (TCP_RTTVAR_SHIFT + TCP_RTT_BASE_SHIFT - 1);
  	}
  	tp->t_rtttime = 0;
  	tp->t_rxtshift = 0;
  
  	/*
  	 * the retransmit should happen at rtt + 4 * rttvar.
  	 * Because of the way we do the smoothing, srtt and rttvar
  	 * will each average +1/2 tick of bias.  When we compute
  	 * the retransmit timer, we want 1/2 tick of rounding and
  	 * 1 extra tick because of +-1/2 tick uncertainty in the
  	 * firing of the timer.  The bias will give us exactly the
  	 * 1.5 tick we need.  But, because the bias is
  	 * statistical, we have to test that we don't drop below
  	 * the minimum feasible timer (which is 2 ticks).
  	 */
  	rttmin = min(max(tp->t_rttmin, rtt + 2 * (TCP_TIME(1) / hz)),
  	    TCPTV_REXMTMAX);
  	TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp), rttmin, TCPTV_REXMTMAX);
  
  	/*
  	 * We received an ack for a packet that wasn't retransmitted;
  	 * it is probably safe to discard any error indications we've
  	 * received recently.  This isn't quite right, but close enough
  	 * for now (a route might have failed after we sent a segment,
  	 * and the return path might not be symmetrical).
  	 */
  	tp->t_softerror = 0;
  }
  
  /*
   * Determine a reasonable value for maxseg size.
   * If the route is known, check route for mtu.
   * If none, use an mss that can be handled on the outgoing
   * interface without forcing IP to fragment; if bigger than
   * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
   * to utilize large mbufs.  If no route is found, route has no mtu,
   * or the destination isn't local, use a default, hopefully conservative
   * size (usually 512 or the default IP max size, but no more than the mtu
   * of the interface), as we can't discover anything about intervening
   * gateways or networks.  We also initialize the congestion/slow start
   * window to be a single segment if the destination isn't local.
   * While looking at the routing entry, we also initialize other path-dependent
   * parameters from pre-set or cached values in the routing entry.
   *
   * Also take into account the space needed for options that we
   * send regularly.  Make maxseg shorter by that amount to assure
   * that we can send maxseg amount of data even when the options
   * are present.  Store the upper limit of the length of options plus
   * data in maxopd.
   *
   * NOTE: offer == -1 indicates that the maxseg size changed due to
   * Path MTU discovery.
   */
  int
  tcp_mss(struct tcpcb *tp, int offer)
  {
  	struct rtentry *rt;
  	struct ifnet *ifp;
  	int mss, mssopt, mssdflt, iphlen, do_rfc3390;
  	u_int rtmtu;
  
  	mss = mssopt = mssdflt = atomic_load_int(&tcp_mssdflt);
  
  	rt = in_pcbrtentry(tp->t_inpcb);
  	if (rt == NULL)
  		goto out;
  
  	ifp = if_get(rt->rt_ifidx);
  	if (ifp == NULL)
  		goto out;
  
  	switch (tp->pf) {
  	case AF_INET:
  		iphlen = sizeof(struct ip);
  		break;
  #ifdef INET6
  	case AF_INET6:
  		iphlen = sizeof(struct ip6_hdr);
  		break;
  #endif
  	default:
  		unhandled_af(tp->pf);
  	}
  
  	/*
  	 * if there's an mtu associated with the route and we support
  	 * path MTU discovery for the underlying protocol family, use it.
  	 */
  	rtmtu = atomic_load_int(&rt->rt_mtu);
  	if (rtmtu) {
  		/*
  		 * One may wish to lower MSS to take into account options,
  		 * especially security-related options.
  		 */
  		if (tp->pf == AF_INET6 && rtmtu < IPV6_MMTU) {
  			/*
  			 * RFC2460 section 5, last paragraph: if path MTU is
  			 * smaller than 1280, use 1280 as packet size and
  			 * attach fragment header.
  			 */
  			mss = IPV6_MMTU - iphlen - sizeof(struct ip6_frag) -
  			    sizeof(struct tcphdr);
  		} else {
  			mss = rtmtu - iphlen - sizeof(struct tcphdr);
  		}
  	} else if (ifp->if_flags & IFF_LOOPBACK) {
  		mss = ifp->if_mtu - iphlen - sizeof(struct tcphdr);
  	} else if (tp->pf == AF_INET) {
  		if (atomic_load_int(&ip_mtudisc))
  			mss = ifp->if_mtu - iphlen - sizeof(struct tcphdr);
  	}
  #ifdef INET6
  	else if (tp->pf == AF_INET6) {
  		/*
  		 * for IPv6, path MTU discovery is always turned on,
  		 * or the node must use packet size <= 1280.
  		 */
  		mss = ifp->if_mtu - iphlen - sizeof(struct tcphdr);
  	}
  #endif /* INET6 */
  
  	/* Calculate the value that we offer in TCPOPT_MAXSEG */
  	if (offer != -1) {
  		mssopt = ifp->if_mtu - iphlen - sizeof(struct tcphdr);
  		mssopt = imax(mssopt, mssdflt);
  	}
  	if_put(ifp);
   out:
  	/*
  	 * The current mss, t_maxseg, is initialized to the default value.
  	 * If we compute a smaller value, reduce the current mss.
  	 * If we compute a larger value, return it for use in sending
  	 * a max seg size option, but don't store it for use
  	 * unless we received an offer at least that large from peer.
  	 *
  	 * However, do not accept offers lower than the minimum of
  	 * the interface MTU and 216.
  	 */
  	if (offer > 0)
  		tp->t_peermss = offer;
  	if (tp->t_peermss)
  		mss = imin(mss, max(tp->t_peermss, 216));
  
  	/* sanity - at least max opt. space */
  	mss = imax(mss, 64);
  
  	/*
  	 * maxopd stores the maximum length of data AND options
  	 * in a segment; maxseg is the amount of data in a normal
  	 * segment.  We need to store this value (maxopd) apart
  	 * from maxseg, because now every segment carries options
  	 * and thus we normally have somewhat less data in segments.
  	 */
  	tp->t_maxopd = mss;
  
  	if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
  	    (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP)
  		mss -= TCPOLEN_TSTAMP_APPA;
  #ifdef TCP_SIGNATURE
  	if (tp->t_flags & TF_SIGNATURE)
  		mss -= TCPOLEN_SIGLEN;
  #endif
  
  	do_rfc3390 = atomic_load_int(&tcp_do_rfc3390);
  	if (offer == -1) {
  		/* mss changed due to Path MTU discovery */
  		tp->t_flags &= ~TF_PMTUD_PEND;
  		tp->t_pmtud_mtu_sent = 0;
  		tp->t_pmtud_mss_acked = 0;
  		if (mss < tp->t_maxseg) {
  			/*
  			 * Follow suggestion in RFC 2414 to reduce the
  			 * congestion window by the ratio of the old
  			 * segment size to the new segment size.
  			 */
  			tp->snd_cwnd = ulmax((tp->snd_cwnd / tp->t_maxseg) *
  			    mss, mss);
  		}
  	} else if (do_rfc3390 == 2) {
  		/* increase initial window  */
  		tp->snd_cwnd = ulmin(10 * mss, ulmax(2 * mss, 14600));
  	} else if (do_rfc3390) {
  		/* increase initial window  */
  		tp->snd_cwnd = ulmin(4 * mss, ulmax(2 * mss, 4380));
  	} else
  		tp->snd_cwnd = mss;
  
  	tp->t_maxseg = mss;
  
  	return (offer != -1 ? mssopt : mss);
  }
  
  u_int
  tcp_hdrsz(struct tcpcb *tp)
  {
  	u_int hlen;
  
  	switch (tp->pf) {
  #ifdef INET6
  	case AF_INET6:
  		hlen = sizeof(struct ip6_hdr);
  		break;
  #endif
  	case AF_INET:
  		hlen = sizeof(struct ip);
  		break;
  	default:
  		hlen = 0;
  		break;
  	}
  	hlen += sizeof(struct tcphdr);
  
  	if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
  	    (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP)
  		hlen += TCPOLEN_TSTAMP_APPA;
  #ifdef TCP_SIGNATURE
  	if (tp->t_flags & TF_SIGNATURE)
  		hlen += TCPOLEN_SIGLEN;
  #endif
  	return (hlen);
  }
  
  /*
   * Set connection variables based on the effective MSS.
   * We are passed the TCPCB for the actual connection.  If we
   * are the server, we are called by the compressed state engine
   * when the 3-way handshake is complete.  If we are the client,
   * we are called when we receive the SYN,ACK from the server.
   *
   * NOTE: The t_maxseg value must be initialized in the TCPCB
   * before this routine is called!
   */
  void
  tcp_mss_update(struct tcpcb *tp)
  {
  	int mss;
  	u_long bufsize;
  	struct rtentry *rt;
  	struct socket *so;
  
  	so = tp->t_inpcb->inp_socket;
  	mss = tp->t_maxseg;
  
  	rt = in_pcbrtentry(tp->t_inpcb);
  	if (rt == NULL)
  		return;
  
  	mtx_enter(&so->so_snd.sb_mtx);
  	bufsize = so->so_snd.sb_hiwat;
  	if (bufsize < mss) {
  		mtx_leave(&so->so_snd.sb_mtx);
  		mss = bufsize;
  		/* Update t_maxseg and t_maxopd */
  		tcp_mss(tp, mss);
  	} else {
  		bufsize = roundup(bufsize, mss);
  		if (bufsize > sb_max)
  			bufsize = sb_max;
  		(void)sbreserve(&so->so_snd, bufsize);
  		mtx_leave(&so->so_snd.sb_mtx);
  	}
  
  	mtx_enter(&so->so_rcv.sb_mtx);
  	bufsize = so->so_rcv.sb_hiwat;
  	if (bufsize > mss) {
  		bufsize = roundup(bufsize, mss);
  		if (bufsize > sb_max)
  			bufsize = sb_max;
  		(void)sbreserve(&so->so_rcv, bufsize);
  	}
  	mtx_leave(&so->so_rcv.sb_mtx);
  }
  
  /*
   * When a partial ack arrives, force the retransmission of the
   * next unacknowledged segment.  Do not clear tp->t_dupacks.
   * By setting snd_nxt to ti_ack, this forces retransmission timer
   * to be started again.
   */
  void
  tcp_newreno_partialack(struct tcpcb *tp, struct tcphdr *th)
  {
  	/*
  	 * snd_una has not been updated and the socket send buffer
  	 * not yet drained of the acked data, so we have to leave
  	 * snd_una as it was to get the correct data offset in
  	 * tcp_output().
  	 */
  	tcp_seq onxt = tp->snd_nxt;
  	u_long  ocwnd = tp->snd_cwnd;
  
  	TCP_TIMER_DISARM(tp, TCPT_REXMT);
  	tp->t_rtttime = 0;
  	tp->snd_nxt = th->th_ack;
  	/*
  	 * Set snd_cwnd to one segment beyond acknowledged offset
  	 * (tp->snd_una not yet updated when this function is called)
  	 */
  	tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
  	(void)tcp_output(tp);
  	tp->snd_cwnd = ocwnd;
  	if (SEQ_GT(onxt, tp->snd_nxt))
  		tp->snd_nxt = onxt;
  	/*
  	 * Partial window deflation.  Relies on fact that tp->snd_una
  	 * not updated yet.
  	 */
  	if (tp->snd_cwnd > th->th_ack - tp->snd_una)
  		tp->snd_cwnd -= th->th_ack - tp->snd_una;
  	else
  		tp->snd_cwnd = 0;
  	tp->snd_cwnd += tp->t_maxseg;
  }
  
  int
  tcp_mss_adv(struct rtentry *rt, int af)
  {
  	struct ifnet *ifp;
  	int iphlen, mss, mssdflt;
  
  	mssdflt = atomic_load_int(&tcp_mssdflt);
  
  	if (rt == NULL)
  		return mssdflt;
  
  	ifp = if_get(rt->rt_ifidx);
  	if (ifp == NULL)
  		return mssdflt;
  
  	switch (af) {
  	case AF_INET:
  		iphlen = sizeof(struct ip);
  		break;
  #ifdef INET6
  	case AF_INET6:
  		iphlen = sizeof(struct ip6_hdr);
  		break;
  #endif
  	default:
  		unhandled_af(af);
  	}
  	mss = ifp->if_mtu - iphlen - sizeof(struct tcphdr);
  	if_put(ifp);
  
  	return imax(mss, mssdflt);
  }
  
  /*
   * TCP compressed state engine.  Currently used to hold compressed
   * state for SYN_RECEIVED.
   */
  
  /*
   * Locks used to protect global data and struct members:
   *	a	atomic operations
   *	N	net lock
   *	S	syn_cache_mtx		tcp syn cache global mutex
   */
  
  /* syn hash parameters */
  int	tcp_syn_hash_size = TCP_SYN_HASH_SIZE;	/* [S] size of hash table */
  int	tcp_syn_cache_limit =			/* [a] global entry limit */
  	    TCP_SYN_HASH_SIZE * TCP_SYN_BUCKET_SIZE;
  int	tcp_syn_bucket_limit =			/* [a] per bucket limit */
  	    3 * TCP_SYN_BUCKET_SIZE;
  int	tcp_syn_use_limit = 100000;		/* [S] reseed after uses */
  
  struct pool syn_cache_pool;
  struct syn_cache_set tcp_syn_cache[2];		/* [S] */
  int tcp_syn_cache_active;			/* [S] */
  struct mutex syn_cache_mtx = MUTEX_INITIALIZER(IPL_SOFTNET);
  
  #define SYN_HASH(sa, sp, dp, rand) \
  	(((sa)->s_addr ^ (rand)[0]) *				\
  	(((((u_int32_t)(dp))<<16) + ((u_int32_t)(sp))) ^ (rand)[4]))
  #ifndef INET6
  #define	SYN_HASHALL(hash, src, dst, rand) \
  do {									\
  	hash = SYN_HASH(&satosin_const(src)->sin_addr,			\
  		satosin_const(src)->sin_port,				\
  		satosin_const(dst)->sin_port, (rand));			\
  } while (/*CONSTCOND*/ 0)
  #else
  #define SYN_HASH6(sa, sp, dp, rand) \
  	(((sa)->s6_addr32[0] ^ (rand)[0]) *			\
  	((sa)->s6_addr32[1] ^ (rand)[1]) *			\
  	((sa)->s6_addr32[2] ^ (rand)[2]) *			\
  	((sa)->s6_addr32[3] ^ (rand)[3]) *			\
  	(((((u_int32_t)(dp))<<16) + ((u_int32_t)(sp))) ^ (rand)[4]))
  
  #define SYN_HASHALL(hash, src, dst, rand) \
  do {									\
  	switch ((src)->sa_family) {					\
  	case AF_INET:							\
  		hash = SYN_HASH(&satosin_const(src)->sin_addr,		\
  			satosin_const(src)->sin_port,			\
  			satosin_const(dst)->sin_port, (rand));		\
  		break;							\
  	case AF_INET6:							\
  		hash = SYN_HASH6(&satosin6_const(src)->sin6_addr,	\
  			satosin6_const(src)->sin6_port,			\
  			satosin6_const(dst)->sin6_port, (rand));	\
  		break;							\
  	default:							\
  		hash = 0;						\
  	}								\
  } while (/*CONSTCOND*/0)
  #endif /* INET6 */
  
  void
  syn_cache_rm(struct syn_cache *sc)
  {
  	MUTEX_ASSERT_LOCKED(&syn_cache_mtx);
  
  	TAILQ_REMOVE(&sc->sc_buckethead->sch_bucket, sc, sc_bucketq);
  	in_pcbunref(sc->sc_inplisten);
  	sc->sc_inplisten = NULL;
  	LIST_REMOVE(sc, sc_tpq);
  	refcnt_rele(&sc->sc_refcnt);
  	sc->sc_buckethead->sch_length--;
  	if (timeout_del(&sc->sc_timer))
  		refcnt_rele(&sc->sc_refcnt);
  	sc->sc_set->scs_count--;
  }
  
  void
  syn_cache_put(struct syn_cache *sc)
  {
  	if (refcnt_rele(&sc->sc_refcnt) == 0)
  		return;
  
  	/* Dealing with last reference, no lock needed. */
  	m_free(sc->sc_ipopts);
  	rtfree(sc->sc_route.ro_rt);
  
  	pool_put(&syn_cache_pool, sc);
  }
  
  void
  syn_cache_init(void)
  {
  	int i;
  
  	/* Initialize the hash buckets. */
  	tcp_syn_cache[0].scs_buckethead = mallocarray(tcp_syn_hash_size,
  	    sizeof(struct syn_cache_head), M_SYNCACHE, M_WAITOK|M_ZERO);
  	tcp_syn_cache[1].scs_buckethead = mallocarray(tcp_syn_hash_size,
  	    sizeof(struct syn_cache_head), M_SYNCACHE, M_WAITOK|M_ZERO);
  	tcp_syn_cache[0].scs_size = tcp_syn_hash_size;
  	tcp_syn_cache[1].scs_size = tcp_syn_hash_size;
  	for (i = 0; i < tcp_syn_hash_size; i++) {
  		TAILQ_INIT(&tcp_syn_cache[0].scs_buckethead[i].sch_bucket);
  		TAILQ_INIT(&tcp_syn_cache[1].scs_buckethead[i].sch_bucket);
  	}
  
  	/* Initialize the syn cache pool. */
  	pool_init(&syn_cache_pool, sizeof(struct syn_cache), 0, IPL_SOFTNET,
  	    0, "syncache", NULL);
  }
  
  void
  syn_cache_insert(struct syn_cache *sc, struct tcpcb *tp)
  {
  	struct syn_cache_set *set;
  	struct syn_cache_head *scp;
  	struct syn_cache *sc2;
  	int i;
  
  	NET_ASSERT_LOCKED();
  	MUTEX_ASSERT_LOCKED(&syn_cache_mtx);
  
  	set = &tcp_syn_cache[tcp_syn_cache_active];
  
  	/*
  	 * If there are no entries in the hash table, reinitialize
  	 * the hash secrets.  To avoid useless cache swaps and
  	 * reinitialization, use it until the limit is reached.
  	 * An empty cache is also the opportunity to resize the hash.
  	 */
  	if (set->scs_count == 0 && set->scs_use <= 0) {
  		set->scs_use = tcp_syn_use_limit;
  		if (set->scs_size != tcp_syn_hash_size) {
  			scp = mallocarray(tcp_syn_hash_size, sizeof(struct
  			    syn_cache_head), M_SYNCACHE, M_NOWAIT|M_ZERO);
  			if (scp == NULL) {
  				/* Try again next time. */
  				set->scs_use = 0;
  			} else {
  				free(set->scs_buckethead, M_SYNCACHE,
  				    set->scs_size *
  				    sizeof(struct syn_cache_head));
  				set->scs_buckethead = scp;
  				set->scs_size = tcp_syn_hash_size;
  				for (i = 0; i < tcp_syn_hash_size; i++)
  					TAILQ_INIT(&scp[i].sch_bucket);
  			}
  		}
  		arc4random_buf(set->scs_random, sizeof(set->scs_random));
  		tcpstat_inc(tcps_sc_seedrandom);
  	}
  
  	SYN_HASHALL(sc->sc_hash, &sc->sc_src.sa, &sc->sc_dst.sa,
  	    set->scs_random);
  	scp = &set->scs_buckethead[sc->sc_hash % set->scs_size];
  	sc->sc_buckethead = scp;
  
  	/*
  	 * Make sure that we don't overflow the per-bucket
  	 * limit or the total cache size limit.
  	 */
  	if (scp->sch_length >= atomic_load_int(&tcp_syn_bucket_limit)) {
  		tcpstat_inc(tcps_sc_bucketoverflow);
  		/*
  		 * Someone might attack our bucket hash function.  Reseed
  		 * with random as soon as the passive syn cache gets empty.
  		 */
  		set->scs_use = 0;
  		/*
  		 * The bucket is full.  Toss the oldest element in the
  		 * bucket.  This will be the first entry in the bucket.
  		 */
  		sc2 = TAILQ_FIRST(&scp->sch_bucket);
  #ifdef DIAGNOSTIC
  		/*
  		 * This should never happen; we should always find an
  		 * entry in our bucket.
  		 */
  		if (sc2 == NULL)
  			panic("%s: bucketoverflow: impossible", __func__);
  #endif
  		syn_cache_rm(sc2);
  		syn_cache_put(sc2);
  	} else if (set->scs_count >= atomic_load_int(&tcp_syn_cache_limit)) {
  		struct syn_cache_head *scp2, *sce;
  
  		tcpstat_inc(tcps_sc_overflowed);
  		/*
  		 * The cache is full.  Toss the oldest entry in the
  		 * first non-empty bucket we can find.
  		 *
  		 * XXX We would really like to toss the oldest
  		 * entry in the cache, but we hope that this
  		 * condition doesn't happen very often.
  		 */
  		scp2 = scp;
  		if (TAILQ_EMPTY(&scp2->sch_bucket)) {
  			sce = &set->scs_buckethead[set->scs_size];
  			for (++scp2; scp2 != scp; scp2++) {
  				if (scp2 >= sce)
  					scp2 = &set->scs_buckethead[0];
  				if (! TAILQ_EMPTY(&scp2->sch_bucket))
  					break;
  			}
  #ifdef DIAGNOSTIC
  			/*
  			 * This should never happen; we should always find a
  			 * non-empty bucket.
  			 */
  			if (scp2 == scp)
  				panic("%s: cacheoverflow: impossible",
  				    __func__);
  #endif
  		}
  		sc2 = TAILQ_FIRST(&scp2->sch_bucket);
  		syn_cache_rm(sc2);
  		syn_cache_put(sc2);
  	}
  
  	/*
  	 * Initialize the entry's timer.  We don't estimate RTT
  	 * with SYNs, so each packet starts with the default RTT
  	 * and each timer step has a fixed timeout value.
  	 */
  	sc->sc_rxttot = 0;
  	sc->sc_rxtshift = 0;
  	TCPT_RANGESET(sc->sc_rxtcur,
  	    TCPTV_SRTTDFLT * tcp_backoff[sc->sc_rxtshift], TCPTV_MIN,
  	    TCPTV_REXMTMAX);
  	if (timeout_add_msec(&sc->sc_timer, sc->sc_rxtcur))
  		refcnt_take(&sc->sc_refcnt);
  
  	/* Link it from tcpcb entry */
  	refcnt_take(&sc->sc_refcnt);
  	LIST_INSERT_HEAD(&tp->t_sc, sc, sc_tpq);
  
  	/* Put it into the bucket. */
  	TAILQ_INSERT_TAIL(&scp->sch_bucket, sc, sc_bucketq);
  	scp->sch_length++;
  	sc->sc_set = set;
  	set->scs_count++;
  	set->scs_use--;
  
  	tcpstat_inc(tcps_sc_added);
  
  	/*
  	 * If the active cache has exceeded its use limit and
  	 * the passive syn cache is empty, exchange their roles.
  	 */
  	if (set->scs_use <= 0 &&
  	    tcp_syn_cache[!tcp_syn_cache_active].scs_count == 0)
  		tcp_syn_cache_active = !tcp_syn_cache_active;
  }
  
  /*
   * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
   * If we have retransmitted an entry the maximum number of times, expire
   * that entry.
   */
  void
  syn_cache_timer(void *arg)
  {
  	struct syn_cache *sc = arg;
  	struct inpcb *inp;
  	struct socket *so;
  	uint64_t now;
  	int lastref, do_ecn = 0;
  
  	mtx_enter(&syn_cache_mtx);
  	inp = in_pcbref(sc->sc_inplisten);
  	if (inp == NULL)
  		goto freeit;
  
  	if (__predict_false(sc->sc_rxtshift == TCP_MAXRXTSHIFT)) {
  		/* Drop it -- too many retransmissions. */
  		goto dropit;
  	}
  
  	/*
  	 * Compute the total amount of time this entry has
  	 * been on a queue.  If this entry has been on longer
  	 * than the keep alive timer would allow, expire it.
  	 */
  	sc->sc_rxttot += sc->sc_rxtcur;
  	if (sc->sc_rxttot >= atomic_load_int(&tcp_keepinit))
  		goto dropit;
  
  	/* Advance the timer back-off. */
  	sc->sc_rxtshift++;
  	TCPT_RANGESET(sc->sc_rxtcur,
  	    TCPTV_SRTTDFLT * tcp_backoff[sc->sc_rxtshift], TCPTV_MIN,
  	    TCPTV_REXMTMAX);
  	if (timeout_add_msec(&sc->sc_timer, sc->sc_rxtcur))
  		refcnt_take(&sc->sc_refcnt);
  	mtx_leave(&syn_cache_mtx);
  
  	NET_LOCK_SHARED();
  	so = in_pcbsolock(inp);
  	if (so != NULL) {
  		now = tcp_now();
  #ifdef TCP_ECN
  		do_ecn = atomic_load_int(&tcp_do_ecn);
  #endif
  		(void) syn_cache_respond(sc, NULL, now, do_ecn);
  		tcpstat_inc(tcps_sc_retransmitted);
  	}
  	in_pcbsounlock(inp, so);
  	NET_UNLOCK_SHARED();
  
  	in_pcbunref(inp);
  	syn_cache_put(sc);
  	return;
  
   dropit:
  	tcpstat_inc(tcps_sc_timed_out);
  	syn_cache_rm(sc);
  	in_pcbunref(inp);
  	/* Decrement reference of the timer and free object after remove. */
  	lastref = refcnt_rele(&sc->sc_refcnt);
  	KASSERT(lastref == 0);
  	(void)lastref;
   freeit:
  	mtx_leave(&syn_cache_mtx);
  	syn_cache_put(sc);
  }
  
  /*
   * Remove syn cache created by the specified tcb entry,
   * because this does not make sense to keep them
   * (if there's no tcb entry, syn cache entry will never be used)
   */
  void
  syn_cache_cleanup(struct tcpcb *tp)
  {
  	struct syn_cache *sc, *nsc;
  
  	NET_ASSERT_LOCKED();
  
  	mtx_enter(&syn_cache_mtx);
  	LIST_FOREACH_SAFE(sc, &tp->t_sc, sc_tpq, nsc) {
  		KASSERT(sc->sc_inplisten == tp->t_inpcb);
  		syn_cache_rm(sc);
  		syn_cache_put(sc);
  	}
  	mtx_leave(&syn_cache_mtx);
  
  	KASSERT(LIST_EMPTY(&tp->t_sc));
  }
  
  /*
   * Find an entry in the syn cache.
   */
  struct syn_cache *
  syn_cache_lookup(const struct sockaddr *src, const struct sockaddr *dst,
      struct syn_cache_head **headp, u_int rtableid)
  {
  	struct syn_cache_set *sets[2];
  	struct syn_cache *sc;
  	struct syn_cache_head *scp;
  	u_int32_t hash;
  	int i;
  
  	NET_ASSERT_LOCKED();
  	MUTEX_ASSERT_LOCKED(&syn_cache_mtx);
  
  	/* Check the active cache first, the passive cache is likely empty. */
  	sets[0] = &tcp_syn_cache[tcp_syn_cache_active];
  	sets[1] = &tcp_syn_cache[!tcp_syn_cache_active];
  	for (i = 0; i < 2; i++) {
  		if (sets[i]->scs_count == 0)
  			continue;
  		SYN_HASHALL(hash, src, dst, sets[i]->scs_random);
  		scp = &sets[i]->scs_buckethead[hash % sets[i]->scs_size];
  		*headp = scp;
  		TAILQ_FOREACH(sc, &scp->sch_bucket, sc_bucketq) {
  			if (sc->sc_hash != hash)
  				continue;
  			if (!bcmp(&sc->sc_src, src, src->sa_len) &&
  			    !bcmp(&sc->sc_dst, dst, dst->sa_len) &&
  			    rtable_l2(rtableid) == rtable_l2(sc->sc_rtableid))
  				return (sc);
  		}
  	}
  	return (NULL);
  }
  
  /*
   * This function gets called when we receive an ACK for a
   * socket in the LISTEN state.  We look up the connection
   * in the syn cache, and if its there, we pull it out of
   * the cache and turn it into a full-blown connection in
   * the SYN-RECEIVED state.
   *
   * The return values may not be immediately obvious, and their effects
   * can be subtle, so here they are:
   *
   *	NULL	SYN was not found in cache; caller should drop the
   *		packet and send an RST.
   *
   *	-1	We were unable to create the new connection, and are
   *		aborting it.  An ACK,RST is being sent to the peer
   *		(unless we got screwy sequence numbers; see below),
   *		because the 3-way handshake has been completed.  Caller
   *		should not free the mbuf, since we may be using it.  If
   *		we are not, we will free it.
   *
   *	Otherwise, the return value is a pointer to the new socket
   *	associated with the connection.
   */
  struct socket *
  syn_cache_get(struct sockaddr *src, struct sockaddr *dst, struct tcphdr *th,
      u_int hlen, u_int tlen, struct socket *so, struct mbuf *m, uint64_t now,
      int do_ecn)
  {
  	struct syn_cache *sc;
  	struct syn_cache_head *scp;
  	struct socket *listenso;
  	struct inpcb *inp, *listeninp;
  	struct tcpcb *tp = NULL;
  	u_int rtableid;
  
  	NET_ASSERT_LOCKED();
  
  	inp = sotoinpcb(so);
  
  	mtx_enter(&syn_cache_mtx);
  	sc = syn_cache_lookup(src, dst, &scp, inp->inp_rtableid);
  	if (sc == NULL) {
  		mtx_leave(&syn_cache_mtx);
  		in_pcbsounlock(inp, so);
  		return (NULL);
  	}
  
  	/*
  	 * Verify the sequence and ack numbers.  Try getting the correct
  	 * response again.
  	 */
  	if ((th->th_ack != sc->sc_iss + 1) ||
  	    SEQ_LEQ(th->th_seq, sc->sc_irs) ||
  	    SEQ_GT(th->th_seq, sc->sc_irs + 1 + sc->sc_win)) {
  		refcnt_take(&sc->sc_refcnt);
  		mtx_leave(&syn_cache_mtx);
  		(void) syn_cache_respond(sc, m, now, do_ecn);
  		in_pcbsounlock(inp, so);
  		syn_cache_put(sc);
  		return ((struct socket *)(-1));
  	}
  
  	/* Remove this cache entry */
  	syn_cache_rm(sc);
  	mtx_leave(&syn_cache_mtx);
  
  	/*
  	 * Ok, create the full blown connection, and set things up
  	 * as they would have been set up if we had created the
  	 * connection when the SYN arrived.  If we can't create
  	 * the connection, abort it.
  	 */
  	listenso = so;
  	listeninp = inp;
  	inp = NULL;
  	so = sonewconn(listenso, SS_ISCONNECTED, M_DONTWAIT);
  	if (so == NULL)
  		goto resetandabort;
  	soassertlocked(so);
  	/* inpcb does refcount socket, both so and inp cannot go away */
  	inp = in_pcbref(sotoinpcb(so));
  	tp = intotcpcb(inp);
  
  #ifdef IPSEC
  	/*
  	 * We need to copy the required security levels from the listen pcb.
  	 * Ditto for any other IPsec-related information.
  	 */
  	inp->inp_seclevel = listeninp->inp_seclevel;
  #endif /* IPSEC */
  #ifdef INET6
  	if (ISSET(inp->inp_flags, INP_IPV6)) {
  		KASSERT(ISSET(listeninp->inp_flags, INP_IPV6));
  
  		inp->inp_ipv6.ip6_hlim = listeninp->inp_ipv6.ip6_hlim;
  		inp->inp_hops = listeninp->inp_hops;
  	} else
  #endif
  	{
  		KASSERT(!ISSET(listeninp->inp_flags, INP_IPV6));
  
  		inp->inp_ip.ip_ttl = listeninp->inp_ip.ip_ttl;
  		inp->inp_options = ip_srcroute(m);
  		if (inp->inp_options == NULL) {
  			inp->inp_options = sc->sc_ipopts;
  			sc->sc_ipopts = NULL;
  		}
  	}
  
  	/* inherit rtable from listening socket */
  	rtableid = sc->sc_rtableid;
  #if NPF > 0
  	if (m->m_pkthdr.pf.flags & PF_TAG_DIVERTED) {
  		struct pf_divert *divert;
  
  		divert = pf_find_divert(m);
  		KASSERT(divert != NULL);
  		rtableid = divert->rdomain;
  	}
  #endif
  	if (in_pcbset_addr(inp, src, dst, rtableid))
  		goto resetandabort;
  
  	/*
  	 * Give the new socket our cached route reference.
  	 */
  	inp->inp_route = sc->sc_route;		/* struct assignment */
  	sc->sc_route.ro_rt = NULL;
  
  	tp->t_flags = intotcpcb(listeninp)->t_flags & (TF_NOPUSH|TF_NODELAY);
  	if (sc->sc_request_r_scale != 15) {
  		tp->requested_s_scale = sc->sc_requested_s_scale;
  		tp->request_r_scale = sc->sc_request_r_scale;
  		tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  	}
  	if (ISSET(sc->sc_fixflags, SCF_TIMESTAMP))
  		tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  
  	tp->t_template = tcp_template(tp);
  	if (tp->t_template == NULL)
  		goto abort;
  	tp->sack_enable = ISSET(sc->sc_fixflags, SCF_SACK_PERMIT);
  	tp->ts_modulate = sc->sc_modulate;
  	tp->ts_recent = sc->sc_timestamp;
  	tp->iss = sc->sc_iss;
  	tp->irs = sc->sc_irs;
  	tcp_sendseqinit(tp);
  	tp->snd_last = tp->snd_una;
  #ifdef TCP_ECN
  	if (ISSET(sc->sc_fixflags, SCF_ECN_PERMIT)) {
  		tp->t_flags |= TF_ECN_PERMIT;
  		tcpstat_inc(tcps_ecn_accepts);
  	}
  #endif
  	if (ISSET(sc->sc_fixflags, SCF_SACK_PERMIT))
  		tp->t_flags |= TF_SACK_PERMIT;
  #ifdef TCP_SIGNATURE
  	if (ISSET(sc->sc_fixflags, SCF_SIGNATURE))
  		tp->t_flags |= TF_SIGNATURE;
  #endif
  	tcp_rcvseqinit(tp);
  	tp->t_state = TCPS_SYN_RECEIVED;
  	tp->t_rcvtime = now;
  	tp->t_sndtime = now;
  	tp->t_rcvacktime = now;
  	tp->t_sndacktime = now;
  	TCP_TIMER_ARM(tp, TCPT_KEEP, atomic_load_int(&tcp_keepinit));
  	tcpstat_inc(tcps_accepts);
  
  	tcp_mss(tp, sc->sc_peermaxseg);	 /* sets t_maxseg */
  	if (sc->sc_peermaxseg)
  		tcp_mss_update(tp);
  	/* Reset initial window to 1 segment for retransmit */
  	if (READ_ONCE(sc->sc_rxtshift) > 0)
  		tp->snd_cwnd = tp->t_maxseg;
  	tp->snd_wl1 = sc->sc_irs;
  	tp->rcv_up = sc->sc_irs + 1;
  
  	/*
  	 * This is what would have happened in tcp_output() when
  	 * the SYN,ACK was sent.
  	 */
  	tp->snd_up = tp->snd_una;
  	tp->snd_max = tp->snd_nxt = tp->iss+1;
  	TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur);
  	if (sc->sc_win > 0 && SEQ_GT(tp->rcv_nxt + sc->sc_win, tp->rcv_adv))
  		tp->rcv_adv = tp->rcv_nxt + sc->sc_win;
  	tp->last_ack_sent = tp->rcv_nxt;
  
  	in_pcbsounlock(listeninp, listenso);
  	tcpstat_inc(tcps_sc_completed);
  	syn_cache_put(sc);
  	return (so);
  
  resetandabort:
  	tcp_respond(NULL, mtod(m, caddr_t), th, (tcp_seq)0, th->th_ack, TH_RST,
  	    m->m_pkthdr.ph_rtableid, now);
  abort:
  	if (tp != NULL)
  		tp = tcp_drop(tp, ECONNABORTED);	/* destroys socket */
  	in_pcbsounlock(inp, so);
  	in_pcbsounlock(listeninp, listenso);
  	in_pcbunref(inp);
  	m_freem(m);
  	syn_cache_put(sc);
  	tcpstat_inc(tcps_sc_aborted);
  	return ((struct socket *)(-1));
  }
  
  /*
   * This function is called when we get a RST for a
   * non-existent connection, so that we can see if the
   * connection is in the syn cache.  If it is, zap it.
   */
  
  void
  syn_cache_reset(struct sockaddr *src, struct sockaddr *dst, struct tcphdr *th,
      u_int rtableid)
  {
  	struct syn_cache *sc;
  	struct syn_cache_head *scp;
  
  	NET_ASSERT_LOCKED();
  
  	mtx_enter(&syn_cache_mtx);
  	sc = syn_cache_lookup(src, dst, &scp, rtableid);
  	if (sc == NULL) {
  		mtx_leave(&syn_cache_mtx);
  		return;
  	}
  	if (SEQ_LT(th->th_seq, sc->sc_irs) ||
  	    SEQ_GT(th->th_seq, sc->sc_irs + 1)) {
  		mtx_leave(&syn_cache_mtx);
  		return;
  	}
  	syn_cache_rm(sc);
  	mtx_leave(&syn_cache_mtx);
  	tcpstat_inc(tcps_sc_reset);
  	syn_cache_put(sc);
  }
  
  void
  syn_cache_unreach(const struct sockaddr *src, const struct sockaddr *dst,
      struct tcphdr *th, u_int rtableid)
  {
  	struct syn_cache *sc;
  	struct syn_cache_head *scp;
  
  	NET_ASSERT_LOCKED();
  
  	mtx_enter(&syn_cache_mtx);
  	sc = syn_cache_lookup(src, dst, &scp, rtableid);
  	if (sc == NULL) {
  		mtx_leave(&syn_cache_mtx);
  		return;
  	}
  	/* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  	if (ntohl (th->th_seq) != sc->sc_iss) {
  		mtx_leave(&syn_cache_mtx);
  		return;
  	}
  
  	/*
  	 * If we've retransmitted 3 times and this is our second error,
  	 * we remove the entry.  Otherwise, we allow it to continue on.
  	 * This prevents us from incorrectly nuking an entry during a
  	 * spurious network outage.
  	 *
  	 * See tcp_notify().
  	 */
  	if (!ISSET(sc->sc_dynflags, SCF_UNREACH) || sc->sc_rxtshift < 3) {
  		SET(sc->sc_dynflags, SCF_UNREACH);
  		mtx_leave(&syn_cache_mtx);
  		return;
  	}
  
  	syn_cache_rm(sc);
  	mtx_leave(&syn_cache_mtx);
  	tcpstat_inc(tcps_sc_unreach);
  	syn_cache_put(sc);
  }
  
  /*
   * Given a LISTEN socket and an inbound SYN request, add
   * this to the syn cache, and send back a segment:
   *	<SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
   * to the source.
   *
   * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
   * Doing so would require that we hold onto the data and deliver it
   * to the application.  However, if we are the target of a SYN-flood
   * DoS attack, an attacker could send data which would eventually
   * consume all available buffer space if it were ACKed.  By not ACKing
   * the data, we avoid this DoS scenario.
   */
  
  int
  syn_cache_add(struct sockaddr *src, struct sockaddr *dst, struct tcphdr *th,
      u_int iphlen, struct socket *so, struct mbuf *m, u_char *optp, int optlen,
      struct tcp_opt_info *oi, tcp_seq *issp, uint64_t now, int do_ecn)
  {
  	struct tcpcb tb, *tp;
  	long win;
  	struct syn_cache *sc;
  	struct syn_cache_head *scp;
  	struct mbuf *ipopts;
  	struct rtentry *rt = NULL;
  
  	soassertlocked(so);
  
  	tp = sototcpcb(so);
  
  	/*
  	 * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
  	 *
  	 * Note this check is performed in tcp_input() very early on.
  	 */
  
  	/*
  	 * Initialize some local state.
  	 */
  	win = sbspace(&so->so_rcv);
  	if (win > TCP_MAXWIN)
  		win = TCP_MAXWIN;
  
  	bzero(&tb, sizeof(tb));
  	if (optp
  #ifdef TCP_SIGNATURE
  	    || (tp->t_flags & TF_SIGNATURE)
  #endif
  	    ) {
  		tb.pf = tp->pf;
  		tb.sack_enable = tp->sack_enable;
  		tb.t_flags = atomic_load_int(&tcp_do_rfc1323) ?
  		    (TF_REQ_SCALE|TF_REQ_TSTMP) : 0;
  #ifdef TCP_SIGNATURE
  		if (tp->t_flags & TF_SIGNATURE)
  			tb.t_flags |= TF_SIGNATURE;
  #endif
  		tb.t_state = TCPS_LISTEN;
  		if (tcp_dooptions(&tb, optp, optlen, th, m, iphlen, oi,
  		    sotoinpcb(so)->inp_rtableid, now))
  			return (-1);
  	}
  
  	switch (src->sa_family) {
  	case AF_INET:
  		/*
  		 * Remember the IP options, if any.
  		 */
  		ipopts = ip_srcroute(m);
  		break;
  	default:
  		ipopts = NULL;
  	}
  
  	/*
  	 * See if we already have an entry for this connection.
  	 * If we do, resend the SYN,ACK.  We do not count this
  	 * as a retransmission (XXX though maybe we should).
  	 */
  	mtx_enter(&syn_cache_mtx);
  	sc = syn_cache_lookup(src, dst, &scp, sotoinpcb(so)->inp_rtableid);
  	if (sc != NULL) {
  		refcnt_take(&sc->sc_refcnt);
  		mtx_leave(&syn_cache_mtx);
  		tcpstat_inc(tcps_sc_dupesyn);
  		if (ipopts) {
  			/*
  			 * If we were remembering a previous source route,
  			 * forget it and use the new one we've been given.
  			 */
  			m_free(sc->sc_ipopts);
  			sc->sc_ipopts = ipopts;
  		}
  		sc->sc_timestamp = tb.ts_recent;
  		if (syn_cache_respond(sc, m, now, do_ecn) == 0) {
  			tcpstat_inc(tcps_sndacks);
  			tcpstat_inc(tcps_sndtotal);
  		}
  		syn_cache_put(sc);
  		return (0);
  	}
  	mtx_leave(&syn_cache_mtx);
  
  	sc = pool_get(&syn_cache_pool, PR_NOWAIT|PR_ZERO);
  	if (sc == NULL) {
  		m_free(ipopts);
  		return (-1);
  	}
  	refcnt_init_trace(&sc->sc_refcnt, DT_REFCNT_IDX_SYNCACHE);
  	timeout_set_flags(&sc->sc_timer, syn_cache_timer, sc,
  	    KCLOCK_NONE, TIMEOUT_PROC | TIMEOUT_MPSAFE);
  
  	/*
  	 * Fill in the cache, and put the necessary IP and TCP
  	 * options into the reply.
  	 */
  	memcpy(&sc->sc_src, src, src->sa_len);
  	memcpy(&sc->sc_dst, dst, dst->sa_len);
  	sc->sc_rtableid = sotoinpcb(so)->inp_rtableid;
  	switch (sc->sc_src.sa.sa_family) {
  	case AF_INET:
  		if (sc->sc_src.sin.sin_addr.s_addr != INADDR_ANY) {
  			rt = route_mpath(&sc->sc_route,
  			    &sc->sc_src.sin.sin_addr,
  			    &sc->sc_dst.sin.sin_addr, sc->sc_rtableid);
  		}
  		break;
  #ifdef INET6
  	case AF_INET6:
  		if (!IN6_IS_ADDR_UNSPECIFIED(&sc->sc_src.sin6.sin6_addr)) {
  			rt = route6_mpath(&sc->sc_route,
  			    &sc->sc_src.sin6.sin6_addr,
  			    &sc->sc_dst.sin6.sin6_addr, sc->sc_rtableid);
  		}
  		break;
  #endif
  	}
  	sc->sc_ipopts = ipopts;
  	sc->sc_irs = th->th_seq;
  
  	sc->sc_iss = issp ? *issp : arc4random();
  	sc->sc_peermaxseg = oi->maxseg;
  	sc->sc_ourmaxseg = tcp_mss_adv(rt, sc->sc_src.sa.sa_family);
  	sc->sc_win = win;
  	sc->sc_timestamp = tb.ts_recent;
  	if ((tb.t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP)) ==
  	    (TF_REQ_TSTMP|TF_RCVD_TSTMP)) {
  		SET(sc->sc_fixflags, SCF_TIMESTAMP);
  		sc->sc_modulate = arc4random();
  	}
  	if ((tb.t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
  	    (TF_RCVD_SCALE|TF_REQ_SCALE)) {
  		sc->sc_requested_s_scale = tb.requested_s_scale;
  		sc->sc_request_r_scale = 0;
  		/*
  		 * Pick the smallest possible scaling factor that
  		 * will still allow us to scale up to sb_max.
  		 *
  		 * We do this because there are broken firewalls that
  		 * will corrupt the window scale option, leading to
  		 * the other endpoint believing that our advertised
  		 * window is unscaled.  At scale factors larger than
  		 * 5 the unscaled window will drop below 1500 bytes,
  		 * leading to serious problems when traversing these
  		 * broken firewalls.
  		 *
  		 * With the default sbmax of 256K, a scale factor
  		 * of 3 will be chosen by this algorithm.  Those who
  		 * choose a larger sbmax should watch out
  		 * for the compatibility problems mentioned above.
  		 *
  		 * RFC1323: The Window field in a SYN (i.e., a <SYN>
  		 * or <SYN,ACK>) segment itself is never scaled.
  		 */
  		while (sc->sc_request_r_scale < TCP_MAX_WINSHIFT &&
  		    (TCP_MAXWIN << sc->sc_request_r_scale) < sb_max)
  			sc->sc_request_r_scale++;
  	} else {
  		sc->sc_requested_s_scale = 15;
  		sc->sc_request_r_scale = 15;
  	}
  #ifdef TCP_ECN
  	/*
  	 * if both ECE and CWR flag bits are set, peer is ECN capable.
  	 */
  	if (do_ecn && (th->th_flags & (TH_ECE|TH_CWR)) == (TH_ECE|TH_CWR))
  		SET(sc->sc_fixflags, SCF_ECN_PERMIT);
  #endif
  	/*
  	 * Set SCF_SACK_PERMIT if peer did send a SACK_PERMITTED option
  	 * (i.e., if tcp_dooptions() did set TF_SACK_PERMIT).
  	 */
  	if (tb.sack_enable && (tb.t_flags & TF_SACK_PERMIT))
  		SET(sc->sc_fixflags, SCF_SACK_PERMIT);
  #ifdef TCP_SIGNATURE
  	if (tb.t_flags & TF_SIGNATURE)
  		SET(sc->sc_fixflags, SCF_SIGNATURE);
  #endif
  	sc->sc_inplisten = in_pcbref(tp->t_inpcb);
  	if (syn_cache_respond(sc, m, now, do_ecn) == 0) {
  		mtx_enter(&syn_cache_mtx);
  		/*
  		 * Socket lock prevents another insert after our
  		 * syn_cache_lookup() and before syn_cache_insert().
  		 */
  		syn_cache_insert(sc, tp);
  		mtx_leave(&syn_cache_mtx);
  		tcpstat_inc(tcps_sndacks);
  		tcpstat_inc(tcps_sndtotal);
  	} else {
  		in_pcbunref(sc->sc_inplisten);
  		syn_cache_put(sc);
  		tcpstat_inc(tcps_sc_dropped);
  	}
  
  	return (0);
  }
  
  int
  syn_cache_respond(struct syn_cache *sc, struct mbuf *m, uint64_t now,
      int do_ecn)
  {
  	u_int8_t *optp;
  	int optlen, error;
  	u_int16_t tlen;
  	struct ip *ip = NULL;
  #ifdef INET6
  	struct ip6_hdr *ip6 = NULL;
  #endif
  	struct tcphdr *th;
  	u_int hlen;
  	struct inpcb *inp;
  
  	NET_ASSERT_LOCKED();
  
  	switch (sc->sc_src.sa.sa_family) {
  	case AF_INET:
  		hlen = sizeof(struct ip);
  		break;
  #ifdef INET6
  	case AF_INET6:
  		hlen = sizeof(struct ip6_hdr);
  		break;
  #endif
  	default:
  		m_freem(m);
  		return (EAFNOSUPPORT);
  	}
  
  	/* Compute the size of the TCP options. */
  	optlen = 4 + (sc->sc_request_r_scale != 15 ? 4 : 0) +
  	    (ISSET(sc->sc_fixflags, SCF_SACK_PERMIT) ? 4 : 0) +
  #ifdef TCP_SIGNATURE
  	    (ISSET(sc->sc_fixflags, SCF_SIGNATURE) ? TCPOLEN_SIGLEN : 0) +
  #endif
  	    (ISSET(sc->sc_fixflags, SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0);
  
  	tlen = hlen + sizeof(struct tcphdr) + optlen;
  
  	/*
  	 * Create the IP+TCP header from scratch.
  	 */
  	m_freem(m);
  #ifdef DIAGNOSTIC
  	if (max_linkhdr + tlen > MCLBYTES)
  		return (ENOBUFS);
  #endif
  	MGETHDR(m, M_DONTWAIT, MT_DATA);
  	if (m && max_linkhdr + tlen > MHLEN) {
  		MCLGET(m, M_DONTWAIT);
  		if ((m->m_flags & M_EXT) == 0) {
  			m_freem(m);
  			m = NULL;
  		}
  	}
  	if (m == NULL)
  		return (ENOBUFS);
  
  	/* Fixup the mbuf. */
  	m->m_data += max_linkhdr;
  	m->m_len = m->m_pkthdr.len = tlen;
  	m->m_pkthdr.ph_ifidx = 0;
  	m->m_pkthdr.ph_rtableid = sc->sc_rtableid;
  	memset(mtod(m, u_char *), 0, tlen);
  
  	switch (sc->sc_src.sa.sa_family) {
  	case AF_INET:
  		ip = mtod(m, struct ip *);
  		ip->ip_dst = sc->sc_src.sin.sin_addr;
  		ip->ip_src = sc->sc_dst.sin.sin_addr;
  		ip->ip_p = IPPROTO_TCP;
  		th = (struct tcphdr *)(ip + 1);
  		th->th_dport = sc->sc_src.sin.sin_port;
  		th->th_sport = sc->sc_dst.sin.sin_port;
  		break;
  #ifdef INET6
  	case AF_INET6:
  		ip6 = mtod(m, struct ip6_hdr *);
  		ip6->ip6_dst = sc->sc_src.sin6.sin6_addr;
  		ip6->ip6_src = sc->sc_dst.sin6.sin6_addr;
  		ip6->ip6_nxt = IPPROTO_TCP;
  		th = (struct tcphdr *)(ip6 + 1);
  		th->th_dport = sc->sc_src.sin6.sin6_port;
  		th->th_sport = sc->sc_dst.sin6.sin6_port;
  		break;
  #endif
  	}
  
  	th->th_seq = htonl(sc->sc_iss);
  	th->th_ack = htonl(sc->sc_irs + 1);
  	th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
  	th->th_flags = TH_SYN|TH_ACK;
  #ifdef TCP_ECN
  	/* Set ECE for SYN-ACK if peer supports ECN. */
  	if (do_ecn && ISSET(sc->sc_fixflags, SCF_ECN_PERMIT))
  		th->th_flags |= TH_ECE;
  #endif
  	th->th_win = htons(sc->sc_win);
  	/* th_sum already 0 */
  	/* th_urp already 0 */
  
  	/* Tack on the TCP options. */
  	optp = (u_int8_t *)(th + 1);
  	*optp++ = TCPOPT_MAXSEG;
  	*optp++ = 4;
  	*optp++ = (sc->sc_ourmaxseg >> 8) & 0xff;
  	*optp++ = sc->sc_ourmaxseg & 0xff;
  
  	/* Include SACK_PERMIT_HDR option if peer has already done so. */
  	if (ISSET(sc->sc_fixflags, SCF_SACK_PERMIT)) {
  		*((u_int32_t *)optp) = htonl(TCPOPT_SACK_PERMIT_HDR);
  		optp += 4;
  	}
  
  	if (sc->sc_request_r_scale != 15) {
  		*((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 |
  		    TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 |
  		    sc->sc_request_r_scale);
  		optp += 4;
  	}
  
  	if (ISSET(sc->sc_fixflags, SCF_TIMESTAMP)) {
  		u_int32_t *lp = (u_int32_t *)(optp);
  		/* Form timestamp option as shown in appendix A of RFC 1323. */
  		*lp++ = htonl(TCPOPT_TSTAMP_HDR);
  		*lp++ = htonl(now + sc->sc_modulate);
  		*lp   = htonl(sc->sc_timestamp);
  		optp += TCPOLEN_TSTAMP_APPA;
  	}
  
  #ifdef TCP_SIGNATURE
  	if (ISSET(sc->sc_fixflags, SCF_SIGNATURE)) {
  		union sockaddr_union src, dst;
  		struct tdb *tdb;
  
  		bzero(&src, sizeof(union sockaddr_union));
  		bzero(&dst, sizeof(union sockaddr_union));
  		src.sa.sa_len = sc->sc_src.sa.sa_len;
  		src.sa.sa_family = sc->sc_src.sa.sa_family;
  		dst.sa.sa_len = sc->sc_dst.sa.sa_len;
  		dst.sa.sa_family = sc->sc_dst.sa.sa_family;
  
  		switch (sc->sc_src.sa.sa_family) {
  		case 0:	/*default to PF_INET*/
  		case AF_INET:
  			src.sin.sin_addr = mtod(m, struct ip *)->ip_src;
  			dst.sin.sin_addr = mtod(m, struct ip *)->ip_dst;
  			break;
  #ifdef INET6
  		case AF_INET6:
  			src.sin6.sin6_addr = mtod(m, struct ip6_hdr *)->ip6_src;
  			dst.sin6.sin6_addr = mtod(m, struct ip6_hdr *)->ip6_dst;
  			break;
  #endif /* INET6 */
  		}
  
  		tdb = gettdbbysrcdst(rtable_l2(sc->sc_rtableid),
  		    0, &src, &dst, IPPROTO_TCP);
  		if (tdb == NULL) {
  			m_freem(m);
  			return (EPERM);
  		}
  
  		/* Send signature option */
  		*(optp++) = TCPOPT_SIGNATURE;
  		*(optp++) = TCPOLEN_SIGNATURE;
  
  		if (tcp_signature(tdb, sc->sc_src.sa.sa_family, m, th,
  		    hlen, 0, optp) < 0) {
  			m_freem(m);
  			tdb_unref(tdb);
  			return (EINVAL);
  		}
  		tdb_unref(tdb);
  		optp += 16;
  
  		/* Pad options list to the next 32 bit boundary and
  		 * terminate it.
  		 */
  		*optp++ = TCPOPT_NOP;
  		*optp++ = TCPOPT_EOL;
  	}
  #endif /* TCP_SIGNATURE */
  
  	SET(m->m_pkthdr.csum_flags, M_TCP_CSUM_OUT);
  
  	/* use IPsec policy and ttl from listening socket, on SYN ACK */
  	mtx_enter(&syn_cache_mtx);
  	inp = in_pcbref(sc->sc_inplisten);
  	mtx_leave(&syn_cache_mtx);
  
  	/*
  	 * Fill in some straggling IP bits.  Note the stack expects
  	 * ip_len to be in host order, for convenience.
  	 */
  	switch (sc->sc_src.sa.sa_family) {
  	case AF_INET:
  		ip->ip_len = htons(tlen);
  		ip->ip_ttl = inp ?
  		    inp->inp_ip.ip_ttl : atomic_load_int(&ip_defttl);
  		if (inp != NULL)
  			ip->ip_tos = inp->inp_ip.ip_tos;
  
  		error = ip_output(m, sc->sc_ipopts, &sc->sc_route,
  		    (atomic_load_int(&ip_mtudisc) ? IP_MTUDISC : 0),  NULL,
  		    inp ? &inp->inp_seclevel : NULL, 0);
  		break;
  #ifdef INET6
  	case AF_INET6:
  		ip6->ip6_vfc &= ~IPV6_VERSION_MASK;
  		ip6->ip6_vfc |= IPV6_VERSION;
  		/* ip6_plen will be updated in ip6_output() */
  		ip6->ip6_hlim = in6_selecthlim(inp);
  		/* leave flowlabel = 0, it is legal and require no state mgmt */
  
  		error = ip6_output(m, NULL /*XXX*/, &sc->sc_route, 0,
  		    NULL, inp ? &inp->inp_seclevel : NULL);
  		break;
  #endif
  	}
  	in_pcbunref(inp);
  	return (error);
  }
  
  #ifndef SMALL_KERNEL
  static int
  tcp_softlro_check(struct mbuf *m, struct ether_extracted *ext)
  {
  	/* Don't merge packets with invalid TCP checksum. */
  	if (!ISSET(m->m_pkthdr.csum_flags, M_TCP_CSUM_IN_OK))
  		return 0;
  
  	if (ext->ip4) {
  		/* Don't merge packets with invalid IP header checksum. */
  		if (!ISSET(m->m_pkthdr.csum_flags, M_IPV4_CSUM_IN_OK))
  			return 0;
  
  		/* Don't merge IPv4 packets with IP options. */
  		if (ext->iphlen != sizeof(struct ip))
  			return 0;
  	}
  
  	/* Check TCP protocol and header. */
  	if (!ext->tcp)
  		return 0;
  
  	/* Don't merge empty TCP segments. */
  	if (ext->paylen == 0)
  		return 0;
  
  	/* Just ACK and PUSH TCP flags are allowed. */
  	if (ISSET(ext->tcp->th_flags, TH_ACK|TH_PUSH) != ext->tcp->th_flags)
  		return 0;
  
  	/* TCP ACK flag has to be set. */
  	if (!ISSET(ext->tcp->th_flags, TH_ACK))
  		return 0;
  
  	/* Either no TCP options or timestamp as in RFC 1323 appendix A. */
  	if (ext->tcphlen > sizeof(struct tcphdr)) {
  		int optlen = ext->tcphlen - sizeof(struct tcphdr);
  		uint8_t *optp = (uint8_t *)(ext->tcp + 1);
  
  		/* Same logic as in TCP input quick retrieval. */
  		if ((optlen != TCPOLEN_TSTAMP_APPA &&
  		    (optlen <= TCPOLEN_TSTAMP_APPA ||
  		    optp[TCPOLEN_TSTAMP_APPA] != TCPOPT_EOL)) ||
  		    ((uint32_t *)optp)[0] != htonl(TCPOPT_TSTAMP_HDR))
  			return 0;
  	}
  
  	return 1;
  }
  
  static int
  tcp_softlro_compare(struct ether_extracted *head, struct ether_extracted *tail)
  {
  	/* Don't merge packets inside and outside of VLANs */
  	if (head->evh && tail->evh) {
  		/* Don't merge packets of different VLANs */
  		if (EVL_VLANOFTAG(head->evh->evl_tag) !=
  		    EVL_VLANOFTAG(tail->evh->evl_tag))
  			return 0;
  
  		/* Don't merge packets of different priorities */
  		if (EVL_PRIOFTAG(head->evh->evl_tag) !=
  		    EVL_PRIOFTAG(tail->evh->evl_tag))
  			return 0;
  	} else if (head->evh || tail->evh)
  		return 0;
  
  	/* Check TCP ports. */
  	if (head->tcp->th_sport != tail->tcp->th_sport ||
  	    head->tcp->th_dport != tail->tcp->th_dport)
  		return 0;
  
  	/* Check IP header. */
  	if (head->ip4 && tail->ip4) {
  		/* Check IPv4 addresses. */
  		if (head->ip4->ip_src.s_addr != tail->ip4->ip_src.s_addr ||
  		    head->ip4->ip_dst.s_addr != tail->ip4->ip_dst.s_addr)
  			return 0;
  
  		/* Check max. IPv4 length. */
  		if (head->iplen + tail->iplen > IP_MAXPACKET)
  			return 0;
  	} else if (head->ip6 && tail->ip6) {
  		/* Check IPv6 addresses. */
  		if (!IN6_ARE_ADDR_EQUAL(&head->ip6->ip6_src,
  		    &tail->ip6->ip6_src) ||
  		    !IN6_ARE_ADDR_EQUAL(&head->ip6->ip6_dst,
  		    &tail->ip6->ip6_dst))
  			return 0;
  
  		/* Check max. IPv6 length. */
  		if ((head->iplen - head->iphlen) +
  		    (tail->iplen - tail->iphlen) > IPV6_MAXPACKET)
  			return 0;
  	} else {
  		/* Address family does not match. */
  		return 0;
  	}
  
  	/* Check for contiguous segments. */
  	if (ntohl(head->tcp->th_seq) + head->paylen != ntohl(tail->tcp->th_seq))
  		return 0;
  
  	/* Ignore segments with different TCP options. */
  	if (head->tcphlen != tail->tcphlen)
  		return 0;
  
  	/* TCP timestamp options must match, type and length already checked. */
  	if (head->tcphlen > sizeof(struct tcphdr)) {
  		uint32_t *hoptp = (uint32_t *)(head->tcp + 1);
  		uint32_t *toptp = (uint32_t *)(tail->tcp + 1);
  
  		/* Tail timestamps must be more recent. */
  		if (TSTMP_LT(ntohl(hoptp[1]), ntohl(toptp[1])) ||
  		    TSTMP_LT(ntohl(hoptp[2]), ntohl(toptp[2])))
  			return 0;
  	}
  
  	return 1;
  }
  
  static void
  tcp_softlro_concat(struct mbuf *mhead, struct ether_extracted *head,
      struct mbuf *mtail, struct ether_extracted *tail)
  {
  	struct mbuf *m;
  	unsigned int hdrlen;
  
  	/* Adjust IP header length. */
  	if (head->ip4) {
  		head->ip4->ip_len = htons(head->iplen + tail->paylen);
  	} else if (head->ip6) {
  		head->ip6->ip6_plen =
  		    htons(head->iplen - head->iphlen + tail->paylen);
  	}
  
  	/* Combine TCP flags from head and tail. */
  	if (ISSET(tail->tcp->th_flags, TH_PUSH))
  		SET(head->tcp->th_flags, TH_PUSH);
  
  	/* Adjust TCP header. */
  	head->tcp->th_win = tail->tcp->th_win;
  	head->tcp->th_ack = tail->tcp->th_ack;
  
  	/* Use more recent timestamps from tail. */
  	if (head->tcphlen > sizeof(struct tcphdr)) {
  		uint32_t *hoptp = (uint32_t *)(head->tcp + 1);
  		uint32_t *toptp = (uint32_t *)(tail->tcp + 1);
  
  		hoptp[1] = toptp[1];
  		hoptp[2] = toptp[2];
  	}
  
  	/* Calculate header length of tail packet. */
  	hdrlen = sizeof(*tail->eh);
  	if (tail->evh)
  		hdrlen = sizeof(*tail->evh);
  	hdrlen += tail->iphlen;
  	hdrlen += tail->tcphlen;
  
  	/* Skip protocol headers in tail. */
  	m_adj(mtail, hdrlen);
  	CLR(mtail->m_flags, M_PKTHDR);
  
  	/* Concatenate */
  	for (m = mhead; m->m_next != NULL; m = m->m_next)
  		;
  	m->m_next = mtail;
  	mhead->m_pkthdr.len += tail->paylen;
  
  	/* Flag mbuf as TSO packet with MSS. */
  	if (!ISSET(mhead->m_pkthdr.csum_flags, M_TCP_TSO)) {
  		/* Set CSUM_OUT flags in case of forwarding. */
  		SET(mhead->m_pkthdr.csum_flags, M_TCP_CSUM_OUT);
  		head->tcp->th_sum = 0;
  		if (head->ip4) {
  			SET(mhead->m_pkthdr.csum_flags, M_IPV4_CSUM_OUT);
  			head->ip4->ip_sum = 0;
  		}
  
  		SET(mhead->m_pkthdr.csum_flags, M_TCP_TSO);
  		mhead->m_pkthdr.ph_mss = head->paylen;
  		tcpstat_inc(tcps_inswlro);
  		tcpstat_inc(tcps_inpktlro);	/* count head */
  	}
  	mhead->m_pkthdr.ph_mss = MAX(mhead->m_pkthdr.ph_mss, tail->paylen);
  	tcpstat_inc(tcps_inpktlro);	/* count tail */
  }
  
  void
  tcp_softlro_glue(struct mbuf_list *ml, struct mbuf *mtail, struct ifnet *ifp)
  {
  	struct ether_extracted head, tail;
  	struct mbuf *m, *mhead;
  	unsigned int headcnt, tailcnt;
  
  	if (!ISSET(ifp->if_xflags, IFXF_LRO))
  		goto dontmerge;
  
  	mtail->m_pkthdr.ph_mss = 0;
  
  	ether_extract_headers(mtail, &tail);
  
  	if (tail.tcp) {
  		int tcpdatalen;
  
  		/* Remove possible ethernet padding at the end. */
  		tcpdatalen = tail.iplen - tail.iphlen - tail.tcphlen;
  		if (tcpdatalen < tail.paylen ) {
  			m_adj(mtail, tcpdatalen - tail.paylen);
  			tail.paylen = tcpdatalen;
  		}
  	}
  
  	if (!tcp_softlro_check(mtail, &tail))
  		goto dontmerge;
  
  	tailcnt = 0;
  	for (m = mtail; m != NULL; m = m->m_next) {
  		if (tailcnt++ >= 8)
  			goto dontmerge;
  	}
  
  	mtail->m_pkthdr.ph_mss = tail.paylen;
  
  	for (mhead = ml->ml_head; mhead != NULL; mhead = mhead->m_nextpkt) {
  		/* This packet has been checked and was not mergable before. */
  		if (mhead->m_pkthdr.ph_mss == 0)
  			continue;
  
  		/* Use RSS hash to skip packets of different connections. */
  		if (ISSET(mhead->m_pkthdr.csum_flags, M_FLOWID) &&
  		    ISSET(mtail->m_pkthdr.csum_flags, M_FLOWID) &&
  		    mhead->m_pkthdr.ph_flowid != mtail->m_pkthdr.ph_flowid)
  			continue;
  
  		/* Don't merge packets inside and outside of VLANs */
  		if (ISSET(mhead->m_flags, M_VLANTAG) !=
  		    ISSET(mtail->m_flags, M_VLANTAG))
  			continue;
  
  		if (ISSET(mhead->m_flags, M_VLANTAG)) {
  			/* Don't merge packets of different VLANs */
  			if (EVL_VLANOFTAG(mhead->m_pkthdr.ether_vtag) !=
  			    EVL_VLANOFTAG(mtail->m_pkthdr.ether_vtag))
  				continue;
  
  			/* Don't merge packets of different priorities */
  			if (EVL_PRIOFTAG(mhead->m_pkthdr.ether_vtag) !=
  			    EVL_PRIOFTAG(mtail->m_pkthdr.ether_vtag))
  				continue;
  		}
  
  		ether_extract_headers(mhead, &head);
  		if (!tcp_softlro_compare(&head, &tail))
  			continue;
  
  		/* Limit mbuf chain to avoid m_defrag calls when forwarding. */
  		headcnt = tailcnt;
  		for (m = mhead; m != NULL; m = m->m_next) {
  			if (headcnt++ >= 8)
  				goto dontmerge;
  		}
  
  		tcp_softlro_concat(mhead, &head, mtail, &tail);
  		return;
  	}
   dontmerge:
  	ml_enqueue(ml, mtail);
  }
  #endif