Differential D4055 Diff 9858 sys/modules/tcp/fastpath/fastpath.c

Changeset View

Standalone View

sys/modules/tcp/fastpath/fastpath.c

Property	Old Value	New Value
svn:eol-style	null	native \ No newline at end of property
svn:keywords	null	FreeBSD=%H \ No newline at end of property
svn:mime-type	null	text/plain \ No newline at end of property

				/*-
				* Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
				* The Regents of the University of California. All rights reserved.
				* Copyright (c) 2007-2008,2010
				* Swinburne University of Technology, Melbourne, Australia.
				* Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
				* Copyright (c) 2010 The FreeBSD Foundation
				* Copyright (c) 2010-2011 Juniper Networks, Inc.
				* Copyright (c) 2015 Netflix Inc.
				* All rights reserved.
				*
				* Portions of this software were developed at the Centre for Advanced Internet
				* Architectures, Swinburne University of Technology, by Lawrence Stewart,
				* James Healy and David Hayes, made possible in part by a grant from the Cisco
				* University Research Program Fund at Community Foundation Silicon Valley.
				*
				* Portions of this software were developed at the Centre for Advanced
				* Internet Architectures, Swinburne University of Technology, Melbourne,
				* Australia by David Hayes under sponsorship from the FreeBSD Foundation.
				*
				* Portions of this software were developed by Robert N. M. Watson under
				* contract to Juniper Networks, Inc.
				*
				* Portions of this software were developed by Randall R. Stewart while
				* working for Netflix Inc.
				*
				* 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.
				* 4. 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.
				*
				* @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
				*/

				#include <sys/cdefs.h>
				__FBSDID("$FreeBSD$");

				#include "opt_ipfw.h" /* for ipfw_fwd */
				#include "opt_inet.h"
				#include "opt_inet6.h"
				#include "opt_ipsec.h"
				#include "opt_kdtrace.h"
				#include "opt_tcpdebug.h"

				#include <sys/param.h>
				#include <sys/module.h>
				#include <sys/kernel.h>
				#include <sys/hhook.h>
				#include <sys/malloc.h>
				#include <sys/mbuf.h>
				#include <sys/proc.h> /* for proc0 declaration */
				#include <sys/protosw.h>
				#include <sys/sdt.h>
				#include <sys/signalvar.h>
				#include <sys/socket.h>
				#include <sys/socketvar.h>
				#include <sys/sysctl.h>
				#include <sys/syslog.h>
				#include <sys/systm.h>

				#include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */

				#include <vm/uma.h>

				#include <net/if.h>
				#include <net/if_var.h>
				#include <net/route.h>
				#include <net/vnet.h>

				#define TCPSTATES /* for logging */

				#include <netinet/cc.h>
				#include <netinet/in.h>
				#include <netinet/in_kdtrace.h>
				#include <netinet/in_pcb.h>
				#include <netinet/in_systm.h>
				#include <netinet/in_var.h>
				#include <netinet/ip.h>
				#include <netinet/ip_icmp.h> /* required for icmp_var.h */
				#include <netinet/icmp_var.h> /* for ICMP_BANDLIM */
				#include <netinet/ip_var.h>
				#include <netinet/ip_options.h>
				#include <netinet/ip6.h>
				#include <netinet/icmp6.h>
				#include <netinet6/in6_pcb.h>
				#include <netinet6/ip6_var.h>
				#include <netinet6/nd6.h>
				#include <netinet/tcp_fsm.h>
				#include <netinet/tcp_seq.h>
				#include <netinet/tcp_timer.h>
				#include <netinet/tcp_var.h>
				#include <netinet6/tcp6_var.h>
				#include <netinet/tcpip.h>
				#include <netinet/tcp_syncache.h>
				#ifdef TCPDEBUG
				#include <netinet/tcp_debug.h>
				#endif /* TCPDEBUG */
				#ifdef TCP_OFFLOAD
				#include <netinet/tcp_offload.h>
				#endif

				#ifdef IPSEC
				#include <netipsec/ipsec.h>
				#include <netipsec/ipsec6.h>
				#endif /IPSEC/

				#include <machine/in_cksum.h>

				#include <security/mac/mac_framework.h>

				const int tcprexmtthresh;

				VNET_DECLARE(int, tcp_autorcvbuf_inc);
				#define V_tcp_autorcvbuf_inc VNET(tcp_autorcvbuf_inc)
				VNET_DECLARE(int, tcp_autorcvbuf_max);
				#define V_tcp_autorcvbuf_max VNET(tcp_autorcvbuf_max)
				VNET_DECLARE(int, tcp_do_rfc3042);
				#define V_tcp_do_rfc3042 VNET(tcp_do_rfc3042)
				VNET_DECLARE(int, tcp_do_autorcvbuf);
				#define V_tcp_do_autorcvbuf VNET(tcp_do_autorcvbuf)
				VNET_DECLARE(int, tcp_insecure_rst);
				#define V_tcp_insecure_rst VNET(tcp_insecure_rst)
				VNET_DECLARE(int, tcp_insecure_syn);
				#define V_tcp_insecure_syn VNET(tcp_insecure_syn)




				extern void tcp_dooptions(struct tcpopt , u_char , int, int);
				extern void tcp_dropwithreset(struct mbuf , struct tcphdr ,
				struct tcpcb *, int, int);
				extern void tcp_pulloutofband(struct socket *,
				struct tcphdr , struct mbuf , int);
				extern void tcp_xmit_timer(struct tcpcb *, int);
				extern void tcp_newreno_partial_ack(struct tcpcb , struct tcphdr );
				extern void tcp_mss(struct tcpcb *tp, int offer);
				extern void cc_ack_received(struct tcpcb tp, struct tcphdr th,
				uint16_t type);
				extern void cc_conn_init(struct tcpcb *tp);
				extern void cc_post_recovery(struct tcpcb tp, struct tcphdr th);
				extern void cc_cong_signal(struct tcpcb tp, struct tcphdr th, uint32_t type);
				extern void hhook_run_tcp_est_in(struct tcpcb *tp,
				struct tcphdr th, struct tcpopt to);

				extern void kmod_tcpstat_inc(int statnum);
				#ifdef TCP_SIGNATURE
				extern int tcp_signature_verify_input(struct mbuf *m, int off0, int tlen, int optlen,
				struct tcpopt to, struct tcphdr th, u_int tcpbflag);
				#endif

				static void tcp_do_segment_fastslow(struct mbuf , struct tcphdr ,
				struct socket , struct tcpcb , int, int, uint8_t,
				int);

				static void tcp_do_segment_fastack(struct mbuf , struct tcphdr ,
				struct socket , struct tcpcb , int, int, uint8_t,
				int);

				/*
				* Indicate whether this ack should be delayed. We can delay the ack if
				* - there is no delayed ack timer in progress and
				* - our last ack wasn't a 0-sized window. We never want to delay
				* the ack that opens up a 0-sized window and
				* - delayed acks are enabled or
				* - this is a half-synchronized T/TCP connection.
				* - the segment size is not larger than the MSS and LRO wasn't used
				* for this segment.
				*/
				#define DELAY_ACK(tp, tlen) \
				((!tcp_timer_active(tp, TT_DELACK) && \
				(tp->t_flags & TF_RXWIN0SENT) == 0) && \
				(tlen <= tp->t_maxopd) && \
				(V_tcp_delack_enabled \|\| (tp->t_flags & TF_NEEDSYN)))


				static void
				tcp_do_fastack(struct mbuf m, struct tcphdr th, struct socket *so,
				struct tcpcb tp, struct tcpopt to, int drop_hdrlen, int tlen,
				int ti_locked, u_long tiwin)
				{
				int acked;
				int winup_only=0;
				/*
				* The following if statment will be true if
				* We have are doing the win_up_in_fp <and>
				* - We have more new data (SEQ_LT(tp->snd_wl1, th->th_seq)) <or>
				* - No more new data, but we have an ack for new data
				* (tp->snd_wl1 == th->th_seq && SEQ_LT(tp->snd_wl2, th->th_ack))
				* - No more new data, the same ack point but the window grew
				* (tp->snd_wl1 == th->th_seq && tp->snd_wl2 == th->th_ack && twin > tp->snd_wnd)
				*/
				if ((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 (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd) {
				winup_only = 1;
				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;
				}
				/*
				* If last ACK falls within this segment's sequence numbers,
				* record the timestamp.
				* NOTE that the test is modified according to the latest
				* proposal of the tcplw@cray.com list (Braden 1993/04/26).
				*/
				if ((to->to_flags & TOF_TS) != 0 &&
				SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
				tp->ts_recent_age = tcp_ts_getticks();
				tp->ts_recent = to->to_tsval;
				}
				/*
				* This is a pure ack for outstanding data.
				*/
				if (ti_locked == TI_RLOCKED) {
				INP_INFO_RUNLOCK(&V_tcbinfo);
				}
				ti_locked = TI_UNLOCKED;

				TCPSTAT_INC(tcps_predack);

				/*
				* "bad retransmit" recovery.
				*/
				if (tp->t_rxtshift == 1 &&
				tp->t_flags & TF_PREVVALID &&
				(int)(ticks - tp->t_badrxtwin) < 0) {
				cc_cong_signal(tp, th, CC_RTO_ERR);
				}

				/*
				* Recalculate the transmit timer / rtt.
				*
				* Some boxes send broken timestamp replies
				* during the SYN+ACK phase, ignore
				* timestamps of 0 or we could calculate a
				* huge RTT and blow up the retransmit timer.
				*/
				if ((to->to_flags & TOF_TS) != 0 &&
				to->to_tsecr) {
				u_int t;

				t = tcp_ts_getticks() - to->to_tsecr;
				if (!tp->t_rttlow \|\| tp->t_rttlow > t)
				tp->t_rttlow = t;
				tcp_xmit_timer(tp,
				TCP_TS_TO_TICKS(t) + 1);
				} else if (tp->t_rtttime &&
				SEQ_GT(th->th_ack, tp->t_rtseq)) {
				if (!tp->t_rttlow \|\|
				tp->t_rttlow > ticks - tp->t_rtttime)
				tp->t_rttlow = ticks - tp->t_rtttime;
				tcp_xmit_timer(tp,
				ticks - tp->t_rtttime);
				}
				if (winup_only == 0) {
				acked = BYTES_THIS_ACK(tp, th);

				/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
				hhook_run_tcp_est_in(tp, th, to);

				TCPSTAT_ADD(tcps_rcvackbyte, acked);
				sbdrop(&so->so_snd, acked);
				if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
				SEQ_LEQ(th->th_ack, tp->snd_recover))
				tp->snd_recover = th->th_ack - 1;

				/*
				* Let the congestion control algorithm update
				* congestion control related information. This
				* typically means increasing the congestion
				* window.
				*/
				cc_ack_received(tp, th, CC_ACK);

				tp->snd_una = th->th_ack;
				/*
				* Pull snd_wl2 up to prevent seq wrap relative
				* to th_ack.
				*/
				tp->snd_wl2 = th->th_ack;
				tp->t_dupacks = 0;
				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.
				*/
				#ifdef TCPDEBUG
				if (so->so_options & SO_DEBUG)
				tcp_trace(TA_INPUT, ostate, tp,
				(void *)tcp_saveipgen,
				&tcp_savetcp, 0);
				#endif
				if (tp->snd_una == tp->snd_max)
				tcp_timer_activate(tp, TT_REXMT, 0);
				else if (!tcp_timer_active(tp, TT_PERSIST))
				tcp_timer_activate(tp, TT_REXMT,
				tp->t_rxtcur);
				} else {
				/*
				* Window update only, just free the mbufs and
				* send out whatever we can.
				*/
				m_freem(m);
				}
				sowwakeup(so);
				if (sbavail(&so->so_snd))
				(void) tcp_output(tp);
				KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
				__func__, ti_locked));
				INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
				INP_WLOCK_ASSERT(tp->t_inpcb);

				if (tp->t_flags & TF_DELACK) {
				tp->t_flags &= ~TF_DELACK;
				tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
				}
				INP_WUNLOCK(tp->t_inpcb);
				}


				static void
				tcp_do_fastnewdata(struct mbuf m, struct tcphdr th, struct socket *so,
				struct tcpcb tp, struct tcpopt to, int drop_hdrlen, int tlen,
				int ti_locked, u_long tiwin)
				{
				int newsize = 0; /* automatic sockbuf scaling */

				/*
				* If last ACK falls within this segment's sequence numbers,
				* record the timestamp.
				* NOTE that the test is modified according to the latest
				* proposal of the tcplw@cray.com list (Braden 1993/04/26).
				*/
				if ((to->to_flags & TOF_TS) != 0 &&
				SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
				tp->ts_recent_age = tcp_ts_getticks();
				tp->ts_recent = to->to_tsval;
				}

				/*
				* This is a pure, in-sequence data packet with
				* nothing on the reassembly queue and we have enough
				* buffer space to take it.
				*/
				if (ti_locked == TI_RLOCKED) {
				INP_INFO_RUNLOCK(&V_tcbinfo);
				}
				ti_locked = TI_UNLOCKED;

				/* Clean receiver SACK report if present */
				if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
				tcp_clean_sackreport(tp);
				TCPSTAT_INC(tcps_preddat);
				tp->rcv_nxt += tlen;
				/*
				* Pull snd_wl1 up to prevent seq wrap relative to
				* th_seq.
				*/
				tp->snd_wl1 = th->th_seq;
				/*
				* Pull rcv_up up to prevent seq wrap relative to
				* rcv_nxt.
				*/
				tp->rcv_up = tp->rcv_nxt;
				TCPSTAT_ADD(tcps_rcvbyte, tlen);
				#ifdef TCPDEBUG
				if (so->so_options & SO_DEBUG)
				tcp_trace(TA_INPUT, ostate, tp,
				(void *)tcp_saveipgen, &tcp_savetcp, 0);
				#endif
				/*
				* Automatic sizing of receive socket buffer. Often the send
				* buffer size is not optimally adjusted to the actual network
				* conditions at hand (delay bandwidth product). Setting the
				* buffer size too small limits throughput on links with high
				* bandwidth and high delay (eg. trans-continental/oceanic links).
				*
				* On the receive side the socket buffer memory is only rarely
				* used to any significant extent. This allows us to be much
				* more aggressive in scaling the receive socket buffer. For
				* the case that the buffer space is actually used to a large
				* extent and we run out of kernel memory we can simply drop
				* the new segments; TCP on the sender will just retransmit it
				* later. Setting the buffer size too big may only consume too
				* much kernel memory if the application doesn't read() from
				* the socket or packet loss or reordering makes use of the
				* reassembly queue.
				*
				* The criteria to step up the receive buffer one notch are:
				* 1. the number of bytes received during the time it takes
				* one timestamp to be reflected back to us (the RTT);
				* 2. received bytes per RTT is within seven eighth of the
				* current socket buffer size;
				* 3. receive buffer size has not hit maximal automatic size;
				*
				* This algorithm does one step per RTT at most and only if
				* we receive a bulk stream w/o packet losses or reorderings.
				* Shrinking the buffer during idle times is not necessary as
				* it doesn't consume any memory when idle.
				*
				* TODO: Only step up if the application is actually serving
				* the buffer to better manage the socket buffer resources.
				*/
				if (V_tcp_do_autorcvbuf &&
				to->to_tsecr &&
				(so->so_rcv.sb_flags & SB_AUTOSIZE)) {
				if (TSTMP_GT(to->to_tsecr, tp->rfbuf_ts) &&
				to->to_tsecr - tp->rfbuf_ts < hz) {
				if (tp->rfbuf_cnt >
				(so->so_rcv.sb_hiwat / 8 * 7) &&
				so->so_rcv.sb_hiwat <
				V_tcp_autorcvbuf_max) {
				newsize =
				min(so->so_rcv.sb_hiwat +
				V_tcp_autorcvbuf_inc,
				V_tcp_autorcvbuf_max);
				}
				/* Start over with next RTT. */
				tp->rfbuf_ts = 0;
				tp->rfbuf_cnt = 0;
				} else
				tp->rfbuf_cnt += tlen; /* add up */
				}

				/* Add data to socket buffer. */
				SOCKBUF_LOCK(&so->so_rcv);
				if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
				m_freem(m);
				} else {
				/*
				* Set new socket buffer size.
				* Give up when limit is reached.
				*/
				if (newsize)
				if (!sbreserve_locked(&so->so_rcv,
				newsize, so, NULL))
				so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
				m_adj(m, drop_hdrlen); /* delayed header drop */
				sbappendstream_locked(&so->so_rcv, m, 0);
				}
				/* NB: sorwakeup_locked() does an implicit unlock. */
				sorwakeup_locked(so);
				if (DELAY_ACK(tp, tlen)) {
				tp->t_flags \|= TF_DELACK;
				} else {
				tp->t_flags \|= TF_ACKNOW;
				tcp_output(tp);
				}
				KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
				__func__, ti_locked));
				INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
				INP_WLOCK_ASSERT(tp->t_inpcb);

				if (tp->t_flags & TF_DELACK) {
				tp->t_flags &= ~TF_DELACK;
				tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
				}
				INP_WUNLOCK(tp->t_inpcb);
				}

				static void
				tcp_do_slowpath(struct mbuf m, struct tcphdr th, struct socket *so,
				struct tcpcb tp, struct tcpopt to, int drop_hdrlen, int tlen,
				int ti_locked, u_long tiwin, int thflags)
				{
				int acked, ourfinisacked, needoutput = 0;
				int rstreason, todrop, win;
				char *s;
				struct in_conninfo *inc;
				struct mbuf *mfree = NULL;

				/*
				* 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.
				*/
				inc = &tp->t_inpcb->inp_inc;
				win = sbspace(&so->so_rcv);
				if (win < 0)
				win = 0;
				tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));

				/* Reset receive buffer auto scaling when not in bulk receive mode. */
				tp->rfbuf_ts = 0;
				tp->rfbuf_cnt = 0;

				switch (tp->t_state) {

				/*
				* If the state is SYN_RECEIVED:
				* if seg contains an ACK, but not for our SYN/ACK, send a RST.
				*/
				case TCPS_SYN_RECEIVED:
				if ((thflags & TH_ACK) &&
				(SEQ_LEQ(th->th_ack, tp->snd_una) \|\|
				SEQ_GT(th->th_ack, tp->snd_max))) {
				rstreason = BANDLIM_RST_OPENPORT;
				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 seg contains an ECE and ECN support is enabled, the stream
				* is ECN capable.
				* 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 ((thflags & TH_ACK) &&
				(SEQ_LEQ(th->th_ack, tp->iss) \|\|
				SEQ_GT(th->th_ack, tp->snd_max))) {
				rstreason = BANDLIM_UNLIMITED;
				goto dropwithreset;
				}
				if ((thflags & (TH_ACK\|TH_RST)) == (TH_ACK\|TH_RST)) {
				TCP_PROBE5(connect__refused, NULL, tp,
				mtod(m, const char *), tp, th);
				tp = tcp_drop(tp, ECONNREFUSED);
				}
				if (thflags & TH_RST)
				goto drop;
				if (!(thflags & TH_SYN))
				goto drop;

				tp->irs = th->th_seq;
				tcp_rcvseqinit(tp);
				if (thflags & TH_ACK) {
				TCPSTAT_INC(tcps_connects);
				soisconnected(so);
				#ifdef MAC
				mac_socketpeer_set_from_mbuf(m, so);
				#endif
				/* Do window scaling on this connection? */
				if ((tp->t_flags & (TF_RCVD_SCALE\|TF_REQ_SCALE)) ==
				(TF_RCVD_SCALE\|TF_REQ_SCALE)) {
				tp->rcv_scale = tp->request_r_scale;
				}
				tp->rcv_adv += imin(tp->rcv_wnd,
				TCP_MAXWIN << tp->rcv_scale);
				tp->snd_una++; /* SYN is acked */
				/*
				* If there's data, delay ACK; if there's also a FIN
				* ACKNOW will be turned on later.
				*/
				if (DELAY_ACK(tp, tlen) && tlen != 0)
				tp->t_fb->tcp_timer_activate(tp, TT_DELACK,
				tcp_delacktime);
				else
				tp->t_flags \|= TF_ACKNOW;

				if ((thflags & TH_ECE) && V_tcp_do_ecn) {
				tp->t_flags \|= TF_ECN_PERMIT;
				TCPSTAT_INC(tcps_ecn_shs);
				}

				/*
				* Received <SYN,ACK> in SYN_SENT[*] state.
				* Transitions:
				* SYN_SENT --> ESTABLISHED
				* SYN_SENT* --> FIN_WAIT_1
				*/
				tp->t_starttime = ticks;
				if (tp->t_flags & TF_NEEDFIN) {
				tcp_state_change(tp, TCPS_FIN_WAIT_1);
				tp->t_flags &= ~TF_NEEDFIN;
				thflags &= ~TH_SYN;
				} else {
				tcp_state_change(tp, TCPS_ESTABLISHED);
				TCP_PROBE5(connect__established, NULL, tp,
				mtod(m, const char *), tp, th);
				cc_conn_init(tp);
				tp->t_fb->tcp_timer_activate(tp, TT_KEEP,
				TP_KEEPIDLE(tp));
				}
				} else {
				/*
				* Received initial SYN in SYN-SENT[*] state =>
				* simultaneous open.
				* If it succeeds, connection is * half-synchronized.
				* Otherwise, do 3-way handshake:
				* SYN-SENT -> SYN-RECEIVED
				* SYN-SENT* -> SYN-RECEIVED*
				*/
				tp->t_flags \|= (TF_ACKNOW \| TF_NEEDSYN);
				tp->t_fb->tcp_timer_activate(tp, TT_REXMT, 0);
				tcp_state_change(tp, TCPS_SYN_RECEIVED);
				}

				KASSERT(ti_locked == TI_RLOCKED, ("%s: trimthenstep6: "
				"ti_locked %d", __func__, ti_locked));
				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
				INP_WLOCK_ASSERT(tp->t_inpcb);

				/*
				* 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;
				thflags &= ~TH_FIN;
				TCPSTAT_INC(tcps_rcvpackafterwin);
				TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
				}
				tp->snd_wl1 = th->th_seq - 1;
				tp->rcv_up = th->th_seq;
				/*
				* Client side of transaction: already sent SYN and data.
				* If the remote host used T/TCP to validate the SYN,
				* our data will be ACK'd; if so, enter normal data segment
				* processing in the middle of step 5, ack processing.
				* Otherwise, goto step 6.
				*/
				if (thflags & TH_ACK)
				goto process_ACK;

				goto step6;

				/*
				* If the state is LAST_ACK or CLOSING or TIME_WAIT:
				* do normal processing.
				*
				* NB: Leftover from RFC1644 T/TCP. Cases to be reused later.
				*/
				case TCPS_LAST_ACK:
				case TCPS_CLOSING:
				break; /* continue normal processing */
				}

				/*
				* States other than LISTEN or SYN_SENT.
				* First check the RST flag and sequence number since reset segments
				* are exempt from the timestamp and connection count tests. This
				* fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
				* below which allowed reset segments in half the sequence space
				* to fall though and be processed (which gives forged reset
				* segments with a random sequence number a 50 percent chance of
				* killing a connection).
				* Then check timestamp, if present.
				* Then check the connection count, 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.
				*/
				if (thflags & TH_RST) {
				/*
				* RFC5961 Section 3.2
				*
				* - RST drops connection only if SEG.SEQ == RCV.NXT.
				* - If RST is in window, we send challenge ACK.
				*
				* Note: to take into account delayed ACKs, we should
				* test against last_ack_sent instead of rcv_nxt.
				* Note 2: we handle special case of closed window, not
				* covered by the RFC.
				*/
				if ((SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
				SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) \|\|
				(tp->rcv_wnd == 0 && tp->last_ack_sent == th->th_seq)) {
				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
				KASSERT(ti_locked == TI_RLOCKED,
				("%s: TH_RST ti_locked %d, th %p tp %p",
				__func__, ti_locked, th, tp));
				KASSERT(tp->t_state != TCPS_SYN_SENT,
				("%s: TH_RST for TCPS_SYN_SENT th %p tp %p",
				__func__, th, tp));

				if (V_tcp_insecure_rst \|\|
				tp->last_ack_sent == th->th_seq) {
				TCPSTAT_INC(tcps_drops);
				/* Drop the connection. */
				switch (tp->t_state) {
				case TCPS_SYN_RECEIVED:
				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:
				tcp_state_change(tp, TCPS_CLOSED);
				/* FALLTHROUGH */
				default:
				tp = tcp_close(tp);
				}
				} else {
				TCPSTAT_INC(tcps_badrst);
				/* Send challenge ACK. */
				tcp_respond(tp, mtod(m, void *), th, m,
				tp->rcv_nxt, tp->snd_nxt, TH_ACK);
				tp->last_ack_sent = tp->rcv_nxt;
				m = NULL;
				}
				}
				goto drop;
				}

				/*
				* RFC5961 Section 4.2
				* Send challenge ACK for any SYN in synchronized state.
				*/
				if ((thflags & TH_SYN) && tp->t_state != TCPS_SYN_SENT) {
				KASSERT(ti_locked == TI_RLOCKED,
				("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);

				TCPSTAT_INC(tcps_badsyn);
				if (V_tcp_insecure_syn &&
				SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
				SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
				tp = tcp_drop(tp, ECONNRESET);
				rstreason = BANDLIM_UNLIMITED;
				} else {
				/* Send challenge ACK. */
				tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
				tp->snd_nxt, TH_ACK);
				tp->last_ack_sent = tp->rcv_nxt;
				m = NULL;
				}
				goto drop;
				}

				/*
				* RFC 1323 PAWS: If we have a timestamp reply on this segment
				* and it's less than ts_recent, drop it.
				*/
				if ((to->to_flags & TOF_TS) != 0 && tp->ts_recent &&
				TSTMP_LT(to->to_tsval, tp->ts_recent)) {

				/* Check to see if ts_recent is over 24 days old. */
				if (tcp_ts_getticks() - 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_INC(tcps_rcvduppack);
				TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
				TCPSTAT_INC(tcps_pawsdrop);
				if (tlen)
				goto dropafterack;
				goto drop;
				}
				}

				/*
				* In the SYN-RECEIVED state, validate that the packet belongs to
				* this connection before trimming the data to fit the receive
				* window. Check the sequence number versus IRS since we know
				* the sequence numbers haven't wrapped. This is a partial fix
				* for the "LAND" DoS attack.
				*/
				if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
				rstreason = BANDLIM_RST_OPENPORT;
				goto dropwithreset;
				}

				todrop = tp->rcv_nxt - th->th_seq;
				if (todrop > 0) {
				if (thflags & TH_SYN) {
				thflags &= ~TH_SYN;
				th->th_seq++;
				if (th->th_urp > 1)
				th->th_urp--;
				else
				thflags &= ~TH_URG;
				todrop--;
				}
				/*
				* Following if statement from Stevens, vol. 2, p. 960.
				*/
				if (todrop > tlen
				\|\| (todrop == tlen && (thflags & TH_FIN) == 0)) {
				/*
				* Any valid FIN must be to the left of the window.
				* At this point the FIN must be a duplicate or out
				* of sequence; drop it.
				*/
				thflags &= ~TH_FIN;

				/*
				* Send an ACK to resynchronize and drop any data.
				* But keep on processing for RST or ACK.
				*/
				tp->t_flags \|= TF_ACKNOW;
				todrop = tlen;
				TCPSTAT_INC(tcps_rcvduppack);
				TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
				} else {
				TCPSTAT_INC(tcps_rcvpartduppack);
				TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
				}
				drop_hdrlen += todrop; /* drop from the top afterwards */
				th->th_seq += todrop;
				tlen -= todrop;
				if (th->th_urp > todrop)
				th->th_urp -= todrop;
				else {
				thflags &= ~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) {
				KASSERT(ti_locked == TI_RLOCKED, ("%s: SS_NOFDEREF && "
				"CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);

				if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
				log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
				"after socket was closed, "
				"sending RST and removing tcpcb\n",
				s, __func__, tcpstates[tp->t_state], tlen);
				free(s, M_TCPLOG);
				}
				tp = tcp_close(tp);
				TCPSTAT_INC(tcps_rcvafterclose);
				rstreason = BANDLIM_UNLIMITED;
				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;
				thflags &= ~(TH_PUSH\|TH_FIN);
				}

				/*
				* If last ACK falls within this segment's sequence numbers,
				* record its timestamp.
				* NOTE:
				* 1) That the test incorporates suggestions from the latest
				* proposal of the tcplw@cray.com list (Braden 1993/04/26).
				* 2) That updating only on newer timestamps interferes with
				* our earlier PAWS tests, so this check should be solely
				* predicated on the sequence space of this segment.
				* 3) That we modify the segment boundary check to be
				* Last.ACK.Sent <= SEG.SEQ + SEG.Len
				* instead of RFC1323's
				* Last.ACK.Sent < SEG.SEQ + SEG.Len,
				* This modified check allows us to overcome RFC1323's
				* limitations as described in Stevens TCP/IP Illustrated
				* Vol. 2 p.869. In such cases, we can still calculate the
				* RTT correctly when RCV.NXT == Last.ACK.Sent.
				*/
				if ((to->to_flags & TOF_TS) != 0 &&
				SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
				SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
				((thflags & (TH_SYN\|TH_FIN)) != 0))) {
				tp->ts_recent_age = tcp_ts_getticks();
				tp->ts_recent = to->to_tsval;
				}

				/*
				* If the ACK bit is off: if in SYN-RECEIVED state or SENDSYN
				* flag is on (half-synchronized state), then queue data for
				* later processing; else drop segment and return.
				*/
				if ((thflags & TH_ACK) == 0) {
				if (tp->t_state == TCPS_SYN_RECEIVED \|\|
				(tp->t_flags & TF_NEEDSYN))
				goto step6;
				else 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);
				soisconnected(so);
				/* Do window scaling? */
				if ((tp->t_flags & (TF_RCVD_SCALE\|TF_REQ_SCALE)) ==
				(TF_RCVD_SCALE\|TF_REQ_SCALE)) {
				tp->rcv_scale = tp->request_r_scale;
				tp->snd_wnd = tiwin;
				}
				/*
				* Make transitions:
				* SYN-RECEIVED -> ESTABLISHED
				* SYN-RECEIVED* -> FIN-WAIT-1
				*/
				tp->t_starttime = ticks;
				if (tp->t_flags & TF_NEEDFIN) {
				tcp_state_change(tp, TCPS_FIN_WAIT_1);
				tp->t_flags &= ~TF_NEEDFIN;
				} else {
				tcp_state_change(tp, TCPS_ESTABLISHED);
				TCP_PROBE5(accept__established, NULL, tp,
				mtod(m, const char *), tp, th);
				cc_conn_init(tp);
				tp->t_fb->tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
				}
				/*
				* If segment contains data or ACK, will call tcp_reass()
				* later; if not, do so now to pass queued data to user.
				*/
				if (tlen == 0 && (thflags & TH_FIN) == 0)
				(void) tcp_reass(tp, (struct tcphdr *)0, 0,
				(struct mbuf *)0);
				tp->snd_wl1 = th->th_seq - 1;
				/* FALLTHROUGH */

				/*
				* 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:
				if (SEQ_GT(th->th_ack, tp->snd_max)) {
				TCPSTAT_INC(tcps_rcvacktoomuch);
				goto dropafterack;
				}
				if ((tp->t_flags & TF_SACK_PERMIT) &&
				((to->to_flags & TOF_SACK) \|\|
				!TAILQ_EMPTY(&tp->snd_holes)))
				tcp_sack_doack(tp, to, th->th_ack);
				else
				/*
				* Reset the value so that previous (valid) value
				* from the last ack with SACK doesn't get used.
				*/
				tp->sackhint.sacked_bytes = 0;

				/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
				hhook_run_tcp_est_in(tp, th, to);

				if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
				if (tlen == 0 && tiwin == tp->snd_wnd) {
				/*
				* If this is the first time we've seen a
				* FIN from the remote, this is not a
				* duplicate and it needs to be processed
				* normally. This happens during a
				* simultaneous close.
				*/
				if ((thflags & TH_FIN) &&
				(TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
				tp->t_dupacks = 0;
				break;
				}
				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 and FIN isn't set),
				* the ack is the biggest we've
				* seen and we've seen exactly our rexmt
				* threshhold 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.
				*
				* When using TCP ECN, notify the peer that
				* we reduced the cwnd.
				*/
				if (!tp->t_fb->tcp_timer_active(tp, TT_REXMT) \|\|
				th->th_ack != tp->snd_una)
				tp->t_dupacks = 0;
				else if (++tp->t_dupacks > tcprexmtthresh \|\|
				IN_FASTRECOVERY(tp->t_flags)) {
				cc_ack_received(tp, th, CC_DUPACK);
				if ((tp->t_flags & TF_SACK_PERMIT) &&
				IN_FASTRECOVERY(tp->t_flags)) {
				int awnd;

				/*
				* Compute the amount of data in flight first.
				* We can inject new data into the pipe iff
				* we have less than 1/2 the original window's
				* worth of data in flight.
				*/
				if (V_tcp_do_rfc6675_pipe)
				awnd = tcp_compute_pipe(tp);
				else
				awnd = (tp->snd_nxt - tp->snd_fack) +
				tp->sackhint.sack_bytes_rexmit;

				if (awnd < tp->snd_ssthresh) {
				tp->snd_cwnd += tp->t_maxseg;
				if (tp->snd_cwnd > tp->snd_ssthresh)
				tp->snd_cwnd = tp->snd_ssthresh;
				}
				} else
				tp->snd_cwnd += tp->t_maxseg;
				(void) tp->t_fb->tcp_output(tp);
				goto drop;
				} else if (tp->t_dupacks == tcprexmtthresh) {
				tcp_seq onxt = tp->snd_nxt;

				/*
				* If we're doing sack, check to
				* see if we're already in sack
				* recovery. If we're not doing sack,
				* check to see if we're in newreno
				* recovery.
				*/
				if (tp->t_flags & TF_SACK_PERMIT) {
				if (IN_FASTRECOVERY(tp->t_flags)) {
				tp->t_dupacks = 0;
				break;
				}
				} else {
				if (SEQ_LEQ(th->th_ack,
				tp->snd_recover)) {
				tp->t_dupacks = 0;
				break;
				}
				}
				/* Congestion signal before ack. */
				cc_cong_signal(tp, th, CC_NDUPACK);
				cc_ack_received(tp, th, CC_DUPACK);
				tp->t_fb->tcp_timer_activate(tp, TT_REXMT, 0);
				tp->t_rtttime = 0;
				if (tp->t_flags & TF_SACK_PERMIT) {
				TCPSTAT_INC(
				tcps_sack_recovery_episode);
				tp->sack_newdata = tp->snd_nxt;
				tp->snd_cwnd = tp->t_maxseg;
				(void) tp->t_fb->tcp_output(tp);
				goto drop;
				}
				tp->snd_nxt = th->th_ack;
				tp->snd_cwnd = tp->t_maxseg;
				(void) tp->t_fb->tcp_output(tp);
				KASSERT(tp->snd_limited <= 2,
				("%s: tp->snd_limited too big",
				__func__));
				tp->snd_cwnd = tp->snd_ssthresh +
				tp->t_maxseg *
				(tp->t_dupacks - tp->snd_limited);
				if (SEQ_GT(onxt, tp->snd_nxt))
				tp->snd_nxt = onxt;
				goto drop;
				} else if (V_tcp_do_rfc3042) {
				/*
				* Process first and second duplicate
				* ACKs. Each indicates a segment
				* leaving the network, creating room
				* for more. Make sure we can send a
				* packet on reception of each duplicate
				* ACK by increasing snd_cwnd by one
				* segment. Restore the original
				* snd_cwnd after packet transmission.
				*/
				cc_ack_received(tp, th, CC_DUPACK);
				u_long oldcwnd = tp->snd_cwnd;
				tcp_seq oldsndmax = tp->snd_max;
				u_int sent;
				int avail;

				KASSERT(tp->t_dupacks == 1 \|\|
				tp->t_dupacks == 2,
				("%s: dupacks not 1 or 2",
				__func__));
				if (tp->t_dupacks == 1)
				tp->snd_limited = 0;
				tp->snd_cwnd =
				(tp->snd_nxt - tp->snd_una) +
				(tp->t_dupacks - tp->snd_limited) *
				tp->t_maxseg;
				/*
				* Only call tcp_output when there
				* is new data available to be sent.
				* Otherwise we would send pure ACKs.
				*/
				SOCKBUF_LOCK(&so->so_snd);
				avail = sbavail(&so->so_snd) -
				(tp->snd_nxt - tp->snd_una);
				SOCKBUF_UNLOCK(&so->so_snd);
				if (avail > 0)
				(void) tp->t_fb->tcp_output(tp);
				sent = tp->snd_max - oldsndmax;
				if (sent > tp->t_maxseg) {
				KASSERT((tp->t_dupacks == 2 &&
				tp->snd_limited == 0) \|\|
				(sent == tp->t_maxseg + 1 &&
				tp->t_flags & TF_SENTFIN),
				("%s: sent too much",
				__func__));
				tp->snd_limited = 2;
				} else if (sent > 0)
				++tp->snd_limited;
				tp->snd_cwnd = oldcwnd;
				goto drop;
				}
				} else
				tp->t_dupacks = 0;
				break;
				}

				KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
				("%s: th_ack <= snd_una", __func__));

				/*
				* If the congestion window was inflated to account
				* for the other side's cached packets, retract it.
				*/
				if (IN_FASTRECOVERY(tp->t_flags)) {
				if (SEQ_LT(th->th_ack, tp->snd_recover)) {
				if (tp->t_flags & TF_SACK_PERMIT)
				tcp_sack_partialack(tp, th);
				else
				tcp_newreno_partial_ack(tp, th);
				} else
				cc_post_recovery(tp, th);
				}
				tp->t_dupacks = 0;
				/*
				* If we reach this point, ACK is not a duplicate,
				* i.e., it ACKs something we sent.
				*/
				if (tp->t_flags & TF_NEEDSYN) {
				/*
				* T/TCP: Connection was half-synchronized, and our
				* SYN has been ACK'd (so connection is now fully
				* synchronized). Go to non-starred state,
				* increment snd_una for ACK of SYN, and check if
				* we can do window scaling.
				*/
				tp->t_flags &= ~TF_NEEDSYN;
				tp->snd_una++;
				/* Do window scaling? */
				if ((tp->t_flags & (TF_RCVD_SCALE\|TF_REQ_SCALE)) ==
				(TF_RCVD_SCALE\|TF_REQ_SCALE)) {
				tp->rcv_scale = tp->request_r_scale;
				/* Send window already scaled. */
				}
				}

				process_ACK:
				INP_WLOCK_ASSERT(tp->t_inpcb);

				acked = BYTES_THIS_ACK(tp, th);
				TCPSTAT_INC(tcps_rcvackpack);
				TCPSTAT_ADD(tcps_rcvackbyte, acked);

				/*
				* If we just performed our first retransmit, and the ACK
				* arrives within our recovery window, then it was a mistake
				* to do the retransmit in the first place. Recover our
				* original cwnd and ssthresh, and proceed to transmit where
				* we left off.
				*/
				if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID &&
				(int)(ticks - tp->t_badrxtwin) < 0)
				cc_cong_signal(tp, th, CC_RTO_ERR);

				/*
				* 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.
				*
				* Some boxes send broken timestamp replies
				* during the SYN+ACK phase, ignore
				* timestamps of 0 or we could calculate a
				* huge RTT and blow up the retransmit timer.
				*/
				if ((to->to_flags & TOF_TS) != 0 && to->to_tsecr) {
				u_int t;

				t = tcp_ts_getticks() - to->to_tsecr;
				if (!tp->t_rttlow \|\| tp->t_rttlow > t)
				tp->t_rttlow = t;
				tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
				} else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
				if (!tp->t_rttlow \|\| tp->t_rttlow > ticks - tp->t_rtttime)
				tp->t_rttlow = ticks - tp->t_rtttime;
				tcp_xmit_timer(tp, ticks - 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) {
				tp->t_fb->tcp_timer_activate(tp, TT_REXMT, 0);
				needoutput = 1;
				} else if (!tp->t_fb->tcp_timer_active(tp, TT_PERSIST))
				tp->t_fb->tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);

				/*
				* If no data (only SYN) was ACK'd,
				* skip rest of ACK processing.
				*/
				if (acked == 0)
				goto step6;

				/*
				* Let the congestion control algorithm update congestion
				* control related information. This typically means increasing
				* the congestion window.
				*/
				cc_ack_received(tp, th, CC_ACK);

				SOCKBUF_LOCK(&so->so_snd);
				if (acked > sbavail(&so->so_snd)) {
				tp->snd_wnd -= sbavail(&so->so_snd);
				mfree = sbcut_locked(&so->so_snd,
				(int)sbavail(&so->so_snd));
				ourfinisacked = 1;
				} else {
				mfree = sbcut_locked(&so->so_snd, acked);
				tp->snd_wnd -= acked;
				ourfinisacked = 0;
				}
				/* NB: sowwakeup_locked() does an implicit unlock. */
				sowwakeup_locked(so);
				m_freem(mfree);
				/* Detect una wraparound. */
				if (!IN_RECOVERY(tp->t_flags) &&
				SEQ_GT(tp->snd_una, tp->snd_recover) &&
				SEQ_LEQ(th->th_ack, tp->snd_recover))
				tp->snd_recover = th->th_ack - 1;
				/* XXXLAS: Can this be moved up into cc_post_recovery? */
				if (IN_RECOVERY(tp->t_flags) &&
				SEQ_GEQ(th->th_ack, tp->snd_recover)) {
				EXIT_RECOVERY(tp->t_flags);
				}
				tp->snd_una = th->th_ack;
				if (tp->t_flags & TF_SACK_PERMIT) {
				if (SEQ_GT(tp->snd_una, tp->snd_recover))
				tp->snd_recover = tp->snd_una;
				}
				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.
				*
				* XXXjl:
				* we should release the tp also, and use a
				* compressed state.
				*/
				if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
				soisdisconnected(so);
				tp->t_fb->tcp_timer_activate(tp, TT_2MSL,
				(tcp_fast_finwait2_recycle ?
				tcp_finwait2_timeout :
				TP_MAXIDLE(tp)));
				}
				tcp_state_change(tp, 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) {
				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
				tcp_twstart(tp);
				INP_INFO_RUNLOCK(&V_tcbinfo);
				m_freem(m);
				return;
				}
				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) {
				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
				tp = tcp_close(tp);
				goto drop;
				}
				break;
				}
				}

				step6:
				INP_WLOCK_ASSERT(tp->t_inpcb);

				/*
				* Update window information.
				* Don't look at window if no ACK: TAC's send garbage on first SYN.
				*/
				if ((thflags & 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;
				needoutput = 1;
				}

				/*
				* Process segments with URG.
				*/
				if ((thflags & TH_URG) && th->th_urp &&
				TCPS_HAVERCVDFIN(tp->t_state) == 0) {
				/*
				* 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.
				*/
				SOCKBUF_LOCK(&so->so_rcv);
				if (th->th_urp + sbavail(&so->so_rcv) > sb_max) {
				th->th_urp = 0; /* XXX */
				thflags &= ~TH_URG; /* XXX */
				SOCKBUF_UNLOCK(&so->so_rcv); /* 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;
				so->so_oobmark = sbavail(&so->so_rcv) +
				(tp->rcv_up - tp->rcv_nxt) - 1;
				if (so->so_oobmark == 0)
				so->so_rcv.sb_state \|= SBS_RCVATMARK;
				sohasoutofband(so);
				tp->t_oobflags &= ~(TCPOOB_HAVEDATA \| TCPOOB_HADDATA);
				}
				SOCKBUF_UNLOCK(&so->so_rcv);
				/*
				* 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_long)tlen &&
				!(so->so_options & SO_OOBINLINE)) {
				/* hdr drop is delayed */
				tcp_pulloutofband(so, th, m, drop_hdrlen);
				}
				} 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 */
				INP_WLOCK_ASSERT(tp->t_inpcb);

				/*
				* 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 \|\| (thflags & TH_FIN)) &&
				TCPS_HAVERCVDFIN(tp->t_state) == 0) {
				tcp_seq save_start = th->th_seq;
				m_adj(m, drop_hdrlen); /* delayed header drop */
				/*
				* Insert segment which includes th into TCP reassembly queue
				* with control block tp. Set thflags to whether reassembly now
				* includes a segment with FIN. This handles 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).
				*/
				if (th->th_seq == tp->rcv_nxt &&
				LIST_EMPTY(&tp->t_segq) &&
				TCPS_HAVEESTABLISHED(tp->t_state)) {
				if (DELAY_ACK(tp, tlen))
				tp->t_flags \|= TF_DELACK;
				else
				tp->t_flags \|= TF_ACKNOW;
				tp->rcv_nxt += tlen;
				thflags = th->th_flags & TH_FIN;
				TCPSTAT_INC(tcps_rcvpack);
				TCPSTAT_ADD(tcps_rcvbyte, tlen);
				SOCKBUF_LOCK(&so->so_rcv);
				if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
				m_freem(m);
				else
				sbappendstream_locked(&so->so_rcv, m, 0);
				/* NB: sorwakeup_locked() does an implicit unlock. */
				sorwakeup_locked(so);
				} else {
				/*
				* XXX: Due to the header drop above "th" is
				* theoretically invalid by now. Fortunately
				* m_adj() doesn't actually frees any mbufs
				* when trimming from the head.
				*/
				thflags = tcp_reass(tp, th, &tlen, m);
				tp->t_flags \|= TF_ACKNOW;
				}
				if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
				tcp_update_sack_list(tp, save_start, save_start + tlen);
				#if 0
				/*
				* Note the amount of data that peer has sent into
				* our window, in order to estimate the sender's
				* buffer size.
				* XXX: Unused.
				*/
				if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
				len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
				else
				len = so->so_rcv.sb_hiwat;
				#endif
				} else {
				m_freem(m);
				thflags &= ~TH_FIN;
				}

				/*
				* If FIN is received ACK the FIN and let the user know
				* that the connection is closing.
				*/
				if (thflags & TH_FIN) {
				if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
				socantrcvmore(so);
				/*
				* If connection is half-synchronized
				* (ie NEEDSYN flag on) then delay ACK,
				* so it may be piggybacked when SYN is sent.
				* Otherwise, since we received a FIN then no
				* more input can be expected, send ACK now.
				*/
				if (tp->t_flags & TF_NEEDSYN)
				tp->t_flags \|= TF_DELACK;
				else
				tp->t_flags \|= TF_ACKNOW;
				tp->rcv_nxt++;
				}
				switch (tp->t_state) {

				/*
				* In SYN_RECEIVED and ESTABLISHED STATES
				* enter the CLOSE_WAIT state.
				*/
				case TCPS_SYN_RECEIVED:
				tp->t_starttime = ticks;
				/* FALLTHROUGH */
				case TCPS_ESTABLISHED:
				tcp_state_change(tp, 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:
				tcp_state_change(tp, 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:
				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
				KASSERT(ti_locked == TI_RLOCKED, ("%s: dodata "
				"TCP_FIN_WAIT_2 ti_locked: %d", __func__,
				ti_locked));

				tcp_twstart(tp);
				INP_INFO_RUNLOCK(&V_tcbinfo);
				return;
				}
				}
				if (ti_locked == TI_RLOCKED) {
				INP_INFO_RUNLOCK(&V_tcbinfo);
				}
				ti_locked = TI_UNLOCKED;

				#ifdef TCPDEBUG
				if (so->so_options & SO_DEBUG)
				tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
				&tcp_savetcp, 0);
				#endif
				TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));

				/*
				* Return any desired output.
				*/
				if (needoutput \|\| (tp->t_flags & TF_ACKNOW))
				(void) tp->t_fb->tcp_output(tp);

				KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
				__func__, ti_locked));
				INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
				INP_WLOCK_ASSERT(tp->t_inpcb);

				if (tp->t_flags & TF_DELACK) {
				tp->t_flags &= ~TF_DELACK;
				tp->t_fb->tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
				}
				INP_WUNLOCK(tp->t_inpcb);
				return;

				dropafterack:
				/*
				* Generate an ACK dropping incoming segment if it occupies
				* sequence space, where the ACK reflects our state.
				*
				* We can now skip the test for the RST flag since all
				* paths to this code happen after packets containing
				* RST have been dropped.
				*
				* In the SYN-RECEIVED state, don't send an ACK unless the
				* segment we received passes the SYN-RECEIVED ACK test.
				* If it fails send a RST. This breaks the loop in the
				* "LAND" DoS attack, and also prevents an ACK storm
				* between two listening ports that have been sent forged
				* SYN segments, each with the source address of the other.
				*/
				if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
				(SEQ_GT(tp->snd_una, th->th_ack) \|\|
				SEQ_GT(th->th_ack, tp->snd_max)) ) {
				rstreason = BANDLIM_RST_OPENPORT;
				goto dropwithreset;
				}
				#ifdef TCPDEBUG
				if (so->so_options & SO_DEBUG)
				tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
				&tcp_savetcp, 0);
				#endif
				TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));
				if (ti_locked == TI_RLOCKED) {
				INP_INFO_RUNLOCK(&V_tcbinfo);
				}
				ti_locked = TI_UNLOCKED;

				tp->t_flags \|= TF_ACKNOW;
				(void) tp->t_fb->tcp_output(tp);
				INP_WUNLOCK(tp->t_inpcb);
				m_freem(m);
				return;

				dropwithreset:
				if (ti_locked == TI_RLOCKED) {
				INP_INFO_RUNLOCK(&V_tcbinfo);
				}
				ti_locked = TI_UNLOCKED;

				if (tp != NULL) {
				tcp_dropwithreset(m, th, tp, tlen, rstreason);
				INP_WUNLOCK(tp->t_inpcb);
				} else
				tcp_dropwithreset(m, th, NULL, tlen, rstreason);
				return;

				drop:
				if (ti_locked == TI_RLOCKED) {
				INP_INFO_RUNLOCK(&V_tcbinfo);
				ti_locked = TI_UNLOCKED;
				}
				#ifdef INVARIANTS
				else
				INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
				#endif

				/*
				* Drop space held by incoming segment and return.
				*/
				#ifdef TCPDEBUG
				if (tp == NULL \|\| (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
				tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
				&tcp_savetcp, 0);
				#endif
				TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));
				if (tp != NULL)
				INP_WUNLOCK(tp->t_inpcb);
				m_freem(m);
				}

				void
				tcp_do_segment_fastslow(struct mbuf m, struct tcphdr th, struct socket *so,
				struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
				int ti_locked)
				{
				int thflags;
				u_long tiwin;
				char *s;
				int can_enter;
				struct in_conninfo *inc;
				struct tcpopt to;

				#ifdef TCPDEBUG
				/*
				* The size of tcp_saveipgen must be the size of the max ip header,
				* now IPv6.
				*/
				u_char tcp_saveipgen[IP6_HDR_LEN];
				struct tcphdr tcp_savetcp;
				short ostate = 0;
				#endif
				thflags = th->th_flags;
				tp->sackhint.last_sack_ack = 0;
				inc = &tp->t_inpcb->inp_inc;
				/*
				* If this is either a state-changing packet or current state isn't
				* established, we require a write lock on tcbinfo. Otherwise, we
				* allow the tcbinfo to be in either alocked or unlocked, as the
				* caller may have unnecessarily acquired a write lock due to a race.
				*/
				if ((thflags & (TH_SYN \| TH_FIN \| TH_RST)) != 0 \|\|
				tp->t_state != TCPS_ESTABLISHED) {
				KASSERT(ti_locked == TI_RLOCKED, ("%s ti_locked %d for "
				"SYN/FIN/RST/!EST", __func__, ti_locked));
				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
				} else {
				#ifdef INVARIANTS
				if (ti_locked == TI_RLOCKED) {
				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
				} else {
				KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
				"ti_locked: %d", __func__, ti_locked));
				INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
				}
				#endif
				}
				INP_WLOCK_ASSERT(tp->t_inpcb);
				KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
				__func__));
				KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
				__func__));

				/*
				* Segment received on connection.
				* Reset idle time and keep-alive timer.
				* XXX: This should be done after segment
				* validation to ignore broken/spoofed segs.
				*/
				tp->t_rcvtime = ticks;
				if (TCPS_HAVEESTABLISHED(tp->t_state))
				tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));

				/*
				* Unscale the window into a 32-bit value.
				* For the SYN_SENT state the scale is zero.
				*/
				tiwin = th->th_win << tp->snd_scale;

				/*
				* TCP ECN processing.
				*/
				if (tp->t_flags & TF_ECN_PERMIT) {
				if (thflags & TH_CWR)
				tp->t_flags &= ~TF_ECN_SND_ECE;
				switch (iptos & IPTOS_ECN_MASK) {
				case IPTOS_ECN_CE:
				tp->t_flags \|= TF_ECN_SND_ECE;
				TCPSTAT_INC(tcps_ecn_ce);
				break;
				case IPTOS_ECN_ECT0:
				TCPSTAT_INC(tcps_ecn_ect0);
				break;
				case IPTOS_ECN_ECT1:
				TCPSTAT_INC(tcps_ecn_ect1);
				break;
				}
				/* Congestion experienced. */
				if (thflags & TH_ECE) {
				cc_cong_signal(tp, th, CC_ECN);
				}
				}

				/*
				* Parse options on any incoming segment.
				*/
				tcp_dooptions(&to, (u_char *)(th + 1),
				(th->th_off << 2) - sizeof(struct tcphdr),
				(thflags & TH_SYN) ? TO_SYN : 0);

				/*
				* If echoed timestamp is later than the current time,
				* fall back to non RFC1323 RTT calculation. Normalize
				* timestamp if syncookies were used when this connection
				* was established.
				*/
				if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
				to.to_tsecr -= tp->ts_offset;
				if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
				to.to_tsecr = 0;
				}
				/*
				* If timestamps were negotiated during SYN/ACK they should
				* appear on every segment during this session and vice versa.
				*/
				if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
				if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
				log(LOG_DEBUG, "%s; %s: Timestamp missing, "
				"no action\n", s, __func__);
				free(s, M_TCPLOG);
				}
				}
				if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
				if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
				log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
				"no action\n", s, __func__);
				free(s, M_TCPLOG);
				}
				}

				/*
				* Process options only when we get SYN/ACK back. The SYN case
				* for incoming connections is handled in tcp_syncache.
				* According to RFC1323 the window field in a SYN (i.e., a <SYN>
				* or <SYN,ACK>) segment itself is never scaled.
				* XXX this is traditional behavior, may need to be cleaned up.
				*/
				if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
				if ((to.to_flags & TOF_SCALE) &&
				(tp->t_flags & TF_REQ_SCALE)) {
				tp->t_flags \|= TF_RCVD_SCALE;
				tp->snd_scale = to.to_wscale;
				}
				/*
				* Initial send window. It will be updated with
				* the next incoming segment to the scaled value.
				*/
				tp->snd_wnd = th->th_win;
				if (to.to_flags & TOF_TS) {
				tp->t_flags \|= TF_RCVD_TSTMP;
				tp->ts_recent = to.to_tsval;
				tp->ts_recent_age = tcp_ts_getticks();
				}
				if (to.to_flags & TOF_MSS)
				tcp_mss(tp, to.to_mss);
				if ((tp->t_flags & TF_SACK_PERMIT) &&
				(to.to_flags & TOF_SACKPERM) == 0)
				tp->t_flags &= ~TF_SACK_PERMIT;
				}
				can_enter = 0;
				if (__predict_true((tlen == 0))) {
				/*
				* The ack moved forward and we have a window (non-zero)
				* <or>
				* The ack did not move forward, but the window increased.
				*/
				if (__predict_true((SEQ_GT(th->th_ack, tp->snd_una) && tiwin) \|\|
				((th->th_ack == tp->snd_una) && tiwin && (tiwin > tp->snd_wnd)))) {
				can_enter = 1;
				}
				} else {
				/*
				* Data incoming, use the old entry criteria
				* for fast-path with data.
				*/
				if ((tiwin && tiwin == tp->snd_wnd)) {
				can_enter = 1;
				}
				}
				/*
				* 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.
				* Make sure that the hidden state-flags are also off.
				* Since we check for TCPS_ESTABLISHED first, it can only
				* be TH_NEEDSYN.
				*/
				if (__predict_true(tp->t_state == TCPS_ESTABLISHED &&
				th->th_seq == tp->rcv_nxt &&
				(thflags & (TH_SYN\|TH_FIN\|TH_RST\|TH_URG\|TH_ACK)) == TH_ACK &&
				tp->snd_nxt == tp->snd_max &&
				can_enter &&
				((tp->t_flags & (TF_NEEDSYN\|TF_NEEDFIN)) == 0) &&
				LIST_EMPTY(&tp->t_segq) &&
				((to.to_flags & TOF_TS) == 0 \|\|
				TSTMP_GEQ(to.to_tsval, tp->ts_recent)))) {
				if (__predict_true((tlen == 0) &&
				(SEQ_LEQ(th->th_ack, tp->snd_max) &&
				!IN_RECOVERY(tp->t_flags) &&
				(to.to_flags & TOF_SACK) == 0 &&
				TAILQ_EMPTY(&tp->snd_holes)))) {
				/* We are done */
				tcp_do_fastack(m, th, so, tp, &to, drop_hdrlen, tlen,
				ti_locked, tiwin);
				return;
				} else if ((tlen) &&
				(th->th_ack == tp->snd_una &&
				tlen <= sbspace(&so->so_rcv))) {
				tcp_do_fastnewdata(m, th, so, tp, &to, drop_hdrlen, tlen,
				ti_locked, tiwin);
				/* We are done */
				return;
				}
				}
				tcp_do_slowpath(m, th, so, tp, &to, drop_hdrlen, tlen,
				ti_locked, tiwin, thflags);
				}

				static int
				tcp_fastack(struct mbuf m, struct tcphdr th, struct socket *so,
				struct tcpcb tp, struct tcpopt to, int drop_hdrlen, int tlen,
				int ti_locked, u_long tiwin)
				{
				int acked;
				int winup_only=0;

				if (__predict_false(SEQ_LEQ(th->th_ack, tp->snd_una))) {
				/* Old ack, behind (or duplicate to) the last one rcv'd */
				return (0);
				}
				if (__predict_false(th->th_ack == tp->snd_una) &&
				__predict_false(tiwin <= tp->snd_wnd)) {
				/* duplicate ack <or> a shrinking dup ack with shrinking window */
				return (0);
				}
				if (__predict_false(tiwin == 0)) {
				/* zero window */
				return (0);
				}
				if (__predict_false(SEQ_GT(th->th_ack, tp->snd_max))) {
				/* Above what we have sent? */
				return (0);
				}
				if (__predict_false(tp->snd_nxt != tp->snd_max)) {
				/* We are retransmitting */
				return (0);
				}
				if (__predict_false(tp->t_flags & (TF_NEEDSYN\|TF_NEEDFIN))) {
				/* We need a SYN or a FIN, unlikely.. */
				return (0);
				}
				if((to->to_flags & TOF_TS) && __predict_false(TSTMP_LT(to->to_tsval, tp->ts_recent))) {
				/* Timestamp is behind .. old ack with seq wrap? */
				return (0);
				}
				if (__predict_false(IN_RECOVERY(tp->t_flags))) {
				/* Still recovering */
				return (0);
				}
				if (__predict_false(to->to_flags & TOF_SACK)) {
				/* Sack included in the ack.. */
				return (0);
				}
				if (!TAILQ_EMPTY(&tp->snd_holes)) {
				/* We have sack holes on our scoreboard */
				return (0);
				}
				/* Ok if we reach here, we can process a fast-ack */

				/* Did the window get updated? */
				if (tiwin != tp->snd_wnd) {
				/* keep track of pure window updates */
				if (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd) {
				winup_only = 1;
				TCPSTAT_INC(tcps_rcvwinupd);
				}
				tp->snd_wnd = tiwin;
				tp->snd_wl1 = th->th_seq;
				if (tp->snd_wnd > tp->max_sndwnd)
				tp->max_sndwnd = tp->snd_wnd;
				}
				/*
				* Pull snd_wl2 up to prevent seq wrap relative
				* to th_ack.
				*/
				tp->snd_wl2 = th->th_ack;
				/*
				* If last ACK falls within this segment's sequence numbers,
				* record the timestamp.
				* NOTE that the test is modified according to the latest
				* proposal of the tcplw@cray.com list (Braden 1993/04/26).
				*/
				if ((to->to_flags & TOF_TS) != 0 &&
				SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
				tp->ts_recent_age = tcp_ts_getticks();
				tp->ts_recent = to->to_tsval;
				}
				/*
				* This is a pure ack for outstanding data.
				*/
				if (ti_locked == TI_RLOCKED) {
				INP_INFO_RUNLOCK(&V_tcbinfo);
				}
				ti_locked = TI_UNLOCKED;

				TCPSTAT_INC(tcps_predack);

				/*
				* "bad retransmit" recovery.
				*/
				if (tp->t_rxtshift == 1 &&
				tp->t_flags & TF_PREVVALID &&
				(int)(ticks - tp->t_badrxtwin) < 0) {
				cc_cong_signal(tp, th, CC_RTO_ERR);
				}

				/*
				* Recalculate the transmit timer / rtt.
				*
				* Some boxes send broken timestamp replies
				* during the SYN+ACK phase, ignore
				* timestamps of 0 or we could calculate a
				* huge RTT and blow up the retransmit timer.
				*/
				if ((to->to_flags & TOF_TS) != 0 &&
				to->to_tsecr) {
				u_int t;

				t = tcp_ts_getticks() - to->to_tsecr;
				if (!tp->t_rttlow \|\| tp->t_rttlow > t)
				tp->t_rttlow = t;
				tcp_xmit_timer(tp,
				TCP_TS_TO_TICKS(t) + 1);
				} else if (tp->t_rtttime &&
				SEQ_GT(th->th_ack, tp->t_rtseq)) {
				if (!tp->t_rttlow \|\|
				tp->t_rttlow > ticks - tp->t_rtttime)
				tp->t_rttlow = ticks - tp->t_rtttime;
				tcp_xmit_timer(tp,
				ticks - tp->t_rtttime);
				}
				if (winup_only == 0) {
				acked = BYTES_THIS_ACK(tp, th);

				/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
				hhook_run_tcp_est_in(tp, th, to);

				TCPSTAT_ADD(tcps_rcvackbyte, acked);
				sbdrop(&so->so_snd, acked);
				if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
				SEQ_LEQ(th->th_ack, tp->snd_recover))
				tp->snd_recover = th->th_ack - 1;

				/*
				* Let the congestion control algorithm update
				* congestion control related information. This
				* typically means increasing the congestion
				* window.
				*/
				cc_ack_received(tp, th, CC_ACK);

				tp->snd_una = th->th_ack;
				tp->t_dupacks = 0;
				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.
				*/
				#ifdef TCPDEBUG
				if (so->so_options & SO_DEBUG)
				tcp_trace(TA_INPUT, ostate, tp,
				(void *)tcp_saveipgen,
				&tcp_savetcp, 0);
				#endif
				if (tp->snd_una == tp->snd_max)
				tcp_timer_activate(tp, TT_REXMT, 0);
				else if (!tcp_timer_active(tp, TT_PERSIST))
				tcp_timer_activate(tp, TT_REXMT,
				tp->t_rxtcur);
				/* Wake up the socket if we have room to write more */
				sowwakeup(so);
				} else {
				/*
				* Window update only, just free the mbufs and
				* send out whatever we can.
				*/
				m_freem(m);
				}
				if (sbavail(&so->so_snd))
				(void) tcp_output(tp);
				KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
				__func__, ti_locked));
				INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
				INP_WLOCK_ASSERT(tp->t_inpcb);

				if (tp->t_flags & TF_DELACK) {
				tp->t_flags &= ~TF_DELACK;
				tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
				}
				INP_WUNLOCK(tp->t_inpcb);
				return (1);
				}

				void
				tcp_do_segment_fastack(struct mbuf m, struct tcphdr th, struct socket *so,
				struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
				int ti_locked)
				{
				int thflags;
				u_long tiwin;
				char *s;
				struct in_conninfo *inc;
				struct tcpopt to;

				#ifdef TCPDEBUG
				/*
				* The size of tcp_saveipgen must be the size of the max ip header,
				* now IPv6.
				*/
				u_char tcp_saveipgen[IP6_HDR_LEN];
				struct tcphdr tcp_savetcp;
				short ostate = 0;
				#endif
				thflags = th->th_flags;
				tp->sackhint.last_sack_ack = 0;
				inc = &tp->t_inpcb->inp_inc;
				/*
				* If this is either a state-changing packet or current state isn't
				* established, we require a write lock on tcbinfo. Otherwise, we
				* allow the tcbinfo to be in either alocked or unlocked, as the
				* caller may have unnecessarily acquired a write lock due to a race.
				*/
				if ((thflags & (TH_SYN \| TH_FIN \| TH_RST)) != 0 \|\|
				tp->t_state != TCPS_ESTABLISHED) {
				KASSERT(ti_locked == TI_RLOCKED, ("%s ti_locked %d for "
				"SYN/FIN/RST/!EST", __func__, ti_locked));
				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
				} else {
				#ifdef INVARIANTS
				if (ti_locked == TI_RLOCKED) {
				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
				} else {
				KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
				"ti_locked: %d", __func__, ti_locked));
				INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
				}
				#endif
				}
				INP_WLOCK_ASSERT(tp->t_inpcb);
				KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
				__func__));
				KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
				__func__));

				/*
				* Segment received on connection.
				* Reset idle time and keep-alive timer.
				* XXX: This should be done after segment
				* validation to ignore broken/spoofed segs.
				*/
				tp->t_rcvtime = ticks;
				if (TCPS_HAVEESTABLISHED(tp->t_state))
				tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));

				/*
				* Unscale the window into a 32-bit value.
				* For the SYN_SENT state the scale is zero.
				*/
				tiwin = th->th_win << tp->snd_scale;

				/*
				* TCP ECN processing.
				*/
				if (tp->t_flags & TF_ECN_PERMIT) {
				if (thflags & TH_CWR)
				tp->t_flags &= ~TF_ECN_SND_ECE;
				switch (iptos & IPTOS_ECN_MASK) {
				case IPTOS_ECN_CE:
				tp->t_flags \|= TF_ECN_SND_ECE;
				TCPSTAT_INC(tcps_ecn_ce);
				break;
				case IPTOS_ECN_ECT0:
				TCPSTAT_INC(tcps_ecn_ect0);
				break;
				case IPTOS_ECN_ECT1:
				TCPSTAT_INC(tcps_ecn_ect1);
				break;
				}
				/* Congestion experienced. */
				if (thflags & TH_ECE) {
				cc_cong_signal(tp, th, CC_ECN);
				}
				}

				/*
				* Parse options on any incoming segment.
				*/
				tcp_dooptions(&to, (u_char *)(th + 1),
				(th->th_off << 2) - sizeof(struct tcphdr),
				(thflags & TH_SYN) ? TO_SYN : 0);

				/*
				* If echoed timestamp is later than the current time,
				* fall back to non RFC1323 RTT calculation. Normalize
				* timestamp if syncookies were used when this connection
				* was established.
				*/
				if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
				to.to_tsecr -= tp->ts_offset;
				if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
				to.to_tsecr = 0;
				}
				/*
				* If timestamps were negotiated during SYN/ACK they should
				* appear on every segment during this session and vice versa.
				*/
				if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
				if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
				log(LOG_DEBUG, "%s; %s: Timestamp missing, "
				"no action\n", s, __func__);
				free(s, M_TCPLOG);
				}
				}
				if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
				if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
				log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
				"no action\n", s, __func__);
				free(s, M_TCPLOG);
				}
				}

				/*
				* Process options only when we get SYN/ACK back. The SYN case
				* for incoming connections is handled in tcp_syncache.
				* According to RFC1323 the window field in a SYN (i.e., a <SYN>
				* or <SYN,ACK>) segment itself is never scaled.
				* XXX this is traditional behavior, may need to be cleaned up.
				*/
				if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
				if ((to.to_flags & TOF_SCALE) &&
				(tp->t_flags & TF_REQ_SCALE)) {
				tp->t_flags \|= TF_RCVD_SCALE;
				tp->snd_scale = to.to_wscale;
				}
				/*
				* Initial send window. It will be updated with
				* the next incoming segment to the scaled value.
				*/
				tp->snd_wnd = th->th_win;
				if (to.to_flags & TOF_TS) {
				tp->t_flags \|= TF_RCVD_TSTMP;
				tp->ts_recent = to.to_tsval;
				tp->ts_recent_age = tcp_ts_getticks();
				}
				if (to.to_flags & TOF_MSS)
				tcp_mss(tp, to.to_mss);
				if ((tp->t_flags & TF_SACK_PERMIT) &&
				(to.to_flags & TOF_SACKPERM) == 0)
				tp->t_flags &= ~TF_SACK_PERMIT;
				}
				/*
				* 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.
				* Make sure that the hidden state-flags are also off.
				* Since we check for TCPS_ESTABLISHED first, it can only
				* be TH_NEEDSYN.
				*/
				if (__predict_true(tp->t_state == TCPS_ESTABLISHED) &&
				__predict_true(((to.to_flags & TOF_SACK) == 0)) &&
				__predict_true(tlen == 0) &&
				__predict_true((thflags & (TH_SYN\|TH_FIN\|TH_RST\|TH_URG\|TH_ACK)) == TH_ACK) &&
				__predict_true(LIST_EMPTY(&tp->t_segq)) &&
				__predict_true(th->th_seq == tp->rcv_nxt)) {
				if (tcp_fastack(m, th, so, tp, &to, drop_hdrlen, tlen,
				ti_locked, tiwin)) {
				return;
				}
				}
				tcp_do_slowpath(m, th, so, tp, &to, drop_hdrlen, tlen,
				ti_locked, tiwin, thflags);
				}

				struct tcp_function_block __tcp_fastslow = {
				"fastslow",
				tcp_timer_activate,
				tcp_timer_active,
				tcp_timer_stop,
				tcp_output,
				tcp_do_segment_fastslow,
				tcp_default_ctloutput,
				NULL,
				NULL,
				0

				};

				struct tcp_function_block __tcp_fastack = {
				"fastack",
				tcp_timer_activate,
				tcp_timer_active,
				tcp_timer_stop,
				tcp_output,
				tcp_do_segment_fastack,
				tcp_default_ctloutput,
				NULL,
				NULL,
				0

				};

				static int
				tcp_addfastpaths(module_t mod, int type, void *data)
				{
				int err=0;

				switch (type) {
				case MOD_LOAD:
				err = register_tcp_functions(&__tcp_fastack, M_WAITOK);
				if (err) {
				printf("Failed to register fastack module -- err:%d\n", err);
				return(err);
				}
				err = register_tcp_functions(&__tcp_fastslow, M_WAITOK);
				if (err) {
				printf("Failed to register fastslow module -- err:%d\n", err);
				deregister_tcp_functions(&__tcp_fastack);
				return(err);
				}
				break;
				case MOD_QUIESCE:
				if ((__tcp_fastslow.refcnt) \|\|( __tcp_fastack.refcnt)) {
				return(EBUSY);
				}
				break;
				case MOD_UNLOAD:
				err = deregister_tcp_functions(&__tcp_fastack);
				if (err == EBUSY)
				break;
				err = deregister_tcp_functions(&__tcp_fastslow);
				if (err == EBUSY)
				break;
				err = 0;
				break;
				default:
				return (EOPNOTSUPP);
				}
				return (err);
				}

				static moduledata_t new_tcp_fastpaths = {
				.name = "tcp_fastpaths",
				.evhand = tcp_addfastpaths,
				.priv = 0
				};

				MODULE_VERSION(kern_tcpfastpaths, 1);
				DECLARE_MODULE(kern_tcpfastpaths, new_tcp_fastpaths, SI_SUB_PSEUDO, SI_ORDER_ANY);