Remove the TCP_FACK option and associated #if{,n}def code.

TCP_FACK was disabled by provos@ in June 1999.
TCP_FACK is an algorithm that decides that when something is lost, all
not SACKed packets until the most forward SACK are lost. It may be a
correct estimate, if network does not reorder packets.

OK visa@ mpi@ mikeb@

8 files changed, 10 insertions, 186 deletions

diff --git a/share/man/man4/options.4 b/share/man/man4/options.4
index c28d4e27896..159d956840f 100644
--- a/share/man/man4/options.4
+++ b/share/man/man4/options.4
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: options.4,v 1.253 2017/10/23 03:13:58 jsg Exp $
+.\"	$OpenBSD: options.4,v 1.254 2017/10/25 12:38:21 job Exp $
 .\"	$NetBSD: options.4,v 1.21 1997/06/25 03:13:00 thorpej Exp $
 .\"
 .\" Copyright (c) 1998 Theo de Raadt
@@ -34,7 +34,7 @@
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
 .\"
-.Dd $Mdocdate: October 23 2017 $
+.Dd $Mdocdate: October 25 2017 $
 .Dt OPTIONS 4
 .Os
 .Sh NAME
@@ -445,11 +445,6 @@ TCP to adjust the transmission rate using this signal.
 Both communication endpoints negotiate enabling
 .Em ECN
 functionality at the TCP connection establishment.
-.It Cd option TCP_FACK
-Turns on forward acknowledgements allowing a more precise estimate of
-outstanding data during the fast recovery phase by using
-.Em SACK
-information.
 .It Cd option TCP_SIGNATURE
 Turns on support for the TCP MD5 Signature option (RFC 2385).
 This is used by
diff --git a/sys/conf/GENERIC b/sys/conf/GENERIC
index 6df800175ed..ff356c01069 100644
--- a/sys/conf/GENERIC
+++ b/sys/conf/GENERIC
@@ -1,4 +1,4 @@
-#	$OpenBSD: GENERIC,v 1.249 2017/10/22 14:11:34 mikeb Exp $
+#	$OpenBSD: GENERIC,v 1.250 2017/10/25 12:38:21 job Exp $
 #
 #	Machine-independent option; used by all architectures for their
 #	GENERIC kernel
@@ -47,7 +47,6 @@ option		FUSE		# FUSE
 option		SOCKET_SPLICE	# Socket Splicing for TCP and UDP
 option		TCP_ECN		# Explicit Congestion Notification for TCP
 option		TCP_SIGNATURE	# TCP MD5 Signatures, for BGP routing sessions
-#option		TCP_FACK	# Forward Acknowledgements for TCP
 
 option		INET6		# IPv6
 option		IPSEC		# IPsec
diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index da128f598ab..323626de9c3 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tcp_input.c,v 1.349 2017/10/24 14:49:29 mikeb Exp $	*/
+/*	$OpenBSD: tcp_input.c,v 1.350 2017/10/25 12:38:21 job Exp $	*/
 /*	$NetBSD: tcp_input.c,v 1.23 1996/02/13 23:43:44 christos Exp $	*/
 
 /*
@@ -974,10 +974,6 @@ findpcb:
 				if (SEQ_GT(tp->snd_una, tp->snd_last))
 #endif
 				tp->snd_last = tp->snd_una;
-#ifdef TCP_FACK
-				tp->snd_fack = tp->snd_una;
-				tp->retran_data = 0;
-#endif
 				m_freem(m);
 
 				/*
@@ -1566,18 +1562,7 @@ trimthenstep6:
 				 */
 				if (TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0)
 					tp->t_dupacks = 0;
-#ifdef TCP_FACK
-				/*
-				 * In FACK, can enter fast rec. if the receiver
-				 * reports a reass. queue longer than 3 segs.
-				 */
-				else if (++tp->t_dupacks == tcprexmtthresh ||
-				    ((SEQ_GT(tp->snd_fack, tcprexmtthresh *
-				    tp->t_maxseg + tp->snd_una)) &&
-				    SEQ_GT(tp->snd_una, tp->snd_last))) {
-#else
 				else if (++tp->t_dupacks == tcprexmtthresh) {
-#endif /* TCP_FACK */
 					tcp_seq onxt = tp->snd_nxt;
 					u_long win =
 					    ulmin(tp->snd_wnd, tp->snd_cwnd) /
@@ -1603,15 +1588,6 @@ trimthenstep6:
 #endif
 						tcpstat_inc(tcps_cwr_frecovery);
 						tcpstat_inc(tcps_sack_recovery_episode);
-#ifdef TCP_FACK
-						tp->t_dupacks = tcprexmtthresh;
-						(void) tcp_output(tp);
-						/*
-						 * During FR, snd_cwnd is held
-						 * constant for FACK.
-						 */
-						tp->snd_cwnd = tp->snd_ssthresh;
-#else
 						/*
 						 * tcp_output() will send
 						 * oldest SACK-eligible rtx.
@@ -1619,7 +1595,6 @@ trimthenstep6:
 						(void) tcp_output(tp);
 						tp->snd_cwnd = tp->snd_ssthresh+
 					           tp->t_maxseg * tp->t_dupacks;
-#endif /* TCP_FACK */
 						goto drop;
 					}
 					TCP_TIMER_DISARM(tp, TCPT_REXMT);
@@ -1639,17 +1614,6 @@ trimthenstep6:
 						tp->snd_nxt = onxt;
 					goto drop;
 				} else if (tp->t_dupacks > tcprexmtthresh) {
-#ifdef TCP_FACK
-					/*
-					 * while (awnd < cwnd)
-					 *         sendsomething();
-					 */
-					if (tp->sack_enable) {
-						if (tp->snd_awnd < tp->snd_cwnd)
-							tcp_output(tp);
-						goto drop;
-					}
-#endif /* TCP_FACK */
 					tp->snd_cwnd += tp->t_maxseg;
 					(void) tcp_output(tp);
 					goto drop;
@@ -1685,11 +1649,6 @@ trimthenstep6:
 					    tcp_seq_subtract(tp->snd_max,
 					    th->th_ack);
 				tp->t_dupacks = 0;
-#ifdef TCP_FACK
-				if (tp->sack_enable &&
-				    SEQ_GT(th->th_ack, tp->snd_fack))
-					tp->snd_fack = th->th_ack;
-#endif
 			}
 		} else {
 			/*
@@ -1789,16 +1748,6 @@ trimthenstep6:
 #endif
 		if (SEQ_LT(tp->snd_nxt, tp->snd_una))
 			tp->snd_nxt = tp->snd_una;
-#ifdef TCP_FACK
-		if (SEQ_GT(tp->snd_una, tp->snd_fack)) {
-			tp->snd_fack = tp->snd_una;
-			/* Update snd_awnd for partial ACK
-			 * without any SACK blocks.
-			 */
-			tp->snd_awnd = tcp_seq_subtract(tp->snd_nxt,
-				tp->snd_fack) + tp->retran_data;
-		}
-#endif
 
 		switch (tp->t_state) {
 
@@ -2467,11 +2416,6 @@ tcp_sack_option(struct tcpcb *tp, struct tcphdr *th, u_char *cp, int optlen)
 			continue; /* bad SACK fields */
 		if (SEQ_LEQ(sack.end, tp->snd_una))
 			continue; /* old block */
-#ifdef TCP_FACK
-		/* Updates snd_fack.  */
-		if (SEQ_GT(sack.end, tp->snd_fack))
-			tp->snd_fack = sack.end;
-#endif
 		if (SEQ_GT(th->th_ack, tp->snd_una)) {
 			if (SEQ_LT(sack.start, th->th_ack))
 				continue;
@@ -2520,16 +2464,6 @@ tcp_sack_option(struct tcpcb *tp, struct tcphdr *th, u_char *cp, int optlen)
 			}
 			if (SEQ_LEQ(sack.start, cur->start)) {
 				/* Data acks at least the beginning of hole */
-#ifdef TCP_FACK
-				if (SEQ_GT(sack.end, cur->rxmit))
-					tp->retran_data -=
-					    tcp_seq_subtract(cur->rxmit,
-					    cur->start);
-				else
-					tp->retran_data -=
-					    tcp_seq_subtract(sack.end,
-					    cur->start);
-#endif
 				if (SEQ_GEQ(sack.end, cur->end)) {
 					/* Acks entire hole, so delete hole */
 					if (p != cur) {
@@ -2554,12 +2488,6 @@ tcp_sack_option(struct tcpcb *tp, struct tcphdr *th, u_char *cp, int optlen)
 			}
 			/* move end of hole backward */
 			if (SEQ_GEQ(sack.end, cur->end)) {
-#ifdef TCP_FACK
-				if (SEQ_GT(cur->rxmit, sack.start))
-					tp->retran_data -=
-					    tcp_seq_subtract(cur->rxmit,
-					    sack.start);
-#endif
 				cur->end = sack.start;
 				cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
 				cur->dups++;
@@ -2580,16 +2508,6 @@ tcp_sack_option(struct tcpcb *tp, struct tcphdr *th, u_char *cp, int optlen)
 				    pool_get(&sackhl_pool, PR_NOWAIT);
 				if (temp == NULL)
 					goto done; /* ENOBUFS */
-#ifdef TCP_FACK
-				if (SEQ_GT(cur->rxmit, sack.end))
-					tp->retran_data -=
-					    tcp_seq_subtract(sack.end,
-					    sack.start);
-				else if (SEQ_GT(cur->rxmit, sack.start))
-					tp->retran_data -=
-					    tcp_seq_subtract(cur->rxmit,
-					    sack.start);
-#endif
 				temp->next = cur->next;
 				temp->start = sack.end;
 				temp->end = cur->end;
@@ -2631,21 +2549,6 @@ tcp_sack_option(struct tcpcb *tp, struct tcphdr *th, u_char *cp, int optlen)
 		}
 	}
 done:
-#ifdef TCP_FACK
-	/*
-	 * Update retran_data and snd_awnd.  Go through the list of
-	 * holes.   Increment retran_data by (hole->rxmit - hole->start).
-	 */
-	tp->retran_data = 0;
-	cur = tp->snd_holes;
-	while (cur) {
-		tp->retran_data += cur->rxmit - cur->start;
-		cur = cur->next;
-	}
-	tp->snd_awnd = tcp_seq_subtract(tp->snd_nxt, tp->snd_fack) +
-	    tp->retran_data;
-#endif
-
 	return;
 }
 
@@ -2705,11 +2608,9 @@ 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;
-#ifndef TCP_FACK
 	/*
 	 * Partial window deflation.  This statement relies on the
-	 * fact that tp->snd_una has not been updated yet.  In FACK
-	 * hold snd_cwnd constant during fast recovery.
+	 * 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;
@@ -2718,11 +2619,6 @@ tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
 		tp->snd_cwnd = tp->t_maxseg;
 	tp->snd_cwnd += tp->t_maxseg;
 	tp->t_flags |= TF_NEEDOUTPUT;
-#else
-	/* Force call to tcp_output */
-	if (tp->snd_awnd < tp->snd_cwnd)
-		tp->t_flags |= TF_NEEDOUTPUT;
-#endif
 }
 
 /*
@@ -3703,11 +3599,6 @@ syn_cache_get(struct sockaddr *src, struct sockaddr *dst, struct tcphdr *th,
 	tp->irs = sc->sc_irs;
 	tcp_sendseqinit(tp);
 	tp->snd_last = tp->snd_una;
-#ifdef TCP_FACK
-	tp->snd_fack = tp->snd_una;
-	tp->retran_data = 0;
-	tp->snd_awnd = 0;
-#endif
 #ifdef TCP_ECN
 	if (sc->sc_flags & SCF_ECN_PERMIT) {
 		tp->t_flags |= TF_ECN_PERMIT;
diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
index a0a88b5ec3d..2e34e0ef949 100644
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tcp_output.c,v 1.122 2017/10/22 14:11:34 mikeb Exp $	*/
+/*	$OpenBSD: tcp_output.c,v 1.123 2017/10/25 12:38:21 job Exp $	*/
 /*	$NetBSD: tcp_output.c,v 1.16 1997/06/03 16:17:09 kml Exp $	*/
 
 /*
@@ -130,17 +130,7 @@ tcp_sack_output(struct tcpcb *tp)
 		return (NULL);
 	p = tp->snd_holes;
 	while (p) {
-#ifndef TCP_FACK
 		if (p->dups >= tcprexmtthresh && SEQ_LT(p->rxmit, p->end)) {
-#else
-		/* In FACK, if p->dups is less than tcprexmtthresh, but
-		 * snd_fack advances more than tcprextmtthresh * tp->t_maxseg,
-		 * tcp_input() will try fast retransmit. This forces output.
-		 */
-		if ((p->dups >= tcprexmtthresh ||
-		     tp->t_dupacks == tcprexmtthresh) &&
-		    SEQ_LT(p->rxmit, p->end)) {
-#endif /* TCP_FACK */
 			if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
 				p = p->next;
 				continue;
@@ -258,15 +248,6 @@ again:
 	if (tp->sack_enable && SEQ_LT(tp->snd_nxt, tp->snd_max))
 		tcp_sack_adjust(tp);
 	off = tp->snd_nxt - tp->snd_una;
-#ifdef TCP_FACK
-	/* Normally, sendable data is limited by off < tp->snd_cwnd.
-	 * But in FACK, sendable data is limited by snd_awnd < snd_cwnd,
-	 * regardless of offset.
-	 */
-	if (tp->sack_enable && (tp->t_dupacks > tcprexmtthresh))
-		win = tp->snd_wnd;
-	else
-#endif
 	win = ulmin(tp->snd_wnd, tp->snd_cwnd);
 
 	flags = tcp_outflags[tp->t_state];
@@ -285,11 +266,8 @@ again:
 			sack_rxmit = 1;
 			/* Coalesce holes into a single retransmission */
 			len = min(tp->t_maxseg, p->end - p->rxmit);
-#ifndef TCP_FACK
-			/* in FACK, hold snd_cwnd constant during recovery */
 			if (SEQ_LT(tp->snd_una, tp->snd_last))
 				tp->snd_cwnd -= tp->t_maxseg;
-#endif
 		}
 	}
 
@@ -329,17 +307,6 @@ again:
 
 	if (!sack_rxmit) {
 		len = ulmin(so->so_snd.sb_cc, win) - off;
-
-#ifdef TCP_FACK
-		/*
-		 * If we're in fast recovery (SEQ_GT(tp->snd_last, tp->snd_una)),
-		 * and amount of outstanding data (snd_awnd) is >= snd_cwnd, then
-		 * do not send data (like zero window conditions)
-		 */
-		if (tp->sack_enable && SEQ_GT(tp->snd_last, tp->snd_una) &&
-		    len && (tp->snd_awnd >= tp->snd_cwnd))
-			len = 0;
-#endif /* TCP_FACK */
 	}
 
 	if (len < 0) {
@@ -794,9 +761,6 @@ send:
 			sendalot = 0;
 		th->th_seq = htonl(p->rxmit);
 		p->rxmit += len;
-#ifdef TCP_FACK
-		tp->retran_data += len;
-#endif
 		tcpstat_pkt(tcps_sack_rexmits, tcps_sack_rexmit_bytes, len);
 	}
 
@@ -1096,12 +1060,6 @@ send:
 #endif /* INET6 */
 	}
 
-#ifdef TCP_FACK
-	/* Update snd_awnd to reflect the new data that was sent.  */
-	tp->snd_awnd = tcp_seq_subtract(tp->snd_max, tp->snd_fack) +
-		tp->retran_data;
-#endif
-
 	if (error) {
 out:
 		if (error == ENOBUFS) {
diff --git a/sys/netinet/tcp_timer.c b/sys/netinet/tcp_timer.c
index 9d2e75942cd..91aa0cbe4dd 100644
--- a/sys/netinet/tcp_timer.c
+++ b/sys/netinet/tcp_timer.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tcp_timer.c,v 1.58 2017/10/22 14:11:34 mikeb Exp $	*/
+/*	$OpenBSD: tcp_timer.c,v 1.59 2017/10/25 12:38:21 job Exp $	*/
 /*	$NetBSD: tcp_timer.c,v 1.14 1996/02/13 23:44:09 christos Exp $	*/
 
 /*
@@ -172,11 +172,6 @@ tcp_timer_freesack(struct tcpcb *tp)
 		pool_put(&sackhl_pool, p);
 	}
 	tp->snd_holes = 0;
-#ifdef TCP_FACK
-	tp->snd_fack = tp->snd_una;
-	tp->retran_data = 0;
-	tp->snd_awnd = 0;
-#endif
 }
 
 void
diff --git a/sys/netinet/tcp_usrreq.c b/sys/netinet/tcp_usrreq.c
index d7ee1ecc517..b4333507447 100644
--- a/sys/netinet/tcp_usrreq.c
+++ b/sys/netinet/tcp_usrreq.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tcp_usrreq.c,v 1.157 2017/10/22 14:11:34 mikeb Exp $	*/
+/*	$OpenBSD: tcp_usrreq.c,v 1.158 2017/10/25 12:38:21 job Exp $	*/
 /*	$NetBSD: tcp_usrreq.c,v 1.20 1996/02/13 23:44:16 christos Exp $	*/
 
 /*
@@ -269,11 +269,6 @@ tcp_usrreq(struct socket *so, int req, struct mbuf *m, struct mbuf *nam,
 		tcp_set_iss_tsm(tp);
 		tcp_sendseqinit(tp);
 		tp->snd_last = tp->snd_una;
-#ifdef TCP_FACK
-		tp->snd_fack = tp->snd_una;
-		tp->retran_data = 0;
-		tp->snd_awnd = 0;
-#endif
 		error = tcp_output(tp);
 		break;
 
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
index d5e4d900778..54e8aecc262 100644
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tcp_var.h,v 1.126 2017/10/24 14:49:29 mikeb Exp $	*/
+/*	$OpenBSD: tcp_var.h,v 1.127 2017/10/25 12:38:21 job Exp $	*/
 /*	$NetBSD: tcp_var.h,v 1.17 1996/02/13 23:44:24 christos Exp $	*/
 
 /*
@@ -119,12 +119,6 @@ struct tcpcb {
 	int	sack_enable;		/* enable SACK for this connection */
 	int	snd_numholes;		/* number of holes seen by sender */
 	struct sackhole *snd_holes;	/* linked list of holes (sorted) */
-#if 1 /*defined(TCP_FACK)*/
-	tcp_seq snd_fack;		/* for FACK congestion control */
-	u_long	snd_awnd;		/* snd_nxt - snd_fack + */
-					/* retransmitted data */
-	int retran_data;		/* amount of outstanding retx. data  */
-#endif /* TCP_FACK */
 	tcp_seq snd_last;		/* for use in fast recovery */
 /* receive sequence variables */
 	u_long	rcv_wnd;		/* receive window */
diff --git a/usr.bin/netstat/inet.c b/usr.bin/netstat/inet.c
index 468d514a22e..4f0917c5097 100644
--- a/usr.bin/netstat/inet.c
+++ b/usr.bin/netstat/inet.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: inet.c,v 1.160 2017/08/12 03:21:02 benno Exp $	*/
+/*	$OpenBSD: inet.c,v 1.161 2017/10/25 12:38:21 job Exp $	*/
 /*	$NetBSD: inet.c,v 1.14 1995/10/03 21:42:37 thorpej Exp $	*/
 
 /*
@@ -1496,9 +1496,6 @@ tcpcb_dump(u_long off)
 	p("%lu", snd_wnd, "\n ");
 	p("%d", sack_enable, ", ");
 	p("%d", snd_numholes, ", ");
-	p("%u", snd_fack, ", ");
-	p("%lu",snd_awnd, "\n ");
-	p("%u", retran_data, ", ");
 	p("%u", snd_last, "\n ");
 	p("%u", irs, "\n ");
 	p("%u", rcv_nxt, ", ");