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Fix a few bugs in the TCP New Reno code:

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- Make sure that snd_recover is always at least snd_una.  If we don't do
  this, there can be confusion when sequence numbers wrap around on a
  large loss-free data transfer.
- When doing a New Reno retransmit, snd_una hasn't been updated yet,
  and the socket's send buffer has not yet dropped off ACK'd data, so
  don't muddle with snd_una, so that tcp_output() gets the correct data
  offset.
- When doing a New Reno retransmit, make sure the congestion window is
  open one segment beyond the ACK'd data, so that we can actually perform
  the retransmit.

Partially derived from, although more complete than, similar changes in
OpenBSD, which in turn originated from Tom Henderson <tomh@cs.berkeley.edu>.
This commit is contained in:
thorpej 1999-08-11 17:37:59 +00:00
parent dc501adfd5
commit af1e02ad91
1 changed files with 31 additions and 12 deletions
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43
sys/netinet/tcp_input.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: tcp_input.c,v 1.90 1999/08/11 03:02:18 thorpej Exp $ */
/* $NetBSD: tcp_input.c,v 1.91 1999/08/11 17:37:59 thorpej Exp $ */
/*
%%% portions-copyright-nrl-95
@ -1110,7 +1110,12 @@ after_listen:
tcpstat.tcps_rcvackpack++;
tcpstat.tcps_rcvackbyte += acked;
sbdrop(&so->so_snd, acked);
tp->snd_una = th->th_ack;
/*
* We want snd_recover to track snd_una to
* avoid sequence wraparound problems for
* very large transfers.
*/
tp->snd_una = tp->snd_recover = th->th_ack;
m_freem(m);
/*
@ -1213,7 +1218,7 @@ after_listen:
if ((tiflags & TH_SYN) == 0)
goto drop;
if (tiflags & TH_ACK) {
tp->snd_una = th->th_ack;
tp->snd_una = tp->snd_recover = th->th_ack;
if (SEQ_LT(tp->snd_nxt, tp->snd_una))
tp->snd_nxt = tp->snd_una;
}
@ -1574,7 +1579,8 @@ after_listen:
u_int win =
min(tp->snd_wnd, tp->snd_cwnd) /
2 / tp->t_segsz;
if (SEQ_LT(th->th_ack, tp->snd_recover)) {
if (SEQ_LT(th->th_ack,
tp->snd_recover)) {
/*
* False fast retransmit after
* timeout. Do not cut window.
@ -1692,7 +1698,12 @@ after_listen:
ourfinisacked = 0;
}
sowwakeup(so);
tp->snd_una = th->th_ack;
/*
* We want snd_recover to track snd_una to
* avoid sequence wraparound problems for
* very large transfers.
*/
tp->snd_una = tp->snd_recover = th->th_ack;
if (SEQ_LT(tp->snd_nxt, tp->snd_una))
tp->snd_nxt = tp->snd_una;
@ -2279,7 +2290,7 @@ tcp_xmit_timer(tp, rtt)
/*
* Checks for partial ack. If partial ack arrives, force the retransmission
* of the next unacknowledged segment, do not clear tp->t_dupacks, and return
* 1. By setting snd_nxt to ti_ack, this forces retransmission timer to
* 1. By setting snd_nxt to th_ack, this forces retransmission timer to
* be started again. If the ack advances at least to tp->snd_recover, return 0.
*/
int
@ -2287,18 +2298,26 @@ tcp_newreno(tp, th)
struct tcpcb *tp;
struct tcphdr *th;
{
tcp_seq onxt = tp->snd_nxt;
u_long ocwnd = tp->snd_cwnd;
if (SEQ_LT(th->th_ack, tp->snd_recover)) {
tcp_seq onxt = tp->snd_nxt;
tcp_seq ouna = tp->snd_una; /* Haven't updated snd_una yet*/
u_long ocwnd = tp->snd_cwnd;
/*
* snd_una has not yet been updated and the socket's send
* buffer has not yet drained off the ACK'd data, so we
* have to leave snd_una as it was to get the correct data
* offset in tcp_output().
*/
TCP_TIMER_DISARM(tp, TCPT_REXMT);
tp->t_rtt = 0;
tp->snd_nxt = th->th_ack;
tp->snd_cwnd = tp->t_segsz;
tp->snd_una = th->th_ack;
/*
* Set snd_cwnd to one segment beyond ACK'd offset. snd_una
* is not yet updated when we're called.
*/
tp->snd_cwnd = tp->t_segsz + (th->th_ack - tp->snd_una);
(void) tcp_output(tp);
tp->snd_cwnd = ocwnd;
tp->snd_una = ouna;
if (SEQ_GT(onxt, tp->snd_nxt))
tp->snd_nxt = onxt;
/*