Ultrix-3.1/sys/net/tcp_output.c
/**********************************************************************
* Copyright (c) Digital Equipment Corporation 1984, 1985, 1986. *
* All Rights Reserved. *
* Reference "/usr/src/COPYRIGHT" for applicable restrictions. *
**********************************************************************/
/*
* Copyright (c) 1982 Regents of the University of California.
* All rights reserved. The Berkeley software License Agreement
* specifies the terms and conditions for redistribution.
*
* SCCSID: @(#)tcp_output.c 3.0 (ULTRIX-11) 4/21/86
* Based on: @(#)tcp_output.c 6.9 (Berkeley) 6/8/85
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <errno.h>
#include <net/route.h>
#include <netinet/in.h>
#include <netinet/in_pcb.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet/tcp.h>
#define TCPOUTFLAGS
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcpip.h>
#include <netinet/tcp_debug.h>
#ifdef pdp11
#define tcp_initopt tcp_IOPT
#endif pdp11
/*
* Initial options.
*/
u_char tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, };
/*
* Tcp output routine: figure out what should be sent and send it.
*/
tcp_output(tp)
register struct tcpcb *tp;
{
register struct socket *so = tp->t_inpcb->inp_socket;
register int len;
struct mbuf *m0;
int off, flags, win, error;
register struct mbuf *m;
register struct tcpiphdr *ti;
u_char *opt;
unsigned optlen = 0;
int sendalot;
#ifdef pdp11
int retval;
#endif pdp11
/*
* Determine length of data that should be transmitted,
* and flags that will be used.
* If there is some data or critical controls (SYN, RST)
* to send, then transmit; otherwise, investigate further.
*/
#ifdef pdp11
MAPSAVE();
#define return(x) {retval = x;goto out;}
#endif
again:
sendalot = 0;
off = tp->snd_nxt - tp->snd_una;
win = MIN(tp->snd_wnd, tp->snd_cwnd);
/*
* If in persist timeout with window of 0, send 1 byte.
* Otherwise, window is small but nonzero
* and timer expired, go to transmit state.
*/
if (tp->t_force) {
if (win == 0)
win = 1;
else {
tp->t_timer[TCPT_PERSIST] = 0;
tp->t_rxtshift = 0;
}
}
len = MIN(so->so_snd.sb_cc, win) - off;
if (len < 0)
return (0); /* ??? */ /* past FIN */
if (len > tp->t_maxseg) {
len = tp->t_maxseg;
/*
* Don't send more than one segment if retransmitting
* (or persisting, but then we shouldn't be here).
*/
if (tp->t_rxtshift == 0)
sendalot = 1;
}
win = sbspace(&so->so_rcv);
flags = tcp_outflags[tp->t_state];
if (tp->snd_nxt + len < tp->snd_una + so->so_snd.sb_cc)
flags &= ~TH_FIN;
if (flags & (TH_SYN|TH_RST|TH_FIN))
goto send;
if (SEQ_GT(tp->snd_up, tp->snd_una))
goto send;
/*
* Sender silly window avoidance. If connection is idle
* and can send all data, a maximum segment,
* at least a maximum default-size segment do it,
* or are forced, do it; otherwise don't bother.
* If retransmitting (possibly after persist timer forced us
* to send into a small window), then must resend.
*/
if (len) {
if (len == tp->t_maxseg || len >= so->so_snd.sb_cc) /* off = 0*/
goto send;
if (len >= TCP_MSS) /* a lot */
goto send;
if (tp->t_force)
goto send;
if (SEQ_LT(tp->snd_nxt, tp->snd_max))
goto send;
}
/*
* Send if we owe peer an ACK.
*/
if (tp->t_flags&TF_ACKNOW)
goto send;
/*
* Calculate available window, and also amount
* of window known to peer (as advertised window less
* next expected input.) If the difference is 35% or more of the
* maximum possible window, then want to send a window update to peer.
*/
win = sbspace(&so->so_rcv);
if (win > 0 &&
((100*(win-(tp->rcv_adv-tp->rcv_nxt))/so->so_rcv.sb_hiwat) >= 35))
goto send;
/*
* TCP window updates are not reliable, rather a polling protocol
* using ``persist'' packets is used to insure receipt of window
* updates. The three ``states'' for the output side are:
* idle not doing retransmits or persists
* persisting to move a zero window
* (re)transmitting and thereby not persisting
*
* tp->t_timer[TCPT_PERSIST]
* is set when we are in persist state.
* tp->t_force
* is set when we are called to send a persist packet.
* tp->t_timer[TCPT_REXMT]
* is set when we are retransmitting
* The output side is idle when both timers are zero.
*
* If send window is too small, there is data to transmit, and no
* retransmit or persist is pending, then go to persist state.
* If nothing happens soon, send when timer expires:
* if window is nonzero, transmit what we can,
* otherwise force out a byte.
*/
if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&
tp->t_timer[TCPT_PERSIST] == 0) {
tp->t_rxtshift = 0;
tcp_setpersist(tp);
}
/*
* No reason to send a segment, just return.
*/
return (0);
send:
/*
* Grab a header mbuf, attaching a copy of data to
* be transmitted, and initialize the header from
* the template for sends on this connection.
*/
MGET(m, M_DONTWAIT, MT_HEADER);
if (m == NULL)
return (ENOBUFS);
m->m_off = MMAXOFF - sizeof (struct tcpiphdr);
m->m_len = sizeof (struct tcpiphdr);
if (len) {
m->m_next = m_copy(so->so_snd.sb_mb, off, len);
if (m->m_next == 0)
len = 0;
}
ti = mtod(m, struct tcpiphdr *);
if (tp->t_template == 0)
panic("tcp_output");
bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr));
/*
* Fill in fields, remembering maximum advertised
* window for use in delaying messages about window sizes.
*/
ti->ti_seq = tp->snd_nxt;
ti->ti_ack = tp->rcv_nxt;
ti->ti_seq = htonl(ti->ti_seq);
ti->ti_ack = htonl(ti->ti_ack);
/*
* Before ESTABLISHED, force sending of initial options
* unless TCP set to not do any options.
*/
if (tp->t_state < TCPS_ESTABLISHED) {
int mss;
if (tp->t_flags&TF_NOOPT)
goto noopt;
mss = MIN(so->so_rcv.sb_hiwat / 2, tcp_mss(tp));
if (mss <= IP_MSS - sizeof(struct tcpiphdr))
goto noopt;
opt = tcp_initopt;
optlen = sizeof (tcp_initopt);
*(u_short *)(opt + 2) = htons(mss);
} else {
if (tp->t_tcpopt == 0)
goto noopt;
opt = mtod(tp->t_tcpopt, u_char *);
optlen = tp->t_tcpopt->m_len;
}
if (opt) {
m0 = m->m_next;
m->m_next = m_get(M_DONTWAIT, MT_DATA);
if (m->m_next == 0) {
(void) m_free(m);
m_freem(m0);
return (ENOBUFS);
}
m->m_next->m_next = m0;
m0 = m->m_next;
m0->m_len = optlen;
#ifndef pdp11
bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen);
#else pdp11
if (opt == tcp_initopt)
bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen);
else
MBCOPY(tp->t_tcpopt, 0, m0, 0, optlen);
#endif pdp11
opt = (u_char *)(mtod(m0, caddr_t) + optlen);
while (m0->m_len & 0x3) {
*opt++ = TCPOPT_EOL;
m0->m_len++;
}
optlen = m0->m_len;
#ifdef pdp11
ti = mtod(m, struct tcpiphdr *); /* needed for 11 */
#endif
ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
}
noopt:
ti->ti_flags = flags;
if (win >= so->so_rcv.sb_hiwat / 4) /* avoid silly window */
ti->ti_win = htons((u_short)win);
if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
ti->ti_urp = tp->snd_up - tp->snd_nxt;
ti->ti_urp = htons(ti->ti_urp);
ti->ti_flags |= TH_URG;
} else
/*
* If no urgent pointer to send, then we pull
* the urgent pointer to the left edge of the send window
* so that it doesn't drift into the send window on sequence
* number wraparound.
*/
tp->snd_up = tp->snd_una; /* drag it along */
/*
* If anything to send and we can send it all, set PUSH.
* (This will keep happy those implementations which only
* give data to the user when a buffer fills or a PUSH comes in.)
*/
if (len && off+len == so->so_snd.sb_cc)
ti->ti_flags |= TH_PUSH;
/*
* Put TCP length in extended header, and then
* checksum extended header and data.
*/
if (len + optlen) {
ti->ti_len = sizeof (struct tcphdr) + optlen + len;
ti->ti_len = htons((u_short)ti->ti_len);
}
#ifdef TCPLOOPBACK
/* Don't checksum if we are staying on this machine */
if (ti->ti_src.s_addr != ti->ti_dst.s_addr)
#endif TCPLOOPBACK
ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + len);
/*
* In transmit state, time the transmission and arrange for
* the retransmit. In persist state, just set snd_max.
*/
if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {
/*
* Advance snd_nxt over sequence space of this segment.
*/
if (flags & (TH_SYN|TH_FIN))
tp->snd_nxt++;
tp->snd_nxt += len;
if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
tp->snd_max = tp->snd_nxt;
/*
* Time this transmission if not a retransmission and
* not currently timing anything.
*/
if (tp->t_rtt == 0) {
tp->t_rtt = 1;
tp->t_rtseq = tp->snd_nxt - len;
}
}
/*
* Set retransmit timer if not currently set,
* and not doing a keep-alive probe.
* Initial value for retransmit timer to tcp_beta*tp->t_srtt.
* Initialize shift counter which is used for exponential
* backoff of retransmit time.
*/
if (tp->t_timer[TCPT_REXMT] == 0 &&
tp->snd_nxt != tp->snd_una) {
TCPT_RANGESET(tp->t_timer[TCPT_REXMT],
#ifdef pdp11
(tcp_beta*tp->t_srtt)/100, TCPTV_MIN, TCPTV_MAX);
#else vax
tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX);
#endif
tp->t_rxtshift = 0;
}
tp->t_timer[TCPT_PERSIST] = 0;
} else {
if (SEQ_GT(tp->snd_una+1, tp->snd_max))
tp->snd_max = tp->snd_una+1;
}
#ifdef TCP_DEBUG
/*
* Trace.
*/
if (so->so_options & SO_DEBUG)
tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0);
#endif TCP_DEBUG
#ifdef TCPLOOPBACK
if (ti->ti_src.s_addr == ti->ti_dst.s_addr) {
/* Fake IP transit and get to TCP layer fast */
((struct ip *)ti)->ip_hl = sizeof (struct ip) >> 2;
((struct ip *)ti)->ip_len = sizeof (struct tcphdr) + optlen + len;
/*
* Data (will be) sent.
* If this advertises a larger window than any other segment,
* then remember the size of the advertised window.
* Drop send for purpose of ACK requirements.
*/
if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
tp->rcv_adv = tp->rcv_nxt + win;
tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
tcp_input(m);
} else {
#endif TCPLOOPBACK
/*
* Fill in IP length and desired time to live and
* send to IP level.
*/
((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len;
((struct ip *)ti)->ip_ttl = TCP_TTL;
if (so->so_options & SO_DONTROUTE)
error =
ip_output(m, tp->t_ipopt, (struct route *)0, IP_ROUTETOIF);
else
error = ip_output(m, tp->t_ipopt, &tp->t_inpcb->inp_route, 0);
if (error)
return (error);
/*
* Data sent (as far as we can tell).
* If this advertises a larger window than any other segment,
* then remember the size of the advertised window.
* Drop send for purpose of ACK requirements.
*/
if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
tp->rcv_adv = tp->rcv_nxt + win;
tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
#ifdef TCPLOOPBACK
}
#endif TCPLOOPBACK
if (sendalot && tp->t_force == 0)
goto again;
#ifdef pdp11
#undef return
retval = 0;
out:
MAPREST();
return(retval);
#else
return (0);
#endif
}
tcp_setpersist(tp)
register struct tcpcb *tp;
{
if (tp->t_timer[TCPT_REXMT])
panic("tcp_output REXMT");
/*
* Start/restart persistance timer.
*/
TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
((int)(tcp_beta * tp->t_srtt)) << tp->t_rxtshift,
TCPTV_PERSMIN, TCPTV_MAX);
tp->t_rxtshift++;
if (tp->t_rxtshift >= TCP_MAXRXTSHIFT)
tp->t_rxtshift = 0;
}