/* * Copyright (c) 1982, 1986, 1988, 1990 Regents of the University of California. * All rights reserved. * * %sccs.include.redist.c% * * @(#)tcp_output.c 7.25 (Berkeley) 01/08/93 */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define TCPOUTFLAGS #include #include #include #include #include #include #ifdef notyet extern struct mbuf *m_copypack(); #endif #define MAX_TCPOPTLEN 32 /* max # bytes that go in options */ /* * 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 long len, win; int off, flags, error; register struct mbuf *m; register struct tcpiphdr *ti; u_char opt[MAX_TCPOPTLEN]; unsigned optlen, hdrlen; int idle, sendalot; /* * 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. */ idle = (tp->snd_max == tp->snd_una); if (idle && tp->t_idle >= tp->t_rxtcur) /* * We have been idle for "a while" and no acks are * expected to clock out any data we send -- * slow start to get ack "clock" running again. */ tp->snd_cwnd = tp->t_maxseg; 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, if window is small but nonzero * and timer expired, we will send what we can * and go to transmit state. */ if (tp->t_force) { if (win == 0) win = 1; else { tp->t_timer[TCPT_PERSIST] = 0; tp->t_rxtshift = 0; } } flags = tcp_outflags[tp->t_state]; len = min(so->so_snd.sb_cc, win) - off; if (len < 0) { /* * If FIN has been sent but not acked, * but we haven't been called to retransmit, * len will be -1. Otherwise, window shrank * after we sent into it. If window shrank to 0, * cancel pending retransmit and pull snd_nxt * back to (closed) window. We will enter persist * state below. If the window didn't close completely, * just wait for an ACK. */ len = 0; if (win == 0) { tp->t_timer[TCPT_REXMT] = 0; tp->snd_nxt = tp->snd_una; } } if (len > tp->t_maxseg) { len = tp->t_maxseg; sendalot = 1; } if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc)) flags &= ~TH_FIN; win = sbspace(&so->so_rcv); /* * 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 peer's buffer is tiny, then send * when window is at least half open. * If retransmitting (possibly after persist timer forced us * to send into a small window), then must resend. */ if (len) { if (len == tp->t_maxseg) goto send; if ((idle || tp->t_flags & TF_NODELAY) && len + off >= so->so_snd.sb_cc) goto send; if (tp->t_force) goto send; if (len >= tp->max_sndwnd / 2) goto send; if (SEQ_LT(tp->snd_nxt, tp->snd_max)) goto send; } /* * Compare available window to amount of window * known to peer (as advertised window less * next expected input). If the difference is at least two * max size segments, or at least 50% of the maximum possible * window, then want to send a window update to peer. */ if (win > 0) { /* * "adv" is the amount we can increase the window, * taking into account that we are limited by * TCP_MAXWIN << tp->rcv_scale. */ long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) - (tp->rcv_adv - tp->rcv_nxt); if (adv >= (long) (2 * tp->t_maxseg)) goto send; if (2 * adv >= (long) so->so_rcv.sb_hiwat) goto send; } /* * Send if we owe peer an ACK. */ if (tp->t_flags & TF_ACKNOW) goto send; if (flags & (TH_SYN|TH_RST)) goto send; if (SEQ_GT(tp->snd_up, tp->snd_una)) goto send; /* * If our state indicates that FIN should be sent * and we have not yet done so, or we're retransmitting the FIN, * then we need to send. */ if (flags & TH_FIN && ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una)) 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 small or 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: /* * Before ESTABLISHED, force sending of initial options * unless TCP set not to do any options. * NOTE: we assume that the IP/TCP header plus TCP options * always fit in a single mbuf, leaving room for a maximum * link header, i.e. * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MHLEN */ optlen = 0; hdrlen = sizeof (struct tcpiphdr); if (flags & TH_SYN && (tp->t_flags & TF_NOOPT) == 0) { u_short mss; opt[0] = TCPOPT_MAXSEG; opt[1] = 4; mss = htons((u_short) tcp_mss(tp, 0)); bcopy((caddr_t)&mss, (caddr_t)(opt + 2), sizeof(mss)); optlen = 4; if ((tp->t_flags & TF_REQ_SCALE) && ((flags & TH_ACK) == 0 || (tp->t_flags & TF_RCVD_SCALE))) { *((u_long *) (opt + optlen)) = htonl( TCPOPT_NOP<<24 | TCPOPT_WINDOW<<16 | TCPOLEN_WINDOW<<8 | tp->request_r_scale); optlen += 4; } #ifdef DO_SACK /* Send a SACK_PERMITTED option in the SYN segment. */ *((u_long *) (opt + optlen)) = htonl( TCPOPT_NOP<<24 | TCPOPT_NOP<<16 | TCPOPT_SACK_PERMITTED<<8 | TCPOLEN_SACK_PERMITTED); optlen += 4; #endif } /* * Send a timestamp and echo-reply if this is a SYN and our side * wants to use timestamps (TF_REQ_TSTMP is set) or both our side * and our peer have sent timestamps in our SYN's. */ if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && (flags & TH_RST) == 0 && ((flags & (TH_SYN|TH_ACK)) == TH_SYN || (tp->t_flags & TF_RCVD_TSTMP))) { u_long *lp = (u_long *)(opt + optlen); /* Form timestamp option as shown in appendix A of RFC 1323. */ *lp++ = htonl(TCPOPT_TSTAMP_HDR); *lp++ = htonl(tcp_now); *lp = htonl(tp->ts_recent); optlen += TCPOLEN_TSTAMP_APPA; } #ifdef DO_SACK /* Send SACK if needed. Don't tack a SACK onto a non-empty segment. */ if (tp->seg_next != (struct tcpiphdr *)tp && len == 0 && (tp->t_flags & (TF_SACK_PERMIT|TF_NOOPT)) == TF_SACK_PERMIT) { register struct tcpiphdr *q = tp->seg_next; register u_long *optl = (u_long *)(opt + optlen) + 1; tcp_seq block_start; u_long block_size; int sack_len = 2; /* * Use these to gather runs of received segments. * The first segment in the queue becomes the initial run. */ block_start = q->ti_seq; block_size = q->ti_len; do { q = (struct tcpiphdr *) q->ti_next; if (q == (struct tcpiphdr *) tp || block_start + block_size != q->ti_seq) { /* * Stick the relative origin and block size * in the SACK option. */ *optl++ = htonl(block_start-tp->rcv_nxt); *optl++ = htonl(block_size); sack_len += 8; /* If no more will fit into options, quit. */ if (sack_len + optlen > MAX_TCPOPTLEN - 8) break; if (q != (struct tcpiphdr *) tp) { block_start = q->ti_seq; block_size = q->ti_len; } } else { /* * This segment just accumulates into previous * run. */ block_size += q->ti_len; } } while (q != (struct tcpiphdr *) tp); *((u_long *) (opt + optlen)) = htonl(TCPOPT_NOP << 24 | TCPOPT_NOP << 16 | TCPOPT_SACK << 8 | sack_len); optlen += sack_len + 2; } #endif hdrlen += optlen; /* * Adjust data length if insertion of options will * bump the packet length beyond the t_maxseg length. */ if (len > tp->t_maxseg - optlen) { len = tp->t_maxseg - optlen; sendalot = 1; } #ifdef DIAGNOSTIC if (max_linkhdr + hdrlen > MHLEN) panic("tcphdr too big"); #endif /* * Grab a header mbuf, attaching a copy of data to * be transmitted, and initialize the header from * the template for sends on this connection. */ if (len) { if (tp->t_force && len == 1) tcpstat.tcps_sndprobe++; else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) { tcpstat.tcps_sndrexmitpack++; tcpstat.tcps_sndrexmitbyte += len; } else { tcpstat.tcps_sndpack++; tcpstat.tcps_sndbyte += len; } #ifdef notyet if ((m = m_copypack(so->so_snd.sb_mb, off, (int)len, max_linkhdr + hdrlen)) == 0) { error = ENOBUFS; goto out; } /* * m_copypack left space for our hdr; use it. */ m->m_len += hdrlen; m->m_data -= hdrlen; #else MGETHDR(m, M_DONTWAIT, MT_HEADER); if (m == NULL) { error = ENOBUFS; goto out; } m->m_data += max_linkhdr; m->m_len = hdrlen; if (len <= MHLEN - hdrlen - max_linkhdr) { m_copydata(so->so_snd.sb_mb, off, (int) len, mtod(m, caddr_t) + hdrlen); m->m_len += len; } else { m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len); if (m->m_next == 0) len = 0; } #endif /* * If we're sending everything we've got, 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 (off + len == so->so_snd.sb_cc) flags |= TH_PUSH; } else { if (tp->t_flags & TF_ACKNOW) tcpstat.tcps_sndacks++; else if (flags & (TH_SYN|TH_FIN|TH_RST)) tcpstat.tcps_sndctrl++; else if (SEQ_GT(tp->snd_up, tp->snd_una)) tcpstat.tcps_sndurg++; else tcpstat.tcps_sndwinup++; MGETHDR(m, M_DONTWAIT, MT_HEADER); if (m == NULL) { error = ENOBUFS; goto out; } m->m_data += max_linkhdr; m->m_len = hdrlen; } m->m_pkthdr.rcvif = (struct ifnet *)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. * If resending a FIN, be sure not to use a new sequence number. */ if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && tp->snd_nxt == tp->snd_max) tp->snd_nxt--; ti->ti_seq = htonl(tp->snd_nxt); ti->ti_ack = htonl(tp->rcv_nxt); if (optlen) { bcopy((caddr_t)opt, (caddr_t)(ti + 1), optlen); ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2; } ti->ti_flags = flags; /* * Calculate receive window. Don't shrink window, * but avoid silly window syndrome. */ if (win < (long)(so->so_rcv.sb_hiwat / 4) && win < (long)tp->t_maxseg) win = 0; if (win > (long)TCP_MAXWIN << tp->rcv_scale) win = (long)TCP_MAXWIN << tp->rcv_scale; if (win < (long)(tp->rcv_adv - tp->rcv_nxt)) win = (long)(tp->rcv_adv - tp->rcv_nxt); ti->ti_win = htons((u_short) (win>>tp->rcv_scale)); if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { ti->ti_urp = htons((u_short)(tp->snd_up - tp->snd_nxt)); 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 */ /* * Put TCP length in extended header, and then * checksum extended header and data. */ if (len + optlen) ti->ti_len = htons((u_short)(sizeof (struct tcphdr) + optlen + len)); ti->ti_sum = in_cksum(m, (int)(hdrlen + 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) { tcp_seq startseq = tp->snd_nxt; /* * Advance snd_nxt over sequence space of this segment. */ if (flags & (TH_SYN|TH_FIN)) { if (flags & TH_SYN) tp->snd_nxt++; if (flags & TH_FIN) { tp->snd_nxt++; tp->t_flags |= TF_SENTFIN; } } 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 = startseq; tcpstat.tcps_segstimed++; } } /* * Set retransmit timer if not currently set, * and not doing an ack or a keep-alive probe. * Initial value for retransmit timer is smoothed * round-trip time + 2 * round-trip time variance. * Initialize shift counter which is used for backoff * of retransmit time. */ if (tp->t_timer[TCPT_REXMT] == 0 && tp->snd_nxt != tp->snd_una) { tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; if (tp->t_timer[TCPT_PERSIST]) { tp->t_timer[TCPT_PERSIST] = 0; tp->t_rxtshift = 0; } } } else if (SEQ_GT(tp->snd_nxt + len, tp->snd_max)) tp->snd_max = tp->snd_nxt + len; /* * Trace. */ if (so->so_options & SO_DEBUG) tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0); /* * Fill in IP length and desired time to live and * send to IP level. There should be a better way * to handle ttl and tos; we could keep them in * the template, but need a way to checksum without them. */ m->m_pkthdr.len = hdrlen + len; ((struct ip *)ti)->ip_len = m->m_pkthdr.len; ((struct ip *)ti)->ip_ttl = tp->t_inpcb->inp_ip.ip_ttl; /* XXX */ ((struct ip *)ti)->ip_tos = tp->t_inpcb->inp_ip.ip_tos; /* XXX */ #if BSD >= 43 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route, so->so_options & SO_DONTROUTE, 0); #else error = ip_output(m, (struct mbuf *)0, &tp->t_inpcb->inp_route, so->so_options & SO_DONTROUTE); #endif if (error) { out: if (error == ENOBUFS) { tcp_quench(tp->t_inpcb); return (0); } if ((error == EHOSTUNREACH || error == ENETDOWN) && TCPS_HAVERCVDSYN(tp->t_state)) { tp->t_softerror = error; return (0); } return (error); } tcpstat.tcps_sndtotal++; /* * 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. * Any pending ACK has now been sent. */ if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) tp->rcv_adv = tp->rcv_nxt + win; tp->last_ack_sent = tp->rcv_nxt; tp->t_flags &= ~(TF_ACKNOW|TF_DELACK); if (sendalot) goto again; return (0); } tcp_setpersist(tp) register struct tcpcb *tp; { register t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; if (tp->t_timer[TCPT_REXMT]) panic("tcp_output REXMT"); /* * Start/restart persistance timer. */ TCPT_RANGESET(tp->t_timer[TCPT_PERSIST], t * tcp_backoff[tp->t_rxtshift], TCPTV_PERSMIN, TCPTV_PERSMAX); if (tp->t_rxtshift < TCP_MAXRXTSHIFT) tp->t_rxtshift++; }