/* * Copyright (c) 1982, 1986, 1988, 1990, 1993 * The Regents of the University of California. All rights reserved. * * 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. * 3. 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_output.c 8.3 (Berkeley) 12/30/93 * tcp_output.c,v 1.3 1994/09/15 10:36:55 davidg Exp */ /* * Changes and additions relating to SLiRP * Copyright (c) 1995 Danny Gasparovski. * * Please read the file COPYRIGHT for the * terms and conditions of the copyright. */ #include "slirp.h" #if BX_NETWORKING && BX_NETMOD_SLIRP_NEW static const u_char tcp_outflags[TCP_NSTATES] = { TH_RST|TH_ACK, 0, TH_SYN, TH_SYN|TH_ACK, TH_ACK, TH_ACK, TH_FIN|TH_ACK, TH_FIN|TH_ACK, TH_FIN|TH_ACK, TH_ACK, TH_ACK, }; #undef MAX_TCPOPTLEN #define MAX_TCPOPTLEN 32 /* max # bytes that go in options */ /* * Tcp output routine: figure out what should be sent and send it. */ int tcp_output(struct tcpcb *tp) { register struct socket *so = tp->t_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; DEBUG_CALL("tcp_output"); DEBUG_ARG("tp = %lx", (long )tp); /* * 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); flags = tcp_outflags[tp->t_state]; DEBUG_MISC((dfd, " --- tcp_output flags = 0x%x\n",flags)); /* * 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) { /* * If we still have some data to send, then * clear the FIN bit. Usually this would * happen below when it realizes that we * aren't sending all the data. However, * if we have exactly 1 byte of unset data, * then it won't clear the FIN bit below, * and if we are in persist state, we wind * up sending the packet without recording * that we sent the FIN bit. * * We can't just blindly clear the FIN bit, * because if we don't have any more data * to send then the probe will be the FIN * itself. */ if (off < (int)so->so_snd.sb_cc) flags &= ~TH_FIN; 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) { /* * 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 ((1 || 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 && tp->max_sndwnd > 0) 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_datalen) 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->snd_nxt = tp->iss; if ((tp->t_flags & TF_NOOPT) == 0) { uint16_t mss; opt[0] = TCPOPT_MAXSEG; opt[1] = 4; mss = htons((uint16_t) tcp_mss(tp, 0)); memcpy((caddr_t)(opt + 2), (caddr_t)&mss, sizeof(mss)); optlen = 4; } } 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; } /* * 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) { m = m_get(so->slirp); if (m == NULL) { error = 1; goto out; } m->m_data += IF_MAXLINKHDR; m->m_len = hdrlen; sbcopy(&so->so_snd, off, (int) len, mtod(m, caddr_t) + hdrlen); m->m_len += len; /* * 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 { m = m_get(so->slirp); if (m == NULL) { error = 1; goto out; } m->m_data += IF_MAXLINKHDR; m->m_len = hdrlen; } ti = mtod(m, struct tcpiphdr *); memcpy((caddr_t)ti, &tp->t_template, 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--; /* * If we are doing retransmissions, then snd_nxt will * not reflect the first unsent octet. For ACK only * packets, we do not want the sequence number of the * retransmitted packet, we want the sequence number * of the next unsent octet. So, if there is no data * (and no SYN or FIN), use snd_max instead of snd_nxt * when filling in ti_seq. But if we are in persist * state, snd_max might reflect one byte beyond the * right edge of the window, so use snd_nxt in that * case, since we know we aren't doing a retransmission. * (retransmit and persist are mutually exclusive...) */ if (len || (flags & (TH_SYN|TH_FIN)) || tp->t_timer[TCPT_PERSIST]) ti->ti_seq = htonl(tp->snd_nxt); else ti->ti_seq = htonl(tp->snd_max); ti->ti_ack = htonl(tp->rcv_nxt); if (optlen) { memcpy((caddr_t)(ti + 1), (caddr_t)opt, 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_datalen / 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((uint16_t) (win>>tp->rcv_scale)); if (SEQ_GT(tp->snd_up, tp->snd_una)) { ti->ti_urp = htons((uint16_t)(tp->snd_up - ntohl(ti->ti_seq))); 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((uint16_t)(sizeof (struct tcphdr) + optlen + len)); ti->ti_sum = 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; } } /* * 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; /* * 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_len = hdrlen + len; /* XXX Needed? m_len should be correct */ { ((struct ip *)ti)->ip_len = m->m_len; ((struct ip *)ti)->ip_ttl = IPDEFTTL; ((struct ip *)ti)->ip_tos = so->so_iptos; error = ip_output(so, m); } if (error) { out: 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. * 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); } void tcp_setpersist(struct tcpcb *tp) { int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; /* * Start/restart persistence 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++; } #endif