| /* SPDX-License-Identifier: BSD-3-Clause */ |
| /* |
| * 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. |
| */ |
| |
| #include "slirp.h" |
| |
| static const uint8_t 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, tcpiph_save; |
| struct ip *ip; |
| struct ip6 *ip6; |
| uint8_t opt[MAX_TCPOPTLEN]; |
| unsigned optlen, hdrlen; |
| int idle, sendalot; |
| |
| DEBUG_CALL("tcp_output"); |
| DEBUG_ARG("tp = %p", 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(" --- tcp_output flags = 0x%x", 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 < 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((char *)(opt + 2), (char *)&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, char *) + 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((char *)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((char *)(ti + 1), (char *)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 */ |
| tcpiph_save = *mtod(m, struct tcpiphdr *); |
| |
| switch (so->so_ffamily) { |
| case AF_INET: |
| m->m_data += |
| sizeof(struct tcpiphdr) - sizeof(struct tcphdr) - sizeof(struct ip); |
| m->m_len -= |
| sizeof(struct tcpiphdr) - sizeof(struct tcphdr) - sizeof(struct ip); |
| ip = mtod(m, struct ip *); |
| |
| ip->ip_len = m->m_len; |
| ip->ip_dst = tcpiph_save.ti_dst; |
| ip->ip_src = tcpiph_save.ti_src; |
| ip->ip_p = tcpiph_save.ti_pr; |
| |
| ip->ip_ttl = IPDEFTTL; |
| ip->ip_tos = so->so_iptos; |
| error = ip_output(so, m); |
| break; |
| |
| case AF_INET6: |
| m->m_data += sizeof(struct tcpiphdr) - sizeof(struct tcphdr) - |
| sizeof(struct ip6); |
| m->m_len -= sizeof(struct tcpiphdr) - sizeof(struct tcphdr) - |
| sizeof(struct ip6); |
| ip6 = mtod(m, struct ip6 *); |
| |
| ip6->ip_pl = tcpiph_save.ti_len; |
| ip6->ip_dst = tcpiph_save.ti_dst6; |
| ip6->ip_src = tcpiph_save.ti_src6; |
| ip6->ip_nh = tcpiph_save.ti_nh6; |
| |
| error = ip6_output(so, m, 0); |
| break; |
| |
| default: |
| g_assert_not_reached(); |
| } |
| |
| 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++; |
| } |
