Logo Search packages:      
Sourcecode: qemu version File versions  Download package

tcp_output.c

/*
 * 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>

/*
 * Since this is only used in "stats socket", we give meaning
 * names instead of the REAL names
 */
const char * const tcpstates[] = {
/*    "CLOSED",       "LISTEN",       "SYN_SENT",     "SYN_RCVD", */
      "REDIRECT", "LISTEN",   "SYN_SENT",     "SYN_RCVD",
      "ESTABLISHED",  "CLOSE_WAIT",   "FIN_WAIT_1",   "CLOSING",
      "LAST_ACK",     "FIN_WAIT_2",   "TIME_WAIT",
};

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,
};


#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(tp)
      register 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 < 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.
       */
      STAT(tcpstat.tcps_didnuttin++);

      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) {
                  u_int16_t mss;

                  opt[0] = TCPOPT_MAXSEG;
                  opt[1] = 4;
                  mss = htons((u_int16_t) tcp_mss(tp, 0));
                  memcpy((caddr_t)(opt + 2), (caddr_t)&mss, sizeof(mss));
                  optlen = 4;

/*                if ((tp->t_flags & TF_REQ_SCALE) &&
 *                    ((flags & TH_ACK) == 0 ||
 *                    (tp->t_flags & TF_RCVD_SCALE))) {
 *                      *((u_int32_t *) (opt + optlen)) = htonl(
 *                            TCPOPT_NOP << 24 |
 *                            TCPOPT_WINDOW << 16 |
 *                            TCPOLEN_WINDOW << 8 |
 *                            tp->request_r_scale);
 *                      optlen += 4;
 *                }
 */
            }
      }

      /*
       * 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_int32_t *lp = (u_int32_t *)(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;
 *    }
 */
      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) {
            if (tp->t_force && len == 1)
                  STAT(tcpstat.tcps_sndprobe++);
            else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
                  STAT(tcpstat.tcps_sndrexmitpack++);
                  STAT(tcpstat.tcps_sndrexmitbyte += len);
            } else {
                  STAT(tcpstat.tcps_sndpack++);
                  STAT(tcpstat.tcps_sndbyte += len);
            }

            m = m_get();
            if (m == NULL) {
/*                error = ENOBUFS; */
                  error = 1;
                  goto out;
            }
            m->m_data += IF_MAXLINKHDR;
            m->m_len = hdrlen;

            /*
             * This will always succeed, since we make sure our mbufs
             * are big enough to hold one MSS packet + header + ... etc.
             */
/*          if (len <= MHLEN - hdrlen - max_linkhdr) { */

                  sbcopy(&so->so_snd, 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;
 *          }
 */
            /*
             * 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)
                  STAT(tcpstat.tcps_sndacks++);
            else if (flags & (TH_SYN|TH_FIN|TH_RST))
                  STAT(tcpstat.tcps_sndctrl++);
            else if (SEQ_GT(tp->snd_up, tp->snd_una))
                  STAT(tcpstat.tcps_sndurg++);
            else
                  STAT(tcpstat.tcps_sndwinup++);

            m = m_get();
            if (m == NULL) {
/*                error = ENOBUFS; */
                  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((u_int16_t) (win>>tp->rcv_scale));

      if (SEQ_GT(tp->snd_up, tp->snd_una)) {
            ti->ti_urp = htons((u_int16_t)(tp->snd_up - ntohl(ti->ti_seq)));
#ifdef notdef
      if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
            ti->ti_urp = htons((u_int16_t)(tp->snd_up - tp->snd_nxt));
#endif
            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_int16_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;
                        STAT(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;

      /*
       * 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;

/* #if BSD >= 43 */
      /* Don't do IP options... */
/*    error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
 *        so->so_options & SO_DONTROUTE, 0);
 */
      error = ip_output(so, m);

/* #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, 0);
 *                return (0);
 *          }
 */
/*          if ((error == EHOSTUNREACH || error == ENETDOWN)
 *              && TCPS_HAVERCVDSYN(tp->t_state)) {
 *                tp->t_softerror = error;
 *                return (0);
 *          }
 */
            return (error);
      }
      STAT(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);
}

void
tcp_setpersist(tp)
      register struct tcpcb *tp;
{
    int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;

/*    if (tp->t_timer[TCPT_REXMT])
 *          panic("tcp_output REXMT");
 */
      /*
       * 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++;
}

Generated by  Doxygen 1.6.0   Back to index