/*
* 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>
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(" --- 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((long)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) >= (long)so->so_snd.sb_cc))
goto send;
if (tp->t_force)
goto send;
if ((len >= (long)(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 > (long)(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++;
}