diff options
Diffstat (limited to 'slirp/src/tcp_input.c')
| -rw-r--r-- | slirp/src/tcp_input.c | 1556 |
1 files changed, 1556 insertions, 0 deletions
diff --git a/slirp/src/tcp_input.c b/slirp/src/tcp_input.c new file mode 100644 index 0000000000..b10477fc57 --- /dev/null +++ b/slirp/src/tcp_input.c @@ -0,0 +1,1556 @@ +/* + * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994 + * 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_input.c 8.5 (Berkeley) 4/10/94 + * tcp_input.c,v 1.10 1994/10/13 18:36:32 wollman 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" +#include "ip_icmp.h" + +#define TCPREXMTTHRESH 3 + +#define TCP_PAWS_IDLE (24 * 24 * 60 * 60 * PR_SLOWHZ) + +/* for modulo comparisons of timestamps */ +#define TSTMP_LT(a,b) ((int)((a)-(b)) < 0) +#define TSTMP_GEQ(a,b) ((int)((a)-(b)) >= 0) + +/* + * Insert segment ti into reassembly queue of tcp with + * control block tp. Return TH_FIN if reassembly now includes + * a segment with FIN. The macro form does the common case inline + * (segment is the next to be received on an established connection, + * and the queue is empty), avoiding linkage into and removal + * from the queue and repetition of various conversions. + * Set DELACK for segments received in order, but ack immediately + * when segments are out of order (so fast retransmit can work). + */ +#define TCP_REASS(tp, ti, m, so, flags) { \ + if ((ti)->ti_seq == (tp)->rcv_nxt && \ + tcpfrag_list_empty(tp) && \ + (tp)->t_state == TCPS_ESTABLISHED) { \ + tp->t_flags |= TF_DELACK; \ + (tp)->rcv_nxt += (ti)->ti_len; \ + flags = (ti)->ti_flags & TH_FIN; \ + if (so->so_emu) { \ + if (tcp_emu((so),(m))) sbappend(so, (m)); \ + } else \ + sbappend((so), (m)); \ + } else { \ + (flags) = tcp_reass((tp), (ti), (m)); \ + tp->t_flags |= TF_ACKNOW; \ + } \ +} + +static void tcp_dooptions(struct tcpcb *tp, uint8_t *cp, int cnt, + struct tcpiphdr *ti); +static void tcp_xmit_timer(register struct tcpcb *tp, int rtt); + +static int +tcp_reass(register struct tcpcb *tp, register struct tcpiphdr *ti, + struct mbuf *m) +{ + register struct tcpiphdr *q; + struct socket *so = tp->t_socket; + int flags; + + /* + * Call with ti==NULL after become established to + * force pre-ESTABLISHED data up to user socket. + */ + if (ti == NULL) + goto present; + + /* + * Find a segment which begins after this one does. + */ + for (q = tcpfrag_list_first(tp); !tcpfrag_list_end(q, tp); + q = tcpiphdr_next(q)) + if (SEQ_GT(q->ti_seq, ti->ti_seq)) + break; + + /* + * If there is a preceding segment, it may provide some of + * our data already. If so, drop the data from the incoming + * segment. If it provides all of our data, drop us. + */ + if (!tcpfrag_list_end(tcpiphdr_prev(q), tp)) { + register int i; + q = tcpiphdr_prev(q); + /* conversion to int (in i) handles seq wraparound */ + i = q->ti_seq + q->ti_len - ti->ti_seq; + if (i > 0) { + if (i >= ti->ti_len) { + m_free(m); + /* + * Try to present any queued data + * at the left window edge to the user. + * This is needed after the 3-WHS + * completes. + */ + goto present; /* ??? */ + } + m_adj(m, i); + ti->ti_len -= i; + ti->ti_seq += i; + } + q = tcpiphdr_next(q); + } + ti->ti_mbuf = m; + + /* + * While we overlap succeeding segments trim them or, + * if they are completely covered, dequeue them. + */ + while (!tcpfrag_list_end(q, tp)) { + register int i = (ti->ti_seq + ti->ti_len) - q->ti_seq; + if (i <= 0) + break; + if (i < q->ti_len) { + q->ti_seq += i; + q->ti_len -= i; + m_adj(q->ti_mbuf, i); + break; + } + q = tcpiphdr_next(q); + m = tcpiphdr_prev(q)->ti_mbuf; + remque(tcpiphdr2qlink(tcpiphdr_prev(q))); + m_free(m); + } + + /* + * Stick new segment in its place. + */ + insque(tcpiphdr2qlink(ti), tcpiphdr2qlink(tcpiphdr_prev(q))); + +present: + /* + * Present data to user, advancing rcv_nxt through + * completed sequence space. + */ + if (!TCPS_HAVEESTABLISHED(tp->t_state)) + return (0); + ti = tcpfrag_list_first(tp); + if (tcpfrag_list_end(ti, tp) || ti->ti_seq != tp->rcv_nxt) + return (0); + if (tp->t_state == TCPS_SYN_RECEIVED && ti->ti_len) + return (0); + do { + tp->rcv_nxt += ti->ti_len; + flags = ti->ti_flags & TH_FIN; + remque(tcpiphdr2qlink(ti)); + m = ti->ti_mbuf; + ti = tcpiphdr_next(ti); + if (so->so_state & SS_FCANTSENDMORE) + m_free(m); + else { + if (so->so_emu) { + if (tcp_emu(so,m)) sbappend(so, m); + } else + sbappend(so, m); + } + } while (ti != (struct tcpiphdr *)tp && ti->ti_seq == tp->rcv_nxt); + return (flags); +} + +/* + * TCP input routine, follows pages 65-76 of the + * protocol specification dated September, 1981 very closely. + */ +void +tcp_input(struct mbuf *m, int iphlen, struct socket *inso, unsigned short af) +{ + struct ip save_ip, *ip; + struct ip6 save_ip6, *ip6; + register struct tcpiphdr *ti; + char *optp = NULL; + int optlen = 0; + int len, tlen, off; + register struct tcpcb *tp = NULL; + register int tiflags; + struct socket *so = NULL; + int todrop, acked, ourfinisacked, needoutput = 0; + int iss = 0; + uint32_t tiwin; + int ret; + struct sockaddr_storage lhost, fhost; + struct sockaddr_in *lhost4, *fhost4; + struct sockaddr_in6 *lhost6, *fhost6; + struct gfwd_list *ex_ptr; + Slirp *slirp; + + DEBUG_CALL("tcp_input"); + DEBUG_ARG("m = %p iphlen = %2d inso = %p", + m, iphlen, inso); + + /* + * If called with m == 0, then we're continuing the connect + */ + if (m == NULL) { + so = inso; + slirp = so->slirp; + + /* Re-set a few variables */ + tp = sototcpcb(so); + m = so->so_m; + so->so_m = NULL; + ti = so->so_ti; + tiwin = ti->ti_win; + tiflags = ti->ti_flags; + + goto cont_conn; + } + slirp = m->slirp; + + ip = mtod(m, struct ip *); + ip6 = mtod(m, struct ip6 *); + + switch (af) { + case AF_INET: + if (iphlen > sizeof(struct ip)) { + ip_stripoptions(m, (struct mbuf *)0); + iphlen = sizeof(struct ip); + } + /* XXX Check if too short */ + + + /* + * Save a copy of the IP header in case we want restore it + * for sending an ICMP error message in response. + */ + save_ip = *ip; + save_ip.ip_len += iphlen; + + /* + * Get IP and TCP header together in first mbuf. + * Note: IP leaves IP header in first mbuf. + */ + m->m_data -= sizeof(struct tcpiphdr) - sizeof(struct ip) + - sizeof(struct tcphdr); + m->m_len += sizeof(struct tcpiphdr) - sizeof(struct ip) + - sizeof(struct tcphdr); + ti = mtod(m, struct tcpiphdr *); + + /* + * Checksum extended TCP header and data. + */ + tlen = ip->ip_len; + tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = NULL; + memset(&ti->ih_mbuf, 0 , sizeof(struct mbuf_ptr)); + memset(&ti->ti, 0, sizeof(ti->ti)); + ti->ti_x0 = 0; + ti->ti_src = save_ip.ip_src; + ti->ti_dst = save_ip.ip_dst; + ti->ti_pr = save_ip.ip_p; + ti->ti_len = htons((uint16_t)tlen); + break; + + case AF_INET6: + /* + * Save a copy of the IP header in case we want restore it + * for sending an ICMP error message in response. + */ + save_ip6 = *ip6; + /* + * Get IP and TCP header together in first mbuf. + * Note: IP leaves IP header in first mbuf. + */ + m->m_data -= sizeof(struct tcpiphdr) - (sizeof(struct ip6) + + sizeof(struct tcphdr)); + m->m_len += sizeof(struct tcpiphdr) - (sizeof(struct ip6) + + sizeof(struct tcphdr)); + ti = mtod(m, struct tcpiphdr *); + + tlen = ip6->ip_pl; + tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = NULL; + memset(&ti->ih_mbuf, 0 , sizeof(struct mbuf_ptr)); + memset(&ti->ti, 0, sizeof(ti->ti)); + ti->ti_x0 = 0; + ti->ti_src6 = save_ip6.ip_src; + ti->ti_dst6 = save_ip6.ip_dst; + ti->ti_nh6 = save_ip6.ip_nh; + ti->ti_len = htons((uint16_t)tlen); + break; + + default: + g_assert_not_reached(); + } + + len = ((sizeof(struct tcpiphdr) - sizeof(struct tcphdr)) + tlen); + if (cksum(m, len)) { + goto drop; + } + + /* + * Check that TCP offset makes sense, + * pull out TCP options and adjust length. XXX + */ + off = ti->ti_off << 2; + if (off < sizeof (struct tcphdr) || off > tlen) { + goto drop; + } + tlen -= off; + ti->ti_len = tlen; + if (off > sizeof (struct tcphdr)) { + optlen = off - sizeof (struct tcphdr); + optp = mtod(m, char *) + sizeof (struct tcpiphdr); + } + tiflags = ti->ti_flags; + + /* + * Convert TCP protocol specific fields to host format. + */ + NTOHL(ti->ti_seq); + NTOHL(ti->ti_ack); + NTOHS(ti->ti_win); + NTOHS(ti->ti_urp); + + /* + * Drop TCP, IP headers and TCP options. + */ + m->m_data += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr); + m->m_len -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr); + + /* + * Locate pcb for segment. + */ +findso: + lhost.ss_family = af; + fhost.ss_family = af; + switch (af) { + case AF_INET: + lhost4 = (struct sockaddr_in *) &lhost; + lhost4->sin_addr = ti->ti_src; + lhost4->sin_port = ti->ti_sport; + fhost4 = (struct sockaddr_in *) &fhost; + fhost4->sin_addr = ti->ti_dst; + fhost4->sin_port = ti->ti_dport; + break; + case AF_INET6: + lhost6 = (struct sockaddr_in6 *) &lhost; + lhost6->sin6_addr = ti->ti_src6; + lhost6->sin6_port = ti->ti_sport; + fhost6 = (struct sockaddr_in6 *) &fhost; + fhost6->sin6_addr = ti->ti_dst6; + fhost6->sin6_port = ti->ti_dport; + break; + default: + g_assert_not_reached(); + } + + so = solookup(&slirp->tcp_last_so, &slirp->tcb, &lhost, &fhost); + + /* + * If the state is CLOSED (i.e., TCB does not exist) then + * all data in the incoming segment is discarded. + * If the TCB exists but is in CLOSED state, it is embryonic, + * but should either do a listen or a connect soon. + * + * state == CLOSED means we've done socreate() but haven't + * attached it to a protocol yet... + * + * XXX If a TCB does not exist, and the TH_SYN flag is + * the only flag set, then create a session, mark it + * as if it was LISTENING, and continue... + */ + if (so == NULL) { + /* TODO: IPv6 */ + if (slirp->restricted) { + /* Any hostfwds will have an existing socket, so we only get here + * for non-hostfwd connections. These should be dropped, unless it + * happens to be a guestfwd. + */ + for (ex_ptr = slirp->guestfwd_list; ex_ptr; ex_ptr = ex_ptr->ex_next) { + if (ex_ptr->ex_fport == ti->ti_dport && + ti->ti_dst.s_addr == ex_ptr->ex_addr.s_addr) { + break; + } + } + if (!ex_ptr) { + goto dropwithreset; + } + } + + if ((tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) != TH_SYN) + goto dropwithreset; + + so = socreate(slirp); + if (tcp_attach(so) < 0) { + g_free(so); /* Not sofree (if it failed, it's not insqued) */ + goto dropwithreset; + } + + sbreserve(&so->so_snd, TCP_SNDSPACE); + sbreserve(&so->so_rcv, TCP_RCVSPACE); + + so->lhost.ss = lhost; + so->fhost.ss = fhost; + + so->so_iptos = tcp_tos(so); + if (so->so_iptos == 0) { + switch (af) { + case AF_INET: + so->so_iptos = ((struct ip *)ti)->ip_tos; + break; + case AF_INET6: + break; + default: + g_assert_not_reached(); + } + } + + tp = sototcpcb(so); + tp->t_state = TCPS_LISTEN; + } + + /* + * If this is a still-connecting socket, this probably + * a retransmit of the SYN. Whether it's a retransmit SYN + * or something else, we nuke it. + */ + if (so->so_state & SS_ISFCONNECTING) + goto drop; + + tp = sototcpcb(so); + + /* XXX Should never fail */ + if (tp == NULL) + goto dropwithreset; + if (tp->t_state == TCPS_CLOSED) + goto drop; + + tiwin = ti->ti_win; + + /* + * Segment received on connection. + * Reset idle time and keep-alive timer. + */ + tp->t_idle = 0; + if (slirp_do_keepalive) + tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL; + else + tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE; + + /* + * Process options if not in LISTEN state, + * else do it below (after getting remote address). + */ + if (optp && tp->t_state != TCPS_LISTEN) + tcp_dooptions(tp, (uint8_t *)optp, optlen, ti); + + /* + * Header prediction: check for the two common cases + * of a uni-directional data xfer. If the packet has + * no control flags, is in-sequence, the window didn't + * change and we're not retransmitting, it's a + * candidate. If the length is zero and the ack moved + * forward, we're the sender side of the xfer. Just + * free the data acked & wake any higher level process + * that was blocked waiting for space. If the length + * is non-zero and the ack didn't move, we're the + * receiver side. If we're getting packets in-order + * (the reassembly queue is empty), add the data to + * the socket buffer and note that we need a delayed ack. + * + * XXX Some of these tests are not needed + * eg: the tiwin == tp->snd_wnd prevents many more + * predictions.. with no *real* advantage.. + */ + if (tp->t_state == TCPS_ESTABLISHED && + (tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK && + ti->ti_seq == tp->rcv_nxt && + tiwin && tiwin == tp->snd_wnd && + tp->snd_nxt == tp->snd_max) { + if (ti->ti_len == 0) { + if (SEQ_GT(ti->ti_ack, tp->snd_una) && + SEQ_LEQ(ti->ti_ack, tp->snd_max) && + tp->snd_cwnd >= tp->snd_wnd) { + /* + * this is a pure ack for outstanding data. + */ + if (tp->t_rtt && + SEQ_GT(ti->ti_ack, tp->t_rtseq)) + tcp_xmit_timer(tp, tp->t_rtt); + acked = ti->ti_ack - tp->snd_una; + sodrop(so, acked); + tp->snd_una = ti->ti_ack; + m_free(m); + + /* + * If all outstanding data are acked, stop + * retransmit timer, otherwise restart timer + * using current (possibly backed-off) value. + * If process is waiting for space, + * wakeup/selwakeup/signal. If data + * are ready to send, let tcp_output + * decide between more output or persist. + */ + if (tp->snd_una == tp->snd_max) + tp->t_timer[TCPT_REXMT] = 0; + else if (tp->t_timer[TCPT_PERSIST] == 0) + tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; + + /* + * This is called because sowwakeup might have + * put data into so_snd. Since we don't so sowwakeup, + * we don't need this.. XXX??? + */ + if (so->so_snd.sb_cc) + (void) tcp_output(tp); + + return; + } + } else if (ti->ti_ack == tp->snd_una && + tcpfrag_list_empty(tp) && + ti->ti_len <= sbspace(&so->so_rcv)) { + /* + * this is a pure, in-sequence data packet + * with nothing on the reassembly queue and + * we have enough buffer space to take it. + */ + tp->rcv_nxt += ti->ti_len; + /* + * Add data to socket buffer. + */ + if (so->so_emu) { + if (tcp_emu(so,m)) sbappend(so, m); + } else + sbappend(so, m); + + /* + * If this is a short packet, then ACK now - with Nagel + * congestion avoidance sender won't send more until + * he gets an ACK. + * + * It is better to not delay acks at all to maximize + * TCP throughput. See RFC 2581. + */ + tp->t_flags |= TF_ACKNOW; + tcp_output(tp); + return; + } + } /* header prediction */ + /* + * Calculate amount of space in receive window, + * and then do TCP input processing. + * Receive window is amount of space in rcv queue, + * but not less than advertised window. + */ + { int win; + win = sbspace(&so->so_rcv); + if (win < 0) + win = 0; + tp->rcv_wnd = MAX(win, (int)(tp->rcv_adv - tp->rcv_nxt)); + } + + switch (tp->t_state) { + + /* + * If the state is LISTEN then ignore segment if it contains an RST. + * If the segment contains an ACK then it is bad and send a RST. + * If it does not contain a SYN then it is not interesting; drop it. + * Don't bother responding if the destination was a broadcast. + * Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial + * tp->iss, and send a segment: + * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> + * Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss. + * Fill in remote peer address fields if not previously specified. + * Enter SYN_RECEIVED state, and process any other fields of this + * segment in this state. + */ + case TCPS_LISTEN: { + + if (tiflags & TH_RST) + goto drop; + if (tiflags & TH_ACK) + goto dropwithreset; + if ((tiflags & TH_SYN) == 0) + goto drop; + + /* + * This has way too many gotos... + * But a bit of spaghetti code never hurt anybody :) + */ + + /* + * If this is destined for the control address, then flag to + * tcp_ctl once connected, otherwise connect + */ + /* TODO: IPv6 */ + if (af == AF_INET && + (so->so_faddr.s_addr & slirp->vnetwork_mask.s_addr) == + slirp->vnetwork_addr.s_addr) { + if (so->so_faddr.s_addr != slirp->vhost_addr.s_addr && + so->so_faddr.s_addr != slirp->vnameserver_addr.s_addr) { + /* May be an add exec */ + for (ex_ptr = slirp->guestfwd_list; ex_ptr; + ex_ptr = ex_ptr->ex_next) { + if(ex_ptr->ex_fport == so->so_fport && + so->so_faddr.s_addr == ex_ptr->ex_addr.s_addr) { + so->so_state |= SS_CTL; + break; + } + } + if (so->so_state & SS_CTL) { + goto cont_input; + } + } + /* CTL_ALIAS: Do nothing, tcp_fconnect will be called on it */ + } + + if (so->so_emu & EMU_NOCONNECT) { + so->so_emu &= ~EMU_NOCONNECT; + goto cont_input; + } + + if ((tcp_fconnect(so, so->so_ffamily) == -1) && + (errno != EAGAIN) && + (errno != EINPROGRESS) && (errno != EWOULDBLOCK) + ) { + uint8_t code; + DEBUG_MISC(" tcp fconnect errno = %d-%s", errno, strerror(errno)); + if(errno == ECONNREFUSED) { + /* ACK the SYN, send RST to refuse the connection */ + tcp_respond(tp, ti, m, ti->ti_seq + 1, (tcp_seq) 0, + TH_RST | TH_ACK, af); + } else { + switch (af) { + case AF_INET: + code = ICMP_UNREACH_NET; + if (errno == EHOSTUNREACH) { + code = ICMP_UNREACH_HOST; + } + break; + case AF_INET6: + code = ICMP6_UNREACH_NO_ROUTE; + if (errno == EHOSTUNREACH) { + code = ICMP6_UNREACH_ADDRESS; + } + break; + default: + g_assert_not_reached(); + } + HTONL(ti->ti_seq); /* restore tcp header */ + HTONL(ti->ti_ack); + HTONS(ti->ti_win); + HTONS(ti->ti_urp); + m->m_data -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr); + m->m_len += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr); + switch (af) { + case AF_INET: + m->m_data += sizeof(struct tcpiphdr) - sizeof(struct ip) + - sizeof(struct tcphdr); + m->m_len -= sizeof(struct tcpiphdr) - sizeof(struct ip) + - sizeof(struct tcphdr); + *ip = save_ip; + icmp_send_error(m, ICMP_UNREACH, code, 0, strerror(errno)); + break; + case AF_INET6: + m->m_data += sizeof(struct tcpiphdr) - (sizeof(struct ip6) + + sizeof(struct tcphdr)); + m->m_len -= sizeof(struct tcpiphdr) - (sizeof(struct ip6) + + sizeof(struct tcphdr)); + *ip6 = save_ip6; + icmp6_send_error(m, ICMP6_UNREACH, code); + break; + default: + g_assert_not_reached(); + } + } + tcp_close(tp); + m_free(m); + } else { + /* + * Haven't connected yet, save the current mbuf + * and ti, and return + * XXX Some OS's don't tell us whether the connect() + * succeeded or not. So we must time it out. + */ + so->so_m = m; + so->so_ti = ti; + tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT; + tp->t_state = TCPS_SYN_RECEIVED; + /* + * Initialize receive sequence numbers now so that we can send a + * valid RST if the remote end rejects our connection. + */ + tp->irs = ti->ti_seq; + tcp_rcvseqinit(tp); + tcp_template(tp); + } + return; + + cont_conn: + /* m==NULL + * Check if the connect succeeded + */ + if (so->so_state & SS_NOFDREF) { + tp = tcp_close(tp); + goto dropwithreset; + } + cont_input: + tcp_template(tp); + + if (optp) + tcp_dooptions(tp, (uint8_t *)optp, optlen, ti); + + if (iss) + tp->iss = iss; + else + tp->iss = slirp->tcp_iss; + slirp->tcp_iss += TCP_ISSINCR/2; + tp->irs = ti->ti_seq; + tcp_sendseqinit(tp); + tcp_rcvseqinit(tp); + tp->t_flags |= TF_ACKNOW; + tp->t_state = TCPS_SYN_RECEIVED; + tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT; + goto trimthenstep6; + } /* case TCPS_LISTEN */ + + /* + * If the state is SYN_SENT: + * if seg contains an ACK, but not for our SYN, drop the input. + * if seg contains a RST, then drop the connection. + * if seg does not contain SYN, then drop it. + * Otherwise this is an acceptable SYN segment + * initialize tp->rcv_nxt and tp->irs + * if seg contains ack then advance tp->snd_una + * if SYN has been acked change to ESTABLISHED else SYN_RCVD state + * arrange for segment to be acked (eventually) + * continue processing rest of data/controls, beginning with URG + */ + case TCPS_SYN_SENT: + if ((tiflags & TH_ACK) && + (SEQ_LEQ(ti->ti_ack, tp->iss) || + SEQ_GT(ti->ti_ack, tp->snd_max))) + goto dropwithreset; + + if (tiflags & TH_RST) { + if (tiflags & TH_ACK) { + tcp_drop(tp, 0); /* XXX Check t_softerror! */ + } + goto drop; + } + + if ((tiflags & TH_SYN) == 0) + goto drop; + if (tiflags & TH_ACK) { + tp->snd_una = ti->ti_ack; + if (SEQ_LT(tp->snd_nxt, tp->snd_una)) + tp->snd_nxt = tp->snd_una; + } + + tp->t_timer[TCPT_REXMT] = 0; + tp->irs = ti->ti_seq; + tcp_rcvseqinit(tp); + tp->t_flags |= TF_ACKNOW; + if (tiflags & TH_ACK && SEQ_GT(tp->snd_una, tp->iss)) { + soisfconnected(so); + tp->t_state = TCPS_ESTABLISHED; + + (void) tcp_reass(tp, (struct tcpiphdr *)0, + (struct mbuf *)0); + /* + * if we didn't have to retransmit the SYN, + * use its rtt as our initial srtt & rtt var. + */ + if (tp->t_rtt) + tcp_xmit_timer(tp, tp->t_rtt); + } else + tp->t_state = TCPS_SYN_RECEIVED; + +trimthenstep6: + /* + * Advance ti->ti_seq to correspond to first data byte. + * If data, trim to stay within window, + * dropping FIN if necessary. + */ + ti->ti_seq++; + if (ti->ti_len > tp->rcv_wnd) { + todrop = ti->ti_len - tp->rcv_wnd; + m_adj(m, -todrop); + ti->ti_len = tp->rcv_wnd; + tiflags &= ~TH_FIN; + } + tp->snd_wl1 = ti->ti_seq - 1; + tp->rcv_up = ti->ti_seq; + goto step6; + } /* switch tp->t_state */ + /* + * States other than LISTEN or SYN_SENT. + * Check that at least some bytes of segment are within + * receive window. If segment begins before rcv_nxt, + * drop leading data (and SYN); if nothing left, just ack. + */ + todrop = tp->rcv_nxt - ti->ti_seq; + if (todrop > 0) { + if (tiflags & TH_SYN) { + tiflags &= ~TH_SYN; + ti->ti_seq++; + if (ti->ti_urp > 1) + ti->ti_urp--; + else + tiflags &= ~TH_URG; + todrop--; + } + /* + * Following if statement from Stevens, vol. 2, p. 960. + */ + if (todrop > ti->ti_len + || (todrop == ti->ti_len && (tiflags & TH_FIN) == 0)) { + /* + * Any valid FIN must be to the left of the window. + * At this point the FIN must be a duplicate or out + * of sequence; drop it. + */ + tiflags &= ~TH_FIN; + + /* + * Send an ACK to resynchronize and drop any data. + * But keep on processing for RST or ACK. + */ + tp->t_flags |= TF_ACKNOW; + todrop = ti->ti_len; + } + m_adj(m, todrop); + ti->ti_seq += todrop; + ti->ti_len -= todrop; + if (ti->ti_urp > todrop) + ti->ti_urp -= todrop; + else { + tiflags &= ~TH_URG; + ti->ti_urp = 0; + } + } + /* + * If new data are received on a connection after the + * user processes are gone, then RST the other end. + */ + if ((so->so_state & SS_NOFDREF) && + tp->t_state > TCPS_CLOSE_WAIT && ti->ti_len) { + tp = tcp_close(tp); + goto dropwithreset; + } + + /* + * If segment ends after window, drop trailing data + * (and PUSH and FIN); if nothing left, just ACK. + */ + todrop = (ti->ti_seq+ti->ti_len) - (tp->rcv_nxt+tp->rcv_wnd); + if (todrop > 0) { + if (todrop >= ti->ti_len) { + /* + * If a new connection request is received + * while in TIME_WAIT, drop the old connection + * and start over if the sequence numbers + * are above the previous ones. + */ + if (tiflags & TH_SYN && + tp->t_state == TCPS_TIME_WAIT && + SEQ_GT(ti->ti_seq, tp->rcv_nxt)) { + iss = tp->rcv_nxt + TCP_ISSINCR; + tp = tcp_close(tp); + goto findso; + } + /* + * If window is closed can only take segments at + * window edge, and have to drop data and PUSH from + * incoming segments. Continue processing, but + * remember to ack. Otherwise, drop segment + * and ack. + */ + if (tp->rcv_wnd == 0 && ti->ti_seq == tp->rcv_nxt) { + tp->t_flags |= TF_ACKNOW; + } else { + goto dropafterack; + } + } + m_adj(m, -todrop); + ti->ti_len -= todrop; + tiflags &= ~(TH_PUSH|TH_FIN); + } + + /* + * If the RST bit is set examine the state: + * SYN_RECEIVED STATE: + * If passive open, return to LISTEN state. + * If active open, inform user that connection was refused. + * ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES: + * Inform user that connection was reset, and close tcb. + * CLOSING, LAST_ACK, TIME_WAIT STATES + * Close the tcb. + */ + if (tiflags&TH_RST) switch (tp->t_state) { + + case TCPS_SYN_RECEIVED: + case TCPS_ESTABLISHED: + case TCPS_FIN_WAIT_1: + case TCPS_FIN_WAIT_2: + case TCPS_CLOSE_WAIT: + tp->t_state = TCPS_CLOSED; + tcp_close(tp); + goto drop; + + case TCPS_CLOSING: + case TCPS_LAST_ACK: + case TCPS_TIME_WAIT: + tcp_close(tp); + goto drop; + } + + /* + * If a SYN is in the window, then this is an + * error and we send an RST and drop the connection. + */ + if (tiflags & TH_SYN) { + tp = tcp_drop(tp,0); + goto dropwithreset; + } + + /* + * If the ACK bit is off we drop the segment and return. + */ + if ((tiflags & TH_ACK) == 0) goto drop; + + /* + * Ack processing. + */ + switch (tp->t_state) { + /* + * In SYN_RECEIVED state if the ack ACKs our SYN then enter + * ESTABLISHED state and continue processing, otherwise + * send an RST. una<=ack<=max + */ + case TCPS_SYN_RECEIVED: + + if (SEQ_GT(tp->snd_una, ti->ti_ack) || + SEQ_GT(ti->ti_ack, tp->snd_max)) + goto dropwithreset; + tp->t_state = TCPS_ESTABLISHED; + /* + * The sent SYN is ack'ed with our sequence number +1 + * The first data byte already in the buffer will get + * lost if no correction is made. This is only needed for + * SS_CTL since the buffer is empty otherwise. + * tp->snd_una++; or: + */ + tp->snd_una=ti->ti_ack; + if (so->so_state & SS_CTL) { + /* So tcp_ctl reports the right state */ + ret = tcp_ctl(so); + if (ret == 1) { + soisfconnected(so); + so->so_state &= ~SS_CTL; /* success XXX */ + } else if (ret == 2) { + so->so_state &= SS_PERSISTENT_MASK; + so->so_state |= SS_NOFDREF; /* CTL_CMD */ + } else { + needoutput = 1; + tp->t_state = TCPS_FIN_WAIT_1; + } + } else { + soisfconnected(so); + } + + (void) tcp_reass(tp, (struct tcpiphdr *)0, (struct mbuf *)0); + tp->snd_wl1 = ti->ti_seq - 1; + /* Avoid ack processing; snd_una==ti_ack => dup ack */ + goto synrx_to_est; + /* fall into ... */ + + /* + * In ESTABLISHED state: drop duplicate ACKs; ACK out of range + * ACKs. If the ack is in the range + * tp->snd_una < ti->ti_ack <= tp->snd_max + * then advance tp->snd_una to ti->ti_ack and drop + * data from the retransmission queue. If this ACK reflects + * more up to date window information we update our window information. + */ + case TCPS_ESTABLISHED: + case TCPS_FIN_WAIT_1: + case TCPS_FIN_WAIT_2: + case TCPS_CLOSE_WAIT: + case TCPS_CLOSING: + case TCPS_LAST_ACK: + case TCPS_TIME_WAIT: + + if (SEQ_LEQ(ti->ti_ack, tp->snd_una)) { + if (ti->ti_len == 0 && tiwin == tp->snd_wnd) { + DEBUG_MISC(" dup ack m = %p so = %p", m, so); + /* + * If we have outstanding data (other than + * a window probe), this is a completely + * duplicate ack (ie, window info didn't + * change), the ack is the biggest we've + * seen and we've seen exactly our rexmt + * threshold of them, assume a packet + * has been dropped and retransmit it. + * Kludge snd_nxt & the congestion + * window so we send only this one + * packet. + * + * We know we're losing at the current + * window size so do congestion avoidance + * (set ssthresh to half the current window + * and pull our congestion window back to + * the new ssthresh). + * + * Dup acks mean that packets have left the + * network (they're now cached at the receiver) + * so bump cwnd by the amount in the receiver + * to keep a constant cwnd packets in the + * network. + */ + if (tp->t_timer[TCPT_REXMT] == 0 || + ti->ti_ack != tp->snd_una) + tp->t_dupacks = 0; + else if (++tp->t_dupacks == TCPREXMTTHRESH) { + tcp_seq onxt = tp->snd_nxt; + unsigned win = + MIN(tp->snd_wnd, tp->snd_cwnd) / + 2 / tp->t_maxseg; + + if (win < 2) + win = 2; + tp->snd_ssthresh = win * tp->t_maxseg; + tp->t_timer[TCPT_REXMT] = 0; + tp->t_rtt = 0; + tp->snd_nxt = ti->ti_ack; + tp->snd_cwnd = tp->t_maxseg; + (void) tcp_output(tp); + tp->snd_cwnd = tp->snd_ssthresh + + tp->t_maxseg * tp->t_dupacks; + if (SEQ_GT(onxt, tp->snd_nxt)) + tp->snd_nxt = onxt; + goto drop; + } else if (tp->t_dupacks > TCPREXMTTHRESH) { + tp->snd_cwnd += tp->t_maxseg; + (void) tcp_output(tp); + goto drop; + } + } else + tp->t_dupacks = 0; + break; + } + synrx_to_est: + /* + * If the congestion window was inflated to account + * for the other side's cached packets, retract it. + */ + if (tp->t_dupacks > TCPREXMTTHRESH && + tp->snd_cwnd > tp->snd_ssthresh) + tp->snd_cwnd = tp->snd_ssthresh; + tp->t_dupacks = 0; + if (SEQ_GT(ti->ti_ack, tp->snd_max)) { + goto dropafterack; + } + acked = ti->ti_ack - tp->snd_una; + + /* + * If transmit timer is running and timed sequence + * number was acked, update smoothed round trip time. + * Since we now have an rtt measurement, cancel the + * timer backoff (cf., Phil Karn's retransmit alg.). + * Recompute the initial retransmit timer. + */ + if (tp->t_rtt && SEQ_GT(ti->ti_ack, tp->t_rtseq)) + tcp_xmit_timer(tp,tp->t_rtt); + + /* + * If all outstanding data is acked, stop retransmit + * timer and remember to restart (more output or persist). + * If there is more data to be acked, restart retransmit + * timer, using current (possibly backed-off) value. + */ + if (ti->ti_ack == tp->snd_max) { + tp->t_timer[TCPT_REXMT] = 0; + needoutput = 1; + } else if (tp->t_timer[TCPT_PERSIST] == 0) + tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; + /* + * When new data is acked, open the congestion window. + * If the window gives us less than ssthresh packets + * in flight, open exponentially (maxseg per packet). + * Otherwise open linearly: maxseg per window + * (maxseg^2 / cwnd per packet). + */ + { + register unsigned cw = tp->snd_cwnd; + register unsigned incr = tp->t_maxseg; + + if (cw > tp->snd_ssthresh) + incr = incr * incr / cw; + tp->snd_cwnd = MIN(cw + incr, TCP_MAXWIN << tp->snd_scale); + } + if (acked > so->so_snd.sb_cc) { + tp->snd_wnd -= so->so_snd.sb_cc; + sodrop(so, (int)so->so_snd.sb_cc); + ourfinisacked = 1; + } else { + sodrop(so, acked); + tp->snd_wnd -= acked; + ourfinisacked = 0; + } + tp->snd_una = ti->ti_ack; + if (SEQ_LT(tp->snd_nxt, tp->snd_una)) + tp->snd_nxt = tp->snd_una; + + switch (tp->t_state) { + + /* + * In FIN_WAIT_1 STATE in addition to the processing + * for the ESTABLISHED state if our FIN is now acknowledged + * then enter FIN_WAIT_2. + */ + case TCPS_FIN_WAIT_1: + if (ourfinisacked) { + /* + * If we can't receive any more + * data, then closing user can proceed. + * Starting the timer is contrary to the + * specification, but if we don't get a FIN + * we'll hang forever. + */ + if (so->so_state & SS_FCANTRCVMORE) { + tp->t_timer[TCPT_2MSL] = TCP_MAXIDLE; + } + tp->t_state = TCPS_FIN_WAIT_2; + } + break; + + /* + * In CLOSING STATE in addition to the processing for + * the ESTABLISHED state if the ACK acknowledges our FIN + * then enter the TIME-WAIT state, otherwise ignore + * the segment. + */ + case TCPS_CLOSING: + if (ourfinisacked) { + tp->t_state = TCPS_TIME_WAIT; + tcp_canceltimers(tp); + tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL; + } + break; + + /* + * In LAST_ACK, we may still be waiting for data to drain + * and/or to be acked, as well as for the ack of our FIN. + * If our FIN is now acknowledged, delete the TCB, + * enter the closed state and return. + */ + case TCPS_LAST_ACK: + if (ourfinisacked) { + tcp_close(tp); + goto drop; + } + break; + + /* + * In TIME_WAIT state the only thing that should arrive + * is a retransmission of the remote FIN. Acknowledge + * it and restart the finack timer. + */ + case TCPS_TIME_WAIT: + tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL; + goto dropafterack; + } + } /* switch(tp->t_state) */ + +step6: + /* + * Update window information. + * Don't look at window if no ACK: TAC's send garbage on first SYN. + */ + if ((tiflags & TH_ACK) && + (SEQ_LT(tp->snd_wl1, ti->ti_seq) || + (tp->snd_wl1 == ti->ti_seq && (SEQ_LT(tp->snd_wl2, ti->ti_ack) || + (tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd))))) { + tp->snd_wnd = tiwin; + tp->snd_wl1 = ti->ti_seq; + tp->snd_wl2 = ti->ti_ack; + if (tp->snd_wnd > tp->max_sndwnd) + tp->max_sndwnd = tp->snd_wnd; + needoutput = 1; + } + + /* + * Process segments with URG. + */ + if ((tiflags & TH_URG) && ti->ti_urp && + TCPS_HAVERCVDFIN(tp->t_state) == 0) { + /* + * This is a kludge, but if we receive and accept + * random urgent pointers, we'll crash in + * soreceive. It's hard to imagine someone + * actually wanting to send this much urgent data. + */ + if (ti->ti_urp + so->so_rcv.sb_cc > so->so_rcv.sb_datalen) { + ti->ti_urp = 0; + tiflags &= ~TH_URG; + goto dodata; + } + /* + * If this segment advances the known urgent pointer, + * then mark the data stream. This should not happen + * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since + * a FIN has been received from the remote side. + * In these states we ignore the URG. + * + * According to RFC961 (Assigned Protocols), + * the urgent pointer points to the last octet + * of urgent data. We continue, however, + * to consider it to indicate the first octet + * of data past the urgent section as the original + * spec states (in one of two places). + */ + if (SEQ_GT(ti->ti_seq+ti->ti_urp, tp->rcv_up)) { + tp->rcv_up = ti->ti_seq + ti->ti_urp; + so->so_urgc = so->so_rcv.sb_cc + + (tp->rcv_up - tp->rcv_nxt); /* -1; */ + tp->rcv_up = ti->ti_seq + ti->ti_urp; + + } + } else + /* + * If no out of band data is expected, + * pull receive urgent pointer along + * with the receive window. + */ + if (SEQ_GT(tp->rcv_nxt, tp->rcv_up)) + tp->rcv_up = tp->rcv_nxt; +dodata: + + /* + * If this is a small packet, then ACK now - with Nagel + * congestion avoidance sender won't send more until + * he gets an ACK. + */ + if (ti->ti_len && (unsigned)ti->ti_len <= 5 && + ((struct tcpiphdr_2 *)ti)->first_char == (char)27) { + tp->t_flags |= TF_ACKNOW; + } + + /* + * Process the segment text, merging it into the TCP sequencing queue, + * and arranging for acknowledgment of receipt if necessary. + * This process logically involves adjusting tp->rcv_wnd as data + * is presented to the user (this happens in tcp_usrreq.c, + * case PRU_RCVD). If a FIN has already been received on this + * connection then we just ignore the text. + */ + if ((ti->ti_len || (tiflags&TH_FIN)) && + TCPS_HAVERCVDFIN(tp->t_state) == 0) { + TCP_REASS(tp, ti, m, so, tiflags); + } else { + m_free(m); + tiflags &= ~TH_FIN; + } + + /* + * If FIN is received ACK the FIN and let the user know + * that the connection is closing. + */ + if (tiflags & TH_FIN) { + if (TCPS_HAVERCVDFIN(tp->t_state) == 0) { + /* + * If we receive a FIN we can't send more data, + * set it SS_FDRAIN + * Shutdown the socket if there is no rx data in the + * buffer. + * soread() is called on completion of shutdown() and + * will got to TCPS_LAST_ACK, and use tcp_output() + * to send the FIN. + */ + sofwdrain(so); + + tp->t_flags |= TF_ACKNOW; + tp->rcv_nxt++; + } + switch (tp->t_state) { + + /* + * In SYN_RECEIVED and ESTABLISHED STATES + * enter the CLOSE_WAIT state. + */ + case TCPS_SYN_RECEIVED: + case TCPS_ESTABLISHED: + if(so->so_emu == EMU_CTL) /* no shutdown on socket */ + tp->t_state = TCPS_LAST_ACK; + else + tp->t_state = TCPS_CLOSE_WAIT; + break; + + /* + * If still in FIN_WAIT_1 STATE FIN has not been acked so + * enter the CLOSING state. + */ + case TCPS_FIN_WAIT_1: + tp->t_state = TCPS_CLOSING; + break; + + /* + * In FIN_WAIT_2 state enter the TIME_WAIT state, + * starting the time-wait timer, turning off the other + * standard timers. + */ + case TCPS_FIN_WAIT_2: + tp->t_state = TCPS_TIME_WAIT; + tcp_canceltimers(tp); + tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL; + break; + + /* + * In TIME_WAIT state restart the 2 MSL time_wait timer. + */ + case TCPS_TIME_WAIT: + tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL; + break; + } + } + + /* + * Return any desired output. + */ + if (needoutput || (tp->t_flags & TF_ACKNOW)) { + (void) tcp_output(tp); + } + return; + +dropafterack: + /* + * Generate an ACK dropping incoming segment if it occupies + * sequence space, where the ACK reflects our state. + */ + if (tiflags & TH_RST) + goto drop; + m_free(m); + tp->t_flags |= TF_ACKNOW; + (void) tcp_output(tp); + return; + +dropwithreset: + /* reuses m if m!=NULL, m_free() unnecessary */ + if (tiflags & TH_ACK) + tcp_respond(tp, ti, m, (tcp_seq)0, ti->ti_ack, TH_RST, af); + else { + if (tiflags & TH_SYN) ti->ti_len++; + tcp_respond(tp, ti, m, ti->ti_seq + ti->ti_len, (tcp_seq) 0, + TH_RST | TH_ACK, af); + } + + return; + +drop: + /* + * Drop space held by incoming segment and return. + */ + m_free(m); +} + +static void +tcp_dooptions(struct tcpcb *tp, uint8_t *cp, int cnt, struct tcpiphdr *ti) +{ + uint16_t mss; + int opt, optlen; + + DEBUG_CALL("tcp_dooptions"); + DEBUG_ARG("tp = %p cnt=%i", tp, cnt); + + for (; cnt > 0; cnt -= optlen, cp += optlen) { + opt = cp[0]; + if (opt == TCPOPT_EOL) + break; + if (opt == TCPOPT_NOP) + optlen = 1; + else { + optlen = cp[1]; + if (optlen <= 0) + break; + } + switch (opt) { + + default: + continue; + + case TCPOPT_MAXSEG: + if (optlen != TCPOLEN_MAXSEG) + continue; + if (!(ti->ti_flags & TH_SYN)) + continue; + memcpy((char *) &mss, (char *) cp + 2, sizeof(mss)); + NTOHS(mss); + (void) tcp_mss(tp, mss); /* sets t_maxseg */ + break; + } + } +} + +/* + * Collect new round-trip time estimate + * and update averages and current timeout. + */ + +static void +tcp_xmit_timer(register struct tcpcb *tp, int rtt) +{ + register short delta; + + DEBUG_CALL("tcp_xmit_timer"); + DEBUG_ARG("tp = %p", tp); + DEBUG_ARG("rtt = %d", rtt); + + if (tp->t_srtt != 0) { + /* + * srtt is stored as fixed point with 3 bits after the + * binary point (i.e., scaled by 8). The following magic + * is equivalent to the smoothing algorithm in rfc793 with + * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed + * point). Adjust rtt to origin 0. + */ + delta = rtt - 1 - (tp->t_srtt >> TCP_RTT_SHIFT); + if ((tp->t_srtt += delta) <= 0) + tp->t_srtt = 1; + /* + * We accumulate a smoothed rtt variance (actually, a + * smoothed mean difference), then set the retransmit + * timer to smoothed rtt + 4 times the smoothed variance. + * rttvar is stored as fixed point with 2 bits after the + * binary point (scaled by 4). The following is + * equivalent to rfc793 smoothing with an alpha of .75 + * (rttvar = rttvar*3/4 + |delta| / 4). This replaces + * rfc793's wired-in beta. + */ + if (delta < 0) + delta = -delta; + delta -= (tp->t_rttvar >> TCP_RTTVAR_SHIFT); + if ((tp->t_rttvar += delta) <= 0) + tp->t_rttvar = 1; + } else { + /* + * No rtt measurement yet - use the unsmoothed rtt. + * Set the variance to half the rtt (so our first + * retransmit happens at 3*rtt). + */ + tp->t_srtt = rtt << TCP_RTT_SHIFT; + tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1); + } + tp->t_rtt = 0; + tp->t_rxtshift = 0; + + /* + * the retransmit should happen at rtt + 4 * rttvar. + * Because of the way we do the smoothing, srtt and rttvar + * will each average +1/2 tick of bias. When we compute + * the retransmit timer, we want 1/2 tick of rounding and + * 1 extra tick because of +-1/2 tick uncertainty in the + * firing of the timer. The bias will give us exactly the + * 1.5 tick we need. But, because the bias is + * statistical, we have to test that we don't drop below + * the minimum feasible timer (which is 2 ticks). + */ + TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp), + (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */ + + /* + * We received an ack for a packet that wasn't retransmitted; + * it is probably safe to discard any error indications we've + * received recently. This isn't quite right, but close enough + * for now (a route might have failed after we sent a segment, + * and the return path might not be symmetrical). + */ + tp->t_softerror = 0; +} + +/* + * Determine a reasonable value for maxseg size. + * If the route is known, check route for mtu. + * If none, use an mss that can be handled on the outgoing + * interface without forcing IP to fragment; if bigger than + * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES + * to utilize large mbufs. If no route is found, route has no mtu, + * or the destination isn't local, use a default, hopefully conservative + * size (usually 512 or the default IP max size, but no more than the mtu + * of the interface), as we can't discover anything about intervening + * gateways or networks. We also initialize the congestion/slow start + * window to be a single segment if the destination isn't local. + * While looking at the routing entry, we also initialize other path-dependent + * parameters from pre-set or cached values in the routing entry. + */ + +int +tcp_mss(struct tcpcb *tp, unsigned offer) +{ + struct socket *so = tp->t_socket; + int mss; + + DEBUG_CALL("tcp_mss"); + DEBUG_ARG("tp = %p", tp); + DEBUG_ARG("offer = %d", offer); + + switch (so->so_ffamily) { + case AF_INET: + mss = MIN(IF_MTU, IF_MRU) - sizeof(struct tcphdr) + - sizeof(struct ip); + break; + case AF_INET6: + mss = MIN(IF_MTU, IF_MRU) - sizeof(struct tcphdr) + - sizeof(struct ip6); + break; + default: + g_assert_not_reached(); + } + + if (offer) + mss = MIN(mss, offer); + mss = MAX(mss, 32); + if (mss < tp->t_maxseg || offer != 0) + tp->t_maxseg = mss; + + tp->snd_cwnd = mss; + + sbreserve(&so->so_snd, TCP_SNDSPACE + ((TCP_SNDSPACE % mss) ? + (mss - (TCP_SNDSPACE % mss)) : + 0)); + sbreserve(&so->so_rcv, TCP_RCVSPACE + ((TCP_RCVSPACE % mss) ? + (mss - (TCP_RCVSPACE % mss)) : + 0)); + + DEBUG_MISC(" returning mss = %d", mss); + + return mss; +} |