1 /* tcp_output.c 4.24 81/12/20 */ 2 3 #include "../h/param.h" 4 #include "../h/systm.h" 5 #include "../h/mbuf.h" 6 #include "../h/protosw.h" 7 #include "../h/socket.h" 8 #include "../h/socketvar.h" 9 #include "../net/in.h" 10 #include "../net/in_pcb.h" 11 #include "../net/in_systm.h" 12 #include "../net/ip.h" 13 #include "../net/ip_var.h" 14 #include "../net/tcp.h" 15 #define TCPOUTFLAGS 16 #include "../net/tcp_fsm.h" 17 #include "../net/tcp_seq.h" 18 #include "../net/tcp_timer.h" 19 #include "../net/tcp_var.h" 20 #include "../net/tcpip.h" 21 #include "../net/tcp_debug.h" 22 #include "../errno.h" 23 24 char *tcpstates[]; /* XXX */ 25 /* 26 * Tcp output routine: figure out what should be sent and send it. 27 */ 28 tcp_output(tp) 29 register struct tcpcb *tp; 30 { 31 register struct socket *so = tp->t_inpcb->inp_socket; 32 register int len; 33 struct mbuf *m0; 34 int off, flags; 35 register struct mbuf *m; 36 register struct tcpiphdr *ti; 37 int win; 38 39 COUNT(TCP_OUTPUT); 40 41 /* 42 * Determine length of data that can be transmitted, 43 * and flags that will be used. 44 * If there is some data or critical controls (SYN, RST) 45 * to send, then transmit; otherwise, investigate further. 46 */ 47 off = tp->snd_nxt - tp->snd_una; 48 len = MIN(so->so_snd.sb_cc, tp->snd_wnd+tp->t_force) - off; 49 if (len > tp->t_maxseg) 50 len = tp->t_maxseg; 51 if (len < 0) 52 len = 0; /* FIN can cause -1 */ 53 flags = tcp_outflags[tp->t_state]; 54 if (len < so->so_snd.sb_cc) 55 flags &= ~TH_FIN; 56 if (len || (flags & (TH_SYN|TH_RST))) 57 goto send; 58 59 /* 60 * See if we owe peer an ACK or have a unacked FIN to send. 61 */ 62 if (tp->t_flags & TF_ACKNOW) 63 goto send; 64 if ((so->so_state & SS_CANTSENDMORE) && 65 TCPS_OURFINNOTACKED(tp->t_state)) 66 goto send; 67 68 /* 69 * Calculate available window in i, and also amount 70 * of window known to peer (as advertised window less 71 * next expected input.) If this is 35% or more of the 72 * maximum possible window, then want to send a segment to peer. 73 */ 74 win = sbspace(&so->so_rcv); 75 if (win > 0 && 76 ((100*(win-(tp->rcv_adv-tp->rcv_nxt))/so->so_rcv.sb_hiwat) >= 35)) 77 goto send; 78 79 /* 80 * No reason to send a segment, just return. 81 */ 82 return (0); 83 84 send: 85 /* 86 * Grab a header mbuf, attaching a copy of data to 87 * be transmitted, and initialize the header from 88 * the template for sends on this connection. 89 */ 90 MGET(m, 0); 91 if (m == 0) 92 return (0); 93 m->m_off = MMAXOFF - sizeof (struct tcpiphdr); 94 m->m_len = sizeof (struct tcpiphdr); 95 if (len) { 96 m->m_next = m_copy(so->so_snd.sb_mb, off, len); 97 if (m->m_next == 0) 98 len = 0; 99 } 100 ti = mtod(m, struct tcpiphdr *); 101 if (tp->t_template == 0) 102 panic("tcp_output"); 103 bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr)); 104 105 /* 106 * Fill in fields, remembering maximum advertised 107 * window for use in delaying messages about window sizes. 108 */ 109 ti->ti_seq = tp->snd_nxt; 110 ti->ti_ack = tp->rcv_nxt; 111 #if vax 112 ti->ti_seq = htonl(ti->ti_seq); 113 ti->ti_ack = htonl(ti->ti_ack); 114 #endif 115 if (tp->t_tcpopt) { 116 m0 = m->m_next; 117 m->m_next = m_get(0); 118 if (m->m_next == 0) { 119 (void) m_free(m); 120 m_freem(m); 121 return (0); 122 } 123 m->m_next->m_next = m0; 124 m->m_off = MMINOFF; 125 m->m_len = tp->t_tcpopt->m_len; 126 bcopy(mtod(tp->t_tcpopt, caddr_t), mtod(m, caddr_t), 127 (unsigned)tp->t_tcpopt->m_len); 128 ti->ti_off = (sizeof (struct tcphdr)+tp->t_tcpopt->m_len) >> 2; 129 } 130 ti->ti_flags = flags; 131 win = sbspace(&so->so_rcv); 132 if (win > 0) 133 ti->ti_win = htons((u_short)win); 134 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 135 ti->ti_urp = htons((u_short)(tp->snd_up - tp->snd_nxt)); 136 ti->ti_flags |= TH_URG; 137 } else 138 /* 139 * If no urgent pointer to send, then we pull 140 * the urgent pointer to the left edge of the send window 141 * so that it doesn't drift into the send window on sequence 142 * number wraparound. 143 */ 144 tp->snd_up = tp->snd_una; /* drag it along */ 145 /* PUSH */ 146 147 /* 148 * Put TCP length in extended header, and then 149 * checksum extended header and data. 150 */ 151 if (len) 152 ti->ti_len = htons((u_short)(len + sizeof (struct tcphdr))); 153 ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + len); 154 155 /* 156 * Advance snd_nxt over sequence space of this segment 157 */ 158 if (flags & (TH_SYN|TH_FIN)) 159 tp->snd_nxt++; 160 tp->snd_nxt += len; 161 162 /* 163 * If this transmission closes the window, 164 * start persistance timer at 2 round trip times 165 * but at least TCPTV_PERSMIN ticks. 166 */ 167 if (SEQ_GT(tp->snd_nxt, tp->snd_una+tp->snd_wnd) && 168 tp->t_timer[TCPT_PERSIST] == 0) 169 TCPT_RANGESET(tp->t_timer[TCPT_PERSIST], 170 2 * tp->t_srtt, TCPTV_PERSMIN, TCPTV_MAX); 171 172 /* 173 * Time this transmission if not a retransmission and 174 * not currently timing anything. 175 */ 176 if (SEQ_GT(tp->snd_nxt, tp->snd_max) && tp->t_rtt == 0) { 177 tp->t_rtt = 1; 178 tp->t_rtseq = tp->snd_nxt - len; 179 } 180 181 /* 182 * Set retransmit timer if not currently set. 183 * Initial value for retransmit timer to tcp_beta*tp->t_srtt. 184 * Initialize shift counter which is used for exponential 185 * backoff of retransmit time. 186 */ 187 if (tp->t_timer[TCPT_REXMT] == 0 && tp->snd_nxt != tp->snd_una) { 188 TCPT_RANGESET(tp->t_timer[TCPT_REXMT], 189 tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX); 190 tp->t_rxtshift = 0; 191 } 192 193 /* 194 * Trace. 195 */ 196 if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG) 197 tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0); 198 199 /* 200 * Fill in IP length and desired time to live and 201 * send to IP level. 202 */ 203 ((struct ip *)ti)->ip_len = len + sizeof (struct tcpiphdr); 204 ((struct ip *)ti)->ip_ttl = TCP_TTL; 205 if (ip_output(m, tp->t_ipopt) == 0) 206 return (0); 207 208 /* 209 * Data sent (as far as we can tell). 210 * If this advertises a larger window than any other segment, 211 * then remember the size of the advertised window. 212 * Drop send for purpose of ACK requirements. 213 */ 214 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 215 tp->rcv_adv = tp->rcv_nxt + win; 216 tp->t_flags &= ~(TF_ACKNOW|TF_DELACK); 217 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) 218 tp->snd_max = tp->snd_nxt; 219 return (1); 220 } 221