1 /* tcp_output.c 4.28 82/01/17 */ 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 < 0) 50 return; /* past FIN */ 51 if (len > tp->t_maxseg) 52 len = tp->t_maxseg; 53 flags = tcp_outflags[tp->t_state]; 54 if (tp->snd_nxt + len < tp->snd_una + so->so_snd.sb_cc) 55 flags &= ~TH_FIN; 56 if (len || (flags & (TH_SYN|TH_RST|TH_FIN))) 57 goto send; 58 59 /* 60 * Send if we owe peer an ACK. 61 */ 62 if (tp->t_flags & TF_ACKNOW) 63 goto send; 64 65 /* 66 * Calculate available window in i, and also amount 67 * of window known to peer (as advertised window less 68 * next expected input.) If this is 35% or more of the 69 * maximum possible window, then want to send a segment to peer. 70 */ 71 win = sbspace(&so->so_rcv); 72 if (win > 0 && 73 ((100*(win-(tp->rcv_adv-tp->rcv_nxt))/so->so_rcv.sb_hiwat) >= 35)) 74 goto send; 75 76 /* 77 * No reason to send a segment, just return. 78 */ 79 return (0); 80 81 send: 82 /* 83 * Grab a header mbuf, attaching a copy of data to 84 * be transmitted, and initialize the header from 85 * the template for sends on this connection. 86 */ 87 MGET(m, 0); 88 if (m == 0) 89 return (0); 90 m->m_off = MMAXOFF - sizeof (struct tcpiphdr); 91 m->m_len = sizeof (struct tcpiphdr); 92 if (len) { 93 m->m_next = m_copy(so->so_snd.sb_mb, off, len); 94 if (m->m_next == 0) 95 len = 0; 96 } 97 ti = mtod(m, struct tcpiphdr *); 98 if (tp->t_template == 0) 99 panic("tcp_output"); 100 bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr)); 101 102 /* 103 * Fill in fields, remembering maximum advertised 104 * window for use in delaying messages about window sizes. 105 */ 106 ti->ti_seq = tp->snd_nxt; 107 ti->ti_ack = tp->rcv_nxt; 108 #if vax 109 ti->ti_seq = htonl(ti->ti_seq); 110 ti->ti_ack = htonl(ti->ti_ack); 111 #endif 112 if (tp->t_tcpopt) { 113 m0 = m->m_next; 114 m->m_next = m_get(0); 115 if (m->m_next == 0) { 116 (void) m_free(m); 117 m_freem(m); 118 return (0); 119 } 120 m->m_next->m_next = m0; 121 m->m_off = MMINOFF; 122 m->m_len = tp->t_tcpopt->m_len; 123 bcopy(mtod(tp->t_tcpopt, caddr_t), mtod(m, caddr_t), 124 (unsigned)tp->t_tcpopt->m_len); 125 ti->ti_off = (sizeof (struct tcphdr)+tp->t_tcpopt->m_len) >> 2; 126 } 127 ti->ti_flags = flags; 128 win = sbspace(&so->so_rcv); 129 if (win > 0) 130 ti->ti_win = htons((u_short)win); 131 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 132 ti->ti_urp = tp->snd_up - tp->snd_nxt; 133 #if vax 134 ti->ti_urp = htons(ti->ti_urp); 135 #endif 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 (TCPS_HAVERCVDSYN(tp->t_state) && 168 SEQ_GEQ(tp->snd_nxt, tp->snd_una+tp->snd_wnd) && 169 tp->t_timer[TCPT_PERSIST] == 0) 170 TCPT_RANGESET(tp->t_timer[TCPT_PERSIST], 171 2 * tp->t_srtt, TCPTV_PERSMIN, TCPTV_MAX); 172 173 /* 174 * Time this transmission if not a retransmission and 175 * not currently timing anything. 176 */ 177 if (SEQ_GT(tp->snd_nxt, tp->snd_max) && tp->t_rtt == 0) { 178 tp->t_rtt = 1; 179 tp->t_rtseq = tp->snd_nxt - len; 180 } 181 182 /* 183 * Set retransmit timer if not currently set. 184 * Initial value for retransmit timer to tcp_beta*tp->t_srtt. 185 * Initialize shift counter which is used for exponential 186 * backoff of retransmit time. 187 */ 188 if (tp->t_timer[TCPT_REXMT] == 0 && tp->snd_nxt != tp->snd_una) { 189 TCPT_RANGESET(tp->t_timer[TCPT_REXMT], 190 tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX); 191 tp->t_rtt = 0; 192 tp->t_rxtshift = 0; 193 } 194 195 /* 196 * Trace. 197 */ 198 if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG) 199 tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0); 200 201 /* 202 * Fill in IP length and desired time to live and 203 * send to IP level. 204 */ 205 ((struct ip *)ti)->ip_len = len + sizeof (struct tcpiphdr); 206 ((struct ip *)ti)->ip_ttl = TCP_TTL; 207 if (ip_output(m, tp->t_ipopt) == 0) 208 return (0); 209 210 /* 211 * Data sent (as far as we can tell). 212 * If this advertises a larger window than any other segment, 213 * then remember the size of the advertised window. 214 * Drop send for purpose of ACK requirements. 215 */ 216 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 217 tp->rcv_adv = tp->rcv_nxt + win; 218 tp->t_flags &= ~(TF_ACKNOW|TF_DELACK); 219 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) 220 tp->snd_max = tp->snd_nxt; 221 return (1); 222 } 223