1 /* tcp_output.c 4.23 81/12/12 */ 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 "../errno.h" 22 23 char *tcpstates[]; /* XXX */ 24 /* 25 * Tcp output routine: figure out what should be sent and send it. 26 */ 27 tcp_output(tp) 28 register struct tcpcb *tp; 29 { 30 register struct socket *so = tp->t_inpcb->inp_socket; 31 register int len; 32 struct mbuf *m0; 33 int off, flags; 34 register struct mbuf *m; 35 register struct tcpiphdr *ti; 36 int win; 37 38 COUNT(TCP_OUTPUT); 39 40 /* 41 * Determine length of data that can be transmitted, 42 * and flags that will be used. 43 * If there is some data or critical controls (SYN, RST) 44 * to send, then transmit; otherwise, investigate further. 45 */ 46 off = tp->snd_nxt - tp->snd_una; 47 len = MIN(so->so_snd.sb_cc, tp->snd_wnd+tp->t_force) - off; 48 if (len > tp->t_maxseg) 49 len = tp->t_maxseg; 50 if (len < 0) 51 len = 0; /* FIN can cause -1 */ 52 flags = tcp_outflags[tp->t_state]; 53 if (len < so->so_snd.sb_cc) 54 flags &= ~TH_FIN; 55 if (len || (flags & (TH_SYN|TH_RST))) 56 goto send; 57 58 /* 59 * See if we owe peer an ACK or have a unacked FIN to send. 60 */ 61 if (tp->t_flags & TF_ACKNOW) 62 goto send; 63 if ((so->so_state & SS_CANTSENDMORE) && 64 TCPS_OURFINNOTACKED(tp->t_state)) 65 goto send; 66 67 /* 68 * Calculate available window in i, and also amount 69 * of window known to peer (as advertised window less 70 * next expected input.) If this is 35% or more of the 71 * maximum possible window, then want to send a segment to peer. 72 */ 73 win = sbspace(&so->so_rcv); 74 if (win > 0 && 75 ((100*(win-(tp->rcv_adv-tp->rcv_nxt))/so->so_rcv.sb_hiwat) >= 35)) 76 goto send; 77 78 /* 79 * No reason to send a segment, just return. 80 */ 81 return (0); 82 83 send: 84 /* 85 * Grab a header mbuf, attaching a copy of data to 86 * be transmitted, and initialize the header from 87 * the template for sends on this connection. 88 */ 89 MGET(m, 0); 90 if (m == 0) 91 return (0); 92 m->m_off = MMAXOFF - sizeof (struct tcpiphdr); 93 m->m_len = sizeof (struct tcpiphdr); 94 if (len) { 95 m->m_next = m_copy(so->so_snd.sb_mb, off, len); 96 if (m->m_next == 0) 97 len = 0; 98 } 99 ti = mtod(m, struct tcpiphdr *); 100 if (tp->t_template == 0) 101 panic("tcp_output"); 102 bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr)); 103 104 /* 105 * Fill in fields, remembering maximum advertised 106 * window for use in delaying messages about window sizes. 107 */ 108 ti->ti_seq = tp->snd_nxt; 109 ti->ti_ack = tp->rcv_nxt; 110 #if vax 111 ti->ti_seq = htonl(ti->ti_seq); 112 ti->ti_ack = htonl(ti->ti_ack); 113 #endif 114 if (tp->t_tcpopt) { 115 m0 = m->m_next; 116 m->m_next = m_get(0); 117 if (m->m_next == 0) { 118 (void) m_free(m); 119 m_freem(m); 120 return (0); 121 } 122 m->m_next->m_next = m0; 123 m->m_off = MMINOFF; 124 m->m_len = tp->t_tcpopt->m_len; 125 bcopy(mtod(tp->t_tcpopt, caddr_t), mtod(m, caddr_t), 126 (unsigned)tp->t_tcpopt->m_len); 127 ti->ti_off = (sizeof (struct tcphdr)+tp->t_tcpopt->m_len) >> 2; 128 } 129 ti->ti_flags = flags; 130 win = sbspace(&so->so_rcv); 131 if (win > 0) 132 ti->ti_win = htons((u_short)win); 133 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 134 ti->ti_urp = htons((u_short)(tp->snd_up - tp->snd_nxt)); 135 ti->ti_flags |= TH_URG; 136 } else 137 /* 138 * If no urgent pointer to send, then we pull 139 * the urgent pointer to the left edge of the send window 140 * so that it doesn't drift into the send window on sequence 141 * number wraparound. 142 */ 143 tp->snd_up = tp->snd_una; /* drag it along */ 144 /* PUSH */ 145 146 /* 147 * Put TCP length in extended header, and then 148 * checksum extended header and data. 149 */ 150 if (len) 151 ti->ti_len = htons((u_short)(len + sizeof (struct tcphdr))); 152 ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + len); 153 154 /* 155 * Advance snd_nxt over sequence space of this segment 156 */ 157 if (flags & (TH_SYN|TH_FIN)) 158 tp->snd_nxt++; 159 tp->snd_nxt += len; 160 161 /* 162 * If this transmission closes the window, 163 * start persistance timer at 2 round trip times 164 * but at least TCPTV_PERSMIN ticks. 165 */ 166 if (SEQ_GT(tp->snd_nxt, tp->snd_una+tp->snd_wnd) && 167 tp->t_timer[TCPT_PERSIST] == 0) 168 TCPT_RANGESET(tp->t_timer[TCPT_PERSIST], 169 2 * tp->t_srtt, TCPTV_PERSMIN, TCPTV_MAX); 170 171 /* 172 * Time this transmission if not a retransmission and 173 * not currently timing anything. 174 */ 175 if (SEQ_GT(tp->snd_nxt, tp->snd_max) && tp->t_rtt == 0) { 176 tp->t_rtt = 1; 177 tp->t_rtseq = tp->snd_nxt - len; 178 } 179 180 /* 181 * Set retransmit timer if not currently set. 182 * Initial value for retransmit timer to tcp_beta*tp->t_srtt. 183 * Initialize shift counter which is used for exponential 184 * backoff of retransmit time. 185 */ 186 if (tp->t_timer[TCPT_REXMT] == 0 && tp->snd_nxt != tp->snd_una) { 187 TCPT_RANGESET(tp->t_timer[TCPT_REXMT], 188 tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX); 189 tp->t_rxtshift = 0; 190 } 191 192 /* 193 * Fill in IP length and desired time to live and 194 * send to IP level. 195 */ 196 ((struct ip *)ti)->ip_len = len + sizeof (struct tcpiphdr); 197 ((struct ip *)ti)->ip_ttl = TCP_TTL; 198 if (ip_output(m, tp->t_ipopt) == 0) 199 return (0); 200 201 /* 202 * Data sent (as far as we can tell). 203 * If this advertises a larger window than any other segment, 204 * then remember the size of the advertised window. 205 * Drop send for purpose of ACK requirements. 206 */ 207 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 208 tp->rcv_adv = tp->rcv_nxt + win; 209 tp->t_flags &= ~(TF_ACKNOW|TF_DELACK); 210 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) 211 tp->snd_max = tp->snd_nxt; 212 return (1); 213 } 214