1 /* tcp_output.c 4.49 82/12/14 */ 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 "../netinet/in.h" 10 #include "../net/route.h" 11 #include "../netinet/in_pcb.h" 12 #include "../netinet/in_systm.h" 13 #include "../netinet/ip.h" 14 #include "../netinet/ip_var.h" 15 #include "../netinet/tcp.h" 16 #define TCPOUTFLAGS 17 #include "../netinet/tcp_fsm.h" 18 #include "../netinet/tcp_seq.h" 19 #include "../netinet/tcp_timer.h" 20 #include "../netinet/tcp_var.h" 21 #include "../netinet/tcpip.h" 22 #include "../netinet/tcp_debug.h" 23 #include <errno.h> 24 25 char *tcpstates[]; /* XXX */ 26 27 /* 28 * Initial options. 29 */ 30 u_char tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, }; 31 32 /* 33 * Tcp output routine: figure out what should be sent and send it. 34 */ 35 tcp_output(tp) 36 register struct tcpcb *tp; 37 { 38 register struct socket *so = tp->t_inpcb->inp_socket; 39 register int len; 40 struct mbuf *m0; 41 int off, flags, win, error; 42 register struct mbuf *m; 43 register struct tcpiphdr *ti; 44 u_char *opt; 45 unsigned optlen = 0; 46 int sendalot; 47 48 49 /* 50 * Determine length of data that should be transmitted, 51 * and flags that will be used. 52 * If there is some data or critical controls (SYN, RST) 53 * to send, then transmit; otherwise, investigate further. 54 */ 55 again: 56 sendalot = 0; 57 off = tp->snd_nxt - tp->snd_una; 58 len = MIN(so->so_snd.sb_cc, tp->snd_wnd+tp->t_force) - off; 59 if (len < 0) 60 return (0); /* ??? */ /* past FIN */ 61 if (len > tp->t_maxseg) { 62 len = tp->t_maxseg; 63 sendalot = 1; 64 } 65 66 flags = tcp_outflags[tp->t_state]; 67 if (tp->snd_nxt + len < tp->snd_una + so->so_snd.sb_cc) 68 flags &= ~TH_FIN; 69 if (flags & (TH_SYN|TH_RST|TH_FIN)) 70 goto send; 71 if (SEQ_GT(tp->snd_up, tp->snd_una)) 72 goto send; 73 74 /* 75 * Sender silly window avoidance. If can send all data, 76 * a maximum segment, at least 1/4 of window do it, 77 * or are forced, do it; otherwise don't bother. 78 */ 79 if (len) { 80 if (len == tp->t_maxseg || off+len >= so->so_snd.sb_cc) 81 goto send; 82 if (len * 4 >= tp->snd_wnd) /* a lot */ 83 goto send; 84 if (tp->t_force) 85 goto send; 86 } 87 88 /* 89 * Send if we owe peer an ACK. 90 */ 91 if (tp->t_flags&TF_ACKNOW) 92 goto send; 93 94 95 /* 96 * Calculate available window in i, and also amount 97 * of window known to peer (as advertised window less 98 * next expected input.) If this is 35% or more of the 99 * maximum possible window, then want to send a segment to peer. 100 */ 101 win = sbspace(&so->so_rcv); 102 if (win > 0 && 103 ((100*(win-(tp->rcv_adv-tp->rcv_nxt))/so->so_rcv.sb_hiwat) >= 35)) 104 goto send; 105 106 /* 107 * TCP window updates are not reliable, rather a polling protocol 108 * using ``persist'' packets is used to insure receipt of window 109 * updates. The three ``states'' for the output side are: 110 * idle not doing retransmits or persists 111 * persisting to move a zero window 112 * (re)transmitting and thereby not persisting 113 * 114 * tp->t_timer[TCPT_PERSIST] 115 * is set when we are in persist state. 116 * tp->t_force 117 * is set when we are called to send a persist packet. 118 * tp->t_timer[TCPT_REXMT] 119 * is set when we are retransmitting 120 * The output side is idle when both timers are zero. 121 * 122 * If send window is closed, there is data to transmit, and no 123 * retransmit or persist is pending, then go to persist state, 124 * arranging to force out a byte to get more current window information 125 * if nothing happens soon. 126 */ 127 if (tp->snd_wnd == 0 && so->so_snd.sb_cc && 128 tp->t_timer[TCPT_REXMT] == 0 && tp->t_timer[TCPT_PERSIST] == 0) { 129 tp->t_rxtshift = 0; 130 tcp_setpersist(tp); 131 } 132 133 /* 134 * No reason to send a segment, just return. 135 */ 136 return (0); 137 138 send: 139 /* 140 * Grab a header mbuf, attaching a copy of data to 141 * be transmitted, and initialize the header from 142 * the template for sends on this connection. 143 */ 144 MGET(m, M_DONTWAIT, MT_DATA); 145 if (m == 0) 146 return (ENOBUFS); 147 m->m_off = MMAXOFF - sizeof (struct tcpiphdr); 148 m->m_len = sizeof (struct tcpiphdr); 149 if (len) { 150 m->m_next = m_copy(so->so_snd.sb_mb, off, len); 151 if (m->m_next == 0) 152 len = 0; 153 } 154 ti = mtod(m, struct tcpiphdr *); 155 if (tp->t_template == 0) 156 panic("tcp_output"); 157 bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr)); 158 159 /* 160 * Fill in fields, remembering maximum advertised 161 * window for use in delaying messages about window sizes. 162 */ 163 ti->ti_seq = tp->snd_nxt; 164 ti->ti_ack = tp->rcv_nxt; 165 ti->ti_seq = htonl(ti->ti_seq); 166 ti->ti_ack = htonl(ti->ti_ack); 167 /* 168 * Before ESTABLISHED, force sending of initial options 169 * unless TCP set to not do any options. 170 */ 171 if (tp->t_state < TCPS_ESTABLISHED) { 172 if (tp->t_flags&TF_NOOPT) 173 goto noopt; 174 opt = tcp_initopt; 175 optlen = sizeof (tcp_initopt); 176 *(u_short *)(opt + 2) = MIN(so->so_rcv.sb_hiwat / 2, 1024); 177 *(u_short *)(opt + 2) = htons(*(u_short *)(opt + 2)); 178 } else { 179 if (tp->t_tcpopt == 0) 180 goto noopt; 181 opt = mtod(tp->t_tcpopt, u_char *); 182 optlen = tp->t_tcpopt->m_len; 183 } 184 if (opt) { 185 m0 = m->m_next; 186 m->m_next = m_get(M_DONTWAIT, MT_DATA); 187 if (m->m_next == 0) { 188 (void) m_free(m); 189 m_freem(m0); 190 return (ENOBUFS); 191 } 192 m->m_next->m_next = m0; 193 m0 = m->m_next; 194 m0->m_len = optlen; 195 bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen); 196 opt = (u_char *)(mtod(m0, caddr_t) + optlen); 197 while (m0->m_len & 0x3) { 198 *opt++ = TCPOPT_EOL; 199 m0->m_len++; 200 } 201 optlen = m0->m_len; 202 ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2; 203 } 204 noopt: 205 ti->ti_flags = flags; 206 win = sbspace(&so->so_rcv); 207 if (win < so->so_rcv.sb_hiwat / 4) /* avoid silly window */ 208 win = 0; 209 if (win > 0) 210 ti->ti_win = htons((u_short)win); 211 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 212 ti->ti_urp = tp->snd_up - tp->snd_nxt; 213 ti->ti_urp = htons(ti->ti_urp); 214 ti->ti_flags |= TH_URG; 215 } else 216 /* 217 * If no urgent pointer to send, then we pull 218 * the urgent pointer to the left edge of the send window 219 * so that it doesn't drift into the send window on sequence 220 * number wraparound. 221 */ 222 tp->snd_up = tp->snd_una; /* drag it along */ 223 /* 224 * If anything to send and we can send it all, set PUSH. 225 * (This will keep happy those implementations which only 226 * give data to the user when a buffer fills or a PUSH comes in. 227 */ 228 if (len && off+len == so->so_snd.sb_cc) 229 ti->ti_flags |= TH_PUSH; 230 231 /* 232 * Put TCP length in extended header, and then 233 * checksum extended header and data. 234 */ 235 if (len + optlen) { 236 ti->ti_len = sizeof (struct tcphdr) + optlen + len; 237 ti->ti_len = htons((u_short)ti->ti_len); 238 } 239 ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + len); 240 241 /* 242 * In transmit state, time the transmission and arrange for 243 * the retransmit. In persist state, reset persist time for 244 * next persist. 245 */ 246 if (tp->t_force == 0) { 247 /* 248 * Advance snd_nxt over sequence space of this segment. 249 */ 250 if (flags & (TH_SYN|TH_FIN)) 251 tp->snd_nxt++; 252 tp->snd_nxt += len; 253 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) 254 tp->snd_max = tp->snd_nxt; 255 256 /* 257 * Time this transmission if not a retransmission and 258 * not currently timing anything. 259 */ 260 if (SEQ_GT(tp->snd_nxt, tp->snd_max) && tp->t_rtt == 0) { 261 tp->t_rtt = 1; 262 tp->t_rtseq = tp->snd_nxt - len; 263 } 264 265 /* 266 * Set retransmit timer if not currently set. 267 * Initial value for retransmit timer to tcp_beta*tp->t_srtt. 268 * Initialize shift counter which is used for exponential 269 * backoff of retransmit time. 270 */ 271 if (tp->t_timer[TCPT_REXMT] == 0 && 272 tp->snd_nxt != tp->snd_una) { 273 TCPT_RANGESET(tp->t_timer[TCPT_REXMT], 274 tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX); 275 tp->t_rtt = 0; 276 tp->t_rxtshift = 0; 277 } 278 tp->t_timer[TCPT_PERSIST] = 0; 279 } else { 280 if (SEQ_GT(tp->snd_una+1, tp->snd_max)) 281 tp->snd_max = tp->snd_una+1; 282 } 283 284 /* 285 * Trace. 286 */ 287 if (so->so_options & SO_DEBUG) 288 tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0); 289 290 /* 291 * Fill in IP length and desired time to live and 292 * send to IP level. 293 */ 294 ((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len; 295 ((struct ip *)ti)->ip_ttl = TCP_TTL; 296 if (error = ip_output(m, tp->t_ipopt, (so->so_options & SO_DONTROUTE) ? 297 &routetoif : &tp->t_inpcb->inp_route, 0)) 298 return (error); 299 300 /* 301 * Data sent (as far as we can tell). 302 * If this advertises a larger window than any other segment, 303 * then remember the size of the advertised window. 304 * Drop send for purpose of ACK requirements. 305 */ 306 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 307 tp->rcv_adv = tp->rcv_nxt + win; 308 tp->t_flags &= ~(TF_ACKNOW|TF_DELACK); 309 if (sendalot && tp->t_force == 0) 310 goto again; 311 return (0); 312 } 313 314 tcp_setpersist(tp) 315 register struct tcpcb *tp; 316 { 317 318 if (tp->t_timer[TCPT_REXMT]) 319 panic("tcp_output REXMT"); 320 /* 321 * Start/restart persistance timer. 322 */ 323 TCPT_RANGESET(tp->t_timer[TCPT_PERSIST], 324 ((int)(tcp_beta * tp->t_srtt)) << tp->t_rxtshift, 325 TCPTV_PERSMIN, TCPTV_MAX); 326 tp->t_rxtshift++; 327 if (tp->t_rxtshift >= TCP_MAXRXTSHIFT) 328 tp->t_rxtshift = 0; 329 } 330