4.3BSD - /usr/src/sys/netinet/tcp_output.c

   1: /*
   2:  * Copyright (c) 1982, 1986 Regents of the University of California.
   3:  * All rights reserved.  The Berkeley software License Agreement
   4:  * specifies the terms and conditions for redistribution.
   5:  *
   6:  *	@(#)tcp_output.c	7.1 (Berkeley) 6/5/86
   7:  */
   8: 
   9: #include "param.h"
  10: #include "systm.h"
  11: #include "mbuf.h"
  12: #include "protosw.h"
  13: #include "socket.h"
  14: #include "socketvar.h"
  15: #include "errno.h"
  16: 
  17: #include "../net/route.h"
  18: 
  19: #include "in.h"
  20: #include "in_pcb.h"
  21: #include "in_systm.h"
  22: #include "ip.h"
  23: #include "ip_var.h"
  24: #include "tcp.h"
  25: #define TCPOUTFLAGS
  26: #include "tcp_fsm.h"
  27: #include "tcp_seq.h"
  28: #include "tcp_timer.h"
  29: #include "tcp_var.h"
  30: #include "tcpip.h"
  31: #include "tcp_debug.h"
  32: 
  33: /*
  34:  * Initial options.
  35:  */
  36: u_char  tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, };
  37: 
  38: /*
  39:  * Tcp output routine: figure out what should be sent and send it.
  40:  */
  41: tcp_output(tp)
  42:     register struct tcpcb *tp;
  43: {
  44:     register struct socket *so = tp->t_inpcb->inp_socket;
  45:     register int len, win;
  46:     struct mbuf *m0;
  47:     int off, flags, error;
  48:     register struct mbuf *m;
  49:     register struct tcpiphdr *ti;
  50:     u_char *opt;
  51:     unsigned optlen = 0;
  52:     int idle, sendalot;
  53: 
  54:     /*
  55: 	 * Determine length of data that should be transmitted,
  56: 	 * and flags that will be used.
  57: 	 * If there is some data or critical controls (SYN, RST)
  58: 	 * to send, then transmit; otherwise, investigate further.
  59: 	 */
  60:     idle = (tp->snd_max == tp->snd_una);
  61: again:
  62:     sendalot = 0;
  63:     off = tp->snd_nxt - tp->snd_una;
  64:     win = MIN(tp->snd_wnd, tp->snd_cwnd);
  65: 
  66:     /*
  67: 	 * If in persist timeout with window of 0, send 1 byte.
  68: 	 * Otherwise, if window is small but nonzero
  69: 	 * and timer expired, we will send what we can
  70: 	 * and go to transmit state.
  71: 	 */
  72:     if (tp->t_force) {
  73:         if (win == 0)
  74:             win = 1;
  75:         else {
  76:             tp->t_timer[TCPT_PERSIST] = 0;
  77:             tp->t_rxtshift = 0;
  78:         }
  79:     }
  80: 
  81:     len = MIN(so->so_snd.sb_cc, win) - off;
  82:     flags = tcp_outflags[tp->t_state];
  83:     if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
  84:         flags &= ~TH_FIN;
  85: 
  86:     if (len < 0) {
  87:         /*
  88: 		 * If FIN has been sent but not acked,
  89: 		 * but we haven't been called to retransmit,
  90: 		 * len will be -1; transmit if acking, otherwise no need.
  91: 		 * Otherwise, window shrank after we sent into it.
  92: 		 * If window shrank to 0, cancel pending retransmit
  93: 		 * and pull snd_nxt back to (closed) window.
  94: 		 * We will enter persist state below.
  95: 		 * If the window didn't close completely,
  96: 		 * just wait for an ACK.
  97: 		 */
  98:         if (flags & TH_FIN) {
  99:             if (tp->t_flags & TF_ACKNOW)
 100:                 len = 0;
 101:             else
 102:                 return (0);
 103:         } else if (win == 0) {
 104:             tp->t_timer[TCPT_REXMT] = 0;
 105:             tp->snd_nxt = tp->snd_una;
 106:             len = 0;
 107:         } else
 108:             return (0);
 109:     }
 110:     if (len > tp->t_maxseg) {
 111:         len = tp->t_maxseg;
 112:         /*
 113: 		 * Don't send more than one segment if retransmitting
 114: 		 * (or persisting, but then we shouldn't be here).
 115: 		 */
 116:         if (tp->t_rxtshift == 0)
 117:             sendalot = 1;
 118:     }
 119:     win = sbspace(&so->so_rcv);
 120: 
 121: 
 122:     /*
 123: 	 * If our state indicates that FIN should be sent
 124: 	 * and we have not yet done so, or we're retransmitting the FIN,
 125: 	 * then we need to send.
 126: 	 */
 127:     if (flags & TH_FIN &&
 128:         ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
 129:         goto send;
 130:     /*
 131: 	 * Send if we owe peer an ACK.
 132: 	 */
 133:     if (tp->t_flags & TF_ACKNOW)
 134:         goto send;
 135:     if (flags & (TH_SYN|TH_RST))
 136:         goto send;
 137:     if (SEQ_GT(tp->snd_up, tp->snd_una))
 138:         goto send;
 139: 
 140:     /*
 141: 	 * Sender silly window avoidance.  If connection is idle
 142: 	 * and can send all data, a maximum segment,
 143: 	 * at least a maximum default-size segment do it,
 144: 	 * or are forced, do it; otherwise don't bother.
 145: 	 * If peer's buffer is tiny, then send
 146: 	 * when window is at least half open.
 147: 	 * If retransmitting (possibly after persist timer forced us
 148: 	 * to send into a small window), then must resend.
 149: 	 */
 150:     if (len) {
 151:         if (len == tp->t_maxseg || len >= TCP_MSS)  /* a lot */
 152:             goto send;
 153:         if ((idle || tp->t_flags & TF_NODELAY) &&
 154:             len + off >= so->so_snd.sb_cc)
 155:             goto send;
 156:         if (tp->t_force)
 157:             goto send;
 158:         if (len >= tp->max_sndwnd / 2)
 159:             goto send;
 160:         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
 161:             goto send;
 162:     }
 163: 
 164:     /*
 165: 	 * Compare available window to amount of window
 166: 	 * known to peer (as advertised window less
 167: 	 * next expected input.)  If the difference is 35% or more of the
 168: 	 * maximum possible window, then want to send a window update to peer.
 169: 	 */
 170:     if (win > 0 &&
 171:         ((100*(win-(tp->rcv_adv-tp->rcv_nxt))/so->so_rcv.sb_hiwat) >= 35))
 172:         goto send;
 173: 
 174:     /*
 175: 	 * TCP window updates are not reliable, rather a polling protocol
 176: 	 * using ``persist'' packets is used to insure receipt of window
 177: 	 * updates.  The three ``states'' for the output side are:
 178: 	 *	idle			not doing retransmits or persists
 179: 	 *	persisting		to move a small or zero window
 180: 	 *	(re)transmitting	and thereby not persisting
 181: 	 *
 182: 	 * tp->t_timer[TCPT_PERSIST]
 183: 	 *	is set when we are in persist state.
 184: 	 * tp->t_force
 185: 	 *	is set when we are called to send a persist packet.
 186: 	 * tp->t_timer[TCPT_REXMT]
 187: 	 *	is set when we are retransmitting
 188: 	 * The output side is idle when both timers are zero.
 189: 	 *
 190: 	 * If send window is too small, there is data to transmit, and no
 191: 	 * retransmit or persist is pending, then go to persist state.
 192: 	 * If nothing happens soon, send when timer expires:
 193: 	 * if window is nonzero, transmit what we can,
 194: 	 * otherwise force out a byte.
 195: 	 */
 196:     if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&
 197:         tp->t_timer[TCPT_PERSIST] == 0) {
 198:         tp->t_rxtshift = 0;
 199:         tcp_setpersist(tp);
 200:     }
 201: 
 202:     /*
 203: 	 * No reason to send a segment, just return.
 204: 	 */
 205:     return (0);
 206: 
 207: send:
 208:     /*
 209: 	 * Grab a header mbuf, attaching a copy of data to
 210: 	 * be transmitted, and initialize the header from
 211: 	 * the template for sends on this connection.
 212: 	 */
 213:     MGET(m, M_DONTWAIT, MT_HEADER);
 214:     if (m == NULL)
 215:         return (ENOBUFS);
 216:     m->m_off = MMAXOFF - sizeof (struct tcpiphdr);
 217:     m->m_len = sizeof (struct tcpiphdr);
 218:     if (len) {
 219:         m->m_next = m_copy(so->so_snd.sb_mb, off, len);
 220:         if (m->m_next == 0)
 221:             len = 0;
 222:     }
 223:     ti = mtod(m, struct tcpiphdr *);
 224:     if (tp->t_template == 0)
 225:         panic("tcp_output");
 226:     bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr));
 227: 
 228:     /*
 229: 	 * Fill in fields, remembering maximum advertised
 230: 	 * window for use in delaying messages about window sizes.
 231: 	 * If resending a FIN, be sure not to use a new sequence number.
 232: 	 */
 233:     if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
 234:         tp->snd_nxt != tp->snd_una)
 235:         tp->snd_nxt--;
 236:     ti->ti_seq = htonl(tp->snd_nxt);
 237:     ti->ti_ack = htonl(tp->rcv_nxt);
 238:     /*
 239: 	 * Before ESTABLISHED, force sending of initial options
 240: 	 * unless TCP set to not do any options.
 241: 	 */
 242:     opt = NULL;
 243:     if (tp->t_state < TCPS_ESTABLISHED && (tp->t_flags & TF_NOOPT) == 0) {
 244:         u_short mss;
 245: 
 246:         mss = MIN(so->so_rcv.sb_hiwat / 2, tcp_mss(tp));
 247:         if (mss > IP_MSS - sizeof(struct tcpiphdr)) {
 248:             opt = tcp_initopt;
 249:             optlen = sizeof (tcp_initopt);
 250:             *(u_short *)(opt + 2) = htons(mss);
 251:         }
 252:     } else if (tp->t_tcpopt) {
 253:         opt = mtod(tp->t_tcpopt, u_char *);
 254:         optlen = tp->t_tcpopt->m_len;
 255:     }
 256:     if (opt) {
 257:         m0 = m->m_next;
 258:         m->m_next = m_get(M_DONTWAIT, MT_DATA);
 259:         if (m->m_next == 0) {
 260:             (void) m_free(m);
 261:             m_freem(m0);
 262:             return (ENOBUFS);
 263:         }
 264:         m->m_next->m_next = m0;
 265:         m0 = m->m_next;
 266:         m0->m_len = optlen;
 267:         bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen);
 268:         opt = (u_char *)(mtod(m0, caddr_t) + optlen);
 269:         while (m0->m_len & 0x3) {
 270:             *opt++ = TCPOPT_EOL;
 271:             m0->m_len++;
 272:         }
 273:         optlen = m0->m_len;
 274:         ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
 275:     }
 276:     ti->ti_flags = flags;
 277:     /*
 278: 	 * Calculate receive window.  Don't shrink window,
 279: 	 * but avoid silly window syndrome.
 280: 	 */
 281:     if (win < so->so_rcv.sb_hiwat / 4 && win < tp->t_maxseg)
 282:         win = 0;
 283:     if (win < (int)(tp->rcv_adv - tp->rcv_nxt))
 284:         win = (int)(tp->rcv_adv - tp->rcv_nxt);
 285:     ti->ti_win = htons((u_short)win);
 286:     if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
 287:         ti->ti_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
 288:         ti->ti_flags |= TH_URG;
 289:     } else
 290:         /*
 291: 		 * If no urgent pointer to send, then we pull
 292: 		 * the urgent pointer to the left edge of the send window
 293: 		 * so that it doesn't drift into the send window on sequence
 294: 		 * number wraparound.
 295: 		 */
 296:         tp->snd_up = tp->snd_una;       /* drag it along */
 297:     /*
 298: 	 * If anything to send and we can send it all, set PUSH.
 299: 	 * (This will keep happy those implementations which only
 300: 	 * give data to the user when a buffer fills or a PUSH comes in.)
 301: 	 */
 302:     if (len && off+len == so->so_snd.sb_cc)
 303:         ti->ti_flags |= TH_PUSH;
 304: 
 305:     /*
 306: 	 * Put TCP length in extended header, and then
 307: 	 * checksum extended header and data.
 308: 	 */
 309:     if (len + optlen)
 310:         ti->ti_len = htons((u_short)(sizeof(struct tcphdr) +
 311:             optlen + len));
 312:     ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + len);
 313: 
 314:     /*
 315: 	 * In transmit state, time the transmission and arrange for
 316: 	 * the retransmit.  In persist state, just set snd_max.
 317: 	 */
 318:     if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {
 319:         /*
 320: 		 * Advance snd_nxt over sequence space of this segment.
 321: 		 */
 322:         if (flags & TH_SYN)
 323:             tp->snd_nxt++;
 324:         if (flags & TH_FIN) {
 325:             tp->snd_nxt++;
 326:             tp->t_flags |= TF_SENTFIN;
 327:         }
 328:         tp->snd_nxt += len;
 329:         if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
 330:             tp->snd_max = tp->snd_nxt;
 331:             /*
 332: 			 * Time this transmission if not a retransmission and
 333: 			 * not currently timing anything.
 334: 			 */
 335:             if (tp->t_rtt == 0) {
 336:                 tp->t_rtt = 1;
 337:                 tp->t_rtseq = tp->snd_nxt - len;
 338:             }
 339:         }
 340: 
 341:         /*
 342: 		 * Set retransmit timer if not currently set,
 343: 		 * and not doing an ack or a keep-alive probe.
 344: 		 * Initial value for retransmit timer is tcp_beta*tp->t_srtt.
 345: 		 * Initialize shift counter which is used for backoff
 346: 		 * of retransmit time.
 347: 		 */
 348:         if (tp->t_timer[TCPT_REXMT] == 0 &&
 349:             tp->snd_nxt != tp->snd_una) {
 350:             TCPT_RANGESET(tp->t_timer[TCPT_REXMT],
 351:               tcp_beta * (tp->t_srtt ? tp->t_srtt : TCPTV_SRTTDFLT),
 352:               TCPTV_MIN, TCPTV_MAX);
 353:             tp->t_rxtshift = 0;
 354:             tp->t_timer[TCPT_PERSIST] = 0;
 355:         }
 356:     } else
 357:         if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))
 358:             tp->snd_max = tp->snd_nxt + len;
 359: 
 360:     /*
 361: 	 * Trace.
 362: 	 */
 363:     if (so->so_options & SO_DEBUG)
 364:         tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0);
 365: 
 366:     /*
 367: 	 * Fill in IP length and desired time to live and
 368: 	 * send to IP level.
 369: 	 */
 370:     ((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len;
 371:     ((struct ip *)ti)->ip_ttl = TCP_TTL;
 372:     error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
 373:         so->so_options & SO_DONTROUTE);
 374:     if (error)
 375:         return (error);
 376: 
 377:     /*
 378: 	 * Data sent (as far as we can tell).
 379: 	 * If this advertises a larger window than any other segment,
 380: 	 * then remember the size of the advertised window.
 381: 	 * Any pending ACK has now been sent.
 382: 	 */
 383:     if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
 384:         tp->rcv_adv = tp->rcv_nxt + win;
 385:     tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
 386:     if (sendalot)
 387:         goto again;
 388:     return (0);
 389: }
 390: 
 391: tcp_setpersist(tp)
 392:     register struct tcpcb *tp;
 393: {
 394: 
 395:     if (tp->t_timer[TCPT_REXMT])
 396:         panic("tcp_output REXMT");
 397:     /*
 398: 	 * Start/restart persistance timer.
 399: 	 */
 400:     TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
 401:         ((int)(tcp_beta * tp->t_srtt)) << tp->t_rxtshift,
 402:         TCPTV_PERSMIN, TCPTV_MAX);
 403:     tp->t_rxtshift++;
 404:     if (tp->t_rxtshift >= TCP_MAXRXTSHIFT)
 405:         tp->t_rxtshift = 0;
 406: }

Defined functions

Defined variables

Defined macros