1: /*
   2:  * Copyright (c) 1982, 1986 Regents of the University of California.
   3:  * All rights reserved.
   4:  *
   5:  * Redistribution and use in source and binary forms are permitted
   6:  * provided that this notice is preserved and that due credit is given
   7:  * to the University of California at Berkeley. The name of the University
   8:  * may not be used to endorse or promote products derived from this
   9:  * software without specific prior written permission. This software
  10:  * is provided ``as is'' without express or implied warranty.
  11:  *
  12:  *	@(#)tcp_output.c	7.13.1.4 (Berkeley) 1995/10/10
  13:  */
  14: 
  15: #include "param.h"
  16: #include "systm.h"
  17: #include "mbuf.h"
  18: #include "protosw.h"
  19: #include "socket.h"
  20: #include "socketvar.h"
  21: #include "errno.h"
  22: 
  23: #include "../net/route.h"
  24: 
  25: #include "domain.h"
  26: #include "in.h"
  27: #include "in_pcb.h"
  28: #include "in_systm.h"
  29: #include "ip.h"
  30: #include "ip_var.h"
  31: #include "tcp.h"
  32: #define TCPOUTFLAGS
  33: #include "tcp_fsm.h"
  34: #include "tcp_seq.h"
  35: #include "tcp_timer.h"
  36: #include "tcp_var.h"
  37: #include "tcpip.h"
  38: #include "tcp_debug.h"
  39: 
  40: /*
  41:  * Initial options.
  42:  */
  43: u_char  tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, };
  44: 
  45: /*
  46:  * Tcp output routine: figure out what should be sent and send it.
  47:  */
  48: tcp_output(tp)
  49:     register struct tcpcb *tp;
  50: {
  51:     register struct socket *so = tp->t_inpcb->inp_socket;
  52:     register int len, win;
  53:     struct mbuf *m0;
  54:     int off, flags, error;
  55:     register struct mbuf *m;
  56:     register struct tcpiphdr *ti;
  57:     u_char *opt;
  58:     unsigned optlen = 0;
  59:     int idle, sendalot;
  60: 
  61:     /*
  62: 	 * Determine length of data that should be transmitted,
  63: 	 * and flags that will be used.
  64: 	 * If there is some data or critical controls (SYN, RST)
  65: 	 * to send, then transmit; otherwise, investigate further.
  66: 	 */
  67:     idle = (tp->snd_max == tp->snd_una);
  68: again:
  69:     sendalot = 0;
  70:     off = tp->snd_nxt - tp->snd_una;
  71:     win = MIN(tp->snd_wnd, tp->snd_cwnd);
  72: 
  73:     /*
  74: 	 * If in persist timeout with window of 0, send 1 byte.
  75: 	 * Otherwise, if window is small but nonzero
  76: 	 * and timer expired, we will send what we can
  77: 	 * and go to transmit state.
  78: 	 */
  79:     if (tp->t_force) {
  80:         if (win == 0)
  81:             win = 1;
  82:         else {
  83:             tp->t_timer[TCPT_PERSIST] = 0;
  84:             tp->t_rxtshift = 0;
  85:         }
  86:     }
  87: 
  88:     len = MIN(so->so_snd.sb_cc, win) - off;
  89:     flags = tcp_outflags[tp->t_state];
  90: 
  91:     if (len < 0) {
  92:         /*
  93: 		 * If FIN has been sent but not acked,
  94: 		 * but we haven't been called to retransmit,
  95: 		 * len will be -1.  Otherwise, window shrank
  96: 		 * after we sent into it.  If window shrank to 0,
  97: 		 * cancel pending retransmit and pull snd_nxt
  98: 		 * back to (closed) window.  We will enter persist
  99: 		 * state below.  If the window didn't close completely,
 100: 		 * just wait for an ACK.
 101: 		 */
 102:         len = 0;
 103:         if (win == 0) {
 104:             tp->t_timer[TCPT_REXMT] = 0;
 105:             tp->snd_nxt = tp->snd_una;
 106:         }
 107:     }
 108:     if (len > tp->t_maxseg) {
 109:         len = tp->t_maxseg;
 110:         sendalot = 1;
 111:     }
 112:     if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
 113:         flags &= ~TH_FIN;
 114:     win = sbspace(&so->so_rcv);
 115: 
 116: 
 117:     /*
 118: 	 * If our state indicates that FIN should be sent
 119: 	 * and we have not yet done so, or we're retransmitting the FIN,
 120: 	 * then we need to send.
 121: 	 */
 122:     if (flags & TH_FIN &&
 123:         ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
 124:         goto send;
 125:     /*
 126: 	 * Send if we owe peer an ACK.
 127: 	 */
 128:     if (tp->t_flags & TF_ACKNOW)
 129:         goto send;
 130:     if (flags & (TH_SYN|TH_RST))
 131:         goto send;
 132:     if (SEQ_GT(tp->snd_up, tp->snd_una))
 133:         goto send;
 134: 
 135:     /*
 136: 	 * Sender silly window avoidance.  If connection is idle
 137: 	 * and can send all data, a maximum segment,
 138: 	 * at least a maximum default-size segment do it,
 139: 	 * or are forced, do it; otherwise don't bother.
 140: 	 * If peer's buffer is tiny, then send
 141: 	 * when window is at least half open.
 142: 	 * If retransmitting (possibly after persist timer forced us
 143: 	 * to send into a small window), then must resend.
 144: 	 */
 145:     if (len) {
 146:         if (len == tp->t_maxseg)
 147:             goto send;
 148:         if ((idle || tp->t_flags & TF_NODELAY) &&
 149:             len + off >= so->so_snd.sb_cc)
 150:             goto send;
 151:         if (tp->t_force)
 152:             goto send;
 153:         if (len >= tp->max_sndwnd / 2)
 154:             goto send;
 155:         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
 156:             goto send;
 157:     }
 158: 
 159:     /*
 160: 	 * Compare available window to amount of window
 161: 	 * known to peer (as advertised window less
 162: 	 * next expected input).  If the difference is at least two
 163: 	 * max size segments or at least 35% of the maximum possible
 164: 	 * window, then want to send a window update to peer.
 165: 	 */
 166:     if (win > 0) {
 167:         int adv = win - (tp->rcv_adv - tp->rcv_nxt);
 168: 
 169:         if (so->so_rcv.sb_cc == 0 && adv >= 2 * tp->t_maxseg)
 170:             goto send;
 171:         if (100 * adv / so->so_rcv.sb_hiwat >= 35)
 172:             goto send;
 173:     }
 174: 
 175:     /*
 176: 	 * TCP window updates are not reliable, rather a polling protocol
 177: 	 * using ``persist'' packets is used to insure receipt of window
 178: 	 * updates.  The three ``states'' for the output side are:
 179: 	 *	idle			not doing retransmits or persists
 180: 	 *	persisting		to move a small or zero window
 181: 	 *	(re)transmitting	and thereby not persisting
 182: 	 *
 183: 	 * tp->t_timer[TCPT_PERSIST]
 184: 	 *	is set when we are in persist state.
 185: 	 * tp->t_force
 186: 	 *	is set when we are called to send a persist packet.
 187: 	 * tp->t_timer[TCPT_REXMT]
 188: 	 *	is set when we are retransmitting
 189: 	 * The output side is idle when both timers are zero.
 190: 	 *
 191: 	 * If send window is too small, there is data to transmit, and no
 192: 	 * retransmit or persist is pending, then go to persist state.
 193: 	 * If nothing happens soon, send when timer expires:
 194: 	 * if window is nonzero, transmit what we can,
 195: 	 * otherwise force out a byte.
 196: 	 */
 197:     if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&
 198:         tp->t_timer[TCPT_PERSIST] == 0) {
 199:         tp->t_rxtshift = 0;
 200:         tcp_setpersist(tp);
 201:     }
 202: 
 203:     /*
 204: 	 * No reason to send a segment, just return.
 205: 	 */
 206:     return (0);
 207: 
 208: send:
 209:     /*
 210: 	 * Grab a header mbuf, attaching a copy of data to
 211: 	 * be transmitted, and initialize the header from
 212: 	 * the template for sends on this connection.
 213: 	 */
 214:     MGET(m, M_DONTWAIT, MT_HEADER);
 215:     if (m == NULL)
 216:         return (ENOBUFS);
 217:     m->m_off = MMAXOFF - sizeof (struct tcpiphdr);
 218:     m->m_len = sizeof (struct tcpiphdr);
 219:     if (len) {
 220:         if (tp->t_force && len == 1)
 221:             tcpstat.tcps_sndprobe++;
 222:         else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
 223:             tcpstat.tcps_sndrexmitpack++;
 224:             tcpstat.tcps_sndrexmitbyte += len;
 225:         } else {
 226:             tcpstat.tcps_sndpack++;
 227:             tcpstat.tcps_sndbyte += len;
 228:         }
 229:         m->m_next = m_copy(so->so_snd.sb_mb, off, len);
 230:         if (m->m_next == 0)
 231:             len = 0;
 232:     } else if (tp->t_flags & TF_ACKNOW)
 233:         tcpstat.tcps_sndacks++;
 234:     else if (flags & (TH_SYN|TH_FIN|TH_RST))
 235:         tcpstat.tcps_sndctrl++;
 236:     else if (SEQ_GT(tp->snd_up, tp->snd_una))
 237:         tcpstat.tcps_sndurg++;
 238:     else
 239:         tcpstat.tcps_sndwinup++;
 240: 
 241:     ti = mtod(m, struct tcpiphdr *);
 242:     if (tp->t_template == 0)
 243:         panic("tcp_output");
 244:     bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr));
 245: 
 246:     /*
 247: 	 * Fill in fields, remembering maximum advertised
 248: 	 * window for use in delaying messages about window sizes.
 249: 	 * If resending a FIN, be sure not to use a new sequence number.
 250: 	 */
 251:     if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
 252:         tp->snd_nxt == tp->snd_max)
 253:         tp->snd_nxt--;
 254:     ti->ti_seq = htonl(tp->snd_nxt);
 255:     ti->ti_ack = htonl(tp->rcv_nxt);
 256:     /*
 257: 	 * Before ESTABLISHED, force sending of initial options
 258: 	 * unless TCP set to not do any options.
 259: 	 */
 260:     opt = NULL;
 261:     if (flags & TH_SYN && (tp->t_flags & TF_NOOPT) == 0) {
 262:         u_short mss;
 263: 
 264:         mss = MIN(so->so_rcv.sb_hiwat / 2, tcp_mss(tp));
 265:         if (mss > IP_MSS - sizeof(struct tcpiphdr)) {
 266:             opt = tcp_initopt;
 267:             optlen = sizeof (tcp_initopt);
 268:             *(u_short *)(opt + 2) = htons(mss);
 269:         }
 270:     }
 271:     if (opt) {
 272:         m0 = m->m_next;
 273:         m->m_next = m_get(M_DONTWAIT, MT_DATA);
 274:         if (m->m_next == 0) {
 275:             (void) m_free(m);
 276:             m_freem(m0);
 277:             return (ENOBUFS);
 278:         }
 279:         m->m_next->m_next = m0;
 280:         m0 = m->m_next;
 281:         m0->m_len = optlen;
 282:         bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen);
 283:         opt = (u_char *)(mtod(m0, caddr_t) + optlen);
 284:         while (m0->m_len & 0x3) {
 285:             *opt++ = TCPOPT_EOL;
 286:             m0->m_len++;
 287:         }
 288:         optlen = m0->m_len;
 289:         ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
 290:     }
 291:     ti->ti_flags = flags;
 292:     /*
 293: 	 * Calculate receive window.  Don't shrink window,
 294: 	 * but avoid silly window syndrome.
 295: 	 */
 296:     if (win < (so->so_rcv.sb_hiwat / 4) && win < tp->t_maxseg)
 297:         win = 0;
 298:     if (win < (int)(tp->rcv_adv - tp->rcv_nxt))
 299:         win = (int)(tp->rcv_adv - tp->rcv_nxt);
 300:     if (win > IP_MAXPACKET)
 301:         win = IP_MAXPACKET;
 302:     ti->ti_win = htons((u_short)win);
 303:     if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
 304:         ti->ti_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
 305:         ti->ti_flags |= TH_URG;
 306:     } else
 307:         /*
 308: 		 * If no urgent pointer to send, then we pull
 309: 		 * the urgent pointer to the left edge of the send window
 310: 		 * so that it doesn't drift into the send window on sequence
 311: 		 * number wraparound.
 312: 		 */
 313:         tp->snd_up = tp->snd_una;       /* drag it along */
 314:     /*
 315: 	 * If anything to send and we can send it all, set PUSH.
 316: 	 * (This will keep happy those implementations which only
 317: 	 * give data to the user when a buffer fills or a PUSH comes in.)
 318: 	 */
 319:     if (len && off+len == so->so_snd.sb_cc)
 320:         ti->ti_flags |= TH_PUSH;
 321: 
 322:     /*
 323: 	 * Put TCP length in extended header, and then
 324: 	 * checksum extended header and data.
 325: 	 */
 326:     if (len + optlen)
 327:         ti->ti_len = htons((u_short)(sizeof(struct tcphdr) +
 328:             optlen + len));
 329:     ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + len);
 330: 
 331:     /*
 332: 	 * In transmit state, time the transmission and arrange for
 333: 	 * the retransmit.  In persist state, just set snd_max.
 334: 	 */
 335:     if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {
 336:         tcp_seq startseq = tp->snd_nxt;
 337: 
 338:         /*
 339: 		 * Advance snd_nxt over sequence space of this segment.
 340: 		 */
 341:         if (flags & TH_SYN)
 342:             tp->snd_nxt++;
 343:         if (flags & TH_FIN) {
 344:             tp->snd_nxt++;
 345:             tp->t_flags |= TF_SENTFIN;
 346:         }
 347:         tp->snd_nxt += len;
 348:         if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
 349:             tp->snd_max = tp->snd_nxt;
 350:             /*
 351: 			 * Time this transmission if not a retransmission and
 352: 			 * not currently timing anything.
 353: 			 */
 354:             if (tp->t_rtt == 0) {
 355:                 tp->t_rtt = 1;
 356:                 tp->t_rtseq = startseq;
 357:                 tcpstat.tcps_segstimed++;
 358:             }
 359:         }
 360: 
 361:         /*
 362: 		 * Set retransmit timer if not currently set,
 363: 		 * and not doing an ack or a keep-alive probe.
 364: 		 * Initial value for retransmit timer is smoothed
 365: 		 * round-trip time + 2 * round-trip time variance.
 366: 		 * Initialize shift counter which is used for backoff
 367: 		 * of retransmit time.
 368: 		 */
 369:         if (tp->t_timer[TCPT_REXMT] == 0 &&
 370:             tp->snd_nxt != tp->snd_una) {
 371:             tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
 372:             if (tp->t_timer[TCPT_PERSIST]) {
 373:                 tp->t_timer[TCPT_PERSIST] = 0;
 374:                 tp->t_rxtshift = 0;
 375:             }
 376:         }
 377:     } else
 378:         if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))
 379:             tp->snd_max = tp->snd_nxt + len;
 380: 
 381:     /*
 382: 	 * Trace.
 383: 	 */
 384:     if (so->so_options & SO_DEBUG)
 385:         tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0);
 386: 
 387:     /*
 388: 	 * Fill in IP length and desired time to live and
 389: 	 * send to IP level.
 390: 	 */
 391:     ((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len;
 392:     ((struct ip *)ti)->ip_ttl = ip_defttl;  /* XXX */
 393: #if BSD>=43
 394:     error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
 395:         so->so_options & SO_DONTROUTE);
 396: #else
 397:     error = ip_output(m, (struct mbuf *)0, &tp->t_inpcb->inp_route,
 398:               so->so_options & SO_DONTROUTE);
 399: #endif
 400:     if (error) {
 401:         if (error == ENOBUFS) {
 402:             tcp_quench(tp->t_inpcb);
 403:             return (0);
 404:         }
 405:         return (error);
 406:     }
 407:     tcpstat.tcps_sndtotal++;
 408: 
 409:     /*
 410: 	 * Data sent (as far as we can tell).
 411: 	 * If this advertises a larger window than any other segment,
 412: 	 * then remember the size of the advertised window.
 413: 	 * Any pending ACK has now been sent.
 414: 	 */
 415:     if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
 416:         tp->rcv_adv = tp->rcv_nxt + win;
 417:     tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
 418:     if (sendalot)
 419:         goto again;
 420:     return (0);
 421: }
 422: 
 423: tcp_setpersist(tp)
 424:     register struct tcpcb *tp;
 425: {
 426:     register t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
 427: 
 428:     if (tp->t_timer[TCPT_REXMT])
 429:         panic("tcp_output REXMT");
 430:     /*
 431: 	 * Start/restart persistance timer.
 432: 	 */
 433:     TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
 434:         t * tcp_backoff[tp->t_rxtshift],
 435:         TCPTV_PERSMIN, TCPTV_PERSMAX);
 436:     if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
 437:         tp->t_rxtshift++;
 438: }

Defined functions

tcp_output defined in line 48; never used
tcp_setpersist defined in line 423; used 1 times

Defined variables

tcp_initopt defined in line 43; used 2 times

Defined macros

TCPOUTFLAGS defined in line 32; never used
Last modified: 1995-10-11
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