| 1 | /* tcp_output.c 4.46 82/10/09 */ |
| 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, 0); |
| 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 | #if vax |
| 166 | ti->ti_seq = htonl(ti->ti_seq); |
| 167 | ti->ti_ack = htonl(ti->ti_ack); |
| 168 | #endif |
| 169 | /* |
| 170 | * Before ESTABLISHED, force sending of initial options |
| 171 | * unless TCP set to not do any options. |
| 172 | */ |
| 173 | if (tp->t_state < TCPS_ESTABLISHED) { |
| 174 | if (tp->t_flags&TF_NOOPT) |
| 175 | goto noopt; |
| 176 | opt = tcp_initopt; |
| 177 | optlen = sizeof (tcp_initopt); |
| 178 | *(u_short *)(opt + 2) = MIN(so->so_rcv.sb_hiwat / 2, 1024); |
| 179 | #if vax |
| 180 | *(u_short *)(opt + 2) = htons(*(u_short *)(opt + 2)); |
| 181 | #endif |
| 182 | } else { |
| 183 | if (tp->t_tcpopt == 0) |
| 184 | goto noopt; |
| 185 | opt = mtod(tp->t_tcpopt, u_char *); |
| 186 | optlen = tp->t_tcpopt->m_len; |
| 187 | } |
| 188 | if (opt) { |
| 189 | m0 = m->m_next; |
| 190 | m->m_next = m_get(M_DONTWAIT); |
| 191 | if (m->m_next == 0) { |
| 192 | (void) m_free(m); |
| 193 | m_freem(m0); |
| 194 | return (ENOBUFS); |
| 195 | } |
| 196 | m->m_next->m_next = m0; |
| 197 | m0 = m->m_next; |
| 198 | m0->m_len = optlen; |
| 199 | bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen); |
| 200 | opt = (u_char *)(mtod(m0, caddr_t) + optlen); |
| 201 | while (m0->m_len & 0x3) { |
| 202 | *opt++ = TCPOPT_EOL; |
| 203 | m0->m_len++; |
| 204 | } |
| 205 | optlen = m0->m_len; |
| 206 | ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2; |
| 207 | } |
| 208 | noopt: |
| 209 | ti->ti_flags = flags; |
| 210 | win = sbspace(&so->so_rcv); |
| 211 | if (win < so->so_rcv.sb_hiwat / 4) /* avoid silly window */ |
| 212 | win = 0; |
| 213 | if (win > 0) |
| 214 | #if vax |
| 215 | ti->ti_win = htons((u_short)win); |
| 216 | #else |
| 217 | ti->ti_win = win; |
| 218 | #endif |
| 219 | if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { |
| 220 | ti->ti_urp = tp->snd_up - tp->snd_nxt; |
| 221 | #if vax |
| 222 | ti->ti_urp = htons(ti->ti_urp); |
| 223 | #endif |
| 224 | ti->ti_flags |= TH_URG; |
| 225 | } else |
| 226 | /* |
| 227 | * If no urgent pointer to send, then we pull |
| 228 | * the urgent pointer to the left edge of the send window |
| 229 | * so that it doesn't drift into the send window on sequence |
| 230 | * number wraparound. |
| 231 | */ |
| 232 | tp->snd_up = tp->snd_una; /* drag it along */ |
| 233 | /* |
| 234 | * If anything to send and we can send it all, set PUSH. |
| 235 | * (This will keep happy those implementations which only |
| 236 | * give data to the user when a buffer fills or a PUSH comes in. |
| 237 | */ |
| 238 | if (len && off+len == so->so_snd.sb_cc) |
| 239 | ti->ti_flags |= TH_PUSH; |
| 240 | |
| 241 | /* |
| 242 | * Put TCP length in extended header, and then |
| 243 | * checksum extended header and data. |
| 244 | */ |
| 245 | if (len + optlen) { |
| 246 | ti->ti_len = sizeof (struct tcphdr) + optlen + len; |
| 247 | #if vax |
| 248 | ti->ti_len = htons((u_short)ti->ti_len); |
| 249 | #endif |
| 250 | } |
| 251 | ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + len); |
| 252 | |
| 253 | /* |
| 254 | * In transmit state, time the transmission and arrange for |
| 255 | * the retransmit. In persist state, reset persist time for |
| 256 | * next persist. |
| 257 | */ |
| 258 | if (tp->t_force == 0) { |
| 259 | /* |
| 260 | * Advance snd_nxt over sequence space of this segment. |
| 261 | */ |
| 262 | if (flags & (TH_SYN|TH_FIN)) |
| 263 | tp->snd_nxt++; |
| 264 | tp->snd_nxt += len; |
| 265 | if (SEQ_GT(tp->snd_nxt, tp->snd_max)) |
| 266 | tp->snd_max = tp->snd_nxt; |
| 267 | |
| 268 | /* |
| 269 | * Time this transmission if not a retransmission and |
| 270 | * not currently timing anything. |
| 271 | */ |
| 272 | if (SEQ_GT(tp->snd_nxt, tp->snd_max) && tp->t_rtt == 0) { |
| 273 | tp->t_rtt = 1; |
| 274 | tp->t_rtseq = tp->snd_nxt - len; |
| 275 | } |
| 276 | |
| 277 | /* |
| 278 | * Set retransmit timer if not currently set. |
| 279 | * Initial value for retransmit timer to tcp_beta*tp->t_srtt. |
| 280 | * Initialize shift counter which is used for exponential |
| 281 | * backoff of retransmit time. |
| 282 | */ |
| 283 | if (tp->t_timer[TCPT_REXMT] == 0 && |
| 284 | tp->snd_nxt != tp->snd_una) { |
| 285 | TCPT_RANGESET(tp->t_timer[TCPT_REXMT], |
| 286 | tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX); |
| 287 | tp->t_rtt = 0; |
| 288 | tp->t_rxtshift = 0; |
| 289 | } |
| 290 | tp->t_timer[TCPT_PERSIST] = 0; |
| 291 | } else { |
| 292 | if (SEQ_GT(tp->snd_una+1, tp->snd_max)) |
| 293 | tp->snd_max = tp->snd_una+1; |
| 294 | } |
| 295 | |
| 296 | /* |
| 297 | * Trace. |
| 298 | */ |
| 299 | if (so->so_options & SO_DEBUG) |
| 300 | tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0); |
| 301 | |
| 302 | /* |
| 303 | * Fill in IP length and desired time to live and |
| 304 | * send to IP level. |
| 305 | */ |
| 306 | ((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len; |
| 307 | ((struct ip *)ti)->ip_ttl = TCP_TTL; |
| 308 | if (error = ip_output(m, tp->t_ipopt, (so->so_options & SO_DONTROUTE) ? |
| 309 | &routetoif : &tp->t_inpcb->inp_route, 0)) |
| 310 | return (error); |
| 311 | |
| 312 | /* |
| 313 | * Data sent (as far as we can tell). |
| 314 | * If this advertises a larger window than any other segment, |
| 315 | * then remember the size of the advertised window. |
| 316 | * Drop send for purpose of ACK requirements. |
| 317 | */ |
| 318 | if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) |
| 319 | tp->rcv_adv = tp->rcv_nxt + win; |
| 320 | tp->t_flags &= ~(TF_ACKNOW|TF_DELACK); |
| 321 | if (sendalot && tp->t_force == 0) |
| 322 | goto again; |
| 323 | return (0); |
| 324 | } |
| 325 | |
| 326 | tcp_setpersist(tp) |
| 327 | register struct tcpcb *tp; |
| 328 | { |
| 329 | |
| 330 | if (tp->t_timer[TCPT_REXMT]) |
| 331 | panic("tcp_output REXMT"); |
| 332 | /* |
| 333 | * Start/restart persistance timer. |
| 334 | */ |
| 335 | TCPT_RANGESET(tp->t_timer[TCPT_PERSIST], |
| 336 | ((int)(tcp_beta * tp->t_srtt)) << tp->t_rxtshift, |
| 337 | TCPTV_PERSMIN, TCPTV_MAX); |
| 338 | tp->t_rxtshift++; |
| 339 | if (tp->t_rxtshift >= TCP_MAXRXTSHIFT) |
| 340 | tp->t_rxtshift = 0; |
| 341 | } |