Annotation of sys/net/slcompress.c, Revision 1.1
1.1 ! nbrk 1: /* $OpenBSD: slcompress.c,v 1.9 2007/02/14 00:53:48 jsg Exp $ */
! 2: /* $NetBSD: slcompress.c,v 1.17 1997/05/17 21:12:10 christos Exp $ */
! 3:
! 4: /*
! 5: * Copyright (c) 1989, 1993, 1994
! 6: * The Regents of the University of California. All rights reserved.
! 7: *
! 8: * Redistribution and use in source and binary forms, with or without
! 9: * modification, are permitted provided that the following conditions
! 10: * are met:
! 11: * 1. Redistributions of source code must retain the above copyright
! 12: * notice, this list of conditions and the following disclaimer.
! 13: * 2. Redistributions in binary form must reproduce the above copyright
! 14: * notice, this list of conditions and the following disclaimer in the
! 15: * documentation and/or other materials provided with the distribution.
! 16: * 3. Neither the name of the University nor the names of its contributors
! 17: * may be used to endorse or promote products derived from this software
! 18: * without specific prior written permission.
! 19: *
! 20: * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
! 21: * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
! 22: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
! 23: * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
! 24: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
! 25: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
! 26: * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
! 27: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
! 28: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
! 29: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
! 30: * SUCH DAMAGE.
! 31: *
! 32: * @(#)slcompress.c 8.2 (Berkeley) 4/16/94
! 33: */
! 34:
! 35: /*
! 36: * Routines to compress and uncompess tcp packets (for transmission
! 37: * over low speed serial lines.
! 38: *
! 39: * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
! 40: * - Initial distribution.
! 41: */
! 42:
! 43: #include <sys/param.h>
! 44: #include <sys/mbuf.h>
! 45: #include <sys/systm.h>
! 46:
! 47: #include <netinet/in.h>
! 48: #include <netinet/in_systm.h>
! 49: #include <netinet/ip.h>
! 50: #include <netinet/tcp.h>
! 51:
! 52: #include <net/slcompress.h>
! 53:
! 54: #ifndef SL_NO_STATS
! 55: #define INCR(counter) ++comp->counter;
! 56: #else
! 57: #define INCR(counter)
! 58: #endif
! 59:
! 60: #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
! 61: #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
! 62: #ifndef _KERNEL
! 63: #define ovbcopy bcopy
! 64: #endif
! 65:
! 66:
! 67: void
! 68: sl_compress_init(comp)
! 69: struct slcompress *comp;
! 70: {
! 71: u_int i;
! 72: struct cstate *tstate = comp->tstate;
! 73:
! 74: bzero((char *)comp, sizeof(*comp));
! 75: for (i = MAX_STATES - 1; i > 0; --i) {
! 76: tstate[i].cs_id = i;
! 77: tstate[i].cs_next = &tstate[i - 1];
! 78: }
! 79: tstate[0].cs_next = &tstate[MAX_STATES - 1];
! 80: tstate[0].cs_id = 0;
! 81: comp->last_cs = &tstate[0];
! 82: comp->last_recv = 255;
! 83: comp->last_xmit = 255;
! 84: comp->flags = SLF_TOSS;
! 85: }
! 86:
! 87:
! 88: /*
! 89: * Like sl_compress_init, but we get to specify the maximum connection
! 90: * ID to use on transmission.
! 91: */
! 92: void
! 93: sl_compress_setup(comp, max_state)
! 94: struct slcompress *comp;
! 95: int max_state;
! 96: {
! 97: u_int i;
! 98: struct cstate *tstate = comp->tstate;
! 99:
! 100: if (max_state == -1) {
! 101: max_state = MAX_STATES - 1;
! 102: bzero((char *)comp, sizeof(*comp));
! 103: } else {
! 104: /* Don't reset statistics */
! 105: bzero((char *)comp->tstate, sizeof(comp->tstate));
! 106: bzero((char *)comp->rstate, sizeof(comp->rstate));
! 107: }
! 108: for (i = max_state; i > 0; --i) {
! 109: tstate[i].cs_id = i;
! 110: tstate[i].cs_next = &tstate[i - 1];
! 111: }
! 112: tstate[0].cs_next = &tstate[max_state];
! 113: tstate[0].cs_id = 0;
! 114: comp->last_cs = &tstate[0];
! 115: comp->last_recv = 255;
! 116: comp->last_xmit = 255;
! 117: comp->flags = SLF_TOSS;
! 118: }
! 119:
! 120:
! 121: /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
! 122: * checks for zero (since zero has to be encoded in the long, 3 byte
! 123: * form).
! 124: */
! 125: #define ENCODE(n) { \
! 126: if ((u_int16_t)(n) >= 256) { \
! 127: *cp++ = 0; \
! 128: cp[1] = (n); \
! 129: cp[0] = (n) >> 8; \
! 130: cp += 2; \
! 131: } else { \
! 132: *cp++ = (n); \
! 133: } \
! 134: }
! 135: #define ENCODEZ(n) { \
! 136: if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
! 137: *cp++ = 0; \
! 138: cp[1] = (n); \
! 139: cp[0] = (n) >> 8; \
! 140: cp += 2; \
! 141: } else { \
! 142: *cp++ = (n); \
! 143: } \
! 144: }
! 145:
! 146: #define DECODEL(f) { \
! 147: if (*cp == 0) {\
! 148: (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
! 149: cp += 3; \
! 150: } else { \
! 151: (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
! 152: } \
! 153: }
! 154:
! 155: #define DECODES(f) { \
! 156: if (*cp == 0) {\
! 157: (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
! 158: cp += 3; \
! 159: } else { \
! 160: (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
! 161: } \
! 162: }
! 163:
! 164: #define DECODEU(f) { \
! 165: if (*cp == 0) {\
! 166: (f) = htons((cp[1] << 8) | cp[2]); \
! 167: cp += 3; \
! 168: } else { \
! 169: (f) = htons((u_int32_t)*cp++); \
! 170: } \
! 171: }
! 172:
! 173: u_int
! 174: sl_compress_tcp(m, ip, comp, compress_cid)
! 175: struct mbuf *m;
! 176: struct ip *ip;
! 177: struct slcompress *comp;
! 178: int compress_cid;
! 179: {
! 180: struct cstate *cs = comp->last_cs->cs_next;
! 181: u_int hlen = ip->ip_hl;
! 182: struct tcphdr *oth;
! 183: struct tcphdr *th;
! 184: u_int deltaS, deltaA;
! 185: u_int changes = 0;
! 186: u_char new_seq[16];
! 187: u_char *cp = new_seq;
! 188:
! 189: /*
! 190: * Bail if this is an IP fragment or if the TCP packet isn't
! 191: * `compressible' (i.e., ACK isn't set or some other control bit is
! 192: * set). (We assume that the caller has already made sure the
! 193: * packet is IP proto TCP).
! 194: */
! 195: if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
! 196: return (TYPE_IP);
! 197:
! 198: th = (struct tcphdr *)&((int32_t *)ip)[hlen];
! 199: if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
! 200: return (TYPE_IP);
! 201: /*
! 202: * Packet is compressible -- we're going to send either a
! 203: * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
! 204: * to locate (or create) the connection state. Special case the
! 205: * most recently used connection since it's most likely to be used
! 206: * again & we don't have to do any reordering if it's used.
! 207: */
! 208: INCR(sls_packets)
! 209: if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
! 210: ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
! 211: *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
! 212: /*
! 213: * Wasn't the first -- search for it.
! 214: *
! 215: * States are kept in a circularly linked list with
! 216: * last_cs pointing to the end of the list. The
! 217: * list is kept in lru order by moving a state to the
! 218: * head of the list whenever it is referenced. Since
! 219: * the list is short and, empirically, the connection
! 220: * we want is almost always near the front, we locate
! 221: * states via linear search. If we don't find a state
! 222: * for the datagram, the oldest state is (re-)used.
! 223: */
! 224: struct cstate *lcs;
! 225: struct cstate *lastcs = comp->last_cs;
! 226:
! 227: do {
! 228: lcs = cs; cs = cs->cs_next;
! 229: INCR(sls_searches)
! 230: if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
! 231: && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
! 232: && *(int32_t *)th ==
! 233: ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
! 234: goto found;
! 235: } while (cs != lastcs);
! 236:
! 237: /*
! 238: * Didn't find it -- re-use oldest cstate. Send an
! 239: * uncompressed packet that tells the other side what
! 240: * connection number we're using for this conversation.
! 241: * Note that since the state list is circular, the oldest
! 242: * state points to the newest and we only need to set
! 243: * last_cs to update the lru linkage.
! 244: */
! 245: INCR(sls_misses)
! 246: comp->last_cs = lcs;
! 247: hlen += th->th_off;
! 248: hlen <<= 2;
! 249: goto uncompressed;
! 250:
! 251: found:
! 252: /*
! 253: * Found it -- move to the front on the connection list.
! 254: */
! 255: if (cs == lastcs)
! 256: comp->last_cs = lcs;
! 257: else {
! 258: lcs->cs_next = cs->cs_next;
! 259: cs->cs_next = lastcs->cs_next;
! 260: lastcs->cs_next = cs;
! 261: }
! 262: }
! 263:
! 264: /*
! 265: * Make sure that only what we expect to change changed. The first
! 266: * line of the `if' checks the IP protocol version, header length &
! 267: * type of service. The 2nd line checks the "Don't fragment" bit.
! 268: * The 3rd line checks the time-to-live and protocol (the protocol
! 269: * check is unnecessary but costless). The 4th line checks the TCP
! 270: * header length. The 5th line checks IP options, if any. The 6th
! 271: * line checks TCP options, if any. If any of these things are
! 272: * different between the previous & current datagram, we send the
! 273: * current datagram `uncompressed'.
! 274: */
! 275: oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
! 276: deltaS = hlen;
! 277: hlen += th->th_off;
! 278: hlen <<= 2;
! 279:
! 280: if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
! 281: ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
! 282: ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
! 283: th->th_off != oth->th_off ||
! 284: (deltaS > 5 &&
! 285: BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
! 286: (th->th_off > 5 &&
! 287: BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
! 288: goto uncompressed;
! 289:
! 290: /*
! 291: * Figure out which of the changing fields changed. The
! 292: * receiver expects changes in the order: urgent, window,
! 293: * ack, seq (the order minimizes the number of temporaries
! 294: * needed in this section of code).
! 295: */
! 296: if (th->th_flags & TH_URG) {
! 297: deltaS = ntohs(th->th_urp);
! 298: ENCODEZ(deltaS);
! 299: changes |= NEW_U;
! 300: } else if (th->th_urp != oth->th_urp)
! 301: /* argh! URG not set but urp changed -- a sensible
! 302: * implementation should never do this but RFC793
! 303: * doesn't prohibit the change so we have to deal
! 304: * with it. */
! 305: goto uncompressed;
! 306:
! 307: deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
! 308: if (deltaS) {
! 309: ENCODE(deltaS);
! 310: changes |= NEW_W;
! 311: }
! 312:
! 313: deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
! 314: if (deltaA) {
! 315: if (deltaA > 0xffff)
! 316: goto uncompressed;
! 317: ENCODE(deltaA);
! 318: changes |= NEW_A;
! 319: }
! 320:
! 321: deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
! 322: if (deltaS) {
! 323: if (deltaS > 0xffff)
! 324: goto uncompressed;
! 325: ENCODE(deltaS);
! 326: changes |= NEW_S;
! 327: }
! 328:
! 329: switch(changes) {
! 330:
! 331: case 0:
! 332: /*
! 333: * Nothing changed. If this packet contains data and the
! 334: * last one didn't, this is probably a data packet following
! 335: * an ack (normal on an interactive connection) and we send
! 336: * it compressed. Otherwise it's probably a retransmit,
! 337: * retransmitted ack or window probe. Send it uncompressed
! 338: * in case the other side missed the compressed version.
! 339: */
! 340: if (ip->ip_len != cs->cs_ip.ip_len &&
! 341: ntohs(cs->cs_ip.ip_len) == hlen)
! 342: break;
! 343:
! 344: /* FALLTHROUGH */
! 345:
! 346: case SPECIAL_I:
! 347: case SPECIAL_D:
! 348: /*
! 349: * actual changes match one of our special case encodings --
! 350: * send packet uncompressed.
! 351: */
! 352: goto uncompressed;
! 353:
! 354: case NEW_S|NEW_A:
! 355: if (deltaS == deltaA &&
! 356: deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
! 357: /* special case for echoed terminal traffic */
! 358: changes = SPECIAL_I;
! 359: cp = new_seq;
! 360: }
! 361: break;
! 362:
! 363: case NEW_S:
! 364: if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
! 365: /* special case for data xfer */
! 366: changes = SPECIAL_D;
! 367: cp = new_seq;
! 368: }
! 369: break;
! 370: }
! 371:
! 372: deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
! 373: if (deltaS != 1) {
! 374: ENCODEZ(deltaS);
! 375: changes |= NEW_I;
! 376: }
! 377: if (th->th_flags & TH_PUSH)
! 378: changes |= TCP_PUSH_BIT;
! 379: /*
! 380: * Grab the cksum before we overwrite it below. Then update our
! 381: * state with this packet's header.
! 382: */
! 383: deltaA = ntohs(th->th_sum);
! 384: BCOPY(ip, &cs->cs_ip, hlen);
! 385:
! 386: /*
! 387: * We want to use the original packet as our compressed packet.
! 388: * (cp - new_seq) is the number of bytes we need for compressed
! 389: * sequence numbers. In addition we need one byte for the change
! 390: * mask, one for the connection id and two for the tcp checksum.
! 391: * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
! 392: * many bytes of the original packet to toss so subtract the two to
! 393: * get the new packet size.
! 394: */
! 395: deltaS = cp - new_seq;
! 396: cp = (u_char *)ip;
! 397: if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
! 398: comp->last_xmit = cs->cs_id;
! 399: hlen -= deltaS + 4;
! 400: cp += hlen;
! 401: *cp++ = changes | NEW_C;
! 402: *cp++ = cs->cs_id;
! 403: } else {
! 404: hlen -= deltaS + 3;
! 405: cp += hlen;
! 406: *cp++ = changes;
! 407: }
! 408: m->m_len -= hlen;
! 409: m->m_data += hlen;
! 410: *cp++ = deltaA >> 8;
! 411: *cp++ = deltaA;
! 412: BCOPY(new_seq, cp, deltaS);
! 413: INCR(sls_compressed)
! 414: return (TYPE_COMPRESSED_TCP);
! 415:
! 416: /*
! 417: * Update connection state cs & send uncompressed packet ('uncompressed'
! 418: * means a regular ip/tcp packet but with the 'conversation id' we hope
! 419: * to use on future compressed packets in the protocol field).
! 420: */
! 421: uncompressed:
! 422: BCOPY(ip, &cs->cs_ip, hlen);
! 423: ip->ip_p = cs->cs_id;
! 424: comp->last_xmit = cs->cs_id;
! 425: return (TYPE_UNCOMPRESSED_TCP);
! 426: }
! 427:
! 428:
! 429: int
! 430: sl_uncompress_tcp(bufp, len, type, comp)
! 431: u_char **bufp;
! 432: int len;
! 433: u_int type;
! 434: struct slcompress *comp;
! 435: {
! 436: u_char *hdr, *cp;
! 437: int hlen, vjlen;
! 438:
! 439: cp = bufp? *bufp: NULL;
! 440: vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
! 441: if (vjlen < 0)
! 442: return (0); /* error */
! 443: if (vjlen == 0)
! 444: return (len); /* was uncompressed already */
! 445:
! 446: cp += vjlen;
! 447: len -= vjlen;
! 448:
! 449: /*
! 450: * At this point, cp points to the first byte of data in the
! 451: * packet. If we're not aligned on a 4-byte boundary, copy the
! 452: * data down so the ip & tcp headers will be aligned. Then back up
! 453: * cp by the tcp/ip header length to make room for the reconstructed
! 454: * header (we assume the packet we were handed has enough space to
! 455: * prepend 128 bytes of header).
! 456: */
! 457: if ((long)cp & 3) {
! 458: if (len > 0)
! 459: (void) ovbcopy(cp, (caddr_t)((long)cp &~ 3), len);
! 460: cp = (u_char *)((long)cp &~ 3);
! 461: }
! 462: cp -= hlen;
! 463: len += hlen;
! 464: BCOPY(hdr, cp, hlen);
! 465:
! 466: *bufp = cp;
! 467: return (len);
! 468: }
! 469:
! 470: /*
! 471: * Uncompress a packet of total length total_len. The first buflen
! 472: * bytes are at buf; this must include the entire (compressed or
! 473: * uncompressed) TCP/IP header. This procedure returns the length
! 474: * of the VJ header, with a pointer to the uncompressed IP header
! 475: * in *hdrp and its length in *hlenp.
! 476: */
! 477: int
! 478: sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)
! 479: u_char *buf;
! 480: int buflen, total_len;
! 481: u_int type;
! 482: struct slcompress *comp;
! 483: u_char **hdrp;
! 484: u_int *hlenp;
! 485: {
! 486: u_char *cp;
! 487: u_int hlen, changes;
! 488: struct tcphdr *th;
! 489: struct cstate *cs;
! 490: struct ip *ip;
! 491: u_int16_t *bp;
! 492: u_int vjlen;
! 493:
! 494: switch (type) {
! 495:
! 496: case TYPE_UNCOMPRESSED_TCP:
! 497: ip = (struct ip *) buf;
! 498: if (ip->ip_p >= MAX_STATES)
! 499: goto bad;
! 500: cs = &comp->rstate[comp->last_recv = ip->ip_p];
! 501: comp->flags &=~ SLF_TOSS;
! 502: ip->ip_p = IPPROTO_TCP;
! 503: /*
! 504: * Calculate the size of the TCP/IP header and make sure that
! 505: * we don't overflow the space we have available for it.
! 506: */
! 507: hlen = ip->ip_hl << 2;
! 508: if (hlen + sizeof(struct tcphdr) > buflen)
! 509: goto bad;
! 510: hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
! 511: if (hlen > MAX_HDR || hlen > buflen)
! 512: goto bad;
! 513: BCOPY(ip, &cs->cs_ip, hlen);
! 514: cs->cs_hlen = hlen;
! 515: INCR(sls_uncompressedin)
! 516: *hdrp = (u_char *) &cs->cs_ip;
! 517: *hlenp = hlen;
! 518: return (0);
! 519:
! 520: default:
! 521: goto bad;
! 522:
! 523: case TYPE_COMPRESSED_TCP:
! 524: break;
! 525: }
! 526: /* We've got a compressed packet. */
! 527: INCR(sls_compressedin)
! 528: cp = buf;
! 529: changes = *cp++;
! 530: if (changes & NEW_C) {
! 531: /* Make sure the state index is in range, then grab the state.
! 532: * If we have a good state index, clear the 'discard' flag. */
! 533: if (*cp >= MAX_STATES)
! 534: goto bad;
! 535:
! 536: comp->flags &=~ SLF_TOSS;
! 537: comp->last_recv = *cp++;
! 538: } else {
! 539: /* this packet has an implicit state index. If we've
! 540: * had a line error since the last time we got an
! 541: * explicit state index, we have to toss the packet. */
! 542: if (comp->flags & SLF_TOSS) {
! 543: INCR(sls_tossed)
! 544: return (-1);
! 545: }
! 546: }
! 547: cs = &comp->rstate[comp->last_recv];
! 548: hlen = cs->cs_ip.ip_hl << 2;
! 549: th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
! 550: th->th_sum = htons((*cp << 8) | cp[1]);
! 551: cp += 2;
! 552: if (changes & TCP_PUSH_BIT)
! 553: th->th_flags |= TH_PUSH;
! 554: else
! 555: th->th_flags &=~ TH_PUSH;
! 556:
! 557: switch (changes & SPECIALS_MASK) {
! 558: case SPECIAL_I:
! 559: {
! 560: u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
! 561: th->th_ack = htonl(ntohl(th->th_ack) + i);
! 562: th->th_seq = htonl(ntohl(th->th_seq) + i);
! 563: }
! 564: break;
! 565:
! 566: case SPECIAL_D:
! 567: th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
! 568: - cs->cs_hlen);
! 569: break;
! 570:
! 571: default:
! 572: if (changes & NEW_U) {
! 573: th->th_flags |= TH_URG;
! 574: DECODEU(th->th_urp)
! 575: } else
! 576: th->th_flags &=~ TH_URG;
! 577: if (changes & NEW_W)
! 578: DECODES(th->th_win)
! 579: if (changes & NEW_A)
! 580: DECODEL(th->th_ack)
! 581: if (changes & NEW_S)
! 582: DECODEL(th->th_seq)
! 583: break;
! 584: }
! 585: if (changes & NEW_I) {
! 586: DECODES(cs->cs_ip.ip_id)
! 587: } else
! 588: cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
! 589:
! 590: /*
! 591: * At this point, cp points to the first byte of data in the
! 592: * packet. Fill in the IP total length and update the IP
! 593: * header checksum.
! 594: */
! 595: vjlen = cp - buf;
! 596: buflen -= vjlen;
! 597: if (buflen < 0)
! 598: /* we must have dropped some characters (crc should detect
! 599: * this but the old slip framing won't) */
! 600: goto bad;
! 601:
! 602: total_len += cs->cs_hlen - vjlen;
! 603: cs->cs_ip.ip_len = htons(total_len);
! 604:
! 605: /* recompute the ip header checksum */
! 606: bp = (u_int16_t *) &cs->cs_ip;
! 607: cs->cs_ip.ip_sum = 0;
! 608: for (changes = 0; hlen > 0; hlen -= 2)
! 609: changes += *bp++;
! 610: changes = (changes & 0xffff) + (changes >> 16);
! 611: changes = (changes & 0xffff) + (changes >> 16);
! 612: cs->cs_ip.ip_sum = ~ changes;
! 613:
! 614: *hdrp = (u_char *) &cs->cs_ip;
! 615: *hlenp = cs->cs_hlen;
! 616: return vjlen;
! 617:
! 618: bad:
! 619: comp->flags |= SLF_TOSS;
! 620: INCR(sls_errorin)
! 621: return (-1);
! 622: }
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