The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/net/slcompress.c

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    1 /*-
    2  * Copyright (c) 1989, 1993, 1994
    3  *      The Regents of the University of California.  All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 3. All advertising materials mentioning features or use of this software
   14  *    must display the following acknowledgement:
   15  *      This product includes software developed by the University of
   16  *      California, Berkeley and its contributors.
   17  * 4. Neither the name of the University nor the names of its contributors
   18  *    may be used to endorse or promote products derived from this software
   19  *    without specific prior written permission.
   20  *
   21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   31  * SUCH DAMAGE.
   32  *
   33  *      @(#)slcompress.c        8.2 (Berkeley) 4/16/94
   34  * $FreeBSD: releng/5.1/sys/net/slcompress.c 113072 2003-04-04 12:11:46Z des $
   35  */
   36 
   37 /*
   38  * Routines to compress and uncompess tcp packets (for transmission
   39  * over low speed serial lines.
   40  *
   41  * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
   42  *      - Initial distribution.
   43  *
   44  */
   45 
   46 #include <sys/param.h>
   47 #include <sys/mbuf.h>
   48 #include <sys/systm.h>
   49 
   50 #include <netinet/in.h>
   51 #include <netinet/in_systm.h>
   52 #include <netinet/ip.h>
   53 #include <netinet/tcp.h>
   54 
   55 #include <net/slcompress.h>
   56 
   57 #ifndef SL_NO_STATS
   58 #define INCR(counter) ++comp->counter;
   59 #else
   60 #define INCR(counter)
   61 #endif
   62 
   63 #define BCMP(p1, p2, n) bcmp((void *)(p1), (void *)(p2), (int)(n))
   64 #define BCOPY(p1, p2, n) bcopy((void *)(p1), (void *)(p2), (int)(n))
   65 
   66 void
   67 sl_compress_init(comp, max_state)
   68         struct slcompress *comp;
   69         int max_state;
   70 {
   71         register u_int i;
   72         register struct cstate *tstate = comp->tstate;
   73 
   74         if (max_state == -1) {
   75                 max_state = MAX_STATES - 1;
   76                 bzero((char *)comp, sizeof(*comp));
   77         } else {
   78                 /* Don't reset statistics */
   79                 bzero((char *)comp->tstate, sizeof(comp->tstate));
   80                 bzero((char *)comp->rstate, sizeof(comp->rstate));
   81         }
   82         for (i = max_state; i > 0; --i) {
   83                 tstate[i].cs_id = i;
   84                 tstate[i].cs_next = &tstate[i - 1];
   85         }
   86         tstate[0].cs_next = &tstate[max_state];
   87         tstate[0].cs_id = 0;
   88         comp->last_cs = &tstate[0];
   89         comp->last_recv = 255;
   90         comp->last_xmit = 255;
   91         comp->flags = SLF_TOSS;
   92 }
   93 
   94 
   95 /* ENCODE encodes a number that is known to be non-zero.  ENCODEZ
   96  * checks for zero (since zero has to be encoded in the long, 3 byte
   97  * form).
   98  */
   99 #define ENCODE(n) { \
  100         if ((u_int16_t)(n) >= 256) { \
  101                 *cp++ = 0; \
  102                 cp[1] = (n); \
  103                 cp[0] = (n) >> 8; \
  104                 cp += 2; \
  105         } else { \
  106                 *cp++ = (n); \
  107         } \
  108 }
  109 #define ENCODEZ(n) { \
  110         if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
  111                 *cp++ = 0; \
  112                 cp[1] = (n); \
  113                 cp[0] = (n) >> 8; \
  114                 cp += 2; \
  115         } else { \
  116                 *cp++ = (n); \
  117         } \
  118 }
  119 
  120 #define DECODEL(f) { \
  121         if (*cp == 0) {\
  122                 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
  123                 cp += 3; \
  124         } else { \
  125                 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
  126         } \
  127 }
  128 
  129 #define DECODES(f) { \
  130         if (*cp == 0) {\
  131                 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
  132                 cp += 3; \
  133         } else { \
  134                 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
  135         } \
  136 }
  137 
  138 #define DECODEU(f) { \
  139         if (*cp == 0) {\
  140                 (f) = htons((cp[1] << 8) | cp[2]); \
  141                 cp += 3; \
  142         } else { \
  143                 (f) = htons((u_int32_t)*cp++); \
  144         } \
  145 }
  146 
  147 /*
  148  * Attempt to compress an outgoing TCP packet and return the type of
  149  * the result.  The caller must have already verified that the protocol
  150  * is TCP.  The first mbuf must contain the complete IP and TCP headers,
  151  * and "ip" must be == mtod(m, struct ip *).  "comp" supplies the
  152  * compression state, and "compress_cid" tells us whether it is OK
  153  * to leave out the CID field when feasible.
  154  *
  155  * The caller is responsible for adjusting m->m_pkthdr.len upon return,
  156  * if m is an M_PKTHDR mbuf.
  157  */
  158 u_int
  159 sl_compress_tcp(m, ip, comp, compress_cid)
  160         struct mbuf *m;
  161         register struct ip *ip;
  162         struct slcompress *comp;
  163         int compress_cid;
  164 {
  165         register struct cstate *cs = comp->last_cs->cs_next;
  166         register u_int hlen = ip->ip_hl;
  167         register struct tcphdr *oth;
  168         register struct tcphdr *th;
  169         register u_int deltaS, deltaA;
  170         register u_int changes = 0;
  171         u_char new_seq[16];
  172         register u_char *cp = new_seq;
  173 
  174         /*
  175          * Bail if this is an IP fragment or if the TCP packet isn't
  176          * `compressible' (i.e., ACK isn't set or some other control bit is
  177          * set).  (We assume that the caller has already made sure the
  178          * packet is IP proto TCP).
  179          */
  180         if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
  181                 return (TYPE_IP);
  182 
  183         th = (struct tcphdr *)&((int32_t *)ip)[hlen];
  184         if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
  185                 return (TYPE_IP);
  186         /*
  187          * Packet is compressible -- we're going to send either a
  188          * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way we need
  189          * to locate (or create) the connection state.  Special case the
  190          * most recently used connection since it's most likely to be used
  191          * again & we don't have to do any reordering if it's used.
  192          */
  193         INCR(sls_packets)
  194         if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
  195             ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
  196             *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
  197                 /*
  198                  * Wasn't the first -- search for it.
  199                  *
  200                  * States are kept in a circularly linked list with
  201                  * last_cs pointing to the end of the list.  The
  202                  * list is kept in lru order by moving a state to the
  203                  * head of the list whenever it is referenced.  Since
  204                  * the list is short and, empirically, the connection
  205                  * we want is almost always near the front, we locate
  206                  * states via linear search.  If we don't find a state
  207                  * for the datagram, the oldest state is (re-)used.
  208                  */
  209                 register struct cstate *lcs;
  210                 register struct cstate *lastcs = comp->last_cs;
  211 
  212                 do {
  213                         lcs = cs; cs = cs->cs_next;
  214                         INCR(sls_searches)
  215                         if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
  216                             && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
  217                             && *(int32_t *)th ==
  218                             ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
  219                                 goto found;
  220                 } while (cs != lastcs);
  221 
  222                 /*
  223                  * Didn't find it -- re-use oldest cstate.  Send an
  224                  * uncompressed packet that tells the other side what
  225                  * connection number we're using for this conversation.
  226                  * Note that since the state list is circular, the oldest
  227                  * state points to the newest and we only need to set
  228                  * last_cs to update the lru linkage.
  229                  */
  230                 INCR(sls_misses)
  231                 comp->last_cs = lcs;
  232                 hlen += th->th_off;
  233                 hlen <<= 2;
  234                 if (hlen > m->m_len)
  235                     return TYPE_IP;
  236                 goto uncompressed;
  237 
  238         found:
  239                 /*
  240                  * Found it -- move to the front on the connection list.
  241                  */
  242                 if (cs == lastcs)
  243                         comp->last_cs = lcs;
  244                 else {
  245                         lcs->cs_next = cs->cs_next;
  246                         cs->cs_next = lastcs->cs_next;
  247                         lastcs->cs_next = cs;
  248                 }
  249         }
  250 
  251         /*
  252          * Make sure that only what we expect to change changed. The first
  253          * line of the `if' checks the IP protocol version, header length &
  254          * type of service.  The 2nd line checks the "Don't fragment" bit.
  255          * The 3rd line checks the time-to-live and protocol (the protocol
  256          * check is unnecessary but costless).  The 4th line checks the TCP
  257          * header length.  The 5th line checks IP options, if any.  The 6th
  258          * line checks TCP options, if any.  If any of these things are
  259          * different between the previous & current datagram, we send the
  260          * current datagram `uncompressed'.
  261          */
  262         oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
  263         deltaS = hlen;
  264         hlen += th->th_off;
  265         hlen <<= 2;
  266         if (hlen > m->m_len)
  267             return TYPE_IP;
  268 
  269         if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
  270             ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
  271             ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
  272             th->th_off != oth->th_off ||
  273             (deltaS > 5 &&
  274              BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
  275             (th->th_off > 5 &&
  276              BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
  277                 goto uncompressed;
  278 
  279         /*
  280          * Figure out which of the changing fields changed.  The
  281          * receiver expects changes in the order: urgent, window,
  282          * ack, seq (the order minimizes the number of temporaries
  283          * needed in this section of code).
  284          */
  285         if (th->th_flags & TH_URG) {
  286                 deltaS = ntohs(th->th_urp);
  287                 ENCODEZ(deltaS);
  288                 changes |= NEW_U;
  289         } else if (th->th_urp != oth->th_urp)
  290                 /* argh! URG not set but urp changed -- a sensible
  291                  * implementation should never do this but RFC793
  292                  * doesn't prohibit the change so we have to deal
  293                  * with it. */
  294                  goto uncompressed;
  295 
  296         deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
  297         if (deltaS) {
  298                 ENCODE(deltaS);
  299                 changes |= NEW_W;
  300         }
  301 
  302         deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
  303         if (deltaA) {
  304                 if (deltaA > 0xffff)
  305                         goto uncompressed;
  306                 ENCODE(deltaA);
  307                 changes |= NEW_A;
  308         }
  309 
  310         deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
  311         if (deltaS) {
  312                 if (deltaS > 0xffff)
  313                         goto uncompressed;
  314                 ENCODE(deltaS);
  315                 changes |= NEW_S;
  316         }
  317 
  318         switch(changes) {
  319 
  320         case 0:
  321                 /*
  322                  * Nothing changed. If this packet contains data and the
  323                  * last one didn't, this is probably a data packet following
  324                  * an ack (normal on an interactive connection) and we send
  325                  * it compressed.  Otherwise it's probably a retransmit,
  326                  * retransmitted ack or window probe.  Send it uncompressed
  327                  * in case the other side missed the compressed version.
  328                  */
  329                 if (ip->ip_len != cs->cs_ip.ip_len &&
  330                     ntohs(cs->cs_ip.ip_len) == hlen)
  331                         break;
  332 
  333                 /* FALLTHROUGH */
  334 
  335         case SPECIAL_I:
  336         case SPECIAL_D:
  337                 /*
  338                  * actual changes match one of our special case encodings --
  339                  * send packet uncompressed.
  340                  */
  341                 goto uncompressed;
  342 
  343         case NEW_S|NEW_A:
  344                 if (deltaS == deltaA &&
  345                     deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
  346                         /* special case for echoed terminal traffic */
  347                         changes = SPECIAL_I;
  348                         cp = new_seq;
  349                 }
  350                 break;
  351 
  352         case NEW_S:
  353                 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
  354                         /* special case for data xfer */
  355                         changes = SPECIAL_D;
  356                         cp = new_seq;
  357                 }
  358                 break;
  359         }
  360 
  361         deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
  362         if (deltaS != 1) {
  363                 ENCODEZ(deltaS);
  364                 changes |= NEW_I;
  365         }
  366         if (th->th_flags & TH_PUSH)
  367                 changes |= TCP_PUSH_BIT;
  368         /*
  369          * Grab the cksum before we overwrite it below.  Then update our
  370          * state with this packet's header.
  371          */
  372         deltaA = ntohs(th->th_sum);
  373         BCOPY(ip, &cs->cs_ip, hlen);
  374 
  375         /*
  376          * We want to use the original packet as our compressed packet.
  377          * (cp - new_seq) is the number of bytes we need for compressed
  378          * sequence numbers.  In addition we need one byte for the change
  379          * mask, one for the connection id and two for the tcp checksum.
  380          * So, (cp - new_seq) + 4 bytes of header are needed.  hlen is how
  381          * many bytes of the original packet to toss so subtract the two to
  382          * get the new packet size.
  383          */
  384         deltaS = cp - new_seq;
  385         cp = (u_char *)ip;
  386         if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
  387                 comp->last_xmit = cs->cs_id;
  388                 hlen -= deltaS + 4;
  389                 cp += hlen;
  390                 *cp++ = changes | NEW_C;
  391                 *cp++ = cs->cs_id;
  392         } else {
  393                 hlen -= deltaS + 3;
  394                 cp += hlen;
  395                 *cp++ = changes;
  396         }
  397         m->m_len -= hlen;
  398         m->m_data += hlen;
  399         *cp++ = deltaA >> 8;
  400         *cp++ = deltaA;
  401         BCOPY(new_seq, cp, deltaS);
  402         INCR(sls_compressed)
  403         return (TYPE_COMPRESSED_TCP);
  404 
  405         /*
  406          * Update connection state cs & send uncompressed packet ('uncompressed'
  407          * means a regular ip/tcp packet but with the 'conversation id' we hope
  408          * to use on future compressed packets in the protocol field).
  409          */
  410 uncompressed:
  411         BCOPY(ip, &cs->cs_ip, hlen);
  412         ip->ip_p = cs->cs_id;
  413         comp->last_xmit = cs->cs_id;
  414         return (TYPE_UNCOMPRESSED_TCP);
  415 }
  416 
  417 
  418 int
  419 sl_uncompress_tcp(bufp, len, type, comp)
  420         u_char **bufp;
  421         int len;
  422         u_int type;
  423         struct slcompress *comp;
  424 {
  425         u_char *hdr, *cp;
  426         int hlen, vjlen;
  427 
  428         cp = bufp? *bufp: NULL;
  429         vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
  430         if (vjlen < 0)
  431                 return (0);     /* error */
  432         if (vjlen == 0)
  433                 return (len);   /* was uncompressed already */
  434 
  435         cp += vjlen;
  436         len -= vjlen;
  437 
  438         /*
  439          * At this point, cp points to the first byte of data in the
  440          * packet.  If we're not aligned on a 4-byte boundary, copy the
  441          * data down so the ip & tcp headers will be aligned.  Then back up
  442          * cp by the tcp/ip header length to make room for the reconstructed
  443          * header (we assume the packet we were handed has enough space to
  444          * prepend 128 bytes of header).
  445          */
  446         if ((intptr_t)cp & 3) {
  447                 if (len > 0)
  448                         BCOPY(cp, ((intptr_t)cp &~ 3), len);
  449                 cp = (u_char *)((intptr_t)cp &~ 3);
  450         }
  451         cp -= hlen;
  452         len += hlen;
  453         BCOPY(hdr, cp, hlen);
  454 
  455         *bufp = cp;
  456         return (len);
  457 }
  458 
  459 /*
  460  * Uncompress a packet of total length total_len.  The first buflen
  461  * bytes are at buf; this must include the entire (compressed or
  462  * uncompressed) TCP/IP header.  This procedure returns the length
  463  * of the VJ header, with a pointer to the uncompressed IP header
  464  * in *hdrp and its length in *hlenp.
  465  */
  466 int
  467 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)
  468         u_char *buf;
  469         int buflen, total_len;
  470         u_int type;
  471         struct slcompress *comp;
  472         u_char **hdrp;
  473         u_int *hlenp;
  474 {
  475         register u_char *cp;
  476         register u_int hlen, changes;
  477         register struct tcphdr *th;
  478         register struct cstate *cs;
  479         register struct ip *ip;
  480         register u_int16_t *bp;
  481         register u_int vjlen;
  482 
  483         switch (type) {
  484 
  485         case TYPE_UNCOMPRESSED_TCP:
  486                 ip = (struct ip *) buf;
  487                 if (ip->ip_p >= MAX_STATES)
  488                         goto bad;
  489                 cs = &comp->rstate[comp->last_recv = ip->ip_p];
  490                 comp->flags &=~ SLF_TOSS;
  491                 ip->ip_p = IPPROTO_TCP;
  492                 /*
  493                  * Calculate the size of the TCP/IP header and make sure that
  494                  * we don't overflow the space we have available for it.
  495                  */
  496                 hlen = ip->ip_hl << 2;
  497                 if (hlen + sizeof(struct tcphdr) > buflen)
  498                         goto bad;
  499                 hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
  500                 if (hlen > MAX_HDR || hlen > buflen)
  501                         goto bad;
  502                 BCOPY(ip, &cs->cs_ip, hlen);
  503                 cs->cs_hlen = hlen;
  504                 INCR(sls_uncompressedin)
  505                 *hdrp = (u_char *) &cs->cs_ip;
  506                 *hlenp = hlen;
  507                 return (0);
  508 
  509         default:
  510                 goto bad;
  511 
  512         case TYPE_COMPRESSED_TCP:
  513                 break;
  514         }
  515         /* We've got a compressed packet. */
  516         INCR(sls_compressedin)
  517         cp = buf;
  518         changes = *cp++;
  519         if (changes & NEW_C) {
  520                 /* Make sure the state index is in range, then grab the state.
  521                  * If we have a good state index, clear the 'discard' flag. */
  522                 if (*cp >= MAX_STATES)
  523                         goto bad;
  524 
  525                 comp->flags &=~ SLF_TOSS;
  526                 comp->last_recv = *cp++;
  527         } else {
  528                 /* this packet has an implicit state index.  If we've
  529                  * had a line error since the last time we got an
  530                  * explicit state index, we have to toss the packet. */
  531                 if (comp->flags & SLF_TOSS) {
  532                         INCR(sls_tossed)
  533                         return (-1);
  534                 }
  535         }
  536         cs = &comp->rstate[comp->last_recv];
  537         hlen = cs->cs_ip.ip_hl << 2;
  538         th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
  539         th->th_sum = htons((*cp << 8) | cp[1]);
  540         cp += 2;
  541         if (changes & TCP_PUSH_BIT)
  542                 th->th_flags |= TH_PUSH;
  543         else
  544                 th->th_flags &=~ TH_PUSH;
  545 
  546         switch (changes & SPECIALS_MASK) {
  547         case SPECIAL_I:
  548                 {
  549                 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
  550                 th->th_ack = htonl(ntohl(th->th_ack) + i);
  551                 th->th_seq = htonl(ntohl(th->th_seq) + i);
  552                 }
  553                 break;
  554 
  555         case SPECIAL_D:
  556                 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
  557                                    - cs->cs_hlen);
  558                 break;
  559 
  560         default:
  561                 if (changes & NEW_U) {
  562                         th->th_flags |= TH_URG;
  563                         DECODEU(th->th_urp)
  564                 } else
  565                         th->th_flags &=~ TH_URG;
  566                 if (changes & NEW_W)
  567                         DECODES(th->th_win)
  568                 if (changes & NEW_A)
  569                         DECODEL(th->th_ack)
  570                 if (changes & NEW_S)
  571                         DECODEL(th->th_seq)
  572                 break;
  573         }
  574         if (changes & NEW_I) {
  575                 DECODES(cs->cs_ip.ip_id)
  576         } else
  577                 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
  578 
  579         /*
  580          * At this point, cp points to the first byte of data in the
  581          * packet.  Fill in the IP total length and update the IP
  582          * header checksum.
  583          */
  584         vjlen = cp - buf;
  585         buflen -= vjlen;
  586         if (buflen < 0)
  587                 /* we must have dropped some characters (crc should detect
  588                  * this but the old slip framing won't) */
  589                 goto bad;
  590 
  591         total_len += cs->cs_hlen - vjlen;
  592         cs->cs_ip.ip_len = htons(total_len);
  593 
  594         /* recompute the ip header checksum */
  595         bp = (u_int16_t *) &cs->cs_ip;
  596         cs->cs_ip.ip_sum = 0;
  597                 for (changes = 0; hlen > 0; hlen -= 2)
  598                         changes += *bp++;
  599                 changes = (changes & 0xffff) + (changes >> 16);
  600                 changes = (changes & 0xffff) + (changes >> 16);
  601         cs->cs_ip.ip_sum = ~ changes;
  602 
  603         *hdrp = (u_char *) &cs->cs_ip;
  604         *hlenp = cs->cs_hlen;
  605         return vjlen;
  606 
  607 bad:
  608         comp->flags |= SLF_TOSS;
  609         INCR(sls_errorin)
  610         return (-1);
  611 }

Cache object: fb794cf70bb80e16f1bd1cb2af92ef19


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