Diff: netif/ppp/vj.c

Revision:

0:51ac1d130fd4

diff -r 000000000000 -r 51ac1d130fd4 netif/ppp/vj.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/netif/ppp/vj.c	Fri Jun 22 09:25:39 2012 +0000
@@ -0,0 +1,652 @@
+/*
+ * Routines to compress and uncompess tcp packets (for transmission
+ * over low speed serial lines.
+ *
+ * Copyright (c) 1989 Regents of the University of California.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms are permitted
+ * provided that the above copyright notice and this paragraph are
+ * duplicated in all such forms and that any documentation,
+ * advertising materials, and other materials related to such
+ * distribution and use acknowledge that the software was developed
+ * by the University of California, Berkeley.  The name of the
+ * University may not be used to endorse or promote products derived
+ * from this software without specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
+ * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
+ *   Initial distribution.
+ *
+ * Modified June 1993 by Paul Mackerras, paulus@cs.anu.edu.au,
+ * so that the entire packet being decompressed doesn't have
+ * to be in contiguous memory (just the compressed header).
+ *
+ * Modified March 1998 by Guy Lancaster, glanca@gesn.com,
+ * for a 16 bit processor.
+ */
+
+#include "lwip/opt.h"
+
+#if PPP_SUPPORT /* don't build if not configured for use in lwipopts.h */
+
+#include "ppp.h"
+#include "pppdebug.h"
+
+#include "vj.h"
+
+#include <string.h>
+
+#if VJ_SUPPORT
+
+#if LINK_STATS
+#define INCR(counter) ++comp->stats.counter
+#else
+#define INCR(counter)
+#endif
+
+void
+vj_compress_init(struct vjcompress *comp)
+{
+  register u_char i;
+  register struct cstate *tstate = comp->tstate;
+  
+#if MAX_SLOTS == 0
+  memset((char *)comp, 0, sizeof(*comp));
+#endif
+  comp->maxSlotIndex = MAX_SLOTS - 1;
+  comp->compressSlot = 0;    /* Disable slot ID compression by default. */
+  for (i = MAX_SLOTS - 1; i > 0; --i) {
+    tstate[i].cs_id = i;
+    tstate[i].cs_next = &tstate[i - 1];
+  }
+  tstate[0].cs_next = &tstate[MAX_SLOTS - 1];
+  tstate[0].cs_id = 0;
+  comp->last_cs = &tstate[0];
+  comp->last_recv = 255;
+  comp->last_xmit = 255;
+  comp->flags = VJF_TOSS;
+}
+
+
+/* ENCODE encodes a number that is known to be non-zero.  ENCODEZ
+ * checks for zero (since zero has to be encoded in the long, 3 byte
+ * form).
+ */
+#define ENCODE(n) { \
+  if ((u_short)(n) >= 256) { \
+    *cp++ = 0; \
+    cp[1] = (u_char)(n); \
+    cp[0] = (u_char)((n) >> 8); \
+    cp += 2; \
+  } else { \
+    *cp++ = (u_char)(n); \
+  } \
+}
+#define ENCODEZ(n) { \
+  if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
+    *cp++ = 0; \
+    cp[1] = (u_char)(n); \
+    cp[0] = (u_char)((n) >> 8); \
+    cp += 2; \
+  } else { \
+    *cp++ = (u_char)(n); \
+  } \
+}
+
+#define DECODEL(f) { \
+  if (*cp == 0) {\
+    u32_t tmp = ntohl(f) + ((cp[1] << 8) | cp[2]); \
+    (f) = htonl(tmp); \
+    cp += 3; \
+  } else { \
+    u32_t tmp = ntohl(f) + (u32_t)*cp++; \
+    (f) = htonl(tmp); \
+  } \
+}
+
+#define DECODES(f) { \
+  if (*cp == 0) {\
+    u_short tmp = ntohs(f) + (((u_short)cp[1] << 8) | cp[2]); \
+    (f) = htons(tmp); \
+    cp += 3; \
+  } else { \
+    u_short tmp = ntohs(f) + (u_short)*cp++; \
+    (f) = htons(tmp); \
+  } \
+}
+
+#define DECODEU(f) { \
+  if (*cp == 0) {\
+    (f) = htons(((u_short)cp[1] << 8) | cp[2]); \
+    cp += 3; \
+  } else { \
+    (f) = htons((u_short)*cp++); \
+  } \
+}
+
+/*
+ * vj_compress_tcp - Attempt to do Van Jacobson header compression on a
+ * packet.  This assumes that nb and comp are not null and that the first
+ * buffer of the chain contains a valid IP header.
+ * Return the VJ type code indicating whether or not the packet was
+ * compressed.
+ */
+u_int
+vj_compress_tcp(struct vjcompress *comp, struct pbuf *pb)
+{
+  register struct ip_hdr *ip = (struct ip_hdr *)pb->payload;
+  register struct cstate *cs = comp->last_cs->cs_next;
+  register u_short hlen = IPH_HL(ip);
+  register struct tcp_hdr *oth;
+  register struct tcp_hdr *th;
+  register u_short deltaS, deltaA;
+  register u_long deltaL;
+  register u_int changes = 0;
+  u_char new_seq[16];
+  register u_char *cp = new_seq;
+
+  /*  
+   * Check that the packet is IP proto TCP.
+   */
+  if (IPH_PROTO(ip) != IP_PROTO_TCP) {
+    return (TYPE_IP);
+  }
+
+  /*
+   * Bail if this is an IP fragment or if the TCP packet isn't
+   * `compressible' (i.e., ACK isn't set or some other control bit is
+   * set).  
+   */
+  if ((IPH_OFFSET(ip) & PP_HTONS(0x3fff)) || pb->tot_len < 40) {
+    return (TYPE_IP);
+  }
+  th = (struct tcp_hdr *)&((long *)ip)[hlen];
+  if ((TCPH_FLAGS(th) & (TCP_SYN|TCP_FIN|TCP_RST|TCP_ACK)) != TCP_ACK) {
+    return (TYPE_IP);
+  }
+  /*
+   * Packet is compressible -- we're going to send either a
+   * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way we need
+   * to locate (or create) the connection state.  Special case the
+   * most recently used connection since it's most likely to be used
+   * again & we don't have to do any reordering if it's used.
+   */
+  INCR(vjs_packets);
+  if (!ip_addr_cmp(&ip->src, &cs->cs_ip.src)
+      || !ip_addr_cmp(&ip->dest, &cs->cs_ip.dest)
+      || *(long *)th != ((long *)&cs->cs_ip)[IPH_HL(&cs->cs_ip)]) {
+    /*
+     * Wasn't the first -- search for it.
+     *
+     * States are kept in a circularly linked list with
+     * last_cs pointing to the end of the list.  The
+     * list is kept in lru order by moving a state to the
+     * head of the list whenever it is referenced.  Since
+     * the list is short and, empirically, the connection
+     * we want is almost always near the front, we locate
+     * states via linear search.  If we don't find a state
+     * for the datagram, the oldest state is (re-)used.
+     */
+    register struct cstate *lcs;
+    register struct cstate *lastcs = comp->last_cs;
+    
+    do {
+      lcs = cs; cs = cs->cs_next;
+      INCR(vjs_searches);
+      if (ip_addr_cmp(&ip->src, &cs->cs_ip.src)
+          && ip_addr_cmp(&ip->dest, &cs->cs_ip.dest)
+          && *(long *)th == ((long *)&cs->cs_ip)[IPH_HL(&cs->cs_ip)]) {
+        goto found;
+      }
+    } while (cs != lastcs);
+
+    /*
+     * Didn't find it -- re-use oldest cstate.  Send an
+     * uncompressed packet that tells the other side what
+     * connection number we're using for this conversation.
+     * Note that since the state list is circular, the oldest
+     * state points to the newest and we only need to set
+     * last_cs to update the lru linkage.
+     */
+    INCR(vjs_misses);
+    comp->last_cs = lcs;
+    hlen += TCPH_OFFSET(th);
+    hlen <<= 2;
+    /* Check that the IP/TCP headers are contained in the first buffer. */
+    if (hlen > pb->len) {
+      return (TYPE_IP);
+    }
+    goto uncompressed;
+
+    found:
+    /*
+     * Found it -- move to the front on the connection list.
+     */
+    if (cs == lastcs) {
+      comp->last_cs = lcs;
+    } else {
+      lcs->cs_next = cs->cs_next;
+      cs->cs_next = lastcs->cs_next;
+      lastcs->cs_next = cs;
+    }
+  }
+
+  oth = (struct tcp_hdr *)&((long *)&cs->cs_ip)[hlen];
+  deltaS = hlen;
+  hlen += TCPH_OFFSET(th);
+  hlen <<= 2;
+  /* Check that the IP/TCP headers are contained in the first buffer. */
+  if (hlen > pb->len) {
+    PPPDEBUG(LOG_INFO, ("vj_compress_tcp: header len %d spans buffers\n", hlen));
+    return (TYPE_IP);
+  }
+
+  /*
+   * Make sure that only what we expect to change changed. The first
+   * line of the `if' checks the IP protocol version, header length &
+   * type of service.  The 2nd line checks the "Don't fragment" bit.
+   * The 3rd line checks the time-to-live and protocol (the protocol
+   * check is unnecessary but costless).  The 4th line checks the TCP
+   * header length.  The 5th line checks IP options, if any.  The 6th
+   * line checks TCP options, if any.  If any of these things are
+   * different between the previous & current datagram, we send the
+   * current datagram `uncompressed'.
+   */
+  if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] 
+      || ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] 
+      || ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] 
+      || TCPH_OFFSET(th) != TCPH_OFFSET(oth) 
+      || (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) 
+      || (TCPH_OFFSET(th) > 5 && BCMP(th + 1, oth + 1, (TCPH_OFFSET(th) - 5) << 2))) {
+    goto uncompressed;
+  }
+
+  /*
+   * Figure out which of the changing fields changed.  The
+   * receiver expects changes in the order: urgent, window,
+   * ack, seq (the order minimizes the number of temporaries
+   * needed in this section of code).
+   */
+  if (TCPH_FLAGS(th) & TCP_URG) {
+    deltaS = ntohs(th->urgp);
+    ENCODEZ(deltaS);
+    changes |= NEW_U;
+  } else if (th->urgp != oth->urgp) {
+    /* argh! URG not set but urp changed -- a sensible
+     * implementation should never do this but RFC793
+     * doesn't prohibit the change so we have to deal
+     * with it. */
+    goto uncompressed;
+  }
+
+  if ((deltaS = (u_short)(ntohs(th->wnd) - ntohs(oth->wnd))) != 0) {
+    ENCODE(deltaS);
+    changes |= NEW_W;
+  }
+
+  if ((deltaL = ntohl(th->ackno) - ntohl(oth->ackno)) != 0) {
+    if (deltaL > 0xffff) {
+      goto uncompressed;
+    }
+    deltaA = (u_short)deltaL;
+    ENCODE(deltaA);
+    changes |= NEW_A;
+  }
+
+  if ((deltaL = ntohl(th->seqno) - ntohl(oth->seqno)) != 0) {
+    if (deltaL > 0xffff) {
+      goto uncompressed;
+    }
+    deltaS = (u_short)deltaL;
+    ENCODE(deltaS);
+    changes |= NEW_S;
+  }
+
+  switch(changes) {
+  case 0:
+    /*
+     * Nothing changed. If this packet contains data and the
+     * last one didn't, this is probably a data packet following
+     * an ack (normal on an interactive connection) and we send
+     * it compressed.  Otherwise it's probably a retransmit,
+     * retransmitted ack or window probe.  Send it uncompressed
+     * in case the other side missed the compressed version.
+     */
+    if (IPH_LEN(ip) != IPH_LEN(&cs->cs_ip) &&
+      ntohs(IPH_LEN(&cs->cs_ip)) == hlen) {
+      break;
+    }
+
+  /* (fall through) */
+
+  case SPECIAL_I:
+  case SPECIAL_D:
+    /*
+     * actual changes match one of our special case encodings --
+     * send packet uncompressed.
+     */
+    goto uncompressed;
+
+  case NEW_S|NEW_A:
+    if (deltaS == deltaA && deltaS == ntohs(IPH_LEN(&cs->cs_ip)) - hlen) {
+      /* special case for echoed terminal traffic */
+      changes = SPECIAL_I;
+      cp = new_seq;
+    }
+    break;
+
+  case NEW_S:
+    if (deltaS == ntohs(IPH_LEN(&cs->cs_ip)) - hlen) {
+      /* special case for data xfer */
+      changes = SPECIAL_D;
+      cp = new_seq;
+    }
+    break;
+  }
+
+  deltaS = (u_short)(ntohs(IPH_ID(ip)) - ntohs(IPH_ID(&cs->cs_ip)));
+  if (deltaS != 1) {
+    ENCODEZ(deltaS);
+    changes |= NEW_I;
+  }
+  if (TCPH_FLAGS(th) & TCP_PSH) {
+    changes |= TCP_PUSH_BIT;
+  }
+  /*
+   * Grab the cksum before we overwrite it below.  Then update our
+   * state with this packet's header.
+   */
+  deltaA = ntohs(th->chksum);
+  BCOPY(ip, &cs->cs_ip, hlen);
+
+  /*
+   * We want to use the original packet as our compressed packet.
+   * (cp - new_seq) is the number of bytes we need for compressed
+   * sequence numbers.  In addition we need one byte for the change
+   * mask, one for the connection id and two for the tcp checksum.
+   * So, (cp - new_seq) + 4 bytes of header are needed.  hlen is how
+   * many bytes of the original packet to toss so subtract the two to
+   * get the new packet size.
+   */
+  deltaS = (u_short)(cp - new_seq);
+  if (!comp->compressSlot || comp->last_xmit != cs->cs_id) {
+    comp->last_xmit = cs->cs_id;
+    hlen -= deltaS + 4;
+    if(pbuf_header(pb, -hlen)){
+      /* Can we cope with this failing?  Just assert for now */
+      LWIP_ASSERT("pbuf_header failed\n", 0);
+    }
+    cp = (u_char *)pb->payload;
+    *cp++ = (u_char)(changes | NEW_C);
+    *cp++ = cs->cs_id;
+  } else {
+    hlen -= deltaS + 3;
+    if(pbuf_header(pb, -hlen)) {
+      /* Can we cope with this failing?  Just assert for now */
+      LWIP_ASSERT("pbuf_header failed\n", 0);
+    }
+    cp = (u_char *)pb->payload;
+    *cp++ = (u_char)changes;
+  }
+  *cp++ = (u_char)(deltaA >> 8);
+  *cp++ = (u_char)deltaA;
+  BCOPY(new_seq, cp, deltaS);
+  INCR(vjs_compressed);
+  return (TYPE_COMPRESSED_TCP);
+
+  /*
+   * Update connection state cs & send uncompressed packet (that is,
+   * a regular ip/tcp packet but with the 'conversation id' we hope
+   * to use on future compressed packets in the protocol field).
+   */
+uncompressed:
+  BCOPY(ip, &cs->cs_ip, hlen);
+  IPH_PROTO_SET(ip, cs->cs_id);
+  comp->last_xmit = cs->cs_id;
+  return (TYPE_UNCOMPRESSED_TCP);
+}
+
+/*
+ * Called when we may have missed a packet.
+ */
+void
+vj_uncompress_err(struct vjcompress *comp)
+{
+  comp->flags |= VJF_TOSS;
+  INCR(vjs_errorin);
+}
+
+/*
+ * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
+ * Return 0 on success, -1 on failure.
+ */
+int
+vj_uncompress_uncomp(struct pbuf *nb, struct vjcompress *comp)
+{
+  register u_int hlen;
+  register struct cstate *cs;
+  register struct ip_hdr *ip;
+  
+  ip = (struct ip_hdr *)nb->payload;
+  hlen = IPH_HL(ip) << 2;
+  if (IPH_PROTO(ip) >= MAX_SLOTS
+      || hlen + sizeof(struct tcp_hdr) > nb->len
+      || (hlen += TCPH_OFFSET(((struct tcp_hdr *)&((char *)ip)[hlen])) << 2)
+          > nb->len
+      || hlen > MAX_HDR) {
+    PPPDEBUG(LOG_INFO, ("vj_uncompress_uncomp: bad cid=%d, hlen=%d buflen=%d\n", 
+      IPH_PROTO(ip), hlen, nb->len));
+    comp->flags |= VJF_TOSS;
+    INCR(vjs_errorin);
+    return -1;
+  }
+  cs = &comp->rstate[comp->last_recv = IPH_PROTO(ip)];
+  comp->flags &=~ VJF_TOSS;
+  IPH_PROTO_SET(ip, IP_PROTO_TCP);
+  BCOPY(ip, &cs->cs_ip, hlen);
+  cs->cs_hlen = (u_short)hlen;
+  INCR(vjs_uncompressedin);
+  return 0;
+}
+
+/*
+ * Uncompress a packet of type TYPE_COMPRESSED_TCP.
+ * The packet is composed of a buffer chain and the first buffer
+ * must contain an accurate chain length.
+ * The first buffer must include the entire compressed TCP/IP header. 
+ * This procedure replaces the compressed header with the uncompressed
+ * header and returns the length of the VJ header.
+ */
+int
+vj_uncompress_tcp(struct pbuf **nb, struct vjcompress *comp)
+{
+  u_char *cp;
+  struct tcp_hdr *th;
+  struct cstate *cs;
+  u_short *bp;
+  struct pbuf *n0 = *nb;
+  u32_t tmp;
+  u_int vjlen, hlen, changes;
+
+  INCR(vjs_compressedin);
+  cp = (u_char *)n0->payload;
+  changes = *cp++;
+  if (changes & NEW_C) {
+    /* 
+     * Make sure the state index is in range, then grab the state.
+     * If we have a good state index, clear the 'discard' flag. 
+     */
+    if (*cp >= MAX_SLOTS) {
+      PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: bad cid=%d\n", *cp));
+      goto bad;
+    }
+
+    comp->flags &=~ VJF_TOSS;
+    comp->last_recv = *cp++;
+  } else {
+    /* 
+     * this packet has an implicit state index.  If we've
+     * had a line error since the last time we got an
+     * explicit state index, we have to toss the packet. 
+     */
+    if (comp->flags & VJF_TOSS) {
+      PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: tossing\n"));
+      INCR(vjs_tossed);
+      return (-1);
+    }
+  }
+  cs = &comp->rstate[comp->last_recv];
+  hlen = IPH_HL(&cs->cs_ip) << 2;
+  th = (struct tcp_hdr *)&((u_char *)&cs->cs_ip)[hlen];
+  th->chksum = htons((*cp << 8) | cp[1]);
+  cp += 2;
+  if (changes & TCP_PUSH_BIT) {
+    TCPH_SET_FLAG(th, TCP_PSH);
+  } else {
+    TCPH_UNSET_FLAG(th, TCP_PSH);
+  }
+
+  switch (changes & SPECIALS_MASK) {
+  case SPECIAL_I:
+    {
+      register u32_t i = ntohs(IPH_LEN(&cs->cs_ip)) - cs->cs_hlen;
+      /* some compilers can't nest inline assembler.. */
+      tmp = ntohl(th->ackno) + i;
+      th->ackno = htonl(tmp);
+      tmp = ntohl(th->seqno) + i;
+      th->seqno = htonl(tmp);
+    }
+    break;
+
+  case SPECIAL_D:
+    /* some compilers can't nest inline assembler.. */
+    tmp = ntohl(th->seqno) + ntohs(IPH_LEN(&cs->cs_ip)) - cs->cs_hlen;
+    th->seqno = htonl(tmp);
+    break;
+
+  default:
+    if (changes & NEW_U) {
+      TCPH_SET_FLAG(th, TCP_URG);
+      DECODEU(th->urgp);
+    } else {
+      TCPH_UNSET_FLAG(th, TCP_URG);
+    }
+    if (changes & NEW_W) {
+      DECODES(th->wnd);
+    }
+    if (changes & NEW_A) {
+      DECODEL(th->ackno);
+    }
+    if (changes & NEW_S) {
+      DECODEL(th->seqno);
+    }
+    break;
+  }
+  if (changes & NEW_I) {
+    DECODES(cs->cs_ip._id);
+  } else {
+    IPH_ID_SET(&cs->cs_ip, ntohs(IPH_ID(&cs->cs_ip)) + 1);
+    IPH_ID_SET(&cs->cs_ip, htons(IPH_ID(&cs->cs_ip)));
+  }
+
+  /*
+   * At this point, cp points to the first byte of data in the
+   * packet.  Fill in the IP total length and update the IP
+   * header checksum.
+   */
+  vjlen = (u_short)(cp - (u_char*)n0->payload);
+  if (n0->len < vjlen) {
+    /* 
+     * We must have dropped some characters (crc should detect
+     * this but the old slip framing won't) 
+     */
+    PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: head buffer %d too short %d\n", 
+          n0->len, vjlen));
+    goto bad;
+  }
+
+#if BYTE_ORDER == LITTLE_ENDIAN
+  tmp = n0->tot_len - vjlen + cs->cs_hlen;
+  IPH_LEN_SET(&cs->cs_ip, htons((u_short)tmp));
+#else
+  IPH_LEN_SET(&cs->cs_ip, htons(n0->tot_len - vjlen + cs->cs_hlen));
+#endif
+
+  /* recompute the ip header checksum */
+  bp = (u_short *) &cs->cs_ip;
+  IPH_CHKSUM_SET(&cs->cs_ip, 0);
+  for (tmp = 0; hlen > 0; hlen -= 2) {
+    tmp += *bp++;
+  }
+  tmp = (tmp & 0xffff) + (tmp >> 16);
+  tmp = (tmp & 0xffff) + (tmp >> 16);
+  IPH_CHKSUM_SET(&cs->cs_ip,  (u_short)(~tmp));
+  
+  /* Remove the compressed header and prepend the uncompressed header. */
+  if(pbuf_header(n0, -((s16_t)(vjlen)))) {
+    /* Can we cope with this failing?  Just assert for now */
+    LWIP_ASSERT("pbuf_header failed\n", 0);
+    goto bad;
+  }
+
+  if(LWIP_MEM_ALIGN(n0->payload) != n0->payload) {
+    struct pbuf *np, *q;
+    u8_t *bufptr;
+
+    np = pbuf_alloc(PBUF_RAW, n0->len + cs->cs_hlen, PBUF_POOL);
+    if(!np) {
+      PPPDEBUG(LOG_WARNING, ("vj_uncompress_tcp: realign failed\n"));
+      goto bad;
+    }
+
+    if(pbuf_header(np, -cs->cs_hlen)) {
+      /* Can we cope with this failing?  Just assert for now */
+      LWIP_ASSERT("pbuf_header failed\n", 0);
+      goto bad;
+    }
+
+    bufptr = n0->payload;
+    for(q = np; q != NULL; q = q->next) {
+      MEMCPY(q->payload, bufptr, q->len);
+      bufptr += q->len;
+    }
+
+    if(n0->next) {
+      pbuf_chain(np, n0->next);
+      pbuf_dechain(n0);
+    }
+    pbuf_free(n0);
+    n0 = np;
+  }
+
+  if(pbuf_header(n0, cs->cs_hlen)) {
+    struct pbuf *np;
+
+    LWIP_ASSERT("vj_uncompress_tcp: cs->cs_hlen <= PBUF_POOL_BUFSIZE", cs->cs_hlen <= PBUF_POOL_BUFSIZE);
+    np = pbuf_alloc(PBUF_RAW, cs->cs_hlen, PBUF_POOL);
+    if(!np) {
+      PPPDEBUG(LOG_WARNING, ("vj_uncompress_tcp: prepend failed\n"));
+      goto bad;
+    }
+    pbuf_cat(np, n0);
+    n0 = np;
+  }
+  LWIP_ASSERT("n0->len >= cs->cs_hlen", n0->len >= cs->cs_hlen);
+  MEMCPY(n0->payload, &cs->cs_ip, cs->cs_hlen);
+
+  *nb = n0;
+
+  return vjlen;
+
+bad:
+  comp->flags |= VJF_TOSS;
+  INCR(vjs_errorin);
+  return (-1);
+}
+
+#endif /* VJ_SUPPORT */
+
+#endif /* PPP_SUPPORT */