[lwip-users] Is it a PPP bug related to VJ?

[WU Rui-Qing]

Hi all,
  I wanted VJ to work well,but failed. I found there are two different data 
structs for IP header. One is struct ip_hdr in ip.h ,the other is struct ip 
defined in vjbsdhdr.h. A header of IP is filled in ip_output_if by struct 
ip_hdr. If VJ is enable, some fields in the IP header are parsed incorrectly in 
vj_compress_tcp by struct ip.
  The bug may be at:
    register struct ip *ip = (struct ip *)pb->payload.
  The size of struct ip is more than 20 bytes,Is it a PPP bug related to VJ?

err_t
ip_output_if(struct pbuf *p, struct ip_addr *src, struct ip_addr *dest,
             u8_t ttl, u8_t tos,
             u8_t proto, struct netif *netif)
{
  struct ip_hdr *iphdr;

..

 IPH_TTL_SET(iphdr, ttl);
    IPH_PROTO_SET(iphdr, proto);

    ip_addr_set(&(iphdr->dest), dest);

    IPH_VHLTOS_SET(iphdr, 4, IP_HLEN / 4, tos);
    IPH_LEN_SET(iphdr, htons(p->tot_len));
    IPH_OFFSET_SET(iphdr, 0);
    IPH_ID_SET(iphdr, htons(ip_id));

..
}


u_int
vj_compress_tcp(struct vjcompress *comp, struct pbuf *pb)
{
  register struct ip *ip = (struct ip *)pb->payload;
  register struct cstate *cs = comp->last_cs->cs_next;
  register u_short hlen = 0;
  register struct tcphdr *oth;
  register struct tcphdr *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 (ip->ip_p != IPPROTO_TCP) {
    return (TYPE_IP);
  }
..

}


The struct ip is defined as the following in vjbsdhdr.h

PACK_STRUCT_BEGIN
struct ip
{
#if defined(NO_CHAR_BITFIELDS)
  u_char   ip_hl_v;  /* bug in GCC for mips means the bitfield stuff will 
sometimes break - so we use a char for both and get round it with macro's 
instead... */
#else
#if BYTE_ORDER == LITTLE_ENDIAN
  unsigned ip_hl:4,              /* header length */
           ip_v :4;              /* version */
#elif BYTE_ORDER == BIG_ENDIAN
  unsigned ip_v :4,              /* version */
           ip_hl:4;              /* header length */
#else
  COMPLAIN - NO BYTE ORDER SELECTED!
#endif
#endif
  u_char  ip_tos;                /* type of service */
  u_short ip_len;                /* total length */
  u_short ip_id;                 /* identification */
  u_short ip_off;                /* fragment offset field */
#define  IP_DF 0x4000            /* dont fragment flag */
#define  IP_MF 0x2000            /* more fragments flag */
#define  IP_OFFMASK 0x1fff       /* mask for fragmenting bits */
  u_char  ip_ttl;                /* time to live */
  u_char  ip_p;                  /* protocol */
  u_short ip_sum;                /* checksum */
  struct  in_addr ip_src,ip_dst; /* source and dest address */
};
PACK_STRUCT_END



        

　　　　　　　　
Best regards
                                
WU Rui-Qing
address@hidden
2009-10-29