Why skbuff.h different for 2.4 and 2.6 kernels?

[linux lover <linux_lover2004@xxxxxxxxx>]

hello,
1) In 2.4 kernel series skbuff.h has following unions
for each TCP/IP layer.
       /*Transport Layer*/
      union
        {
                struct tcphdr   *th;
                struct udphdr   *uh;
                struct icmphdr  *icmph;
                struct igmphdr  *igmph;
                struct iphdr    *ipiph;
                struct spxhdr   *spxh;
                unsigned char   *raw;
        } h;

        /* Network layer header */
        union
        {
                struct iphdr    *iph;
                struct ipv6hdr  *ipv6h;
                struct arphdr   *arph;
                struct ipxhdr   *ipxh;
                unsigned char   *raw;
        } nh;

        /* Link layer header */
        union 
        {       
                struct ethhdr   *ethernet;
                unsigned char   *raw;
        } mac;

AND In 2.6 kernel series skbuff.h has following unions
for each TCP/IP layer.
        union {
                struct tcphdr   *th;
                struct udphdr   *uh;
                struct icmphdr  *icmph;
                struct igmphdr  *igmph;
                struct iphdr    *ipiph;
                struct ipv6hdr  *ipv6h;
                unsigned char   *raw;
        } h;

        union {
                struct iphdr    *iph;
                struct ipv6hdr  *ipv6h;
                struct arphdr   *arph;
                unsigned char   *raw;
        } nh;

        union {
                unsigned char   *raw;
        } mac;

 why mac union in 2.6 not have ethernet header? Also
spxhdr and ipxhdr structures are removed from nh and h
unions.

2) Why header structures for ipcomp,eh,esp(IPSEC) not
included in skbuff.h?
 Then how can skbuff adds/removes those headers in
skbuff? 

regards,
linux_lover

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com