Hi,
>
> im programming in linux sockets, but i need a help in this
> lines:
>
> struct etherpacket
> {
> struct ethhdr eth;
> struct iphdr ip;
> struct tcphdr tcp;
> char buff[8193];
> }ep;
>
> struct iphdr *ip;
> struct tcphdr *tcp;
>
> -> ip=(struct iphdr *)(((unsigned long)&ep.ip)-2);
> -> tcp=(struct tcphdr *)(((unsigned long)&ep.tcp)-2);
-------------> The ethhdr is 14 bytes long. So, the next field
ip of the struct etherpacket starts from the next
4 byte multiple. Thus we have a 2 byte 'gap' in the
structure. But, while reading the packet from the
net there is no question of any alignment and hence
the ip field would start immediately after the end
of eth structure. So, the minus 2 from the &ep.ip.
Experts please correct me if I am wrong.
--gopi
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