[mpls-linux-general] question about skbuff

[Yan, X. Q. (Rex) <re...@lu...>]

Hi James,
I'm going to add some features into your mpls-linux code for our research
use.
I am confused with mpls_opcode_pop() and mpls_opcode_push().

In mpls_opcode_pop()
Why do you need to shift the skb->h.raw and skb->nh.raw? My understanding is
that all the L3/L4 headers remain in the same address, We do not need to
shift skb->h.raw and skb->nh.raw
====================from mpls_opcode.c=======
...
skb_pull(skb, sizeof(u32));
skb->h.raw += sizeof(u32);
skb->nh.raw += sizeof(u32);
...
==========================================
in mpls_opcode_push()
...
/*if we have room between data and end of mac.raw*/
skb->push(o,sizeof(u32));
o->h.raw -= sizeof(u32);
o->nh.raw -= sizeof(u32);
...
/*if we have tailroom, just move the data down...*/
/* My understanding is YOU NEED TO ADJUST ALL TH POINTERS HERE IN THIS CASE
*/
....

I'm new to linux kernel, maybe its a very stupid question.
Thanks in advance.
Rex