skbuff about skbuff

Hi,
Does anyone know how to adjust the skb->h.raw, skb->nh.raw?
I'm going to add a shim header between layer2 header and layer3 header
	+--------+============+----------+--------
	|   L2   |   Shim     | L3       |   L4
	+--------+============+----------+--------
The code to insert the shim:

skb_push(skb, 4); /*say the size of shim is 4 bytes. */
memmove(skb->data, &shim, 4);

Do I need to adjust the skb->h.raw and skb->nh.raw? How to?

Thanks in advance,

Rex

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