sk_buff for frame fragmentation and reassembly

["Seong Moon" <seong@etri.re.kr>]

Hi,there.

I'm writing virtual network device driver.
I want to write the function of fragmentation and reassembly of a frame
which is larger than physical MTU.

So, I've looked into the ip_fragment() and ip_defrag() and sk_buff.h .
But I couldn't understand the process of fragmentation and reassembly of
datagram.

My questions are as follows :

<fragmentation>
- ip_fragment() uses alloc_skb() and skb_copy_bit(),
Is the original sk_buff shared ? or Is another sk_buff created?
I want to know the meaning of alloc_skb() and skb_copy_bit().

<reassembly>
- ip_defrag() uses skb_shinfo(skb)->frag_list.
When I pass a reassembled frame to network layer, can I
use skb_shinfo(skb)->frag_list ?
If not, How can I pass the reassembled frame to upper layer?

<sk_buff>
what does the usage of pskb_pull() and pskb_trim()?

Thanks in advance.