On Friday 16 April 2004 05.52, Kiran Kumar wrote:
> > 3. What are data_len and len in sk_buff, how are
> > they used?
>
> An skbuff structure has some storage in the main
> body of the structure, more can be added to the frag
> list. The amount of data in the main structure is
> called the headlen, the total length is len, data_len,
> is the total amount of data in the frags. Refer to
> skbuff.h in the linux kernel sources.
Actually I have read a lot of kernel code to understand it
(mainly __pskb_pull_tail and such) but those comments
in skbuff.h are pretty meaningless (not understandable) to me.
Now I have these assumptions, is it correct? :
"end" is the real end of the buffer.
"tail" is the current end of the buffer.
"head" is the real head/start of the buffer.
"data" is the current head/start of the buffer.
"len" is the currently used data in the buffer.
"data_len" is the amount of data in the fragments
len == tail - data
> frag_list is the linked list of skbuffs
> corresponding to the continuation of the skbuff's
> data. frags is the array which holds pointers to the
> pages (which hold the actual data). That is frag_list
> is the list of skbuffs and frags is the associated
> data.
So, in those fragments is the header of a packet repeated or those
are just pure payload? That is, where the nh.raw, h.raw pointers point for
fragment skbuffs?
I mean:
skb frag 1 frag 2
(hdr,payload) (hdr,frag1) (hdr,frag2) ...
or
(hdr,payload) (frag1) (frag2) ...
?
Thanks a lot,
Gabor
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