--- bunty <bunty123_4@rediffmail.com> wrote:
> 1)I want to know where are actaully packet
> layer headers are stored by sk_buff structure? i got
> some diagrams that tells that area between data and
> tail contains compelete packet.then what is stored
> between skb->head and skb->data area?
Ok, let me try to sort things out. This diagram
might help.
-> head
{headroom space}
->data
->tail
{tailroom space}
->end
Also,
len = total lenght of the data in the skb;
data_len = length of the data not in the main body of
the skb, ie, is in the frags.
headlen = len - data_len = data in the main body of
the skb.
When you normally create an skb (using alloc_skb()),
there is no headroom, and there is tailroom of how
many ever bytes you requested.
A packet will be like this in the skb
->head, data
eth hdr
nw hdr
tran hdr
->tail
->end
Then, you say,
ethhdr = skb->dat;
skb_pull(skb, ethhdr size);
next
iphdr = skb->data;
skb_pull(skb, iphdr size);
and so on;
Hope this clarfies to some extent. Please do correct
me if I am wrong anywhere.
> 2) what exactly skb_put does?
This adds data to the buffer, by decreasing the
tailroom, that is it moves the tail pointer towards
the end pointer.
> 3) which functions very first takes data
> from application layer and store in skbuff?
Every 'struct sock' has a sk_proto field which in turn
has a protocol specific function generally
proto_sendmsg (like tcp_sendmsg) which actually
allocates the skbuff.
> 4) Is there any main alloc_skb call that
> allocates total length skb buffer for whole packet?
net/core/skbuff.c:alloc_skb() is the function
=====
Regards,
Kiran Kumar Immidi
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