netdev - Query about skb scatter / gather

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Message-ID: <c8028d330903060917r4af01c7ew2426bcb30af90b5e@mail.gmail.com>
Date:	Fri, 6 Mar 2009 22:47:43 +0530
From:	Amar Mudrankit <amar.mudrankit@...il.com>
To:	netdev@...r.kernel.org
Subject: Query about skb scatter / gather

Can I have a socket buffer received over network having protocol
headers (IP, TCP/UDP/ICMP) in first page of skb_frags_t array of the
skb?

So, in such a situation the skb->data is almost 0 and all the data
along with headers is in pages listed in skb_frags_t array.

Can linux networking stack handle such socket buffer? Or is it
mandatory that, at least some minimum data should be accessible
through skb->data and rest can be in pages described in skb_frags_t
array?

Also can anyone suggest good pointers for making use of frag_list in
skb_shared_info structure? Is it meant to represent one network packet
as the list of multiple skbs each skb holding part of packet data in
the order they are linked?

I tried finding it in UNDERSTANDING LINUX NETWORK INTERNALS by
CHRISTIAN BENVENUTI, but couldn't find anything conclusive.  As I
understand, it is enabled through NETIF_F_FRAGLIST feature of the
device.

Thanks in Advance.

Regards,
Amar
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