netdev - Re: [B.A.T.M.A.N.] pull request: batman-adv 2011-11-26

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Date:	Fri, 02 Dec 2011 20:59:55 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	ordex@...istici.org
Cc:	lindner_marek@...oo.de, netdev@...r.kernel.org,
	b.a.t.m.a.n@...ts.open-mesh.org
Subject: Re: [B.A.T.M.A.N.] pull request: batman-adv 2011-11-26

From: Antonio Quartulli <ordex@...istici.org>
Date: Sat, 3 Dec 2011 02:55:29 +0100

> We first call pskb_may_pull() to pull the header only and then, under certain
> conditions, we linearise the whole skb to access it all. Should I use
> pskb_may_pull() even in this case?

Why would you need to access the whole thing?

There are only two types of possible accesses:

1) Header parsing --> use pskb_may_pull() as needed.

2) Copying the data to some other location, such as a user
   buffer.  Use skb_copy_datagram_iovec or similar which handle
   fragmented SKBs just fine.

You should handle fragmented SKBs as much as possible, because
linearization is expensive and often amounts to a memory allocation
plus a copy if you linearize the whole thing.
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