netdev - Re: alignment faults in 3.6

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Message-ID: <1349956055.1232.9.camel@sakura.staff.proxad.net>
Date:	Thu, 11 Oct 2012 13:47:35 +0200
From:	Maxime Bizon <mbizon@...ebox.fr>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Måns Rullgård <mans@...sr.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	netdev@...r.kernel.org, David Laight <David.Laight@...LAB.COM>,
	Jon Masters <jonathan@...masters.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: alignment faults in 3.6


On Thu, 2012-10-11 at 13:28 +0200, Eric Dumazet wrote:

> You probably are aware that a driver can use : 
> 
> - a fragment to hold the frame given by the hardware, with whatever
> alignment is needed by the hardware.
> 
> Then allocate an skb with enough room (128 bytes) to pull the headers as
> needed later.
> 
> skb = netdev_alloc_skb_ip_align(dev, 128);

What happen at tx time, supposing that same hardware cannot do SG ?

Aren't we going to memcpy the data into the head ?

-- 
Maxime


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