netdev - Re: [PATCH v2] solos-pci: Increase headroom on received packets

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Message-Id: <20150917.212921.1620012798738986807.davem@davemloft.net>
Date:	Thu, 17 Sep 2015 21:29:21 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	dwmw2@...radead.org
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org, simon@...e.lp0.eu,
	guy@...verse.com.au, linux-atm-general@...ts.sourceforge.net
Subject: Re: [PATCH v2] solos-pci: Increase headroom on received packets

From: David Woodhouse <dwmw2@...radead.org>
Date: Wed, 16 Sep 2015 12:35:00 +0100

> A comment in include/linux/skbuff.h says that:
> 
>  * Various parts of the networking layer expect at least 32 bytes of
>  * headroom, you should not reduce this.
> 
> This was demonstrated by a panic when handling fragmented IPv6 packets:
> http://marc.info/?l=linux-netdev&m=144236093519172&w=2
> 
> It's not entirely clear if that comment is still valid ― and if it is,
> perhaps netif_rx() ought to be enforcing it with a warning.
> 
> But either way, it is rather stupid from a performance point of view
> for us to be receiving packets into a buffer which doesn't have enough
> room to prepend an Ethernet header ― it means that *every* incoming
> packet is going to be need to be reallocated. So let's fix that.
> 
> Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>

Applied, thanks David.
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