netdev - Re: [PATCH 2/2] IP_GRE: Linearize skb before csum.

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Date:	Tue, 22 Jan 2013 21:30:50 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	jesse@...ira.com, pshelar@...ira.com, netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] IP_GRE: Linearize skb before csum.

On Wed, 2013-01-23 at 00:19 -0500, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Tue, 22 Jan 2013 21:02:53 -0800
> 
> > GSO was a bad idea from the very beginning, if you want
> > such use case. 
> 
> It's perfectly fine when the card checksums the packet.  Because it
> will checksum the exact data that will hit the wire and thus the
> checksum will be correct always.
> 
> It's only buggy when we do pure software GSO and have page frags.

Right.

We could add a new SKB_GSO_SHARED_FRAG bit for that, and force an extra
copy of frags, instead of a linearize call.

Basically, splice(pipe -> socket)/sendfile()/vmsplice() should set this
flag.

Its a bit late here, I'll do that tomorrow.

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