netdev - Re: [RFC PATCH 1/3] Avoid making inappropriate requests of NETIF_F_V[46]

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Date:	Wed, 16 Jan 2013 22:34:18 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [RFC PATCH 1/3] Avoid making inappropriate requests of
 NETIF_F_V[46]_CSUM devices

On Wed, 2013-01-16 at 15:54 -0500, David Miller wrote:
> 
> My opinion on this is that the injectors of packets are responsible
> for ensuring checksum types are set on SKBs in an appropriate way.
> 
> So we ensure this in the local protocol stacks that generate packets,
> and if foreign alien entities can inject SKBs with these checksum
> settings (like the tun device can) the burdon of verification falls
> upon whatever layer allows that to happen.
> 
> So really, the fix is in the tun device and the virtio layer.

The virtio layer (and the tun device) expose the equivalent of the
NETIF_F_HW_CSUM capability to the guest. In the case where we have a
real device on the host which *also* has NETIF_F_HW_CSUM capability, are
you saying that the tun driver should do the checksum for non-UDP/TCP
packets in software *anyway*, just because the packet might end up going
out a device *without* that capability, and the check in
harmonize_features() isn't sophisticated enough to cope properly?

-- 
dwmw2

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