netdev - Re: [patch 7/9] lguest: the net driver

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Message-Id: <E1HljA6-0001E4-00@gondolin.me.apana.org.au>
Date:	Wed, 09 May 2007 20:12:46 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	akpm@...ux-foundation.org, rusty@...tcorp.com.au, ak@...e.de,
	jeff@...zik.org, jmorris@...ei.org, netdev@...r.kernel.org
Subject: Re: [patch 7/9] lguest: the net driver

akpm@...ux-foundation.org wrote:
>
> +       if (desc->features & LGUEST_NET_F_NOCSUM)
> +               dev->features |= NETIF_F_NO_CSUM;

Any reason why you're using NO_CSUM here instead of HW_CSUM?
Practically there is no difference but NO_CSUM could be treated
differently in future and I'm not sure whether such changes would
be desirable in this driver (i.e., not even generating a partial
checksum).

Also, there doesn't seem to be any passing of metadata to the
backend which means that neither NO_CSUM/HW_CSUM can work if
somebody needs to look at the checksum field.  You could use
IP_CSUM if you do the same hack on the backend that Xen does.
Otherwise you'll have to make do with no checksum offload at all.

I think you'd also need a change_mtu function if the SG feature
is going to be of some use since the default Ethernet one limits
the MTU to 1500.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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