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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] Re: [PATCH-RFC 13/13] virtio-net: connect to vhost
	net backend
Date: Wed, 24 Feb 2010 03:14:25 +0000
References: <cover.1263230079.git.mst@redhat.com>
	<20100125202711.GA16928@redhat.com>
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To: qemu-devel@nongnu.org
Cc: "Michael S. Tsirkin" <mst@redhat.com>

> vnet_hdr is IMHO a really bad example to copy from.
> 
> vnet_hdr leaks into the migration state via n->has_vnet_hdr.  What this
> means is that if you want to migrate from -net tap -net nic,model=virtio
> to -net user -net nic,model=virtio, it will fail.
> 
> This is a hard problem to solve in qemu though because it would require
> that we implement software GSO which so far, no one has stepped up to do.

Or make virtio-net pass this on to the guest, and have that deal with the 
problem. If you implement software GSO, then devices can assume it's always 
present and don't need to probe.

Paul