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Date: Wed, 2 Dec 2015 11:11:28 +0100
From: Cornelia Huck <cornelia.huck@de.ibm.com>
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Subject: Re: [Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost
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To: Jason Wang <jasowang@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>, qemu-devel@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>

On Wed, 2 Dec 2015 13:54:09 +0800
Jason Wang <jasowang@redhat.com> wrote:

> I wonder instead of rolling back in post_plugged(), maybe we could just
> delay the region setups to post_plugged(). 

If this is the saner thing to do for pci, sure.

> Or just call transport
> specific device_plugged() after get_features() call in
> virtio_bus_device_plugged(). 

The problem is that the VERSION_1 bit is only added in the
->device_plugged() callbacks by the transport, so ->get_features() can
only be called after that. We have a dependency in both directions :(

> And I'm not sure we need to handle
> migration compatibility in this case.

The thing we would need to care about is basically the host kernel on
the target supporting less than the host kernel on the source. Do we
care about that in other contexts right now?