Re: [libvirt] [Qemu-devel] clean/simple Q35 support in libvirt+QEMU for guest OSes that don't support virtio-1.0
Eduardo Habkost <ehabkost(a)redhat.com> writes:
On Thu, Aug 23, 2018 at 05:26:47PM +0100, Daniel P. Berrangé wrote:
[...]
> There are countless mistakes in both QEMU & libvirt, but only some of
> them are worth the cost of changing.
Agreed.
> I'm not seeing a
compelling reason
> why this change is worthwhile. The impact of the design mistake is narrow
> and only raised because of downstream desire to change even legacy OS
> to use Q35 when there's no benefit to those OS of such a change.
I think you underestimate the impact of the design mistake.
And overstate the "this is just for a downstream need".
Maintaining and working around badly designed interfaces have
costs.
The virtio device model was already an obstacle when designing
new bus/device introspection interfaces. It will be an obstacle
for adding mechanisms to tell applications that legacy virtio
devices can't be plugged on PCI Express slots.
Thus, there's a genuine upstream motivation to clean up this mess.
Whether it's worthwhile is of course a fair question.
The argument for "it is worthwhile" I like to see in general is patches.
Anyway, if we want to fix the design mistake it wouldn't make
sense to do it only on the libvirt side and not on QEMU. We can
address that on QEMU first, and then let libvirt decide how to
handle it.
Yes.