Re: [libvirt] [Qemu-devel] clean/simple Q35 support in libvirt+QEMU for guest OSes that don't support virtio-1.0

On Fri, Aug 17, 2018 at 12:35:11PM +0200, Andrea Bolognani wrote: > If we decide we want to explicitly spell out the options instead > of relying on QEMU changing behavior based on the slot type, which > is probably a good idea anyway, I think we should have > > virtio-0.9 => disable-legacy=no,disable-modern=no > virtio-1.0 => disable-legacy=yes,disable-modern=no > > There's basically no reason to have a device legacy-only rather > than transitional, and spelling out both options instead of only > one of them just seems more robust. From a testing POV it is desirable to be able to have legacy-only. There is also possibility that guest OS impl 1.0 in a buggy manner, so forcing legacy only is desirable. The existing device still already provides a transitional option on i440fx, and on Q35 if you do explicit placement in a PCI slot. So I don't think there's a good reason to have a second transitional device type, especially if we're naming it virtio-0.9, it is rather misleading if it would be in fact able to run virtio-1.0 mode.