Re: [Qemu-stable] [PATCH for-2.8] qdev: apply global properties in reverse order

[Cornelia Huck]

On Mon, 5 Dec 2016 16:42:00 +0100
Cornelia Huck <address@hidden> wrote:

> On Mon, 05 Dec 2016 16:21:22 +0100
> Greg Kurz <address@hidden> wrote:

> > AFAIK, libvirt's XML doesn't know about modern/legacy modes for virtio
> > devices. Early adopters of virtio 1.0 had to rely on the <qemu:commandline>
> > tag to pass global properties to QEMU. This patch ensures that XML files
> > used with older machine types remain valid with newer versions of QEMU.

I recall some libvirt patches floating around for this legacy/modern
stuff, but I don't know their status.

> > 
> > FWIW I guess it could help to have this fix in 2.8, and also probably in
> > 2.7.1.
> 
> ...but I'm a bit worried about doing that change this late in the
> cycle, as we may introduce subtle changes for other configurations. At
> the very least, we should look over the existing backwards compat
> properties (I'll look at those I'm familiar with).

The s390x properties seem safe.

For virtio-pci, the ability to override extra state might become
problematic for modern devices. Although manually setting this property
is probably a patholotical case...