Re: [Qemu-devel] [PATCH V15 4/5] i386: add a Virtual Machine Generation ID device

["Daniel P. Berrange" <berrange@redhat.com>]

On Mon, Jun 08, 2015 at 03:55:14PM +0200, Paolo Bonzini wrote:
> 
> 
> On 08/06/2015 15:52, Gal Hammer wrote:
> >>> 2. Is it possible to create a sysbus device using the "-device" command
> >>> line argument? I vaguely recall that it is not possible to do it and
> >>> that's the reason that I specifically add the device in the pc init.
> >>
> >> It's now possible, but it is somewhat complicated.  I think it's simpler
> >> to initialize this unconditionally and hide it (via ACPI _STA) if the
> >> vmgenid is all zeros.
> > 
> > I didn't understand. I need the device to be a sysbus device so it won't
> > be found as an ISA or a PCI device by Windows. So I need to know what
> > ever or not it is possible to create a sysbus device using "-device". In
> > either way it won't be created if vmgenid is not given so no need to
> > hide it using _STA.
> 
> Windows doesn't enumerate ISA devices when you create them with -device.
>  It just enumerates devices from the ACPI DSDT/SSDT.  So it's okay to
> make it an ISADevice, or to make it a part of another device (e.g. the
> ISA bridge or the power management device).  It's still ugly though.
> 
> If you make it a sysbus device, you can just add it unconditionally, and
> define _STA so that Windows only sees it under the appropriate
> circumstances: for example, return 0 from _STA if the vmgenid (from the
> command line) is all zeroes.
> 
> What is the command line option like?  Is it "-global vmgenid.uuid=foo"?

FWIW, although the spec for this feature comes from Windows/Microsoft,
I'd expect that when we enable it in libvirt, we'll want to make it
unconditionally available to all VMs, since its a generically useful
information source for guest OS'.

Regards,
Daniel
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