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

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jun 08, 2015 at 02:58:54PM +0100, Daniel P. Berrange wrote:
> 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

Are there applications that would actually use this?  For microsoft this
seems to be mostly driven by ActiveDirectory needs.
It seems quite possible that applications solve the problem
differently on Linux.


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