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


From: Gal Hammer
Subject: Re: [Qemu-devel] [PATCH V15 4/5] i386: add a Virtual Machine Generation ID device
Date: Mon, 08 Jun 2015 17:05:01 +0300
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 08/06/2015 16:58, 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'.

Once qemu part will be completed it will be possible to add a module to Linux as well (and maybe use it as a RNG generator source too).

    Gal.

Regards,
Daniel





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