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Re: [Qemu-devel] Byte ordering of VM Generation ID in Windows VMs

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] Byte ordering of VM Generation ID in Windows VMs
Date: Thu, 5 Jul 2018 20:34:00 +0300

On Thu, Jul 05, 2018 at 07:15:34PM +0200, Laszlo Ersek wrote:
> > It has to be said that after reading the spec again [the MSFT spec,
> > not qemu's spec] and what other hypervisors are doing, I'm not sure
> > qemu is doing the right thing here.
> That's the thing about specs -- interpretation. I've read the vmgenid
> spec several times as well, and I've always understood it as Microsoft
> meaning UUID / GUID as a primary representation for VMGENID. I may have
> been biased by UUID/GUID usage in UEFI.
> When the feature was being developed for QEMU, we struggled with the
> interpretation of a good number of other bits as well; hence the
> "Requirements" section of QEMU's spec: "this is how we understood it".
> Without an open list to discuss things with Microsoft, sometimes we can
> only guess what is a "likely faithful" interpretation, and test it in
> practice.
> I still believe QEMU's current interpretation is the right one; but I
> can't prove it.
> Laszlo

Well it does seem that at least some guest code wants a counter
there. So if someone posts a patch adding a count property there
to be stored in LE format, plus a unit test - I'll merge it, even
though it does not look like libvirt wants that.


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