Re: [Libguestfs] [PATCH v2v 0/5] convert: Find out if Windows guest is expecting BIOS localtime or UTC
On Mon, Sep 25, 2023 at 04:26:59PM +0200, Alice Frosi wrote:
Hi Rich,
On Mon, Sep 25, 2023 at 4:10 PM Richard W.M. Jones <rjones(a)redhat.com> wrote:
[Alice: See patch 2]
I'm not 100% sure about the source of this work. However, we had in
KubeVirt people interested in using localtime with Windows [1]. Yes,
I see that you pointed to that PR in patch 2. The problem with that
PR is the migration. What happens if we migrate the VM to a host
that is in another timezone? Is it going to break the application
running inside the VM?
Does every Windows VM running in Kubevirt have its registry adjusted
so it expects the BIOS to be set to UTC? (ie:
https://wiki.archlinux.org/title/System_time#UTC_in_Microsoft_Windows).
This is a non-standard setting, but I can't understand how Windows VMs
would have correct clocks if this were not the case.
BTW you could find out by running:
$ virt-win-reg window.img 'HKLM\SYSTEM'
on some Kubevirt Windows VMs, and looking for:
[\ControlSet001\Control\TimeZoneInformation]
in the output. See if there is a key called "RealTimeIsUniversal" and
what it is set to.
If it is the case that this is always set for existing Kubevirt
guests, then virt-v2v would have to be changed so it also sets this
registry entry when the output is Kubevirt.
I agree that migration across timezones is highly problematic for the
BIOS = localtime situation. I don't see any solution for that except
disallowing it.
IMO, that was the major blocker of that PR. I initially suggested
that we
either avoid migration as a first step or try to migrate only on nodes at the
same timezone,
Do you know if anyone has experience on this particular problem?
I guess RHV must have encountered this before, but I don't know any
specifics.
Thanks,
Rich.
[1] https://github.com/kubevirt/kubevirt/pull/9587
Many thanks,
Alice
--
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