[libvirt] [RFC] Automatically sync time on domain resume?

Daniel P. Berrange berrange at redhat.com
Tue Oct 13 12:20:00 UTC 2015

On Tue, Oct 13, 2015 at 01:13:04PM +0200, Michal Privoznik wrote:
> So I came across this bug:
> https://bugzilla.redhat.com/show_bug.cgi?id=1156194
> There's a request for us to automatically sync guest time on domain
> resume (e.g. bare virDomainResume(), or virDomainRestore() or after
> migration). I'd like to explore our options here and what would be
> acceptable upstream. I can think of two possibilities:
> 1) Invent new flag to all APIs in question and let mgmt applications
> call it. If the flag is set we would sync the guest time too. However,
> this masks two different operations under single API. What should be
> reported if resuming succeeded but syncing time did not? Success or
> failure? Mgmt applications will end up calling two APIs to distinguish
> error states anyway.
> 2) Do this as best effort. Unconditionally, whenever guest agent is
> available just issue the time sync command (possibly without waiting for
> reply). This, however, takes away control from users - they will no
> longer have possibility to just resume domain without time sync.
> There's of course the obvious solution - not change anything and have
> mgmt apps calling two separate APIs - like they oughtta be doing today.

That's the right solution IMHO

> What's your view?

I see no compelling reason to add anything to the API or implementation.
We provide enough functionality already to deal with this scenario. Trying
to overload multiple operations into a single API "for convenience" ends
up not being convenient at all, due to the error reporting scenarios you
mention. I don't see any real burden on applications to call these
existing APIs when they wish to.

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