Re: [Qemu-devel] [RFC 4/6] CLI: add -paused option

[Peter Krempa]

On Tue, Oct 17, 2017 at 12:56:28 +0200, Laszlo Ersek wrote:
> On 10/17/17 10:17, Igor Mammedov wrote:
> > On Mon, 16 Oct 2017 17:35:15 +0100
> > "Daniel P. Berrange" <address@hidden> wrote:
> > 
> >> On Mon, Oct 16, 2017 at 06:22:54PM +0200, Igor Mammedov wrote:
> >>
> >> This really needs to have a commit message that provides justification
> >> for why this option is needed when we already have -S that is used
> >> to allow configuration before the guest starts.
> > Sorry, I've should have added here what I've tried to describe in cover 
> > letter.
> > 
> > -S pauses machine too late as machine is already created by the time
> > it's paused so trying to reconfigure it might require machine to be 
> > recreated.
> > In case of NUMA options it might be possible to hack x86 target to
> > rebuild/override acpi/fw_cfg so it would reflect the new settings set
> > this late but I wouldn't expect that it would work in general.
> > 
> > The cleanest way to configure it is pausing and configuring numa mapping
> > before machine is build.
> 
> Asking from the sideline: if the NUMA mapping has to be configured so
> early, why can't it be done on the QEMU command line?
> 
> (I asked myself the same question when I first saw your patches -- I
> couldn't find an explanation in the blurb --, so I assumed it was
> obvious and/or others would ask the same question.)

Because libvirt needs to be able to query qemu before setting stuff up.
As we already established, it's not okay to run a throwaway qemu process
to do so, so we are getting into the chicken/egg problem zone.

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