Re: [Qemu-devel] QMP event for suspend to disk

[Eric Blake <eblake@redhat.com>]

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On 07/18/2012 08:02 AM, Luiz Capitulino wrote:
> Hi,
> 
> QEMU can now distinguish between S4 and power off for the guest OSes that
> suspends to disk through S4. This means that we can have a QMP event for S4
> (so that QMP clients can distinguish between S3 and S4).
> 
> However, as we already emit the SHUTDOWN event for this, it turns out that
> there are three different ways of supporting the new event. We could:
> 
>  1. not emit the SHUTDOWN event and only emit the SUSPEND_DISK event
> 
>     cons: breaks compatibility, as we'll stop sending an event we send today.

At least the new 'query-events' monitor command will allow libvirt to
know which events to listen for; so this is workable.

> 
>  2. emit both, that is, first SUSPEND_DISK and then SHUTDOWN
> 
>     cons: emitting two very similar events.

This has the most back-compat, but is noisier in that it generates more
events.

> 
>  3. extend the SHUTDOWN event to say whether it's a suspend to disk or not,
>     like this:
> 
>        { "event": "SHUTDOWN", "data": { "suspend-to-disk": true }, ... }
> 
>     cons: we already have the SUSPEND event, so from an API perspective
>           it would make sense to have SUSPEND_DISK.
> 
> I prefer item 3, because it seems to be cleanest one.

I'm also liking 3, then 1, then 2; but think any of them will work from
libvirt's POV.

-- 
Eric Blake   eblake@redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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