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