-enable-kvm - can it be a required option?

What I mean is: if asked to enable kvm but kvm can't be initialized for some reason (lack of virt extensions on the cpu, permission denied and so on), can we stop with a fatal error instead of continuing in emulated mode?

Or maybe with another option, like -require-kvm?

I understand that -enable-kvm is now in upstream qemu too, and _there_ it means something different, that is, it enables something that is disabled by default. But even with that, if user asks for something and that something isn't available, it seems like a good idea to stop here instead of producing a warning and continuing...

This is especially true for kvm where -enable-kvm is the default anyway.

I see more and more people are using this option now in a hope that kvm will actually stop when no virt extensions are available. It was my first reaction too, "wow, now I can force it to require kvm extensions instead of running 1000 times slower!". So this has something to think about, it looks like... ;)

Thanks!

/mjt

What I've been thinking, is that we should make kvm enablement a -cpu option. Something like:

-cpu host,accel=kvm
-cpu host,accel=tcg
-cpu host,accel=kvm:tcg

(1) would be KVM only, (2) would be TCG only, (3) would be KVM falling back to TCG.

What's nice about this approach, is that we already pull CPU model definitions from a global config file which means that you could tweak this parameter to your liking.

Regards,

Anthony Liguori