Re: [RFC] Unify KVM kernel-space and user-space code into a single project

Anthony Liguori
2010-03-22T18:41:36Z

On 03/22/2010 12:34 PM, Ingo Molnar wrote:
> This is really just the much-discredited microkernel approach for keeping
> global enumeration data that should be kept by the kernel ...
>
> Lets look at the ${HOME}/.qemu/qmp/ enumeration method suggested by Anthony.
> There's numerous ways that this can break:
>
> - Those special files can get corrupted, mis-setup, get out of sync, or can
> be hard to discover.
>
> - The ${HOME}/.qemu/qmp/ solution suggested by Anthony has a very obvious
> design flaw: it is per user. When i'm root i'd like to query _all_ current
> guest images, not just the ones started by root. A system might not even
> have a notion of '${HOME}'.
>
> - Apps might start KVM vcpu instances without adhering to the
> ${HOME}/.qemu/qmp/ access method.
>
> - There is no guarantee for the Qemu process to reply to a request - while
> the kernel can always guarantee an enumeration result. I dont want 'perf
> kvm' to hang or misbehave just because Qemu has hung.
>

If your position basically boils down to, we can't trust userspace and
we can always trust the kernel, I want to eliminate any userspace path,
then I can't really help you out.

I believe we can come up with an infrastructure that satisfies your
actual requirements within qemu but if you're also insisting upon the
above implementation detail then there's nothing I can do.

Regards,

Anthony Liguori