Re: [Qemu-devel] [PATCH v2] hmp: allow cpu index for "info lapic"

[Eduardo Habkost]

On Wed, Jul 19, 2017 at 10:17:36AM -0500, Eric Blake wrote:
> On 07/19/2017 10:07 AM, Daniel P. Berrange wrote:
> >> It doesn't.  Perhaps we should add that as a future libvirt-qemu.so API
> >> addition, although it's probably easier to just use QMP than HMP when
> >> using 'virsh qemu-monitor-command' if HMP doesn't do what you want.
> > 
> > Or special case the "cpu 1" command - ie notice that it is being
> > requested and don't execute 'human-montor-command'. Instead just
> > record the CPU index, and use that for future "human-monitor-command"
> > invokations, so we get full compat with the (dubious) stateful HMP
> > semantics that traditionally existed.
> 
> Is 'cpu' (and the followup commands affected by it) the only stateful
> HMP command pairing?  Is there a way to specify multiple HMP commands in
> a single human-monitor-command QMP call?
> 
> Indeed, tweaking qemu's human-monitor-command call to track the state
> might be cleaner than having libvirt have to tweak API to work around
> this wart of HMP.

The CPU index was the only state kept by the human monitor, and I
think it's by design that it stopped being considered "monitor
state" to be tracked, and became just an argument to
human-monitor-command.

It's true that it broke compatibility of
  "virsh qemu-monitor-command <domain> --hmp 'cpu <n>'",
when we moved to QMP, but this happened years ago, and it looks
like nobody was relying on it.  I don't see the point of trying
to emulate the previous stateful interface.

-- 
Eduardo