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

[Dr. David Alan Gilbert]

* Eduardo Habkost (ehabkost at redhat.com) wrote:
> 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.

IMHO Yi's fix (once reworked) is the right fix - it removes the
use of that piece of state, when the optional parameter is used.
(OK, so it needs rework not to change that state and to
come to some agreement as to what to use instead of cpu index number
etc).

Dave

> -- 
> Eduardo
--
Dr. David Alan Gilbert / dgilbert at redhat.com / Manchester, UK