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

[Daniel P. Berrange]

On Wed, Jul 19, 2017 at 10:02:04AM -0500, Eric Blake wrote:
> [adding libvirt]
> 
> On 07/19/2017 07:41 AM, Eduardo Habkost wrote:
> 
> >> virsh  qemu-monitor-command --domain rhel6.8 --hmp --cmd "cpu 1"
> >> virsh  qemu-monitor-command --domain rhel6.8 --hmp --cmd "info lapic"
> >> dumping local APIC state for CPU 0
> > 
> > Right, the "cpu" command is useless inside a
> > 'human-monitor-command' QMP command.  The 'cpu-index' argument
> > should be used instead. should make "cpu" print an error if ran
> > inside 'human-monitor-command' instead of silently pretend it
> > worked.
> > 
> > If virsh doesn't support the 'cpu-index' argument to
> > 'human-monitor-command',
> 
> 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.

> 
> > it's possible to work around that
> > limitation by building your own QMP command.  e.g.:
> > 
> >   # virsh qemu-monitor-command f26test '{"execute":"human-monitor-command", "arguments":{"command-line":"info lapic", "cpu-index":1}}' | jq -r '.return'
> 
> Indeed, there's the use of QMP to work around the HMP deficiency.
> 
> -- 
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3266
> Virtualization:  qemu.org | libvirt.org
> 



Regards,
Daniel
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