Re: [Qemu-devel] [RFC 0/5] Allow object-add on X86CPU subclasses, for CPU model probing

[Eduardo Habkost]

On Fri, May 02, 2014 at 03:45:03PM +0200, Igor Mammedov wrote:
> On Wed, 30 Apr 2014 17:29:28 -0300
> Eduardo Habkost <address@hidden> wrote:
> 
> > This series allows management code to use object-add on X86CPU subclasses, 
> > so it
> Is there any reason why "device-add" couldn't be used?

It needs to work with "-machine none", device_add requires a bus to
exist, and there is no icc-bus on machine_none.

The first thing I considered was making icc-bus user-creatable. Then I
noticed it wouldn't work because object-add always add objects to
/objects, not inside the qdev hierarchy (that's where device_add looks
for the bus).

So, allowing device_add could be possible, but would require changing
more basic infrastructure: either allowing bus-less devices on
device_add, or allowing device_add to add devices outside the qdev
hierarchy, or allowing object-add to create objects outside /objects.

Simply making CPU objects work with object-add was much simpler and less
intrusive. And it had the interesting side-effect of _not_ doing things
that are not required for CPU model probing (like creating an actual
VCPU thread).

> 
> 
> > can use it to probe for CPU model information without re-running QEMU. The 
> > main
> > use case for this is to allow management code to create CPU objects and 
> > query
> > the "feature-words" and "filtered-features" properties on the new objects, 
> > to
> > find out which features each CPU model needs, and to do the same using the
> > "host" CPU model to check which features can be enabled in a given host.
> > 
> > There's experimental libvirt code to use the new command at:
> >     https://github.com/ehabkost/libvirt/tree/work/cpu-feature-word-query
> > The experimental code just create the CPU objects to query for feature
> > information, but doesn't do anything with that data.
> > 
> > Eduardo Habkost (5):
> >   cpu: Initialize cpu->stopped=true earlier
> >   cpu: Don't try to pause CPUs if they are already stopped
> >   pc: Don't crash on apic_accept_pic_intr() if CPU has no apic_state
> >   target-i386: Make CPU objects user-creatable
> >   target-i386: Report QOM class name for CPU definitions
> > 
> >  cpus.c            | 13 ++++++++++---
> >  exec.c            |  1 +
> >  hw/i386/pc.c      |  2 +-
> >  qapi-schema.json  |  6 +++++-
> >  target-i386/cpu.c |  7 +++++++
> >  5 files changed, 24 insertions(+), 5 deletions(-)
> > 
> 

-- 
Eduardo