Re: [Qemu-arm] [Qemu-devel] -nodefaults and available buses (was Re: [RFC 00/15] qmp: Report supported device types on 'query-machines')

[Eduardo Habkost <ehabkost@redhat.com>]

On Thu, Nov 24, 2016 at 05:30:19PM +0100, Cornelia Huck wrote:
> On Thu, 24 Nov 2016 12:51:19 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > On Wed, Nov 23, 2016 at 03:10:47PM -0200, Eduardo Habkost wrote:
> > > (CCing the maintainers of the machines that crash when using
> > > -nodefaults)
> > > 
> > > On Tue, Nov 22, 2016 at 08:34:50PM -0200, Eduardo Habkost wrote:
> > > [...]
> > > > "default defaults" vs "-nodefault defaults"
> > > > -------------------------------------------
> > > > 
> > > > Two bad news:
> > > > 
> > > > 1) We need to differentiate buses created by the machine with
> > > >    "-nodefaults" and buses that are created only without
> > > >    "-nodefaults".
> > > > 
> > > > libvirt use -nodefaults when starting QEMU, so knowing which
> > > > buses are available when using -nodefaults is more interesting
> > > > for them.
> > > > 
> > > > Other software, on the other hand, might be interested in the
> > > > results without -nodefaults.
> > > > 
> > > > We need to be able model both cases in the new interface.
> > > > Suggestions are welcome.
> > > 
> > > The good news is that the list is short. The only[1] machines
> > > where the list of buses seem to change when using -nodefaults
> > > are:
> > > 
> > > * mpc8544ds
> > > * ppce500
> > > * mpc8544ds
> > > * ppce500
> > > * s390-ccw-virtio-*
> > > 
> > > On all cases above, the only difference is that a virtio bus is
> > > available if not using -nodefaults.
> > 
> > Hrm.. that's odd.  Well, it makes sense for the s390 which has special
> > virtio arrangements.  
> 
> I don't think it makes much sense for s390 either... is this a 'virtio'
> bus or a 'virtio-{pci,ccw}' bus? The transport bus should be present
> with -nodefaults; the virtio bus is basically a glue bus for virtio
> devices...

I mean no device of type "virtio-ccw-bus" (which is a subtype of
"virtio-bus") is present on the device tree.

Is the TYPE_VIRTIO_BUS bus supposed to be user-visible, or is it
just internal?

-- 
Eduardo