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

[David Gibson <david@gibson.dropbear.id.au>]

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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.  However, the others are all embedded ppc
machines, whose virtio should be bog-standard virtio-pci.  I'm
wondering if the addition of the virtio "bus" is a side-effect of the
NIC or storage device created without -nodefaults being virtio.

> Considering that the list is short, I plan to rename
> 'supported-device-types' to 'always-available-buses', and
> document that it will include only the buses that are not
> disabled by -nodefaults.
> 
> [1] I mean, the only ones from the set that don't crash with
>     -nodefaults. The ones below could not be tested:
> 
> > 2) A lot of machine-types won't start if using
> >    "-nodefaults -machine <machine>" without any extra devices or
> >    drives.
> > 
> > Lots of machines require some drives or devices to be created
> > (especially ARM machines that require a SD drive to be
> > available).
> > 
> > Some machines will make QEMU exit, some of them simply segfault.
> > I am looking for ways to work around it so we can still validate
> > -nodefaults-based info on the test code.
> 
> The following machines won't work with -nodefaults:
> 
> These make QEMU segfault:
> * cubieboard
> * petalogix-ml605
> * or32-sim
> * virtex-ml507
> * Niagara
> 
> These exit with a "missing SecureDigital device" error:
> * akita
> * borzoi
> * cheetah
> * connex
> * mainstone
> * n800
> * n810
> * spitz
> * sx1
> * sx1-v1
> * terrier
> * tosa
> * verdex
> * z2
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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