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

[Markus Armbruster]

Eduardo Habkost <ehabkost at redhat.com> writes:

> (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.

Yes.

>> Other software, on the other hand, might be interested in the
>> results without -nodefaults.

Maybe.

Related: other machine options, such as usb=on.

>> 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.
>
> 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

Bugs.

> These exit with a "missing SecureDigital device" error:
> * akita
> * borzoi
> * cheetah
> * connex
> * mainstone
> * n800
> * n810
> * spitz
> * sx1
> * sx1-v1
> * terrier
> * tosa
> * verdex
> * z2

Bugs only if there is no other way to provide the SD device.  I believe
some variation if -drive if=sd,... should do fine.