Re: [Qemu-devel] [RFC 1/4] [UNTESTED] xen: Don't force has_dynamic_sysbus on machine class

[Thomas Huth <thuth@redhat.com>]

On 24.03.2017 11:09, Peter Maydell wrote:
> On 24 March 2017 at 08:23, Juergen Gross <jgross@suse.com> wrote:
>> On 23/03/17 22:28, Eduardo Habkost wrote:
>>> The xen-backend devices created by the Xen code are not supposed
>>> to be treated as dynamic sysbus devices. This is an attempt to
>>> change that and see what happens, but I couldn't test it because
>>> I don't have a Xen host set up.
>>>
>>> If this patch breaks anything, this means we have a bug in
>>> foreach_dynamic_sysbus_device(), which is supposed to return only
>>> devices created using -device.
>>>
>>> The original code that sets has_dynamic_sysbus was added by
>>> commit 3a6c9172ac5951e6dac2b3f6cbce3cfccdec5894, but I don't see
>>> any comment explaining why it was necessary.
>>
>> xen-backend devices are created via qmp commands when attaching new
>> pv-devices to a domain. They can be dynamically removed, too. Setting
>> has_dynamic_sysbus was necessary to support this feature.
> 
> This seems like it ought to be handled by marking the xen-backend
> devices as being ok-to-dynamically-create somehow, not by marking
> the machine as supporting dynamic-sysbus (which it doesn't).
> Maybe we don't have the necessary support code to do that though?

Do the xen devices have to be sysbus devices? If no, I think you could
change them to be of type TYPE_DEVICE nowadays - TYPE_DEVICE can be
instantiated with "-device" nowadays, too. That's what we do with the
spapr-rng device for example (see hw/ppc/spapr_rng.c).

 Thomas