Re: [Qemu-devel] [PATCH] hw/arm/bcm283x: Fix crash with device_add bcm2837 on unsupported machines

[Peter Maydell]

On 12 July 2018 at 13:06, Markus Armbruster <address@hidden> wrote:
> Peter Maydell <address@hidden> writes:
>
>> On 11 July 2018 at 17:12, Eduardo Habkost <address@hidden> wrote:
>>> On Wed, Jul 11, 2018 at 09:21:48AM +0200, Thomas Huth wrote:
>>>> Hm, ok, so how to continue here now? Shall we at least mark the
>>>> bcm2836/7 devices with user_creatable=false, so that users can not crash
>>>> their QEMU so easily with device_add? The problem with introspection via
>>>> device-list-properties would still continue to exist, but I think that's
>>>> less likely used in practice... otherwise we could still move the
>>>> qdev_set_parent_bus() calls to the realize() function instead, and just
>>>> add a big fat FIXME comment in front of the code block, so that we
>>>> remember to clean that up one day...
>>>
>>> Crashing device-list-properties should be a blocker bug, IMO.
>
> Seconded.
>
>>> Moving to realize is not the best solution, but I would prefer to
>>> do that in 3.0 instead of leaving the device-list-properties
>>> crash unfixed.
>>
>> I would like to see the crash fixed too. But I'd like to
>> see it fixed:
>>  (a) by having clear documentation about how the QOM
>> system works, what you should do in init and what you
>> should do in realize, when and why you need to manually
>> parent objects, etc
>>  (b) as far as possible making our APIs for doing this
>> easy to use correctly and difficult to use wrongly. At
>> the moment we have APIs that are far too easy to misuse,
>> which means we will continue to get bugs like this and spend
>> a lot of time on one-off fixes for them.
>>
>> In particular I don't understand why we need to manually
>> parent these objects at all.
>
> I want both (a) and (b) as badly as anyone, but we should not hold any
> particular crash bug hostage to get them.

Without at least (a) I can't review this patch or any other
patch that fixes this kind of crash bug...

thanks
-- PMM