Re: [PATCH v2 for-5.0 0/8] ppc: Consolidate QOM links and pointers to the same object

["Cédric Le Goater" <clg@kaod.org>]

On 18/11/2019 10:26, Markus Armbruster wrote:
> Greg Kurz <groug@kaod.org> writes:
> 
>> There's a recurring pattern in the code where a const link is added to a
>> newly instanciated object and the link is then used in the object's realize
>> function to keep a pointer to the QOM entity which the link points to.
>>
>> void create_obj_b(Object *obj_a)
>> {
>>     Object *obj_b;
>>
>>     obj_b = object_new(TYPE_B);
>>     object_property_add_const_link(obj_b, "link-to-a", obj_a, &error_abort);
>>     object_property_set_bool(obj_b, true, "realized", &error_abort);
>> }
>>
>> void object_b_realize(DeviceState *dev, Error **errp)
>> {
>>     Object *obj_a;
>>
>>     obj_a = object_property_get_link(OBJECT(dev), "link-to-a", errp);
>>     if (!obj_a) {
>>         return;
>>     }
>>
>>     obj_b->obj_a = A(obj_a); // If obj_b->obj_a is changed, the link property
>>                              // still points to the original obj_a that was
>>                              // passed to object_property_add_const_link()
>> }
>>
>> Confusing bugs could arise if the pointer and the link go out of sync for
>> some reason. This can be avoided if the property is defined to directly use
>> the pointer with the DEFINE_PROP_LINK() macro.
>>
>> This series just does that for all occurences of the fragile pattern in
>> the XIVE and PNV code.
> 
> Have you looked for the pattern elsewhere?

I can take care of the Aspeed machine. I followed the same pattern there.

C.