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

[Markus Armbruster]

Greg Kurz <address@hidden> 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?