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

[David Gibson]

On Fri, Nov 15, 2019 at 04:55:21PM +0100, Greg Kurz wrote:
> 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.
> 
> Changes in v2:
> - use DEFINE_PROP_LINK() instead of object_property_add_link()
> - dropped public -> private changes in type definitions

Applied to ppc-for-5.0.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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