Re: [PATCH] qom: reverse order of instance_post_init calls

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Paolo,

On 3/2/25 12:41, Paolo Bonzini wrote:
> Currently, the instance_post_init calls are performed from the leaf
> class and all the way up to Object.  This is incorrect because the
> leaf class cannot observe property values applied by the superclasses;
> for example, a compat property will be set on a device *after*
> the class's post_init callback has run.
> 
> In particular this makes it impossible for implementations of
> accel_cpu_instance_init() to operate based on the actual values of
> the properties, though it seems that cxl_dsp_instance_post_init and
> rp_instance_post_init might have similar issues.
> 
> Follow instead the same order as instance_init, starting with Object
> and running the child class's instance_post_init after the parent.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   qom/object.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/qom/object.c b/qom/object.c
> index 157a45c5f8b..c03cd3c7339 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -423,13 +423,13 @@ static void object_init_with_type(Object *obj, TypeImpl *ti)
>   
>   static void object_post_init_with_type(Object *obj, TypeImpl *ti)
>   {
> -    if (ti->instance_post_init) {
> -        ti->instance_post_init(obj);
> -    }
> -
>       if (type_has_parent(ti)) {
>           object_post_init_with_type(obj, type_get_parent(ti));
>       }
> +
> +    if (ti->instance_post_init) {
> +        ti->instance_post_init(obj);
> +    }
>   }

I'm not opposed to this change as I had a similar issue there few weeks
ago, but I feel we are changing one problem by another. IIRC some class
post_init() handlers check the instance correctly did something. But I
don't recall any example in particular. The documentation isn't clear
about order (include/qom/object.h):

   * @instance_post_init: This function is called to finish
   *                      initialization of an object, after
   *                      all @instance_init functions were
   *                      called.