Re: [RFC PATCH 001/134] qom: Introduce object_new_child()

On Sat, Jul 11, 2026 at 10:34:54PM +0000, Alexander Graf wrote:
> We already have two ways of creating a QOM object with a parent set
> from birth: object_initialize_child() for objects embedded in the
> parent struct, and object_new_with_props() for heap-allocated objects
> that also want a list of string properties applied.  What we do not
> have is the plain heap-allocated dual of object_initialize_child():
> create the object, add it as a child<> of a given parent under a given
> name, and hand the reference to the parent.
> 
> Board and composite-device code that heap-allocates children today
> therefore either open-codes object_new()+object_property_add_child()
> +object_unref(), or skips the parenting step entirely and lets
> device_set_realized() dump the object into /machine/unattached.
> 
> Add object_new_child(parent, id, typename) as that missing primitive.
> The reference created by object_new() is transferred to the parent's
> child<> property, so on return the sole reference is held by @parent
> and the caller does not need to unref.  Later patches build the qdev
> and per-bus creation helpers on top of this.
> 
> Suggested-by: Markus Armbruster <[email protected]>
> Link: https://lore.kernel.org/qemu-devel/[email protected]/
> Assisted-by: Kiro

QEMU does not currently permit contributions assisted by AI
coding tools.

There is an open discussion about altering the policy but that
is not conclude with agreement yet.

> Signed-off-by: Alexander Graf <[email protected]>
> ---
>  include/qom/object.h | 25 +++++++++++++++++++++++++
>  qom/object.c         | 13 +++++++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/include/qom/object.h b/include/qom/object.h
> index 11f55613fc..ce6a23b5a1 100644
> --- a/include/qom/object.h
> +++ b/include/qom/object.h
> @@ -632,6 +632,31 @@ Object *object_new_with_class(ObjectClass *klass);
>   */
>  Object *object_new(const char *typename);
>  
> +/**
> + * object_new_child:
> + * @parent: the QOM composition-tree parent
> + * @id: the child<> property name; the object's canonical QOM path
> + *      becomes @parent's path plus "/" plus @id
> + * @typename: the name of the type of the object to instantiate
> + *
> + * Create a heap-allocated object and immediately add it to the QOM
> + * composition tree as a child of @parent.
> + *
> + * This is the heap-allocated dual of object_initialize_child(): use
> + * this when the child is a pointer member of the parent, and use
> + * object_initialize_child() when the child is embedded in the parent
> + * struct.  See also object_new_with_props() for the variant that
> + * additionally sets a list of properties.
> + *
> + * The reference returned by object_new() is transferred to the child<>
> + * property of @parent, so the object has a reference count of 1 held
> + * by @parent, and the caller does not need to unref.
> + *
> + * Returns: the newly allocated, instantiated and parented object.
> + */
> +Object *object_new_child(Object *parent, const char *id,
> +                         const char *typename);
> +
>  /**
>   * object_new_with_props:
>   * @typename:  The name of the type of the object to instantiate.
> diff --git a/qom/object.c b/qom/object.c
> index f79b2cf361..b4d181b617 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -718,6 +718,19 @@ Object *object_new(const char *typename)
>      return object_new_with_type(ti);
>  }
>  
> +Object *object_new_child(Object *parent, const char *id,
> +                          const char *typename)
> +{
> +    Object *obj;
> +
> +    g_assert(parent);
> +    g_assert(id);
> +
> +    obj = object_new(typename);
> +    object_property_add_child(parent, id, obj);
> +    object_unref(obj);
> +    return obj;
> +}
>  
>  Object *object_new_with_props(const char *typename,
>                                Object *parent,
> -- 
> 2.47.1
> 

With regards,
Daniel
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