Re: [Qemu-devel] [PATCH v2 01/16] qom/object: Add a new function object_initialize_child()

[Eduardo Habkost]

On Fri, Jul 13, 2018 at 10:27:29AM +0200, Thomas Huth wrote:
> A lot of code is using the object_initialize() function followed by a call
> to object_property_add_child() to add the newly initialized object as a child
> of the current object. Both functions increase the reference counter of the
> new object, but many spots that call these two functions then forget to drop
> one of the superfluous references. So the newly created object is often not
> cleaned up correctly when the parent is destroyed. In the worst case, this
> can cause crashes, e.g. because device objects are not correctly removed from
> their parent_bus.
> 
> Since this is a common pattern between many code spots, let's introdcue a
> new function that takes care of calling all three required initialization
> functions, first object_initialize(), then object_property_add_child() and
> finally object_unref().
> 
> And while we're at object.h, also fix some copy-n-paste errors in the
> comments there ("to store the area" --> "to store the error").
> 
> Signed-off-by: Thomas Huth <address@hidden>
> ---
>  include/qom/object.h | 23 +++++++++++++++++++++--
>  qom/object.c         | 15 +++++++++++++++
>  2 files changed, 36 insertions(+), 2 deletions(-)
> 
> diff --git a/include/qom/object.h b/include/qom/object.h
> index f3d2308..3362db0 100644
> --- a/include/qom/object.h
> +++ b/include/qom/object.h
> @@ -749,6 +749,25 @@ int object_set_propv(Object *obj,
>  void object_initialize(void *obj, size_t size, const char *typename);
>  
>  /**
> + * object_initialize_child:
> + * @parentobj: The parent object to add a property to
> + * @propname: The name of the property
> + * @childobj: A pointer to the memory to be used for the object.
> + * @size: The maximum size available at @obj for the object.
> + * @type: The name of the type of the object to instantiate.
> + * @errp: If an error occurs, a pointer to an area to store the error
> + *
> + * This function will initialize an object. The memory for the object should
> + * have already been allocated. The object will then be added as child 
> property
> + * to a parent with object_property_add_child() function. The returned object
> + * has a reference count of 1 (for the "child<...>" property from the 
> parent),
> + * so the object will get finalized automatically when the parent gets 
> removed.
> + */
> +void object_initialize_child(Object *parentobj, const char *propname,
> +                             void *childobj, size_t size, const char *type,
> +                             Error **errp);

I wonder if we should deprecate object_initialize() and support
only object_initialize_child() later.  Initializing an object
contained inside another one without making it a child of the
parent object is a recipe for trouble.

Reviewed-by: Eduardo Habkost <address@hidden>

-- 
Eduardo