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

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/07/2018 10:27, 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").

Even though I'd prefer the full cleanup, I can live with this. :)

Series

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

except for patch 6 for which I've sent a replacement.

Paolo

> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  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);
> +
> +/**
>   * object_dynamic_cast:
>   * @obj: The object to cast.
>   * @typename: The @typename to cast to.
> @@ -1382,7 +1401,7 @@ Object *object_resolve_path_component(Object *parent, const gchar *part);
>   * @obj: the object to add a property to
>   * @name: the name of the property
>   * @child: the child object
> - * @errp: if an error occurs, a pointer to an area to store the area
> + * @errp: if an error occurs, a pointer to an area to store the error
>   *
>   * Child properties form the composition tree.  All objects need to be a child
>   * of another object.  Objects can only be a child of one object.
> @@ -1420,7 +1439,7 @@ void object_property_allow_set_link(const Object *, const char *,
>   * @child: a pointer to where the link object reference is stored
>   * @check: callback to veto setting or NULL if the property is read-only
>   * @flags: additional options for the link
> - * @errp: if an error occurs, a pointer to an area to store the area
> + * @errp: if an error occurs, a pointer to an area to store the error
>   *
>   * Links establish relationships between objects.  Links are unidirectional
>   * although two links can be combined to form a bidirectional relationship
> diff --git a/qom/object.c b/qom/object.c
> index 4609e34..7be7638 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -392,6 +392,21 @@ void object_initialize(void *data, size_t size, const char *typename)
>      object_initialize_with_type(data, size, type);
>  }
>  
> +void object_initialize_child(Object *parentobj, const char *propname,
> +                             void *childobj, size_t size, const char *type,
> +                             Error **errp)
> +{
> +    object_initialize(childobj, size, type);
> +    object_property_add_child(parentobj, propname, OBJECT(childobj), errp);
> +    /*
> +     * Since object_property_add_child added a reference to the child object,
> +     * we can drop the reference added by object_initialize(), so the child
> +     * property will own the only reference to the object.
> +     */
> +    object_unref(OBJECT(childobj));
> +}
> +
> +
>  static inline bool object_property_is_child(ObjectProperty *prop)
>  {
>      return strstart(prop->type, "child<", NULL);
>