On 04/17/2018 08:35 AM, Marc-André Lureau wrote: > By moving the base fields to a QObjectBase_, QObject can be a type > which also has a 'base' field. This allows to write a generic
either "allows us to write" or "allows writing"
> QOBJECT() macro that will work with any QObject type, including
> QObject itself. The container_of() macro ensures that the object to
> cast has a QObjectBase_ base field, giving some type safety
> guarantees. QObject must have no members but QObjectBase_ base, or
> else QOBJECT() breaks.
>
> QObjectBase_ is not typedef and use a trailing underscore to make it
s/not typedef and use/not a typedef and uses/
> obvious it is not for normal use and to avoid potential abuse.
>
> Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
> ---
> +++ b/include/qapi/qmp/qobject.h
> @@ -34,13 +34,20 @@
>
> #include "qapi/qapi-builtin-types.h"
>
> -struct QObject {
> +/* Not for use outside include/qapi/qmp/ */
> +struct QObjectBase_ {
> QType type;
> size_t refcnt;
> };
>
> -/* Get the 'base' part of an object */
> -#define QOBJECT(obj) (&(obj)->base)
> +struct QObject {
> + struct QObjectBase_ base;
I'd add a comment here that this struct must have no other members than
base.
> +};
> +
> +#define QOBJECT(x) ({ \
> + typeof(x) __x = (x); \
> + __x ? container_of(&(__x)->base, QObject, base) : NULL; \
> +})
>
With those changes,
Reviewed-by: Eric Blake <ebl...@redhat.com>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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