Re: [Qemu-devel] [PATCH v5 2/5] qobject: use a QObjectBase_ struct

[Eric Blake]

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 <address@hidden>
> ---

> +++ 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 <address@hidden>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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