Re: [PATCH v2 08/20] Implement container_of_safe() in terms of container_of()

[Arnd Bergmann]

On Sat, Nov 20, 2021 at 2:00 PM Alejandro Colomar
<alx.manpages@xxxxxxxxx> wrote:
>
> There's no more a need for the temporary variable __mptr,
> since now it's only passed to functions that accept a 'const void *',
> and everything can convert automatically to it,
> reducing the need for the cast too.

The purpose of the temporary variable is to avoid evaluating the macro
multiple times, this is still required.

>   * If IS_ERR_OR_NULL(ptr), ptr is returned unchanged.
>   */
> -#define container_of_safe(ptr, type, member) ({                                \
> -       void *__mptr = (void *)(ptr);                                   \
> -       static_assert(__same_type(*(ptr), ((type *)0)->member) ||       \
> -                     __same_type(*(ptr), void),                        \
> -                     "pointer type mismatch in container_of_safe()");  \
> -       IS_ERR_OR_NULL(__mptr) ? ERR_CAST(__mptr) :                     \
> -               ((type *)(__mptr - offsetof(type, member))); })
> +#define container_of_safe(ptr, type, member)                           \
> +       (IS_ERR_OR_NULL(ptr) ? ERR_CAST(ptr) : container_of(type, member))

It's possible that you may find a way to improve this macro using
__auto_type, as a way to reduce the macro expansion further.

        Arnd