Re: [PATCH 1/2] xen/kernel.h: Import __struct_group from Linux

[Jan Beulich <jbeulich@suse.com>]

On 30.04.2024 13:09, Luca Fancellu wrote:
> --- a/xen/include/xen/kernel.h
> +++ b/xen/include/xen/kernel.h
> @@ -54,6 +54,27 @@
>          typeof_field(type, member) *__mptr = (ptr);             \
>          (type *)( (char *)__mptr - offsetof(type,member) );})
>  
> +/**
> + * __struct_group() - Create a mirrored named and anonyomous struct
> + *
> + * @TAG: The tag name for the named sub-struct (usually empty)
> + * @NAME: The identifier name of the mirrored sub-struct
> + * @ATTRS: Any struct attributes (usually empty)
> + * @MEMBERS: The member declarations for the mirrored structs
> + *
> + * Used to create an anonymous union of two structs with identical layout
> + * and size: one anonymous and one named. The former's members can be used
> + * normally without sub-struct naming, and the latter can be used to
> + * reason about the start, end, and size of the group of struct members.
> + * The named struct can also be explicitly tagged for layer reuse, as well
> + * as both having struct attributes appended.
> + */
> +#define __struct_group(TAG, NAME, ATTRS, MEMBERS...) \
> +    union { \
> +        struct { MEMBERS } ATTRS; \
> +        struct TAG { MEMBERS } ATTRS NAME; \
> +    } ATTRS

Besides my hesitance towards having this construct, can you explain why
ATTR needs using 3 times, i.e. also on the wrapping union?

Jan