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


  • To: Luca Fancellu <luca.fancellu@xxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Tue, 30 Apr 2024 13:43:00 +0200
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  • Cc: consulting@xxxxxxxxxxx, nicola.vetrini@xxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Tue, 30 Apr 2024 11:43:13 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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



 


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