Re: [Xen-devel] [PATCH] xen: add macro for defining variable length array in public headers

[Jan Beulich <jbeulich@xxxxxxxx>]

On 30.08.2019 10:32, Juergen Gross wrote:
> --- a/xen/include/public/xen.h
> +++ b/xen/include/public/xen.h
> @@ -53,6 +53,15 @@ DEFINE_XEN_GUEST_HANDLE(uint64_t);
>  DEFINE_XEN_GUEST_HANDLE(xen_pfn_t);
>  DEFINE_XEN_GUEST_HANDLE(xen_ulong_t);
>  
> +/* Define a variable length array (depends on compiler). */
> +#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
> +#define __XEN_VARLEN_ARRAY_SIZE
> +#elif defined(__GNUC__)
> +#define __XEN_VARLEN_ARRAY_SIZE  0
> +#else
> +#define __XEN_VARLEN_ARRAY_SIZE  1 /* variable size */
> +#endif

To be in line with the intentions, the C90 standard, and io/ring.h
I'd suggest to use FLEX instead of VARLEN. Furthermore, especially
in a public header, two double leading underscores need to go away.

And then, with FLEX in the name, SIZE isn't really appropriate
anymore. Therefore I see three possible names: XEN_FLEXIBLE_ARRAY,
XEN_FLEX_ARRAY_DIMENSION (possibly just _DIM at its end), or
XEN_FLEX_ARRAY_DESIGNATOR.

Jan

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