Re: [PATCH v3 2/8] xen/hypfs: switch write function handles to const

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.12.2020 17:09, Juergen Gross wrote:
> --- a/xen/include/xen/guest_access.h
> +++ b/xen/include/xen/guest_access.h
> @@ -26,6 +26,11 @@
>      type *_x = (hnd).p;                         \
>      (XEN_GUEST_HANDLE_PARAM(type)) { _x };      \
>  })
> +/* Same for casting to a const type. */
> +#define guest_handle_const_cast(hnd, type) ({       \
> +    const type *_x = (const type *)((hnd).p);       \
> +    (XEN_GUEST_HANDLE_PARAM(const_##type)) { _x };  \
> +})

Afaict this allow casting from e.g. uint to const_ulong. We
don't want to permit this (i.e. if really needed one is to
go through two steps). I think all it takes is dropping the
cast:

#define guest_handle_const_cast(hnd, type) ({      \
    const type *_x = (hnd).p;                      \
    (XEN_GUEST_HANDLE_PARAM(const_##type)) { _x }; \
})

With this
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
and I'd be okay making the adjustment while committing
(provided it works and I didn't overlook anything).

Jan