Re: [PATCH v3 1/7] x86/time: introduce helper to fetch Xen wallclock when running as a guest

[Jan Beulich <jbeulich@xxxxxxxx>]

On 03.09.2024 15:02, Roger Pau Monne wrote:
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -785,6 +785,31 @@ static struct platform_timesource __initdata_cf_clobber 
> plt_xen_timer =
>      .resume = resume_xen_timer,
>      .counter_bits = 63,
>  };
> +
> +static unsigned long read_xen_wallclock(void)
> +{
> +    struct shared_info *sh_info = XEN_shared_info;
> +    uint32_t wc_version;
> +    uint64_t wc_sec;
> +
> +    ASSERT(xen_guest);
> +
> +    do {
> +        wc_version = sh_info->wc_version & ~1;
> +        smp_rmb();
> +
> +        wc_sec  = sh_info->wc_sec;
> +        smp_rmb();
> +    } while ( wc_version != sh_info->wc_version );
> +
> +    return wc_sec + read_xen_timer() / 1000000000;
> +}
> +#else
> +static unsigned long read_xen_wallclock(void)
> +{
> +    ASSERT_UNREACHABLE();
> +    return 0;
> +}
>  #endif

I understand you try to re-use an existing #ifdef here, but I wonder if I
could talk you into not doing so and instead placing the #ifdef inside the
(then single) function body. Less redundancy, less room for mistakes /
oversights.

Jan