netdev - Re: [patch 1/3] timekeeping: Provide ktime_get_clock

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Message-ID: <CANDhNCrxj9w+mcKOiGuOuLgJ26SairQTJ0Sqv8XteUtJRyWdwA@mail.gmail.com>
Date: Thu, 26 Jun 2025 22:22:46 -0700
From: John Stultz <jstultz@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org, 
	Richard Cochran <richardcochran@...il.com>, Christopher Hall <christopher.s.hall@...el.com>, 
	Frederic Weisbecker <frederic@...nel.org>, Anna-Maria Behnsen <anna-maria@...utronix.de>, 
	Miroslav Lichvar <mlichvar@...hat.com>, Werner Abt <werner.abt@...nberg-usa.com>, 
	David Woodhouse <dwmw2@...radead.org>, Stephen Boyd <sboyd@...nel.org>, 
	Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
	Kurt Kanzenbach <kurt@...utronix.de>, Nam Cao <namcao@...utronix.de>, 
	Antoine Tenart <atenart@...nel.org>
Subject: Re: [patch 1/3] timekeeping: Provide ktime_get_clock_ts64()

On Thu, Jun 26, 2025 at 6:27 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> PTP implements an inline switch case for taking timestamps from various
> POSIX clock IDs, which already consumes quite some text space. Expanding it
> for auxiliary clocks really becomes too big for inlining.
>
> Provide a out of line version.
>
> The function invalidates the timestamp in case the clock is invalid. The
> invalidation allows to implement a validation check without the need to
> propagate a return value through deep existing call chains.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  include/linux/timekeeping.h |    1 +
>  kernel/time/timekeeping.c   |   34 ++++++++++++++++++++++++++++++++++
>  2 files changed, 35 insertions(+)
>
> --- a/include/linux/timekeeping.h
> +++ b/include/linux/timekeeping.h
> @@ -44,6 +44,7 @@ extern void ktime_get_ts64(struct timesp
>  extern void ktime_get_real_ts64(struct timespec64 *tv);
>  extern void ktime_get_coarse_ts64(struct timespec64 *ts);
>  extern void ktime_get_coarse_real_ts64(struct timespec64 *ts);
> +extern void ktime_get_clock_ts64(clockid_t id, struct timespec64 *ts);
>
>  /* Multigrain timestamp interfaces */
>  extern void ktime_get_coarse_real_ts64_mg(struct timespec64 *ts);
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -1636,6 +1636,40 @@ void ktime_get_raw_ts64(struct timespec6
>  EXPORT_SYMBOL(ktime_get_raw_ts64);
>
>  /**
> + * ktime_get_clock_ts64 - Returns time of a clock in a timespec
> + * @id:                POSIX clock ID of the clock to read
> + * @ts:                Pointer to the timespec64 to be set
> + *
> + * The timestamp is invalidated (@ts->sec is set to -1) if the
> + * clock @id is not available.
> + */
> +void ktime_get_clock_ts64(clockid_t id, struct timespec64 *ts)
> +{
> +       /* Invalidate time stamp */
> +       ts->tv_sec = -1;
> +       ts->tv_nsec = 0;
> +
> +       switch (id) {
> +       case CLOCK_REALTIME:
> +               ktime_get_real_ts64(ts);
> +               return;
> +       case CLOCK_MONOTONIC:
> +               ktime_get_ts64(ts);
> +               return;
> +       case CLOCK_MONOTONIC_RAW:
> +               ktime_get_raw_ts64(ts);
> +               return;
> +       case CLOCK_AUX ... CLOCK_AUX_LAST:
> +               if (IS_ENABLED(CONFIG_POSIX_AUX_CLOCKS))
> +                       ktime_get_aux_ts64(id, ts);
> +               return;
> +       default:
> +               WARN_ON_ONCE(1);
> +       }
> +}
> +EXPORT_SYMBOL_GPL(ktime_get_clock_ts64);

While I recognize this is mainly focused on the ptp use case, as the
interface looks generic from headers point of view, should we add the
other clockids for completeness?

Other than that,
Acked-by: John Stultz <jstultz@...gle.com>

thanks
-john