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

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Message-ID: <745fd720-4cf5-42c4-9cb6-a4932c6f68ee@linux.dev>
Date: Sun, 29 Jun 2025 16:49:14 +0100
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Thomas Gleixner <tglx@...utronix.de>, LKML <linux-kernel@...r.kernel.org>
Cc: netdev@...r.kernel.org, Richard Cochran <richardcochran@...il.com>,
 Christopher Hall <christopher.s.hall@...el.com>,
 John Stultz <jstultz@...gle.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 26/06/2025 14:27, Thomas Gleixner 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);
> +
> +/**
>    * timekeeping_valid_for_hres - Check if timekeeping is suitable for hres
>    */
>   int timekeeping_valid_for_hres(void)
> 

Reviewed-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>