[PATCHv6 10/36] kernel: Add do_timens_ktime_to_host() helper

Thomas Gleixner tglx at linutronix.de
Thu Aug 15 17:38:04 UTC 2019


On Thu, 15 Aug 2019, Dmitry Safonov wrote:
> +ktime_t do_timens_ktime_to_host(clockid_t clockid, ktime_t tim,
> +				struct timens_offsets *ns_offsets)
> +{
> +	ktime_t offset;
> +
> +	switch (clockid) {
> +	case CLOCK_MONOTONIC:
> +		offset = timespec64_to_ktime(ns_offsets->monotonic);
> +		break;
> +	case CLOCK_BOOTTIME:
> +	case CLOCK_BOOTTIME_ALARM:
> +		offset = timespec64_to_ktime(ns_offsets->boottime);
> +		break;
> +	default:
> +		return tim;
> +	}
> +
> +	/*
> +	 * Check that @tim value is in [offset, KTIME_MAX + offset]
> +	 * and subtract offset.
> +	 */
> +	if (tim < offset) {
> +		/*
> +		 * User can specify @tim *absolute* value - if it's lesser than
> +		 * the time namespace's offset - it's already expired.
> +		 */
> +		tim = 0;
> +	} else if (KTIME_MAX - tim < -offset) {
> +		/*
> +		 * User-supplied @tim may be close or even equal KTIME_MAX
> +		 * and time namespace offset can be negative.
> +		 * Let's check (tim - offset) for an overflow.
> +		 * Return KTIME_MAX in such case, as the time value is
> +		 * thousands *years* in future anyway.
> +		 */
> +		tim = KTIME_MAX;
> +	} else {
> +		tim = ktime_sub(tim, offset);
> +	}

While the overflow check is correct, wouldn't it be more intuitive to do:

      	  	tim = ktime_sub(tim, offset);
		if (unlikely(tim > KTIME_MAX))
			tim = KTIME_MAX;

Thanks,

	tglx


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