linux-kernel - Re: ktime_set() does not check for nanoseconds

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Date:	Mon, 1 Sep 2008 15:06:23 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Matt Fleming <mattjfleming@...glemail.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: ktime_set() does not check for nanoseconds > one second

On Mon, 1 Sep 2008, Matt Fleming wrote:
> > Yeah, a check for this in ktime_set() might make sense. Currently it's
> > up to the programmer to provide sane values. :)
> >
> > Thanks,
> >
> >        tglx
> >
> 
> How about the attached patch?

Won't work with arbitrary numbers. i.e. >= 2* NSEC_PER_SEC. Looking at
it, I'm even less convinced that it is a good idea.

      tglx

> Matt
> 
> diff --git a/include/linux/ktime.h b/include/linux/ktime.h
> index ce59832..7c0ad35 100644
> --- a/include/linux/ktime.h
> +++ b/include/linux/ktime.h
> @@ -150,7 +150,19 @@ static inline ktime_t timeval_to_ktime(struct timeval tv)
>  /* Set a ktime_t variable to a value in sec/nsec representation: */
>  static inline ktime_t ktime_set(const long secs, const unsigned long nsecs)
>  {
> -       return (ktime_t) { .tv = { .sec = secs, .nsec = nsecs } };
> +       ktime_t res = { .tv = { .sec = secs, .nsec = nsecs }};;
> +
> +       /*
> +        * performance trick: the (u32) -NSEC gives 0x00000000Fxxxxxxx
> +        * so we subtract NSEC_PER_SEC and add 1 to the upper 32 bit.
> +        *
> +        * it's equivalent to:
> +        *   tv.nsec -= NSEC_PER_SEC
> +        *   tv.sec ++;
> +        */
> +       if (nsecs >= NSEC_PER_SEC)
> +               res.tv64 += (u32)-NSEC_PER_SEC;
> +       return res;
>  }
> 
>  /**
> 
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