linux-kernel - Re: [PATCH v2 1/7] timekeeping: introduce __current_kernel

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Date:	Tue, 10 Nov 2015 10:31:33 -0500 (EST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	John Stultz <john.stultz@...aro.org>
cc:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	xen-devel@...ts.xensource.com, Ian.Campbell@...rix.com,
	Peter Zijlstra <peterz@...radead.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v2 1/7] timekeeping: introduce __current_kernel_time64

On Tue, 10 Nov 2015, John Stultz wrote:
> On Tue, Nov 10, 2015 at 7:10 AM, Stefano Stabellini
> <stefano.stabellini@...citrix.com> wrote:
> > On Tue, 10 Nov 2015, Arnd Bergmann wrote:
> >> On Tuesday 10 November 2015 11:57:49 Stefano Stabellini wrote:
> >> > __current_kernel_time64 returns a struct timespec64, without taking the
> >> > xtime lock. Mirrors __current_kernel_time/current_kernel_time.
> >> >
> >>
> >> Actually it doesn't mirror __current_kernel_time/current_kernel_time
> >>
> >> > diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
> >> > index ec89d84..b5802bf 100644
> >> > --- a/include/linux/timekeeping.h
> >> > +++ b/include/linux/timekeeping.h
> >> > @@ -19,7 +19,8 @@ extern int do_sys_settimeofday(const struct timespec *tv,
> >> >   */
> >> >  unsigned long get_seconds(void);
> >> >  struct timespec64 current_kernel_time64(void);
> >> > -/* does not take xtime_lock */
> >> > +/* do not take xtime_lock */
> >> > +struct timespec64 __current_kernel_time64(void);
> >> >  struct timespec __current_kernel_time(void);
> >>
> >> Please change __current_kernel_time into a static inline function
> >> while you are introducing the new one, to match the patch description ;-)
> >
> > The implementation is:
> >
> >         struct timekeeper *tk = &tk_core.timekeeper;
> >
> >         return timespec64_to_timespec(tk_xtime(tk));
> >
> > which cannot be easily made into a static inline, unless we start
> > exporting tk_core.
> 
> So the timekeeper is passed to the notifier. So you probably want something like
> 
> struct timespec64 __current_kernel_time64(struct timekeeper *tk)
> {
>  return timespec64_to_timespec(tk_xtime(tk));
> }
> 
> Then you can cast the priv pointer in the notifier to a timekeeper and
> use it that way?

Err no. Look at commit 8758a240e2d74c5932ab51a73377e6507b7fd441

i.e. Add the new 64bit function and make the existing one a static
inline which does the timespec64 to timespec conversion.

Thanks,

	tglx
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