linux-kernel - Re: [PATCH RFC 2/8] clock device: convert clock

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Message-Id: <201011091347.00310.arnd@arndb.de>
Date:	Tue, 9 Nov 2010 13:47:00 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Christoph Lameter <cl@...ux.com>,
	John Stultz <johnstul@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RFC 2/8] clock device: convert clock_gettime

On Tuesday 09 November 2010, Richard Cochran wrote:
> On Mon, Nov 08, 2010 at 07:56:50AM +0100, Arnd Bergmann wrote:
> > On Thursday 04 November 2010, Richard Cochran wrote:
> > >  #define CPUCLOCK_PERTHREAD_MASK	4
> > >  #define CPUCLOCK_WHICH(clock)	((clock) & (clockid_t) CPUCLOCK_CLOCK_MASK)
> > >  #define CPUCLOCK_CLOCK_MASK	3
> > > @@ -28,12 +40,17 @@ struct cpu_timer_list {
> > >  #define CPUCLOCK_VIRT		1
> > >  #define CPUCLOCK_SCHED		2
> > >  #define CPUCLOCK_MAX		3
> > > +#define CLOCKFD			CPUCLOCK_MAX
> > > +#define CLOCKFD_MASK		(CPUCLOCK_PERTHREAD_MASK|CPUCLOCK_CLOCK_MASK)
> > 
> > It looks like you are turning a kernel internal interface into a user ABI,
> > which I think is highly questionable. Using the bits like this internally is
> > ok, but making it part of the syscall ABI means that we can never change this
> > in the future.
> 
> This set of defines is already part of the ABI and has been copied
> into glibc.  I am extending the (mis)use of the clock id by adding one
> more case.

Ok, that is very different then. I wonder why posix-timers.h is not an exported
header file, it might be good to change that to make it explicit which parts of
it define the ABI and which parts are kernel internal.

	Arnd
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