From mboxrd@z Thu Jan 1 00:00:00 1970 From: john stultz Subject: Re: [PATCH RFC 2/8] clock device: convert clock_gettime Date: Tue, 09 Nov 2010 13:37:02 -0800 Message-ID: <1289338622.9434.46.camel@localhost.localdomain> References: <81ccd2674ebf26332898761ba6b7b54f395a15bd.1288897199.git.richard.cochran@omicron.at> <201011080756.50930.arnd@arndb.de> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <201011080756.50930.arnd-r2nGTMty4D4@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Arnd Bergmann Cc: Richard Cochran , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Alan Cox , Christoph Lameter , Peter Zijlstra , Thomas Gleixner List-Id: linux-api@vger.kernel.org On Mon, 2010-11-08 at 07:56 +0100, Arnd Bergmann wrote: > On Thursday 04 November 2010, Richard Cochran wrote: > > diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h > > index 3e23844..70f40e6 100644 > > --- a/include/linux/posix-timers.h > > +++ b/include/linux/posix-timers.h > > @@ -17,10 +17,22 @@ struct cpu_timer_list { > > int firing; > > }; > > > > +/* Bit fields within a clockid: > > + * > > + * The most significant 29 bits hold either a pid or a file descriptor. > > + * > > + * Bit 2 indicates whether a cpu clock refers to a thread or a process. > > + * > > + * Bits 1 and 0 give the type: PROF=0, VIRT=1, SCHED=2, or FD=3. > > + * > > + * A clockid is invalid if bits 2, 1, and 0 all set (see also CLOCK_INVALID > > + * in include/linux/time.h) > > + */ > > + > > #define (clock) ((pid_t) ~((clock) >> 3)) > > #define CPUCLOCK_PERTHREAD(clock) \ > > (((clock) & (clockid_t) CPUCLOCK_PERTHREAD_MASK) != 0) > > -#define CPUCLOCK_PID_MASK 7 > > + > > #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. > > Maybe I was misunderstanding your patch though. As Richard already mentioned, the cpuclocks has already exported this as ABI and its used in pthread_getcpuclockid(). I wonder thought if it would be worth having a syscall to convert from fd to clock_id so it could be more flexible in the future. But it may not be worth it, as we're probably already limited by the cpuclock implementation. thanks -john