From: David Laight <David.Laight@ACULAB.COM>
To: 'Thomas Gleixner' <tglx@linutronix.de>, Arnd Bergmann <arnd@arndb.de>
Cc: "pang.xunlei@linaro.org" <pang.xunlei@linaro.org>,
Peter Zijlstra <peterz@infradead.org>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Paul Mackerras <paulus@samba.org>, "cl@linux.com" <cl@linux.com>,
Ingo Molnar <mingo@kernel.org>,
"heenasirwani@gmail.com" <heenasirwani@gmail.com>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
"y2038@lists.linaro.org" <y2038@lists.linaro.org>,
"rafael.j.wysocki@intel.com" <rafael.j.wysocki@intel.com>,
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Frederic Weisbecker <fweisbec@gmail.com>,
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Tejun Heo <tj@kernel.org>, John Stultz <john.stultz@linaro.org>,
"rth@twiddle.net" <rth@twiddle.net>,
Baolin Wang <baolin.wang@linaro.org>,
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LKML <linux-kernel@vger.kernel.org>,
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Subject: RE: [Y2038] [PATCH 04/11] posix timers:Introduce the 64bit methods with timespec64 type for k_clock structure
Date: Wed, 22 Apr 2015 10:44:50 +0000 [thread overview]
Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CB23A45@AcuExch.aculab.com> (raw)
In-Reply-To: <alpine.DEB.2.11.1504220946460.13914@nanos>
From: Thomas Gleixner
> Sent: 22 April 2015 09:45
> On Tue, 21 Apr 2015, Thomas Gleixner wrote:
> > On Tue, 21 Apr 2015, Arnd Bergmann wrote:
> > > I know there are concerns about this, in particular because C11 and
> > > POSIX both require tv_nsec to be 'long', unlike timeval->tv_usec,
> > > which is a 'suseconds_t' and can be defined as 'long long'.
> > >
> > > a)
> > >
> > > struct timespec {
> > > time_t tv_sec;
> > > long long tv_nsec; /* or typedef long long snseconds_t */
> > > };
> > >
> > > This is not directly compatible with C11 or POSIX.1-2008, but it
> > > matches what we do inside of 64-bit kernels, so probably has the
> > > highest chance of working correctly in practice
> >
> > After reading Linus rant in the x32 thread again (thanks for the
> > reminder), and looking at b/c/d - which rate between ugly and butt
> > ugly - I think we should go for a) and screw POSIX and C11 as those
> > committee dinosaurs seem to completely ignore the 2038 problem on
> > 32bit machines. At least I have not found any hint that these folks
> > care at all. So why should we comply to something which is completely
> > useless?
> >
> > That also makes the question about the upper 32bits check moot, so
> > it's the simplest and clearest of the possible solutions.
>=20
> Second thoughts after some sleep.
>=20
> So the outcome of this is going to be that user space libraries will
> not expose the syscall variant of
>=20
> syscall_timespec64 {
> s64 tv_sec;
> s64 tv_nsec;
> };
>=20
> to applications. The libs will translate them to spec conforming
>=20
> timespec {
> time_t tv_sec;
> long tv_nsec;
> };
>=20
> anyway. That means we have two translation steps on 32bit systems:
>=20
> 1) user space timespec -> syscall timespec64
>=20
> 2) syscall timespec64 -> scalar nsec s64 (ktime_t)
>=20
> and the other way round. The kernel internal representation is simply
> s64 (nsec) based all over the place.
Do you need the double-translation?
If all the kernel uses a 64bit nsec value the in-kernel syscall stub
can convert the user-supplied values appropriately before calling
the standard function.
Not that a syscall that takes a linear nsec value isn't useful.
FWIW I can't remember what NetBSD did when they extended time_t to 64bits.
David
next prev parent reply other threads:[~2015-04-22 10:46 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-20 5:57 [PATCH 00/11] Convert the posix_clock_operations and k_clock structure to ready for 2038 Baolin Wang
2015-04-20 5:57 ` [PATCH 01/11] linux/time64.h:Introduce the 'struct itimerspec64' for 64bit Baolin Wang
2015-04-20 9:49 ` Sergei Shtylyov
2015-04-20 10:55 ` Baolin Wang
2015-04-20 19:14 ` Thomas Gleixner
2015-04-20 19:59 ` Thomas Gleixner
2015-04-21 8:19 ` Baolin Wang
2015-04-20 5:57 ` [PATCH 02/11] timekeeping:Introduce the current_kernel_time64() function with timespec64 type Baolin Wang
2015-04-20 5:57 ` [PATCH 03/11] time/hrtimer:Introduce hrtimer_get_res64() with timespec64 type for getting the timer resolution Baolin Wang
2015-04-20 19:15 ` Thomas Gleixner
2015-04-20 5:57 ` [PATCH 04/11] posix timers:Introduce the 64bit methods with timespec64 type for k_clock structure Baolin Wang
2015-04-20 20:40 ` Thomas Gleixner
2015-04-21 8:59 ` [Y2038] " Arnd Bergmann
2015-04-21 14:14 ` Thomas Gleixner
2015-04-21 14:57 ` Arnd Bergmann
2015-04-21 15:13 ` Thomas Gleixner
2015-04-21 15:40 ` Arnd Bergmann
2015-04-21 20:13 ` Thomas Gleixner
2015-04-22 8:45 ` Thomas Gleixner
2015-04-22 10:11 ` Richard Cochran
2015-04-22 10:44 ` David Laight [this message]
2015-04-22 11:07 ` Arnd Bergmann
2015-04-22 13:37 ` Thomas Gleixner
2015-04-22 13:50 ` Arnd Bergmann
2015-04-22 14:54 ` Richard Cochran
2015-04-22 15:37 ` Arnd Bergmann
2015-04-22 15:14 ` Luc Van Oostenryck
2015-04-22 15:38 ` Arnd Bergmann
2015-04-20 5:57 ` [PATCH 05/11] time/posix-timers:Convert to the 64bit methods for k_clock callback functions Baolin Wang
2015-04-20 20:48 ` Thomas Gleixner
2015-04-21 8:36 ` Baolin Wang
2015-04-21 8:45 ` [Y2038] " Arnd Bergmann
2015-04-21 8:55 ` Baolin Wang
2015-04-20 5:57 ` [PATCH 06/11] char/mmtimer:Convert to the 64bit methods for k_clock callback function Baolin Wang
2015-04-20 5:57 ` [PATCH 07/11] time/alarmtimer:Convert to the new methods for k_clock structure Baolin Wang
2015-04-20 5:57 ` [PATCH 08/11] time/posix-clock:Convert to the 64bit methods for k_clock and posix_clock_operations structure Baolin Wang
2015-04-20 5:57 ` [PATCH 09/11] cputime:Introduce the cputime_to_timespec64/timespec64_to_cputime function Baolin Wang
2015-04-20 21:09 ` Thomas Gleixner
2015-04-20 5:57 ` [PATCH 10/11] time/posix-cpu-timers:Convert to the 64bit methods for k_clock structure Baolin Wang
2015-04-20 5:57 ` [PATCH 11/11] k_clock:Remove the 32bit methods with timespec type Baolin Wang
2015-04-20 8:42 ` Richard Cochran
2015-04-20 9:00 ` Baolin Wang
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