linux-kernel - Re: [PATCH] alarmtimer: return EINVAL instead of ENOTSUPP if rtcdev doesn't exist

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Message-ID: <5261C450.1000204@linaro.org>
Date:	Fri, 18 Oct 2013 16:29:20 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	kosaki.motohiro@...il.com
CC:	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	fweisbec@...il.com
Subject: Re: [PATCH] alarmtimer: return EINVAL instead of ENOTSUPP if rtcdev
 doesn't exist

On 10/18/2013 04:12 PM, KOSAKI Motohiro wrote:
> On 10/18/2013 6:39 PM, John Stultz wrote:
>> On 10/17/2013 06:12 PM, KOSAKI Motohiro wrote:
>>> (10/17/13 1:05 PM), John Stultz wrote:
>>>> On 10/14/2013 02:33 PM, kosaki.motohiro@...il.com wrote:
>>>>> From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>>>>>
>>>>> Fedora Ruby maintainer reported latest Ruby doesn't work on Fedora
>>>>> Rawhide
>>>>> on ARM. (http://bugs.ruby-lang.org/issues/9008)
>>>>>
>>>>> Because of, commit 1c6b39ad3f (alarmtimers: Return -ENOTSUPP if no
>>>>> RTC device is present) intruduced to return ENOTSUPP when
>>>>> clock_get{time,res} can't find a RTC device. However it is incorrect.
>>>>>
>>>>> Posix and Linux man pages agree that clock_gettime and clock_getres
>>>>> should return EINVAL if clk_id argument is invalid. This is significant
>>>>> different from timer_create API.
>>>>>
>>>>> This patch fixes it.
>>>> Hrm... So I feel like there is a difference here. The clockid for
>>>> CLOCK_BOOTTIME_ALARM and CLOCK_REALTIME_ALARM are both valid.
>>>>
>>>> Its just that they're not supported on this specific hardware because it
>>>> apparently lacks a RTC that has told the system it can be used as a
>>>> wakeup device (Its actually quite likely on the hardware that the RTC
>>>> can be a wakeup device, but that the driver is probably setting the
>>>> wakeup flag after the RTC registered - so there is probably a driver bug
>>>> here too).
>>>>
>>>> So I feel like in this case EINVAL isn't quite right.  I'll admit it is
>>>> somewhat new behavior, because we haven't had any clockids before that
>>>> were dependent on the particular hardware, they either existed in a
>>>> kernel verison or didn't.
>>>>
>>>> Would updating the manpage be a better route?
>>> Nope.
>>>
>>> ENOTSUPP is not exported to userland. ENOTSUP (single P) and EOPNOTSUP is
>>> valid errno (and they are same on linux), but ENOTSUPP is a kernel
>>> internal specific.
>>>
>>> Moreover, I completely disagree your position. Both
>>> CLOCK_REALTIME_ALARM unsupported
>>> kernel and ARM which doesn't support RTC should use the same error
>>> because application
>>> need the same fallback.
>> Ok. You're right. The technicality that the clockid is valid but
>> unsupported isn't really useful to the applications, since the effect is
>> the same.
>>
>> What is the urgency on this? As the issue has been around since 3.0, is
>> it ok if it gets queued for 3.13 and marked for stable, or does it need
>> to land in 3.12?
> 3.13 is OK to me.

Ok. Applied to my 3.13 queue.

thanks
-john

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