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

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Date:	Thu, 17 Oct 2013 21:12:07 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	John Stultz <john.stultz@...aro.org>
CC:	kosaki.motohiro@...il.com, linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] alarmtimer: return EINVAL instead of ENOTSUPP if rtcdev
 doesn't exist

(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.



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