Re: [PATCH] alarmtimer: return EINVAL instead of ENOTSUPP if rtcdevdoesn't exist

[KOSAKI Motohiro]

(10/17/13 1:05 PM), John Stultz wrote:
> On 10/14/2013 02:33 PM, kosaki.motohiro@xxxxxxxxx wrote:
> > From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> >
> > 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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