Re: [PATCH] [RFCv2] notify userspace about time changes

[john stultz <johnstul@us.ibm.com>]

On Wed, 2010-08-18 at 16:55 +0300, Alexander Shishkin wrote:
> Changes since v1:
>  - updated against 2.6.36-rc1,
>  - added notification/filtering options,
>  - added Documentation/ABI/sysfs-kernel-time-notify interface description.
> 
> Certain userspace applications (like "clock" desktop applets or cron) might
> want to be notified when some other application changes the system time. It
> might also be important for an application to be able to distinguish between
> its own and somebody else's time changes.
> 
> This patch implements a notification interface via eventfd mechanism. Proccess
> wishing to be notified about time changes should create an eventfd and echo
> its file descriptor along with notification options to /sys/kernel/time_notify.
> After that, any calls to settimeofday()/stime()/adjtimex() made by other
> processes will be signalled to this eventfd. Credits for suggesting the eventfd
> mechanism for this purpose go to Kirill Shutemov.

Hey Alexander, 
	Glad to see this work continue! One thing did strike me as odd in
reading over this: Does adjtimex really make sense to trigger a
notification?  Its not actually changing the time, but alters the freq
that time runs. This freq adjustment is transparent to applications or
timers (unlike something like settimeofday).  So I'm not sure I see why
it is included here.

What use case did you have in mind for it?

thanks
-john