Re: question about linux time change

[George Anzinger <george@mvista.com>]

Chris Friesen wrote:
> 
> I have been asked to add the ability to notify userspace when the time 
> of day changes.  The actual notification is the easy part.  I'm having 
> issues with where exactly the time is really changed.

Just what sort of time changes do you want to notify on?  The ntp code "drifts" 
time a lot.  Do you want to know about this?  If it is only cases where there is 
a jump in time, you might do well to look at "clock_was_set()".  It is in 
kernel/posix-timers.c and is called when ever do_settimeofday() is called AND on 
leap second calls.

You will even find code in there to push the ladder out of the softirq context.
> 
> do_settimeofday() is pretty straightforward.  No problems there.
> adjtimex() with ADJ_OFFSET_SINGLESHOT mode seems reasonable as well.
> 
> adjtimex() with ADJ_OFFSET is a bit harder to follow.  Can you give me 
> any pointers on what's going on with ADJ_OFFSET?

> 
> Thanks,
> 
> Chris
> 

-- 
George Anzinger   george@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml