On Tue, Jan 11, 2011 at 6:06 AM, john stultz <johnstul@xxxxxxxxxx> wrote: > On Tue, 2011-01-11 at 05:45 +0900, Kuwahara,T. wrote: >> On Tue, Jan 11, 2011 at 1:49 AM, john stultz <johnstul@xxxxxxxxxx> wrote: >> > Leapsecond processing is done via an absolute hrtimer. Thus when the >> > time offset is set, the hrtimers that should have expired will fire >> > (just like with settimeofday) and the adjustment will then be made. >> >> How do you convert relative time to absolute time? ÂIt's not trivial >> because TAI offset is also a variable. > > I don't believe I understand what you're getting at. > > The proposed interface is almost identical in functionality to a > userland application doing the following: > > Â Â Â Âoffset = my_calculate_offset(); > Â Â Â Âclock_gettime(CLOCK_REALTIME, &now); > Â Â Â Ânewtime = my_add_ts(now, offset); > Â Â Â Âsettimeofday(&newtime, 0); > > The only difference is that you avoid the error from the delay between > the gettime call and the settime call. It just adds the offset directly > to the CLOCK_REALTIME. For example, what time was it 3 seconds after 2008-12-31 23:59:59? You may say, of course it's 2009-01-01 00:00:02. But it's not true. You wonder why? Because a leap second had been added at midnight. unix time UTC offset ---------- -------- --- 1230767997 23:59:57 -2 1230767998 23:59:58 -1 1230767999 23:59:59 0 1230768000 23:59:60 1 (leap second) 1230768000 00:00:00 2 1230768001 00:00:01 3 1230768002 00:00:02 4 That's why I said it's not trivial, and that your patch is broken and thus useless. Unfortunately, there's no remedy for this as long as a nonlinear timescale such as the unix time is being used, since the leap second insertion/deletion is a non-deterministic event. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
