Ok, that makes a lot of sense, I was confusing timedated and timesyncd, and indeed the latter is what would be able to broadcast the event, even if it does not yet.
I wasn't aware of /run/systemd/timesync/synchronized, looks fine to me, will investigate that. Thanks! Le mer. 17 août 2022 à 15:17, Mantas Mikulėnas <graw...@gmail.com> a écrit : > > On Wed, Aug 17, 2022 at 1:59 PM Etienne Doms <etienne.d...@gmail.com> wrote: >> >> Hi, >> >> I'm developing an application for an embedded system that needs to >> wait for proper NTP synchronization. systemd-timesyncd is running and >> I can read NTPSynchronized from /org/freedesktop/timedate1 using >> D-Bus. I read in the manual that this property is not signaled, and >> that I need to do some weird magic with timerfd's >> TFD_TIMER_CANCEL_ON_SET flag. >> >> It works, but having the ECANCELLED on the read() means that something >> somewhere did clock_settime(CLOCK_REALTIME, <...>), not especially >> that I got a proper NTP synchronization. Then, I still need to query >> NTPSynchronized after, and retry the timerfd thing if it didn't switch >> to "true", which is still some kind of polling (but very unlikely, >> sure). >> >> As a result, I'm a bit curious, what was the rationale of not simply >> signaling NTPSynchronized? > > > timedated itself doesn't have knowledge of that event, because it isn't the > daemon that performs actual synchronization (that's timesyncd), so all that > the D-Bus property does is report you the status of adjtimex() – specifically > it returns whether ".maxerror < 16000000". Timedated would still need to poll > and/or do timerfd tricks in order to see that state being reached. (Currently > timedated is not a continuously running daemon – it starts up only whenever > properties are queried and exits when idle.) > > A better question is why the timesyncd daemon does not have such a D-Bus > signal; looks like it *almost* does > (org.freedesktop.timesync1.Manager.NTPMessage) but it looks like it only > emits the raw messages and not whether they resulted in a successful sync. > > For now, if you're using timesyncd you can use inotify to watch > /run/systemd/timesync/synchronized, which is touched after a sync. > > -- > Mantas Mikulėnas
