[PATCH] libc/time: Add CLOCK_TAI

[Corinna Vinschen]

On Jul 16 11:18, Corinna Vinschen via Newlib wrote:
> On Jul 15 15:01, brian.inglis--- via Newlib wrote:
> > On 2025-07-15 02:43, Corinna Vinschen via Newlib wrote:
> > > On Jul 14 14:38, Brian Inglis via Newlib wrote:
> > > > On 2025-07-14 09:45, Corinna Vinschen via Newlib wrote:
> > > > > On Jul 11 06:35, Sebastian Huber wrote:
> > > > > > FreeBSD also provides this clock identifier, maybe it should be
> > > > > > #if __BSD_VISIBLE
> > > > > > #define CLOCK_TAI		(11)
> > > > > > #endif
> > > > > > ?
> > > > 
> > > > > Probably, but I seriously wonder how to implement CLOCK_TAI on Cygwin.
> > > > 
> > > > > IIUC, if you don't do anything special, the CLOCK_REALTIME and CLOCK_TAI
> > > > > return the same value, because the leap second is set to 0 at kernel
> > > > > startup.  Maybe that's enough...
> > > > 
> > > > If you are running an NTP server you just have to ask for the system variable:
> > > > [...]
> > > What we could do is to define CLOCK_TAI as CLOCK_REALTIME + 37 in the DLL
> > > for the time being, and the DLL could check if a file "/etc/leapsecs"
> > > exists and read it to compensate for new leap secs.  We can add such a
> > > file to the distro when a new leap sec has been defined.
> > 
> > It may be better to just use the standard approach and standard file name
> > which is /etc/leap-seconds.list, often symlinked from /etc/ntp/ which may
> > itself be symlinked from /var/lib/ntp/.
> 
> Actually, yesterday I hacked some POC code in my local Cygwin sandbox
> using the file /usr/share/zoneinfo/leapseconds from tzdata.  If the file
> isn't present, the DLL uses the current leap secs offset of 37 secs.
> Seems to work nicely.
> 
> So I'm looking forward to Sebastian adding the CLOCK_TAI macro to time.h.

I pushed Sebastians patch at his request.

Btw, Brian, the Fedora tzdata package contains not only the file
/usr/share/zoneinfo/leapseconds, but additionally the original file
/usr/share/zoneinfo/leap-seconds.list.

Can you please add it to your Cygwin tzdata package as well?


Thanks,
Corinna