Timekeeping

TFD_TIMER_CANCEL_ON_SET Reports Realtime Clock Discontinuities

A timerfd armed against wall-clock time can cross a discontinuous clock adjustment before its deadline. With TFD_TIMER_CANCEL_ON_SET, Linux exposes that event through the descriptor: a subsequent read() fails with ECANCELED rather than presenting the clock jump as an ordinary timer expiration. The flag is deliberately narrow. It applies only when timerfd_settime() arms an absolute timer on CLOCK_REALTIME or CLOCK_REALTIME_ALARM, and it changes the handling of discontinuous changes to those clocks.