file descriptor referring to the timer
0 starts a relative timer using new_value.it_interval; TFD_TIMER_ABSTIME starts an absolute timer using new_value.it_value.
- it_value: Specifies the initial expiration of the timer. Setting either field to a non-zero value arms the timer. Setting both fields to zero disarms the timer. - it_interval: Setting one or both fields to non-zero values specifies the period for repeated timer expirations after the initial expiration. If both fields are zero, the timer expires just once, at the time specified by it_value.
Returns the old expiration time as timerfd_gettime().
0 on success or -1 on error. Sets errno in case of error.
Sets next expiration time of interval timer source fd to new_value.