timerfdgettime

timerfdgettime is a system call in Linux that retrieves the current settings of a timer file descriptor. A timer file descriptor, created by the timerfd_create system call, allows a process to receive notifications at specified time intervals. The timerfd_gettime function populates a structure pointed to by the `ktimerfd_t` argument with information about the timer's expiration time and interval. This information includes the remaining time until the next expiration and the time interval between successive expirations.

The function takes two arguments: the file descriptor of the timer and a pointer to a `struct itimerspec`. The `struct itimerspec` contains two members: `it_value` and `it_interval`. `it_value` represents the time until the next expiration, and `it_interval` specifies the interval between subsequent expirations. If `it_interval` is zero, the timer will only expire once. The time values are represented using `struct timespec`, which includes seconds and nanoseconds.

Calling timerfd_gettime allows an application to monitor the state of a timer without altering it. This can be useful for debugging or for implementing more complex timing mechanisms. The retrieved values are relative to the system's monotonic clock, meaning they are not affected by system time changes. If the timer has already expired, `it_value` will be zero.