Mastering Linux Kernel Development

Timeval and timespec

In Linux, the current time is maintained by keeping the number of seconds elapsed since midnight of January 01, 1970 (called epoch); the second elements in each of these represent the time elapsed since the last second in microseconds and nanoseconds, respectively:

struct timespec {
        __kernel_time_t  tv_sec;                   /* seconds */
        long            tv_nsec;          /* nanoseconds */
};
#endif

struct timeval {
        __kernel_time_t          tv_sec;           /* seconds */
        __kernel_suseconds_t     tv_usec;  /* microseconds */
};

Time (counter value) read from the clock source needs to be accumulated and tracked somewhere; the structure struct tk_read_base, defined in include/linux/timekeeper_internal.h, serves this purpose:

struct tk_read_base {
        struct clocksource        *clock;
        cycle_t ...