Function dtrace_gethrtime

/ We cannot call do_gettimeofday, or ktime_get_ts or any of their */ inferiors because they will attempt to lock on a mutex, and we */ end up not being able to trace fbt::kernel:nr_active. We have */ to emulate a stable clock reading ourselves. */ */ Later Linux kernels hide the xtime_cache data inside the */ 'timekeeper' struct (kernel/time/timekeeping.c). So */