Function sysclock_getsnapshot

freebsd/kern/kern_tc.c:1022–1090

* Take a snapshot of sysclock data which can be used to compare system clocks * and generate timestamps after the fact. */

 * and generate timestamps after the fact.
 */
void
sysclock_getsnapshot(struct sysclock_snap *clock_snap, int fast)
{
	struct fbclock_info *fbi;
	struct timehands *th;
	struct bintime bt;
	unsigned int delta, gen;
#ifdef FFCLOCK
	ffcounter ffcount;
	struct fftimehands *ffth;
	struct ffclock_info *ffi;
	struct ffclock_estimate cest;

	ffi = &clock_snap->ff_info;
#endif

	fbi = &clock_snap->fb_info;
	delta = 0;

	do {
		th = timehands;
		gen = atomic_load_acq_int(&th->th_generation);
		fbi->th_scale = th->th_scale;
		fbi->tick_time = th->th_offset;
#ifdef FFCLOCK
		ffth = fftimehands;
		ffi->tick_time = ffth->tick_time_lerp;
		ffi->tick_time_lerp = ffth->tick_time_lerp;
		ffi->period = ffth->cest.period;
		ffi->period_lerp = ffth->period_lerp;
		clock_snap->ffcount = ffth->tick_ffcount;
		cest = ffth->cest;
#endif
		if (!fast)
			delta = tc_delta(th);
		atomic_thread_fence_acq();
	} while (gen == 0 || gen != th->th_generation);

	clock_snap->delta = delta;
	clock_snap->sysclock_active = sysclock_active;

	/* Record feedback clock status and error. */
	clock_snap->fb_info.status = time_status;
	/* XXX: Very crude estimate of feedback clock error. */
	bt.sec = time_esterror / 1000000;
	bt.frac = ((time_esterror - bt.sec) * 1000000) *
	    (uint64_t)18446744073709ULL;
	clock_snap->fb_info.error = bt;

#ifdef FFCLOCK
	if (!fast)
		clock_snap->ffcount += delta;

	/* Record feed-forward clock leap second adjustment. */
	ffi->leapsec_adjustment = cest.leapsec_total;
	if (clock_snap->ffcount > cest.leapsec_next)
		ffi->leapsec_adjustment -= cest.leapsec;