kernel/time/ntp.c - linux - Git at Google

 /*
  * NTP state machine interfaces and logic.
  *
  * This code was mainly moved from kernel/timer.c and kernel/time.c
  * Please see those files for relevant copyright info and historical
  * changelogs.
  */
 #include <linux/capability.h>
 #include <linux/clocksource.h>
 #include <linux/workqueue.h>
 #include <linux/hrtimer.h>
 #include <linux/jiffies.h>
 #include <linux/math64.h>
 #include <linux/timex.h>
 #include <linux/time.h>
 #include <linux/mm.h>

 /*
  * NTP timekeeping variables:
  */

 /* USER_HZ period (usecs): */
 unsigned long			tick_usec = TICK_USEC;

 /* ACTHZ period (nsecs): */
 unsigned long			tick_nsec;

 u64				tick_length;
 static u64			tick_length_base;

 static struct hrtimer		leap_timer;

 #define MAX_TICKADJ		500LL		/* usecs */
 #define MAX_TICKADJ_SCALED \
 	(((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)

 /*
  * phase-lock loop variables
  */

 /*
  * clock synchronization status
  *
  * (TIME_ERROR prevents overwriting the CMOS clock)
  */
 static int			time_state = TIME_OK;

 /* clock status bits:							*/
 int				time_status = STA_UNSYNC;

 /* TAI offset (secs):							*/
 static long			time_tai;

 /* time adjustment (nsecs):						*/
 static s64			time_offset;

 /* pll time constant:							*/
 static long			time_constant = 2;

 /* maximum error (usecs):						*/
 long				time_maxerror = NTP_PHASE_LIMIT;

 /* estimated error (usecs):						*/
 long				time_esterror = NTP_PHASE_LIMIT;

 /* frequency offset (scaled nsecs/secs):				*/
 static s64			time_freq;

 /* time at last adjustment (secs):					*/
 static long			time_reftime;

 long				time_adjust;

 /* constant (boot-param configurable) NTP tick adjustment (upscaled)	*/
 static s64			ntp_tick_adj;

 /*
  * NTP methods:
  */

 /*
  * Update (tick_length, tick_length_base, tick_nsec), based
  * on (tick_usec, ntp_tick_adj, time_freq):
  */
 static void ntp_update_frequency(void)
 {
 	u64 second_length;
 	u64 new_base;

 	second_length		 = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
 						<< NTP_SCALE_SHIFT;

 	second_length		+= ntp_tick_adj;
 	second_length		+= time_freq;

 	tick_nsec		 = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
 	new_base		 = div_u64(second_length, NTP_INTERVAL_FREQ);

 	/*
 	 * Don't wait for the next second_overflow, apply
 	 * the change to the tick length immediately:
 	 */
 	tick_length		+= new_base - tick_length_base;
 	tick_length_base	 = new_base;
 }

 static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
 {
 	time_status &= ~STA_MODE;

 	if (secs < MINSEC)
 		return 0;

 	if (!(time_status & STA_FLL) && (secs <= MAXSEC))
 		return 0;

 	time_status |= STA_MODE;

 	return div_s64(offset64 << (NTP_SCALE_SHIFT - SHIFT_FLL), secs);
 }

 static void ntp_update_offset(long offset)
 {
 	s64 freq_adj;
 	s64 offset64;
 	long secs;

 	if (!(time_status & STA_PLL))
 		return;

 	if (!(time_status & STA_NANO))
 		offset *= NSEC_PER_USEC;

 	/*
 	 * Scale the phase adjustment and
 	 * clamp to the operating range.
 	 */
 	offset = min(offset, MAXPHASE);
 	offset = max(offset, -MAXPHASE);

 	/*
 	 * Select how the frequency is to be controlled
 	 * and in which mode (PLL or FLL).
 	 */
 	secs = xtime.tv_sec - time_reftime;
 	if (unlikely(time_status & STA_FREQHOLD))
 		secs = 0;

 	time_reftime = xtime.tv_sec;

 	offset64    = offset;
 	freq_adj    = (offset64 * secs) <<
 			(NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));

 	freq_adj    += ntp_update_offset_fll(offset64, secs);

 	freq_adj    = min(freq_adj + time_freq, MAXFREQ_SCALED);

 	time_freq   = max(freq_adj, -MAXFREQ_SCALED);

 	time_offset = div_s64(offset64 << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
 }

 /**
  * ntp_clear - Clears the NTP state variables
  *
  * Must be called while holding a write on the xtime_lock
  */
 void ntp_clear(void)
 {
 	time_adjust	= 0;		/* stop active adjtime() */
 	time_status	|= STA_UNSYNC;
 	time_maxerror	= NTP_PHASE_LIMIT;
 	time_esterror	= NTP_PHASE_LIMIT;

 	ntp_update_frequency();

 	tick_length	= tick_length_base;
 	time_offset	= 0;
 }

 /*
  * Leap second processing. If in leap-insert state at the end of the
  * day, the system clock is set back one second; if in leap-delete
  * state, the system clock is set ahead one second.
  */
 static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
 {
 	enum hrtimer_restart res = HRTIMER_NORESTART;

 	write_seqlock(&xtime_lock);

 	switch (time_state) {
 	case TIME_OK:
 		break;
 	case TIME_INS:
 		xtime.tv_sec--;
 		wall_to_monotonic.tv_sec++;
 		time_state = TIME_OOP;
 		printk(KERN_NOTICE
 			"Clock: inserting leap second 23:59:60 UTC\n");
 		hrtimer_add_expires_ns(&leap_timer, NSEC_PER_SEC);
 		res = HRTIMER_RESTART;
 		break;
 	case TIME_DEL:
 		xtime.tv_sec++;
 		time_tai--;
 		wall_to_monotonic.tv_sec--;
 		time_state = TIME_WAIT;
 		printk(KERN_NOTICE
 			"Clock: deleting leap second 23:59:59 UTC\n");
 		break;
 	case TIME_OOP:
 		time_tai++;
 		time_state = TIME_WAIT;
 		/* fall through */
 	case TIME_WAIT:
 		if (!(time_status & (STA_INS | STA_DEL)))
 			time_state = TIME_OK;
 		break;
 	}
 	update_vsyscall(&xtime, clock);

 	write_sequnlock(&xtime_lock);

 	return res;
 }

 /*
  * this routine handles the overflow of the microsecond field
  *
  * The tricky bits of code to handle the accurate clock support
  * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
  * They were originally developed for SUN and DEC kernels.
  * All the kudos should go to Dave for this stuff.
  */
 void second_overflow(void)
 {
 	s64 delta;

 	/* Bump the maxerror field */
 	time_maxerror += MAXFREQ / NSEC_PER_USEC;
 	if (time_maxerror > NTP_PHASE_LIMIT) {
 		time_maxerror = NTP_PHASE_LIMIT;
 		time_status |= STA_UNSYNC;
 	}

 	/*
 	 * Compute the phase adjustment for the next second. The offset is
 	 * reduced by a fixed factor times the time constant.
 	 */
 	tick_length	 = tick_length_base;

 	delta		 = shift_right(time_offset, SHIFT_PLL + time_constant);
 	time_offset	-= delta;
 	tick_length	+= delta;

 	if (!time_adjust)
 		return;

 	if (time_adjust > MAX_TICKADJ) {
 		time_adjust -= MAX_TICKADJ;
 		tick_length += MAX_TICKADJ_SCALED;
 		return;
 	}

 	if (time_adjust < -MAX_TICKADJ) {
 		time_adjust += MAX_TICKADJ;
 		tick_length -= MAX_TICKADJ_SCALED;
 		return;
 	}

 	tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
 							 << NTP_SCALE_SHIFT;
 	time_adjust = 0;
 }

 #ifdef CONFIG_GENERIC_CMOS_UPDATE

 /* Disable the cmos update - used by virtualization and embedded */
 int no_sync_cmos_clock  __read_mostly;

 static void sync_cmos_clock(struct work_struct *work);

 static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);

 static void sync_cmos_clock(struct work_struct *work)
 {
 	struct timespec now, next;
 	int fail = 1;

 	/*
 	 * If we have an externally synchronized Linux clock, then update
 	 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
 	 * called as close as possible to 500 ms before the new second starts.
 	 * This code is run on a timer.  If the clock is set, that timer
 	 * may not expire at the correct time.  Thus, we adjust...
 	 */
 	if (!ntp_synced()) {
 		/*
 		 * Not synced, exit, do not restart a timer (if one is
 		 * running, let it run out).
 		 */
 		return;
 	}

 	getnstimeofday(&now);
 	if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
 		fail = update_persistent_clock(now);

 	next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
 	if (next.tv_nsec <= 0)
 		next.tv_nsec += NSEC_PER_SEC;

 	if (!fail)
 		next.tv_sec = 659;
 	else
 		next.tv_sec = 0;

 	if (next.tv_nsec >= NSEC_PER_SEC) {
 		next.tv_sec++;
 		next.tv_nsec -= NSEC_PER_SEC;
 	}
 	schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
 }

 static void notify_cmos_timer(void)
 {
 	if (!no_sync_cmos_clock)
 		schedule_delayed_work(&sync_cmos_work, 0);
 }

 #else
 static inline void notify_cmos_timer(void) { }
 #endif

 /*
  * Start the leap seconds timer:
  */
 static inline void ntp_start_leap_timer(struct timespec *ts)
 {
 	long now = ts->tv_sec;

 	if (time_status & STA_INS) {
 		time_state = TIME_INS;
 		now += 86400 - now % 86400;
 		hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);

 		return;
 	}

 	if (time_status & STA_DEL) {
 		time_state = TIME_DEL;
 		now += 86400 - (now + 1) % 86400;
 		hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);
 	}
 }

 /*
  * Propagate a new txc->status value into the NTP state:
  */
 static inline void process_adj_status(struct timex *txc, struct timespec *ts)
 {
 	if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
 		time_state = TIME_OK;
 		time_status = STA_UNSYNC;
 	}

 	/*
 	 * If we turn on PLL adjustments then reset the
 	 * reference time to current time.
 	 */
 	if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
 		time_reftime = xtime.tv_sec;

 	/* only set allowed bits */
 	time_status &= STA_RONLY;
 	time_status |= txc->status & ~STA_RONLY;

 	switch (time_state) {
 	case TIME_OK:
 		ntp_start_leap_timer(ts);
 		break;
 	case TIME_INS:
 	case TIME_DEL:
 		time_state = TIME_OK;
 		ntp_start_leap_timer(ts);
 	case TIME_WAIT:
 		if (!(time_status & (STA_INS | STA_DEL)))
 			time_state = TIME_OK;
 		break;
 	case TIME_OOP:
 		hrtimer_restart(&leap_timer);
 		break;
 	}
 }
 /*
  * Called with the xtime lock held, so we can access and modify
  * all the global NTP state:
  */
 static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts)
 {
 	if (txc->modes & ADJ_STATUS)
 		process_adj_status(txc, ts);

 	if (txc->modes & ADJ_NANO)
 		time_status |= STA_NANO;

 	if (txc->modes & ADJ_MICRO)
 		time_status &= ~STA_NANO;

 	if (txc->modes & ADJ_FREQUENCY) {
 		time_freq = txc->freq * PPM_SCALE;
 		time_freq = min(time_freq, MAXFREQ_SCALED);
 		time_freq = max(time_freq, -MAXFREQ_SCALED);
 	}

 	if (txc->modes & ADJ_MAXERROR)
 		time_maxerror = txc->maxerror;

 	if (txc->modes & ADJ_ESTERROR)
 		time_esterror = txc->esterror;

 	if (txc->modes & ADJ_TIMECONST) {
 		time_constant = txc->constant;
 		if (!(time_status & STA_NANO))
 			time_constant += 4;
 		time_constant = min(time_constant, (long)MAXTC);
 		time_constant = max(time_constant, 0l);
 	}

 	if (txc->modes & ADJ_TAI && txc->constant > 0)
 		time_tai = txc->constant;

 	if (txc->modes & ADJ_OFFSET)
 		ntp_update_offset(txc->offset);

 	if (txc->modes & ADJ_TICK)
 		tick_usec = txc->tick;

 	if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
 		ntp_update_frequency();
 }

 /*
  * adjtimex mainly allows reading (and writing, if superuser) of
  * kernel time-keeping variables. used by xntpd.
  */
 int do_adjtimex(struct timex *txc)
 {
 	struct timespec ts;
 	int result;

 	/* Validate the data before disabling interrupts */
 	if (txc->modes & ADJ_ADJTIME) {
 		/* singleshot must not be used with any other mode bits */
 		if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
 			return -EINVAL;
 		if (!(txc->modes & ADJ_OFFSET_READONLY) &&
 		    !capable(CAP_SYS_TIME))
 			return -EPERM;
 	} else {
 		/* In order to modify anything, you gotta be super-user! */
 		 if (txc->modes && !capable(CAP_SYS_TIME))
 			return -EPERM;

 		/*
 		 * if the quartz is off by more than 10% then
 		 * something is VERY wrong!
 		 */
 		if (txc->modes & ADJ_TICK &&
 		    (txc->tick <  900000/USER_HZ ||
 		     txc->tick > 1100000/USER_HZ))
 			return -EINVAL;

 		if (txc->modes & ADJ_STATUS && time_state != TIME_OK)
 			hrtimer_cancel(&leap_timer);
 	}

 	getnstimeofday(&ts);

 	write_seqlock_irq(&xtime_lock);

 	if (txc->modes & ADJ_ADJTIME) {
 		long save_adjust = time_adjust;

 		if (!(txc->modes & ADJ_OFFSET_READONLY)) {
 			/* adjtime() is independent from ntp_adjtime() */
 			time_adjust = txc->offset;
 			ntp_update_frequency();
 		}
 		txc->offset = save_adjust;
 	} else {

 		/* If there are input parameters, then process them: */
 		if (txc->modes)
 			process_adjtimex_modes(txc, &ts);

 		txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
 				  NTP_SCALE_SHIFT);
 		if (!(time_status & STA_NANO))
 			txc->offset /= NSEC_PER_USEC;
 	}

 	result = time_state;	/* mostly `TIME_OK' */
 	if (time_status & (STA_UNSYNC|STA_CLOCKERR))
 		result = TIME_ERROR;

 	txc->freq	   = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
 					 PPM_SCALE_INV, NTP_SCALE_SHIFT);
 	txc->maxerror	   = time_maxerror;
 	txc->esterror	   = time_esterror;
 	txc->status	   = time_status;
 	txc->constant	   = time_constant;
 	txc->precision	   = 1;
 	txc->tolerance	   = MAXFREQ_SCALED / PPM_SCALE;
 	txc->tick	   = tick_usec;
 	txc->tai	   = time_tai;

 	/* PPS is not implemented, so these are zero */
 	txc->ppsfreq	   = 0;
 	txc->jitter	   = 0;
 	txc->shift	   = 0;
 	txc->stabil	   = 0;
 	txc->jitcnt	   = 0;
 	txc->calcnt	   = 0;
 	txc->errcnt	   = 0;
 	txc->stbcnt	   = 0;

 	write_sequnlock_irq(&xtime_lock);

 	txc->time.tv_sec = ts.tv_sec;
 	txc->time.tv_usec = ts.tv_nsec;
 	if (!(time_status & STA_NANO))
 		txc->time.tv_usec /= NSEC_PER_USEC;

 	notify_cmos_timer();

 	return result;
 }

 static int __init ntp_tick_adj_setup(char *str)
 {
 	ntp_tick_adj = simple_strtol(str, NULL, 0);
 	ntp_tick_adj <<= NTP_SCALE_SHIFT;

 	return 1;
 }

 __setup("ntp_tick_adj=", ntp_tick_adj_setup);

 void __init ntp_init(void)
 {
 	ntp_clear();
 	hrtimer_init(&leap_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
 	leap_timer.function = ntp_leap_second;
 }
	/*
	* NTP state machine interfaces and logic.
	*
	* This code was mainly moved from kernel/timer.c and kernel/time.c
	* Please see those files for relevant copyright info and historical
	* changelogs.
	*/
	#include <linux/capability.h>
	#include <linux/clocksource.h>
	#include <linux/workqueue.h>
	#include <linux/hrtimer.h>
	#include <linux/jiffies.h>
	#include <linux/math64.h>
	#include <linux/timex.h>
	#include <linux/time.h>
	#include <linux/mm.h>

	/*
	* NTP timekeeping variables:
	*/

	/* USER_HZ period (usecs): */
	unsigned long tick_usec = TICK_USEC;

	/* ACTHZ period (nsecs): */
	unsigned long tick_nsec;

	u64 tick_length;
	static u64 tick_length_base;

	static struct hrtimer leap_timer;

	#define MAX_TICKADJ 500LL /* usecs */
	#define MAX_TICKADJ_SCALED \
	(((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)

	/*
	* phase-lock loop variables
	*/

	/*
	* clock synchronization status
	*
	* (TIME_ERROR prevents overwriting the CMOS clock)
	*/
	static int time_state = TIME_OK;

	/* clock status bits: */
	int time_status = STA_UNSYNC;

	/* TAI offset (secs): */
	static long time_tai;

	/* time adjustment (nsecs): */
	static s64 time_offset;

	/* pll time constant: */
	static long time_constant = 2;

	/* maximum error (usecs): */
	long time_maxerror = NTP_PHASE_LIMIT;

	/* estimated error (usecs): */
	long time_esterror = NTP_PHASE_LIMIT;

	/* frequency offset (scaled nsecs/secs): */
	static s64 time_freq;

	/* time at last adjustment (secs): */
	static long time_reftime;

	long time_adjust;

	/* constant (boot-param configurable) NTP tick adjustment (upscaled) */
	static s64 ntp_tick_adj;

	/*
	* NTP methods:
	*/

	/*
	* Update (tick_length, tick_length_base, tick_nsec), based
	* on (tick_usec, ntp_tick_adj, time_freq):
	*/
	static void ntp_update_frequency(void)
	{
	u64 second_length;
	u64 new_base;

	second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
	<< NTP_SCALE_SHIFT;

	second_length += ntp_tick_adj;
	second_length += time_freq;

	tick_nsec = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
	new_base = div_u64(second_length, NTP_INTERVAL_FREQ);

	/*
	* Don't wait for the next second_overflow, apply
	* the change to the tick length immediately:
	*/
	tick_length += new_base - tick_length_base;
	tick_length_base = new_base;
	}

	static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
	{
	time_status &= ~STA_MODE;

	if (secs < MINSEC)
	return 0;

	if (!(time_status & STA_FLL) && (secs <= MAXSEC))
	return 0;

	time_status \|= STA_MODE;

	return div_s64(offset64 << (NTP_SCALE_SHIFT - SHIFT_FLL), secs);
	}

	static void ntp_update_offset(long offset)
	{
	s64 freq_adj;
	s64 offset64;
	long secs;

	if (!(time_status & STA_PLL))
	return;

	if (!(time_status & STA_NANO))
	offset *= NSEC_PER_USEC;

	/*
	* Scale the phase adjustment and
	* clamp to the operating range.
	*/
	offset = min(offset, MAXPHASE);
	offset = max(offset, -MAXPHASE);

	/*
	* Select how the frequency is to be controlled
	* and in which mode (PLL or FLL).
	*/
	secs = xtime.tv_sec - time_reftime;
	if (unlikely(time_status & STA_FREQHOLD))
	secs = 0;

	time_reftime = xtime.tv_sec;

	offset64 = offset;
	freq_adj = (offset64 * secs) <<
	(NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));

	freq_adj += ntp_update_offset_fll(offset64, secs);

	freq_adj = min(freq_adj + time_freq, MAXFREQ_SCALED);

	time_freq = max(freq_adj, -MAXFREQ_SCALED);

	time_offset = div_s64(offset64 << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
	}

	/**
	* ntp_clear - Clears the NTP state variables
	*
	* Must be called while holding a write on the xtime_lock
	*/
	void ntp_clear(void)
	{
	time_adjust = 0; /* stop active adjtime() */
	time_status \|= STA_UNSYNC;
	time_maxerror = NTP_PHASE_LIMIT;
	time_esterror = NTP_PHASE_LIMIT;

	ntp_update_frequency();

	tick_length = tick_length_base;
	time_offset = 0;
	}

	/*
	* Leap second processing. If in leap-insert state at the end of the
	* day, the system clock is set back one second; if in leap-delete
	* state, the system clock is set ahead one second.
	*/
	static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
	{
	enum hrtimer_restart res = HRTIMER_NORESTART;

	write_seqlock(&xtime_lock);

	switch (time_state) {
	case TIME_OK:
	break;
	case TIME_INS:
	xtime.tv_sec--;
	wall_to_monotonic.tv_sec++;
	time_state = TIME_OOP;
	printk(KERN_NOTICE
	"Clock: inserting leap second 23:59:60 UTC\n");
	hrtimer_add_expires_ns(&leap_timer, NSEC_PER_SEC);
	res = HRTIMER_RESTART;
	break;
	case TIME_DEL:
	xtime.tv_sec++;
	time_tai--;
	wall_to_monotonic.tv_sec--;
	time_state = TIME_WAIT;
	printk(KERN_NOTICE
	"Clock: deleting leap second 23:59:59 UTC\n");
	break;
	case TIME_OOP:
	time_tai++;
	time_state = TIME_WAIT;
	/* fall through */
	case TIME_WAIT:
	if (!(time_status & (STA_INS \| STA_DEL)))
	time_state = TIME_OK;
	break;
	}
	update_vsyscall(&xtime, clock);

	write_sequnlock(&xtime_lock);

	return res;
	}

	/*
	* this routine handles the overflow of the microsecond field
	*
	* The tricky bits of code to handle the accurate clock support
	* were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
	* They were originally developed for SUN and DEC kernels.
	* All the kudos should go to Dave for this stuff.
	*/
	void second_overflow(void)
	{
	s64 delta;

	/* Bump the maxerror field */
	time_maxerror += MAXFREQ / NSEC_PER_USEC;
	if (time_maxerror > NTP_PHASE_LIMIT) {
	time_maxerror = NTP_PHASE_LIMIT;
	time_status \|= STA_UNSYNC;
	}

	/*
	* Compute the phase adjustment for the next second. The offset is
	* reduced by a fixed factor times the time constant.
	*/
	tick_length = tick_length_base;

	delta = shift_right(time_offset, SHIFT_PLL + time_constant);
	time_offset -= delta;
	tick_length += delta;

	if (!time_adjust)
	return;

	if (time_adjust > MAX_TICKADJ) {
	time_adjust -= MAX_TICKADJ;
	tick_length += MAX_TICKADJ_SCALED;
	return;
	}

	if (time_adjust < -MAX_TICKADJ) {
	time_adjust += MAX_TICKADJ;
	tick_length -= MAX_TICKADJ_SCALED;
	return;
	}

	tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
	<< NTP_SCALE_SHIFT;
	time_adjust = 0;
	}

	#ifdef CONFIG_GENERIC_CMOS_UPDATE

	/* Disable the cmos update - used by virtualization and embedded */
	int no_sync_cmos_clock __read_mostly;

	static void sync_cmos_clock(struct work_struct *work);

	static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);

	static void sync_cmos_clock(struct work_struct *work)
	{
	struct timespec now, next;
	int fail = 1;

	/*
	* If we have an externally synchronized Linux clock, then update
	* CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
	* called as close as possible to 500 ms before the new second starts.
	* This code is run on a timer. If the clock is set, that timer
	* may not expire at the correct time. Thus, we adjust...
	*/
	if (!ntp_synced()) {
	/*
	* Not synced, exit, do not restart a timer (if one is
	* running, let it run out).
	*/
	return;
	}

	getnstimeofday(&now);
	if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
	fail = update_persistent_clock(now);

	next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
	if (next.tv_nsec <= 0)
	next.tv_nsec += NSEC_PER_SEC;

	if (!fail)
	next.tv_sec = 659;
	else
	next.tv_sec = 0;

	if (next.tv_nsec >= NSEC_PER_SEC) {
	next.tv_sec++;
	next.tv_nsec -= NSEC_PER_SEC;
	}
	schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
	}

	static void notify_cmos_timer(void)
	{
	if (!no_sync_cmos_clock)
	schedule_delayed_work(&sync_cmos_work, 0);
	}

	#else
	static inline void notify_cmos_timer(void) { }
	#endif

	/*
	* Start the leap seconds timer:
	*/
	static inline void ntp_start_leap_timer(struct timespec *ts)
	{
	long now = ts->tv_sec;

	if (time_status & STA_INS) {
	time_state = TIME_INS;
	now += 86400 - now % 86400;
	hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);

	return;
	}

	if (time_status & STA_DEL) {
	time_state = TIME_DEL;
	now += 86400 - (now + 1) % 86400;
	hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);
	}
	}

	/*
	* Propagate a new txc->status value into the NTP state:
	*/
	static inline void process_adj_status(struct timex txc, struct timespec ts)
	{
	if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
	time_state = TIME_OK;
	time_status = STA_UNSYNC;
	}

	/*
	* If we turn on PLL adjustments then reset the
	* reference time to current time.
	*/
	if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
	time_reftime = xtime.tv_sec;

	/* only set allowed bits */
	time_status &= STA_RONLY;
	time_status \|= txc->status & ~STA_RONLY;

	switch (time_state) {
	case TIME_OK:
	ntp_start_leap_timer(ts);
	break;
	case TIME_INS:
	case TIME_DEL:
	time_state = TIME_OK;
	ntp_start_leap_timer(ts);
	case TIME_WAIT:
	if (!(time_status & (STA_INS \| STA_DEL)))
	time_state = TIME_OK;
	break;
	case TIME_OOP:
	hrtimer_restart(&leap_timer);
	break;
	}
	}
	/*
	* Called with the xtime lock held, so we can access and modify
	* all the global NTP state:
	*/
	static inline void process_adjtimex_modes(struct timex txc, struct timespec ts)
	{
	if (txc->modes & ADJ_STATUS)
	process_adj_status(txc, ts);

	if (txc->modes & ADJ_NANO)
	time_status \|= STA_NANO;

	if (txc->modes & ADJ_MICRO)
	time_status &= ~STA_NANO;

	if (txc->modes & ADJ_FREQUENCY) {
	time_freq = txc->freq * PPM_SCALE;
	time_freq = min(time_freq, MAXFREQ_SCALED);
	time_freq = max(time_freq, -MAXFREQ_SCALED);
	}

	if (txc->modes & ADJ_MAXERROR)
	time_maxerror = txc->maxerror;

	if (txc->modes & ADJ_ESTERROR)
	time_esterror = txc->esterror;

	if (txc->modes & ADJ_TIMECONST) {
	time_constant = txc->constant;
	if (!(time_status & STA_NANO))
	time_constant += 4;
	time_constant = min(time_constant, (long)MAXTC);
	time_constant = max(time_constant, 0l);
	}

	if (txc->modes & ADJ_TAI && txc->constant > 0)
	time_tai = txc->constant;

	if (txc->modes & ADJ_OFFSET)
	ntp_update_offset(txc->offset);

	if (txc->modes & ADJ_TICK)
	tick_usec = txc->tick;

	if (txc->modes & (ADJ_TICK\|ADJ_FREQUENCY\|ADJ_OFFSET))
	ntp_update_frequency();
	}

	/*
	* adjtimex mainly allows reading (and writing, if superuser) of
	* kernel time-keeping variables. used by xntpd.
	*/
	int do_adjtimex(struct timex *txc)
	{
	struct timespec ts;
	int result;

	/* Validate the data before disabling interrupts */
	if (txc->modes & ADJ_ADJTIME) {
	/* singleshot must not be used with any other mode bits */
	if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
	return -EINVAL;
	if (!(txc->modes & ADJ_OFFSET_READONLY) &&
	!capable(CAP_SYS_TIME))
	return -EPERM;
	} else {
	/* In order to modify anything, you gotta be super-user! */
	if (txc->modes && !capable(CAP_SYS_TIME))
	return -EPERM;

	/*
	* if the quartz is off by more than 10% then
	* something is VERY wrong!
	*/
	if (txc->modes & ADJ_TICK &&
	(txc->tick < 900000/USER_HZ \|\|
	txc->tick > 1100000/USER_HZ))
	return -EINVAL;

	if (txc->modes & ADJ_STATUS && time_state != TIME_OK)
	hrtimer_cancel(&leap_timer);
	}

	getnstimeofday(&ts);

	write_seqlock_irq(&xtime_lock);

	if (txc->modes & ADJ_ADJTIME) {
	long save_adjust = time_adjust;

	if (!(txc->modes & ADJ_OFFSET_READONLY)) {
	/* adjtime() is independent from ntp_adjtime() */
	time_adjust = txc->offset;
	ntp_update_frequency();
	}
	txc->offset = save_adjust;
	} else {

	/* If there are input parameters, then process them: */
	if (txc->modes)
	process_adjtimex_modes(txc, &ts);

	txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
	NTP_SCALE_SHIFT);
	if (!(time_status & STA_NANO))
	txc->offset /= NSEC_PER_USEC;
	}

	result = time_state; /* mostly `TIME_OK' */
	if (time_status & (STA_UNSYNC\|STA_CLOCKERR))
	result = TIME_ERROR;

	txc->freq = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
	PPM_SCALE_INV, NTP_SCALE_SHIFT);
	txc->maxerror = time_maxerror;
	txc->esterror = time_esterror;
	txc->status = time_status;
	txc->constant = time_constant;
	txc->precision = 1;
	txc->tolerance = MAXFREQ_SCALED / PPM_SCALE;
	txc->tick = tick_usec;
	txc->tai = time_tai;

	/* PPS is not implemented, so these are zero */
	txc->ppsfreq = 0;
	txc->jitter = 0;
	txc->shift = 0;
	txc->stabil = 0;
	txc->jitcnt = 0;
	txc->calcnt = 0;
	txc->errcnt = 0;
	txc->stbcnt = 0;

	write_sequnlock_irq(&xtime_lock);

	txc->time.tv_sec = ts.tv_sec;
	txc->time.tv_usec = ts.tv_nsec;
	if (!(time_status & STA_NANO))
	txc->time.tv_usec /= NSEC_PER_USEC;

	notify_cmos_timer();

	return result;
	}

	static int __init ntp_tick_adj_setup(char *str)
	{
	ntp_tick_adj = simple_strtol(str, NULL, 0);
	ntp_tick_adj <<= NTP_SCALE_SHIFT;

	return 1;
	}

	__setup("ntp_tick_adj=", ntp_tick_adj_setup);

	void __init ntp_init(void)
	{
	ntp_clear();
	hrtimer_init(&leap_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
	leap_timer.function = ntp_leap_second;
	}