--- a/include/applets.h
+++ b/include/applets.h
@@ -285,6 +285,7 @@ IF_NICE(APPLET(nice, _BB_DIR_BIN, _BB_SU
 IF_NMETER(APPLET(nmeter, _BB_DIR_USR_BIN, _BB_SUID_DROP))
 IF_NOHUP(APPLET(nohup, _BB_DIR_USR_BIN, _BB_SUID_DROP))
 IF_NSLOOKUP(APPLET(nslookup, _BB_DIR_USR_BIN, _BB_SUID_DROP))
+IF_NTPD(APPLET(ntpd, _BB_DIR_USR_SBIN, _BB_SUID_DROP))
 IF_OD(APPLET(od, _BB_DIR_USR_BIN, _BB_SUID_DROP))
 IF_OPENVT(APPLET(openvt, _BB_DIR_USR_BIN, _BB_SUID_DROP))
 //IF_PARSE(APPLET(parse, _BB_DIR_USR_BIN, _BB_SUID_DROP))
--- a/include/usage.h
+++ b/include/usage.h
@@ -3183,6 +3183,22 @@
        "Name:       debian\n" \
        "Address:    127.0.0.1\n"
 
+#define ntpd_trivial_usage \
+       "[-dnqNw"IF_FEATURE_NTPD_SERVER("l")"] [-S PROG] [-p PEER]..."
+#define ntpd_full_usage "\n\n" \
+       "NTP client/server\n" \
+       "\nOptions:" \
+       "\n    -d  Verbose" \
+       "\n    -n  Do not daemonize" \
+       "\n    -q  Quit after clock is set" \
+       "\n    -N  Run at high priority" \
+       "\n    -w  Do not set time (only query peers), implies -n" \
+       IF_FEATURE_NTPD_SERVER( \
+       "\n    -l  Run as server on port 123" \
+       ) \
+       "\n    -S PROG Run PROG after stepping time, stratum change, and every 11 mins" \
+       "\n    -p PEER Obtain time from PEER (may be repeated)"
+
 #define od_trivial_usage \
        "[-aBbcDdeFfHhIiLlOovXx] " IF_DESKTOP("[-t TYPE] ") "[FILE]"
 #define od_full_usage "\n\n" \
--- a/networking/Config.in
+++ b/networking/Config.in
@@ -667,6 +667,20 @@ config NSLOOKUP
 	help
 	  nslookup is a tool to query Internet name servers.
 
+config NTPD
+	bool "ntpd"
+	default y
+	help
+	  The NTP client/server daemon.
+
+config FEATURE_NTPD_SERVER
+	bool "Make ntpd usable as a NTP server"
+	default y
+	depends on NTPD
+	help
+	  Make ntpd usable as a NTP server. If you disable this option
+	  ntpd will be usable only as a NTP client.
+
 config PING
 	bool "ping"
 	default n
--- /dev/null
+++ b/networking/ntpd.c
@@ -0,0 +1,2262 @@
+/*
+ * NTP client/server, based on OpenNTPD 3.9p1
+ *
+ * Author: Adam Tkac <vonsch@gmail.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ *
+ * Parts of OpenNTPD clock syncronization code is replaced by
+ * code which is based on ntp-4.2.6, whuch carries the following
+ * copyright notice:
+ *
+ ***********************************************************************
+ *                                                                     *
+ * Copyright (c) University of Delaware 1992-2009                      *
+ *                                                                     *
+ * Permission to use, copy, modify, and distribute this software and   *
+ * its documentation for any purpose with or without fee is hereby     *
+ * granted, provided that the above copyright notice appears in all    *
+ * copies and that both the copyright notice and this permission       *
+ * notice appear in supporting documentation, and that the name        *
+ * University of Delaware not be used in advertising or publicity      *
+ * pertaining to distribution of the software without specific,        *
+ * written prior permission. The University of Delaware makes no       *
+ * representations about the suitability this software for any         *
+ * purpose. It is provided "as is" without express or implied          *
+ * warranty.                                                           *
+ *                                                                     *
+ ***********************************************************************
+ */
+#include "libbb.h"
+#include <math.h>
+#include <netinet/ip.h> /* For IPTOS_LOWDELAY definition */
+#include <sys/timex.h>
+#ifndef IPTOS_LOWDELAY
+# define IPTOS_LOWDELAY 0x10
+#endif
+#ifndef IP_PKTINFO
+# error "Sorry, your kernel has to support IP_PKTINFO"
+#endif
+
+
+/* Verbosity control (max level of -dddd options accepted).
+ * max 5 is very talkative (and bloated). 2 is non-bloated,
+ * production level setting.
+ */
+#define MAX_VERBOSE     2
+
+
+/* High-level description of the algorithm:
+ *
+ * We start running with very small poll_exp, BURSTPOLL,
+ * in order to quickly accumulate INITIAL_SAMPLES datapoints
+ * for each peer. Then, time is stepped if the offset is larger
+ * than STEP_THRESHOLD, otherwise it isn't; anyway, we enlarge
+ * poll_exp to MINPOLL and enter frequency measurement step:
+ * we collect new datapoints but ignore them for WATCH_THRESHOLD
+ * seconds. After WATCH_THRESHOLD seconds we look at accumulated
+ * offset and estimate frequency drift.
+ *
+ * (frequency measurement step seems to not be strictly needed,
+ * it is conditionally disabled with USING_INITIAL_FREQ_ESTIMATION
+ * define set to 0)
+ *
+ * After this, we enter "steady state": we collect a datapoint,
+ * we select the best peer, if this datapoint is not a new one
+ * (IOW: if this datapoint isn't for selected peer), sleep
+ * and collect another one; otherwise, use its offset to update
+ * frequency drift, if offset is somewhat large, reduce poll_exp,
+ * otherwise increase poll_exp.
+ *
+ * If offset is larger than STEP_THRESHOLD, which shouldn't normally
+ * happen, we assume that something "bad" happened (computer
+ * was hibernated, someone set totally wrong date, etc),
+ * then the time is stepped, all datapoints are discarded,
+ * and we go back to steady state.
+ */
+
+#define RETRY_INTERVAL  5       /* on error, retry in N secs */
+#define RESPONSE_INTERVAL 15    /* wait for reply up to N secs */
+#define INITIAL_SAMPLES 4       /* how many samples do we want for init */
+
+/* Clock discipline parameters and constants */
+
+/* Step threshold (sec). std ntpd uses 0.128.
+ * Using exact power of 2 (1/8) results in smaller code */
+#define STEP_THRESHOLD  0.125
+#define WATCH_THRESHOLD 128     /* stepout threshold (sec). std ntpd uses 900 (11 mins (!)) */
+/* NB: set WATCH_THRESHOLD to ~60 when debugging to save time) */
+//UNUSED: #define PANIC_THRESHOLD 1000    /* panic threshold (sec) */
+
+#define FREQ_TOLERANCE  0.000015 /* frequency tolerance (15 PPM) */
+#define BURSTPOLL       0       /* initial poll */
+#define MINPOLL         5       /* minimum poll interval. std ntpd uses 6 (6: 64 sec) */
+#define BIGPOLL         10      /* drop to lower poll at any trouble (10: 17 min) */
+#define MAXPOLL         12      /* maximum poll interval (12: 1.1h, 17: 36.4h). std ntpd uses 17 */
+/* Actively lower poll when we see such big offsets.
+ * With STEP_THRESHOLD = 0.125, it means we try to sync more aggressively
+ * if offset increases over 0.03 sec */
+#define POLLDOWN_OFFSET (STEP_THRESHOLD / 4)
+#define MINDISP         0.01    /* minimum dispersion (sec) */
+#define MAXDISP         16      /* maximum dispersion (sec) */
+#define MAXSTRAT        16      /* maximum stratum (infinity metric) */
+#define MAXDIST         1       /* distance threshold (sec) */
+#define MIN_SELECTED    1       /* minimum intersection survivors */
+#define MIN_CLUSTERED   3       /* minimum cluster survivors */
+
+#define MAXDRIFT        0.000500 /* frequency drift we can correct (500 PPM) */
+
+/* Poll-adjust threshold.
+ * When we see that offset is small enough compared to discipline jitter,
+ * we grow a counter: += MINPOLL. When it goes over POLLADJ_LIMIT,
+ * we poll_exp++. If offset isn't small, counter -= poll_exp*2,
+ * and when it goes below -POLLADJ_LIMIT, we poll_exp--
+ * (bumped from 30 to 36 since otherwise I often see poll_exp going *2* steps down)
+ */
+#define POLLADJ_LIMIT   36
+/* If offset < POLLADJ_GATE * discipline_jitter, then we can increase
+ * poll interval (we think we can't improve timekeeping
+ * by staying at smaller poll).
+ */
+#define POLLADJ_GATE    4
+/* Compromise Allan intercept (sec). doc uses 1500, std ntpd uses 512 */
+#define ALLAN           512
+/* PLL loop gain */
+#define PLL             65536
+/* FLL loop gain [why it depends on MAXPOLL??] */
+#define FLL             (MAXPOLL + 1)
+/* Parameter averaging constant */
+#define AVG             4
+
+
+enum {
+	NTP_VERSION     = 4,
+	NTP_MAXSTRATUM  = 15,
+
+	NTP_DIGESTSIZE     = 16,
+	NTP_MSGSIZE_NOAUTH = 48,
+	NTP_MSGSIZE        = (NTP_MSGSIZE_NOAUTH + 4 + NTP_DIGESTSIZE),
+
+	/* Status Masks */
+	MODE_MASK       = (7 << 0),
+	VERSION_MASK    = (7 << 3),
+	VERSION_SHIFT   = 3,
+	LI_MASK         = (3 << 6),
+
+	/* Leap Second Codes (high order two bits of m_status) */
+	LI_NOWARNING    = (0 << 6),    /* no warning */
+	LI_PLUSSEC      = (1 << 6),    /* add a second (61 seconds) */
+	LI_MINUSSEC     = (2 << 6),    /* minus a second (59 seconds) */
+	LI_ALARM        = (3 << 6),    /* alarm condition */
+
+	/* Mode values */
+	MODE_RES0       = 0,    /* reserved */
+	MODE_SYM_ACT    = 1,    /* symmetric active */
+	MODE_SYM_PAS    = 2,    /* symmetric passive */
+	MODE_CLIENT     = 3,    /* client */
+	MODE_SERVER     = 4,    /* server */
+	MODE_BROADCAST  = 5,    /* broadcast */
+	MODE_RES1       = 6,    /* reserved for NTP control message */
+	MODE_RES2       = 7,    /* reserved for private use */
+};
+
+//TODO: better base selection
+#define OFFSET_1900_1970 2208988800UL  /* 1970 - 1900 in seconds */
+
+#define NUM_DATAPOINTS  8
+
+typedef struct {
+	uint32_t int_partl;
+	uint32_t fractionl;
+} l_fixedpt_t;
+
+typedef struct {
+	uint16_t int_parts;
+	uint16_t fractions;
+} s_fixedpt_t;
+
+typedef struct {
+	uint8_t     m_status;     /* status of local clock and leap info */
+	uint8_t     m_stratum;
+	uint8_t     m_ppoll;      /* poll value */
+	int8_t      m_precision_exp;
+	s_fixedpt_t m_rootdelay;
+	s_fixedpt_t m_rootdisp;
+	uint32_t    m_refid;
+	l_fixedpt_t m_reftime;
+	l_fixedpt_t m_orgtime;
+	l_fixedpt_t m_rectime;
+	l_fixedpt_t m_xmttime;
+	uint32_t    m_keyid;
+	uint8_t     m_digest[NTP_DIGESTSIZE];
+} msg_t;
+
+typedef struct {
+	double d_recv_time;
+	double d_offset;
+	double d_dispersion;
+} datapoint_t;
+
+typedef struct {
+	len_and_sockaddr *p_lsa;
+	char             *p_dotted;
+	/* when to send new query (if p_fd == -1)
+	 * or when receive times out (if p_fd >= 0): */
+	int              p_fd;
+	int              datapoint_idx;
+	uint32_t         lastpkt_refid;
+	uint8_t          lastpkt_status;
+	uint8_t          lastpkt_stratum;
+	uint8_t          reachable_bits;
+	double           next_action_time;
+	double           p_xmttime;
+	double           lastpkt_recv_time;
+	double           lastpkt_delay;
+	double           lastpkt_rootdelay;
+	double           lastpkt_rootdisp;
+	/* produced by filter algorithm: */
+	double           filter_offset;
+	double           filter_dispersion;
+	double           filter_jitter;
+	datapoint_t      filter_datapoint[NUM_DATAPOINTS];
+	/* last sent packet: */
+	msg_t            p_xmt_msg;
+} peer_t;
+
+
+#define USING_KERNEL_PLL_LOOP          1
+#define USING_INITIAL_FREQ_ESTIMATION  0
+
+enum {
+	OPT_n = (1 << 0),
+	OPT_q = (1 << 1),
+	OPT_N = (1 << 2),
+	OPT_x = (1 << 3),
+	/* Insert new options above this line. */
+	/* Non-compat options: */
+	OPT_w = (1 << 4),
+	OPT_p = (1 << 5),
+	OPT_S = (1 << 6),
+	OPT_l = (1 << 7) * ENABLE_FEATURE_NTPD_SERVER,
+};
+
+struct globals {
+	double   cur_time;
+	/* total round trip delay to currently selected reference clock */
+	double   rootdelay;
+	/* reference timestamp: time when the system clock was last set or corrected */
+	double   reftime;
+	/* total dispersion to currently selected reference clock */
+	double   rootdisp;
+
+	double   last_script_run;
+	char     *script_name;
+	llist_t  *ntp_peers;
+#if ENABLE_FEATURE_NTPD_SERVER
+	int      listen_fd;
+#endif
+	unsigned verbose;
+	unsigned peer_cnt;
+	/* refid: 32-bit code identifying the particular server or reference clock
+	 *  in stratum 0 packets this is a four-character ASCII string,
+	 *  called the kiss code, used for debugging and monitoring
+	 *  in stratum 1 packets this is a four-character ASCII string
+	 *  assigned to the reference clock by IANA. Example: "GPS "
+	 *  in stratum 2+ packets, it's IPv4 address or 4 first bytes of MD5 hash of IPv6
+	 */
+	uint32_t refid;
+	uint8_t  ntp_status;
+	/* precision is defined as the larger of the resolution and time to
+	 * read the clock, in log2 units.  For instance, the precision of a
+	 * mains-frequency clock incrementing at 60 Hz is 16 ms, even when the
+	 * system clock hardware representation is to the nanosecond.
+	 *
+	 * Delays, jitters of various kinds are clamper down to precision.
+	 *
+	 * If precision_sec is too large, discipline_jitter gets clamped to it
+	 * and if offset is much smaller than discipline_jitter, poll interval
+	 * grows even though we really can benefit from staying at smaller one,
+	 * collecting non-lagged datapoits and correcting the offset.
+	 * (Lagged datapoits exist when poll_exp is large but we still have
+	 * systematic offset error - the time distance between datapoints
+	 * is significat and older datapoints have smaller offsets.
+	 * This makes our offset estimation a bit smaller than reality)
+	 * Due to this effect, setting G_precision_sec close to
+	 * STEP_THRESHOLD isn't such a good idea - offsets may grow
+	 * too big and we will step. I observed it with -6.
+	 *
+	 * OTOH, setting precision too small would result in futile attempts
+	 * to syncronize to the unachievable precision.
+	 *
+	 * -6 is 1/64 sec, -7 is 1/128 sec and so on.
+	 */
+#define G_precision_exp  -8
+#define G_precision_sec  (1.0 / (1 << (- G_precision_exp)))
+	uint8_t  stratum;
+	/* Bool. After set to 1, never goes back to 0: */
+	smallint initial_poll_complete;
+
+#define STATE_NSET      0       /* initial state, "nothing is set" */
+//#define STATE_FSET    1       /* frequency set from file */
+#define STATE_SPIK      2       /* spike detected */
+//#define STATE_FREQ    3       /* initial frequency */
+#define STATE_SYNC      4       /* clock synchronized (normal operation) */
+	uint8_t  discipline_state;      // doc calls it c.state
+	uint8_t  poll_exp;              // s.poll
+	int      polladj_count;         // c.count
+	long     kernel_freq_drift;
+	peer_t   *last_update_peer;
+	double   last_update_offset;    // c.last
+	double   last_update_recv_time; // s.t
+	double   discipline_jitter;     // c.jitter
+	//double   cluster_offset;        // s.offset
+	//double   cluster_jitter;        // s.jitter
+#if !USING_KERNEL_PLL_LOOP
+	double   discipline_freq_drift; // c.freq
+	/* Maybe conditionally calculate wander? it's used only for logging */
+	double   discipline_wander;     // c.wander
+#endif
+};
+#define G (*ptr_to_globals)
+
+static const int const_IPTOS_LOWDELAY = IPTOS_LOWDELAY;
+
+
+#define VERB1 if (MAX_VERBOSE && G.verbose)
+#define VERB2 if (MAX_VERBOSE >= 2 && G.verbose >= 2)
+#define VERB3 if (MAX_VERBOSE >= 3 && G.verbose >= 3)
+#define VERB4 if (MAX_VERBOSE >= 4 && G.verbose >= 4)
+#define VERB5 if (MAX_VERBOSE >= 5 && G.verbose >= 5)
+
+
+static double LOG2D(int a)
+{
+	if (a < 0)
+		return 1.0 / (1UL << -a);
+	return 1UL << a;
+}
+static ALWAYS_INLINE double SQUARE(double x)
+{
+	return x * x;
+}
+static ALWAYS_INLINE double MAXD(double a, double b)
+{
+	if (a > b)
+		return a;
+	return b;
+}
+static ALWAYS_INLINE double MIND(double a, double b)
+{
+	if (a < b)
+		return a;
+	return b;
+}
+static NOINLINE double my_SQRT(double X)
+{
+	union {
+		float   f;
+		int32_t i;
+	} v;
+	double invsqrt;
+	double Xhalf = X * 0.5;
+
+	/* Fast and good approximation to 1/sqrt(X), black magic */
+	v.f = X;
+	/*v.i = 0x5f3759df - (v.i >> 1);*/
+	v.i = 0x5f375a86 - (v.i >> 1); /* - this constant is slightly better */
+	invsqrt = v.f; /* better than 0.2% accuracy */
+
+	/* Refining it using Newton's method: x1 = x0 - f(x0)/f'(x0)
+	 * f(x) = 1/(x*x) - X  (f==0 when x = 1/sqrt(X))
+	 * f'(x) = -2/(x*x*x)
+	 * f(x)/f'(x) = (X - 1/(x*x)) / (2/(x*x*x)) = X*x*x*x/2 - x/2
+	 * x1 = x0 - (X*x0*x0*x0/2 - x0/2) = 1.5*x0 - X*x0*x0*x0/2 = x0*(1.5 - (X/2)*x0*x0)
+	 */
+	invsqrt = invsqrt * (1.5 - Xhalf * invsqrt * invsqrt); /* ~0.05% accuracy */
+	/* invsqrt = invsqrt * (1.5 - Xhalf * invsqrt * invsqrt); 2nd iter: ~0.0001% accuracy */
+	/* With 4 iterations, more than half results will be exact,
+	 * at 6th iterations result stabilizes with about 72% results exact.
+	 * We are well satisfied with 0.05% accuracy.
+	 */
+
+	return X * invsqrt; /* X * 1/sqrt(X) ~= sqrt(X) */
+}
+static ALWAYS_INLINE double SQRT(double X)
+{
+	/* If this arch doesn't use IEEE 754 floats, fall back to using libm */
+	if (sizeof(float) != 4)
+		return sqrt(X);
+
+	/* This avoids needing libm, saves about 0.5k on x86-32 */
+	return my_SQRT(X);
+}
+
+static double
+gettime1900d(void)
+{
+	struct timeval tv;
+	gettimeofday(&tv, NULL); /* never fails */
+	G.cur_time = tv.tv_sec + (1.0e-6 * tv.tv_usec) + OFFSET_1900_1970;
+	return G.cur_time;
+}
+
+static void
+d_to_tv(double d, struct timeval *tv)
+{
+	tv->tv_sec = (long)d;
+	tv->tv_usec = (d - tv->tv_sec) * 1000000;
+}
+
+static double
+lfp_to_d(l_fixedpt_t lfp)
+{
+	double ret;
+	lfp.int_partl = ntohl(lfp.int_partl);
+	lfp.fractionl = ntohl(lfp.fractionl);
+	ret = (double)lfp.int_partl + ((double)lfp.fractionl / UINT_MAX);
+	return ret;
+}
+static double
+sfp_to_d(s_fixedpt_t sfp)
+{
+	double ret;
+	sfp.int_parts = ntohs(sfp.int_parts);
+	sfp.fractions = ntohs(sfp.fractions);
+	ret = (double)sfp.int_parts + ((double)sfp.fractions / USHRT_MAX);
+	return ret;
+}
+#if ENABLE_FEATURE_NTPD_SERVER
+static l_fixedpt_t
+d_to_lfp(double d)
+{
+	l_fixedpt_t lfp;
+	lfp.int_partl = (uint32_t)d;
+	lfp.fractionl = (uint32_t)((d - lfp.int_partl) * UINT_MAX);
+	lfp.int_partl = htonl(lfp.int_partl);
+	lfp.fractionl = htonl(lfp.fractionl);
+	return lfp;
+}
+static s_fixedpt_t
+d_to_sfp(double d)
+{
+	s_fixedpt_t sfp;
+	sfp.int_parts = (uint16_t)d;
+	sfp.fractions = (uint16_t)((d - sfp.int_parts) * USHRT_MAX);
+	sfp.int_parts = htons(sfp.int_parts);
+	sfp.fractions = htons(sfp.fractions);
+	return sfp;
+}
+#endif
+
+static double
+dispersion(const datapoint_t *dp)
+{
+	return dp->d_dispersion + FREQ_TOLERANCE * (G.cur_time - dp->d_recv_time);
+}
+
+static double
+root_distance(peer_t *p)
+{
+	/* The root synchronization distance is the maximum error due to
+	 * all causes of the local clock relative to the primary server.
+	 * It is defined as half the total delay plus total dispersion
+	 * plus peer jitter.
+	 */
+	return MAXD(MINDISP, p->lastpkt_rootdelay + p->lastpkt_delay) / 2
+		+ p->lastpkt_rootdisp
+		+ p->filter_dispersion
+		+ FREQ_TOLERANCE * (G.cur_time - p->lastpkt_recv_time)
+		+ p->filter_jitter;
+}
+
+static void
+set_next(peer_t *p, unsigned t)
+{
+	p->next_action_time = G.cur_time + t;
+}
+
+/*
+ * Peer clock filter and its helpers
+ */
+static void
+filter_datapoints(peer_t *p)
+{
+	int i, idx;
+	int got_newest;
+	double minoff, maxoff, wavg, sum, w;
+	double x = x; /* for compiler */
+	double oldest_off = oldest_off;
+	double oldest_age = oldest_age;
+	double newest_off = newest_off;
+	double newest_age = newest_age;
+
+	minoff = maxoff = p->filter_datapoint[0].d_offset;
+	for (i = 1; i < NUM_DATAPOINTS; i++) {
+		if (minoff > p->filter_datapoint[i].d_offset)
+			minoff = p->filter_datapoint[i].d_offset;
+		if (maxoff < p->filter_datapoint[i].d_offset)
+			maxoff = p->filter_datapoint[i].d_offset;
+	}
+
+	idx = p->datapoint_idx; /* most recent datapoint */
+	/* Average offset:
+	 * Drop two outliers and take weighted average of the rest:
+	 * most_recent/2 + older1/4 + older2/8 ... + older5/32 + older6/32
+	 * we use older6/32, not older6/64 since sum of weights should be 1:
+	 * 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/32 = 1
+	 */
+	wavg = 0;
+	w = 0.5;
+	/*                     n-1
+	 *                     ---    dispersion(i)
+	 * filter_dispersion =  \     -------------
+	 *                      /       (i+1)
+	 *                     ---     2
+	 *                     i=0
+	 */
+	got_newest = 0;
+	sum = 0;
+	for (i = 0; i < NUM_DATAPOINTS; i++) {
+		VERB4 {
+			bb_error_msg("datapoint[%d]: off:%f disp:%f(%f) age:%f%s",
+				i,
+				p->filter_datapoint[idx].d_offset,
+				p->filter_datapoint[idx].d_dispersion, dispersion(&p->filter_datapoint[idx]),
+				G.cur_time - p->filter_datapoint[idx].d_recv_time,
+				(minoff == p->filter_datapoint[idx].d_offset || maxoff == p->filter_datapoint[idx].d_offset)
+					? " (outlier by offset)" : ""
+			);
+		}
+
+		sum += dispersion(&p->filter_datapoint[idx]) / (2 << i);
+
+		if (minoff == p->filter_datapoint[idx].d_offset) {
+			minoff -= 1; /* so that we don't match it ever again */
+		} else
+		if (maxoff == p->filter_datapoint[idx].d_offset) {
+			maxoff += 1;
+		} else {
+			oldest_off = p->filter_datapoint[idx].d_offset;
+			oldest_age = G.cur_time - p->filter_datapoint[idx].d_recv_time;
+			if (!got_newest) {
+				got_newest = 1;
+				newest_off = oldest_off;
+				newest_age = oldest_age;
+			}
+			x = oldest_off * w;
+			wavg += x;
+			w /= 2;
+		}
+
+		idx = (idx - 1) & (NUM_DATAPOINTS - 1);
+	}
+	p->filter_dispersion = sum;
+	wavg += x; /* add another older6/64 to form older6/32 */
+	/* Fix systematic underestimation with large poll intervals.
+	 * Imagine that we still have a bit of uncorrected drift,
+	 * and poll interval is big (say, 100 sec). Offsets form a progression:
+	 * 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 - 0.7 is most recent.
+	 * The algorithm above drops 0.0 and 0.7 as outliers,
+	 * and then we have this estimation, ~25% off from 0.7:
+	 * 0.1/32 + 0.2/32 + 0.3/16 + 0.4/8 + 0.5/4 + 0.6/2 = 0.503125
+	 */
+	x = oldest_age - newest_age;
+	if (x != 0) {
+		x = newest_age / x; /* in above example, 100 / (600 - 100) */
+		if (x < 1) { /* paranoia check */
+			x = (newest_off - oldest_off) * x; /* 0.5 * 100/500 = 0.1 */
+			wavg += x;
+		}
+	}
+	p->filter_offset = wavg;
+
+	/*                  +-----                 -----+ ^ 1/2
+	 *                  |       n-1                 |
+	 *                  |       ---                 |
+	 *                  |  1    \                2  |
+	 * filter_jitter =  | --- * /  (avg-offset_j)   |
+	 *                  |  n    ---                 |
+	 *                  |       j=0                 |
+	 *                  +-----                 -----+
+	 * where n is the number of valid datapoints in the filter (n > 1);
+	 * if filter_jitter < precision then filter_jitter = precision
+	 */
+	sum = 0;
+	for (i = 0; i < NUM_DATAPOINTS; i++) {
+		sum += SQUARE(wavg - p->filter_datapoint[i].d_offset);
+	}
+	sum = SQRT(sum / NUM_DATAPOINTS);
+	p->filter_jitter = sum > G_precision_sec ? sum : G_precision_sec;
+
+	VERB3 bb_error_msg("filter offset:%f(corr:%e) disp:%f jitter:%f",
+			p->filter_offset, x,
+			p->filter_dispersion,
+			p->filter_jitter);
+}
+
+static void
+reset_peer_stats(peer_t *p, double offset)
+{
+	int i;
+	bool small_ofs = fabs(offset) < 16 * STEP_THRESHOLD;
+
+	for (i = 0; i < NUM_DATAPOINTS; i++) {
+		if (small_ofs) {
+			p->filter_datapoint[i].d_recv_time += offset;
+			if (p->filter_datapoint[i].d_offset != 0) {
+				p->filter_datapoint[i].d_offset += offset;
+			}
+		} else {
+			p->filter_datapoint[i].d_recv_time  = G.cur_time;
+			p->filter_datapoint[i].d_offset     = 0;
+			p->filter_datapoint[i].d_dispersion = MAXDISP;
+		}
+	}
+	if (small_ofs) {
+		p->lastpkt_recv_time += offset;
+	} else {
+		p->reachable_bits = 0;
+		p->lastpkt_recv_time = G.cur_time;
+	}
+	filter_datapoints(p); /* recalc p->filter_xxx */
+	VERB5 bb_error_msg("%s->lastpkt_recv_time=%f", p->p_dotted, p->lastpkt_recv_time);
+}
+
+static void
+add_peers(char *s)
+{
+	peer_t *p;
+
+	p = xzalloc(sizeof(*p));
+	p->p_lsa = xhost2sockaddr(s, 123);
+	p->p_dotted = xmalloc_sockaddr2dotted_noport(&p->p_lsa->u.sa);
+	p->p_fd = -1;
+	p->p_xmt_msg.m_status = MODE_CLIENT | (NTP_VERSION << 3);
+	p->next_action_time = G.cur_time; /* = set_next(p, 0); */
+	reset_peer_stats(p, 16 * STEP_THRESHOLD);
+
+	llist_add_to(&G.ntp_peers, p);
+	G.peer_cnt++;
+}
+
+static int
+do_sendto(int fd,
+		const struct sockaddr *from, const struct sockaddr *to, socklen_t addrlen,
+		msg_t *msg, ssize_t len)
+{
+	ssize_t ret;
+
+	errno = 0;
+	if (!from) {
+		ret = sendto(fd, msg, len, MSG_DONTWAIT, to, addrlen);
+	} else {
+		ret = send_to_from(fd, msg, len, MSG_DONTWAIT, to, from, addrlen);
+	}
+	if (ret != len) {
+		bb_perror_msg("send failed");
+		return -1;
+	}
+	return 0;
+}
+
+static void
+send_query_to_peer(peer_t *p)
+{
+	/* Why do we need to bind()?
+	 * See what happens when we don't bind:
+	 *
+	 * socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 3
+	 * setsockopt(3, SOL_IP, IP_TOS, [16], 4) = 0
+	 * gettimeofday({1259071266, 327885}, NULL) = 0
+	 * sendto(3, "xxx", 48, MSG_DONTWAIT, {sa_family=AF_INET, sin_port=htons(123), sin_addr=inet_addr("10.34.32.125")}, 16) = 48
+	 * ^^^ we sent it from some source port picked by kernel.
+	 * time(NULL)              = 1259071266
+	 * write(2, "ntpd: entering poll 15 secs\n", 28) = 28
+	 * poll([{fd=3, events=POLLIN}], 1, 15000) = 1 ([{fd=3, revents=POLLIN}])
+	 * recv(3, "yyy", 68, MSG_DONTWAIT) = 48
+	 * ^^^ this recv will receive packets to any local port!
+	 *
+	 * Uncomment this and use strace to see it in action:
+	 */
+#define PROBE_LOCAL_ADDR /* { len_and_sockaddr lsa; lsa.len = LSA_SIZEOF_SA; getsockname(p->query.fd, &lsa.u.sa, &lsa.len); } */
+
+	if (p->p_fd == -1) {
+		int fd, family;
+		len_and_sockaddr *local_lsa;
+
+		family = p->p_lsa->u.sa.sa_family;
+		p->p_fd = fd = xsocket_type(&local_lsa, family, SOCK_DGRAM);
+		/* local_lsa has "null" address and port 0 now.
+		 * bind() ensures we have a *particular port* selected by kernel
+		 * and remembered in p->p_fd, thus later recv(p->p_fd)
+		 * receives only packets sent to this port.
+		 */
+		PROBE_LOCAL_ADDR
+		xbind(fd, &local_lsa->u.sa, local_lsa->len);
+		PROBE_LOCAL_ADDR
+#if ENABLE_FEATURE_IPV6
+		if (family == AF_INET)
+#endif
+			setsockopt(fd, IPPROTO_IP, IP_TOS, &const_IPTOS_LOWDELAY, sizeof(const_IPTOS_LOWDELAY));
+		free(local_lsa);
+	}
+
+	/*
+	 * Send out a random 64-bit number as our transmit time.  The NTP
+	 * server will copy said number into the originate field on the
+	 * response that it sends us.  This is totally legal per the SNTP spec.
+	 *
+	 * The impact of this is two fold: we no longer send out the current
+	 * system time for the world to see (which may aid an attacker), and
+	 * it gives us a (not very secure) way of knowing that we're not
+	 * getting spoofed by an attacker that can't capture our traffic
+	 * but can spoof packets from the NTP server we're communicating with.
+	 *
+	 * Save the real transmit timestamp locally.
+	 */
+	p->p_xmt_msg.m_xmttime.int_partl = random();
+	p->p_xmt_msg.m_xmttime.fractionl = random();
+	p->p_xmttime = gettime1900d();
+
+	if (do_sendto(p->p_fd, /*from:*/ NULL, /*to:*/ &p->p_lsa->u.sa, /*addrlen:*/ p->p_lsa->len,
+			&p->p_xmt_msg, NTP_MSGSIZE_NOAUTH) == -1
+	) {
+		close(p->p_fd);
+		p->p_fd = -1;
+		set_next(p, RETRY_INTERVAL);
+		return;
+	}
+
+	p->reachable_bits <<= 1;
+	VERB1 bb_error_msg("sent query to %s", p->p_dotted);
+	set_next(p, RESPONSE_INTERVAL);
+}
+
+
+/* Note that there is no provision to prevent several run_scripts
+ * to be done in quick succession. In fact, it happens rather often
+ * if initial syncronization results in a step.
+ * You will see "step" and then "stratum" script runs, sometimes
+ * as close as only 0.002 seconds apart.
+ * Script should be ready to deal with this.
+ */
+static void run_script(const char *action, double offset)
+{
+	char *argv[3];
+	char *env1, *env2, *env3, *env4;
+
+	if (!G.script_name)
+		return;
+
+	argv[0] = (char*) G.script_name;
+	argv[1] = (char*) action;
+	argv[2] = NULL;
+
+	VERB1 bb_error_msg("executing '%s %s'", G.script_name, action);
+
+	env1 = xasprintf("%s=%u", "stratum", G.stratum);
+	putenv(env1);
+	env2 = xasprintf("%s=%ld", "freq_drift_ppm", G.kernel_freq_drift);
+	putenv(env2);
+	env3 = xasprintf("%s=%u", "poll_interval", 1 << G.poll_exp);
+	putenv(env3);
+	env4 = xasprintf("%s=%f", "offset", offset);
+	putenv(env4);
+	/* Other items of potential interest: selected peer,
+	 * rootdelay, reftime, rootdisp, refid, ntp_status,
+	 * last_update_offset, last_update_recv_time, discipline_jitter,
+	 * how many peers have reachable_bits = 0?
+	 */
+
+	/* Don't want to wait: it may run hwclock --systohc, and that
+	 * may take some time (seconds): */
+	/*spawn_and_wait(argv);*/
+	spawn(argv);
+
+	unsetenv("stratum");
+	unsetenv("freq_drift_ppm");
+	unsetenv("poll_interval");
+	unsetenv("offset");
+	free(env1);
+	free(env2);
+	free(env3);
+	free(env4);
+
+	G.last_script_run = G.cur_time;
+}
+
+static NOINLINE void
+step_time(double offset)
+{
+	llist_t *item;
+	double dtime;
+	struct timeval tv;
+	char buf[80];
+	time_t tval;
+
+	gettimeofday(&tv, NULL); /* never fails */
+	dtime = offset + tv.tv_sec;
+	dtime += 1.0e-6 * tv.tv_usec;
+	d_to_tv(dtime, &tv);
+
+	if (settimeofday(&tv, NULL) == -1)
+		bb_perror_msg_and_die("settimeofday");
+
+	tval = tv.tv_sec;
+	strftime(buf, sizeof(buf), "%a %b %e %H:%M:%S %Z %Y", localtime(&tval));
+
+	bb_error_msg("setting clock to %s (offset %fs)", buf, offset);
+
+	/* Correct various fields which contain time-relative values: */
+
+	/* p->lastpkt_recv_time, p->next_action_time and such: */
+	for (item = G.ntp_peers; item != NULL; item = item->link) {
+		peer_t *pp = (peer_t *) item->data;
+		reset_peer_stats(pp, offset);
+		//bb_error_msg("offset:%f pp->next_action_time:%f -> %f",
+		//	offset, pp->next_action_time, pp->next_action_time + offset);
+		pp->next_action_time += offset;
+	}
+	/* Globals: */
+	G.cur_time += offset;
+	G.last_update_recv_time += offset;
+	G.last_script_run += offset;
+}
+
+
+/*
+ * Selection and clustering, and their helpers
+ */
+typedef struct {
+	peer_t *p;
+	int    type;
+	double edge;
+	double opt_rd; /* optimization */
+} point_t;
+static int
+compare_point_edge(const void *aa, const void *bb)
+{
+	const point_t *a = aa;
+	const point_t *b = bb;
+	if (a->edge < b->edge) {
+		return -1;
+	}
+	return (a->edge > b->edge);
+}
+typedef struct {
+	peer_t *p;
+	double metric;
+} survivor_t;
+static int
+compare_survivor_metric(const void *aa, const void *bb)
+{
+	const survivor_t *a = aa;
+	const survivor_t *b = bb;
+	if (a->metric < b->metric) {
+		return -1;
+	}
+	return (a->metric > b->metric);
+}
+static int
+fit(peer_t *p, double rd)
+{
+	if ((p->reachable_bits & (p->reachable_bits-1)) == 0) {
+		/* One or zero bits in reachable_bits */
+		VERB3 bb_error_msg("peer %s unfit for selection: unreachable", p->p_dotted);
+		return 0;
+	}
+#if 0 /* we filter out such packets earlier */
+	if ((p->lastpkt_status & LI_ALARM) == LI_ALARM
+	 || p->lastpkt_stratum >= MAXSTRAT
+	) {
+		VERB3 bb_error_msg("peer %s unfit for selection: bad status/stratum", p->p_dotted);
+		return 0;
+	}
+#endif
+	/* rd is root_distance(p) */
+	if (rd > MAXDIST + FREQ_TOLERANCE * (1 << G.poll_exp)) {
+		VERB3 bb_error_msg("peer %s unfit for selection: root distance too high", p->p_dotted);
+		return 0;
+	}
+//TODO
+//	/* Do we have a loop? */
+//	if (p->refid == p->dstaddr || p->refid == s.refid)
+//		return 0;
+        return 1;
+}
+static peer_t*
+select_and_cluster(void)
+{
+	peer_t     *p;
+	llist_t    *item;
+	int        i, j;
+	int        size = 3 * G.peer_cnt;
+	/* for selection algorithm */
+	point_t    point[size];
+	unsigned   num_points, num_candidates;
+	double     low, high;
+	unsigned   num_falsetickers;
+	/* for cluster algorithm */
+	survivor_t survivor[size];
+	unsigned   num_survivors;
+
+	/* Selection */
+
+	num_points = 0;
+	item = G.ntp_peers;
+	if (G.initial_poll_complete) while (item != NULL) {
+		double rd, offset;
+
+		p = (peer_t *) item->data;
+		rd = root_distance(p);
+		offset = p->filter_offset;
+		if (!fit(p, rd)) {
+			item = item->link;
+			continue;
+		}
+
+		VERB4 bb_error_msg("interval: [%f %f %f] %s",
+				offset - rd,
+				offset,
+				offset + rd,
+				p->p_dotted
+		);
+		point[num_points].p = p;
+		point[num_points].type = -1;
+		point[num_points].edge = offset - rd;
+		point[num_points].opt_rd = rd;
+		num_points++;
+		point[num_points].p = p;
+		point[num_points].type = 0;
+		point[num_points].edge = offset;
+		point[num_points].opt_rd = rd;
+		num_points++;
+		point[num_points].p = p;
+		point[num_points].type = 1;
+		point[num_points].edge = offset + rd;
+		point[num_points].opt_rd = rd;
+		num_points++;
+		item = item->link;
+	}
+	num_candidates = num_points / 3;
+	if (num_candidates == 0) {
+		VERB3 bb_error_msg("no valid datapoints, no peer selected");
+		return NULL;
+	}
+//TODO: sorting does not seem to be done in reference code
+	qsort(point, num_points, sizeof(point[0]), compare_point_edge);
+
+	/* Start with the assumption that there are no falsetickers.
+	 * Attempt to find a nonempty intersection interval containing
+	 * the midpoints of all truechimers.
+	 * If a nonempty interval cannot be found, increase the number
+	 * of assumed falsetickers by one and try again.
+	 * If a nonempty interval is found and the number of falsetickers
+	 * is less than the number of truechimers, a majority has been found
+	 * and the midpoint of each truechimer represents
+	 * the candidates available to the cluster algorithm.
+	 */
+	num_falsetickers = 0;
+	while (1) {
+		int c;
+		unsigned num_midpoints = 0;
+
+		low = 1 << 9;
+		high = - (1 << 9);
+		c = 0;
+		for (i = 0; i < num_points; i++) {
+			/* We want to do:
+			 * if (point[i].type == -1) c++;
+			 * if (point[i].type == 1) c--;
+			 * and it's simpler to do it this way:
+			 */
+			c -= point[i].type;
+			if (c >= num_candidates - num_falsetickers) {
+				/* If it was c++ and it got big enough... */
+				low = point[i].edge;
+				break;
+			}
+			if (point[i].type == 0)
+				num_midpoints++;
+		}
+		c = 0;
+		for (i = num_points-1; i >= 0; i--) {
+			c += point[i].type;
+			if (c >= num_candidates - num_falsetickers) {
+				high = point[i].edge;
+				break;
+			}
+			if (point[i].type == 0)
+				num_midpoints++;
+		}
+		/* If the number of midpoints is greater than the number
+		 * of allowed falsetickers, the intersection contains at
+		 * least one truechimer with no midpoint - bad.
+		 * Also, interval should be nonempty.
+		 */
+		if (num_midpoints <= num_falsetickers && low < high)
+			break;
+		num_falsetickers++;
+		if (num_falsetickers * 2 >= num_candidates) {
+			VERB3 bb_error_msg("too many falsetickers:%d (candidates:%d), no peer selected",
+					num_falsetickers, num_candidates);
+			return NULL;
+		}
+	}
+	VERB3 bb_error_msg("selected interval: [%f, %f]; candidates:%d falsetickers:%d",
+			low, high, num_candidates, num_falsetickers);
+
+	/* Clustering */
+
+	/* Construct a list of survivors (p, metric)
+	 * from the chime list, where metric is dominated
+	 * first by stratum and then by root distance.
+	 * All other things being equal, this is the order of preference.
+	 */
+	num_survivors = 0;
+	for (i = 0; i < num_points; i++) {
+		if (point[i].edge < low || point[i].edge > high)
+			continue;
+		p = point[i].p;
+		survivor[num_survivors].p = p;
+		/* x.opt_rd == root_distance(p); */
+		survivor[num_survivors].metric = MAXDIST * p->lastpkt_stratum + point[i].opt_rd;
+		VERB4 bb_error_msg("survivor[%d] metric:%f peer:%s",
+			num_survivors, survivor[num_survivors].metric, p->p_dotted);
+		num_survivors++;
+	}
+	/* There must be at least MIN_SELECTED survivors to satisfy the
+	 * correctness assertions. Ordinarily, the Byzantine criteria
+	 * require four survivors, but for the demonstration here, one
+	 * is acceptable.
+	 */
+	if (num_survivors < MIN_SELECTED) {
+		VERB3 bb_error_msg("num_survivors %d < %d, no peer selected",
+				num_survivors, MIN_SELECTED);
+		return NULL;
+	}
+
+//looks like this is ONLY used by the fact that later we pick survivor[0].
+//we can avoid sorting then, just find the minimum once!
+	qsort(survivor, num_survivors, sizeof(survivor[0]), compare_survivor_metric);
+
+	/* For each association p in turn, calculate the selection
+	 * jitter p->sjitter as the square root of the sum of squares
+	 * (p->offset - q->offset) over all q associations. The idea is
+	 * to repeatedly discard the survivor with maximum selection
+	 * jitter until a termination condition is met.
+	 */
+	while (1) {
+		unsigned max_idx = max_idx;
+		double max_selection_jitter = max_selection_jitter;
+		double min_jitter = min_jitter;
+
+		if (num_survivors <= MIN_CLUSTERED) {
+			VERB3 bb_error_msg("num_survivors %d <= %d, not discarding more",
+					num_survivors, MIN_CLUSTERED);
+			break;
+		}
+
+		/* To make sure a few survivors are left
+		 * for the clustering algorithm to chew on,
+		 * we stop if the number of survivors
+		 * is less than or equal to MIN_CLUSTERED (3).
+		 */
+		for (i = 0; i < num_survivors; i++) {
+			double selection_jitter_sq;
+
+			p = survivor[i].p;
+			if (i == 0 || p->filter_jitter < min_jitter)
+				min_jitter = p->filter_jitter;
+
+			selection_jitter_sq = 0;
+			for (j = 0; j < num_survivors; j++) {
+				peer_t *q = survivor[j].p;
+				selection_jitter_sq += SQUARE(p->filter_offset - q->filter_offset);
+			}
+			if (i == 0 || selection_jitter_sq > max_selection_jitter) {
+				max_selection_jitter = selection_jitter_sq;
+				max_idx = i;
+			}
+			VERB5 bb_error_msg("survivor %d selection_jitter^2:%f",
+					i, selection_jitter_sq);
+		}
+		max_selection_jitter = SQRT(max_selection_jitter / num_survivors);
+		VERB4 bb_error_msg("max_selection_jitter (at %d):%f min_jitter:%f",
+				max_idx, max_selection_jitter, min_jitter);
+
+		/* If the maximum selection jitter is less than the
+		 * minimum peer jitter, then tossing out more survivors
+		 * will not lower the minimum peer jitter, so we might
+		 * as well stop.
+		 */
+		if (max_selection_jitter < min_jitter) {
+			VERB3 bb_error_msg("max_selection_jitter:%f < min_jitter:%f, num_survivors:%d, not discarding more",
+					max_selection_jitter, min_jitter, num_survivors);
+			break;
+		}
+
+		/* Delete survivor[max_idx] from the list
+		 * and go around again.
+		 */
+		VERB5 bb_error_msg("dropping survivor %d", max_idx);
+		num_survivors--;
+		while (max_idx < num_survivors) {
+			survivor[max_idx] = survivor[max_idx + 1];
+			max_idx++;
+		}
+	}
+
+	if (0) {
+		/* Combine the offsets of the clustering algorithm survivors
+		 * using a weighted average with weight determined by the root
+		 * distance. Compute the selection jitter as the weighted RMS
+		 * difference between the first survivor and the remaining
+		 * survivors. In some cases the inherent clock jitter can be
+		 * reduced by not using this algorithm, especially when frequent
+		 * clockhopping is involved. bbox: thus we don't do it.
+		 */
+		double x, y, z, w;
+		y = z = w = 0;
+		for (i = 0; i < num_survivors; i++) {
+			p = survivor[i].p;
+			x = root_distance(p);
+			y += 1 / x;
+			z += p->filter_offset / x;
+			w += SQUARE(p->filter_offset - survivor[0].p->filter_offset) / x;
+		}
+		//G.cluster_offset = z / y;
+		//G.cluster_jitter = SQRT(w / y);
+	}
+
+	/* Pick the best clock. If the old system peer is on the list
+	 * and at the same stratum as the first survivor on the list,
+	 * then don't do a clock hop. Otherwise, select the first
+	 * survivor on the list as the new system peer.
+	 */
+	p = survivor[0].p;
+	if (G.last_update_peer
+	 && G.last_update_peer->lastpkt_stratum <= p->lastpkt_stratum
+	) {
+		/* Starting from 1 is ok here */
+		for (i = 1; i < num_survivors; i++) {
+			if (G.last_update_peer == survivor[i].p) {
+				VERB4 bb_error_msg("keeping old synced peer");
+				p = G.last_update_peer;
+				goto keep_old;
+			}
+		}
+	}
+	G.last_update_peer = p;
+ keep_old:
+	VERB3 bb_error_msg("selected peer %s filter_offset:%f age:%f",
+			p->p_dotted,
+			p->filter_offset,
+			G.cur_time - p->lastpkt_recv_time
+	);
+	return p;
+}
+
+
+/*
+ * Local clock discipline and its helpers
+ */
+static void
+set_new_values(int disc_state, double offset, double recv_time)
+{
+	/* Enter new state and set state variables. Note we use the time
+	 * of the last clock filter sample, which must be earlier than
+	 * the current time.
+	 */
+	VERB3 bb_error_msg("disc_state=%d last update offset=%f recv_time=%f",
+			disc_state, offset, recv_time);
+	G.discipline_state = disc_state;
+	G.last_update_offset = offset;
+	G.last_update_recv_time = recv_time;
+}
+/* Return: -1: decrease poll interval, 0: leave as is, 1: increase */
+static NOINLINE int
+update_local_clock(peer_t *p)
+{
+	int rc;
+	struct timex tmx;
+	/* Note: can use G.cluster_offset instead: */
+	double offset = p->filter_offset;
+	double recv_time = p->lastpkt_recv_time;
+	double abs_offset;
+#if !USING_KERNEL_PLL_LOOP
+	double freq_drift;
+#endif
+	double since_last_update;
+	double etemp, dtemp;
+
+	abs_offset = fabs(offset);
+
+#if 0
+	/* If needed, -S script can do it by looking at $offset
+	 * env var and killing parent */
+	/* If the offset is too large, give up and go home */
+	if (abs_offset > PANIC_THRESHOLD) {
+		bb_error_msg_and_die("offset %f far too big, exiting", offset);
+	}
+#endif
+
+	/* If this is an old update, for instance as the result
+	 * of a system peer change, avoid it. We never use
+	 * an old sample or the same sample twice.
+	 */
+	if (recv_time <= G.last_update_recv_time) {
+		VERB3 bb_error_msg("same or older datapoint: %f >= %f, not using it",
+				G.last_update_recv_time, recv_time);
+		return 0; /* "leave poll interval as is" */
+	}
+
+	/* Clock state machine transition function. This is where the
+	 * action is and defines how the system reacts to large time
+	 * and frequency errors.
+	 */
+	since_last_update = recv_time - G.reftime;
+#if !USING_KERNEL_PLL_LOOP
+	freq_drift = 0;
+#endif
+#if USING_INITIAL_FREQ_ESTIMATION
+	if (G.discipline_state == STATE_FREQ) {
+		/* Ignore updates until the stepout threshold */
+		if (since_last_update < WATCH_THRESHOLD) {
+			VERB3 bb_error_msg("measuring drift, datapoint ignored, %f sec remains",
+					WATCH_THRESHOLD - since_last_update);
+			return 0; /* "leave poll interval as is" */
+		}
+# if !USING_KERNEL_PLL_LOOP
+		freq_drift = (offset - G.last_update_offset) / since_last_update;
+# endif
+	}
+#endif
+
+	/* There are two main regimes: when the
+	 * offset exceeds the step threshold and when it does not.
+	 */
+	if (abs_offset > STEP_THRESHOLD) {
+		switch (G.discipline_state) {
+		case STATE_SYNC:
+			/* The first outlyer: ignore it, switch to SPIK state */
+			VERB3 bb_error_msg("offset:%f - spike detected", offset);
+			G.discipline_state = STATE_SPIK;
+			return -1; /* "decrease poll interval" */
+
+		case STATE_SPIK:
+			/* Ignore succeeding outlyers until either an inlyer
+			 * is found or the stepout threshold is exceeded.
+			 */
+			if (since_last_update < WATCH_THRESHOLD) {
+				VERB3 bb_error_msg("spike detected, datapoint ignored, %f sec remains",
+						WATCH_THRESHOLD - since_last_update);
+				return -1; /* "decrease poll interval" */
+			}
+			/* fall through: we need to step */
+		} /* switch */
+
+		/* Step the time and clamp down the poll interval.
+		 *
+		 * In NSET state an initial frequency correction is
+		 * not available, usually because the frequency file has
+		 * not yet been written. Since the time is outside the
+		 * capture range, the clock is stepped. The frequency
+		 * will be set directly following the stepout interval.
+		 *
+		 * In FSET state the initial frequency has been set
+		 * from the frequency file. Since the time is outside
+		 * the capture range, the clock is stepped immediately,
+		 * rather than after the stepout interval. Guys get
+		 * nervous if it takes 17 minutes to set the clock for
+		 * the first time.
+		 *
+		 * In SPIK state the stepout threshold has expired and
+		 * the phase is still above the step threshold. Note
+		 * that a single spike greater than the step threshold
+		 * is always suppressed, even at the longer poll
+		 * intervals.
+		 */
+		VERB3 bb_error_msg("stepping time by %f; poll_exp=MINPOLL", offset);
+		step_time(offset);
+		if (option_mask32 & OPT_q) {
+			/* We were only asked to set time once. Done. */
+			exit(0);
+		}
+
+		G.polladj_count = 0;
+		G.poll_exp = MINPOLL;
+		G.stratum = MAXSTRAT;
+
+		run_script("step", offset);
+
+#if USING_INITIAL_FREQ_ESTIMATION
+		if (G.discipline_state == STATE_NSET) {
+			set_new_values(STATE_FREQ, /*offset:*/ 0, recv_time);
+			return 1; /* "ok to increase poll interval" */
+		}
+#endif
+		set_new_values(STATE_SYNC, /*offset:*/ 0, recv_time);
+
+	} else { /* abs_offset <= STEP_THRESHOLD */
+
+		if (G.poll_exp < MINPOLL && G.initial_poll_complete) {
+			VERB3 bb_error_msg("small offset:%f, disabling burst mode", offset);
+			G.polladj_count = 0;
+			G.poll_exp = MINPOLL;
+		}
+
+		/* Compute the clock jitter as the RMS of exponentially
+		 * weighted offset differences. Used by the poll adjust code.
+		 */
+		etemp = SQUARE(G.discipline_jitter);
+		dtemp = SQUARE(MAXD(fabs(offset - G.last_update_offset), G_precision_sec));
+		G.discipline_jitter = SQRT(etemp + (dtemp - etemp) / AVG);
+		VERB3 bb_error_msg("discipline jitter=%f", G.discipline_jitter);
+
+		switch (G.discipline_state) {
+		case STATE_NSET:
+			if (option_mask32 & OPT_q) {
+				/* We were only asked to set time once.
+				 * The clock is precise enough, no need to step.
+				 */
+				exit(0);
+			}
+#if USING_INITIAL_FREQ_ESTIMATION
+			/* This is the first update received and the frequency
+			 * has not been initialized. The first thing to do
+			 * is directly measure the oscillator frequency.
+			 */
+			set_new_values(STATE_FREQ, offset, recv_time);
+#else
+			set_new_values(STATE_SYNC, offset, recv_time);
+#endif
+			VERB3 bb_error_msg("transitioning to FREQ, datapoint ignored");
+			return 0; /* "leave poll interval as is" */
+
+#if 0 /* this is dead code for now */
+		case STATE_FSET:
+			/* This is the first update and the frequency
+			 * has been initialized. Adjust the phase, but
+			 * don't adjust the frequency until the next update.
+			 */
+			set_new_values(STATE_SYNC, offset, recv_time);
+			/* freq_drift remains 0 */
+			break;
+#endif
+
+#if USING_INITIAL_FREQ_ESTIMATION
+		case STATE_FREQ:
+			/* since_last_update >= WATCH_THRESHOLD, we waited enough.
+			 * Correct the phase and frequency and switch to SYNC state.
+			 * freq_drift was already estimated (see code above)
+			 */
+			set_new_values(STATE_SYNC, offset, recv_time);
+			break;
+#endif
+
+		default:
+#if !USING_KERNEL_PLL_LOOP
+			/* Compute freq_drift due to PLL and FLL contributions.
+			 *
+			 * The FLL and PLL frequency gain constants
+			 * depend on the poll interval and Allan
+			 * intercept. The FLL is not used below one-half
+			 * the Allan intercept. Above that the loop gain
+			 * increases in steps to 1 / AVG.
+			 */
+			if ((1 << G.poll_exp) > ALLAN / 2) {
+				etemp = FLL - G.poll_exp;
+				if (etemp < AVG)
+					etemp = AVG;
+				freq_drift += (offset - G.last_update_offset) / (MAXD(since_last_update, ALLAN) * etemp);
+			}
+			/* For the PLL the integration interval
+			 * (numerator) is the minimum of the update
+			 * interval and poll interval. This allows
+			 * oversampling, but not undersampling.
+			 */
+			etemp = MIND(since_last_update, (1 << G.poll_exp));
+			dtemp = (4 * PLL) << G.poll_exp;
+			freq_drift += offset * etemp / SQUARE(dtemp);
+#endif
+			set_new_values(STATE_SYNC, offset, recv_time);
+			break;
+		}
+		if (G.stratum != p->lastpkt_stratum + 1) {
+			G.stratum = p->lastpkt_stratum + 1;
+			run_script("stratum", offset);
+		}
+	}
+
+	G.reftime = G.cur_time;
+	G.ntp_status = p->lastpkt_status;
+	G.refid = p->lastpkt_refid;
+	G.rootdelay = p->lastpkt_rootdelay + p->lastpkt_delay;
+	dtemp = p->filter_jitter; // SQRT(SQUARE(p->filter_jitter) + SQUARE(G.cluster_jitter));
+	dtemp += MAXD(p->filter_dispersion + FREQ_TOLERANCE * (G.cur_time - p->lastpkt_recv_time) + abs_offset, MINDISP);
+	G.rootdisp = p->lastpkt_rootdisp + dtemp;
+	VERB3 bb_error_msg("updating leap/refid/reftime/rootdisp from peer %s", p->p_dotted);
+
+	/* We are in STATE_SYNC now, but did not do adjtimex yet.
+	 * (Any other state does not reach this, they all return earlier)
+	 * By this time, freq_drift and G.last_update_offset are set
+	 * to values suitable for adjtimex.
+	 */
+#if !USING_KERNEL_PLL_LOOP
+	/* Calculate the new frequency drift and frequency stability (wander).
+	 * Compute the clock wander as the RMS of exponentially weighted
+	 * frequency differences. This is not used directly, but can,
+	 * along with the jitter, be a highly useful monitoring and
+	 * debugging tool.
+	 */
+	dtemp = G.discipline_freq_drift + freq_drift;
+	G.discipline_freq_drift = MAXD(MIND(MAXDRIFT, dtemp), -MAXDRIFT);
+	etemp = SQUARE(G.discipline_wander);
+	dtemp = SQUARE(dtemp);
+	G.discipline_wander = SQRT(etemp + (dtemp - etemp) / AVG);
+
+	VERB3 bb_error_msg("discipline freq_drift=%.9f(int:%ld corr:%e) wander=%f",
+			G.discipline_freq_drift,
+			(long)(G.discipline_freq_drift * 65536e6),
+			freq_drift,
+			G.discipline_wander);
+#endif
+	VERB3 {
+		memset(&tmx, 0, sizeof(tmx));
+		if (adjtimex(&tmx) < 0)
+			bb_perror_msg_and_die("adjtimex");
+		VERB3 bb_error_msg("p adjtimex freq:%ld offset:%ld constant:%ld status:0x%x",
+				tmx.freq, tmx.offset, tmx.constant, tmx.status);
+	}
+
+	memset(&tmx, 0, sizeof(tmx));
+#if 0
+//doesn't work, offset remains 0 (!) in kernel:
+//ntpd:  set adjtimex freq:1786097 tmx.offset:77487
+//ntpd: prev adjtimex freq:1786097 tmx.offset:0
+//ntpd:  cur adjtimex freq:1786097 tmx.offset:0
+	tmx.modes = ADJ_FREQUENCY | ADJ_OFFSET;
+	/* 65536 is one ppm */
+	tmx.freq = G.discipline_freq_drift * 65536e6;
+	tmx.offset = G.last_update_offset * 1000000; /* usec */
+#endif
+	tmx.modes = ADJ_OFFSET | ADJ_STATUS | ADJ_TIMECONST;// | ADJ_MAXERROR | ADJ_ESTERROR;
+	tmx.offset = (G.last_update_offset * 1000000); /* usec */
+			/* + (G.last_update_offset < 0 ? -0.5 : 0.5) - too small to bother */
+	tmx.status = STA_PLL;
+	if (G.ntp_status & LI_PLUSSEC)
+		tmx.status |= STA_INS;
+	if (G.ntp_status & LI_MINUSSEC)
+		tmx.status |= STA_DEL;
+	tmx.constant = G.poll_exp - 4;
+	//tmx.esterror = (u_int32)(clock_jitter * 1e6);
+	//tmx.maxerror = (u_int32)((sys_rootdelay / 2 + sys_rootdisp) * 1e6);
+	rc = adjtimex(&tmx);
+	if (rc < 0)
+		bb_perror_msg_and_die("adjtimex");
+	/* NB: here kernel returns constant == G.poll_exp, not == G.poll_exp - 4.
+	 * Not sure why. Perhaps it is normal.
+	 */
+	VERB3 bb_error_msg("adjtimex:%d freq:%ld offset:%ld constant:%ld status:0x%x",
+				rc, tmx.freq, tmx.offset, tmx.constant, tmx.status);
+#if 0
+	VERB3 {
+		/* always gives the same output as above msg */
+		memset(&tmx, 0, sizeof(tmx));
+		if (adjtimex(&tmx) < 0)
+			bb_perror_msg_and_die("adjtimex");
+		VERB3 bb_error_msg("c adjtimex freq:%ld offset:%ld constant:%ld status:0x%x",
+				tmx.freq, tmx.offset, tmx.constant, tmx.status);
+	}
+#endif
+	G.kernel_freq_drift = tmx.freq / 65536;
+	VERB2 bb_error_msg("update peer:%s, offset:%f, clock drift:%ld ppm",
+			p->p_dotted, G.last_update_offset, G.kernel_freq_drift);
+
+	return 1; /* "ok to increase poll interval" */
+}
+
+
+/*
+ * We've got a new reply packet from a peer, process it
+ * (helpers first)
+ */
+static unsigned
+retry_interval(void)
+{
+	/* Local problem, want to retry soon */
+	unsigned interval, r;
+	interval = RETRY_INTERVAL;
+	r = random();
+	interval += r % (unsigned)(RETRY_INTERVAL / 4);
+	VERB3 bb_error_msg("chose retry interval:%u", interval);
+	return interval;
+}
+static unsigned
+poll_interval(int exponent)
+{
+	unsigned interval, r;
+	exponent = G.poll_exp + exponent;
+	if (exponent < 0)
+		exponent = 0;
+	interval = 1 << exponent;
+	r = random();
+	interval += ((r & (interval-1)) >> 4) + ((r >> 8) & 1); /* + 1/16 of interval, max */
+	VERB3 bb_error_msg("chose poll interval:%u (poll_exp:%d exp:%d)", interval, G.poll_exp, exponent);
+	return interval;
+}
+static NOINLINE void
+recv_and_process_peer_pkt(peer_t *p)
+{
+	int         rc;
+	ssize_t     size;
+	msg_t       msg;
+	double      T1, T2, T3, T4;
+	unsigned    interval;
+	datapoint_t *datapoint;
+	peer_t      *q;
+
+	/* We can recvfrom here and check from.IP, but some multihomed
+	 * ntp servers reply from their *other IP*.
+	 * TODO: maybe we should check at least what we can: from.port == 123?
+	 */
+	size = recv(p->p_fd, &msg, sizeof(msg), MSG_DONTWAIT);
+	if (size == -1) {
+		bb_perror_msg("recv(%s) error", p->p_dotted);
+		if (errno == EHOSTUNREACH || errno == EHOSTDOWN
+		 || errno == ENETUNREACH || errno == ENETDOWN
+		 || errno == ECONNREFUSED || errno == EADDRNOTAVAIL
+		 || errno == EAGAIN
+		) {
+//TODO: always do this?
+			interval = retry_interval();
+			goto set_next_and_close_sock;
+		}
+		xfunc_die();
+	}
+
+	if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE) {
+		bb_error_msg("malformed packet received from %s", p->p_dotted);
+		goto bail;
+	}
+
+	if (msg.m_orgtime.int_partl != p->p_xmt_msg.m_xmttime.int_partl
+	 || msg.m_orgtime.fractionl != p->p_xmt_msg.m_xmttime.fractionl
+	) {
+		goto bail;
+	}
+
+	if ((msg.m_status & LI_ALARM) == LI_ALARM
+	 || msg.m_stratum == 0
+	 || msg.m_stratum > NTP_MAXSTRATUM
+	) {
+// TODO: stratum 0 responses may have commands in 32-bit m_refid field:
+// "DENY", "RSTR" - peer does not like us at all
+// "RATE" - peer is overloaded, reduce polling freq
+		interval = poll_interval(0);
+		bb_error_msg("reply from %s: not synced, next query in %us", p->p_dotted, interval);
+		goto set_next_and_close_sock;
+	}
+
+//	/* Verify valid root distance */
+//	if (msg.m_rootdelay / 2 + msg.m_rootdisp >= MAXDISP || p->lastpkt_reftime > msg.m_xmt)
+//		return;                 /* invalid header values */
+
+	p->lastpkt_status = msg.m_status;
+	p->lastpkt_stratum = msg.m_stratum;
+	p->lastpkt_rootdelay = sfp_to_d(msg.m_rootdelay);
+	p->lastpkt_rootdisp = sfp_to_d(msg.m_rootdisp);
+	p->lastpkt_refid = msg.m_refid;
+
+	/*
+	 * From RFC 2030 (with a correction to the delay math):
+	 *
+	 * Timestamp Name          ID   When Generated
+	 * ------------------------------------------------------------
+	 * Originate Timestamp     T1   time request sent by client
+	 * Receive Timestamp       T2   time request received by server
+	 * Transmit Timestamp      T3   time reply sent by server
+	 * Destination Timestamp   T4   time reply received by client
+	 *
+	 * The roundtrip delay and local clock offset are defined as
+	 *
+	 * delay = (T4 - T1) - (T3 - T2); offset = ((T2 - T1) + (T3 - T4)) / 2
+	 */
+	T1 = p->p_xmttime;
+	T2 = lfp_to_d(msg.m_rectime);
+	T3 = lfp_to_d(msg.m_xmttime);
+	T4 = G.cur_time;
+
+	p->lastpkt_recv_time = T4;
+
+	VERB5 bb_error_msg("%s->lastpkt_recv_time=%f", p->p_dotted, p->lastpkt_recv_time);
+	p->datapoint_idx = p->reachable_bits ? (p->datapoint_idx + 1) % NUM_DATAPOINTS : 0;
+	datapoint = &p->filter_datapoint[p->datapoint_idx];
+	datapoint->d_recv_time = T4;
+	datapoint->d_offset    = ((T2 - T1) + (T3 - T4)) / 2;
+	/* The delay calculation is a special case. In cases where the
+	 * server and client clocks are running at different rates and
+	 * with very fast networks, the delay can appear negative. In
+	 * order to avoid violating the Principle of Least Astonishment,
+	 * the delay is clamped not less than the system precision.
+	 */
+	p->lastpkt_delay = (T4 - T1) - (T3 - T2);
+	if (p->lastpkt_delay < G_precision_sec)
+		p->lastpkt_delay = G_precision_sec;
+	datapoint->d_dispersion = LOG2D(msg.m_precision_exp) + G_precision_sec;
+	if (!p->reachable_bits) {
+		/* 1st datapoint ever - replicate offset in every element */
+		int i;
+		for (i = 1; i < NUM_DATAPOINTS; i++) {
+			p->filter_datapoint[i].d_offset = datapoint->d_offset;
+		}
+	}
+
+	p->reachable_bits |= 1;
+	if ((MAX_VERBOSE && G.verbose) || (option_mask32 & OPT_w)) {
+		bb_error_msg("reply from %s: reach 0x%02x offset %f delay %f status 0x%02x strat %d refid 0x%08x rootdelay %f",
+			p->p_dotted,
+			p->reachable_bits,
+			datapoint->d_offset,
+			p->lastpkt_delay,
+			p->lastpkt_status,
+			p->lastpkt_stratum,
+			p->lastpkt_refid,
+			p->lastpkt_rootdelay
+			/* not shown: m_ppoll, m_precision_exp, m_rootdisp,
+			 * m_reftime, m_orgtime, m_rectime, m_xmttime
+			 */
+		);
+	}
+
+	/* Muck with statictics and update the clock */
+	filter_datapoints(p);
+	q = select_and_cluster();
+	rc = -1;
+	if (q) {
+		rc = 0;
+		if (!(option_mask32 & OPT_w)) {
+			rc = update_local_clock(q);
+			/* If drift is dangerously large, immediately
+			 * drop poll interval one step down.
+			 */
+			if (fabs(q->filter_offset) >= POLLDOWN_OFFSET) {
+				VERB3 bb_error_msg("offset:%f > POLLDOWN_OFFSET", q->filter_offset);
+				goto poll_down;
+			}
+		}
+	}
+	/* else: no peer selected, rc = -1: we want to poll more often */
+
+	if (rc != 0) {
+		/* Adjust the poll interval by comparing the current offset
+		 * with the clock jitter. If the offset is less than
+		 * the clock jitter times a constant, then the averaging interval
+		 * is increased, otherwise it is decreased. A bit of hysteresis
+		 * helps calm the dance. Works best using burst mode.
+		 */
+		VERB4 if (rc > 0) {
+			bb_error_msg("offset:%f POLLADJ_GATE*discipline_jitter:%f poll:%s",
+				q->filter_offset, POLLADJ_GATE * G.discipline_jitter,
+				fabs(q->filter_offset) < POLLADJ_GATE * G.discipline_jitter
+					? "grows" : "falls"
+			);
+		}
+		if (rc > 0 && fabs(q->filter_offset) < POLLADJ_GATE * G.discipline_jitter) {
+			/* was += G.poll_exp but it is a bit
+			 * too optimistic for my taste at high poll_exp's */
+			G.polladj_count += MINPOLL;
+			if (G.polladj_count > POLLADJ_LIMIT) {
+				G.polladj_count = 0;
+				if (G.poll_exp < MAXPOLL) {
+					G.poll_exp++;
+					VERB3 bb_error_msg("polladj: discipline_jitter:%f ++poll_exp=%d",
+							G.discipline_jitter, G.poll_exp);
+				}
+			} else {
+				VERB3 bb_error_msg("polladj: incr:%d", G.polladj_count);
+			}
+		} else {
+			G.polladj_count -= G.poll_exp * 2;
+			if (G.polladj_count < -POLLADJ_LIMIT || G.poll_exp >= BIGPOLL) {
+ poll_down:
+				G.polladj_count = 0;
+				if (G.poll_exp > MINPOLL) {
+					llist_t *item;
+
+					G.poll_exp--;
+					/* Correct p->next_action_time in each peer
+					 * which waits for sending, so that they send earlier.
+					 * Old pp->next_action_time are on the order
+					 * of t + (1 << old_poll_exp) + small_random,
+					 * we simply need to subtract ~half of that.
+					 */
+					for (item = G.ntp_peers; item != NULL; item = item->link) {
+						peer_t *pp = (peer_t *) item->data;
+						if (pp->p_fd < 0)
+							pp->next_action_time -= (1 << G.poll_exp);
+					}
+					VERB3 bb_error_msg("polladj: discipline_jitter:%f --poll_exp=%d",
+							G.discipline_jitter, G.poll_exp);
+				}
+			} else {
+				VERB3 bb_error_msg("polladj: decr:%d", G.polladj_count);
+			}
+		}
+	}
+
+	/* Decide when to send new query for this peer */
+	interval = poll_interval(0);
+
+ set_next_and_close_sock:
+	set_next(p, interval);
+	/* We do not expect any more packets from this peer for now.
+	 * Closing the socket informs kernel about it.
+	 * We open a new socket when we send a new query.
+	 */
+	close(p->p_fd);
+	p->p_fd = -1;
+ bail:
+	return;
+}
+
+#if ENABLE_FEATURE_NTPD_SERVER
+static NOINLINE void
+recv_and_process_client_pkt(void /*int fd*/)
+{
+	ssize_t          size;
+	uint8_t          version;
+	len_and_sockaddr *to;
+	struct sockaddr  *from;
+	msg_t            msg;
+	uint8_t          query_status;
+	l_fixedpt_t      query_xmttime;
+
+	to = get_sock_lsa(G.listen_fd);
+	from = xzalloc(to->len);
+
+	size = recv_from_to(G.listen_fd, &msg, sizeof(msg), MSG_DONTWAIT, from, &to->u.sa, to->len);
+	if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE) {
+		char *addr;
+		if (size < 0) {
+			if (errno == EAGAIN)
+				goto bail;
+			bb_perror_msg_and_die("recv");
+		}
+		addr = xmalloc_sockaddr2dotted_noport(from);
+		bb_error_msg("malformed packet received from %s: size %u", addr, (int)size);
+		free(addr);
+		goto bail;
+	}
+
+	query_status = msg.m_status;
+	query_xmttime = msg.m_xmttime;
+
+	/* Build a reply packet */
+	memset(&msg, 0, sizeof(msg));
+	msg.m_status = G.stratum < MAXSTRAT ? G.ntp_status : LI_ALARM;
+	msg.m_status |= (query_status & VERSION_MASK);
+	msg.m_status |= ((query_status & MODE_MASK) == MODE_CLIENT) ?
+			 MODE_SERVER : MODE_SYM_PAS;
+	msg.m_stratum = G.stratum;
+	msg.m_ppoll = G.poll_exp;
+	msg.m_precision_exp = G_precision_exp;
+	/* this time was obtained between poll() and recv() */
+	msg.m_rectime = d_to_lfp(G.cur_time);
+	msg.m_xmttime = d_to_lfp(gettime1900d()); /* this instant */
+	if (G.peer_cnt == 0) {
+		/* we have no peers: "stratum 1 server" mode. reftime = our own time */
+		G.reftime = G.cur_time;
+	}
+	msg.m_reftime = d_to_lfp(G.reftime);
+	msg.m_orgtime = query_xmttime;
+	msg.m_rootdelay = d_to_sfp(G.rootdelay);
+//simple code does not do this, fix simple code!
+	msg.m_rootdisp = d_to_sfp(G.rootdisp);
+	version = (query_status & VERSION_MASK); /* ... >> VERSION_SHIFT - done below instead */
+	msg.m_refid = G.refid; // (version > (3 << VERSION_SHIFT)) ? G.refid : G.refid3;
+
+	/* We reply from the local address packet was sent to,
+	 * this makes to/from look swapped here: */
+	do_sendto(G.listen_fd,
+		/*from:*/ &to->u.sa, /*to:*/ from, /*addrlen:*/ to->len,
+		&msg, size);
+
+ bail:
+	free(to);
+	free(from);
+}
+#endif
+
+/* Upstream ntpd's options:
+ *
+ * -4   Force DNS resolution of host names to the IPv4 namespace.
+ * -6   Force DNS resolution of host names to the IPv6 namespace.
+ * -a   Require cryptographic authentication for broadcast client,
+ *      multicast client and symmetric passive associations.
+ *      This is the default.
+ * -A   Do not require cryptographic authentication for broadcast client,
+ *      multicast client and symmetric passive associations.
+ *      This is almost never a good idea.
+ * -b   Enable the client to synchronize to broadcast servers.
+ * -c conffile
+ *      Specify the name and path of the configuration file,
+ *      default /etc/ntp.conf
+ * -d   Specify debugging mode. This option may occur more than once,
+ *      with each occurrence indicating greater detail of display.
+ * -D level
+ *      Specify debugging level directly.
+ * -f driftfile
+ *      Specify the name and path of the frequency file.
+ *      This is the same operation as the "driftfile FILE"
+ *      configuration command.
+ * -g   Normally, ntpd exits with a message to the system log
+ *      if the offset exceeds the panic threshold, which is 1000 s
+ *      by default. This option allows the time to be set to any value
+ *      without restriction; however, this can happen only once.
+ *      If the threshold is exceeded after that, ntpd will exit
+ *      with a message to the system log. This option can be used
+ *      with the -q and -x options. See the tinker command for other options.
+ * -i jaildir
+ *      Chroot the server to the directory jaildir. This option also implies
+ *      that the server attempts to drop root privileges at startup
+ *      (otherwise, chroot gives very little additional security).
+ *      You may need to also specify a -u option.
+ * -k keyfile
+ *      Specify the name and path of the symmetric key file,
+ *      default /etc/ntp/keys. This is the same operation
+ *      as the "keys FILE" configuration command.
+ * -l logfile
+ *      Specify the name and path of the log file. The default
+ *      is the system log file. This is the same operation as
+ *      the "logfile FILE" configuration command.
+ * -L   Do not listen to virtual IPs. The default is to listen.
+ * -n   Don't fork.
+ * -N   To the extent permitted by the operating system,
+ *      run the ntpd at the highest priority.
+ * -p pidfile
+ *      Specify the name and path of the file used to record the ntpd
+ *      process ID. This is the same operation as the "pidfile FILE"
+ *      configuration command.
+ * -P priority
+ *      To the extent permitted by the operating system,
+ *      run the ntpd at the specified priority.
+ * -q   Exit the ntpd just after the first time the clock is set.
+ *      This behavior mimics that of the ntpdate program, which is
+ *      to be retired. The -g and -x options can be used with this option.
+ *      Note: The kernel time discipline is disabled with this option.
+ * -r broadcastdelay
+ *      Specify the default propagation delay from the broadcast/multicast
+ *      server to this client. This is necessary only if the delay
+ *      cannot be computed automatically by the protocol.
+ * -s statsdir
+ *      Specify the directory path for files created by the statistics
+ *      facility. This is the same operation as the "statsdir DIR"
+ *      configuration command.
+ * -t key
+ *      Add a key number to the trusted key list. This option can occur
+ *      more than once.
+ * -u user[:group]
+ *      Specify a user, and optionally a group, to switch to.
+ * -v variable
+ * -V variable
+ *      Add a system variable listed by default.
+ * -x   Normally, the time is slewed if the offset is less than the step
+ *      threshold, which is 128 ms by default, and stepped if above
+ *      the threshold. This option sets the threshold to 600 s, which is
+ *      well within the accuracy window to set the clock manually.
+ *      Note: since the slew rate of typical Unix kernels is limited
+ *      to 0.5 ms/s, each second of adjustment requires an amortization
+ *      interval of 2000 s. Thus, an adjustment as much as 600 s
+ *      will take almost 14 days to complete. This option can be used
+ *      with the -g and -q options. See the tinker command for other options.
+ *      Note: The kernel time discipline is disabled with this option.
+ */
+
+/* By doing init in a separate function we decrease stack usage
+ * in main loop.
+ */
+static NOINLINE void ntp_init(char **argv)
+{
+	unsigned opts;
+	llist_t *peers;
+
+	srandom(getpid());
+
+	if (getuid())
+		bb_error_msg_and_die("you must be root");
+
+	/* Set some globals */
+	G.stratum = MAXSTRAT;
+	if (BURSTPOLL != 0)
+		G.poll_exp = BURSTPOLL; /* speeds up initial sync */
+	G.last_script_run = G.reftime = G.last_update_recv_time = gettime1900d(); /* sets G.cur_time too */
+
+	/* Parse options */
+	peers = NULL;
+	opt_complementary = "dd:p::wn"; /* d: counter; p: list; -w implies -n */
+	opts = getopt32(argv,
+			"nqNx" /* compat */
+			"wp:S:"IF_FEATURE_NTPD_SERVER("l") /* NOT compat */
+			"d" /* compat */
+			"46aAbgL", /* compat, ignored */
+			&peers, &G.script_name, &G.verbose);
+	if (!(opts & (OPT_p|OPT_l)))
+		bb_show_usage();
+//	if (opts & OPT_x) /* disable stepping, only slew is allowed */
+//		G.time_was_stepped = 1;
+	if (peers) {
+		while (peers)
+			add_peers(llist_pop(&peers));
+	} else {
+		/* -l but no peers: "stratum 1 server" mode */
+		G.stratum = 1;
+	}
+	if (!(opts & OPT_n)) {
+		bb_daemonize_or_rexec(DAEMON_DEVNULL_STDIO, argv);
+		logmode = LOGMODE_NONE;
+	}
+#if ENABLE_FEATURE_NTPD_SERVER
+	G.listen_fd = -1;
+	if (opts & OPT_l) {
+		G.listen_fd = create_and_bind_dgram_or_die(NULL, 123);
+		socket_want_pktinfo(G.listen_fd);
+		setsockopt(G.listen_fd, IPPROTO_IP, IP_TOS, &const_IPTOS_LOWDELAY, sizeof(const_IPTOS_LOWDELAY));
+	}
+#endif
+	/* I hesitate to set -20 prio. -15 should be high enough for timekeeping */
+	if (opts & OPT_N)
+		setpriority(PRIO_PROCESS, 0, -15);
+
+	/* If network is up, syncronization occurs in ~10 seconds.
+	 * We give "ntpd -q" a full minute to finish, then we exit.
+	 *
+	 * I tested ntpd 4.2.6p1 and apparently it never exits
+	 * (will try forever), but it does not feel right.
+	 * The goal of -q is to act like ntpdate: set time
+	 * after a reasonably small period of polling, or fail.
+	 */
+	if (opts & OPT_q)
+		alarm(60);
+
+	bb_signals(0
+		| (1 << SIGTERM)
+		| (1 << SIGINT)
+		| (1 << SIGALRM)
+		, record_signo
+	);
+	bb_signals(0
+		| (1 << SIGPIPE)
+		| (1 << SIGCHLD)
+		, SIG_IGN
+	);
+}
+
+int ntpd_main(int argc UNUSED_PARAM, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int ntpd_main(int argc UNUSED_PARAM, char **argv)
+{
+#undef G
+	struct globals G;
+	struct pollfd *pfd;
+	peer_t **idx2peer;
+	unsigned cnt;
+
+	memset(&G, 0, sizeof(G));
+	SET_PTR_TO_GLOBALS(&G);
+
+	ntp_init(argv);
+
+	/* If ENABLE_FEATURE_NTPD_SERVER, + 1 for listen_fd: */
+	cnt = G.peer_cnt + ENABLE_FEATURE_NTPD_SERVER;
+	idx2peer = xzalloc(sizeof(idx2peer[0]) * cnt);
+	pfd = xzalloc(sizeof(pfd[0]) * cnt);
+
+	/* Countdown: we never sync before we sent INITIAL_SAMPLES+1
+	 * packets to each peer.
+	 * NB: if some peer is not responding, we may end up sending
+	 * fewer packets to it and more to other peers.
+	 * NB2: sync usually happens using INITIAL_SAMPLES packets,
+	 * since last reply does not come back instantaneously.
+	 */
+	cnt = G.peer_cnt * (INITIAL_SAMPLES + 1);
+
+	while (!bb_got_signal) {
+		llist_t *item;
+		unsigned i, j;
+		int nfds, timeout;
+		double nextaction;
+
+		/* Nothing between here and poll() blocks for any significant time */
+
+		nextaction = G.cur_time + 3600;
+
+		i = 0;
+#if ENABLE_FEATURE_NTPD_SERVER
+		if (G.listen_fd != -1) {
+			pfd[0].fd = G.listen_fd;
+			pfd[0].events = POLLIN;
+			i++;
+		}
+#endif
+		/* Pass over peer list, send requests, time out on receives */
+		for (item = G.ntp_peers; item != NULL; item = item->link) {
+			peer_t *p = (peer_t *) item->data;
+
+			if (p->next_action_time <= G.cur_time) {
+				if (p->p_fd == -1) {
+					/* Time to send new req */
+					if (--cnt == 0) {
+						G.initial_poll_complete = 1;
+					}
+					send_query_to_peer(p);
+				} else {
+					/* Timed out waiting for reply */
+					close(p->p_fd);
+					p->p_fd = -1;
+					timeout = poll_interval(-2); /* -2: try a bit sooner */
+					bb_error_msg("timed out waiting for %s, reach 0x%02x, next query in %us",
+							p->p_dotted, p->reachable_bits, timeout);
+					set_next(p, timeout);
+				}
+			}
+
+			if (p->next_action_time < nextaction)
+				nextaction = p->next_action_time;
+
+			if (p->p_fd >= 0) {
+				/* Wait for reply from this peer */
+				pfd[i].fd = p->p_fd;
+				pfd[i].events = POLLIN;
+				idx2peer[i] = p;
+				i++;
+			}
+		}
+
+		timeout = nextaction - G.cur_time;
+		if (timeout < 0)
+			timeout = 0;
+		timeout++; /* (nextaction - G.cur_time) rounds down, compensating */
+
+		/* Here we may block */
+		VERB2 bb_error_msg("poll %us, sockets:%u, poll interval:%us", timeout, i, 1 << G.poll_exp);
+		nfds = poll(pfd, i, timeout * 1000);
+		gettime1900d(); /* sets G.cur_time */
+		if (nfds <= 0) {
+			if (G.script_name && G.cur_time - G.last_script_run > 11*60) {
+				/* Useful for updating battery-backed RTC and such */
+				run_script("periodic", G.last_update_offset);
+				gettime1900d(); /* sets G.cur_time */
+			}
+			continue;
+		}
+
+		/* Process any received packets */
+		j = 0;
+#if ENABLE_FEATURE_NTPD_SERVER
+		if (G.listen_fd != -1) {
+			if (pfd[0].revents /* & (POLLIN|POLLERR)*/) {
+				nfds--;
+				recv_and_process_client_pkt(/*G.listen_fd*/);
+				gettime1900d(); /* sets G.cur_time */
+			}
+			j = 1;
+		}
+#endif
+		for (; nfds != 0 && j < i; j++) {
+			if (pfd[j].revents /* & (POLLIN|POLLERR)*/) {
+				nfds--;
+				recv_and_process_peer_pkt(idx2peer[j]);
+				gettime1900d(); /* sets G.cur_time */
+			}
+		}
+	} /* while (!bb_got_signal) */
+
+	kill_myself_with_sig(bb_got_signal);
+}
+
+
+
+
+
+
+/*** openntpd-4.6 uses only adjtime, not adjtimex ***/
+
+/*** ntp-4.2.6/ntpd/ntp_loopfilter.c - adjtimex usage ***/
+
+#if 0
+static double
+direct_freq(double fp_offset)
+{
+#ifdef KERNEL_PLL
+	/*
+	 * If the kernel is enabled, we need the residual offset to
+	 * calculate the frequency correction.
+	 */
+	if (pll_control && kern_enable) {
+		memset(&ntv, 0, sizeof(ntv));
+		ntp_adjtime(&ntv);
+#ifdef STA_NANO
+		clock_offset = ntv.offset / 1e9;
+#else /* STA_NANO */
+		clock_offset = ntv.offset / 1e6;
+#endif /* STA_NANO */
+		drift_comp = FREQTOD(ntv.freq);
+	}
+#endif /* KERNEL_PLL */
+	set_freq((fp_offset - clock_offset) / (current_time - clock_epoch) + drift_comp);
+	wander_resid = 0;
+	return drift_comp;
+}
+
+static void
+set_freq(double freq) /* frequency update */
+{
+	char tbuf[80];
+
+	drift_comp = freq;
+
+#ifdef KERNEL_PLL
+	/*
+	 * If the kernel is enabled, update the kernel frequency.
+	 */
+	if (pll_control && kern_enable) {
+		memset(&ntv, 0, sizeof(ntv));
+		ntv.modes = MOD_FREQUENCY;
+		ntv.freq = DTOFREQ(drift_comp);
+		ntp_adjtime(&ntv);
+		snprintf(tbuf, sizeof(tbuf), "kernel %.3f PPM", drift_comp * 1e6);
+		report_event(EVNT_FSET, NULL, tbuf);
+	} else {
+		snprintf(tbuf, sizeof(tbuf), "ntpd %.3f PPM", drift_comp * 1e6);
+		report_event(EVNT_FSET, NULL, tbuf);
+	}
+#else /* KERNEL_PLL */
+	snprintf(tbuf, sizeof(tbuf), "ntpd %.3f PPM", drift_comp * 1e6);
+	report_event(EVNT_FSET, NULL, tbuf);
+#endif /* KERNEL_PLL */
+}
+
+...
+...
+...
+
+#ifdef KERNEL_PLL
+	/*
+	 * This code segment works when clock adjustments are made using
+	 * precision time kernel support and the ntp_adjtime() system
+	 * call. This support is available in Solaris 2.6 and later,
+	 * Digital Unix 4.0 and later, FreeBSD, Linux and specially
+	 * modified kernels for HP-UX 9 and Ultrix 4. In the case of the
+	 * DECstation 5000/240 and Alpha AXP, additional kernel
+	 * modifications provide a true microsecond clock and nanosecond
+	 * clock, respectively.
+	 *
+	 * Important note: The kernel discipline is used only if the
+	 * step threshold is less than 0.5 s, as anything higher can
+	 * lead to overflow problems. This might occur if some misguided
+	 * lad set the step threshold to something ridiculous.
+	 */
+	if (pll_control && kern_enable) {
+
+#define MOD_BITS (MOD_OFFSET | MOD_MAXERROR | MOD_ESTERROR | MOD_STATUS | MOD_TIMECONST)
+
+		/*
+		 * We initialize the structure for the ntp_adjtime()
+		 * system call. We have to convert everything to
+		 * microseconds or nanoseconds first. Do not update the
+		 * system variables if the ext_enable flag is set. In
+		 * this case, the external clock driver will update the
+		 * variables, which will be read later by the local
+		 * clock driver. Afterwards, remember the time and
+		 * frequency offsets for jitter and stability values and
+		 * to update the frequency file.
+		 */
+		memset(&ntv,  0, sizeof(ntv));
+		if (ext_enable) {
+			ntv.modes = MOD_STATUS;
+		} else {
+#ifdef STA_NANO
+			ntv.modes = MOD_BITS | MOD_NANO;
+#else /* STA_NANO */
+			ntv.modes = MOD_BITS;
+#endif /* STA_NANO */
+			if (clock_offset < 0)
+				dtemp = -.5;
+			else
+				dtemp = .5;
+#ifdef STA_NANO
+			ntv.offset = (int32)(clock_offset * 1e9 + dtemp);
+			ntv.constant = sys_poll;
+#else /* STA_NANO */
+			ntv.offset = (int32)(clock_offset * 1e6 + dtemp);
+			ntv.constant = sys_poll - 4;
+#endif /* STA_NANO */
+			ntv.esterror = (u_int32)(clock_jitter * 1e6);
+			ntv.maxerror = (u_int32)((sys_rootdelay / 2 + sys_rootdisp) * 1e6);
+			ntv.status = STA_PLL;
+
+			/*
+			 * Enable/disable the PPS if requested.
+			 */
+			if (pps_enable) {
+				if (!(pll_status & STA_PPSTIME))
+					report_event(EVNT_KERN,
+					    NULL, "PPS enabled");
+				ntv.status |= STA_PPSTIME | STA_PPSFREQ;
+			} else {
+				if (pll_status & STA_PPSTIME)
+					report_event(EVNT_KERN,
+					    NULL, "PPS disabled");
+				ntv.status &= ~(STA_PPSTIME |
+				    STA_PPSFREQ);
+			}
+			if (sys_leap == LEAP_ADDSECOND)
+				ntv.status |= STA_INS;
+			else if (sys_leap == LEAP_DELSECOND)
+				ntv.status |= STA_DEL;
+		}
+
+		/*
+		 * Pass the stuff to the kernel. If it squeals, turn off
+		 * the pps. In any case, fetch the kernel offset,
+		 * frequency and jitter.
+		 */
+		if (ntp_adjtime(&ntv) == TIME_ERROR) {
+			if (!(ntv.status & STA_PPSSIGNAL))
+				report_event(EVNT_KERN, NULL,
+				    "PPS no signal");
+		}
+		pll_status = ntv.status;
+#ifdef STA_NANO
+		clock_offset = ntv.offset / 1e9;
+#else /* STA_NANO */
+		clock_offset = ntv.offset / 1e6;
+#endif /* STA_NANO */
+		clock_frequency = FREQTOD(ntv.freq);
+
+		/*
+		 * If the kernel PPS is lit, monitor its performance.
+		 */
+		if (ntv.status & STA_PPSTIME) {
+#ifdef STA_NANO
+			clock_jitter = ntv.jitter / 1e9;
+#else /* STA_NANO */
+			clock_jitter = ntv.jitter / 1e6;
+#endif /* STA_NANO */
+		}
+
+#if defined(STA_NANO) && NTP_API == 4
+		/*
+		 * If the TAI changes, update the kernel TAI.
+		 */
+		if (loop_tai != sys_tai) {
+			loop_tai = sys_tai;
+			ntv.modes = MOD_TAI;
+			ntv.constant = sys_tai;
+			ntp_adjtime(&ntv);
+		}
+#endif /* STA_NANO */
+	}
+#endif /* KERNEL_PLL */
+#endif
--- a/networking/Kbuild
+++ b/networking/Kbuild
@@ -28,6 +28,7 @@ lib-$(CONFIG_NC)           += nc.o
 lib-$(CONFIG_NETMSG)       += netmsg.o
 lib-$(CONFIG_NETSTAT)      += netstat.o
 lib-$(CONFIG_NSLOOKUP)     += nslookup.o
+lib-$(CONFIG_NTPD)         += ntpd.o
 lib-$(CONFIG_PING)         += ping.o
 lib-$(CONFIG_PING6)        += ping.o
 lib-$(CONFIG_PSCAN)        += pscan.o
