ntpd: ntpd.c -> ntpd_simple.c

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 1007 insertions, 0 deletions

diff --git a/networking/ntpd_simple.c b/networking/ntpd_simple.c
new file mode 100644
index 000000000..5e48306c7
--- /dev/null
+++ b/networking/ntpd_simple.c
@@ -0,0 +1,1007 @@
+/*
+ * NTP client/server, based on OpenNTPD 3.9p1
+ *
+ * Author: Adam Tkac <vonsch@gmail.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this tarball for details.
+ */
+#include "libbb.h"
+#include <netinet/ip.h> /* For IPTOS_LOWDELAY definition */
+#ifndef IPTOS_LOWDELAY
+# define IPTOS_LOWDELAY 0x10
+#endif
+#ifndef IP_PKTINFO
+# error "Sorry, your kernel has to support IP_PKTINFO"
+#endif
+
+
+/* Sync to peers every N secs */
+#define INTERVAL_QUERY_NORMAL    30
+#define INTERVAL_QUERY_PATHETIC  60
+#define INTERVAL_QUERY_AGRESSIVE  5
+
+/* Bad if *less than* TRUSTLEVEL_BADPEER */
+#define TRUSTLEVEL_BADPEER        6
+#define TRUSTLEVEL_PATHETIC       2
+#define TRUSTLEVEL_AGRESSIVE      8
+#define TRUSTLEVEL_MAX           10
+
+#define QSCALE_OFF_MIN         0.05
+#define QSCALE_OFF_MAX         0.50
+
+/* Single query might take N secs max */
+#define QUERYTIME_MAX            15
+/* Min offset for settime at start. "man ntpd" says it's 128 ms */
+#define STEPTIME_MIN_OFFSET   0.128
+
+typedef struct {
+	uint32_t int_partl;
+	uint32_t fractionl;
+} l_fixedpt_t;
+
+typedef struct {
+	uint16_t int_parts;
+	uint16_t fractions;
+} s_fixedpt_t;
+
+enum {
+	NTP_DIGESTSIZE     = 16,
+	NTP_MSGSIZE_NOAUTH = 48,
+	NTP_MSGSIZE        = (NTP_MSGSIZE_NOAUTH + 4 + NTP_DIGESTSIZE),
+};
+
+typedef struct {
+	uint8_t     m_status;     /* status of local clock and leap info */
+	uint8_t     m_stratum;    /* stratum level */
+	uint8_t     m_ppoll;      /* poll value */
+	int8_t      m_precision_exp;
+	s_fixedpt_t m_rootdelay;
+	s_fixedpt_t m_dispersion;
+	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;
+
+enum {
+	NTP_VERSION     = 4,
+	NTP_MAXSTRATUM  = 15,
+
+	/* 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 */
+};
+
+#define OFFSET_1900_1970 2208988800UL  /* 1970 - 1900 in seconds */
+
+typedef struct {
+	double   d_offset;
+	double   d_delay;
+	//UNUSED: double d_error;
+	time_t   d_rcv_time;
+	uint32_t d_refid4;
+	uint8_t  d_leap;
+	uint8_t  d_stratum;
+	uint8_t  d_good;
+} datapoint_t;
+
+#define NUM_DATAPOINTS  8
+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): */
+	time_t           next_action_time;
+	int              p_fd;
+	uint8_t          p_datapoint_idx;
+	uint8_t          p_trustlevel;
+	double           p_xmttime;
+	datapoint_t      update;
+	datapoint_t      p_datapoint[NUM_DATAPOINTS];
+	msg_t            p_xmt_msg;
+} peer_t;
+
+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_p = (1 << 4),
+	OPT_l = (1 << 5) * ENABLE_FEATURE_NTPD_SERVER,
+};
+
+
+struct globals {
+	/* 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;
+	llist_t  *ntp_peers;
+#if ENABLE_FEATURE_NTPD_SERVER
+	int      listen_fd;
+#endif
+	unsigned verbose;
+	unsigned peer_cnt;
+	unsigned scale;
+	uint32_t refid;
+	uint32_t refid4;
+	uint8_t  synced;
+	uint8_t  leap;
+#define G_precision_exp -6
+//	int8_t   precision_exp;
+	uint8_t  stratum;
+	uint8_t  time_was_stepped;
+	uint8_t  first_adj_done;
+};
+#define G (*ptr_to_globals)
+
+static const int const_IPTOS_LOWDELAY = IPTOS_LOWDELAY;
+
+
+static void
+set_next(peer_t *p, unsigned t)
+{
+	p->next_action_time = time(NULL) + t;
+}
+
+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->p_trustlevel = TRUSTLEVEL_PATHETIC;
+	p->next_action_time = time(NULL); /* = set_next(p, 0); */
+
+	llist_add_to(&G.ntp_peers, p);
+	G.peer_cnt++;
+}
+
+static double
+gettime1900d(void)
+{
+	struct timeval tv;
+	gettimeofday(&tv, NULL); /* never fails */
+	return (tv.tv_sec + 1.0e-6 * tv.tv_usec + OFFSET_1900_1970);
+}
+
+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;
+}
+
+#if 0 //UNUSED
+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;
+}
+#endif
+
+#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 unsigned
+error_interval(void)
+{
+	unsigned interval, r;
+	interval = INTERVAL_QUERY_PATHETIC * QSCALE_OFF_MAX / QSCALE_OFF_MIN;
+	r = (unsigned)random() % (unsigned)(interval / 10);
+	return (interval + r);
+}
+
+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 int
+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, INTERVAL_QUERY_PATHETIC);
+		return -1;
+	}
+
+	if (G.verbose)
+		bb_error_msg("sent query to %s", p->p_dotted);
+	set_next(p, QUERYTIME_MAX);
+
+	return 0;
+}
+
+
+/* Time is stepped only once, when the first packet from a peer is received.
+ */
+static void
+step_time_once(double offset)
+{
+	double dtime;
+	llist_t *item;
+	struct timeval tv;
+	char buf[80];
+	time_t tval;
+
+	if (G.time_was_stepped)
+		goto bail;
+	G.time_was_stepped = 1;
+
+	/* if the offset is small, don't step, slew (later) */
+	if (offset < STEPTIME_MIN_OFFSET && offset > -STEPTIME_MIN_OFFSET)
+		goto bail;
+
+	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);
+
+	for (item = G.ntp_peers; item != NULL; item = item->link) {
+		peer_t *p = (peer_t *) item->data;
+		p->next_action_time -= (time_t)offset;
+	}
+
+ bail:
+	if (option_mask32 & OPT_q)
+		exit(0);
+}
+
+
+/* Time is periodically slewed when we collect enough
+ * good data points.
+ */
+static int
+compare_offsets(const void *aa, const void *bb)
+{
+	const peer_t *const *a = aa;
+	const peer_t *const *b = bb;
+	if ((*a)->update.d_offset < (*b)->update.d_offset)
+		return -1;
+	return ((*a)->update.d_offset > (*b)->update.d_offset);
+}
+static unsigned
+updated_scale(double offset)
+{
+	if (offset < 0)
+		offset = -offset;
+	if (offset > QSCALE_OFF_MAX)
+		return 1;
+	if (offset < QSCALE_OFF_MIN)
+		return QSCALE_OFF_MAX / QSCALE_OFF_MIN;
+	return QSCALE_OFF_MAX / offset;
+}
+static void
+slew_time(void)
+{
+	llist_t *item;
+	double offset_median;
+	struct timeval tv;
+
+	{
+		peer_t **peers = xzalloc(sizeof(peers[0]) * G.peer_cnt);
+		unsigned goodpeer_cnt = 0;
+		unsigned middle;
+
+		for (item = G.ntp_peers; item != NULL; item = item->link) {
+			peer_t *p = (peer_t *) item->data;
+			if (p->p_trustlevel < TRUSTLEVEL_BADPEER)
+				continue;
+			if (!p->update.d_good) {
+				free(peers);
+				return;
+			}
+			peers[goodpeer_cnt++] = p;
+		}
+
+		if (goodpeer_cnt == 0) {
+			free(peers);
+			goto clear_good;
+		}
+
+		qsort(peers, goodpeer_cnt, sizeof(peers[0]), compare_offsets);
+
+		middle = goodpeer_cnt / 2;
+		if (middle != 0 && (goodpeer_cnt & 1) == 0) {
+			offset_median = (peers[middle-1]->update.d_offset + peers[middle]->update.d_offset) / 2;
+			G.rootdelay = (peers[middle-1]->update.d_delay + peers[middle]->update.d_delay) / 2;
+			G.stratum = 1 + MAX(peers[middle-1]->update.d_stratum, peers[middle]->update.d_stratum);
+		} else {
+			offset_median = peers[middle]->update.d_offset;
+			G.rootdelay = peers[middle]->update.d_delay;
+			G.stratum = 1 + peers[middle]->update.d_stratum;
+		}
+		G.leap = peers[middle]->update.d_leap;
+		G.refid4 = peers[middle]->update.d_refid4;
+		G.refid =
+#if ENABLE_FEATURE_IPV6
+			peers[middle]->p_lsa->u.sa.sa_family != AF_INET ?
+				G.refid4 :
+#endif
+				peers[middle]->p_lsa->u.sin.sin_addr.s_addr;
+		free(peers);
+	}
+//TODO: if (offset_median > BIG) step_time(offset_median)?
+
+	G.scale = updated_scale(offset_median);
+
+	bb_error_msg("adjusting clock by %fs, our stratum is %u, time scale %u",
+			offset_median, G.stratum, G.scale);
+
+	errno = 0;
+	d_to_tv(offset_median, &tv);
+	if (adjtime(&tv, &tv) == -1)
+		bb_perror_msg_and_die("adjtime failed");
+	if (G.verbose >= 2)
+		bb_error_msg("old adjust: %d.%06u", (int)tv.tv_sec, (unsigned)tv.tv_usec);
+
+	if (G.first_adj_done) {
+		uint8_t synced = (tv.tv_sec == 0 && tv.tv_usec == 0);
+		if (synced != G.synced) {
+			G.synced = synced;
+			bb_error_msg("clock is %ssynced", synced ? "" : "un");
+		}
+	}
+	G.first_adj_done = 1;
+
+	G.reftime = gettime1900d();
+
+ clear_good:
+	for (item = G.ntp_peers; item != NULL; item = item->link) {
+		peer_t *p = (peer_t *) item->data;
+		p->update.d_good = 0;
+	}
+}
+
+static void
+update_peer_data(peer_t *p)
+{
+	/* Clock filter.
+	 * Find the datapoint with the lowest delay.
+	 * Use that as the peer update.
+	 * Invalidate it and all older ones.
+	 */
+	int i;
+	int best = -1;
+	int good = 0;
+
+	for (i = 0; i < NUM_DATAPOINTS; i++) {
+		if (p->p_datapoint[i].d_good) {
+			good++;
+			if (best < 0 || p->p_datapoint[i].d_delay < p->p_datapoint[best].d_delay)
+				best = i;
+		}
+	}
+
+	if (good < 8) //FIXME: was it meant to be NUM_DATAPOINTS, not 8?
+		return;
+
+	p->update = p->p_datapoint[best]; /* struct copy */
+	slew_time();
+
+	for (i = 0; i < NUM_DATAPOINTS; i++)
+		if (p->p_datapoint[i].d_rcv_time <= p->p_datapoint[best].d_rcv_time)
+			p->p_datapoint[i].d_good = 0;
+}
+
+static unsigned
+scale_interval(unsigned requested)
+{
+	unsigned interval, r;
+	interval = requested * G.scale;
+	r = (unsigned)random() % (unsigned)(MAX(5, interval / 10));
+	return (interval + r);
+}
+static void
+recv_and_process_peer_pkt(peer_t *p)
+{
+	ssize_t     size;
+	msg_t       msg;
+	double      T1, T2, T3, T4;
+	unsigned    interval;
+	datapoint_t *datapoint;
+
+	/* 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?
+			set_next(p, error_interval());
+			goto 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 = error_interval();
+		bb_error_msg("reply from %s: not synced, next query in %us", p->p_dotted, interval);
+		goto close_sock;
+	}
+
+	/*
+	 * 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 = gettime1900d();
+
+	datapoint = &p->p_datapoint[p->p_datapoint_idx];
+
+	datapoint->d_offset = ((T2 - T1) + (T3 - T4)) / 2;
+	datapoint->d_delay = (T4 - T1) - (T3 - T2);
+	if (datapoint->d_delay < 0) {
+		bb_error_msg("reply from %s: negative delay %f", p->p_dotted, datapoint->d_delay);
+		interval = error_interval();
+		set_next(p, interval);
+		goto close_sock;
+	}
+	//UNUSED: datapoint->d_error = (T2 - T1) - (T3 - T4);
+	datapoint->d_rcv_time = (time_t)(T4 - OFFSET_1900_1970); /* = time(NULL); */
+	datapoint->d_good = 1;
+
+	datapoint->d_leap = (msg.m_status & LI_MASK);
+	//UNUSED: datapoint->o_precision = msg.m_precision_exp;
+	//UNUSED: datapoint->o_rootdelay = sfp_to_d(msg.m_rootdelay);
+	//UNUSED: datapoint->o_rootdispersion = sfp_to_d(msg.m_dispersion);
+	//UNUSED: datapoint->d_refid = ntohl(msg.m_refid);
+	datapoint->d_refid4 = msg.m_xmttime.fractionl;
+	//UNUSED: datapoint->o_reftime = lfp_to_d(msg.m_reftime);
+	//UNUSED: datapoint->o_poll = msg.m_ppoll;
+	datapoint->d_stratum = msg.m_stratum;
+
+	if (p->p_trustlevel < TRUSTLEVEL_PATHETIC)
+		interval = scale_interval(INTERVAL_QUERY_PATHETIC);
+	else if (p->p_trustlevel < TRUSTLEVEL_AGRESSIVE)
+		interval = scale_interval(INTERVAL_QUERY_AGRESSIVE);
+	else
+		interval = scale_interval(INTERVAL_QUERY_NORMAL);
+
+	set_next(p, interval);
+
+	/* Every received reply which we do not discard increases trust */
+	if (p->p_trustlevel < TRUSTLEVEL_MAX) {
+		p->p_trustlevel++;
+		if (p->p_trustlevel == TRUSTLEVEL_BADPEER)
+			bb_error_msg("peer %s now valid", p->p_dotted);
+	}
+
+	if (G.verbose)
+		bb_error_msg("reply from %s: offset %f delay %f, next query in %us", p->p_dotted,
+			datapoint->d_offset, datapoint->d_delay, interval);
+
+	update_peer_data(p);
+//TODO: do it after all peers had a chance to return at least one reply?
+	step_time_once(datapoint->d_offset);
+
+	p->p_datapoint_idx++;
+	if (p->p_datapoint_idx >= NUM_DATAPOINTS)
+		p->p_datapoint_idx = 0;
+
+ close_sock:
+	/* 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 void
+recv_and_process_client_pkt(void /*int fd*/)
+{
+	ssize_t          size;
+	uint8_t          version;
+	double           rectime;
+	len_and_sockaddr *to;
+	struct sockaddr  *from;
+	msg_t            msg;
+	uint8_t          query_status;
+	uint8_t          query_ppoll;
+	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_ppoll = msg.m_ppoll;
+	query_xmttime = msg.m_xmttime;
+
+	/* Build a reply packet */
+	memset(&msg, 0, sizeof(msg));
+	msg.m_status = G.synced ? G.leap : 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 = query_ppoll;
+	msg.m_precision_exp = G_precision_exp;
+	rectime = gettime1900d();
+	msg.m_xmttime = msg.m_rectime = d_to_lfp(rectime);
+	msg.m_reftime = d_to_lfp(G.reftime);
+	//msg.m_xmttime = d_to_lfp(gettime1900d()); // = msg.m_rectime
+	msg.m_orgtime = query_xmttime;
+	msg.m_rootdelay = d_to_sfp(G.rootdelay);
+	version = (query_status & VERSION_MASK); /* ... >> VERSION_SHIFT - done below instead */
+	msg.m_refid = (version > (3 << VERSION_SHIFT)) ? G.refid4 : G.refid;
+
+	/* 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(bb_msg_you_must_be_root);
+
+	peers = NULL;
+	opt_complementary = "dd:p::"; /* d: counter, p: list */
+	opts = getopt32(argv,
+			"nqNx" /* compat */
+			"p:"IF_FEATURE_NTPD_SERVER("l") /* NOT compat */
+			"d" /* compat */
+			"46aAbgL", /* compat, ignored */
+			&peers, &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;
+	while (peers)
+		add_peers(llist_pop(&peers));
+	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);
+
+	/* Set some globals */
+#if 0
+	/* With constant b = 100, G.precision_exp is also constant -6.
+	 * Uncomment this and you'll see */
+	{
+		int prec = 0;
+		int b;
+# if 0
+		struct timespec	tp;
+		/* We can use sys_clock_getres but assuming 10ms tick should be fine */
+		clock_getres(CLOCK_REALTIME, &tp);
+		tp.tv_sec = 0;
+		tp.tv_nsec = 10000000;
+		b = 1000000000 / tp.tv_nsec;  /* convert to Hz */
+# else
+		b = 100; /* b = 1000000000/10000000 = 100 */
+# endif
+		while (b > 1)
+			prec--, b >>= 1;
+		//G.precision_exp = prec;
+		bb_error_msg("G.precision_exp:%d", prec); /* -6 */
+	}
+#endif
+	G.scale = 1;
+
+	bb_signals((1 << SIGTERM) | (1 << SIGINT), record_signo);
+	bb_signals((1 << SIGPIPE) | (1 << SIGHUP), SIG_IGN);
+}
+
+int ntpd_main(int argc UNUSED_PARAM, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int ntpd_main(int argc UNUSED_PARAM, char **argv)
+{
+	struct globals g;
+	struct pollfd *pfd;
+	peer_t **idx2peer;
+
+	memset(&g, 0, sizeof(g));
+	SET_PTR_TO_GLOBALS(&g);
+
+	ntp_init(argv);
+
+	{
+		/* if ENABLE_FEATURE_NTPD_SERVER, + 1 for listen_fd: */
+		unsigned cnt = g.peer_cnt + ENABLE_FEATURE_NTPD_SERVER;
+		idx2peer = xzalloc(sizeof(idx2peer[0]) * cnt);
+		pfd = xzalloc(sizeof(pfd[0]) * cnt);
+	}
+
+	while (!bb_got_signal) {
+		llist_t *item;
+		unsigned i, j;
+		unsigned sent_cnt, trial_cnt;
+		int nfds, timeout;
+		time_t cur_time, nextaction;
+
+		/* Nothing between here and poll() blocks for any significant time */
+
+		cur_time = time(NULL);
+		nextaction = 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 */
+		sent_cnt = trial_cnt = 0;
+		for (item = g.ntp_peers; item != NULL; item = item->link) {
+			peer_t *p = (peer_t *) item->data;
+
+			/* Overflow-safe "if (p->next_action_time <= cur_time) ..." */
+			if ((int)(cur_time - p->next_action_time) >= 0) {
+				if (p->p_fd == -1) {
+					/* Time to send new req */
+					trial_cnt++;
+					if (send_query_to_peer(p) == 0)
+						sent_cnt++;
+				} else {
+					/* Timed out waiting for reply */
+					close(p->p_fd);
+					p->p_fd = -1;
+					timeout = error_interval();
+					bb_error_msg("timed out waiting for %s, "
+							"next query in %us", p->p_dotted, timeout);
+					if (p->p_trustlevel >= TRUSTLEVEL_BADPEER) {
+						p->p_trustlevel /= 2;
+						if (p->p_trustlevel < TRUSTLEVEL_BADPEER)
+							bb_error_msg("peer %s now invalid", p->p_dotted);
+					}
+					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++;
+			}
+		}
+
+		if ((trial_cnt > 0 && sent_cnt == 0) || g.peer_cnt == 0)
+			step_time_once(0); /* no good peers, don't wait */
+
+		timeout = nextaction - cur_time;
+		if (timeout < 1)
+			timeout = 1;
+
+		/* Here we may block */
+		if (g.verbose >= 2)
+			bb_error_msg("poll %us, sockets:%u", timeout, i);
+		nfds = poll(pfd, i, timeout * 1000);
+		if (nfds <= 0)
+			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*/);
+			}
+			j = 1;
+		}
+#endif
+		for (; nfds != 0 && j < i; j++) {
+			if (pfd[j].revents /* & (POLLIN|POLLERR)*/) {
+				nfds--;
+				recv_and_process_peer_pkt(idx2peer[j]);
+			}
+		}
+	} /* while (!bb_got_signal) */
+
+	kill_myself_with_sig(bb_got_signal);
+}