ntptimeset.c

网络时间协议NTP 源码 版本v4.2.0b 该源码用于linux平台下

	 * Make sure the server is at least somewhat sane.  If not, ignore
	 * it for later.
	 */
	if (L_ISZERO(&rec) || !L_ISHIS(&server->org, &rec)) {
		if (debug > 1)
			printf("receive: pkt insane\n");
		return;
	}

	/*
	 * Calculate the round trip delay (di) and the clock offset (ci).
	 * We use the equations (reordered from those in the spec):
	 *
	 * d = (t2 - t3) - (t1 - t0)
	 * c = ((t2 - t3) + (t1 - t0)) / 2
	 */
	t10 = server->org;		/* pkt.xmt == t1 */
	L_SUB(&t10, &rbufp->recv_time);	/* recv_time == t0*/

	t23 = rec;			/* pkt.rec == t2 */
	L_SUB(&t23, &org);		/* pkt->org == t3 */

	/* now have (t2 - t3) and (t0 - t1).  Calculate (ci) and (di) */
	ci = t10;
	L_ADD(&ci, &t23);
	L_RSHIFT(&ci);

	/*
	 * Calculate di in t23 in full precision, then truncate
	 * to an s_fp.
	 */
	L_SUB(&t23, &t10);
	di = LFPTOFP(&t23);

	if (debug > 3)
		printf("offset: %s, delay %s\n", lfptoa(&ci, 6), fptoa(di, 5));

	di += (FP_SECOND >> (-(int)NTPDATE_PRECISION))
	    + (FP_SECOND >> (-(int)server->precision)) + NTP_MAXSKW;

	if (di <= 0) {		/* value still too raunchy to use? */
		L_CLR(&ci);
		di = 0;
	} else {
		di = max(di, NTP_MINDIST);
	}


	/*
	 * This one is valid.  Give it to clock_filter(),
	 */
	clock_filter(server, di, &ci);
	if (debug > 1)
		printf("receive from %s\n", ntoa(&rbufp->srcadr));

	/*
	 * See if we should goes the transmission. If not return now
	 * otherwise have the next event time be shortened
	 */
	if (server->stratum <= NTP_INFIN)
	    return;	/* server does not have a stratum */
	if (server->leap == LEAP_NOTINSYNC)
	    return;	/* just booted server or out of sync */
	if (!L_ISHIS(&server->org, &server->reftime))
	    return;	/* broken host */
	if (server->trust != 0)
	    return;	/* can not trust it */

	if (server->dispersion < DESIREDDISP)
	    return;	/* we have the desired dispersion */

	server->event_time -= (TIMER_HZ+1);
}


/*
 * clock_filter - add clock sample, determine a server's delay, dispersion
 *                and offset
 */
static void
clock_filter(
	register struct server *server,
	s_fp di,
	l_fp *c
	)
{
	register int i, j;
	int ord[NTP_SHIFT];

	/*
	 * Insert sample and increment nextpt
	 */

	i = server->filter_nextpt;
	server->filter_delay[i] = di;
	server->filter_offset[i] = *c;
	server->filter_soffset[i] = LFPTOFP(c);
	server->filter_nextpt++;
	if (server->filter_nextpt >= NTP_SHIFT)
		server->filter_nextpt = 0;

	/*
	 * Sort indices into increasing delay order
	 */
	for (i = 0; i < NTP_SHIFT; i++)
		ord[i] = i;
	
	for (i = 0; i < (NTP_SHIFT-1); i++) {
		for (j = i+1; j < NTP_SHIFT; j++) {
			if (server->filter_delay[ord[j]] == 0)
				continue;
			if (server->filter_delay[ord[i]] == 0
			    || (server->filter_delay[ord[i]]
			    > server->filter_delay[ord[j]])) {
				register int tmp;

				tmp = ord[i];
				ord[i] = ord[j];
				ord[j] = tmp;
			}
		}
	}

	/*
	 * Now compute the dispersion, and assign values to delay and
	 * offset.  If there are no samples in the register, delay and
	 * offset go to zero and dispersion is set to the maximum.
	 */
	if (server->filter_delay[ord[0]] == 0) {
		server->delay = 0;
		L_CLR(&server->offset);
		server->soffset = 0;
		server->dispersion = PEER_MAXDISP;
	} else {
		register s_fp d;

		server->delay = server->filter_delay[ord[0]];
		server->offset = server->filter_offset[ord[0]];
		server->soffset = LFPTOFP(&server->offset);
		server->dispersion = 0;
		for (i = 1; i < NTP_SHIFT; i++) {
			if (server->filter_delay[ord[i]] == 0)
				d = PEER_MAXDISP;
			else {
				d = server->filter_soffset[ord[i]]
				    - server->filter_soffset[ord[0]];
				if (d < 0)
					d = -d;
				if (d > PEER_MAXDISP)
					d = PEER_MAXDISP;
			}
			/*
			 * XXX This *knows* PEER_FILTER is 1/2
			 */
			server->dispersion += (u_fp)(d) >> i;
		}
	}
	/*
	 * We're done
	 */
}


/* clock_count - count the clock sources we have
 */
static void
clock_count(void)
{
	register struct server *server;
	register int n;

	/* reset counts */
	validcount = valid_n_low = 0;

	/* go through the list of servers and count the clocks we believe
	 * and that have low dispersion
	 */
	for (n = 0; n < sys_numservers; n++) {
		server = sys_servers[n];
		if (server->delay == 0) {
			continue;	/* no data */
		}
		if (server->stratum > NTP_INFIN) {
			continue;	/* stratum no good */
		}
		if (server->delay > NTP_MAXWGT) {
			continue;	/* too far away */
		}
		if (server->leap == LEAP_NOTINSYNC)
			continue;	/* he's in trouble */
		if (!L_ISHIS(&server->org, &server->reftime)) {
			continue;	/* very broken host */
		}
		if ((server->org.l_ui - server->reftime.l_ui) >= NTP_MAXAGE) {
			continue;	/* too long without sync */
		}
		if (server->trust != 0) {
			continue;
		}

		/*
		 * This one is a valid time source..
		 */
		validcount++;

		/*
		 * See if this one has a okay low dispersion
		 */
		if (server->dispersion <= DESIREDDISP)
		    valid_n_low++;
	}

	if (debug > 1)
		printf("have %d, valid %d, low %d\n",
			responding, validcount, valid_n_low);
}


/*
 * clock_select - select the pick-of-the-litter clock from the samples
 *		  we've got.
 */
static struct server *
clock_select(void)
{
	register struct server *server;
	register int i;
	register int nlist;
	register s_fp d;
	register int j;
	register int n;
	s_fp local_threshold;
	struct server *server_list[NTP_MAXCLOCK];
	u_fp server_badness[NTP_MAXCLOCK];
	struct server *sys_server;

	/*
	 * This first chunk of code is supposed to go through all
	 * servers we know about to find the NTP_MAXLIST servers which
	 * are most likely to succeed.  We run through the list
	 * doing the sanity checks and trying to insert anyone who
	 * looks okay.  We are at all times aware that we should
	 * only keep samples from the top two strata and we only need
	 * NTP_MAXLIST of them.
	 */
	nlist = 0;	/* none yet */
	for (n = 0; n < sys_numservers; n++) {
		server = sys_servers[n];
		if (server->delay == 0)
			continue;	/* no data */
		if (server->stratum > NTP_INFIN)
			continue;	/* stratum no good */
		if (server->delay > NTP_MAXWGT) {
			continue;	/* too far away */
		}
		if (server->leap == LEAP_NOTINSYNC)
			continue;	/* he's in trouble */
		if (!L_ISHIS(&server->org, &server->reftime)) {
			continue;	/* very broken host */
		}
		if ((server->org.l_ui - server->reftime.l_ui)
		    >= NTP_MAXAGE) {
			continue;	/* too long without sync */
		}
		if (server->trust != 0) {
			continue;
		}

		/*
		 * This one seems sane.  Find where he belongs
		 * on the list.
		 */
		d = server->dispersion + server->dispersion;
		for (i = 0; i < nlist; i++)
			if (server->stratum <= server_list[i]->stratum)
				break;
		for ( ; i < nlist; i++) {
			if (server->stratum < server_list[i]->stratum)
				break;
			if (d < (s_fp) server_badness[i])
				break;
		}

		/*
		 * If i points past the end of the list, this
		 * guy is a loser, else stick him in.
		 */
		if (i >= NTP_MAXLIST)
			continue;
		for (j = nlist; j > i; j--)
			if (j < NTP_MAXLIST) {
				server_list[j] = server_list[j-1];
				server_badness[j]
				    = server_badness[j-1];
			}

		server_list[i] = server;
		server_badness[i] = d;
		if (nlist < NTP_MAXLIST)
			nlist++;
	}

	/*
	 * Got the five-or-less best.  Cut the list where the number of
	 * strata exceeds two.
	 */
	j = 0;
	for (i = 1; i < nlist; i++)
		if (server_list[i]->stratum > server_list[i-1]->stratum)
			if (++j == 2) {
				nlist = i;
				break;
			}

	/*
	 * Whew!  What we should have by now is 0 to 5 candidates for
	 * the job of syncing us.  If we have none, we're out of luck.
	 * If we have one, he's a winner.  If we have more, do falseticker
	 * detection.
	 */

	if (nlist == 0)
		sys_server = 0;
	else if (nlist == 1) {
		sys_server = server_list[0];
	} else {
		/*
		 * Re-sort by stratum, bdelay estimate quality and
		 * server.delay.
		 */
		for (i = 0; i < nlist-1; i++)
			for (j = i+1; j < nlist; j++) {
				if (server_list[i]->stratum
				    < server_list[j]->stratum)
					break;	/* already sorted by stratum */
				if (server_list[i]->delay
				    < server_list[j]->delay)
					continue;
				server = server_list[i];
				server_list[i] = server_list[j];
				server_list[j] = server;
			}
		
		/*
		 * Calculate the fixed part of the dispersion limit
		 */
		local_threshold = (FP_SECOND >> (-(int)NTPDATE_PRECISION))
		    + NTP_MAXSKW;

		/*
		 * Now drop samples until we're down to one.
		 */
		while (nlist > 1) {
			for (n = 0; n < nlist; n++) {
				server_badness[n] = 0;
				for (j = 0; j < nlist; j++) {
					if (j == n)	/* with self? */
						continue;
					d = server_list[j]->soffset
					    - server_list[n]->soffset;
					if (d < 0)	/* absolute value */
						d = -d;
					/*
					 * XXX This code *knows* that
					 * NTP_SELECT is 3/4
					 */
					for (i = 0; i < j; i++)
						d = (d>>1) + (d>>2);
					server_badness[n] += d;
				}
			}

			/*
			 * We now have an array of nlist badness
			 * coefficients.  Find the badest.  Find
			 * the minimum precision while we're at
			 * it.
			 */
			i = 0;
			n = server_list[0]->precision;;
			for (j = 1; j < nlist; j++) {
				if (server_badness[j] >= server_badness[i])
					i = j;
				if (n > server_list[j]->precision)
					n = server_list[j]->precision;
			}
			
			/*
			 * i is the index of the server with the worst
			 * dispersion.  If his dispersion is less than
			 * the threshold, stop now, else delete him and
			 * continue around again.
			 */
			if (server_badness[i] < (local_threshold
						 + (FP_SECOND >> (-n))))
				break;
			for (j = i + 1; j < nlist; j++)
				server_list[j-1] = server_list[j];
			nlist--;
		}

		/*
		 * What remains is a list of less than 5 servers.  Take
		 * the best.
		 */
		sys_server = server_list[0];
	}

	/*
	 * That's it.  Return our server.
	 */
	return sys_server;
}


/*
 * set_local_clock -- handle setting the local clock or displaying info.
 */
static void
set_local_clock(void)
{
	register int i;
	register struct server *server;
	time_t tmp;
	double dtemp;

	/*
	 * if setting time then print final analysis
	 */
	if (set_time)
	    analysis(1);

	/*
	 * pick a clock
	 */
	server = clock_select();

	/*
	 * do some display of information
	 */
	if (debug || verbose) {
		for (i = 0; i < sys_numservers; i++)
			printserver(sys_servers[i], stdout);
		if (debug)
			printf("packets sent %ld, received %ld\n",
				total_xmit, total_recv);
	}

	/*
	 * see if we have a server to set the time with
	 */
	if (server == 0) {
	    if (!set_time || verbose)
		fprintf(stdout,"No servers available to sync time with\n");
	    exit(1);
	}

	/*
	 * we have a valid and selected time to use!!!!!
	 */

	/*
	 * if we are not setting the time then display offset and exit
	 */
	if (!set_time) {
		fprintf(stdout,
			"Your clock is off by %s seconds. (%s) [%ld/%ld]\n",
			lfptoa(&server->offset, 7),
			ntoa(&server->srcadr),
			total_xmit, total_recv);
		exit(0);
	}

	/*
	 * set the clock
	 * XXX: Examine the more flexible approach used by ntpdate.
	 * Note that a design consideration here is that we sometimes
	 * _want_ to step the clock by a _huge_ amount in either
	 * direction, because the local clock is completely bogus.
	 * This condition must be recognized and dealt with, so
	 * that we always get a good time when this completes.
	 * -- [e-mail], 16-Aug-1999
	 */
	LFPTOD(&server->offset, dtemp);
	step_systime(dtemp);
	time(&tmp);
	fprintf(stdout,"Time set to %.20s [%s %s %ld/%ld]\n",
		ctime(&tmp)+4,
		ntoa(&server->srcadr),
		lfptoa(&server->offset, 7),
		total_xmit, total_recv);
	exit(0);
}


/*
 * findserver - find a server in the list given its address
 */
static struct server *
findserver(
	struct sockaddr_in *addr
	)
{
	register int i;
	register u_int32 netnum;

	if (htons(addr->sin_port) != NTP_PORT)
		return 0;
	netnum = addr->sin_addr.s_addr;

	for (i = 0; i < sys_numservers; i++) {
		if (netnum == sys_servers[i]->srcadr.sin_addr.s_addr)
			return sys_servers[i];
	}
	return 0;
}


/*
 * timer - process a timer interrupt
 */
static void
timer(void)
{
	register int k;

	/*
	 * Bump the current idea of the time
	 */
	current_time++;

	/*
	 * see if we have reached half time
	 */
	if (current_time >= half_time && !secondhalf) {
	    secondhalf++;
	    if (debug)
		printf("\nSecond Half of Timeout!\n");
	    printmsg++;
	}

	/*
	 * We only want to send a few packets per transmit interrupt