NETWORK TIME PROTOCOL SOURCE CODE

[feiutm9898]

I did't found source code for NTP.

Can someone guide me????? Thanks........

 

[dainis]

I did't found source code for NTP.

Can someone guide me????? Thanks........

**broken link removed**

 

[feiutm9898]

Hi dainis.

Thanks very much!

I still don't know how to search and get the source code.

Can U give me the link can direct search the linux source code?

Can give some useful link?

Thanks again........

 

[dainis]

It is very simple:
Open google.com and enter serch string, look results (first page), if not good results, change search string.
For NTP source, I first try "ntp", next iteration "ntp.c" .....

 

[adscrz]

/* $OpenBSD: ntp.c,v 1.15 2004/02/16 21:25:41 jakob Exp $ */

/*
* Copyright (c) 1996, 1997 by N.M. Maclaren. All rights reserved.
* Copyright (c) 1996, 1997 by University of Cambridge. All rights reserved.
* Copyright (c) 2002 by Thorsten "mirabile" Glaser.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the author nor the university may be used to
* endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

#include <sys/param.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <float.h>
#include <limits.h>
#include <math.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#include "ntpleaps.h"

/*
* NTP definitions. Note that these assume 8-bit bytes - sigh. There
* is little point in parameterising everything, as it is neither
* feasible nor useful. It would be very useful if more fields could
* be defined as unspecified. The NTP packet-handling routines
* contain a lot of extra assumptions.
*/

#define JAN_1970 2208988800.0 /* 1970 - 1900 in seconds */
#define NTP_SCALE 4294967296.0 /* 2^32, of course! */

#define NTP_MODE_CLIENT 3 /* NTP client mode */
#define NTP_MODE_SERVER 4 /* NTP server mode */
#define NTP_VERSION 3 /* The current version */
#define NTP_VERSION_MIN 1 /* The minum valid version */
#define NTP_VERSION_MAX 4 /* The maximum valid version */
#define NTP_STRATUM_MIN 1 /* The minum valid stratum */
#define NTP_STRATUM_MAX 15 /* The maximum valid stratum */
#define NTP_INSANITY 3600.0 /* Errors beyond this are hopeless */

#define NTP_PACKET_MIN 48 /* Without authentication */
#define NTP_PACKET_MAX 68 /* With authentication (ignored) */

#define NTP_DISP_FIELD 8 /* Offset of dispersion field */
#define NTP_REFERENCE 16 /* Offset of reference timestamp */
#define NTP_ORIGINATE 24 /* Offset of originate timestamp */
#define NTP_RECEIVE 32 /* Offset of receive timestamp */
#define NTP_TRANSMIT 40 /* Offset of transmit timestamp */

#define MAX_QUERIES 25
#define MAX_DELAY 15

#define MILLION_L 1000000l /* For conversion to/from timeval */
#define MILLION_D 1.0e6 /* Must be equal to MILLION_L */

struct ntp_data {
u_char status;
u_char version;
u_char mode;
u_char stratum;
u_char polling;
u_char precision;
double dispersion;
double reference;
double originate;
double receive;
double transmit;
double current;
};

void ntp_client(const char *, int, struct timeval *, struct timeval *, int);
int sync_ntp(int, const struct sockaddr *, double *, double *);
void make_packet(struct ntp_data *);
int write_packet(int, const struct sockaddr *, struct ntp_data *);
int read_packet(int, struct ntp_data *, double *, double *, double *);
void pack_ntp(u_char *, int, struct ntp_data *);
void unpack_ntp(struct ntp_data *, u_char *, int);
double current_time(double);
void create_timeval(double, struct timeval *, struct timeval *);

int corrleaps;

void
ntp_client(const char *hostname, int family, struct timeval *new,
struct timeval *adjust, int leapflag)
{
struct addrinfo hints, *res0, *res;
double offset, error;
int packets = 0, s, ierror;

memset(&hints, 0, sizeof(hints));
hints.ai_family = family;
hints.ai_socktype = SOCK_DGRAM;
ierror = getaddrinfo(hostname, "ntp", &hints, &res0);
if (ierror) {
errx(1, "%s: %s", hostname, gai_strerror(ierror));
/*NOTREACHED*/
}

corrleaps = leapflag;
if (corrleaps)
ntpleaps_init();

s = -1;
for (res = res0; res; res = res->ai_next) {
s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
if (s < 0)
continue;

packets = sync_ntp(s, res->ai_addr, &offset, &error);
if (packets == 0) {
#ifdef DEBUG
fprintf(stderr, "try the next address\n");
#endif
close(s);
s = -1;
continue;
}
if (error > NTP_INSANITY) {
/* should we try the next address instead? */
errx(1, "Unable to get a reasonable time estimate");
}
break;
}
freeaddrinfo(res0);

#ifdef DEBUG
fprintf(stderr,"Correction: %.6f +/- %.6f\n", offset,error);
#endif

create_timeval(offset, new, adjust);
}

int
sync_ntp(int fd, const struct sockaddr *peer, double *offset, double *error)
{
int attempts = 0, accepts = 0, rejects = 0;
int delay = MAX_DELAY;
double deadline;
double a, b, x, y;
double minerr = 0.1; /* Maximum ignorable variation */
double dispersion = 0.0; /* The source dispersion in seconds */
struct ntp_data data;

deadline = current_time(JAN_1970) + delay;
*offset = 0.0;
*error = NTP_INSANITY;

while (accepts < MAX_QUERIES && attempts < 2 * MAX_QUERIES) {
if (current_time(JAN_1970) > deadline)
errx(1, "Not enough valid responses received in time");

make_packet(&data);
write_packet(fd, peer, &data);

if (read_packet(fd, &data, &x, &y, &dispersion)) {
if (++rejects > MAX_QUERIES)
errx(1, "Too many bad or lost packets");
else
continue;
} else
++accepts;

#ifdef DEBUG
fprintf(stderr,"Offset: %.6f +/- %.6f disp=%.6f\n",
x, y, dispersion);
#endif

if ((a = x - *offset) < 0.0)
a = -a;
if (accepts <= 1)
a = 0.0;
b = *error + y;
if (y < *error) {
*offset = x;
*error = y;
}

#ifdef DEBUG
fprintf(stderr,"Best: %.6f +/- %.6f\n", *offset, *error);
#endif

if (a > b)
errx(1, "Inconsistent times received from NTP server");

if (*error <= minerr)
break;
}

return accepts;
}

/* Create an outgoing NTP packet */
void
make_packet(struct ntp_data *data)
{
data->status = 0;
data->version = NTP_VERSION;
data->mode = NTP_MODE_CLIENT;
data->stratum = 0;
data->polling = 0;
data->precision = 0;
data->reference = data->dispersion = 0.0;
data->receive = data->originate = 0.0;
data->current = data->transmit = current_time(JAN_1970);
}

int
write_packet(int fd, const struct sockaddr *peer, struct ntp_data *data)
{
u_char transmit[NTP_PACKET_MIN];
int length;

pack_ntp(transmit, NTP_PACKET_MIN, data);
length = sendto(fd, transmit, NTP_PACKET_MIN, 0, peer, SA_LEN(peer));
if (length <= 0) {
warnx("Unable to send NTP packet to server");
return 1;
}

return 0;
}

/*
* Check the packet and work out the offset and optionally the error.
* Note that this contains more checking than xntp does. Return 0 for
* success, 1 for failure. Note that it must not change its arguments
* if it fails.
*/
int
read_packet(int fd, struct ntp_data *data, double *off, double *error,
double *dispersion)
{
u_char receive[NTP_PACKET_MAX+1];
double delay1, delay2, x, y;
int length, r;
fd_set *rfds;
struct timeval tv;

rfds = (fd_set *)calloc(howmany(fd + 1, NFDBITS), sizeof(fd_mask));
if (!rfds) {
warnx("calloc() failed");
return 1;
}

FD_SET(fd, rfds);

retry:
tv.tv_sec = 0;
tv.tv_usec = 1000000 * MAX_DELAY / MAX_QUERIES;

r = select(fd + 1, rfds, NULL, NULL, &tv);
if (r < 1 || !FD_ISSET(fd, rfds)) {
if (r < 0) {
if (errno == EINTR)
goto retry;
else
warnx("select() failed");
}
free(rfds);
return 1;
}
free(rfds);

length = recvfrom(fd, receive, NTP_PACKET_MAX + 1, 0, NULL, 0);
if (length < 0) {
warnx("Unable to receive NTP packet from server");
return 1;
}

if (length < NTP_PACKET_MIN || length > NTP_PACKET_MAX) {
warnx("Invalid NTP packet size, packet reject");
return 1;
}

unpack_ntp(data, receive, length);

if (data->version < NTP_VERSION_MIN ||
data->version > NTP_VERSION_MAX) {
warnx("Invalid NTP version, packet rejected");
return 1;
}

if (data->mode != NTP_MODE_SERVER) {
warnx("Invalid NTP server mode, packet rejected");
return 1;
}

/*
* Note that the conventions are very poorly defined in the NTP
* protocol, so we have to guess. Any full NTP server perpetrating
* completely unsynchronised packets is an abomination, anyway, so
* reject it.
*/
delay1 = data->transmit - data->receive;
delay2 = data->current - data->originate;

if (data->reference == 0.0 ||
data->transmit == 0.0 ||
data->receive == 0.0 ||
(data->reference != 0.0 && data->receive < data->reference) ||
delay1 < 0.0 ||
delay1 > NTP_INSANITY ||
delay2 < 0.0 ||
delay2 > NTP_INSANITY ||
data->dispersion > NTP_INSANITY) {
warnx("Incomprehensible NTP packet rejected");
return 1;
}

if (*dispersion < data->dispersion)
*dispersion = data->dispersion;

x = data->receive - data->originate;
y = (data->transmit == 0.0 ? 0.0 : data->transmit-data->current);
*off = 0.5*(x+y);
*error = x-y;
x = data->current - data->originate;
if (0.5*x > *error)
*error = 0.5*x;

return 0;
}

/*
* Pack the essential data into an NTP packet, bypassing struct layout
* and endian problems. Note that it ignores fields irrelevant to
* SNTP.
*/
void
pack_ntp(u_char *packet, int length, struct ntp_data *data)
{
int i, k;
double d;

memset(packet,0, (size_t)length);

packet[0] = (data->status<<6)|(data->version<<3)|data->mode;
packet[1] = data->stratum;
packet[2] = data->polling;
packet[3] = data->precision;

d = data->originate/NTP_SCALE;
for (i = 0; i < 8; ++i) {
if ((k = (int)(d *= 256.0)) >= 256) k = 255;
packet[NTP_ORIGINATE+i] = k;
d -= k;
}

d = data->receive/NTP_SCALE;
for (i = 0; i < 8; ++i) {
if ((k = (int)(d *= 256.0)) >= 256) k = 255;
packet[NTP_RECEIVE+i] = k;
d -= k;
}

d = data->transmit/NTP_SCALE;
for (i = 0; i < 8; ++i) {
if ((k = (int)(d *= 256.0)) >= 256) k = 255;
packet[NTP_TRANSMIT+i] = k;
d -= k;
}
}

/*
* Unpack the essential data from an NTP packet, bypassing struct
* layout and endian problems. Note that it ignores fields irrelevant
* to SNTP.
*/
void
unpack_ntp(struct ntp_data *data, u_char *packet, int length)
{
int i;
double d;

data->current = current_time(JAN_1970);

data->status = (packet[0] >> 6);
data->version = (packet[0] >> 3)&0x07;
data->mode = packet[0]&0x07;
data->stratum = packet[1];
data->polling = packet[2];
data->precision = packet[3];

for (i = 0, d = 0.0; i < 4; ++i)
d = 256.0*d+packet[NTP_DISP_FIELD+i];
data->dispersion = d/65536.0;

for (i = 0, d = 0.0; i < 8; ++i)
d = 256.0*d+packet[NTP_REFERENCE+i];
data->reference = d/NTP_SCALE;

for (i = 0, d = 0.0; i < 8; ++i)
d = 256.0*d+packet[NTP_ORIGINATE+i];
data->originate = d/NTP_SCALE;

for (i = 0, d = 0.0; i < 8; ++i)
d = 256.0*d+packet[NTP_RECEIVE+i];
data->receive = d/NTP_SCALE;

for (i = 0, d = 0.0; i < 8; ++i)
d = 256.0*d+packet[NTP_TRANSMIT+i];
data->transmit = d/NTP_SCALE;
}

/*
* Get the current UTC time in seconds since the Epoch plus an offset
* (usually the time from the beginning of the century to the Epoch)
*/
double
current_time(double offset)
{
struct timeval current;
u_int64_t t;

if (gettimeofday(&current, NULL))
err(1, "Could not get local time of day");

/*
* At this point, current has the current TAI time.
* Now subtract leap seconds to set the posix tick.
*/

t = SEC_TO_TAI64(current.tv_sec);
if (corrleaps)
ntpleaps_sub(&t);

return offset + TAI64_TO_SEC(t) + 1.0e-6 * current.tv_usec;
}

/*
* Change offset into current UTC time. This is portable, even if
* struct timeval uses an unsigned long for tv_sec.
*/
void
create_timeval(double difference, struct timeval *new, struct timeval *adjust)
{
struct timeval old;
long n;

/* Start by converting to timeval format. Note that we have to
* cater for negative, unsigned values. */
if ((n = (long) difference) > difference)
--n;
adjust->tv_sec = n;
adjust->tv_usec = (long) (MILLION_D * (difference-n));
errno = 0;
if (gettimeofday(&old, NULL))
err(1, "Could not get local time of day");
new->tv_sec = old.tv_sec + adjust->tv_sec;
new->tv_usec = (n = (long) old.tv_usec + (long) adjust->tv_usec);

if (n < 0) {
new->tv_usec += MILLION_L;
--new->tv_sec;
} else if (n >= MILLION_L) {
new->tv_usec -= MILLION_L;
++new->tv_sec;
}
}

#ifdef DEBUG
void
print_packet(const struct ntp_data *data)
{
printf("status: %u\n", data->status);
printf("version: %u\n", data->version);
printf("mode: %u\n", data->mode);
printf("stratum: %u\n", data->stratum);
printf("polling: %u\n", data->polling);
printf("precision: %u\n", data->precision);
printf("dispersion: %e\n", data->dispersion);
printf("reference: %e\n", data->reference);
printf("originate: %e\n", data->originate);
printf("receive: %e\n", data->receive);
printf("transmit: %e\n", data->transmit);
printf("current: %e\n", data->current);
};
#endif