Utility for setting RTC based on gpsd time
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/* gps-wd - small utility to restart gpsd if no data is received
* (C) 2013-2015 by sysmocom - s.f.m.c. GmbH, Author: Harald Welte
* All Rights Reserved
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
/* The idea of this program is that you run it once at system boot time,
* to set the local RTC to the time received by GPS. Further synchronization
* during system runtime is then handled by ntpd, interfacing with gpsd using
* the ntp shared memory protocol.
*
* However, ntpd is unable to accept a GPS time that's off by more than four
* hours from the system RTC, so initial synchronization has to be done
* externally. 'ntpdate' is the usual option, but doesn't work if you're
* offline. Thus, this gpsdate utilith was created to fill the gap.
*/
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <syslog.h>
#include <getopt.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <gps.h>
#define NUM_RETRIES 60 /* Number of gpsd re-connects */
#define RETRY_SLEEP 1 /* Seconds to sleep between re-connects */
#define TIMEOUT 10 /* max Number of seconds without sentence */
static int no_detach = 0;
static int timeout = TIMEOUT;
static struct gps_data_t gpsdata;
static char *service_name = "gpsd.service";
static void callback(struct gps_data_t *gpsdata)
{
/* we received some data but gpsd itself believes the receiver
* to be offline */
if (gpsdata->online == 0)
return;
/* re-set the alarm to the timeout */
alarm(timeout);
}
static int osmo_daemonize(void)
{
int rc;
pid_t pid, sid;
/* Check if parent PID == init, in which case we are already a daemon */
if (getppid() == 1)
return -EEXIST;
/* Fork from the parent process */
pid = fork();
if (pid < 0) {
/* some error happened */
return pid;
}
if (pid > 0) {
/* if we have received a positive PID, then we are the parent
* and can exit */
exit(0);
}
/* FIXME: do we really want this? */
umask(0);
/* Create a new session and set process group ID */
sid = setsid();
if (sid < 0)
return sid;
/* Change to the /tmp directory, which prevents the CWD from being locked
* and unable to remove it */
rc = chdir("/tmp");
if (rc < 0)
return rc;
/* Redirect stdio to /dev/null */
/* since C89/C99 says stderr is a macro, we can safely do this! */
#ifdef stderr
freopen("/dev/null", "r", stdin);
freopen("/dev/null", "w", stdout);
freopen("/dev/null", "w", stderr);
#endif
return 0;
}
/* local copy, as the libgps official version ignores gps_read() result */
static int my_gps_mainloop(struct gps_data_t *gdata,
int timeout,
void (*hook)(struct gps_data_t *gdata))
{
int rc;
for (;;) {
if (!gps_waiting(gdata, timeout)) {
return -1;
} else {
rc = gps_read(gdata);
if (rc < 0)
return rc;
(*hook)(gdata);
}
}
return 0;
}
static int attempt_reconnect(const char *host, const char *port,
struct gps_data_t *gpsdata)
{
int rc;
rc = gps_open(host, port, gpsdata);
if (rc)
return -1;
syslog(LOG_INFO, "(re)connected to gpsd\n");
gps_stream(gpsdata, WATCH_ENABLE|WATCH_JSON, NULL);
return 0;
}
enum state {
S_CONNECTED,
S_RECONNECT,
};
static void alarm_hdlr(int signal)
{
char buf[256];
if (signal != SIGALRM)
return;
/* the timeout has expired. restart gpsd */
syslog(LOG_ERR, "%d seconds without data from gpsd, "
"stopping gpsd\n", timeout);
snprintf(buf, sizeof(buf), "systemctl kill %s", service_name);
system(buf);
exit(EXIT_FAILURE);
}
int main(int argc, char **argv)
{
char *host = "localhost";
char *port = DEFAULT_GPSD_PORT;
int num_retries = NUM_RETRIES;
int retry_sleep = RETRY_SLEEP;
int i, rc;
enum state state;
openlog("gps-wd", LOG_PERROR, LOG_CRON);
while (1) {
int option_index = 0, c;
static struct option long_options[] = {
{"num-retries", 1, 0, 'n'},
{"retry-sleep", 1, 0, 's'},
{"no-detach", 0, 0, 'd'},
{"timeout", 1, 0, 't'},
{"service-name", 1, 0, 'r'},
{0,0,0,0}
};
c = getopt_long(argc, argv, "n:s:dt:r:",
long_options, &option_index);
if (c == -1)
break;
switch (c) {
case 'n':
num_retries = atoi(optarg);
break;
case 's':
retry_sleep = atoi(optarg);
break;
case 'd':
no_detach = 1;
break;
case 't':
timeout = atoi(optarg);
break;
case 'r':
service_name = optarg;
break;
}
}
if (optind < argc)
host = argv[optind++];
if (optind < argc)
port = argv[optind++];
syslog(LOG_INFO, "starting gps-wd for %s:%s (timeout %ds, service %s)",
host, port, timeout, service_name);
/* attempt up to NUM_RETRIES times to connect to gpsd while we are
* still running in foreground. The idea is that we will block the
* boot process (init scripts) until we have a connection */
for (i = 1; i <= num_retries; i++) {
printf("Attempt #%d to connect to gpsd at %s...\n", i, host);
rc = attempt_reconnect(host, port, &gpsdata);
if (rc >= 0)
break;
sleep(retry_sleep);
}
if (rc < 0) {
syslog(LOG_ERR, "no gpsd running or network error: %d, %s\n",
errno, gps_errstr(errno));
closelog();
exit(EXIT_FAILURE);
}
state = S_CONNECTED;
if (!no_detach)
osmo_daemonize();
signal(SIGALRM, alarm_hdlr);
/* We run in an endless loop. The only reasonable way to exit is after
* a correct GPS timestamp has been received in callback() */
while (1) {
switch (state) {
case S_CONNECTED:
alarm(timeout);
rc = my_gps_mainloop(&gpsdata, INT_MAX, callback);
if (rc < 1) {
syslog(LOG_ERR, "connection to gpsd was "
"closed: %d, reconnecting\n", rc);
gps_close(&gpsdata);
alarm(0);
state = S_RECONNECT;
}
break;
case S_RECONNECT:
rc = attempt_reconnect(host, port, &gpsdata);
if (rc < 0)
sleep(RETRY_SLEEP);
else
state = S_CONNECTED;
break;
}
}
gps_close(&gpsdata);
closelog();
exit(EXIT_SUCCESS);
}