165 lines
4.1 KiB
C
165 lines
4.1 KiB
C
/* gpsdate - small utility to set system RTC based on gpsd time
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* (C) 2013 by sysmocom - s.f.m.c. GmbH, Author: Harald Welte
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* All Rights Reserved
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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/* The idea of this program is that you run it once at system boot time,
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* to set the local RTC to the time received by GPS. Further synchronization
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* during system runtime is then handled by ntpd, interfacing with gpsd using
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* the ntp shared memory protocol.
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*
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* However, ntpd is unable to accept a GPS time that's off by more than four
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* hours from the system RTC, so initial synchronization has to be done
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* externally. 'ntpdate' is the usual option, but doesn't work if you're
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* offline. Thus, this gpsdate utilith was created to fill the gap.
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <errno.h>
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#include <unistd.h>
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#include <string.h>
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#include <syslog.h>
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#include <sys/time.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <gps.h>
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#define NUM_RETRIES 60 /* Number of gpsd re-connects */
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#define RETRY_SLEEP 1 /* Seconds to sleep between re-connects */
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static struct gps_data_t gpsdata;
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static void callback(struct gps_data_t *gpsdata)
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{
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struct timeval tv;
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time_t time;
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int rc;
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if (!(gpsdata->set & TIME_SET))
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return;
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tv.tv_sec = gpsdata->fix.time;
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/* FIXME: use the fractional part for microseconds */
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tv.tv_usec = 0;
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time = tv.tv_sec;
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rc = settimeofday(&tv, NULL);
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gps_close(gpsdata);
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if (rc == 0) {
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syslog(LOG_NOTICE, "Successfully set RTC time to GPSD time:"
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" %s", ctime(&time));
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closelog();
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exit(EXIT_SUCCESS);
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} else {
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syslog(LOG_ERR, "Error setting RTC: %d (%s)\n",
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errno, strerror(errno));
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closelog();
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exit(EXIT_FAILURE);
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}
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}
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static int osmo_daemonize(void)
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{
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int rc;
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pid_t pid, sid;
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/* Check if parent PID == init, in which case we are already a daemon */
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if (getppid() == 1)
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return -EEXIST;
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/* Fork from the parent process */
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pid = fork();
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if (pid < 0) {
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/* some error happened */
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return pid;
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}
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if (pid > 0) {
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/* if we have received a positive PID, then we are the parent
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* and can exit */
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exit(0);
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}
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/* FIXME: do we really want this? */
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umask(0);
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/* Create a new session and set process group ID */
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sid = setsid();
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if (sid < 0)
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return sid;
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/* Change to the /tmp directory, which prevents the CWD from being locked
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* and unable to remove it */
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rc = chdir("/tmp");
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if (rc < 0)
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return rc;
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/* Redirect stdio to /dev/null */
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/* since C89/C99 says stderr is a macro, we can safely do this! */
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#ifdef stderr
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freopen("/dev/null", "r", stdin);
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freopen("/dev/null", "w", stdout);
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freopen("/dev/null", "w", stderr);
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#endif
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return 0;
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}
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int main(int argc, char **argv)
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{
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char *host = "localhost";
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int i, rc;
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openlog("gpsdate", LOG_PERROR, LOG_CRON);
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if (argc > 1)
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host = argv[1];
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for (i = 1; i <= NUM_RETRIES; i++) {
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printf("Attempt #%d to connect to gpsd at %s...\n", i, host);
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rc = gps_open(host, DEFAULT_GPSD_PORT, &gpsdata);
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if (!rc)
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break;
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sleep(RETRY_SLEEP);
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}
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if (rc) {
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syslog(LOG_ERR, "no gpsd running or network error: %d, %s\n",
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errno, gps_errstr(errno));
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closelog();
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exit(EXIT_FAILURE);
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}
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osmo_daemonize();
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gps_stream(&gpsdata, WATCH_ENABLE|WATCH_JSON, NULL);
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/* We run in an endless loop. The only reasonable way to exit is after
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* a correct GPS timestamp has been received in callback() */
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while (1)
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gps_mainloop(&gpsdata, INT_MAX, callback);
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gps_close(&gpsdata);
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closelog();
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exit(EXIT_SUCCESS);
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}
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