yasnd/yasnd.c

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <syslog.h>
#include <signal.h>
#include <string.h>
// #include <gammu/gammu.h>

// Target hosts count
#define NUM_HOSTS 3

// Should we do excessive debug logging or not
#define DEBUG

typedef struct {
	char* hostname; // address of host
	pid_t helper_pid; // pid of helper('pinger') child process
	int fail_count; // how many times in a row host was unreachable
} host_decl;

host_decl hosts[NUM_HOSTS];

void init()
{
	hosts[0].hostname="10.0.0.1";
	hosts[0].fail_count=0;
	hosts[1].hostname="10.0.0.2";
	hosts[1].fail_count=0;
	hosts[2].hostname="10.0.0.254";
	hosts[2].fail_count=0;
}

void log_event(const char *message)
{
	#ifdef DEBUG
		syslog(LOG_INFO,"%s",message);
	#endif
}

void check_host(int num,host_decl host)
{
	pid_t pid = fork();
	if (pid < 0) {
                exit(EXIT_FAILURE);
        }
        // If pid == 0, then we are in the child
        if (pid == 0) {
		char tmp[50];
		sprintf(tmp, "Pinging host %s", host.hostname);
		log_event(tmp);
		execl("/bin/ping","/bin/ping","-c 4","-n",host.hostname,(char*) 0);
		// STUB: check result of exec call
		exit(EXIT_SUCCESS);
        }
	// Save child's pid
	host.helper_pid=pid;
}

void loop_function()
{
	for (int i=0;i<NUM_HOSTS;i++)
	{
		check_host(i,hosts[i]);
	}
	for (int i=0;i<NUM_HOSTS;i++)
	{
		int pid_status;
		int result = waitpid(hosts[i].helper_pid, &pid_status, NULL);
		if (result > 0)
		{
			if (WIFEXITED(pid_status))
			{
				char tmp[50];
				sprintf(tmp, "Finished child %d with result %d", result, WEXITSTATUS(pid_status));
				log_event(tmp);
				// if host is alive - reset failure counter
				// otherwise - increment it
				if (WEXITSTATUS(pid_status) == 0)
					hosts[i].fail_count=0;
				else
					hosts[i].fail_count++;
			}
		}
	}
}

void termination_handler(int signum)
{
	closelog();
	exit(EXIT_SUCCESS);
}

int main(void) {
	/* Our process ID and Session ID */
	pid_t pid, sid;

	/* Fork off the parent process */
	pid = fork();
	if (pid < 0) {
		exit(EXIT_FAILURE);
	}
	/* If we got a good PID, then we can exit the parent process. */
	if (pid > 0) {
		exit(EXIT_SUCCESS);
	}

	/* Change the file mode mask */
	umask(0);

	/* Open any logs here */
	openlog("yasnd", LOG_PID|LOG_CONS, LOG_USER);

	/* Create a new SID for the child process */
	sid = setsid();
	if (sid < 0) {
		/* Log the failure */
		exit(EXIT_FAILURE);
	}

	/* Change the current working directory */
	if ((chdir("/")) < 0) {
		/* Log the failure */
		exit(EXIT_FAILURE);
	}

	/* Close out the standard file descriptors */
	close(STDIN_FILENO);
	close(STDOUT_FILENO);
	close(STDERR_FILENO);

	// Set signal handler for SIGTERM
	signal(SIGTERM, termination_handler);

	// Init apropriate structures
	init();

	/* The Big Loop */
	while (1) {
		loop_function();
//		sleep(60); /* wait 60 seconds */
		exit(EXIT_SUCCESS);
	}
	exit(EXIT_SUCCESS);
}