Daemon program that talks to devices - linux

Question

I read about Daemon Programming and i think I'll be needing this to detect my devices if online or not eg(RS232, usb, ethernet). then fetch in a webservice PHP.
The code from this site. http://www.netzmafia.de/skripten/unix/linux-daemon-howto.html
I added some parts to test if i can detect devices.
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <syslog.h>
#include <string.h>
int devfd;
int main(int argc, char *argv[]) {
int c;
while((c=getopt(argc,argv,"s")) != -1)
switch(c){
case 's': devfd = open("/dev/ttyUSB0", O_RDWR);
if(devfd==-1){
printf("offline\n");
}
else{
printf("online\n");
}
break;
default: printf("Wrong command\n");
}
/* 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 */
/* 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);
}
/* Daemon-specific initialization goes here */
/* The Big Loop */
while (1) {
}
exit(EXIT_SUCCESS);
}
I added this code..
while((c=getopt(argc,argv,"s")) != -1)
switch(c){
case 's': devfd = open("/dev/ttyUSB0", O_RDWR);
if(devfd==-1){
printf("offline\n");
}
else{
printf("online\n");
}
break;
default: printf("Wrong command\n");
}
so doing it like this in the terminal.
./daemon -s //prints offline because the device USB0 is not connected.
Is there another way for me to detect my devices?
Thanks,

Answer 1

If it has udev, you can use libudev to detect and monitor your devices. Checkout nice tutorial from signal11.