cdrom tray status: 偵測光碟機狀態

/*
 * cdstatus.c  <device>
 *
 * This loads a CDROM from a specified slot in a changer, and displays 
 * information about the changer status.  The drive should be unmounted before 
 * using this program.
 *
 * Based on code originally from Gerhard Zuber .
 * Changer status information, and rewrite for the new Uniform CDROM driver
 * interface by Erik Andersen <andersee@debian.org>.
 */

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/cdrom.h>

int
main (int argc, char **argv)
{
  char *program;
  char *device;
  int fd;           /* file descriptor for CD-ROM device */
  int status;       /* return status for system calls */

  if (argc != 2) {
    fprintf (stderr, "usage: %s \n", program);
    exit (1);
  }
 
  program = argv[0];
  device = argv[1];

  /* open device */ 
  fd = open(device, O_RDONLY | O_NONBLOCK);
  if (fd < 0) {
    fprintf (stderr, "%s: open failed for `%s': %s\n",
       program, device, strerror (errno));
    exit (1);
  }

  status = ioctl (fd, CDROM_DRIVE_STATUS, CDSL_CURRENT);
  if (status<0) {
    perror(" CDROM_DRIVE_STATUS");
  } else switch(status) {
    case CDS_NO_INFO: printf ("NO_INFO\n"); break;
    case CDS_NO_DISC: printf ("NO_DISC\n"); break;
    case CDS_TRAY_OPEN: printf ("TRAY_OPEN\n"); break;
    case CDS_DRIVE_NOT_READY: printf ("NOT_READY\n"); break;
    case CDS_DISC_OK: printf ("DISC_OK\n"); break;
    default: printf ("ERROR: %d\n", status); break;
  }

  /* close device */
  close (fd);
  exit (0);
}