NAME

       FAT_IOCTL_GET_VOLUME_ID - read the volume ID in a FAT filesystem

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <linux/msdos_fs.h>  /* Definition of FAT_* constants */
       #include <sys/ioctl.h>

       int ioctl(int fd, FAT_IOCTL_GET_VOLUME_ID, uint32_t *id);

DESCRIPTION

       FAT  filesystems  are  identified  by  a  volume  ID.   The  volume  ID  can  be read with
       FAT_IOCTL_GET_VOLUME_ID.

       The fd argument can be a file descriptor for any file or directory of the filesystem.   It
       is sufficient to create the file descriptor by calling open(2) with the O_RDONLY flag.

       The  id  argument  is  a  pointer  to  the  field  that will be filled with the volume ID.
       Typically the volume ID is displayed to the user as a group of two 16-bit fields:

           printf("Volume ID %04x-%04x\n", id >> 16, id & 0xFFFF);

RETURN VALUE

       On success, 0 is returned.  On error, -1 is returned, and errno is  set  to  indicate  the
       error.

STANDARDS

       Linux.

HISTORY

       Linux 3.11.

EXAMPLES

       The  following  program demonstrates the use of ioctl(2) to display the volume ID of a FAT
       filesystem.

       The following output was recorded when applying the program for directory /mnt/user:

           $ ./display_fat_volume_id /mnt/user
           Volume ID 6443-6241

   Program source (display_fat_volume_id.c)

       #include <fcntl.h>
       #include <linux/msdos_fs.h>
       #include <stdint.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <sys/ioctl.h>
       #include <unistd.h>

       int
       main(int argc, char *argv[])
       {
           int       fd;
           int       ret;
           uint32_t  id;

           if (argc != 2) {
               printf("Usage: %s FILENAME\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           fd = open(argv[1], O_RDONLY);
           if (fd == -1) {
               perror("open");
               exit(EXIT_FAILURE);
           }

           /*
            * Read volume ID.
            */
           ret = ioctl(fd, FAT_IOCTL_GET_VOLUME_ID, &id);
           if (ret == -1) {
               perror("ioctl");
               exit(EXIT_FAILURE);
           }

           /*
            * Format the output as two groups of 16 bits each.
            */
           printf("Volume ID %04x-%04x\n", id >> 16, id & 0xFFFF);

           close(fd);

           exit(EXIT_SUCCESS);
       }

SEE ALSO

       ioctl(2), ioctl_fat(2)