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

#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)