FAT_IOCTL_GET_VOLUME_ID(2const)

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);
}