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);
}