VFAT_IOCTL_READDIR_BOTH(2const)

NAME

VFAT_IOCTL_READDIR_BOTH, VFAT_IOCTL_READDIR_SHORT - read filenames of a directory in a FAT filesystem

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

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

int ioctl(int fd, VFAT_IOCTL_READDIR_BOTH,
          struct __fat_dirent entry[2]);
int ioctl(int fd, VFAT_IOCTL_READDIR_SHORT,
          struct __fat_dirent entry[2]);

DESCRIPTION

A file or directory on a FAT filesystem always has a short filename consisting of up to 8 capital letters, optionally followed by a period and up to 3 capital letters for the file extension. If the actual filename does not fit into this scheme, it is stored as a long filename of up to 255 UTF-16 characters.

The short filenames in a directory can be read with VFAT_IOCTL_READDIR_SHORT. VFAT_IOCTL_READDIR_BOTH reads both the short and the long filenames.

The fd argument must be a file descriptor for a directory. It is sufficient to create the file descriptor by calling open(2) with the O_RDONLY flag. The file descriptor can be used only once to iterate over the directory entries by calling ioctl(2) repeatedly.

The entry argument is a two-element array of the following structures:

struct __fat_dirent {
    long            d_ino;
    __kernel_off_t  d_off;
    uint32_t short  d_reclen;
    char            d_name[256];
};

The first entry in the array is for the short filename. The second entry is for the long filename.

The d_ino and d_off fields are filled only for long filenames. The d_ino field holds the inode number of the directory. The d_off field holds the offset of the file entry in the directory. As these values are not available for short filenames, the user code should simply ignore them.

The field d_reclen contains the length of the filename in the field d_name. To keep backward compatibility, a length of 0 for the short filename signals that the end of the directory has been reached. However, the preferred method for detecting the end of the directory is to test the ioctl(2) return value. If no long filename exists, field d_reclen is set to 0 and d_name is a character string of length 0 for the long filename.

RETURN VALUE

A return value of 1 signals that a new directory entry has been read and a return value of 0 signals that the end of the directory has been reached.

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

ERRORS

ENOENT: fd refers to a removed, but still open directory.
ENOTDIR: fd does not refer to a directory.

STANDARDS

Linux.

HISTORY

Linux 2.0.

EXAMPLES

The following program demonstrates the use of ioctl(2) to list a directory.

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

$ ./fat_dir /mnt/user
. -> ''
.. -> ''
ALONGF~1.TXT -> 'a long filename.txt'
UPPER.TXT -> ''
LOWER.TXT -> 'lower.txt'

Program source

#include <fcntl.h>
#include <linux/msdos_fs.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
    int                  fd;
    int                  ret;
    struct __fat_dirent  entry[2];
    if (argc != 2) {
        printf("Usage: %s DIRECTORY\n", argv[0]);
        exit(EXIT_FAILURE);
    }
    /*
     * Open file descriptor for the directory.
     */
    fd = open(argv[1], O_RDONLY | O_DIRECTORY);
    if (fd == -1) {
        perror("open");
        exit(EXIT_FAILURE);
    }
    for (;;) {
        /*
         * Read next directory entry.
         */
        ret = ioctl(fd, VFAT_IOCTL_READDIR_BOTH, entry);
        /*
         * If an error occurs, the return value is -1.
         * If the end of the directory list has been reached,
         * the return value is 0.
         * For backward compatibility the end of the directory
         * list is also signaled by d_reclen == 0.
         */
        if (ret < 1)
            break;
        /*
         * Write both the short name and the long name.
         */
        printf("%s -> '%s'\n", entry[0].d_name, entry[1].d_name);
    }
    if (ret == -1) {
        perror("VFAT_IOCTL_READDIR_BOTH");
        exit(EXIT_FAILURE);
    }
    /*
     * Close the file descriptor.
     */
    close(fd);
    exit(EXIT_SUCCESS);
}