.\" Copyright 2014, Heinrich Schuchardt <xypron.glpk@gmx.de>
.\" Copyright 2024, Alejandro Colomar <alx@kernel.org>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH VFAT_IOCTL_READDIR_BOTH 2const 2024-06-15 "Linux man-pages (unreleased)"
.SH NAME
VFAT_IOCTL_READDIR_BOTH,
VFAT_IOCTL_READDIR_SHORT
\-
read filenames of a directory in a FAT filesystem
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.BR "#include <linux/msdos_fs.h>" "  /* Definition of " VFAT_* " constants */"
.B #include <sys/ioctl.h>
.P
.BI "int ioctl(int " fd ", VFAT_IOCTL_READDIR_BOTH,"
.BI "          struct __fat_dirent " entry [2]);
.BI "int ioctl(int " fd ", VFAT_IOCTL_READDIR_SHORT,"
.BI "          struct __fat_dirent " entry [2]);
.fi
.SH 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.
.P
The short filenames in a directory can be read with
.BR VFAT_IOCTL_READDIR_SHORT .
.B VFAT_IOCTL_READDIR_BOTH
reads both the short and the long filenames.
.P
The
.I fd
argument must be a file descriptor for a directory.
It is sufficient to create the file descriptor by calling
.BR open (2)
with the
.B O_RDONLY
flag.
The file descriptor can be used only once to iterate over the directory
entries by calling
.BR ioctl (2)
repeatedly.
.P
The
.I entry
argument is a two-element array of the following structures:
.P
.in +4n
.EX
struct __fat_dirent {
    long            d_ino;
    __kernel_off_t  d_off;
    uint32_t short  d_reclen;
    char            d_name[256];
};
.EE
.in
.P
The first entry in the array is for the short filename.
The second entry is for the long filename.
.P
The
.I d_ino
and
.I d_off
fields are filled only for long filenames.
The
.I d_ino
field holds the inode number of the directory.
The
.I 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.
.P
The field
.I d_reclen
contains the length of the filename in the field
.IR 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
.BR ioctl (2)
return value.
If no long filename exists, field
.I d_reclen
is set to 0 and
.I d_name
is a character string of length 0 for the long filename.
.SH 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.
.P
On error, \-1 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B ENOENT
.I fd
refers to a removed, but still open directory.
.TP
.B ENOTDIR
.I fd
does not refer to a directory.
.SH STANDARDS
Linux.
.SH HISTORY
Linux 2.0.
.SH EXAMPLES
The following program demonstrates the use of
.BR ioctl (2)
to list a directory.
.P
The following was recorded when applying the program to the directory
.IR /mnt/user :
.P
.in +4n
.EX
$ \fB./fat_dir /mnt/user\fP
\&. \-> \[aq]\[aq]
\&.. \-> \[aq]\[aq]
ALONGF\[ti]1.TXT \-> \[aq]a long filename.txt\[aq]
UPPER.TXT \-> \[aq]\[aq]
LOWER.TXT \-> \[aq]lower.txt\[aq]
.EE
.in
.\"
.SS Program source
.\" SRC BEGIN (ioctl_fat.c)
.EX
#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\[rs]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 \-> \[aq]%s\[aq]\[rs]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);
}
.EE
.\" SRC END
.SH SEE ALSO
.BR ioctl (2),
.BR ioctl_fat (2)