man2/readdir.2

.\" Copyright (C) 1995 Andries Brouwer (aeb@cwi.nl)
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.\" Written 11 June 1995 by Andries Brouwer <aeb@cwi.nl>
.\" Modified 22 July 1995 by Michael Chastain <mec@duracef.shout.net>:
.\"   In 1.3.X, returns only one entry each time; return value is different.
.\" Modified 2004-12-01, mtk, fixed headers listed in SYNOPSIS
.\"
.TH READDIR 2  2021-03-22 "Linux" "Linux Programmer's Manual"
.SH NAME
readdir \- read directory entry
.SH SYNOPSIS
.nf
.PP
.BI "int readdir(unsigned int " fd ", struct old_linux_dirent *" dirp ","
.BI "            unsigned int " count );
.fi
.PP
.IR Note :
There is no glibc wrapper for this system call; see NOTES.
.SH DESCRIPTION
This is not the function you are interested in.
Look at
.BR readdir (3)
for the POSIX conforming C library interface.
This page documents the bare kernel system call interface,
which is superseded by
.BR getdents (2).
.PP
.BR readdir ()
reads one
.I old_linux_dirent
structure from the directory
referred to by the file descriptor
.I fd
into the buffer pointed to by
.IR dirp .
The argument
.I count
is ignored; at most one
.I old_linux_dirent
structure is read.
.PP
The
.I old_linux_dirent
structure is declared (privately in Linux kernel file
.BR fs/readdir.c )
as follows:
.PP
.in +4n
.EX
struct old_linux_dirent {
    unsigned long d_ino;     /* inode number */
    unsigned long d_offset;  /* offset to this \fIold_linux_dirent\fP */
    unsigned short d_namlen; /* length of this \fId_name\fP */
    char  d_name[1];         /* filename (null\-terminated) */
}
.EE
.in
.PP
.I d_ino
is an inode number.
.I d_offset
is the distance from the start of the directory to this
.IR old_linux_dirent .
.I d_reclen
is the size of
.IR d_name ,
not counting the terminating null byte (\(aq\e0\(aq).
.I d_name
is a null-terminated filename.
.SH RETURN VALUE
On success, 1 is returned.
On end of directory, 0 is returned.
On error, \-1 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EBADF
Invalid file descriptor
.IR fd .
.TP
.B EFAULT
Argument points outside the calling process's address space.
.TP
.B EINVAL
Result buffer is too small.
.TP
.B ENOENT
No such directory.
.TP
.B ENOTDIR
File descriptor does not refer to a directory.
.SH CONFORMING TO
This system call is Linux-specific.
.SH NOTES
Glibc does not provide a wrapper for this system call; call it using
.BR syscall (2).
You will need to define the
.I old_linux_dirent
structure yourself.
However, probably you should use
.BR readdir (3)
instead.
.PP
This system call does not exist on x86-64.
.SH SEE ALSO
.BR getdents (2),
.BR readdir (3)