.\" Copyright (c) 1983, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" %sccs.include.redist.man%
.\"
.\"     @(#)dir.5	8.2 (Berkeley) %G%
.\"
.Dd 
.Dt DIR 5
.Os BSD 4.2
.Sh NAME
.Nm dir ,
.Nm dirent
.Nd directory file format
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/dir.h>
.Sh DESCRIPTION
Directories provide a convenient hierarchical method of grouping
files while obscuring the underlying details of the storage medium.
A directory file is differentiated from a plain file
by a flag in its
.Xr inode 5
entry.
It consists of records (directory entries) each of which contains
information about a file and a pointer to the file itself.
Directory entries may contain other directories
as well as plain files; such nested directories are refered to as
subdirectories. 
A hierarchy of directories and files is formed in this manner
and is called a file system (or refered to as a file system tree).
.\" An entry in this tree,
.\" nested or not nested,
.\" is a pathname.
.Pp
Each directory file contains two special directory entries; one is a pointer
to the directory itself
called dot
.Ql \&.
and the other a pointer to its parent directory called dot-dot
.Ql \&.. .
Dot and dot-dot
are valid pathnames, however,
the system root directory
.Ql / ,
has no parent and dot-dot points to itself like dot.
.Pp
File system nodes are ordinary directory files on which has
been grafted a file system object, such as a physical disk or a
partitioned area of such a disk.
(See
.Xr mount 1
and
.Xr mount 8 . )
.Pp
The directory entry format is defined in the file
.Aq dirent.h :
.Bd -literal
#ifndef _DIRENT_H_
#define _DIRENT_H_

/*
* A directory entry has a struct dirent at the front of it, containing its
* inode number, the length of the entry, and the length of the name
* contained in the entry.  These are followed by the name padded to a 4
* byte boundary with null bytes.  All names are guaranteed null terminated.
* The maximum length of a name in a directory is MAXNAMLEN.
*/

struct dirent {
	u_long	d_fileno;	/* file number of entry */
	u_short	d_reclen;	/* length of this record */
	u_short	d_namlen;	/* length of string in d_name */
#ifdef _POSIX_SOURCE
	char	d_name[MAXNAMLEN + 1];	/* maximum name length */
#else
#define MAXNAMLEN       255
	char    d_name[MAXNAMLEN + 1];  /* maximum name length */
#endif

};

#ifdef _POSIX_SOURCE
typedef void *	DIR;
#else

#define	d_ino		d_fileno	/* backward compatibility */

/* definitions for library routines operating on directories. */
#define	DIRBLKSIZ	1024

/* structure describing an open directory. */
typedef struct _dirdesc {
	int	dd_fd;    /* file descriptor associated with directory */
	long	dd_loc;	  /* offset in current buffer */
	long	dd_size;  /* amount of data returned by getdirentries */
	char	*dd_buf;  /* data buffer */
	int	dd_len;   /* size of data buffer */
	long	dd_seek;  /* magic cookie returned by getdirentries */
} DIR;

#define	dirfd(dirp)	((dirp)->dd_fd)

#ifndef NULL
#define	NULL	0
#endif

#endif /* _POSIX_SOURCE */

#ifndef KERNEL

#include <sys/cdefs.h>

#endif /* !KERNEL */

#endif /* !_DIRENT_H_ */
.Ed
.Sh SEE ALSO
.Xr fs 5
.Xr inode 5
.Sh HISTORY
A
.Nm
file format appeared in
.At v7 .