.\"	$OpenBSD: dir.5,v 1.15 2011/07/14 02:16:00 deraadt Exp $
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.Dd $Mdocdate: July 14 2011 $
.Dt DIR 5
.Os
.Sh NAME
.Nm dir ,
.Nm dirent
.Nd directory file format
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <dirent.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 referred to as subdirectories.
A hierarchy of directories and files is formed in this manner
and is called a file system (or referred 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
.Pq Dq \&.
and the other a pointer to its parent directory called dot-dot
.Pq Dq \&.. .
Dot and dot-dot are valid pathnames, however, the system root directory
.Pq Dq / ,
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 8 ) .
.Pp
The directory entry format is defined in the file
.Aq Pa dirent.h :
.Bd -literal
/*
 * 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 NUL terminated.
 * The maximum length of a name in a directory is MAXNAMLEN.
 */

struct dirent {
	u_int32_t	d_fileno;	/* file number of entry */
	u_int16_t	d_reclen;	/* length of this record */
	u_int8_t	d_type;		/* file type, see below */
	u_int8_t	d_namlen;	/* length of string in d_name */
#define MAXNAMLEN       255
	char    d_name[MAXNAMLEN + 1];  /* maximum name length */
};

/*
 * File types
 */
#define DT_UNKNOWN	0
#define DT_FIFO		1
#define DT_CHR		2
#define DT_DIR		4
#define DT_BLK		6
#define DT_REG		8
#define DT_LNK		10
#define DT_SOCK		12

/*
 * Convert between stat structure types and directory types.
 */
#define IFTODT(mode)	(((mode) & 0170000) >> 12)
#define DTTOIF(dirtype)	((dirtype) << 12)

#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 */
	off_t	dd_seek;   /* magic cookie returned by getdirentries */
	off_t	dd_rewind; /* magic cookie for rewinding */
	int	dd_unused; /* was flags for readdir */
	struct _telldir *dd_td; /* telldir position recording */
	void	*dd_lock;  /* mutex to protect struct */
} DIR;

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

#endif /* _POSIX_SOURCE */
.Ed
.Sh SEE ALSO
.Xr getdirentries 2 ,
.Xr fs 5 ,
.Xr inode 5
.Sh HISTORY
A
.Nm dir
file format appeared in
.At v7 .