FreeBSD-5.3/share/man/man5/dir.5
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.\" @(#)dir.5 8.3 (Berkeley) 4/19/94
.\" $FreeBSD: src/share/man/man5/dir.5,v 1.20 2003/09/10 19:24:35 ru Exp $
.\"
.Dd April 19, 1994
.Dt DIR 5
.Os
.Sh NAME
.Nm dir ,
.Nm dirent
.Nd directory file format
.Sh SYNOPSIS
.In 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
.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 2
and
.Xr mount 8 . )
.Pp
The directory entry format is defined in the file
.In sys/dirent.h
(which should not be included directly by applications):
.Bd -literal
#ifndef _SYS_DIRENT_H_
#define _SYS_DIRENT_H_
#include <machine/ansi.h>
/*
* The dirent structure defines the format of directory entries returned by
* the getdirentries(2) system call.
*
* 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 {
__uint32_t d_fileno; /* file number of entry */
__uint16_t d_reclen; /* length of this record */
__uint8_t d_type; /* file type, see below */
__uint8_t d_namlen; /* length of string in d_name */
#ifdef _POSIX_SOURCE
char d_name[255 + 1]; /* name must be no longer than this */
#else
#define MAXNAMLEN 255
char d_name[MAXNAMLEN + 1]; /* name must be no longer than this */
#endif
};
/*
* 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
#define DT_WHT 14
/*
* Convert between stat structure types and directory types.
*/
#define IFTODT(mode) (((mode) & 0170000) >> 12)
#define DTTOIF(dirtype) ((dirtype) << 12)
/*
* The _GENERIC_DIRSIZ macro gives the minimum record length which will hold
* the directory entry. This requires the amount of space in struct direct
* without the d_name field, plus enough space for the name with a terminating
* null byte (dp->d_namlen+1), rounded up to a 4 byte boundary.
*/
#define _GENERIC_DIRSIZ(dp) \
((sizeof (struct dirent) - (MAXNAMLEN+1)) + (((dp)->d_namlen+1 + 3) &~ 3))
#ifdef _KERNEL
#define GENERIC_DIRSIZ(dp) _GENERIC_DIRSIZ(dp)
#endif
#endif /* !_SYS_DIRENT_H_ */
.Ed
.Sh SEE ALSO
.Xr fs 5 ,
.Xr inode 5
.Sh BUGS
The usage of the member d_type of struct dirent is unportable as it is
.Fx Ns -specific .
It also may fail on certain file systems, for example the cd9660 file system.
.Sh HISTORY
A
.Nm
file format appeared in
.At v7 .