DIR(5) MidnightBSD File Formats Manual DIR(5)

NAME

dir, dirent — directory file format

SYNOPSIS

#include <dirent.h>

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 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).

Each directory file contains two special directory entries; one is a pointer to the directory itself called dot ‘.’ and the other a pointer to its parent directory called dot-dot ‘..’. Dot and dot-dot are valid pathnames, however, the system root directory ‘/’, has no parent and dot-dot points to itself like dot.

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 mount(2) and mount(8).)

The directory entry format is defined in the file <sys/dirent.h> (which should not be included directly by applications):

#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_ */

SEE ALSO

fs(5), inode(5)

HISTORY

A dir file format appeared in Version 7 AT&T UNIX.

BUGS

The usage of the member d_type of struct dirent is unportable as it is FreeBSD-specific. It also may fail on certain file systems, for example the cd9660 file system.

MidnightBSD 0.3 April 19, 1994 MidnightBSD 0.3