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 medi

um. 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 dotdot 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 parti

tioned area of
such a disk. (See mount(2) and mount(8).)

The directory entry format is defined in the file #include

<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 en

tries 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 bound

ary.
*/

#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 un

portable as it is
FreeBSD-specific. It also may fail on certain file systems,

for example
the cd9660 file system.

BSD April 19, 1994

BSD