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DIR (5) | File formats and conventions | Unix Manual Pages | :man

NAME

dir, dirent - directory file format

CONTENTS

Synopsis
Description
See Also
History
Bugs

SYNOPSIS


.In 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
.In 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_FIFO1
#define DT_CHR 2
#define DT_DIR 4
#define DT_BLK 6
#define DT_REG 8
#define DT_LNK10
#define DT_SOCK 12
#define DT_WHT14


/*
* 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

BUGS


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