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DIR(5) BSD File Formats Manual DIR(5)

NAME

dir, dirent — directory file format

SYNOPSIS

#include <sys/types.h>
#include <sys/dir.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 refered 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(1) and mount(8).)

The directory entry format is defined in the file ⟨ sys/dirent.h⟩ and further in the file ⟨ dirent.h⟩ :

/*** Excerpt from <sys/dirent.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.
* The dirent structure defines the format of directory entries returned by
* the getdirentries(2) system call.
*/

#ifndef _SYS_DIRENT_H
#define _SYS_DIRENT_H

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 */
#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

#endif /* !_SYS_DIRENT_H_ */

-----------------------------------------

/*** Excerpt from <dirent.h> ***/

#ifndef _DIRENT_H
#define _DIRENT_H

#ifdef _POSIX_SOURCE
typedef void * DIR;
#else

#define d_ino d_fileno /* backward compatibility */

/* definitions for library routines operating on directories. */
#define DIRBLKSIZ 1024

struct _telldir; /* see telldir.h */

/* 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 */
long dd_seek; /* magic cookie returned by getdirentries */
long dd_rewind; /* magic cookie for rewinding */
int dd_flags; /* flags for readdir */
pthread_mutex_t dd_lock; /* for thread locking */
struct _telldir *dd_td; /* telldir position recording */
} DIR;

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

/* flags for opendir2 */
#define DTF_HIDEW 0x0001 /* hide whiteout entries */
#define DTF_NODUP 0x0002 /* don’t return duplicate names */
/* 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 */
long dd_seek; /* magic cookie returned by getdirentries */
long dd_rewind; /* magic cookie for rewinding */
int dd_flags; /* flags for readdir */
pthread_mutex_t dd_lock; /* for thread locking */
struct _telldir *dd_td; /* telldir position recording */
} DIR;

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

/* flags for opendir2 */
#define DTF_HIDEW 0x0001 /* hide whiteout entries */
#define DTF_NODUP 0x0002 /* don’t return duplicate names */
#define DTF_REWIND 0x0004 /* rewind after reading union stack */
#define __DTF_READALL 0x0008 /* everything has been read */

#ifndef NULL
#define NULL 0
#endif

#endif /* _POSIX_SOURCE */

#endif /* !_DIRENT_H_ */

SEE ALSO

fs(5), inode(5)

HISTORY

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

4.2 Berkeley Distribution April 19, 1994 4.2 Berkeley Distribution

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