| DIR(5) | File Formats Manual | DIR(5) |
dir, dirent
— directory file format
#include
<sys/types.h>
#include <sys/dir.h>
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⟩. When the macro
_DARWIN_FEATURE_64_BIT_INODE is not defined (see
stat(2) for more information on this macro), the
dirent structure is defined as:
/*** Excerpt from <sys/dirent.h> ***/
/*
* The dirent structure defines the format of directory entries.
*
* 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 255.
*/
struct dirent { /* when _DARWIN_FEATURE_64_BIT_INODE is NOT defined */
ino_t d_ino; /* 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 */
char d_name[255 + 1]; /* name must be no longer than this */
};
However, when the macro
_DARWIN_FEATURE_64_BIT_INODE is defined, the
dirent structure is defined as:
/*
* The dirent structure defines the format of directory entries.
*
* 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 1023.
*/
struct dirent { /* when _DARWIN_FEATURE_64_BIT_INODE is defined */
ino_t d_fileno; /* file number of entry */
__uint64_t d_seekoff; /* seek offset (optional, used by servers) */
__uint16_t d_reclen; /* length of this record */
__uint16_t d_namlen; /* length of string in d_name */
__uint8_t d_type; /* file type, see below */
char d_name[1024]; /* name must be no longer than this */
};
In addition:
/* * 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
/*** Excerpt from <dirent.h> ***/
#define d_fileno d_ino /* 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 */
#define DTF_REWIND 0x0004 /* rewind after reading union stack */
#define __DTF_READALL 0x0008 /* everything has been read */
A dir file format appeared in
Version 7 AT&T UNIX.
| April 19, 1994 | BSD 4.2 |