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 8
* byte boundary with null bytes. All names are guaranteed null terminated.
* The maximum length of a name in a directory is MAXNAMLEN.
* Explicit pad is added between the last member of the header and
* d_name, to avoid having the ABI padding in the end of dirent on
* LP64 arches. There is code depending on d_name being last. Also,
* keeping this pad for ILP32 architectures simplifies compat32 layer.
*/
struct dirent {
ino_t d_fileno; /* file number of entry */
off_t d_off; /* directory offset of the next 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 */
__uint32_t d_pad0;
#if __BSD_VISIBLE
#define MAXNAMLEN 255
char d_name[MAXNAMLEN + 1]; /* name must be no longer than this */
#else
char d_name[255 + 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 returns 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 8 byte boundary.
*
* XXX although this macro is in the implementation namespace, it requires
* a manifest constant that is not.
*/
#define _GENERIC_DIRLEN(namlen) ((__offsetof(struct dirent, d_name) + (namlen) + 1 + 7) & ~7)
#define _GENERIC_DIRSIZ(dp) _GENERIC_DIRLEN((dp)->d_namlen)
#endif /* __BSD_VISIBLE */
#ifdef _KERNEL
#define GENERIC_DIRSIZ(dp) _GENERIC_DIRSIZ(dp)
#endif
#endif /* !_SYS_DIRENT_H_ */
SEE ALSO
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.