xref: /freebsd/share/man/man5/dir.5 (revision 97759ccc715c4b365432c16d763c50eecfcb1100)

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.Dd November 14, 2018
.Dt DIR 5
.Os
.Sh NAME
.Nm dir ,
.Nm dirent
.Nd directory file format
.Sh SYNOPSIS
.In dirent.h
.Sh 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
.Xr 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).
.\" An entry in this tree,
.\" nested or not nested,
.\" is a pathname.
.Pp
Each directory file contains two special directory entries; one is a pointer
to the directory itself
called dot
.Ql .\&
and the other a pointer to its parent directory called dot-dot
.Ql \&.. .
Dot and dot-dot
are valid pathnames, however,
the system root directory
.Ql / ,
has no parent and dot-dot points to itself like dot.
.Pp
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
.Xr mount 2
and
.Xr mount 8 . )
.Pp
The directory entry format is defined in the file
.In sys/dirent.h
(which should not be included directly by applications):
.Bd -literal
#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_ */
.Ed
.Sh SEE ALSO
.Xr fs 5 ,
.Xr inode 5
.Sh HISTORY
A
.Nm
file format appeared in
.At v7 .
.Sh BUGS
The usage of the member d_type of struct dirent is unportable as it is
.Fx Ns -specific .
It also may fail on certain file systems, for example the cd9660 file system.