.\" Copyright (c) 1983 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)dir.5	6.1 (Berkeley) 5/15/85
.\"
.TH DIR 5  "May 15, 1985"
.UC 5
.SH NAME
dir \- format of directories
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <sys/dir.h>
.SH DESCRIPTION
A directory behaves exactly like an ordinary file, save that no
user may write into a directory.
The fact that a file is a directory is indicated by
a bit in the flag word of its i-node entry; see
.IR fs (5).
The structure of a directory entry as given in the include file is:
.RS
.ta 8n +10n +10n
.PP
.nf
/*
 * A directory consists of some number of blocks of DIRBLKSIZ
 * bytes, where DIRBLKSIZ is chosen such that it can be transferred
 * to disk in a single atomic operation (e.g. 512 bytes on most machines).
 *
 * Each DIRBLKSIZ byte block contains some number of directory entry
 * structures, which are of variable length.  Each directory entry has
 * a struct direct 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 macro DIRSIZ(dp) gives the amount of space required to represent
 * a directory entry.  Free space in a directory is represented by
 * entries which have dp->d_reclen > DIRSIZ(dp).  All DIRBLKSIZ bytes
 * in a directory block are claimed by the directory entries.  This
 * usually results in the last entry in a directory having a large
 * dp->d_reclen.  When entries are deleted from a directory, the
 * space is returned to the previous entry in the same directory
 * block by increasing its dp->d_reclen.  If the first entry of
 * a directory block is free, then its dp->d_ino is set to 0.
 * Entries other than the first in a directory do not normally have
 * dp->d_ino set to 0.
 */
#ifdef KERNEL
#define DIRBLKSIZ DEV_BSIZE
#else
#define	DIRBLKSIZ 512
#endif

#define MAXNAMLEN 255

/*
 * The 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.
 */
#undef DIRSIZ
#define DIRSIZ(dp) \e
    ((sizeof (struct direct) - (MAXNAMLEN+1)) + (((dp)->d_namlen+1 + 3) &~ 3))

struct	direct {
	u_long	d_ino;
	short	d_reclen;
	short	d_namlen;
	char	d_name[MAXNAMLEN + 1];
	/* typically shorter */
};

struct _dirdesc {
	int	dd_fd;
	long	dd_loc;
	long	dd_size;
	char	dd_buf[DIRBLKSIZ];
};
.fi
.RE
.PP
By convention, the first two entries in each directory
are for `.' and `..'.  The first is an entry for the
directory itself.  The second is for the parent directory.
The meaning of `..' is modified for the root directory
of the master file system (\*(lq/\*(rq),
where `..' has the same meaning as `.'.
.SH "SEE ALSO"
fs(5)