BSD 4_3 release

[unix-history] / usr / man / man5 / dir.5

.\" 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)