1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.Dd November 14, 2018 29.Dt DIR 5 30.Os 31.Sh NAME 32.Nm dir , 33.Nm dirent 34.Nd directory file format 35.Sh SYNOPSIS 36.In dirent.h 37.Sh DESCRIPTION 38Directories provide a convenient hierarchical method of grouping 39files while obscuring the underlying details of the storage medium. 40A directory file is differentiated from a plain file 41by a flag in its 42.Xr inode 5 43entry. 44It consists of records (directory entries) each of which contains 45information about a file and a pointer to the file itself. 46Directory entries may contain other directories 47as well as plain files; such nested directories are referred to as 48subdirectories. 49A hierarchy of directories and files is formed in this manner 50and is called a file system (or referred to as a file system tree). 51.\" An entry in this tree, 52.\" nested or not nested, 53.\" is a pathname. 54.Pp 55Each directory file contains two special directory entries; one is a pointer 56to the directory itself 57called dot 58.Ql .\& 59and the other a pointer to its parent directory called dot-dot 60.Ql \&.. . 61Dot and dot-dot 62are valid pathnames, however, 63the system root directory 64.Ql / , 65has no parent and dot-dot points to itself like dot. 66.Pp 67File system nodes are ordinary directory files on which has 68been grafted a file system object, such as a physical disk or a 69partitioned area of such a disk. 70(See 71.Xr mount 2 72and 73.Xr mount 8 . ) 74.Pp 75The directory entry format is defined in the file 76.In sys/dirent.h 77(which should not be included directly by applications): 78.Bd -literal 79#ifndef _SYS_DIRENT_H_ 80#define _SYS_DIRENT_H_ 81 82#include <machine/ansi.h> 83 84/* 85 * The dirent structure defines the format of directory entries returned by 86 * the getdirentries(2) system call. 87 * 88 * A directory entry has a struct dirent at the front of it, containing its 89 * inode number, the length of the entry, and the length of the name 90 * contained in the entry. These are followed by the name padded to a 8 91 * byte boundary with null bytes. All names are guaranteed null terminated. 92 * The maximum length of a name in a directory is MAXNAMLEN. 93 * Explicit pad is added between the last member of the header and 94 * d_name, to avoid having the ABI padding in the end of dirent on 95 * LP64 arches. There is code depending on d_name being last. Also, 96 * keeping this pad for ILP32 architectures simplifies compat32 layer. 97 */ 98 99struct dirent { 100 ino_t d_fileno; /* file number of entry */ 101 off_t d_off; /* directory offset of the next entry */ 102 __uint16_t d_reclen; /* length of this record */ 103 __uint8_t d_type; /* file type, see below */ 104 __uint8_t d_namlen; /* length of string in d_name */ 105 __uint32_t d_pad0; 106#if __BSD_VISIBLE 107#define MAXNAMLEN 255 108 char d_name[MAXNAMLEN + 1]; /* name must be no longer than this */ 109#else 110 char d_name[255 + 1]; /* name must be no longer than this */ 111#endif 112}; 113 114/* 115 * File types 116 */ 117#define DT_UNKNOWN 0 118#define DT_FIFO 1 119#define DT_CHR 2 120#define DT_DIR 4 121#define DT_BLK 6 122#define DT_REG 8 123#define DT_LNK 10 124#define DT_SOCK 12 125#define DT_WHT 14 126 127/* 128 * Convert between stat structure types and directory types. 129 */ 130#define IFTODT(mode) (((mode) & 0170000) >> 12) 131#define DTTOIF(dirtype) ((dirtype) << 12) 132 133/* 134 * The _GENERIC_DIRSIZ macro gives the minimum record length which will hold 135 * the directory entry. This returns the amount of space in struct direct 136 * without the d_name field, plus enough space for the name with a terminating 137 * null byte (dp->d_namlen+1), rounded up to a 8 byte boundary. 138 * 139 * XXX although this macro is in the implementation namespace, it requires 140 * a manifest constant that is not. 141 */ 142#define _GENERIC_DIRLEN(namlen) \ 143 ((__offsetof(struct dirent, d_name) + (namlen) + 1 + 7) & ~7) 144#define _GENERIC_DIRSIZ(dp) _GENERIC_DIRLEN((dp)->d_namlen) 145#endif /* __BSD_VISIBLE */ 146 147#ifdef _KERNEL 148#define GENERIC_DIRSIZ(dp) _GENERIC_DIRSIZ(dp) 149#endif 150 151#endif /* !_SYS_DIRENT_H_ */ 152.Ed 153.Sh SEE ALSO 154.Xr fs 5 , 155.Xr inode 5 156.Sh HISTORY 157A 158.Nm 159file format appeared in 160.At v7 . 161.Sh BUGS 162The usage of the member d_type of struct dirent is unportable as it is 163.Fx Ns -specific . 164It also may fail on certain file systems, for example the cd9660 file system. 165