Commit | Line | Data |
---|---|---|
49625d7c KM |
1 | .\" Copyright (c) 1983 Regents of the University of California. |
2 | .\" All rights reserved. The Berkeley software License Agreement | |
3 | .\" specifies the terms and conditions for redistribution. | |
3bd54658 | 4 | .\" |
95f51977 | 5 | .\" @(#)dir.5 6.1 (Berkeley) 5/15/85 |
49625d7c | 6 | .\" |
95f51977 | 7 | .TH DIR 5 "May 15, 1985" |
49625d7c | 8 | .UC 5 |
3bd54658 KM |
9 | .SH NAME |
10 | dir \- format of directories | |
11 | .SH SYNOPSIS | |
12 | .B #include <sys/types.h> | |
13 | .br | |
14 | .B #include <sys/dir.h> | |
15 | .SH DESCRIPTION | |
49625d7c | 16 | A directory behaves exactly like an ordinary file, save that no |
3bd54658 KM |
17 | user may write into a directory. |
18 | The fact that a file is a directory is indicated by | |
49625d7c KM |
19 | a bit in the flag word of its i-node entry; see |
20 | .IR fs (5). | |
21 | The structure of a directory entry as given in the include file is: | |
3bd54658 | 22 | .RS |
49625d7c | 23 | .ta 8n +10n +10n |
3bd54658 KM |
24 | .PP |
25 | .nf | |
49625d7c KM |
26 | /* |
27 | * A directory consists of some number of blocks of DIRBLKSIZ | |
28 | * bytes, where DIRBLKSIZ is chosen such that it can be transferred | |
29 | * to disk in a single atomic operation (e.g. 512 bytes on most machines). | |
30 | * | |
31 | * Each DIRBLKSIZ byte block contains some number of directory entry | |
32 | * structures, which are of variable length. Each directory entry has | |
33 | * a struct direct at the front of it, containing its inode number, | |
34 | * the length of the entry, and the length of the name contained in | |
35 | * the entry. These are followed by the name padded to a 4 byte boundary | |
36 | * with null bytes. All names are guaranteed null terminated. | |
37 | * The maximum length of a name in a directory is MAXNAMLEN. | |
38 | * | |
39 | * The macro DIRSIZ(dp) gives the amount of space required to represent | |
40 | * a directory entry. Free space in a directory is represented by | |
41 | * entries which have dp->d_reclen > DIRSIZ(dp). All DIRBLKSIZ bytes | |
42 | * in a directory block are claimed by the directory entries. This | |
43 | * usually results in the last entry in a directory having a large | |
44 | * dp->d_reclen. When entries are deleted from a directory, the | |
45 | * space is returned to the previous entry in the same directory | |
46 | * block by increasing its dp->d_reclen. If the first entry of | |
47 | * a directory block is free, then its dp->d_ino is set to 0. | |
48 | * Entries other than the first in a directory do not normally have | |
49 | * dp->d_ino set to 0. | |
50 | */ | |
51 | #ifdef KERNEL | |
52 | #define DIRBLKSIZ DEV_BSIZE | |
53 | #else | |
54 | #define DIRBLKSIZ 512 | |
3bd54658 | 55 | #endif |
49625d7c KM |
56 | |
57 | #define MAXNAMLEN 255 | |
58 | ||
59 | /* | |
60 | * The DIRSIZ macro gives the minimum record length which will hold | |
61 | * the directory entry. This requires the amount of space in struct direct | |
62 | * without the d_name field, plus enough space for the name with a terminating | |
63 | * null byte (dp->d_namlen+1), rounded up to a 4 byte boundary. | |
64 | */ | |
65 | #undef DIRSIZ | |
66 | #define DIRSIZ(dp) \e | |
67 | ((sizeof (struct direct) - (MAXNAMLEN+1)) + (((dp)->d_namlen+1 + 3) &~ 3)) | |
68 | ||
69 | struct direct { | |
70 | u_long d_ino; | |
71 | short d_reclen; | |
72 | short d_namlen; | |
73 | char d_name[MAXNAMLEN + 1]; | |
74 | /* typically shorter */ | |
75 | }; | |
76 | ||
77 | struct _dirdesc { | |
78 | int dd_fd; | |
79 | long dd_loc; | |
80 | long dd_size; | |
81 | char dd_buf[DIRBLKSIZ]; | |
3bd54658 KM |
82 | }; |
83 | .fi | |
84 | .RE | |
85 | .PP | |
86 | By convention, the first two entries in each directory | |
49625d7c KM |
87 | are for `.' and `..'. The first is an entry for the |
88 | directory itself. The second is for the parent directory. | |
89 | The meaning of `..' is modified for the root directory | |
90 | of the master file system (\*(lq/\*(rq), | |
91 | where `..' has the same meaning as `.'. | |
3bd54658 | 92 | .SH "SEE ALSO" |
49625d7c | 93 | fs(5) |