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28 .\" @(#)dir.5 8.3 (Berkeley) 4/19/94
37 .Nd directory file format
41 Directories provide a convenient hierarchical method of grouping
42 files while obscuring the underlying details of the storage medium.
43 A directory file is differentiated from a plain file
47 It consists of records (directory entries) each of which contains
48 information about a file and a pointer to the file itself.
49 Directory entries may contain other directories
50 as well as plain files; such nested directories are referred to as
52 A hierarchy of directories and files is formed in this manner
53 and is called a file system (or referred to as a file system tree).
54 .\" An entry in this tree,
55 .\" nested or not nested,
58 Each directory file contains two special directory entries; one is a pointer
59 to the directory itself
62 and the other a pointer to its parent directory called dot-dot
65 are valid pathnames, however,
66 the system root directory
68 has no parent and dot-dot points to itself like dot.
70 File system nodes are ordinary directory files on which has
71 been grafted a file system object, such as a physical disk or a
72 partitioned area of such a disk.
78 The directory entry format is defined in the file
80 (which should not be included directly by applications):
82 #ifndef _SYS_DIRENT_H_
83 #define _SYS_DIRENT_H_
85 #include <machine/ansi.h>
88 * The dirent structure defines the format of directory entries returned by
89 * the getdirentries(2) system call.
91 * A directory entry has a struct dirent at the front of it, containing its
92 * inode number, the length of the entry, and the length of the name
93 * contained in the entry. These are followed by the name padded to a 8
94 * byte boundary with null bytes. All names are guaranteed null terminated.
95 * The maximum length of a name in a directory is MAXNAMLEN.
96 * Explicit pad is added between the last member of the header and
97 * d_name, to avoid having the ABI padding in the end of dirent on
98 * LP64 arches. There is code depending on d_name being last. Also,
99 * keeping this pad for ILP32 architectures simplifies compat32 layer.
103 ino_t d_fileno; /* file number of entry */
104 off_t d_off; /* directory offset of the next entry */
105 __uint16_t d_reclen; /* length of this record */
106 __uint8_t d_type; /* file type, see below */
107 __uint8_t d_namlen; /* length of string in d_name */
110 #define MAXNAMLEN 255
111 char d_name[MAXNAMLEN + 1]; /* name must be no longer than this */
113 char d_name[255 + 1]; /* name must be no longer than this */
131 * Convert between stat structure types and directory types.
133 #define IFTODT(mode) (((mode) & 0170000) >> 12)
134 #define DTTOIF(dirtype) ((dirtype) << 12)
137 * The _GENERIC_DIRSIZ macro gives the minimum record length which will hold
138 * the directory entry. This returns the amount of space in struct direct
139 * without the d_name field, plus enough space for the name with a terminating
140 * null byte (dp->d_namlen+1), rounded up to a 8 byte boundary.
142 * XXX although this macro is in the implementation namespace, it requires
143 * a manifest constant that is not.
145 #define _GENERIC_DIRLEN(namlen) \
146 ((__offsetof(struct dirent, d_name) + (namlen) + 1 + 7) & ~7)
147 #define _GENERIC_DIRSIZ(dp) _GENERIC_DIRLEN((dp)->d_namlen)
148 #endif /* __BSD_VISIBLE */
151 #define GENERIC_DIRSIZ(dp) _GENERIC_DIRSIZ(dp)
154 #endif /* !_SYS_DIRENT_H_ */
162 file format appeared in
165 The usage of the member d_type of struct dirent is unportable as it is
167 It also may fail on certain file systems, for example the cd9660 file system.