DIRENT(3) BSD Library Functions Manual DIRENT(3)
dirent -- directory format
Directories provide a convenient hierarchical method of grouping files while obscuring the
underlying details of the storage medium. A directory file is differentiated from a plain
file by a flag in its inode(5) entry. It consists of records (directory entries) each of
which contains information about a file and a pointer to the file itself. Directory entries
may contain other directories as well as plain files; such nested directories are referred
to as subdirectories. A hierarchy of directories and files is formed in this manner and is
called a file system (or referred to as a file system tree).
Each directory file contains two special directory entries; one is a pointer to the direc-
tory itself called dot '.' and the other a pointer to its parent directory called dot-dot
'..'. Dot and dot-dot are valid pathnames, however, the system root directory '/', has no
parent and dot-dot points to itself like dot.
File system nodes are ordinary directory files on which has been grafted a file system
object, such as a physical disk or a partitioned area of such a disk. (See mount(8).)
The directory entry format is defined in the file <sys/dirent.h>, which is also included by
<dirent.h>. The format is represented by the dirent structure, which contains the following
char d_name[MAXNAMLEN + 1];
1. The d_fileno entry is a number which is unique for each distinct file in the
filesystem. Files that are linked by hard links (see link(2)) have the same
d_fileno. If d_fileno is zero, the entry refers to a deleted file. The type
ino_t is defined in <sys/types.h>.
2. The d_reclen entry is the length, in bytes, of the directory record.
3. The d_namlen entry specifies the length of the file name excluding the NUL. Thus
the actual size of d_name may vary from 1 to MAXNAMLEN + 1.
4. The d_type is the type of the file.
5. The d_name entry contains a NUL-terminated file name.
The following table lists the types available for d_type and the corresponding ones used in
the struct stat (see stat(2)), respectively:
Dirent Stat Description
DT_UNKNOWN - unknown file type
DT_FIFO S_IFIFO named pipe
DT_CHR S_IFCHR character device
DT_DIR S_IFDIR directory
DT_BLK S_IFBLK block device
DT_REG S_IFREG regular file
DT_LNK S_IFLNK symbolic link
DT_SOCK S_IFSOCK UNIX domain socket
DT_WHT S_IFWHT dummy ``whiteout inode''
The DT_WHT type is internal to the implementation and should not be seen in normal user
applications. The macros DTTOIF() and IFTODT() can be used to convert from struct dirent
types to struct stat types, and vice versa.
The IEEE Std 1003.1-2001 (``POSIX.1'') standard specifies only the fields d_ino and d_name.
The remaining fields are available on many, but not all systems.
Furthermore, the standard leaves the size of d_name as unspecified, mentioning only that the
number of bytes preceding the terminating NUL shall not exceed NAME_MAX. Because of this,
and because the d_namlen field may not be present, a portable application should determine
the size of d_name by using strlen(3) instead of applying the sizeof() operator.
getdents(2), fs(5), inode(5)
A dir structure appeared in Version 7 AT&T UNIX. The dirent structure appeared in
BSD May 16, 2010 BSD