DIR(5) BSD Programmer's Manual DIR(5)
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\bt - directory file format
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Directories provide a convienent hierarchical method of grouping files
while obscuring the underlying details of the storage medium. A directo-
ry file is differentiated from a plain file by a flag in its inode(5) en-
try. It consists of records (directory entries) each of which contain
information about a file and a pointer to the file itself. Directory en-
tries may contain other directories as well as plain files; such nested
directories are refered to as subdirectories. A hierarchy of directories
and files is formed in this manner and is called a file system (or ref-
ered to as a file system tree).
Each directory file contains two special directory entries; one is a
pointer to the directory itself called dot `.' and the other a pointer to
its parent directory called dot-dot `..'. Dot and dot-dot are valid path-
names, 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(1) and mount(8).)
The directory entry format is defined in the file <dirent.h>:
* A directory entry has a struct dirent 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.
u_long d_fileno; /* file number of entry */
u_short d_reclen; /* length of this record */
u_short d_namlen; /* length of string in d_name */
char d_name[MAXNAMLEN + 1]; /* maximum name length */
char d_name[MAXNAMLEN + 1]; /* maximum name length */
#define d_ino d_fileno /* backward compatibility */
/* definitions for library routines operating on directories. */
/* structure describing an open directory. */
typedef struct _dirdesc {
int dd_fd; /* file descriptor associated with directory */
long dd_loc; /* offset in current buffer */
long dd_size; /* amount of data returned by getdirentries */
char *dd_buf; /* data buffer */
int dd_len; /* size of data buffer */
long dd_seek; /* magic cookie returned by getdirentries */
#define dirfd(dirp) ((dirp)->dd_fd)
#endif /* _POSIX_SOURCE */
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A d
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\br file format appeared in Version 7 AT&T UNIX.
4.2 Berkeley Distribution June 5, 1993 2