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 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(1) and mount(8).)
The directory entry format is defined in the file Aq dirent.h :
#ifndef _DIRENT_H_
#define _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.
*/
struct dirent {
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 */
#ifdef _POSIX_SOURCE
char d_name[MAXNAMLEN + 1]; /* maximum name length */
#else
#define MAXNAMLEN 255
char d_name[MAXNAMLEN + 1]; /* maximum name length */
#endif
};
#ifdef _POSIX_SOURCE
typedef void * DIR;
#else
#define d_ino d_fileno /* backward compatibility */
/* definitions for library routines operating on directories. */
#define DIRBLKSIZ 1024
/* 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 */
} DIR;
#define dirfd(dirp) ((dirp)->dd_fd)
#ifndef NULL
#define NULL 0
#endif
#endif /* _POSIX_SOURCE */
#ifndef _KERNEL
#include <sys/cdefs.h>
#endif /* !_KERNEL */
#endif /* !_DIRENT_H_ */