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@(#)dir.5 8.3 (Berkeley) 4/19/94
.Dd April 19, 1994 .Dt DIR 5 .Os BSD 4.2 .Sh NAME .Nm dir , .Nm dirent .Nd directory file format .Sh SYNOPSIS .Fd #include <sys/types.h> .Fd #include <sys/dir.h> .Sh DESCRIPTION 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 .Xr 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). An entry in this tree,
nested or not nested,
is a pathname.
p Each directory file contains two special directory entries; one is a pointer to the directory itself called dot .Ql . and the other a pointer to its parent directory called dot-dot .Ql .. . Dot and dot-dot are valid pathnames, however, the system root directory .Ql / , has no parent and dot-dot points to itself like dot.
p 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 .Xr mount 1 and .Xr mount 8 . )
p The directory entry format is defined in the file .Aq dirent.h : d -literal #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_ */ .Ed .Sh SEE ALSO .Xr fs 5 .Xr inode 5 .Sh HISTORY A .Nm file format appeared in .At v7 .