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DIR(5)                    NetBSD Programmer's Manual                    DIR(5)


NAME

     dir, dirent - directory file format


SYNOPSIS

     #include <sys/types.h>
     #include <sys/dir.h>


DESCRIPTION

     Directories provide a convenient 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 contains
     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 re-
     ferred 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
     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 <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_ */


SEE ALSO

     fs(5), inode(5)


HISTORY

     A dir file format appeared in Version 7 AT&T UNIX.

NetBSD 1.4                      April 19, 1994                               2