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     dir, dirent -- directory file format


     #include <dirent.h>


     Directories provide a convenient hierarchical method of grouping files
     while obscuring the underlying details of the storage medium.  A direc-
     tory 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 directo-
     ries 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 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(2) and mount(8).)

     The directory entry format is defined in the file <sys/dirent.h> (which
     should not be included directly by applications):

     #ifndef _SYS_DIRENT_H_
     #define _SYS_DIRENT_H_

     #include <machine/ansi.h>

      * The dirent structure defines the format of directory entries returned by
      * the getdirentries(2) system call.
      * 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 {
	     __uint32_t d_fileno;	     /* file number of entry */
	     __uint16_t d_reclen;	     /* length of this record */
	     __uint8_t	d_type; 	     /* file type, see below */
	     __uint8_t	d_namlen;	     /* length of string in d_name */
     #ifdef _POSIX_SOURCE
	     char    d_name[255 + 1];	     /* name must be no longer than this */
     #define MAXNAMLEN	     255
	     char    d_name[MAXNAMLEN + 1];  /* name must be no longer than this */
     #define DT_DIR	      4
     #define DT_BLK	      6
     #define DT_REG	      8
     #define DT_LNK	     10
     #define DT_SOCK	     12
     #define DT_WHT	     14

      * Convert between stat structure types and directory types.
     #define IFTODT(mode)    (((mode) & 0170000) >> 12)
     #define DTTOIF(dirtype) ((dirtype) << 12)

      * The _GENERIC_DIRSIZ macro gives the minimum record length which will hold
      * the directory entry.  This requires the amount of space in struct direct
      * without the d_name field, plus enough space for the name with a terminating
      * null byte (dp->d_namlen+1), rounded up to a 4 byte boundary.
     #define _GENERIC_DIRSIZ(dp)     ((sizeof (struct dirent) - (MAXNAMLEN+1)) + (((dp)->d_namlen+1 + 3) &~ 3))

     #ifdef _KERNEL
     #define GENERIC_DIRSIZ(dp)      _GENERIC_DIRSIZ(dp)

     #endif /* !_SYS_DIRENT_H_ */


     fs(5), inode(5)


     The usage of the member d_type of struct dirent is unportable as it is
     FreeBSD-specific.	It also may fail on certain file systems, for example
     the cd9660 file system.


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

FreeBSD 5.4			April 19, 1994			   FreeBSD 5.4


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