DIR(5)							      BSD File Formats 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
     directory 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 refered 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).

     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 <sys/dirent.h> and further in the file <dirent.h>.  When the macro
     _DARWIN_FEATURE_64_BIT_INODE is not defined (see stat(2) for more information on this macro), the dirent structure is defined as:

     /*** Excerpt from <sys/dirent.h> ***/
     /*
      * The dirent structure defines the format of directory entries.
      *
      * 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 255.
      */

     struct dirent { /* when _DARWIN_FEATURE_64_BIT_INODE is NOT defined */
	     ino_t	d_ino;		      /* 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 */
	     char    d_name[255 + 1];	/* name must be no longer than this */
     };

     However, when the macro _DARWIN_FEATURE_64_BIT_INODE is defined, the dirent structure is defined as:

     /*
      * The dirent structure defines the format of directory entries.
      *
      * 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 1023.
      */

     struct dirent { /* when _DARWIN_FEATURE_64_BIT_INODE is defined */
	     ino_t	d_fileno;     /* file number of entry */
	     __uint64_t d_seekoff;    /* seek offset (optional, used by servers) */
	     __uint16_t d_reclen;     /* length of this record */
	     __uint16_t d_namlen;     /* length of string in d_name */
	     __uint8_t	d_type;       /* file type, see below */
	     char    d_name[1024];    /* name must be no longer than this */
     };

     In addition:

     /*
      * File types
      */
     #define DT_UNKNOWN       0
     #define DT_FIFO	      1
     #define DT_CHR	      2
     #define DT_DIR	      4
     #define DT_BLK	      6
     #define DT_REG	      8
     #define DT_LNK	     10
     #define DT_SOCK	     12
     #define DT_WHT	     14

     -----------------------------------------

     /*** Excerpt from <dirent.h> ***/

     #define d_fileno	     d_ino	  /* backward compatibility */

     /* definitions for library routines operating on directories. */
     #define DIRBLKSIZ	     1024

     struct _telldir;		     /* see telldir.h */

     /* 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 */
	     long    __dd_rewind;  /* magic cookie for rewinding */
	     int     __dd_flags;   /* flags for readdir */
	     pthread_mutex_t __dd_lock; /* for thread locking */
	     struct _telldir *__dd_td; /* telldir position recording */
     } DIR;

     #define dirfd(dirp)     ((dirp)->dd_fd)

     /* flags for opendir2 */
     #define DTF_HIDEW	     0x0001  /* hide whiteout entries */
     #define DTF_NODUP	     0x0002  /* don't return duplicate names */
     #define DTF_REWIND      0x0004  /* rewind after reading union stack */
     #define __DTF_READALL   0x0008  /* everything has been read */

SEE ALSO

     fs(5), inode(5)

HISTORY

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

4.2 Berkeley Distribution					  April 19, 1994					 4.2 Berkeley Distribution