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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 (the ino_t type is 32-bits), 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 ino_t type will be 64-bits (force
     64-bit inode mode by defining the _DARWIN_USE_64_BIT_INODE macro before including header files).  This
     will cause symbol variants of the directory routines, with the $INODE64 suffixes, to be automatically
     linked in.  In addition, the dirent structure will now be 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 */
             __uint16_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