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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 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).
.\" An entry in this tree,
.\" nested or not nested,
.\" is a pathname.
.Pp
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.
.Pp
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 . )
.Pp
The directory entry format is defined in the file
.Aq sys/dirent.h 
and further in the file
.Aq dirent.h .
When the macro
.Dv _DARWIN_FEATURE_64_BIT_INODE
is not defined (see
.Xr stat 2
for more information on this macro), the
.Fa dirent
structure is defined as:
.Bd -literal
/*** 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 */
};
.Ed
.Pp
However, when the macro
.Dv _DARWIN_FEATURE_64_BIT_INODE
is defined, the
.Fa dirent
structure is defined as:
.Bd -literal
/*
 * 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 */
};
.Ed
.Pp
In addition:
.Bd -literal
/*
 * 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

.Ed
-----------------------------------------
.Bd -literal
/*** 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 */
.Ed
.Sh SEE ALSO
.Xr fs 5 ,
.Xr inode 5
.Sh HISTORY
A
.Nm
file format appeared in
.At v7 .