June 22, 2007 DIRENT 5

### NAME

dirent - directory format

### SYNOPSIS

### 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 referred 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(8).)

The directory entry format is defined in the file <```sys/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 an
     * 8 byte boundary with null bytes.  All names are guaranteed null
     * terminated.  The maximum length of a name in a directory is MAXNAMLEN.
     */

    struct dirent {
            ino_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 */
    #define MAXNAMLEN       511
            char d_name[MAXNAMLEN + 1]; /* name must be no longer than this */
    };

    /*
     * 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

### SEE ALSO

getdents(2), fs(5), inode(5)

### HISTORY

A dir structure appeared in Version 7 `AT&T UNIX`. The dirent structure appeared in NetBSD1.3.