Manual Pages  — DIR

#include <dirent.h>

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 ‘.amp;’ and the other a pointer to its parent directory called dot-dot ‘amp;..’. 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 8
 * byte boundary with null bytes.  All names are guaranteed null terminated.
 * The maximum length of a name in a directory is MAXNAMLEN.
 * Explicit pad is added between the last member of the header and
 * d_name, to avoid having the ABI padding in the end of dirent on
 * LP64 arches.  There is code depending on d_name being last.  Also,
 * keeping this pad for ILP32 architectures simplifies compat32 layer.
 */

struct dirent {
        ino_t      d_fileno;            /* file number of entry */
        off_t      d_off;               /* directory offset of the next 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 */
        __uint32_t d_pad0;
#if __BSD_VISIBLE
#define MAXNAMLEN       255
        char    d_name[MAXNAMLEN + 1];  /* name must be no longer than this */
#else
        char    d_name[255 + 1];        /* name must be no longer than this */
#endif
};

/*
 * 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

/*
 * 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 returns 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 8 byte boundary.
 *
 * XXX although this macro is in the implementation namespace, it requires
 * a manifest constant that is not.
 */
#define _GENERIC_DIRLEN(namlen)                                 
        ((__offsetof(struct dirent, d_name) + (namlen) + 1 + 7) & ~7)
#define _GENERIC_DIRSIZ(dp)     _GENERIC_DIRLEN((dp)->d_namlen)
#endif /* __BSD_VISIBLE */

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

#endif /* !_SYS_DIRENT_H_ */

fs(5), inode(5)