tail head cat sleep
QR code linking to this page

Manual Pages  — DIR


dir, dirent – directory file format



#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)


A dir file format appeared in AT&T v7 .


The usage of the member d_type of struct dirent is unportable as it is FreeBSD Ns -specific . It also may fail on certain file systems, for example the cd9660 file system.

DIR (5) November 14, 2018

tail head cat sleep
QR code linking to this page

Please direct any comments about this manual page service to Ben Bullock. Privacy policy.