dir(5) [bsd man page]
DIR(5) File Formats Manual DIR(5) NAME
dir - format of directories SYNOPSIS
#include <sys/types.h> #include <sys/dir.h> DESCRIPTION
A directory behaves exactly like an ordinary file, save that no user may write into a directory. The fact that a file is a directory is indicated by a bit in the flag word of its i-node entry; see fs(5). The structure of a directory entry as given in the include file is: /* * A directory consists of some number of blocks of DIRBLKSIZ * bytes, where DIRBLKSIZ is chosen such that it can be transferred * to disk in a single atomic operation (e.g. 512 bytes on most machines). * * Each DIRBLKSIZ byte block contains some number of directory entry * structures, which are of variable length. Each directory entry has * a struct direct 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 MAXNAMLEN. * * The macro DIRSIZ(dp) gives the amount of space required to represent * a directory entry. Free space in a directory is represented by * entries which have dp->d_reclen > DIRSIZ(dp). All DIRBLKSIZ bytes * in a directory block are claimed by the directory entries. This * usually results in the last entry in a directory having a large * dp->d_reclen. When entries are deleted from a directory, the * space is returned to the previous entry in the same directory * block by increasing its dp->d_reclen. If the first entry of * a directory block is free, then its dp->d_ino is set to 0. * Entries other than the first in a directory do not normally have * dp->d_ino set to 0. */ #define DIRBLKSIZ 512 #define MAXNAMLEN 63 /* * The DIRSIZ macro gives the minimum record length which will hold * the directory entry. This requires 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 4 byte boundary. */ #undef DIRSIZ #define DIRSIZ(dp) ((((sizeof (struct direct) - (MAXNAMLEN+1)) + (dp)->d_namlen+1) + 3) &~ 3) struct direct { ino_t d_ino; short d_reclen; short d_namlen; char d_name[MAXNAMLEN + 1]; /* typically shorter */ }; struct _dirdesc { int dd_fd; long dd_loc; long dd_size; char dd_buf[DIRBLKSIZ]; }; By convention, the first two entries in each directory are for `.' and `..'. The first is an entry for the directory itself. The second is for the parent directory. The meaning of `..' is modified for the root directory of the master file system ("/"), where `..' has the same meaning as `.'. SEE ALSO
fs(5) BUGS
The 63 character MAXNAMLEN value is shorter than the 255 characters allowed by 4BSD. This could lead to file name portability problems in unusual circumstances. The disk format of directories is only slightly different from the 4BSD directory format, the inode number is of type ino_t rather than u_long to reduce the amount of 32 bit arithmetic in the kernel. 4.2 Berkeley Distribution May 15, 1985 DIR(5)
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DIR(5) BSD File Formats Manual DIR(5) NAME
dir, dirent -- directory file format SYNOPSIS
#include <dirent.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 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(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 4 * byte boundary with null bytes. All names are guaranteed null terminated. * The maximum length of a name in a directory is MAXNAMLEN. */ struct dirent { __uint32_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 */ #ifdef _POSIX_SOURCE char d_name[255 + 1]; /* name must be no longer than this */ #else #define MAXNAMLEN 255 char d_name[MAXNAMLEN + 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 requires 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 4 byte boundary. */ #define _GENERIC_DIRSIZ(dp) ((sizeof (struct dirent) - (MAXNAMLEN+1)) + (((dp)->d_namlen+1 + 3) &~ 3)) #ifdef _KERNEL #define GENERIC_DIRSIZ(dp) _GENERIC_DIRSIZ(dp) #endif #endif /* !_SYS_DIRENT_H_ */ SEE ALSO
fs(5), inode(5) HISTORY
A dir file format appeared in Version 7 AT&T UNIX. BUGS
The usage of the member d_type of struct dirent is unportable as it is FreeBSD-specific. It also may fail on certain file systems, for exam- ple the cd9660 file system. BSD
April 19, 1994 BSD