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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 <sys/types.h> #include <sys/dir.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 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). 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(1) and mount(8).) The directory entry format is defined in the file <sys/dirent.h> and further in the file <dirent.h>. When the macro _DARWIN_FEATURE_64_BIT_INODE is not defined (see stat(2) for more information on this macro), the dirent structure is defined as: /*** 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 */ }; However, when the macro _DARWIN_FEATURE_64_BIT_INODE is defined, the dirent structure is defined as: /* * 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 */ __uint16_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 */ }; In addition: /* * 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 ----------------------------------------- /*** 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 */ SEE ALSO
fs(5), inode(5) HISTORY
A dir file format appeared in Version 7 AT&T UNIX. 4.2 Berkeley Distribution April 19, 1994 4.2 Berkeley Distribution

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