Linux and UNIX Man Pages

Test Your Knowledge in Computers #343
Difficulty: Medium
Scott McNealy, Andy Bechtolsheim, and Vinod Khosla, all Caltech graduate students, founded Sun Microsystems.
True or False?
Linux & Unix Commands - Search Man Pages

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

Featured Tech Videos