DIR(5)DIR(5)NAMEdir - 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.
*/
#ifdef KERNEL
#define DIRBLKSIZ DEV_BSIZE
#else
#define DIRBLKSIZ 512
#endif
#define MAXNAMLEN 255
/*
* 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 {
u_long 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 ALSOfs(5)4.2 Berkeley Distribution May 15, 1985 DIR(5)
