DIR(5)                               BSD                                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, except 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 inode entry.  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 (for example 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.
           */
          /* so user programs can just include dir.h */
          #if !defined(KERNEL) && !defined(DEV_BSIZE)
          #define DEV_BSIZE 1024
          #endif
          #define DIRBLKSIZ DEV_BSIZE
          #define MAXNAMLEN 255

          struct  direct {
                  u_long    d_ino;    /* inode number of entry */
                  u_short   d_reclen; /* length of this record */
                  u_short   d_namlen; /* length of string in d_name */
                  off_t     d_off;    /* offset of disk directory entry */
                  char      d_name[MAXNAMLEN + 1];/* name must be no longer than this */
          };

          /*
           * 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))

          #ifndef KERNEL
          /*
           * Definitions for library routines operating on directories.
           */
          typedef struct _dirdesc {
                  int       dd_fd;
                  long      dd_loc;
                  long      dd_size;
                  char      *dd_buf;
          } DIR;

     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
     directory(3).