DIR(5)                  COMMAND REFERENCE                  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
     inode 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



Printed 10/17/86                                                1

DIR(5)                  COMMAND REFERENCE                  DIR(5)



      * 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];
     };


     The library routines for manipulating directories use the
     structure _dirdesc for storing directory pointers (as with
     FILE in the standard I/O library).  The library routines are
     closedir(3c), opendir(3c), readdir(3c), scandir(3c),
     seekdir(3c), and telldir(3c).

     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), closedir(3c), opendir(3c), readdir(3c), scandir(3c),
     seekdir(3c), telldir(3c).

















Printed 10/17/86                                                2

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