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
           * 4 byte boundary.



Printed 3/13/89                                                 1

DIR(5)                  COMMAND REFERENCE                  DIR(5)



           */
          #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), and telldir(3c).



















Printed 3/13/89                                                 2

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