4.3BSD-Reno/share/man/cat5/dir.0

DIR(5)			      1985			   DIR(5)



NNAAMMEE
     dir - format of directories

SSYYNNOOPPSSIISS
     ##iinncclluuddee <<ssyyss//ttyyppeess..hh>>
     ##iinncclluuddee <<ssyyss//ddiirr..hh>>

DDEESSCCRRIIPPTTIIOONN
     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 _f_s(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 7/27/90                May				1






DIR(5)			      1985			   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];
	  };

     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 mean-
     ing of `..' is modified for the root directory of the master
     file system ("/"), where `..' has the same meaning as `.'.

SSEEEE AALLSSOO
     fs(5)



























Printed 7/27/90                May				2