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DIR(5)                        File Formats Manual                       DIR(5)



NAME
       dir - format of directories

SYNOPSIS
       #include <&lt;sys/types.h>&gt;
       #include <&lt;sys/dir.h>&gt;

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 ALSO
       fs(5)



4th Berkeley Distribution       15 January 1983                         DIR(5)