(tar.info.gz) Dumpdir

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 Dumpdir
 =======
 
 Incremental archives keep information about contents of each dumped
 directory in special data blocks called "dumpdirs".
 
    Dumpdir is a sequence of entries of the following form:
 
      C FILENAME \0
 
 where C is one of the "control codes" described below, FILENAME is the
 name of the file C operates upon, and '\0' represents a nul character
 (ASCII 0).  The white space characters were added for readability, real
 dumpdirs do not contain them.
 
    Each dumpdir ends with a single nul character.
 
    The following table describes control codes and their meanings:
 
 'Y'
      FILENAME is contained in the archive.
 
 'N'
      FILENAME was present in the directory at the time the archive was
      made, yet it was not dumped to the archive, because it had not
      changed since the last backup.
 
 'D'
      FILENAME is a directory.
 
 'R'
      This code requests renaming of the FILENAME to the name specified
      with the 'T' command, that immediately follows it.
 
 'T'
      Specify target file name for 'R' command (see below).
 
 'X'
      Specify "temporary directory" name for a rename operation (see
      below).
 
    Codes 'Y', 'N' and 'D' require FILENAME argument to be a relative
 file name to the directory this dumpdir describes, whereas codes 'R',
 'T' and 'X' require their argument to be an absolute file name.
 
    The three codes 'R', 'T' and 'X' specify a "renaming operation".  In
 the simplest case it is:
 
      Rsource\0Tdest\0
 
 which means "rename file 'source' to file 'dest'".
 
    However, there are cases that require using a "temporary directory".
 For example, consider the following scenario:
 
   1. Previous run dumped a directory 'foo' which contained the following
      three directories:
 
           a
           b
           c
 
   2. They were renamed _cyclically_, so that:
 
           a became b
           b became c
           c became a
 
   3. New incremental dump was made.
 
    This case cannot be handled by three successive renames, since
 renaming 'a' to 'b' will destroy the existing directory.  To correctly
 process it, GNU 'tar' needs a temporary directory, so it creates the
 following dumpdir (newlines have been added for readability):
 
      Xfoo\0
      Rfoo/a\0T\0
      Rfoo/b\0Tfoo/c\0
      Rfoo/c\0Tfoo/a\0
      R\0Tfoo/a\0
 
    The first command, 'Xfoo\0', instructs the extractor to create a
 temporary directory in the directory 'foo'.  Second command,
 'Rfoo/aT\0', says "rename file 'foo/a' to the temporary directory that
 has just been created" (empty file name after a command means use
 temporary directory).  Third and fourth commands work as usual, and,
 finally, the last command, 'R\0Tfoo/a\0' tells tar to rename the
 temporary directory to 'foo/a'.
 
    The exact placement of a dumpdir in the archive depends on the
 archive format ( Formats):
 
    * PAX archives
 
      In PAX archives, dumpdir is stored in the extended header of the
      corresponding directory, in variable 'GNU.dumpdir'.
 
    * GNU and old GNU archives
 
      These formats implement special header type 'D', which is similar
      to ustar header '5' (directory), except that it precedes a data
      block containing the dumpdir.
 

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