8/12    Is there a way to combine two files without writing?  I mean
        unlinking the 2nd file but instead of freeing its blocks, adding them
        to the end of the 1st file.  Suppose gap is not an issue.
        \_ Instead of asking for an answer to some obscure no-details technical
           question, how about you ask us what you're actually really trying to
           do and maybe we can then help you solve the real problem?
           \_ Well, I want to make some kind of revision control except I
              don't want to do diffs (suppose it's binary) and just want to
              keep copies of old files up to a certain number (sort of like
              what VMS did).  As such, I don't want to read and write the
              files but just chain old copies together with some control info
              recorded separately.  If you have a better solution I would like
              to hear it, but my original question is quite well specified.
              \_ How about moving the files into a special directory?  I know
                 it's boring, but it would be easy, portable, and work.
              \_ You're describing tar.  Rename the old file and move it into
                 a tar file you've created for this purpose.  Tar will append,
                 allow searching, has control info, allow extracting by file
                 name, etc, etc.  Don't re-invent the wheel.
                 \_ Yeah it is like tar, but tar actually has to read the file
                    and then copy it bit by bit to another file.  I want to
                    just append the list of data blocks of the 2nd file to
                    that of the 1st file before unlinking it.
                    \_ Why?
                       \_ More efficient?????  You don't have to read and write
                          1000 50 MB files if you are not changing them.