> Tar uses inode numbers to determine which files are hardlinked. So
 > if you tar up a tree containing 0-byte files, then untar it
 > somewhere, all 0-byte files will end up being hardlinked to each
 > other. The same happens when you use cp -a.

Ahhh!  O.k., that changes everything.

 > Or take a hybrid approach: use your scheme for directories and my
 > scheme for files; use bit 0 or bit 31 to indicate what scheme is
 > used. Then directories have unique inode numbers, and files too as
 > long as their directory records are in the first 64Gb of the disc.

An incremental patch is attached that should apply cleanly to the
latest -mm tree.  It's not a hybrid.  It is a straight implementation
of your suggestion.  Hopefully this will make all inode numbers unique
for images less than 128GB in size.

Thanks