[Bug-tar] Proposed enhancements to "Sparse format 1.0"

[Tim Kientzle]

I've just finished implementing read support
for the new GNU tar sparse file formats in
libarchive/bsdtar, and have a couple of suggestions
you might consider if you ever create a format 1.1:

  * Don't pad.  The 1.0 format pads the prepended
sparse block description out to a multiple of 512
bytes.  There's no compelling need for this; it
just makes the archive larger.

  * Include a format specifier ("magic number")
in the prepended block description.  Specifically,
I'd like to see something like the following added
to the beginning of the block description:

   #!gnu_sparse_file
   #format=1.1

This would be compatible with the current
1.0 format if readers of that format ignored
comment lines.  (hint, hint ;-)

Cheers,

Tim Kientzle