[Nottingham] Calculating the overhead of "tar"

[Paul Sladen]

On Sun, 12 Dec 2004, Mike Cardwell wrote:

Hello Mister Cardwell.

> I was hoping to not have to reverse engineer tar. :(

"Reverse Engineer?".  ...You have the source code!

> > A Google search might find some docs...
> That's the problem. It doesn't. :)

  file:///usr/include/tar.h

Complete with a nice description of the file format; the code would be
something like:

  total = 1024  #  2*512 Null termination blocks at end, plus
  for f in files:
      total += (filesize(f) + 1023) & ~511     # 512 header + n*512 data

GNU tar appears to round up to the nearest 20 blocks (10kB), so also:

  total = ((total + 10239) / 10240) * 10240

depending on what your perl library does.

	-Paul
-- 
Is there no safe way to travel?  Mataro, ES