Re: [PATCH 1/2] archive-tar: write extended headers for file sizes >= 8GB

Am 21.06.2016 um 23:02 schrieb Jeff King:

On Tue, Jun 21, 2016 at 10:42:52PM +0200, René Scharfe wrote:

quoted

quoted

quoted

If we could set the limit to a lower value than 8GB for testing then we
could at least check if the extended header is written, e.g. if ustar_size()
could be convinced to return 0 every time using a hidden command line
parameter or an environment variable or something better.

Yes, we could do that, though I think it loses most of the value of the
test. We can check that if we hit an arbitrary value we generate the pax
header, but I think what we _really_ care about is: did we generate an
output that somebody else's tar implementation can handle.

I agree with the last point, but don't see how that diminishes the
value of such a test.  If we provide file sizes only through extended
headers (the normal header field being set to 0) and we can extract
files with correct sizes then tar must have interpreted those header
as intended, right?

The diminished value is:

   1. This is a situation that doesn't actually happen in real life.

   2. Now we're carrying extra code inside git only for the sake of
      testing (which can have its own bugs, etc).

Still, it may be better than nothing.

quoted

-- >8 --
Subject: archive-tar: test creation of pax extended size headers

---
The value 120 is magic; we need it to pass the tests.  That's
because prepare_header() is used for building extended header
records as well and we don't create extended headers for extended
headers (not sure if that would work anyway), so they simply
vanish when they're over the limit as their size field is set to
zero.

Right, so this is sort of what I meant in (2). Now we have a
tar.ustarsizemax setting shipped in git that is totally broken if you
set it to "1".

I can live with it as a tradeoff, but it is definitely a negative IMHO.

Yes, it's only useful as a debug flag, but the fact that it breaks 
highlights a (admittedly mostly theoretical) shortcoming: The code 
doesn't handle extended headers that are over the size limit as nicely 
as it could.  So the test was already worth it, even if won't land in 
master. :)

René