Re: [PATCH] reopen_tempfile(): truncate opened file

> > > +       after=$(wc -c <.git/index) &&
> > > +
> > > +       # double check that the index shrank
> > > +       test $before -gt $after &&
> > > +
> > > +       # and that our index was not corrupted
> > > +       git fsck
> >
> > If the index is not shrunk, we parse remaining rubbish as extensions.
> > If by chance the rubbish extension name is in uppercase, then we
> > ignore (and not flag it as error). But then the chances of the next 4
> > bytes being the "right" extension size is so small that we would end
> > up flagging it as bad extension anyway. So it's good. But if you want
> > to be even stricter (not necessary in my opinion), make sure that
> > stderr is empty.
>
> In this case, the size difference is only a few bytes, so the rubbish
> actually ends up in the trailing sha1. The reason I use git-fsck here is
> that it actually verifies the whole sha1 (since normal index reads no
> longer do). In fact, a normal index read won't show any problem for this
> case (since it is _only_ the trailing sha1 which is junk, and we no
> longer verify it on every read).
>
> In the original sparse-dev case, the size of the rubbish is much larger
> (because we deleted a lot more entries), and we do interpret it as a
> bogus extension. But it also triggers here, because the trailing sha1 is
> _also_ wrong.
>
> So AFAIK this fsck catches everything and yields a non-zero exit in the
> error case. And it should work for even a single byte of rubbish.