Re: [PATCH 0/2] git-config and large integers

From: Jeff King <peff@peff.net>
Date: Aug 21, 2013, 02:43 UTC
Message-ID: <20130821024355.GB25296@sigill.intra.peff.net>
In-Reply-To: <xmqqhaekudzp.fsf@gitster.dls.corp.google.com>

On Tue, Aug 20, 2013 at 04:41:30PM -0700, Junio C Hamano wrote:

Show 5 quoted lines

> If this applied on the writing side, I would understand it very
> much, i.e.
> 
> 	$ git config --int32 foo.size 2g
>         fatal: "2g" is too large to be read as "int32".

It does, by the way. When you request a type on the writing side, we normalize (and complain in the same way as we do when reading).

Show 10 quoted lines

> and as a complement it may make sense as a warning mechanism to also
> error out when existing value does not fit on the "platform" int, so
> your 
> 
> >>   $ git config --int foo.size
> >>   fatal: bad config value for 'foo.size' in .git/config
> 
> might make sense (even though I'd suggest being more explicit than
> "bad value" in this case---"the value specified will not fit when
> used in a variable of type int on this platform").

Yes, the error message is terrible, and I think an extra patch on top to improve it is worth doing. But note that I am not introducing that error here at all. On 32-bit systems, we already correctly range-checked and produced that error. It is only on 64-bit systems that the range check was flat out wrong. It checked against "long"'s precision, but then cast the result to an int, losing bits. A possibly worse example than the negative one is:

  $ git config foo.bar 4g
  $ git config --int foo.bar
  0

Again, that is what git's internal code is seeing. And that is why keeping the range check for git-config has value: it lets you see what git would see internally.

> When .git/config is shared on two different boxes (think: NFS), the
> size of "int" might be different between them, so the logic to produce
> such a warning may have to explicitly check against int32_t, not
> platform int and say "will not fit in 'int' on some machines".

I don't really see the value in that. You can always write whatever you like in the config file. The reader is responsible during parsing for saying "Hey, I am 32-bit and I can't handle this". And we already do that, and it works fine. So if you have an NFS-shared .git/config, and you set "pack.deltacachesize" to "4g", a 64-bit machine will do fine with that, and a 32-bit machine will complain. Which seems like the only sane thing to do.

There are a few config options that use "unsigned long" that I would argue should be "off_t" or something (for example, core.bigFileThreshold, which cannot be more than 4G on a 32-bit machine, simply because we can't represent the size. On the other hand, there is probably a ton of stuff that does not work with 4G files on such a system, because we use unsigned long all over the place inside the code). -Peff