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Re: [PATCH v4 4/4] sha1_name: minimize OID comparisons during disambiguation

On Tue, Oct 10, 2017 at 09:56:38PM +0900, Junio C Hamano wrote:

> Jeff King <peff@xxxxxxxx> writes:
> > OK, I think that makes more sense. But note the p->num_objects thing I
> > mentioned. If I do:
> >
> >   git pack-objects .git/objects/pack/pack </dev/null
> >
> > then I have a pack with zero objects, which I think we'd similarly want
> > to return early from. I.e., I think we need:
> >
> >   if (p->num_objects)
> > 	return;
> >
> > Technically that also covers open_pack_index() failure, too, but that's
> > a subtlety I don't think we should rely on.
> True.  I notice that the early part of the two functions look almost
> identical.  Do we need error condition handling for the other one,
> too?

I'm not sure which two you mean. Do you mean find_pack_entry_one() in
packfile.c as the other one? If so, I think it is fine in the
zero-object case, because it does not do the "this is the sha1 at the
position where it _would_ be found" trick, which is what causes us to
potentially dereference nonsense.