Re: Be more careful about updating refs

[Junio C Hamano <gitster@pobox.com>]

"Shawn O. Pearce" <spearce@spearce.org> writes:

> I think the problem is nobody has tested fast-import updating an
> existing ref while using NO_MMAP.  Or if they did, they didn't report
> the problem as they didn't figure they needed fast-import that badly.
>
> Updating an existing ref is not a common operation, but the test
> suite does test for it.  So it must be the NO_MMAP configuration
> is simply not being tested well enough.

Ok, thanks.

Now a more important question is how we would properly fix this
issue?

I suspect that fast-import is the only one that opens windows
into an unfinalized pack, and if that is the case, it would be
the only program that may be hit by the issue of mmap emulation
getting stale data.

I do not think the patch I posted was correct at all.

Especially, I am not sure if the issue only exists at the
end_packfile() boundary.  Don't we have the same issue reading
from the packfile being built, and isn't the only reason my hack
works it around is because access patterns of the testsuite
happens to not trigger it?