Re: [PATCH v3 1/9] t5326: demonstrate bitmap corruption after permutation

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 20, 2022, 22:41 UTC
Message-ID: <xmqq5yqeghck.fsf@gitster.g>
In-Reply-To: <YeneJrzjp160edGG@nand.local>

Taylor Blau <me@ttaylorr.com> writes:

Show 5 quoted lines

> Right. The problem being that it's possible to change the MIDX's
> object order without changing its checksum. Since the .rev file's
> contents encodes the pseudo-pack order, embedding it into the MIDX is
> sufficient to guarantee that the MIDX's checksum changes whenever the
> object order does.

To slightly rephrase,

    The problem being that before the change to embed reverse table in
    MIDX, it was possible to change the object order without changing
    the checksum, but with that change alone, if a rebuilt MIDX has the
    same checksum, it is guaranteed that it records the same objects in
    the same order.

Hence, shuffling between rename(2) and link(2), which was the code change that is only necessary to force updating the existing MIDX with newly recreated one because two MIDX with the same checksum could record objects in different orders, is no longer necessary.

Am I on the same page as you two?