Re: [PATCH 26/26] midx: switch to using the_hash_algo

> On 2019-08-22 at 14:04:16, Derrick Stolee wrote:
>> On 8/18/2019 4:04 PM, brian m. carlson wrote:
>>> diff --git a/midx.c b/midx.c
>>> index d649644420..f29afc0d2d 100644
>>> --- a/midx.c
>>> +++ b/midx.c
>>> @@ -19,8 +19,7 @@
>>>  #define MIDX_BYTE_NUM_PACKS 8
>>>  #define MIDX_HASH_VERSION 1
>>
>> This hash version "1" is the same as we used in the commit-graph. It's
>> a byte value from the file format, and we've already discussed how it
>> would have been better to use the 4-byte identifier, but that ship has
>> sailed. I'm just pointing this out to say that we are not done in this
>> file yet, but we can get to that when we want to test the midx with
>> multiple hash lengths.
> 
> My approach so far has been to assume everything in the .git directory
> is in the same hash except for the translation functionality. Therefore,
> it doesn't make sense to distinguish between hashes in the midx files,
> because we'll never have files that differ in hash.  So essentially the
> MIDX_HASH_VERSION being 1 is "whatever hash is being used in the .git
> directory", not just SHA-1.
> 
> In addition, the current multi-pack index format isn't capable (from my
> reading of the documentation, at least) of handling multiple hash
> algorithms at once.  So we'd need a midx v2 format for folks who are
> using SHA-256 with SHA-1 compatibility and we could then write separate
> sets of object chunks with an appropriate format identifier, much like
> the proposed pack index v3.