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From: Jonathan Nieder <jrnieder@gmail.com>
To: "brian m. carlson" <sandals@crustytoothpaste.net>
Cc: git@vger.kernel.org, Duy Nguyen <pclouds@gmail.com>
Subject: Re: State of NewHash work, future directions, and discussion
Date: Mon, 11 Jun 2018 19:42:52 -0700
Message-ID: <20180612024252.GA141166@aiede.svl.corp.google.com> (raw)
In-Reply-To: <20180612022815.GL38834@genre.crustytoothpaste.net>

brian m. carlson wrote:
> On Mon, Jun 11, 2018 at 12:01:03PM -0700, Jonathan Nieder wrote:

>>  1. Hash to be used for command output to the terminal
>>  2. Hash used in pack files
>>  3. Additional hashes (beyond (2)) that we can look up using the
>>     translation table
>>  4. Additional hashes (beyond (1)) accepted in input from the command
>>     line and stdin
>>
>> In principle, (1) and (4) would be globals, and (2) and (3) would be
>> tied to the repository.  I think this is always what Duy was hinting

Here, by 'always' I meant 'also'.  Sorry for the confusion.

>> at.
>>
>> All that said, as long as there is some notion of (1) and (4), I'm
>> excited. :)  Details of how they are laid out in memory are less
>> important.
>
> I'm happy to hear suggestions on how this should or shouldn't work.  I'm
> seeing these things in my head, but it can be helpful to have feedback
> about what people expect out of the code before I spend a bunch of time
> writing it.

So far you're doing pretty well. :)

I just noticed that I have some copy-edits for the
hash-function-transition doc from last year that I hadn't sent out yet
(oops).  I'll send them tonight or tomorrow morning.

[...]
>> brian m. carlson wrote:

>>> The transition plan anticipates a stage 1 where accept only SHA-1 on
>>> input and produce only SHA-1 on output, but store in NewHash.  As I've
>>> worked with our tests, I've realized such an implementation is not
>>> entirely possible.  We have various tools that expect to accept invalid
>>> object IDs, and obviously there's no way to have those continue to work.
>>
>> Can you give an example?  Do you mean commands like "git mktree"?
>
> I mean situations like git update-index.  We allow the user to insert
> any old invalid value (and in fact check that the user can do this).
> t0000 does this, for example.

I think we can forbid this in the new mode (using a test prereq to
ensure the relevant tests don't get run).  Likewise for the similar
functionality in "git mktree" and "git hash-object -w".

>> You can always use something like e.g. "doubled SHA-1" as a proof of
>> concept, but I agree that it's nice to be able to avoid some churn by
>> using an actual hash function that we're likely to switch to.
>
> I have a hash that I've been using, but redoing the work would be less
> enjoyable.  I'd rather write the tests only once if I can help it.

Thanks for the test fixes so far that make most of the test suite
hash-agnostic!

For t0000, yeah, there's no way around having to hard-code the new
hash there.

Thanks,
Jonathan

      reply index

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-09 20:56 brian m. carlson
2018-06-09 21:26 ` Ævar Arnfjörð Bjarmason
2018-06-09 22:49 ` Hash algorithm analysis brian m. carlson
2018-06-11 19:29   ` Jonathan Nieder
2018-06-11 20:20     ` Linus Torvalds
2018-06-11 23:27       ` Ævar Arnfjörð Bjarmason
2018-06-12  0:11         ` David Lang
2018-06-12  0:45         ` Linus Torvalds
2018-06-11 22:35     ` brian m. carlson
2018-06-12 16:21       ` Gilles Van Assche
2018-06-13 23:58         ` brian m. carlson
2018-06-15 10:33           ` Gilles Van Assche
2018-07-20 21:52     ` brian m. carlson
2018-07-21  0:31       ` Jonathan Nieder
2018-07-21 19:52       ` Ævar Arnfjörð Bjarmason
2018-07-21 20:25         ` brian m. carlson
2018-07-21 22:38       ` Johannes Schindelin
2018-07-21 23:09         ` Linus Torvalds
2018-07-21 23:59         ` brian m. carlson
2018-07-22  9:34           ` Eric Deplagne
2018-07-22 14:21             ` brian m. carlson
2018-07-22 14:55               ` Eric Deplagne
2018-07-26 10:05                 ` Johannes Schindelin
2018-07-22 15:23           ` Joan Daemen
2018-07-22 18:54             ` Adam Langley
2018-07-26 10:31             ` Johannes Schindelin
2018-07-23 12:40           ` demerphq
2018-07-23 12:48             ` Sitaram Chamarty
2018-07-23 12:55               ` demerphq
2018-07-23 18:23               ` Linus Torvalds
2018-07-23 17:57             ` Stefan Beller
2018-07-23 18:35             ` Jonathan Nieder
2018-07-24 19:01       ` Edward Thomson
2018-07-24 20:31         ` Linus Torvalds
2018-07-24 20:49           ` Jonathan Nieder
2018-07-24 21:13           ` Junio C Hamano
2018-07-24 22:10             ` brian m. carlson
2018-07-30  9:06               ` Johannes Schindelin
2018-07-30 20:01                 ` Dan Shumow
2018-08-03  2:57                   ` Jonathan Nieder
2018-09-18 15:18                   ` Joan Daemen
2018-09-18 15:32                     ` Jonathan Nieder
2018-09-18 16:50                     ` Linus Torvalds
2018-07-25  8:30             ` [PATCH 0/2] document that NewHash is now SHA-256 Ævar Arnfjörð Bjarmason
2018-07-25  8:30             ` [PATCH 1/2] doc hash-function-transition: note the lack of a changelog Ævar Arnfjörð Bjarmason
2018-07-25  8:30             ` [PATCH 2/2] doc hash-function-transition: pick SHA-256 as NewHash Ævar Arnfjörð Bjarmason
2018-07-25 16:45               ` Junio C Hamano
2018-07-25 17:25                 ` Jonathan Nieder
2018-07-25 21:32                   ` Junio C Hamano
2018-07-26 13:41                     ` [PATCH v2 " Ævar Arnfjörð Bjarmason
2018-08-03  7:20                       ` Jonathan Nieder
2018-08-03 16:40                         ` Junio C Hamano
2018-08-03 17:01                           ` Linus Torvalds
2018-08-03 16:42                         ` Linus Torvalds
2018-08-03 17:43                         ` Ævar Arnfjörð Bjarmason
2018-08-04  8:52                           ` Jonathan Nieder
2018-08-03 17:45                         ` brian m. carlson
2018-07-25 22:56                 ` [PATCH " brian m. carlson
2018-06-11 21:19   ` Hash algorithm analysis Ævar Arnfjörð Bjarmason
2018-06-21  8:20     ` Johannes Schindelin
2018-06-21 22:39     ` brian m. carlson
2018-06-11 18:09 ` State of NewHash work, future directions, and discussion Duy Nguyen
2018-06-12  1:28   ` brian m. carlson
2018-06-11 19:01 ` Jonathan Nieder
2018-06-12  2:28   ` brian m. carlson
2018-06-12  2:42     ` Jonathan Nieder [this message]

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