From: Junio C Hamano <gitster@pobox.com>
To: "brian m. carlson" <sandals@crustytoothpaste.net>
Cc: git@vger.kernel.org
Subject: Re: Design of multiple hash support
Date: Mon, 05 Nov 2018 11:36:01 +0900 [thread overview]
Message-ID: <xmqqlg68jlny.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20181105010032.GN731755@genre.crustytoothpaste.net> (brian m. carlson's message of "Mon, 5 Nov 2018 01:00:33 +0000")
"brian m. carlson" <sandals@crustytoothpaste.net> writes:
> I'm currently working on getting Git to support multiple hash algorithms
> in the same binary (SHA-1 and SHA-256). In order to have a fully
> functional binary, we'll need to have some way of indicating to certain
> commands (such as init and show-index) that they should assume a certain
> hash algorithm.
>
> There are basically two approaches I can take. The first is to provide
> each command that needs to learn about this with its own --hash
> argument. So we'd have:
>
> git init --hash=sha256
> git show-index --hash=sha256 <some-file
>
> The other alternative is that we provide a global option to git, which
> is parsed by all programs, like so:
>
> git --hash=sha256 init
> git --hash=sha256 show-index <some-file
I am assuming that "show-index" above is a typo for something like
"hash-object"?
It is hard to answer the question without knowing what exactly does
"(to) support multiple hash algorithms" mean. For example, inside
today's repository, what should this command do?
git --hash=sha256 cat-file commit HEAD
It can work this way:
- read HEAD, discover that I am on 'master' branch, read refs/heads/master
to learn the object name in 40-hex, realize that it cannot be
sha256 and report "corrupt ref".
Or it can work this way:
- read repository format, realize it is a good old sha1 repository.
- do the usual thing to get to read_object() to read the commit
object data for the commit at HEAD, doing all of it in sha1.
- in the commit object data, locate references to other objects
that use sha1 name.
- replace these sha1 references with their sha256 counterparts and
show the result.
I am guessing that you are doing the former as a good first step, in
which case, as an option that changes/affects the behaviour of git
globally, I think "git --hash=sha256" would make sense, like other
global options like --literal-pathspecs and --no-replace-objects.
Thanks.
next prev parent reply other threads:[~2018-11-05 2:36 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-05 1:00 Design of multiple hash support brian m. carlson
2018-11-05 2:36 ` Junio C Hamano [this message]
2018-11-05 18:03 ` Stefan Beller
2018-11-05 23:54 ` brian m. carlson
2018-11-05 19:03 ` Duy Nguyen
2018-11-05 22:00 ` Jonathan Nieder
2018-11-06 0:13 ` brian m. carlson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: http://vger.kernel.org/majordomo-info.html
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=xmqqlg68jlny.fsf@gitster-ct.c.googlers.com \
--to=gitster@pobox.com \
--cc=git@vger.kernel.org \
--cc=sandals@crustytoothpaste.net \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://80x24.org/mirrors/git.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).