From: Johannes Schindelin <Johannes.Schindelin@gmx•de>
To: Phillip Wood <phillip.wood123@gmail•com>
Cc: Ezekiel Newren via GitGitGadget <gitgitgadget@gmail•com>,
git@vger•kernel.org, Elijah Newren <newren@gmail•com>,
Ezekiel Newren <ezekielnewren@gmail•com>,
"brian m. carlson" <sandals@crustytoothpaste•net>
Subject: gitoxide-compatible licensing of Git's Rust code, was Re: [PATCH 6/7] xdiff: conditionally use Rust's implementation of xxhash
Date: Tue, 23 Sep 2025 11:57:18 +0200 (CEST) [thread overview]
Message-ID: <9818dc92-3569-3e6f-0252-245c2bf0bf84@gmx.de> (raw)
In-Reply-To: <dd3a7ab0-947b-4592-a086-8c7028f02ffd@gmail.com>
Hi Phillip,
On Sun, 20 Jul 2025, Phillip Wood wrote:
> Hi Johannes
>
> On 19/07/2025 22:53, Johannes Schindelin wrote:
> > Hi Ezekiel,
> >
> > On Thu, 17 Jul 2025, Ezekiel Newren via GitGitGadget wrote:
> >
> > > diff --git a/rust/xdiff/src/lib.rs b/rust/xdiff/src/lib.rs
> > > index e69de29bb2d1..96975975a1ba 100644
> > > --- a/rust/xdiff/src/lib.rs
> > > +++ b/rust/xdiff/src/lib.rs
> > > @@ -0,0 +1,7 @@
> > > +
> > > +
> > > +#[no_mangle]
> > > +unsafe extern "C" fn xxh3_64(ptr: *const u8, size: usize) -> u64 {
> > > + let slice = std::slice::from_raw_parts(ptr, size);
> > > + xxhash_rust::xxh3::xxh3_64(slice)
> > > +}
> >
> > I know that this is a pretty small file, but I do notice that it does not
> > have a license header.
> >
> > This reminds me of the unfortunate oversight to be careful about making
> > (and keeping) libgit.a's source files compatible with libgit2's license to
> > nurture a fruitful exchange between those two projects.
>
> I'm not sure I follow your reasoning here. libgit2 was started after git and
> chose to use an incompatible license. I wasn't around at the time but isn't
> there a list of git contributors who are happy to re-license their
> contributions with the linking exception used by libgit2?
Let me provide some historical context that might clarify the licensing
concern.
When libgit2 was created, the goal was to demonstrate that Git
functionality could be packaged as a reusable library, inviting innovation
via 3rd-party products. The project took existing Git code (with
permission) and wrapped it with a proper API. The hope was that this would
eventually become the foundation for Git itself.
What we learned from that experience is instructive: license
incompatibility became an insurmountable barrier to code sharing between
the projects.
Lack of functionality prevented commercial products using libgit2 to
provide powerful user interfaces that outshine Git's own user experience,
unless they accepted the limited functionality.
Even when volunteers wanted to port new Git features to libgit2, the
licensing prevented it.
This fragmentation weakened both projects - libgit2 couldn't benefit from
Git's innovations, and Git couldn't leverage libgit2's API improvements
nor corporate contributions that would have been more likely to target
libgit2 than Git.
You can see this in full action: merge ORT, partial clone, sparse index,
etc. All of those features are missing from libgit2, with little hope to
end up otherwise.
Innovations such as geographically-distributed, redundant data stores, or
Xet-like big-file storage to replace e.g. Git LFS with a fully native
solution, haven't happened, despite libgit2's architecture offering the
extensibility and proper delineation to make such improvements cleaner
and much more straight-forward than Git's own source code would allow.
> > With Rust, we still have a really good chance to learn from history and
> > avoid that mistake: Gitoxide is a very exciting project with clear overlap
> > in its mission to implement Git functionality in Rust. Gitoxide is
> > dual-licensed under the Apache License v2 and the MIT license (see
> > https://github.com/GitoxideLabs/gitoxide?tab=readme-ov-file#license).
> >
> > Would you mind adding a license header to that file that explicitly allows
> > the contents of the file to be used in Gitoxide, to get the Rust effort
> > started on a good foot?
>
> I wary of that for two reasons. Firstly over time it is de-facto re-licensing
> git as the amount of rust code grows and the amount of C code shrinks which
> deserves a wider discussion. Secondly it makes it harder to convert our C code
> which is licensed under GPL2 (or in the case of xdiff LGPL) to rust if the
> rust code uses a different license.
The industry adopted libgit2 widely precisely because it provided what Git
didn't: a clean API for building tools. But the licensing barrier meant
that innovation had to happen in isolation.
Due to the feature disparity, we saw "libgit2 evacuation" efforts,
starting with Visual Studio, later GitHub and GitLab followed, where work
was duplicated by moving away from libgit2 towards a distinctly non-API
way to invoke Git functionality: by spawning full-blown `git` processes
and communicating by parsing `stdout`, risking regressions due to typo
fixes such as the infamous "up-to-date -> up to date" patches. Such a lot
of extra work, away from proper API calls, just because of that
fragmentation!
With Rust and Gitoxide, we have a rare opportunity to avoid this
fragmentation from the start. Gitoxide's permissive dual licensing means
code can flow both ways. This isn't about "slipping in" a license change -
it's about learning from what happened before.
By the way, you made it sound as if I asked to re-license existing code,
which is not the case. I specifically asked for new code to be licensed in
a way that avoids to straight up prevent collaboration with the Gitoxide
project from the get-go.
It would not even take more than something as simple as GPLv2+exception.
We do have prior art for that: The Git project itself suggests in its very
own `COPYING` file to use the following license in new files:
This file is licensed under the GPL v2, or a later version
at the discretion of Linus.
Note the exception? For new Rust code (and of course excluding code that
has been ported verbatim from GPLv2-licensed code), GPL v2 could be used
with an exception along these lines: This file is licensed under the GPL
v2, with the exception that it can be freely used in the Gitoxide project.
I am not a lawyer (which everybody but laywers are nowadays required to
say), therefore this likely needs some tweaking.
> If someone wants to start a discussion about re-licensing git (and is
> prepared to do all of the associated admin in the event that it happens)
> then by all means do so but I don't think it we want to slip such a
> change into this series.
The "wider discussion" you mention is exactly what we need; Starting with
compatible licensing makes that discussion possible rather than
purely theoretical and moot.
Ciao,
Johannes
next prev parent reply other threads:[~2025-09-23 9:57 UTC|newest]
Thread overview: 204+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-17 20:32 [PATCH 0/7] RFC: Accelerate xdiff and begin its rustification Ezekiel Newren via GitGitGadget
2025-07-17 20:32 ` [PATCH 1/7] xdiff: introduce rust Ezekiel Newren via GitGitGadget
2025-07-17 21:30 ` brian m. carlson
2025-07-17 21:54 ` Junio C Hamano
2025-07-17 22:39 ` Taylor Blau
2025-07-18 23:15 ` Ezekiel Newren
2025-07-23 21:57 ` brian m. carlson
2025-07-23 22:26 ` Junio C Hamano
2025-07-28 19:11 ` Ezekiel Newren
2025-07-31 22:37 ` brian m. carlson
2025-07-22 22:02 ` Mike Hommey
2025-07-22 23:52 ` brian m. carlson
2025-07-17 22:38 ` Taylor Blau
2025-07-17 20:32 ` [PATCH 2/7] xdiff/xprepare: remove superfluous forward declarations Ezekiel Newren via GitGitGadget
2025-07-17 22:41 ` Taylor Blau
2025-07-17 20:32 ` [PATCH 3/7] xdiff: delete unnecessary fields from xrecord_t and xdfile_t Ezekiel Newren via GitGitGadget
2025-07-17 20:32 ` [PATCH 4/7] xdiff: make fields of xrecord_t Rust friendly Ezekiel Newren via GitGitGadget
2025-07-17 22:46 ` Taylor Blau
2025-07-17 23:13 ` brian m. carlson
2025-07-17 23:37 ` Elijah Newren
2025-07-18 0:23 ` Taylor Blau
2025-07-18 0:21 ` Taylor Blau
2025-07-18 13:35 ` Phillip Wood
2025-07-28 19:34 ` Ezekiel Newren
2025-07-28 19:52 ` Phillip Wood
2025-07-28 20:14 ` Ezekiel Newren
2025-07-31 14:20 ` Phillip Wood
2025-07-31 20:58 ` Ezekiel Newren
2025-08-01 9:14 ` Phillip Wood
2025-07-28 20:53 ` Junio C Hamano
2025-07-28 20:00 ` Collin Funk
2025-07-20 1:39 ` Johannes Schindelin
2025-07-17 20:32 ` [PATCH 5/7] xdiff: separate parsing lines from hashing them Ezekiel Newren via GitGitGadget
2025-07-17 22:59 ` Taylor Blau
2025-07-18 13:34 ` Phillip Wood
2025-07-17 20:32 ` [PATCH 6/7] xdiff: conditionally use Rust's implementation of xxhash Ezekiel Newren via GitGitGadget
2025-07-17 23:29 ` Taylor Blau
2025-07-18 19:00 ` Junio C Hamano
2025-07-31 21:13 ` Ezekiel Newren
2025-08-02 7:53 ` Matthias Aßhauer
2025-07-19 21:53 ` Johannes Schindelin
2025-07-20 10:14 ` Phillip Wood
2025-09-23 9:57 ` Johannes Schindelin [this message]
2025-09-23 17:48 ` gitoxide-compatible licensing of Git's Rust code, was " Jeff King
2025-09-24 13:48 ` Phillip Wood
2025-09-25 2:25 ` Jeff King
2025-09-25 5:42 ` Patrick Steinhardt
2025-09-26 10:06 ` Phillip Wood
2025-10-03 3:18 ` Jeff King
2025-10-03 9:51 ` Phillip Wood
2025-10-07 9:11 ` Patrick Steinhardt
2025-11-17 13:37 ` Johannes Schindelin
2025-10-05 5:32 ` Yee Cheng Chin
2025-07-17 20:32 ` [PATCH 7/7] github_workflows: install rust Ezekiel Newren via GitGitGadget
2025-07-17 21:23 ` brian m. carlson
2025-07-18 23:01 ` Ezekiel Newren
2025-07-25 23:56 ` Ben Knoble
2025-07-19 21:54 ` Johannes Schindelin
2025-07-17 21:51 ` [PATCH 0/7] RFC: Accelerate xdiff and begin its rustification brian m. carlson
2025-07-17 22:25 ` Taylor Blau
2025-07-18 0:29 ` brian m. carlson
2025-07-22 12:21 ` Patrick Steinhardt
2025-07-22 15:56 ` Junio C Hamano
2025-07-22 16:03 ` Sam James
2025-07-22 21:37 ` Elijah Newren
2025-07-22 21:55 ` Sam James
2025-07-22 22:08 ` Collin Funk
2025-07-18 9:23 ` Christian Brabandt
2025-07-18 16:26 ` Junio C Hamano
2025-07-19 0:32 ` Elijah Newren
2025-07-18 13:34 ` Phillip Wood
2025-07-18 21:25 ` Eli Schwartz
2025-07-19 0:48 ` Haelwenn (lanodan) Monnier
2025-07-22 12:21 ` Patrick Steinhardt
2025-07-22 14:24 ` Patrick Steinhardt
2025-07-22 15:14 ` Eli Schwartz
2025-07-22 15:56 ` Sam James
2025-07-23 4:32 ` Patrick Steinhardt
2025-07-24 9:01 ` Pierre-Emmanuel Patry
2025-07-24 10:00 ` Patrick Steinhardt
2025-07-28 9:06 ` Pierre-Emmanuel Patry
2025-07-18 14:38 ` Junio C Hamano
2025-07-18 21:56 ` Ezekiel Newren
2025-07-21 10:14 ` Phillip Wood
2025-07-21 18:33 ` Junio C Hamano
2025-07-19 21:53 ` Johannes Schindelin
2025-07-20 8:45 ` Matthias Aßhauer
2025-08-15 1:22 ` [PATCH v2 00/17] " Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 01/17] doc: add a policy for using Rust brian m. carlson via GitGitGadget
2025-08-15 17:03 ` Matthias Aßhauer
2025-08-15 21:31 ` Junio C Hamano
2025-08-16 8:06 ` Matthias Aßhauer
2025-08-19 2:06 ` Ezekiel Newren
2025-08-15 1:22 ` [PATCH v2 02/17] xdiff: introduce rust Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 03/17] xdiff/xprepare: remove superfluous forward declarations Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 04/17] xdiff: delete unnecessary fields from xrecord_t and xdfile_t Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 05/17] xdiff: make fields of xrecord_t Rust friendly Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 06/17] xdiff: separate parsing lines from hashing them Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 07/17] xdiff: conditionally use Rust's implementation of xxhash Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 08/17] github workflows: install rust Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 09/17] Do support Windows again after requiring Rust Johannes Schindelin via GitGitGadget
2025-08-15 17:12 ` Matthias Aßhauer
2025-08-15 21:48 ` Junio C Hamano
2025-08-15 22:11 ` Johannes Schindelin
2025-08-15 23:37 ` Junio C Hamano
2025-08-15 23:37 ` Junio C Hamano
2025-08-16 8:53 ` Matthias Aßhauer
2025-08-17 15:57 ` Junio C Hamano
2025-08-19 2:22 ` Ezekiel Newren
2025-08-15 1:22 ` [PATCH v2 10/17] win+Meson: allow for xdiff to be compiled with MSVC Johannes Schindelin via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 11/17] win+Meson: do allow linking with the Rust-built xdiff Johannes Schindelin via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 12/17] github workflows: define rust versions and targets in the same place Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 13/17] github workflows: upload Cargo.lock Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 14/17] xdiff: implement a white space iterator in Rust Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 15/17] xdiff: create line_hash() and line_equal() Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 16/17] xdiff: optimize case where --ignore-cr-at-eol is the only whitespace flag Ezekiel Newren via GitGitGadget
2025-08-15 1:22 ` [PATCH v2 17/17] xdiff: use rust's version of whitespace processing Ezekiel Newren via GitGitGadget
2025-08-15 15:07 ` [-SPAM-] [PATCH v2 00/17] RFC: Accelerate xdiff and begin its rustification Ramsay Jones
2025-08-19 2:00 ` Elijah Newren
2025-08-24 16:52 ` Patrick Steinhardt
2025-08-18 22:31 ` Junio C Hamano
2025-08-18 23:52 ` Ben Knoble
2025-08-19 1:52 ` Elijah Newren
2025-08-19 9:47 ` Junio C Hamano
2025-08-23 3:55 ` [PATCH v3 00/15] RFC: Cleanup " Ezekiel Newren via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 01/15] doc: add a policy for using Rust brian m. carlson via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 02/15] xdiff: introduce rust Ezekiel Newren via GitGitGadget
2025-08-23 13:43 ` rsbecker
2025-08-23 14:26 ` Kristoffer Haugsbakk
2025-08-23 15:06 ` rsbecker
2025-08-23 18:30 ` Elijah Newren
2025-08-23 19:24 ` brian m. carlson
2025-08-23 20:04 ` rsbecker
2025-08-23 20:36 ` Sam James
2025-08-23 21:17 ` Haelwenn (lanodan) Monnier
2025-08-27 1:57 ` Taylor Blau
2025-08-27 14:39 ` rsbecker
2025-08-27 17:06 ` Junio C Hamano
2025-08-27 17:15 ` rsbecker
2025-08-27 20:12 ` Taylor Blau
2025-08-27 20:22 ` Junio C Hamano
2025-09-02 11:16 ` Patrick Steinhardt
2025-09-02 11:30 ` Sam James
2025-09-02 17:27 ` brian m. carlson
2025-09-02 18:47 ` Sam James
2025-09-03 18:22 ` Collin Funk
2025-09-03 5:40 ` Patrick Steinhardt
2025-09-03 16:22 ` Ramsay Jones
2025-09-03 22:10 ` Junio C Hamano
2025-09-03 22:48 ` Josh Steadmon
2025-09-04 11:10 ` Patrick Steinhardt
2025-09-04 15:45 ` Junio C Hamano
2025-09-05 8:23 ` Patrick Steinhardt
2025-09-04 0:57 ` brian m. carlson
2025-09-04 11:39 ` Patrick Steinhardt
2025-09-04 13:53 ` Sam James
2025-09-05 3:55 ` Elijah Newren
2025-09-04 23:17 ` Ezekiel Newren
2025-09-05 3:54 ` Elijah Newren
2025-09-05 6:50 ` Patrick Steinhardt
2025-09-07 4:10 ` Elijah Newren
2025-09-07 16:09 ` rsbecker
2025-09-08 10:12 ` Phillip Wood
2025-09-08 15:32 ` rsbecker
2025-09-08 15:10 ` Ezekiel Newren
2025-09-08 15:41 ` rsbecker
2025-09-08 15:31 ` Elijah Newren
2025-09-08 15:36 ` rsbecker
2025-09-08 16:13 ` Elijah Newren
2025-09-08 17:01 ` rsbecker
2025-09-08 6:40 ` Patrick Steinhardt
2025-09-05 10:31 ` Phillip Wood
2025-09-05 11:32 ` Sam James
2025-09-05 13:14 ` Phillip Wood
2025-09-05 13:23 ` Patrick Steinhardt
2025-09-05 15:37 ` Junio C Hamano
2025-09-08 6:40 ` Patrick Steinhardt
2025-08-23 14:29 ` Ezekiel Newren
2025-08-23 3:55 ` [PATCH v3 03/15] github workflows: install rust Ezekiel Newren via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 04/15] win+Meson: do allow linking with the Rust-built xdiff Johannes Schindelin via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 05/15] github workflows: upload Cargo.lock Ezekiel Newren via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 06/15] ivec: create a vector type that is interoperable between C and Rust Ezekiel Newren via GitGitGadget
2025-08-23 8:12 ` Kristoffer Haugsbakk
2025-08-23 9:29 ` Ezekiel Newren
2025-08-23 16:14 ` Junio C Hamano
2025-08-23 16:37 ` Ezekiel Newren
2025-08-23 18:05 ` Junio C Hamano
2025-08-23 20:29 ` Ezekiel Newren
2025-08-25 19:16 ` Elijah Newren
2025-08-26 5:40 ` Junio C Hamano
2025-08-24 13:31 ` Ben Knoble
2025-08-25 20:40 ` Ezekiel Newren
2025-08-26 13:30 ` D. Ben Knoble
2025-08-26 18:47 ` Ezekiel Newren
2025-08-26 22:01 ` brian m. carlson
2025-08-23 3:55 ` [PATCH v3 07/15] xdiff/xprepare: remove superfluous forward declarations Ezekiel Newren via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 08/15] xdiff: delete unnecessary fields from xrecord_t and xdfile_t Ezekiel Newren via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 09/15] xdiff: make fields of xrecord_t Rust friendly Ezekiel Newren via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 10/15] xdiff: use one definition for freeing xdfile_t Ezekiel Newren via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 11/15] xdiff: replace chastore with an ivec in xdfile_t Ezekiel Newren via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 12/15] xdiff: delete nrec field from xdfile_t Ezekiel Newren via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 13/15] xdiff: delete recs " Ezekiel Newren via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 14/15] xdiff: make xdfile_t more rust friendly Ezekiel Newren via GitGitGadget
2025-08-23 3:55 ` [PATCH v3 15/15] xdiff: implement xdl_trim_ends() in Rust Ezekiel Newren via GitGitGadget
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