Re: [MAINTAINERS SUMMIT] [4/4] Discuss how to better prevent backports of commits that turn out to cause regressions

Lee Jones
2024-06-14T09:19:52Z

On Thu, 13 Jun 2024, Konstantin Ryabitsev wrote:

> On Thu, Jun 13, 2024 at 11:59:17AM GMT, Jan Kara wrote:
> > > * One cause of regressions that happen in stable trees (and not in
> > > mainline) I've seen quite a few times are backports of commits with
> > > Fixes: tags that were part of a patch-series and depend on earlier
> > > patches from the series. The stable-team afaics has no easy way to spot
> > > this, as there is no way to check "was this change part of a series".
> > > Sometimes I wonder if a dedicated tag linking to the submission of a
> > > patch could help -- and is something quite a few maintainers already
> > > really want and add using a "Link" tag despite Linus dislike for that
> > > (IIRC).
> >
> > FWIW I (and a few other maintainers) use 'Message-Id' tag to link to
> > submission. This is still easily convertible to lore link and unlike 'Link'
> > tag it is clear what this tag is about and that it is not just a link to
> > related discussion or something like that. AFAIK this also addresses Linus'
> > dislike because what he was complaining about is that 'Link' should be
> > linking to some useful context for the changelog, not just patch
> > submission.
>
> I am strongly in favour of that from the tooling perspective. Linus suggested
> that we can always trace the original patch submission from the commit by
> using the patch-id, but that doesn't work reliably. I mused on that here:
>
> https://lore.kernel.org/git/20240605-hilarious-dramatic-mushroom-7fd941@lemur/
>
> The gist is that we cannot reliably match the patch-id of the original
> submission from the git commit, because there are multiple ways to generate
> the same patch, such as changing the diff algorithm (myers vs. minimal vs.
> histogram), or changing the number of context lines. If the original author
> generated their patch with --histogram, but we try to find it by generating
> the same patch using the default myers algorithm, we may not find it.
>
> The "Message-Id" trailer is already documented in git:
> https://www.git-scm.com/docs/git-am#Documentation/git-am.txt---message-id
>
> I suggest we move away from the practice of using Link: trailers to indicate
> the patch provenance to using Message-Id: trailers for the same purpose. This
> solves multiple problems:
>
> 1. disambiguates Link: trailers so they point to relevant online discussions
> 2. allows tooling like b4, patchwork, etc, to reliably match commits to
> submissions for the purposes of better code review automation
> 3. allows stable and similar projects to better track series grouping for
> commits

Sounds good to me.

So `b4 am -l` should be replaced with `b4 am ?`.

--
Lee Jones [李琼斯]