Re: Link trailers revisited (was Re: [GIT PULL] io_uring fix for 6.17-rc5)

[Konstantin Ryabitsev <konstantin@linuxfoundation.org>]

On Sat, Sep 06, 2025 at 08:31:59AM -0700, Linus Torvalds wrote:
> On Sat, 6 Sept 2025 at 06:51, Konstantin Ryabitsev
> <konstantin@linuxfoundation.org> wrote:
> >
> > Unfortunately, `shazam -M` is not perfect, because we do need to know the
> > base-commit, and there's still way too many series sent without this info.
> 
> No, no. You're thinking about it wrong.
> 
> An emailed patch series is *not* a git pull. If you want actual real
> git history, just use git. Using a patch series and shazam for that
> would be *bad*. It's actively worse than just using git, with zero
> upside.

The primary consumer of this are the CI systems, though, like those that plug
into patchwork. In order to be able to run a bunch of tests they need to be
able to apply the patches to a tree, so, in a sense, they do need to recreate
git as much as possible, including the branch point.

> No, the upside of a patch series is that it's *not* fixed in stone yet
> - not in history, not in acks, not in actual code. So do *not*
> encourage people to think of it as some second-rate "git history"
> model. It's not, and it would be *BAD* at it.

b4 will tell you if a series applies cleanly to the current tree, but I don't
think we make use of this with `shazam -M` -- we always try to parent it
against the indicated base commit. Is the recommendation then to always try to
use the latest tree and bail out if it doesn't apply?

> That kind of global history would be *worse* for the whole "send
> patches by email" model.
> 
> So don't strive to replicate git - badly. Strive to do a *good* job.

But people do want to replicate git, if only so they can run integration tests
in a more automated fashion. If I understand correctly, you suggest two modes
of operations:

1. recreate the tree exactly as the author intended, so that CI systems can
   run tests.

2. try to create a merge commit on top of the latest HEAD and bail if it's not
   working, letting the maintainer fix any conflicts on their own.

> Your comment about how you want to know the base commit makes me think
> you are missing the point.

No, I'm mostly implementing what people tell me they'd like to see. :) Someone
once told me that they really wanted to be able to treat mailed series exactly
like a pull request, hence why this feature exists. You're actually the first
person to say that this behaviour is not what we should be doing.

-K