linux-kernel - Re: Rust kernel policy

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Message-ID: <Z7bO1jT2onZFZwgH@infradead.org>
Date: Wed, 19 Feb 2025 22:42:30 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: Christoph Hellwig <hch@...radead.org>,
	rust-for-linux <rust-for-linux@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	David Airlie <airlied@...il.com>, linux-kernel@...r.kernel.org,
	ksummit@...ts.linux.dev
Subject: Re: Rust kernel policy

On Tue, Feb 18, 2025 at 07:46:29PM +0100, Miguel Ojeda wrote:
> > while Linus in private said that he absolutely is going to merge Rust
> > code over a maintainers objection.  (He did so in private in case you
> > are looking for a reference).
> 
> The document does not claim Linus cannot override maintainers anymore.

The document claims no subsystem is forced to take Rust.  That's proven
to be wrong by Linus.  And while you might not have known that when
writing the document, you absolutely did when posting it to the list.

That is a very dishonest way of communication.

> You were in the meeting that the document mentions in the next
> paragraph, so I am not sure why you bring this point up again. I know
> you have raised your concerns about Rust before; and, as we talked in
> private, I understand your reasoning, and I agree with part of it. But
> I still do not understand what you expect us to do -- we still think
> that, today, Rust is worth the tradeoffs for Linux.

And I fundamentally disagree with that approach.

> If the only option you are offering is dropping Rust completely, that
> is fine and something that a reasonable person could argue, but it is
> not on our plate to decide.

We'll it's up to Linus to decide, and he hides behind the experiment
thing in public without giving much guidance, and then decides
differently in private.  Coupled with the misleading policy document
this doesn't even make it clear what contributors and maintainers are
getting themselves into.

> > So as of now, as a Linux developer or maintainer you must deal with
> > Rust if you want to or not.
> 
> It only affects those that maintain APIs that are needed by a Rust
> user, not every single developer.

Which given the binding creep means every single non-leaf subsystem
eventually.

> But it is also true that there are kernel maintainers saying publicly
> that they want to proceed with this. Even someone with 20 years of
> experience saying "I don't ever want to go back to C based development
> again". Please see the slides above for the quotes.

I'm not sure how that matters.  Of course your Rust testimonials are
going to like it, otherwise you would not have quoted it.  They
generally are not the people who do the grunt work to keep the core
kernel alive.  And I absolutely do understand everyone who would rather
spend their time on a higher level language with more safety, but that's
not the point here.

> We also have a bunch of groups and companies waiting to use Rust.

Well, obviously you do.  But as in many other things I would usually
not count corporate pressure as a good thing.