Re: [PATCH 00/13] [RFC] Rust support

From: Peter Zijlstra <peterz@infradead.org>
To: ojeda@kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	rust-for-linux@vger.kernel.org, linux-kbuild@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/13] [RFC] Rust support
Date: Thu, 15 Apr 2021 20:58:16 +0200	[thread overview]
Message-ID: <YHiMyE4E1ViDcVPi@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210414184604.23473-1-ojeda@kernel.org>

On Wed, Apr 14, 2021 at 08:45:51PM +0200, ojeda@kernel.org wrote:

> Rust is a systems programming language that brings several key
> advantages over C in the context of the Linux kernel:
> 
>   - No undefined behavior in the safe subset (when unsafe code is
>     sound), including memory safety and the absence of data races.

And yet I see not a single mention of the Rust Memory Model and how it
aligns (or not) with the LKMM. The C11 memory model for example is a
really poor fit for LKMM.

> ## Why not?
> 
> Rust also has disadvantages compared to C in the context of
> the Linux kernel:
> 
>   - The many years of effort in tooling for C around the kernel,
>     including compiler plugins, sanitizers, Coccinelle, lockdep,
>     sparse... However, this will likely improve if Rust usage in
>     the kernel grows over time.

This; can we mercilessly break the .rs bits when refactoring? What
happens the moment we cannot boot x86_64 without Rust crap on?

We can ignore this as a future problem, but I think it's only fair to
discuss now. I really don't care for that future, and IMO adding this
Rust or any other second language is a fail.

> Thirdly, in Rust code bases, most documentation is written alongside
> the source code, in Markdown. We follow this convention, thus while
> we have a few general documents in `Documentation/rust/`, most of
> the actual documentation is in the source code itself.
> 
> In order to read this documentation easily, Rust provides a tool
> to generate HTML documentation, just like Sphinx/kernel-doc, but
> suited to Rust code bases and the language concepts.

HTML is not a valid documentation format. Heck, markdown itself is
barely readable.

> Moreover, as explained above, we are taking the chance to enforce
> some documentation guidelines. We are also enforcing automatic code
> formatting, a set of Clippy lints, etc. We decided to go with Rust's
> idiomatic style, i.e. keeping `rustfmt` defaults. For instance, this
> means 4 spaces are used for indentation, rather than a tab. We are
> happy to change that if needed -- we think what is important is
> keeping the formatting automated.

It is really *really* hard to read. It has all sorts of weird things,
like operators at the beginning after a line break:

	if (foo
	    || bar)

which is just wrong. And it suffers from CamelCase, which is just about
the worst thing ever. Not even the C++ std libs have that (or had, back
when I still did knew C++).

I also see:

	if (foo) {
		...
	}

and

	if foo {
	}

the latter, ofcourse, being complete rubbish.

> Another important topic we would like feedback on is the Rust
> "native" documentation that is written alongside the code, as
> explained above. We have uploaded it here:
> 
>     https://rust-for-linux.github.io/docs/kernel/
> 
> We like how this kind of generated documentation looks. Please take
> a look and let us know what you think!

I cannot view with less or vim. Therefore it looks not at all.

>   - Boqun Feng is working hard on the different options for
>     threading abstractions and has reviewed most of the `sync` PRs.

Boqun, I know you're familiar with LKMM, can you please talk about how
Rust does things and how it interacts?