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From: Linus Walleij <linus.walleij@linaro.org>
To: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc: Wedson Almeida Filho <wedsonaf@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Miguel Ojeda <ojeda@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	rust-for-linux <rust-for-linux@vger.kernel.org>,
	linux-kbuild <linux-kbuild@vger.kernel.org>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 00/13] [RFC] Rust support
Date: Tue, 4 May 2021 23:21:13 +0200
Message-ID: <CACRpkdYzqy69G1Fpj4rFQFS+mYmpbQAzTszwCUBuEhe4YW4cuQ@mail.gmail.com> (raw)
In-Reply-To: <CANiq72m9V3dVG59jAoR-OM+7QtJauQgrix3DZkw=oCuaaf3H5w@mail.gmail.com>

On Wed, Apr 28, 2021 at 5:10 AM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
> On Tue, Apr 27, 2021 at 1:13 PM Linus Walleij <linus.walleij@linaro.org> wrote:
> >
> > Actually my reply to Wedson brought up a new issue, which is the
> > quality of learning resources and the lack of an equivalent to
> > The C Programming Language book.
>
> I recall having a similar feeling when initially jumping into
> individual chapters of The Rust Programming Language book. I think it
> is intended to be read from cover to cover instead.
>
> There are other resources, see [1]. For instance, there is The
> Embedded Rust Book [2]. Some of those are a WIP, but perhaps others
> can recommend better finished/published books.
>
> In any case, Rust has more features than C, some of them quite unique,
> and they are routinely used, so it does take some time to learn.

No joke, I do try. I thought it would be easier since I have written
a fair share of Haskell in my years but Rust is this hybrid of
imperative and functional that just make things a bit hard
to pin down: is this part functional? is it imperative?
is it object oriented? etc.

But the reference that Robin pointed to is better to read. It
is not as talkative and more to the point. So now I am working
with that.

> > I think a good starting point would be to either fix Rust support in
> > GCC or implement some more important ISAs in LLVM,
> > whichever is easiest. I don't mind having just *one* compiler but
> > I mind having *a* compiler for every arch we support.
> >
> > [...]
> >
> > Portability to old systems and ISAs is a virtue in itself
> > because of the effect it has on code quality, not necessarily
> > for the support itself.
>
> I agree that there are benefits of keeping compiler technology
> flexible, but one cannot force or expect any project (including the
> Linux kernel) to maintain all code forever.
>
> In the end, we need to balance that adaptability against the benefits
> of adding Rust. In particular because nowadays LLVM is able to cover
> the majority of devices that want to run the very latest Linux
> kernels. Thus those benefits apply to most users. If LLVM only
> supported, say, x86_64, I would agree that it would not be enough.
>
> By contrast, compiler flexibility only matters indirectly to users,
> and at some point there are diminishing returns to keeping all
> architectures around.

My values in this regard are 180 degrees opposed to yours.

My attitude to the problem, was I to fix it, would be
"let's go fix a frontend for Rust to GCC, how hard can it be"
rather than trying to avoid that work with this kind of
reasoning trying to one way or other prove that it is not
worth the effort.

A GCC front-end will allow you to run Rust on all Linux
target architectures which is a big win. LLVM can be
expanded with backends for all archs as well but that
seems like a much bigger job to me.

Another argument can be made that for Rust to be
perceived as mature, two independent implementations
should exist anyway.

The IETF Standards Process (RFC 2026, updated by
RFC 6410) requires at least two independent and
interoperable implementations for advancing a protocol
specification to Internet Standard.

Why should the kernel programming languages have any
lower standards than that?

The C programming language has earned its place thanks
to perseverance of implementing and reimplementing
compilers for it again and again.

Fixing proper compilers may take a few years, like
5 or 10. But who cares? We are in it for the long run
anyway. When I designed the character device interface
for GPIO I said I expect it to be maintained for at least
100 years. This is my honest perspective of things.

Torvalds has this saying (from Edison) that kernel
engineering is 1% inspiration and 99% perspiration.
Well let's live by that and fix those compilers.

When Linux was developed in 1992 C had existed since
1973 so it was 19 years old.

Now Linux is 28 years old and C is 47 years old.

This discussion needs perspective. And we really
cannot have development with a finger constantly
pushing the fastforward button.

> In any case, adding Rust (in particular for "leaf" modules) does not
> imply that we will lose those architectures any time soon.

But I am not convinced that writing device drivers is the right
thing to use Rust for in the kernel.

There are some stuff in device driver frameworks, such as USB
hierarchies or (battery) charging state machines, that can be
really good to rewrite in Rust. But these rewrites would affect
anything with a USB port for example, including Nios II and
Motorola 68k systems.  So then the compiler support for all
archs is needed first.

> That would
> take at least several years, and would require quite a few things to
> happen at the same time:
>
>   - That Rust got so widely used in the kernel (because the benefits
> turned out to be important) that maintainers went as far as wanting to
> drop C drivers from mainline for Rust equivalents.
>
>   - That GCC did not get any way to compile Rust (no Rust frontend for
> GCC, no GCC backend for `rustc`, etc.) and, moreover, that the plans
> for that had been dropped.
>
>   - That LLVM did not add support for the missing architectures.
>
> The first point is unlikely any time soon. The second point is
> unlikely, too, given there is funding for that now (and I assume those
> projects will receive more support if Rust lands in the kernel). The
> third point is likely, though.

What about patience?

I am thrilled to hear that GCC is growing Rust support and has funding
to fix a proper front-end. This is what Rust needs in general and
what the kernel needs in particular.

I think right now the right thing for Rust is to work out-of-tree until
there is Rust support for all archs, while encouraging kernel
developers to learn the language.

Yours,
Linus Walleij

  reply index

Thread overview: 187+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-14 18:45 ojeda
2021-04-14 18:45 ` [PATCH 01/13] kallsyms: Support "big" kernel symbols (2-byte lengths) ojeda
2021-04-14 19:44   ` Matthew Wilcox
2021-04-14 19:59     ` Miguel Ojeda
2021-04-14 18:45 ` [PATCH 02/13] kallsyms: Increase maximum kernel symbol length to 512 ojeda
2021-04-14 23:48   ` Nick Desaulniers
2021-04-14 18:45 ` [PATCH 03/13] Makefile: Generate CLANG_FLAGS even in GCC builds ojeda
2021-04-14 18:59   ` Nathan Chancellor
2021-04-15 10:18     ` Miguel Ojeda
2021-04-14 23:46   ` Nick Desaulniers
2021-04-15  0:47     ` Miguel Ojeda
2021-04-14 18:45 ` [PATCH 04/13] Kbuild: Rust support ojeda
2021-04-14 23:19   ` Nick Desaulniers
2021-04-15  0:43     ` Miguel Ojeda
2021-04-15 18:03       ` Nick Desaulniers
2021-04-16 12:23         ` Miguel Ojeda
2021-04-17 19:35       ` Masahiro Yamada
2021-04-16 13:38   ` Peter Zijlstra
2021-04-16 17:05     ` Linus Torvalds
2021-04-16 17:47       ` Miguel Ojeda
2021-04-16 18:09         ` Al Viro
2021-04-16 18:57           ` Miguel Ojeda
2021-04-16 20:22             ` Willy Tarreau
2021-04-16 20:34               ` Connor Kuehl
2021-04-16 20:58                 ` Willy Tarreau
2021-04-16 21:39                   ` Miguel Ojeda
2021-04-16 22:04                     ` Willy Tarreau
2021-04-16 22:45                       ` Al Viro
2021-04-16 23:46                       ` Miguel Ojeda
2021-04-17  4:24                         ` Willy Tarreau
2021-04-17 15:38                           ` Miguel Ojeda
2021-04-16 21:19               ` Miguel Ojeda
2021-04-16 17:34     ` Miguel Ojeda
2021-04-19 19:58       ` David Sterba
2021-04-19 20:17         ` Matthew Wilcox
2021-04-19 21:03           ` Miguel Ojeda
2021-04-19 20:54         ` Miguel Ojeda
2021-04-14 18:45 ` [PATCH 05/13] Rust: Compiler builtins crate ojeda
2021-04-14 19:19   ` Linus Torvalds
2021-04-14 19:34     ` Miguel Ojeda
2021-04-14 18:45 ` [PATCH 06/13] Rust: Module crate ojeda
2021-04-14 18:45 ` [PATCH 07/13] Rust: Kernel crate ojeda
2021-04-14 19:31   ` Linus Torvalds
2021-04-14 19:50     ` Miguel Ojeda
2021-04-14 18:45 ` [PATCH 08/13] Rust: Export generated symbols ojeda
2021-04-14 18:46 ` [PATCH 09/13] Samples: Rust examples ojeda
2021-04-14 19:34   ` Linus Torvalds
2021-04-14 19:42     ` Miguel Ojeda
2021-04-14 19:49       ` Matthew Wilcox
2021-04-16 11:46       ` Andrej Shadura
2021-04-14 23:24     ` Nick Desaulniers
2021-04-15  7:10       ` Greg Kroah-Hartman
2021-04-15  7:39         ` Nick Desaulniers
2021-04-15 12:42         ` Miguel Ojeda
2021-04-16 13:07         ` Sven Van Asbroeck
2021-04-16 13:20           ` Greg Kroah-Hartman
2021-04-14 18:46 ` [PATCH 10/13] Documentation: Rust general information ojeda
2021-04-14 22:17   ` Nick Desaulniers
2021-04-14 23:34     ` Miguel Ojeda
2021-04-14 18:46 ` [PATCH 11/13] MAINTAINERS: Rust ojeda
2021-04-14 21:55   ` Nick Desaulniers
2021-04-14 22:02     ` Miguel Ojeda
2021-04-14 22:36   ` Nick Desaulniers
2021-04-14 18:46 ` [PATCH 12/13] Rust: add abstractions for Binder (WIP) ojeda
2021-04-14 18:46 ` [PATCH 13/13] Android: Binder IPC in Rust (WIP) ojeda
2021-04-14 19:44 ` [PATCH 00/13] [RFC] Rust support Linus Torvalds
2021-04-14 20:20   ` Miguel Ojeda
2021-04-15  1:38     ` Kees Cook
2021-04-15  8:26       ` David Laight
2021-04-15 18:08         ` Kees Cook
2021-04-15 12:39       ` Miguel Ojeda
2021-04-14 20:09 ` Matthew Wilcox
2021-04-14 20:21   ` Linus Torvalds
2021-04-14 20:35     ` Josh Triplett
2021-04-14 22:08     ` David Laight
2021-04-14 20:29   ` Miguel Ojeda
2021-04-18 15:31   ` Wedson Almeida Filho
2021-04-15  0:22 ` Nick Desaulniers
2021-04-15 10:05   ` Miguel Ojeda
2021-04-15 18:58 ` Peter Zijlstra
2021-04-16  2:22   ` Wedson Almeida Filho
2021-04-16  4:25     ` Al Viro
2021-04-16  5:02       ` Wedson Almeida Filho
2021-04-16  5:39         ` Paul Zimmerman
2021-04-16  7:46         ` Peter Zijlstra
2021-04-16  7:09     ` Peter Zijlstra
2021-04-17  5:23       ` comex
2021-04-17 12:46       ` David Laight
2021-04-17 14:51       ` Paolo Bonzini
2021-04-19  7:32         ` Peter Zijlstra
2021-04-19  7:53           ` Paolo Bonzini
2021-04-19  8:26             ` Peter Zijlstra
2021-04-19  8:35               ` Peter Zijlstra
2021-04-19  9:02               ` Paolo Bonzini
2021-04-19  9:36                 ` Peter Zijlstra
2021-04-19  9:40                   ` Paolo Bonzini
2021-04-19 11:01                     ` Will Deacon
2021-04-19 17:14                   ` Linus Torvalds
2021-04-19 18:38                     ` Paolo Bonzini
2021-04-19 18:50                       ` Linus Torvalds
2021-04-22 10:03     ` Linus Walleij
2021-04-22 14:09       ` David Laight
2021-04-22 15:24       ` Wedson Almeida Filho
2021-04-26  0:18         ` Linus Walleij
2021-04-26 14:26           ` Miguel Ojeda
2021-04-26 14:40           ` Wedson Almeida Filho
2021-04-26 16:03             ` Miguel Ojeda
2021-04-27 10:54             ` Linus Walleij
2021-04-27 11:13               ` Robin Randhawa
2021-04-29  1:52               ` Wedson Almeida Filho
2021-04-26 18:01           ` Miguel Ojeda
2021-04-22 21:28       ` Miguel Ojeda
2021-04-26  0:31         ` Linus Walleij
2021-04-26 18:18           ` Miguel Ojeda
2021-04-27 11:13             ` Linus Walleij
2021-04-28  2:51               ` Kyle Strand
2021-04-28  3:10               ` Miguel Ojeda
2021-05-04 21:21                 ` Linus Walleij [this message]
2021-05-04 23:30                   ` Miguel Ojeda
2021-05-05 11:34                     ` Linus Walleij
2021-05-05 14:17                       ` Miguel Ojeda
2021-05-05 15:13                         ` Enrico Weigelt, metux IT consult
2021-05-06 12:47                         ` Linus Walleij
2021-05-07 18:23                           ` Miguel Ojeda
2021-04-16  4:27   ` Boqun Feng
2021-04-16  6:04     ` Nick Desaulniers
2021-04-16 18:47       ` Paul E. McKenney
2021-04-19 20:35         ` Nick Desaulniers
2021-04-19 21:37           ` Paul E. McKenney
2021-04-19 22:03           ` Miguel Ojeda
2021-04-16 20:48     ` Josh Triplett
2021-04-16  8:16   ` Michal Kubecek
2021-04-16  9:29     ` Willy Tarreau
2021-04-16 11:24 ` Peter Zijlstra
2021-04-16 13:07   ` Wedson Almeida Filho
2021-04-16 14:19     ` Peter Zijlstra
2021-04-16 15:04       ` Miguel Ojeda
2021-04-16 15:43         ` Peter Zijlstra
2021-04-16 16:21           ` Miguel Ojeda
2021-04-16 15:33       ` Wedson Almeida Filho
2021-04-16 16:14         ` Willy Tarreau
2021-04-16 17:10           ` Miguel Ojeda
2021-04-16 17:18             ` Peter Zijlstra
2021-04-16 18:08               ` Matthew Wilcox
2021-04-17 11:17                 ` Peter Zijlstra
2021-04-17 11:46                   ` Willy Tarreau
2021-04-17 14:24                     ` Peter Zijlstra
2021-04-17 14:36                       ` Willy Tarreau
2021-04-17 13:46                   ` David Laight
2021-04-16 17:37             ` Willy Tarreau
2021-04-16 17:46               ` Connor Kuehl
2021-04-20  0:24               ` Nick Desaulniers
2021-04-20  3:47                 ` Willy Tarreau
2021-04-20  5:56                 ` Greg Kroah-Hartman
2021-04-20  6:16                   ` Willy Tarreau
2021-04-29 15:38                     ` peter enderborg
2021-04-17 13:53           ` Wedson Almeida Filho
2021-04-17 14:21             ` Willy Tarreau
2021-04-17 15:23               ` Miguel Ojeda
2021-04-18 15:51               ` Wedson Almeida Filho
2021-04-17 12:41       ` David Laight
2021-04-17 13:01         ` Wedson Almeida Filho
2021-04-16 15:03     ` Matthew Wilcox
2021-04-17 13:29       ` Wedson Almeida Filho
2021-04-16 15:58     ` Theodore Ts'o
2021-04-16 16:21       ` Wedson Almeida Filho
2021-04-17 15:11       ` Paolo Bonzini
2021-04-16 14:21   ` Miguel Ojeda
2021-04-17 20:42 ` Richard Weinberger
2021-04-28 18:34 ` Mariusz Ceier
2021-04-28 20:25   ` Nick Desaulniers
2021-04-28 21:21   ` David Laight
2021-04-29 11:14     ` Kajetan Puchalski
2021-04-29 11:25   ` Kajetan Puchalski
2021-04-29 14:06     ` Mariusz Ceier
2021-04-29 14:13       ` Sven Van Asbroeck
2021-04-29 14:26         ` Willy Tarreau
2021-04-29 15:06       ` Al Viro
2021-04-29 16:09         ` Mariusz Ceier
2021-04-30  6:39     ` Thomas Schoebel-Theuer
2021-04-30  8:30       ` David Laight
2021-05-05 13:58       ` Enrico Weigelt, metux IT consult
2021-05-05 14:41         ` Miguel Ojeda
2021-04-29  5:20 Mariusz Ceier
2021-04-29  5:21 Mariusz Ceier
2021-04-29  8:18 ` David Laight
2021-07-30 23:22 Dillan Jackson

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