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From: Linus Walleij <linus.walleij@linaro.org>
To: Wedson Almeida Filho <wedsonaf@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	ojeda@kernel.org, Linus Torvalds <torvalds@linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	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: Thu, 22 Apr 2021 12:03:13 +0200
Message-ID: <CACRpkdat8bny=D2mAsUXcDQvFJ=9jSZSccMMZzH=10dHQ_bXrQ@mail.gmail.com> (raw)
In-Reply-To: <YHj02M3jMSweoP4l@google.com>

Hi folks,

"we will do less critical stuff, like device drivers, first".

OK I mostly do device drivers. Kind of like it. So I'd like to provide
feedback from that angle.

On Fri, Apr 16, 2021 at 4:22 AM Wedson Almeida Filho
<wedsonaf@google.com> wrote:

> We don't intend to directly expose C data structures to Rust code (outside the
> kernel crate). Instead, we intend to provide wrappers that expose safe
> interfaces even though the implementation may use unsafe blocks. So we expect
> the vast majority of Rust code to just care about the Rust memory model.

I'm a bit worried about this.

I am sure you are aware of this document:
Documentation/process/stable-api-nonsense.rst

We really like to change the internal APIs of the kernel, and it sounds to
me like Rust really likes a rust-side-vs-C-side approach to APIs, requiring
these wrappers to be written and maintained all over the place, and that
is going to affect the mobility of the kernel-internal APIs and make them
less mobile.

If it means I need to write and review less patches related to NULL
dereference and use-after-free etc etc, then it may very well be worth
it.

But as subsystem maintainer I'd like a clear picture of this wrapper
overhead, what does it usually entail? A typical kernel API has
vtable and a few variables, not much more than that.

I go to patch 12/13 and I see things like this:

+/// A descriptor of wrapped list elements.
+pub trait GetLinksWrapped: GetLinks {
+    /// Specifies which wrapper (e.g., `Box` and `Arc`) wraps the list entries.
+    type Wrapped: Wrapper<Self::EntryType>;
+}
+
+impl<T: ?Sized> GetLinksWrapped for Box<T>
+where
+    Box<T>: GetLinks,
+{
+    type Wrapped = Box<<Box<T> as GetLinks>::EntryType>;
+}
+
+impl<T: GetLinks + ?Sized> GetLinks for Box<T> {
+    type EntryType = T::EntryType;
+    fn get_links(data: &Self::EntryType) -> &Links<Self::EntryType> {
+        <T as GetLinks>::get_links(data)
+    }
+}

My God. Lose the horrible CamelCase to begin with. I hope the
language spec does not mandate that because our kernel C style
does not use it.

It becomes obvious that as subsystem maintainer for the Linux kernel
a casual drive-by experience with Rust is not going to suffice by far.

All subsystem maintainers are expected to understand and maintain
wrappers like these, right? That means all subsystem maintainers need
to be elevated to understand the above without effort if you wake them
up in their sleep at 4 in the morning.

This makes me a bit sceptic.

Get me right, we are of course good at doing really complicated stuff,
that's what engineers do. But we are not Iron Man. We need a clear
way into understanding and maintaining wrappers and we need support
with it when we don't understand it, so the kernel would need a Rust
wrapper maintainer that we can trust to stay around for the long term,
i.e. until their retirement, while actively teaching others for decades.
For an example see how RCU is maintained.

Developing trust in the people Miguel and Wedson is going to be more
important than trust in Google the company for this.

Yours,
Linus Walleij

  parent 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 [this message]
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
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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