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Date: Tue, 6 Jul 2021 07:30:28 +0300
From: Leon Romanovsky <leon@kernel.org>
To: Linus Walleij <linus.walleij@linaro.org>,
	"a. Miguel Ojeda" <miguel.ojeda.sandonis@gmail.com>
Cc: ksummit@lists.linux.dev
Subject: Re: [TECH TOPIC] Rust for Linux
Message-ID: <YOPcZE+WjlwNueTa@unreal>
References: <CANiq72kF7AbiJCTHca4A0CxDDJU90j89uh80S3pDqDt7-jthOg@mail.gmail.com>
 <CACRpkdbbPEnNTLYSP-YP+hTnqhUGQ8FjJLNY_fpSNWWd8tCFTQ@mail.gmail.com>
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On Tue, Jul 06, 2021 at 01:51:11AM +0200, Linus Walleij wrote:
> On Sat, Jun 26, 2021 at 12:09 AM Miguel Ojeda
> <miguel.ojeda.sandonis@gmail.com> wrote:
> 
> > The Rust for Linux project is adding support for the Rust language to
> > the Linux kernel. This talk describes the work done so far and also
> > serves as an introduction for other kernel developers interested in
> > using Rust in the kernel.
> 
> I think this is a good tech topic.

<...>

> Demonstrate how the Rust code now elegantly avoid
> ever seeing problems A,B,C again.
> 
> From this it is very easy for the kernel community to deduce that
> introducing Rust as an implementation language is worth it.

I don't know about advantages of Rust, but from what I see there are
some disadvantages that no one talks about them.

1. The addition of another language to the mix will hurt a lot our
ability to refactor code for cross-subsystem changes.

Just as an example, there are many changes in DMA/SG areas that are
applicable for many drivers. Even simple grep->replace pattern will
be harder and longer if it is needed for the drivers that are written
in different languages.

2. Testing matrix will be duplicated, both in compilation tests and in
verification coverage. Even now, there are some kernel subsystems that 
so much in-love with CONFIG_* options that their combination is slightly
tested or not tested at all. So imagine, we will need to recompile
everything with Rust too and execute same coverage tests again.

And yes, proper testing costs a lot of money, which IMHO better to
invest in improving coverage/fixing bugs/tooling instead of adding
new language to the pack.

Thanks

> 
> Yours,
> Linus Walleij
>