Re: [TECH TOPIC] Rust for Linux

[Linus Walleij <linus.walleij@linaro.org>]

On Tue, Jul 6, 2021 at 10:00 PM Roland Dreier <roland@kernel.org> wrote:

> One area I see where Rust could make a big improvement for drivers is
> in using RAII for error paths.  Drivers often have a lot of code like
>
>     if (something())
>         return err;
>
>     if (something_else())
>         goto undo_something;
>
>     if (a_third_thing())
>         goto undo_two_things;
>
> and so on, which is difficult to get right in the first place and even
> harder to keep correct in the face of changes.

Yes.

> "devres" / devm_xxx was an attempt to deal with this in C, but it only
> solves some cases of this and has not received a lot of adoption (we
> can argue about the reasons).

Really? From my point of view that is adopted all over the map.
I add new users all the time and use it as much as I can when
writing new drivers.

$ git grep devm_  | wc -l
26112

Dmitry in the input subsystem even insist to use it for e.g. powering
down and disabling regulators on remove(), like recently in
drivers/input/touchscreen/cy8ctma140.c

/* Called from the registered devm action */
static void cy8ctma140_power_off_action(void *d)
{
        struct cy8ctma140 *ts = d;

        cy8ctma140_power_down(ts);
}
(...)
error = devm_add_action_or_reset(dev, cy8ctma140_power_off_action, ts);
if (error) {
        dev_err(dev, "failed to install power off handler\n");
        return error;
}

I think it's a formidable success, people just need to learn to do it more.

But if an easier path to learn better behaviours is to shuffle the whole
chessboard and replace it with drivers written in Rust, I don't know?
Maybe?

Yours,
Linus Walleij