linux-kernel - Re: [PATCH 7/7] rust: sample: misc: implement device driver sample

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Message-ID: <CANiq72nx8VNjKw_P+49AcMUuY_pE2jYoybLMCAyjhGv-Z-a22w@mail.gmail.com>
Date: Sat, 31 May 2025 13:05:21 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Benno Lossin <lossin@...nel.org>
Cc: Danilo Krummrich <dakr@...nel.org>, gregkh@...uxfoundation.org, rafael@...nel.org, 
	ojeda@...nel.org, alex.gaynor@...il.com, boqun.feng@...il.com, 
	gary@...yguo.net, bjorn3_gh@...tonmail.com, benno.lossin@...ton.me, 
	a.hindborg@...nel.org, aliceryhl@...gle.com, tmgross@...ch.edu, 
	chrisi.schrefl@...il.com, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] rust: sample: misc: implement device driver sample

On Sat, May 31, 2025 at 10:11 AM Benno Lossin <lossin@...nel.org> wrote:
>
> We could separate the common parts into a single file and then
> `include!` that file from the two samples. (Or if the build system
> supports multi-file samples then just use that, but my gut feeling is
> that it doesn't)

It does, in the sense that you can use Rust modules (i.e. different
files). Multi-file in the sense of linking several C files + a single
Rust crate root also works (we have a sample doing that).

Reusing the same `mod` from two different crate roots should also work
(well, unless `rustc` doesn't like it for some reason, but from a
quick test it seems OK), plus games with `#[path]` and symlinks.

> I really would like to avoid `cfg` in samples.

I think the `cfg` is not the end of the world w.r.t. learning (after
all, `cfg`s are part of the kernel all the time, and it is not the
first sample). In fact, one could argue that it is a good way to show
what `cfg` can do, in a way.

But another disadvantage of `cfg` is that then one cannot have both
modules at the same time, and thus 2 builds to test both etc.

Cheers,
Miguel