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

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Message-ID: <aDr1EWOIeDVgjau9@pollux>
Date: Sat, 31 May 2025 14:24:49 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Benno Lossin <lossin@...nel.org>
Cc: 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 02:03:05PM +0200, Benno Lossin wrote:
> On Sat May 31, 2025 at 12:29 PM CEST, Danilo Krummrich wrote:
> > On Sat, May 31, 2025 at 10:11:08AM +0200, Benno Lossin wrote:
> >> On Sat May 31, 2025 at 12:24 AM CEST, Danilo Krummrich wrote:
> >> > On Fri, May 30, 2025 at 10:15:37PM +0200, Benno Lossin wrote:
> >> >> On Fri May 30, 2025 at 4:24 PM CEST, Danilo Krummrich wrote:
> >> >> > +config SAMPLE_RUST_MISC_DEVICE_WITH_PARENT
> >> >> > +	bool "Create a misc device with a parent device"
> >> >> > +	depends on SAMPLE_RUST_MISC_DEVICE
> >> >> > +	default n
> >> >> > +	help
> >> >> > +	  Say Y here if you want the misc device sample to create a misc
> >> >> > +	  device with a parent device.
> >> >> > +
> >> >> 
> >> >> Why not create a separate file? The `cfg`s might confuse newcomers
> >> >> looking at the sample.
> >> >
> >> > It would be a lot of duplicated code, unless we really *only* exercise the
> >> > device creation and registration part, which would be a bit unfortunate, given
> >> > that this sample is also a pretty good test.
> >> 
> >> 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)
> >
> > The samples are normal modules, where we can have multiple files. But I don't
> > see how that helps.
> >
> > `include!` works, but I'm not sure it's that much better.
> >
> > Another option would be to put the `cfg` on the module!() macro itself and have
> > two separate module types, this way there is only a `cfg` on the two module!()
> > invocations.
> 
> How about we do it like this:
> 
> We create samples/rust/rust_misc_device/{module.rs,parent.rs,common.rs}
> and `module.rs`/`parent.rs` are the two entry points. Both of these
> files:
> * include `common.rs` using `include!` at the very top.
> * define a `RustMiscDeviceModule` struct and implmement `InPlaceModule`
>   for it.
> 
> The module-level docs, common imports constants, `module!` invocation &
> other definitions stay in `common.rs`.
> 
> This way we can build them at the same time and have no cfgs :)

Seems reasonable to me -- let's do that then.