linux-kernel - Re: [PATCH 1/2] samples: rust: Provide example using the new Rust MiscDevice abstraction

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Message-ID: <20241205094610.GH7451@google.com>
Date: Thu, 5 Dec 2024 09:46:10 +0000
From: Lee Jones <lee@...nel.org>
To: Benoît du Garreau <benoit@...arreau.fr>
Cc: linux-kernel@...r.kernel.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, rust-for-linux@...r.kernel.org,
	gregkh@...uxfoundation.org
Subject: Re: [PATCH 1/2] samples: rust: Provide example using the new Rust
 MiscDevice abstraction

On Thu, 05 Dec 2024, Benoît du Garreau wrote:

> On Wed, 4 Dec 2024 17:46:24 +0000 Lee Jones <lee@...nel.org> wrote:
> 
> > This sample driver demonstrates the following basic operations:
> >
> > * Register a Misc Device
> > * Create /dev/rust-misc-device
> > * Open the aforementioned character device
> > * Operate on the character device via a simple ioctl()
> > * Close the character device
> >
> > Signed-off-by: Lee Jones <lee@...nel.org>
> > ---
> >  samples/rust/Kconfig             | 10 ++++
> >  samples/rust/Makefile            |  1 +
> >  samples/rust/rust_misc_device.rs | 84 ++++++++++++++++++++++++++++++++
> >  3 files changed, 95 insertions(+)
> >  create mode 100644 samples/rust/rust_misc_device.rs
> >
> > diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
> > index b0f74a81c8f9..df384e679901 100644
> > --- a/samples/rust/Kconfig
> > +++ b/samples/rust/Kconfig
> > @@ -20,6 +20,16 @@ config SAMPLE_RUST_MINIMAL
> >
> >  	  If unsure, say N.
> >
> > +config SAMPLE_RUST_MISC_DEVICE
> > +	tristate "Misc device"
> > +	help
> > +	  This option builds the Rust misc device.
> > +
> > +	  To compile this as a module, choose M here:
> > +	  the module will be called rust_misc_device.
> > +
> > +	  If unsure, say N.
> > +
> >  config SAMPLE_RUST_PRINT
> >  	tristate "Printing macros"
> >  	help
> > diff --git a/samples/rust/Makefile b/samples/rust/Makefile
> > index c1a5c1655395..ad4b97a98580 100644
> > --- a/samples/rust/Makefile
> > +++ b/samples/rust/Makefile
> > @@ -2,6 +2,7 @@
> >  ccflags-y += -I$(src)				# needed for trace events
> >
> >  obj-$(CONFIG_SAMPLE_RUST_MINIMAL)		+= rust_minimal.o
> > +obj-$(CONFIG_SAMPLE_RUST_MISC_DEVICE)		+= rust_misc_device.o
> >  obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
> >
> >  rust_print-y := rust_print_main.o rust_print_events.o
> > diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
> > new file mode 100644
> > index 000000000000..5f1b69569ef7
> > --- /dev/null
> > +++ b/samples/rust/rust_misc_device.rs
> > @@ -0,0 +1,84 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +//! Rust misc device sample.
> > +
> > +use kernel::{
> > +    c_str,
> > +    ioctl::_IO,
> > +    miscdevice::{MiscDevice, MiscDeviceOptions, MiscDeviceRegistration},
> > +    prelude::*,
> > +};
> > +
> > +const RUST_MISC_DEV_HELLO: u32 = _IO('R' as u32, 9);
> > +
> > +module! {
> > +    type: RustMiscDeviceModule,
> > +    name: "rust_misc_device",
> > +    author: "Lee Jones",
> > +    description: "Rust misc device sample",
> > +    license: "GPL",
> > +}
> > +
> > +struct RustMiscDeviceModule {
> > +    _miscdev: Pin<KBox<MiscDeviceRegistration<RustMiscDevice>>>,
> > +}
> > +
> > +impl kernel::Module for RustMiscDeviceModule {
> 
> This could probably use `kernel::InPlaceModule` and avoid allocating
> the registration.

Is there a way to do this and keep the print?

> > +    fn init(_module: &'static ThisModule) -> Result<Self> {
> > +        pr_info!("Initialising Rust Misc Device Sample\n");
> > +
> > +        let options = MiscDeviceOptions {
> > +            name: c_str!("rust-misc-device"),
> > +        };
> > +
> > +        Ok(Self {
> > +            _miscdev: KBox::pin_init(
> > +                MiscDeviceRegistration::<RustMiscDevice>::register(options),
> > +                GFP_KERNEL,
> > +            )?,
> > +        })
> > +    }
> > +}
> > +
> > +struct RustMiscDevice;
> > +
> > +impl RustMiscDevice {
> > +    fn new() -> Self {
> > +        Self
> > +    }
> > +}
> 
> Given that this function is nearly empty and removed in the next commit,
> it could probably not exist in the first place.

This is showing my Rust immaturity here.

How does one create a new Self without new() in this context?

> > +
> > +#[vtable]
> > +impl MiscDevice for RustMiscDevice {
> > +    type Ptr = KBox<Self>;
> > +
> > +    fn open() -> Result<KBox<Self>> {
> > +        pr_info!("Opening Rust Misc Device Sample\n");
> > +
> > +        Ok(KBox::new(RustMiscDevice::new(), GFP_KERNEL)?)
> > +    }
> > +
> > +    fn ioctl(
> > +        _device: <Self::Ptr as kernel::types::ForeignOwnable>::Borrowed<'_>,
> > +        cmd: u32,
> > +        _arg: usize,
> > +    ) -> Result<isize> {
> > +        pr_info!("IOCTLing Rust Misc Device Sample\n");
> > +
> > +        match cmd {
> > +            RUST_MISC_DEV_HELLO => pr_info!("Hello from the Rust Misc Device\n"),
> > +            _ => {
> > +                pr_err!("IOCTL not recognised: {}\n", cmd);
> > +                return Err(EINVAL);
> > +            }
> > +        }
> > +
> > +        Ok(0)
> > +    }
> > +}
> > +
> > +impl Drop for RustMiscDevice {
> > +    fn drop(&mut self) {
> > +        pr_info!("Exiting the Rust Misc Device Sample\n");
> > +    }
> > +}
> > --
> > 2.47.0.338.g60cca15819-goog
> 
> 
> Benoît du Garreau

-- 
Lee Jones [李琼斯]