linux-kernel - Re: [PATCH v3 3/5] samples: rust: Provide example using the new Rust MiscDevice abstraction

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Message-ID: <Z1K9gk3Mel4h98gA@pollux>
Date: Fri, 6 Dec 2024 10:01:54 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Lee Jones <lee@...nel.org>
Cc: linux-kernel@...r.kernel.org, arnd@...db.de, gregkh@...uxfoundation.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
Subject: Re: [PATCH v3 3/5] samples: rust: Provide example using the new Rust
 MiscDevice abstraction

On Thu, Dec 05, 2024 at 04:25:20PM +0000, Lee Jones 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 | 80 ++++++++++++++++++++++++++++++++
>  3 files changed, 91 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..f50925713f1a
> --- /dev/null
> +++ b/samples/rust/rust_misc_device.rs
> @@ -0,0 +1,80 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2024 Google LLC.
> +
> +//! 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>>>,

Why do we add examples where we ask people to allocate those structures with
kmalloc()?

`MiscDevice` should switch to the generic `Registration` type in [1] and use
`InPlaceModule`, such that those structures land in the .data section of the
binary.

[1] https://lore.kernel.org/rust-for-linux/20241205141533.111830-3-dakr@kernel.org/

> +}
> +
> +impl kernel::Module for RustMiscDeviceModule {
> +    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;
> +
> +#[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, 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(ENOIOCTLCMD);
> +            }
> +        }
> +
> +        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
> 
>