samples: rust: Provide example using the new Rust MiscDevice abstraction

This sample driver demonstrates the following basic operations:

* Register a Misc Device
* Create /dev/rust-misc-device
* Provide open call-back for the aforementioned character device
* Operate on the character device via a simple ioctl()
* Provide close call-back for the character device

Signed-off-by: Lee Jones <lee@kernel.org>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20241213134715.601415-3-lee@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

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

samples/rust/rust_misc_device.rs

@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2024 Google LLC.
+
+//! Rust misc device sample.
+
+use kernel::{
+    c_str,
+    device::Device,
+    fs::File,
+    ioctl::_IO,
+    miscdevice::{MiscDevice, MiscDeviceOptions, MiscDeviceRegistration},
+    prelude::*,
+    types::ARef,
+};
+
+const RUST_MISC_DEV_HELLO: u32 = _IO('|' as u32, 0x80);
+
+module! {
+    type: RustMiscDeviceModule,
+    name: "rust_misc_device",
+    author: "Lee Jones",
+    description: "Rust misc device sample",
+    license: "GPL",
+}
+
+#[pin_data]
+struct RustMiscDeviceModule {
+    #[pin]
+    _miscdev: MiscDeviceRegistration<RustMiscDevice>,
+}
+
+impl kernel::InPlaceModule for RustMiscDeviceModule {
+    fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
+        pr_info!("Initialising Rust Misc Device Sample\n");
+
+        let options = MiscDeviceOptions {
+            name: c_str!("rust-misc-device"),
+        };
+
+        try_pin_init!(Self {
+            _miscdev <- MiscDeviceRegistration::register(options),
+        })
+    }
+}
+
+struct RustMiscDevice {
+    dev: ARef<Device>,
+}
+
+#[vtable]
+impl MiscDevice for RustMiscDevice {
+    type Ptr = KBox<Self>;
+
+    fn open(_file: &File, misc: &MiscDeviceRegistration<Self>) -> Result<KBox<Self>> {
+        let dev = ARef::from(misc.device());
+
+        dev_info!(dev, "Opening Rust Misc Device Sample\n");
+
+        Ok(KBox::new(RustMiscDevice { dev }, GFP_KERNEL)?)
+    }
+
+    fn ioctl(
+        me: <Self::Ptr as kernel::types::ForeignOwnable>::Borrowed<'_>,
+        _file: &File,
+        cmd: u32,
+        _arg: usize,
+    ) -> Result<isize> {
+        dev_info!(me.dev, "IOCTLing Rust Misc Device Sample\n");
+
+        match cmd {
+            RUST_MISC_DEV_HELLO => dev_info!(me.dev, "Hello from the Rust Misc Device\n"),
+            _ => {
+                dev_err!(me.dev, "-> IOCTL not recognised: {}\n", cmd);
+                return Err(ENOTTY);
+            }
+        }
+
+        Ok(0)
+    }
+}
+
+impl Drop for RustMiscDevice {
+    fn drop(&mut self) {
+        dev_info!(self.dev, "Exiting the Rust Misc Device Sample\n");
+    }
+}