[PATCH v4 2/4] samples: rust: Provide example using the new Rust MiscDevice abstraction

[Lee Jones <lee@kernel.org>]

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>
---
 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..3837532d259e
--- /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('|' 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 {
+    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(ENOTTY);
+            }
+        }
+
+        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