[RFC PATCH 3/3] samples: rust: add kobject sample

[Daniel Sedlak <daniel@sedlak.dev>]

Add basic example using the kobject API using Rust.
The example is similar to the already existing
examples samples/kobject/{kobject-example.c,kset-example.c}.

Signed-off-by: Daniel Sedlak <daniel@sedlak.dev>
---
 samples/rust/Kconfig            |  8 ++++
 samples/rust/Makefile           |  1 +
 samples/rust/kobject_example.rs | 66 +++++++++++++++++++++++++++++++++
 3 files changed, 75 insertions(+)
 create mode 100644 samples/rust/kobject_example.rs

diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index b0f74a81c8f9..75e6db1ba6c0 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -37,4 +37,12 @@ config SAMPLE_RUST_HOSTPROGS
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_KOBJECT
+	bool "Build kobject example in Rust"
+	help
+	  This config option allows to build kobject
+	  exampel written in Rust.
+
+	  If unsure, say N.
+
 endif # SAMPLES_RUST
diff --git a/samples/rust/Makefile b/samples/rust/Makefile
index c1a5c1655395..b3ae09ef2c24 100644
--- a/samples/rust/Makefile
+++ b/samples/rust/Makefile
@@ -3,6 +3,7 @@ ccflags-y += -I$(src)				# needed for trace events
 
 obj-$(CONFIG_SAMPLE_RUST_MINIMAL)		+= rust_minimal.o
 obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
+obj-$(CONFIG_SAMPLE_RUST_KOBJECT)		+= kobject_example.o
 
 rust_print-y := rust_print_main.o rust_print_events.o
 
diff --git a/samples/rust/kobject_example.rs b/samples/rust/kobject_example.rs
new file mode 100644
index 000000000000..90db937dea5a
--- /dev/null
+++ b/samples/rust/kobject_example.rs
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust example using kobjects.
+
+use kernel::{
+    c_str,
+    kobject::{subsystems, KObject, KObjectTextAttribute},
+    prelude::*,
+    str::CString,
+};
+
+module! {
+    type: RustKObject,
+    name: "rust_kobject",
+    author: "Rust for Linux Contributors",
+    license: "GPL",
+}
+
+struct RustKObject {
+    // This kobject may be referenced later by other parts of code to update
+    // the values stored within [`MyKObject`].
+    _kobject: Pin<KBox<KObject<MyKObject>>>,
+}
+
+/// Sample KObject state which creates directory in the `/sys/kernel/my_kobject`.
+#[derive(Default)]
+pub struct MyKObject {
+    text: Option<CString>,
+}
+
+/// Attribute of the [`MyKObject`], creates file in the `/sys/kernel/my_kobject/my-text`.
+/// Where `show()` is triggered when read is called and `store()` is called
+/// when new data are written.
+pub struct MyKObjectAttribute;
+#[vtable]
+impl KObjectTextAttribute<MyKObject> for MyKObjectAttribute {
+    const NAME: &'static CStr = c_str!("my-text");
+
+    /// Called for example by `cat /sys/kernel/my_kobject/my-text`.
+    fn show(this: &mut MyKObject) -> Result<CString> {
+        if let Some(text) = &this.text {
+            CString::try_from_fmt(fmt!("Text that was stored: '{text:?}'\n"))
+        } else {
+            CString::try_from_fmt(fmt!("No one stored anything yet, value {}.\n", this.value))
+        }
+    }
+
+    /// Called for example by `echo "Hi Rust!" > /sys/kernel/my_kobject/my-text`.
+    fn store(this: &mut MyKObject, input: &CStr) -> Result {
+        this.text = Some(input.to_cstring()?);
+        Ok(())
+    }
+}
+
+impl kernel::Module for RustKObject {
+    fn init(_module: &'static ThisModule) -> kernel::error::Result<Self> {
+        let mut kobject = KObject::new_with_dynamic_kobject_parent(
+            CString::try_from_fmt(fmt!("my_kobject"))?,
+            &subsystems::KERNEL_KOBJECT,
+            MyKObject::default(),
+        )?;
+        kobject.add_attribute(MyKObjectAttribute)?;
+
+        Ok(RustKObject { _kobject: kobject })
+    }
+}
-- 
2.47.1