rust: configfs: add a sample demonstrating configfs usage

Add a sample to the samples folder, demonstrating the intended use of the
Rust configfs API.

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Andreas Hindborg <[email protected]>

Author: Andreas Hindborg

samples/rust/Kconfig

@@ -10,6 +10,17 @@ menuconfig SAMPLES_RUST
 
 if SAMPLES_RUST
 
+config SAMPLE_RUST_CONFIGFS
+	tristate "Configfs sample"
+	depends on CONFIGFS_FS
+	help
+	  This option builds the Rust configfs sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_configfs.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_MINIMAL
 	tristate "Minimal"
 	help

samples/rust/Makefile

@@ -8,6 +8,7 @@ obj-$(CONFIG_SAMPLE_RUST_DMA)			+= rust_dma.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_PCI)		+= rust_driver_pci.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM)	+= rust_driver_platform.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_FAUX)		+= rust_driver_faux.o
+obj-$(CONFIG_SAMPLE_RUST_CONFIGFS)		+= rust_configfs.o
 
 rust_print-y := rust_print_main.o rust_print_events.o
 

samples/rust/rust_configfs.rs

@@ -0,0 +1,192 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust configfs sample.
+
+use kernel::alloc::flags;
+use kernel::c_str;
+use kernel::configfs;
+use kernel::configfs_attrs;
+use kernel::new_mutex;
+use kernel::page::PAGE_SIZE;
+use kernel::prelude::*;
+use kernel::sync::Mutex;
+
+module! {
+    type: RustConfigfs,
+    name: "rust_configfs",
+    author: "Rust for Linux Contributors",
+    description: "Rust configfs sample",
+    license: "GPL",
+}
+
+#[pin_data]
+struct RustConfigfs {
+    #[pin]
+    config: configfs::Subsystem<Configuration>,
+}
+
+#[pin_data]
+struct Configuration {
+    message: &'static CStr,
+    #[pin]
+    bar: Mutex<(KBox<[u8; PAGE_SIZE]>, usize)>,
+}
+
+impl Configuration {
+    fn new() -> impl PinInit<Self, Error> {
+        try_pin_init!(Self {
+            message: c_str!("Hello World\n"),
+            bar <- new_mutex!((KBox::new([0; PAGE_SIZE], flags::GFP_KERNEL)?, 0)),
+        })
+    }
+}
+
+impl kernel::InPlaceModule for RustConfigfs {
+    fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
+        pr_info!("Rust configfs sample (init)\n");
+
+        // Define a subsystem with the data type `Configuration`, two
+        // attributes, `message` and `bar` and child group type `Child`. `mkdir`
+        // in the directory representing this subsystem will create directories
+        // backed by the `Child` type.
+        let item_type = configfs_attrs! {
+            container: configfs::Subsystem<Configuration>,
+            data: Configuration,
+            child: Child,
+            attributes: [
+                message: 0,
+                bar: 1,
+            ],
+        };
+
+        try_pin_init!(Self {
+            config <- configfs::Subsystem::new(
+                c_str!("rust_configfs"), item_type, Configuration::new()
+            ),
+        })
+    }
+}
+
+#[vtable]
+impl configfs::GroupOperations for Configuration {
+    type Child = Child;
+
+    fn make_group(&self, name: &CStr) -> Result<impl PinInit<configfs::Group<Child>, Error>> {
+        // Define a group with data type `Child`, one attribute `baz` and child
+        // group type `GrandChild`. `mkdir` in the directory representing this
+        // group will create directories backed by the `GrandChild` type.
+        let tpe = configfs_attrs! {
+            container: configfs::Group<Child>,
+            data: Child,
+            child: GrandChild,
+            attributes: [
+                baz: 0,
+            ],
+        };
+
+        Ok(configfs::Group::new(name.try_into()?, tpe, Child::new()))
+    }
+}
+
+#[vtable]
+impl configfs::AttributeOperations<0> for Configuration {
+    type Data = Configuration;
+
+    fn show(container: &Configuration, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
+        pr_info!("Show message\n");
+        let data = container.message;
+        page[0..data.len()].copy_from_slice(data);
+        Ok(data.len())
+    }
+}
+
+#[vtable]
+impl configfs::AttributeOperations<1> for Configuration {
+    type Data = Configuration;
+
+    fn show(container: &Configuration, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
+        pr_info!("Show bar\n");
+        let guard = container.bar.lock();
+        let data = guard.0.as_slice();
+        let len = guard.1;
+        page[0..len].copy_from_slice(&data[0..len]);
+        Ok(len)
+    }
+
+    fn store(container: &Configuration, page: &[u8]) -> Result {
+        pr_info!("Store bar\n");
+        let mut guard = container.bar.lock();
+        guard.0[0..page.len()].copy_from_slice(page);
+        guard.1 = page.len();
+        Ok(())
+    }
+}
+
+// `pin_data` cannot handle structs without braces.
+#[pin_data]
+struct Child {}
+
+impl Child {
+    fn new() -> impl PinInit<Self, Error> {
+        try_pin_init!(Self {})
+    }
+}
+
+#[vtable]
+impl configfs::GroupOperations for Child {
+    type Child = GrandChild;
+
+    fn make_group(&self, name: &CStr) -> Result<impl PinInit<configfs::Group<GrandChild>, Error>> {
+        // Define a group with data type `GrandChild`, one attribute `gc`. As no
+        // child type is specified, it will not be possible to create subgroups
+        // in this group, and `mkdir`in the directory representing this group
+        // will return an error.
+        let tpe = configfs_attrs! {
+            container: configfs::Group<GrandChild>,
+            data: GrandChild,
+            attributes: [
+                gc: 0,
+            ],
+        };
+
+        Ok(configfs::Group::new(
+            name.try_into()?,
+            tpe,
+            GrandChild::new(),
+        ))
+    }
+}
+
+#[vtable]
+impl configfs::AttributeOperations<0> for Child {
+    type Data = Child;
+
+    fn show(_container: &Child, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
+        pr_info!("Show baz\n");
+        let data = c"Hello Baz\n".to_bytes();
+        page[0..data.len()].copy_from_slice(data);
+        Ok(data.len())
+    }
+}
+
+// `pin_data` cannot handle structs without braces.
+#[pin_data]
+struct GrandChild {}
+
+impl GrandChild {
+    fn new() -> impl PinInit<Self, Error> {
+        try_pin_init!(Self {})
+    }
+}
+
+#[vtable]
+impl configfs::AttributeOperations<0> for GrandChild {
+    type Data = GrandChild;
+
+    fn show(_container: &GrandChild, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
+        pr_info!("Show grand child\n");
+        let data = c"Hello GC\n".to_bytes();
+        page[0..data.len()].copy_from_slice(data);
+        Ok(data.len())
+    }
+}