samples: rust: Add scoped debugfs sample driver

Adds a new sample driver `rust_scoped_debugfs` that demonstrates the
use of the scoped debugfs APIs.

The driver creates a `control` directory with two write-only files,
`create` and `remove`. Writing a name and a series of numbers to
`create` will create a new subdirectory under a `dynamic` directory.
This new subdirectory will contain files that expose the numbers as
atomic values.

Writing a name to `remove` will remove the corresponding subdirectory
from the `dynamic` directory.

This sample serves as an example of how to use the `debugfs::Scope`
and `debugfs::ScopedDir` APIs to create and manage debugfs entries
that are tied to the lifetime of a data structure.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250904-debugfs-rust-v11-7-7d12a165685a@google.com
[ Rename "scoped_debugfs" -> "debugfs_scoped", fix up
  Result<(), Error> -> Result. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Author: maurer

MAINTAINERS

@@ -7497,6 +7497,7 @@ F:	rust/kernel/driver.rs
 F:	rust/kernel/faux.rs
 F:	rust/kernel/platform.rs
 F:	samples/rust/rust_debugfs.rs
+F:	samples/rust/rust_debugfs_scoped.rs
 F:	samples/rust/rust_driver_platform.rs
 F:	samples/rust/rust_driver_faux.rs
 

samples/rust/Kconfig

@@ -73,6 +73,17 @@ config SAMPLE_RUST_DEBUGFS
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_DEBUGFS_SCOPED
+	tristate "Scoped DebugFS Test Module"
+	depends on DEBUG_FS
+	help
+	  This option builds the Rust Scoped DebugFS Test module sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_debugfs_scoped.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_DRIVER_PCI
 	tristate "PCI Driver"
 	depends on PCI

samples/rust/Makefile

@@ -5,6 +5,7 @@ obj-$(CONFIG_SAMPLE_RUST_MINIMAL)		+= rust_minimal.o
 obj-$(CONFIG_SAMPLE_RUST_MISC_DEVICE)		+= rust_misc_device.o
 obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
 obj-$(CONFIG_SAMPLE_RUST_DEBUGFS)		+= rust_debugfs.o
+obj-$(CONFIG_SAMPLE_RUST_DEBUGFS_SCOPED)	+= rust_debugfs_scoped.o
 obj-$(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

samples/rust/rust_debugfs_scoped.rs

@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+//! Sample DebugFS exporting platform driver that demonstrates the use of
+//! `Scope::dir` to create a variety of files without the need to separately
+//! track them all.
+
+use core::sync::atomic::AtomicUsize;
+use kernel::debugfs::{Dir, Scope};
+use kernel::prelude::*;
+use kernel::sync::Mutex;
+use kernel::{c_str, new_mutex, str::CString};
+
+module! {
+    type: RustScopedDebugFs,
+    name: "rust_debugfs_scoped",
+    authors: ["Matthew Maurer"],
+    description: "Rust Scoped DebugFS usage sample",
+    license: "GPL",
+}
+
+fn remove_file_write(
+    mod_data: &ModuleData,
+    reader: &mut kernel::uaccess::UserSliceReader,
+) -> Result {
+    let mut buf = [0u8; 128];
+    if reader.len() >= buf.len() {
+        return Err(EINVAL);
+    }
+    let n = reader.len();
+    reader.read_slice(&mut buf[..n])?;
+
+    let s = core::str::from_utf8(&buf[..n]).map_err(|_| EINVAL)?.trim();
+    let nul_idx = s.len();
+    buf[nul_idx] = 0;
+    let to_remove = CStr::from_bytes_with_nul(&buf[..nul_idx + 1]).map_err(|_| EINVAL)?;
+    mod_data
+        .devices
+        .lock()
+        .retain(|device| device.name.as_bytes() != to_remove.as_bytes());
+    Ok(())
+}
+
+fn create_file_write(
+    mod_data: &ModuleData,
+    reader: &mut kernel::uaccess::UserSliceReader,
+) -> Result {
+    let mut buf = [0u8; 128];
+    if reader.len() > buf.len() {
+        return Err(EINVAL);
+    }
+    let n = reader.len();
+    reader.read_slice(&mut buf[..n])?;
+
+    let mut nums = KVec::new();
+
+    let s = core::str::from_utf8(&buf[..n]).map_err(|_| EINVAL)?.trim();
+    let mut items = s.split_whitespace();
+    let name_str = items.next().ok_or(EINVAL)?;
+    let name = CString::try_from_fmt(fmt!("{name_str}"))?;
+    let file_name = CString::try_from_fmt(fmt!("{name_str}"))?;
+    for sub in items {
+        nums.push(
+            AtomicUsize::new(sub.parse().map_err(|_| EINVAL)?),
+            GFP_KERNEL,
+        )?;
+    }
+
+    let scope = KBox::pin_init(
+        mod_data
+            .device_dir
+            .scope(DeviceData { name, nums }, &file_name, |dev_data, dir| {
+                for (idx, val) in dev_data.nums.iter().enumerate() {
+                    let Ok(name) = CString::try_from_fmt(fmt!("{idx}")) else {
+                        return;
+                    };
+                    dir.read_write_file(&name, val);
+                }
+            }),
+        GFP_KERNEL,
+    )?;
+    (*mod_data.devices.lock()).push(scope, GFP_KERNEL)?;
+
+    Ok(())
+}
+
+struct RustScopedDebugFs {
+    _data: Pin<KBox<Scope<ModuleData>>>,
+}
+
+#[pin_data]
+struct ModuleData {
+    device_dir: Dir,
+    #[pin]
+    devices: Mutex<KVec<Pin<KBox<Scope<DeviceData>>>>>,
+}
+
+impl ModuleData {
+    fn init(device_dir: Dir) -> impl PinInit<Self> {
+        pin_init! {
+            Self {
+                device_dir: device_dir,
+                devices <- new_mutex!(KVec::new())
+            }
+        }
+    }
+}
+
+struct DeviceData {
+    name: CString,
+    nums: KVec<AtomicUsize>,
+}
+
+fn init_control(base_dir: &Dir, dyn_dirs: Dir) -> impl PinInit<Scope<ModuleData>> + '_ {
+    base_dir.scope(
+        ModuleData::init(dyn_dirs),
+        c_str!("control"),
+        |data, dir| {
+            dir.write_only_callback_file(c_str!("create"), data, &create_file_write);
+            dir.write_only_callback_file(c_str!("remove"), data, &remove_file_write);
+        },
+    )
+}
+
+impl kernel::Module for RustScopedDebugFs {
+    fn init(_module: &'static kernel::ThisModule) -> Result<Self> {
+        let base_dir = Dir::new(c_str!("rust_scoped_debugfs"));
+        let dyn_dirs = base_dir.subdir(c_str!("dynamic"));
+        Ok(Self {
+            _data: KBox::pin_init(init_control(&base_dir, dyn_dirs), GFP_KERNEL)?,
+        })
+    }
+}