[PATCH 8/8] rust: samples: Add debugfs sample

[Matthew Maurer <mmaurer@google.com>]

Provides an example of using the Rust DebugFS bindings.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 MAINTAINERS                  |   1 +
 samples/rust/Kconfig         |  11 ++++
 samples/rust/Makefile        |   1 +
 samples/rust/rust_debugfs.rs | 120 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 133 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index a3b835e427b083a4ddd690d9e7739851f0af47ae..426bcdac025134e20911de8e2cf5c9efb0591814 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7278,6 +7278,7 @@ F:	rust/kernel/devres.rs
 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_driver_platform.rs
 F:	samples/rust/rust_driver_faux.rs
 
diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index 43cb72d72631bb2d6e06185e1d88778edff6ee13..6c42ed73f842cda26256039e6917bb443738d3f1 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -51,6 +51,17 @@ config SAMPLE_RUST_DMA
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_DEBUGFS
+	tristate "DebugFS Test Driver"
+	depends on DEBUG_FS
+	help
+	  This option builds the Rust DebugFS Test driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_debugfs.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_DRIVER_PCI
 	tristate "PCI Driver"
 	depends on PCI
diff --git a/samples/rust/Makefile b/samples/rust/Makefile
index 6a466afd2a21eba84a3b7b2be29f25dce44e9053..b1fc4677ed53fcf7d0f5a3dbf322f65851bc1784 100644
--- a/samples/rust/Makefile
+++ b/samples/rust/Makefile
@@ -4,6 +4,7 @@ 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
+obj-$(CONFIG_SAMPLE_RUST_DEBUGFS)		+= rust_debugfs.o
 obj-$(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
diff --git a/samples/rust/rust_debugfs.rs b/samples/rust/rust_debugfs.rs
new file mode 100644
index 0000000000000000000000000000000000000000..3fd25848f2d096b03fa70679103bd725d0e42fcf
--- /dev/null
+++ b/samples/rust/rust_debugfs.rs
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+//! Sample DebugFS exporting module
+
+use core::fmt;
+use core::fmt::{Display, Formatter};
+use core::sync::atomic::{AtomicU32, Ordering};
+use kernel::c_str;
+use kernel::debugfs::{Builder, Dir, Values};
+use kernel::debugfs_fmt_file;
+use kernel::new_mutex;
+use kernel::prelude::*;
+use kernel::sync::{Arc, Mutex};
+
+module! {
+    type: RustDebugFs,
+    name: "rust_debugfs",
+    authors: ["Matthew Maurer"],
+    description: "Rust DebugFS usage sample",
+    license: "GPL",
+}
+
+struct RustDebugFs {
+    _debugfs: Pin<KBox<Values<Backing>>>,
+}
+
+struct Composite {
+    major: u32,
+    minor: u32,
+}
+
+impl Display for Composite {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "{}.{}", self.major, self.minor)
+    }
+}
+
+struct Record {
+    name: &'static CStr,
+    size: usize,
+    stride: usize,
+}
+
+struct Backing {
+    simple: u32,
+    composite: Composite,
+    custom: u32,
+    many: KVec<Record>,
+    atomic: AtomicU32,
+    locked: Arc<Mutex<u32>>,
+}
+
+impl Backing {
+    fn new() -> Result<Self> {
+        let mut many = KVec::new();
+        many.push(
+            Record {
+                name: c_str!("foo"),
+                size: 1,
+                stride: 2,
+            },
+            GFP_KERNEL,
+        )?;
+        many.push(
+            Record {
+                name: c_str!("bar"),
+                size: 3,
+                stride: 4,
+            },
+            GFP_KERNEL,
+        )?;
+        Ok(Self {
+            simple: 10,
+            composite: Composite { major: 1, minor: 2 },
+            custom: 37,
+            many,
+            atomic: AtomicU32::new(7),
+            locked: Arc::pin_init(new_mutex!(0), GFP_KERNEL)?,
+        })
+    }
+    fn build<'a>(&'a self, builder: Builder<'a>) -> Result<()> {
+        builder.display_file(c_str!("simple"), &self.simple)?;
+        builder.display_file(c_str!("composite"), &self.composite)?;
+        debugfs_fmt_file!(
+            builder,
+            c_str!("custom"),
+            &self.custom,
+            "Foo! {:#010x} Bar!\n"
+        )?;
+        for record in self.many.iter() {
+            let dir = builder.dir(record.name)?;
+            dir.display_file(c_str!("size"), &record.size)?;
+            dir.display_file(c_str!("stride"), &record.stride)?;
+        }
+        builder.fmt_file(c_str!("atomic"), &self.atomic, &|atomic, f| {
+            write!(f, "{}\n", atomic.load(Ordering::Relaxed))
+        })?;
+        builder.fmt_file(c_str!("locked"), &self.locked, &|locked, f| {
+            write!(f, "{}\n", *locked.lock())
+        })?;
+        Ok(())
+    }
+}
+
+impl kernel::Module for RustDebugFs {
+    fn init(_this: &'static ThisModule) -> Result<Self> {
+        let dir = Dir::new(c_str!("sample_debugfs"), None)?;
+        let backing = Backing::new()?;
+        let locked = backing.locked.clone();
+        let debugfs = KBox::pin_init(Values::attach(backing, dir), GFP_KERNEL)?;
+        debugfs.as_ref().build(Backing::build)?;
+        // These mutations could occur at any time in the future, and would remain visible through
+        // debugfs.
+        debugfs.as_ref().atomic.store(8, Ordering::Relaxed);
+        *locked.lock() = 42;
+        Ok(Self { _debugfs: debugfs })
+    }
+}

-- 
2.49.0.901.g37484f566f-goog