linux-kernel - [PATCH v4 4/4] rust: samples: Add debugfs sample

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Message-ID: <20250502-debugfs-rust-v4-4-788a9c6c2e77@google.com>
Date: Fri, 02 May 2025 19:49:33 +0000
From: Matthew Maurer <mmaurer@...gle.com>
To: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Sami Tolvanen <samitolvanen@...gle.com>, Timur Tabi <ttabi@...dia.com>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	Matthew Maurer <mmaurer@...gle.com>
Subject: [PATCH v4 4/4] rust: samples: Add debugfs sample

Provides an example of using the Rust DebugFS bindings.

Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
---
 MAINTAINERS                  |  1 +
 samples/rust/Kconfig         | 11 +++++++++
 samples/rust/Makefile        |  1 +
 samples/rust/rust_debugfs.rs | 56 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 69 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..2b1119b7281fd15109b542e6853d4206c2c80afc
--- /dev/null
+++ b/samples/rust/rust_debugfs.rs
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+//! Sample DebugFS exporting module
+
+use core::sync::atomic::{AtomicU32, Ordering};
+use kernel::c_str;
+use kernel::debugfs::Dir;
+use kernel::prelude::*;
+
+module! {
+    type: RustDebugFs,
+    name: "rust_debugfs",
+    authors: ["Matthew Maurer"],
+    description: "Rust DebugFS usage sample",
+    license: "GPL",
+}
+
+struct RustDebugFs {
+    // As we only hold this for drop effect (to remove the directory) we have a leading underscore
+    // to indicate to the compiler that we don't expect to use this field directly.
+    _debugfs: Dir<'static>,
+}
+
+static EXAMPLE: AtomicU32 = AtomicU32::new(8);
+
+impl kernel::Module for RustDebugFs {
+    fn init(_this: &'static ThisModule) -> Result<Self> {
+        // Create a debugfs directory in the root of the filesystem called "sample_debugfs".
+        let debugfs = Dir::new(c_str!("sample_debugfs"));
+
+        {
+            // Create a subdirectory, so "sample_debugfs/subdir" now exists.
+            let sub = debugfs.subdir(c_str!("subdir"));
+
+            // Create a single file in the subdirectory called "example" that will read from the
+            // `EXAMPLE` atomic variable.
+            sub.fmt_file(c_str!("example"), &EXAMPLE, &|example, f| {
+                writeln!(f, "Reading atomic: {}", example.load(Ordering::Relaxed))
+            });
+            // Now, "sample_debugfs/subdir/example" will print "Reading atomic: 8\n" when read.
+        }
+
+        // Change the value in the variable displayed by the file. This is intended to demonstrate
+        // that the module can continue to change the value used by the file.
+        EXAMPLE.store(10, Ordering::Relaxed);
+        // Now, "sample_debugfs/subdir/example" will print "Reading atomic: 10\n" when read.
+
+        // Save the root debugfs directory we created to our module object. It will be
+        // automatically cleaned up when our module is unloaded because dropping the module object
+        // will drop the `Dir` handle. The base directory, the subdirectory, and the file will all
+        // continue to exist until the module is unloaded.
+        Ok(Self { _debugfs: debugfs })
+    }
+}

-- 
2.49.0.906.g1f30a19c02-goog