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Message-ID: <20250618-debugfs-rust-v6-5-72cae211b133@google.com>
Date: Wed, 18 Jun 2025 02:28:17 +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>, 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>, Benno Lossin <lossin@...nel.org>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
Matthew Maurer <mmaurer@...gle.com>
Subject: [PATCH v6 5/5] 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 | 76 ++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 89 insertions(+)
diff --git a/MAINTAINERS b/MAINTAINERS
index fda422023e30fe8821e4cd79b503693ecc6eb48c..7faa088cc08514acfec371b043d324bb52d2e7ba 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7382,6 +7382,7 @@ 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 7f7371a004ee0a8f67dca99c836596709a70c4fa..8eb2088b66b0646c7a1fba9cdccc9a6bb328defb 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -62,6 +62,17 @@ 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 bd2faad63b4f3befe7d1ed5139fe25c7a8b6d7f6..61276222a99f8cc6d7f84c26d0533b30815ebadd 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..6af9177c711a07764f0323e03a72d115287f1205
--- /dev/null
+++ b/samples/rust/rust_debugfs.rs
@@ -0,0 +1,76 @@
+// 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, File};
+use kernel::prelude::*;
+use kernel::sync::{new_mutex, Arc};
+
+module! {
+ type: RustDebugFs,
+ name: "rust_debugfs",
+ authors: ["Matthew Maurer"],
+ description: "Rust DebugFS usage sample",
+ license: "GPL",
+}
+
+struct RustDebugFs {
+ // As we only hold these for drop effect (to remove the directory/files) we have a leading
+ // underscore to indicate to the compiler that we don't expect to use this field directly.
+ _debugfs: Dir,
+ _subdir: Dir,
+ _file: File,
+ _file_2: File,
+}
+
+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.
+ // We `forget` the result to avoid deleting the file at the end of the scope.
+ let file = 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.
+
+ // In addition to globals, we can also attach any kind of owned data. Most commonly, this
+ // will look like an `Arc<MyObject>` as those can be shared with the rest of the module.
+ let my_arc = Arc::pin_init(new_mutex!(10), GFP_KERNEL)?;
+ // An `Arc<Mutex<usize>>` doesn't implement display, so let's give explicit instructions on
+ // how to print it
+ let file_2 = sub.fmt_file(c_str!("arc_backed"), my_arc.clone(), &|val, f| {
+ writeln!(f, "locked value: {:#010x}", *val.lock())
+ });
+
+ // Since it's an `Arc` and we cloned it, we continue to have access to `my_arc`. If this
+ // were real, we'd probably stash it in our module struct and do something with it when
+ // handling real calls.
+ *my_arc.lock() = 99;
+
+ // Save the handles we want to preserve to our module object. They will be automatically
+ // cleaned up when our module is unloaded.
+ Ok(Self {
+ _debugfs: debugfs,
+ _subdir: sub,
+ _file: file,
+ _file_2: file_2,
+ })
+ }
+}
--
2.50.0.rc2.696.g1fc2a0284f-goog
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