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Message-ID: <20250506-debugfs-rust-attach-v2-2-c6f88be3890a@google.com>
Date: Tue, 06 May 2025 01:04:14 +0000
From: Matthew Maurer <mmaurer@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
Danilo Krummrich <dakr@...nel.org>, 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>, Sami Tolvanen <samitolvanen@...gle.com>,
Timur Tabi <ttabi@...dia.com>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
Matthew Maurer <mmaurer@...gle.com>
Subject: [PATCH WIP v2 2/2] rust: debugfs: Extend sample to use attached data
Demonstrates how to attach data/handles needed for implementing DebugFS
file to a directory.
Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
---
samples/rust/rust_debugfs.rs | 110 +++++++++++++++++++++++++++++++++++++++++--
1 file changed, 106 insertions(+), 4 deletions(-)
diff --git a/samples/rust/rust_debugfs.rs b/samples/rust/rust_debugfs.rs
index a4b17c8241330b2f6caf8f17a5b2366138de6ced..efaca1b140f710fcc7d0467e9b00e02a69c2cf55 100644
--- a/samples/rust/rust_debugfs.rs
+++ b/samples/rust/rust_debugfs.rs
@@ -4,11 +4,15 @@
//! Sample DebugFS exporting module
+use core::fmt;
+use core::fmt::{Display, Formatter};
use core::mem::{forget, ManuallyDrop};
use core::sync::atomic::{AtomicU32, Ordering};
use kernel::c_str;
-use kernel::debugfs::Dir;
+use kernel::debugfs::{BoundDir, Dir, Values};
+use kernel::new_mutex;
use kernel::prelude::*;
+use kernel::sync::{Arc, Mutex};
module! {
type: RustDebugFs,
@@ -21,7 +25,89 @@
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>,
+ _debugfs: Pin<KBox<Values<Backing>>>,
+}
+
+struct Composite {
+ major: u32,
+ minor: u32,
+}
+
+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 Display for Composite {
+ fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+ write!(f, "{}.{}", self.major, self.minor)
+ }
+}
+
+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, root: BoundDir<'a>) {
+ // Just prints out the number in the field
+ forget(root.display_file(c_str!("simple"), &self.simple));
+ // Uses the custom display implementation to print major.minor
+ forget(root.display_file(c_str!("composite"), &self.composite));
+ // Uses the custom hook print the number in 0-padded hex with some decorations.
+ forget(root.fmt_file(c_str!("custom"), &self.custom, &|custom, f| {
+ writeln!(f, "Foo! {:#010x} Bar!", custom)
+ }));
+ // Creates a directory for every record in the list, named the name of the item, with files
+ // for each attribute.
+ for record in self.many.iter() {
+ let dir = ManuallyDrop::new(root.subdir(record.name));
+ forget(dir.display_file(c_str!("size"), &record.size));
+ forget(dir.display_file(c_str!("stride"), &record.stride));
+ }
+ // Access the attached atomic via `.load()`
+ forget(root.fmt_file(c_str!("atomic"), &self.atomic, &|atomic, f| {
+ writeln!(f, "{}", atomic.load(Ordering::Relaxed))
+ }));
+ // Access the attached mutex-guarded data via `.lock()`
+ forget(root.fmt_file(c_str!("locked"), &self.locked, &|locked, f| {
+ writeln!(f, "{}", *locked.lock())
+ }));
+ }
}
static EXAMPLE: AtomicU32 = AtomicU32::new(8);
@@ -29,13 +115,13 @@ struct RustDebugFs {
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"));
+ let root = Dir::new(c_str!("sample_debugfs"));
{
// Create a subdirectory, so "sample_debugfs/subdir" now exists.
// We wrap it in `ManuallyDrop` so that the subdirectory is not automatically discarded
// at the end of the scope - it will be cleaned up when `debugfs` is.
- let sub = ManuallyDrop::new(debugfs.subdir(c_str!("subdir")));
+ let sub = ManuallyDrop::new(root.subdir(c_str!("subdir")));
// Create a single file in the subdirectory called "example" that will read from the
// `EXAMPLE` atomic variable.
@@ -51,6 +137,22 @@ fn init(_this: &'static ThisModule) -> Result<Self> {
EXAMPLE.store(10, Ordering::Relaxed);
// Now, "sample_debugfs/subdir/example" will print "Reading atomic: 10\n" when read.
+ // We can also attach data scoped to our root directory
+ let backing = Backing::new()?;
+ // Grab a refcount pointing to the locked data
+ let locked = backing.locked.clone();
+ let debugfs = KBox::pin_init(Values::attach(backing, root), GFP_KERNEL)?;
+
+ // Once it's attached, we can invoke `Backing::build` to create the relevant files:
+ debugfs.as_ref().build(Backing::build);
+
+ // We can still access read-only references the contents of the attached values. If the
+ // values allow interior mutability, like atomics, this lets us still change them:
+ debugfs.as_ref().atomic.store(8, Ordering::Relaxed);
+
+ // If we attached refcounted data, we can use an external handle to access it
+ *locked.lock() = 42;
+
// 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
--
2.49.0.967.g6a0df3ecc3-goog
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