linux-kernel - [PATCH 6/8] rust: debugfs: Implement display_file in terms of fmt

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Message-ID: <20250429-debugfs-rust-v1-6-6b6e7cb7929f@google.com>
Date: Tue, 29 Apr 2025 23:16:00 +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>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	Matthew Maurer <mmaurer@...gle.com>
Subject: [PATCH 6/8] rust: debugfs: Implement display_file in terms of fmt_file

fmt_file is fundamentally more flexible, this reduces the number of
unsafe blocks, and allows us to append a newline for display_file which
is a good default.

Previous display_file did not append a newline to ensure that all output
strings, including those without trailing newlines, were an option.

Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
---
 rust/kernel/debugfs.rs | 18 ++++--------------
 1 file changed, 4 insertions(+), 14 deletions(-)

diff --git a/rust/kernel/debugfs.rs b/rust/kernel/debugfs.rs
index 2faa59d2dae44ab708cb8fca0d23f06f73a95a3a..835df2b5d7311f278d1d15fc8d688809d0ca363f 100644
--- a/rust/kernel/debugfs.rs
+++ b/rust/kernel/debugfs.rs
@@ -108,7 +108,7 @@ fn as_ptr(&self) -> *mut bindings::dentry {
     }
 
     /// Create a file in a DebugFS directory with the provided name, and contents from invoking
-    /// [`Display::fmt`] on the provided reference.
+    /// [`Display::fmt`] on the provided reference with a trailing newline.
     ///
     /// # Example
     ///
@@ -124,8 +124,7 @@ pub fn display_file<T: Display + Sized>(
         name: &CStr,
         data: &'static T,
     ) -> Result<ARef<Self>> {
-        // SAFETY: As `data` lives for the static lifetime, it outlives the file.
-        unsafe { self.display_file_raw(name, data) }
+        self.fmt_file(name, data, &|val, f| write!(f, "{val}\n"))
     }
 
     /// Create a file in a DebugFS directory with the provided name, and contents from invoking `f`
@@ -367,7 +366,7 @@ unsafe fn new(inner: &'a Dir) -> Self {
     }
 
     /// Create a file in a DebugFS directory with the provided name, and contents from invoking
-    /// [`Display::fmt`] on the provided reference.
+    /// [`Display::fmt`] on the provided reference with a trailing newline.
     ///
     /// # Example
     ///
@@ -384,16 +383,7 @@ unsafe fn new(inner: &'a Dir) -> Self {
     /// # Ok::<(), Error>(())
     /// ```
     pub fn display_file<T: Display + Sized>(&self, name: &CStr, data: &'a T) -> Result<()> {
-        // We forget the reference because its reference count is implicitly "owned" by the root
-        // builder, which we know will use `debugfs_remove` to clean this up. If we release the
-        // file here, it will be immediately deleted.
-        // SAFETY:
-        // Because `Builder`'s invariant says that our lifetime is how long the directory will
-        // be available, and is equivariant, `'a` will outlive the base directory, which will be
-        // torn down by `debugfs_remove` to prevent access even if an extra refcount is held
-        // somewhere.
-        core::mem::forget(unsafe { self.inner.display_file_raw(name, data)? });
-        Ok(())
+        self.fmt_file(name, data, &|val, f| write!(f, "{val}\n"))
     }
 
     /// Creates a nested directory that may live as long as its parent

-- 
2.49.0.901.g37484f566f-goog