linux-kernel - Re: [PATCH v5 4/4] rust: samples: Add debugfs sample

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <D9VPA1M45WBK.1TB4KOUXD24BD@kernel.org>
Date: Wed, 14 May 2025 09:20:49 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Matthew Maurer" <mmaurer@...gle.com>, "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>
Subject: Re: [PATCH v5 4/4] rust: samples: Add debugfs sample

On Tue May 6, 2025 at 1:51 AM CEST, Matthew Maurer wrote:
> +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.
> +            // 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")));

I dislike the direct usage of `ManuallyDrop`. To me the usage of
`ManuallyDrop` signifies that one has to opt out of `Drop` without the
support of the wrapped type. But in this case, `Dir` is sometimes
intended to not be dropped, so I'd rather have a `.keep()` function I
saw mentioned somewhere.

> +
> +            // 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.
> +            forget(sub.fmt_file(c_str!("example"), &EXAMPLE, &|example, f| {
> +                writeln!(f, "Reading atomic: {}", example.load(Ordering::Relaxed))
> +            }));

Similarly here, I'd rather have a `.keep()` function than people start
using `forget` all over the place.

---
Cheers,
Benno

> +            // 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 })
> +    }
> +}