linux-kernel - Re: [PATCH v8 6/6] rust: samples: Add debugfs sample

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Message-ID: <2025070148-primer-stillness-0409@gregkh>
Date: Tue, 1 Jul 2025 16:03:52 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Matthew Maurer <mmaurer@...gle.com>
Cc: 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>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Timur Tabi <ttabi@...dia.com>, Benno Lossin <lossin@...nel.org>,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	Dirk Behme <dirk.behme@...bosch.com>
Subject: Re: [PATCH v8 6/6] rust: samples: Add debugfs sample

On Fri, Jun 27, 2025 at 11:18:29PM +0000, Matthew Maurer wrote:
> +        // 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())
> +        });

While cute, is this really going to be the way to describe all "custom"
debugfs function callbacks?  No other way to point to a function itself
instead?  Look at "fun" debugfs functions like qh_lines() in
drivers/usb/host/ehci-dbg.c that is dumping tons of data out.  Putting
that inline here is going to be a bit ackward :)

So can you show an example of a "traditional" debugfs file output with
multiple lines that is dealing with a dynamically allocated device that
is associated with the module (not the static example you showed here),
as that's going to be the real way this is used, not with static
variables.

thanks,

greg k-h