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

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Message-ID: <CAGSQo00UiOUAgYODhXT9BWLW0bXoCxMzt9fV2F2aiTEOG1vwyA@mail.gmail.com>
Date: Tue, 1 Jul 2025 10:24:04 -0700
From: Matthew Maurer <mmaurer@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 Tue, Jul 1, 2025 at 7:03 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> 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 :)

Good news, function pointers are legal to pass in here as well
already, I can add that usage to make it clear.

>
> 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.

Sure, do we want to:
* Finish creating the driver struct early in `init`, then call dynamic
`.create(&str)` or `.destroy(&str)` `.modify(&str)` type things on it
in `init` to show how it would work
* Actually wire up an input source to drive create/destroy/modify
dynamically (e.g. I could implement a miscdevice) - if you want this
one, do you have a preference on where I get my input signal from?

>
> thanks,
>
> greg k-h