linux-kernel - Re: [PATCH v10 5/7] samples: rust: Add debugfs sample driver

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Message-Id: <DC6U02DZSX1W.1SXD7XQTNHXQL@kernel.org>
Date: Wed, 20 Aug 2025 02:34:09 +0200
From: "Danilo Krummrich" <dakr@...nel.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>,
 "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, "Sami Tolvanen" <samitolvanen@...gle.com>, "Timur
 Tabi" <ttabi@...dia.com>, "Benno Lossin" <lossin@...nel.org>, "Dirk Beheme"
 <dirk.behme@...bosch.com>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v10 5/7] samples: rust: Add debugfs sample driver

On Wed Aug 20, 2025 at 12:53 AM CEST, Matthew Maurer wrote:
> Adds a new sample driver that demonstrates the debugfs APIs.
>
> The driver creates a directory in debugfs and populates it with a few
> files:
> - A read-only file that displays a fwnode property.
> - A read-write file that exposes an atomic counter.
> - A read-write file that exposes a custom struct.
>
> This sample serves as a basic example of how to use the `debugfs::Dir`
> and `debugfs::File` APIs to create and manage debugfs entries.
>
> Signed-off-by: Matthew Maurer <mmaurer@...gle.com>

This is a great example, thanks! I really like how the API turned out.

When it comes to the newly added Scope API - and I assume this does not come at
a surprise - I have some concerns.

But first, thanks a lot for posting the socinfo driver in both variants, with
and without the Scope API.

I had a brief look at both of those and I can see why you want this.

With the Scope thing you can indeed write things a bit more compressed (I think
in the patches the differences looks quite a bit bigger than it actually is,
because the scope-based one uses quite some code from the file-based one).

I think the downsides are mainly:

  - The degree of complexity added for a rather specific use-case, that is also
    perfectly representable with the file-based API.

  - It makes it convinient to expose multiple fields grouped under the same lock
    as separate files, which design wise we shouln't encourage for the reasons
    we discussed in v8.

I think for the sake of getting this series merged, which I would really love to
see, I think we should focus on the file-based API first. Once we got this
landed I think we can still revisit the Scope idea and have some more discussion
about it.

I will have a more detailed look tomorrow (at least for the patches 1-5).

Thanks again for working on this!

- Danilo