linux-kernel - Re: [PATCH v2 5/6] rust: debugfs: Allow access to device in Devres-wrapped scopes

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Message-Id: <DG5HAM6F5QYE.1ZFO7GD3SL9V0@garyguo.net>
Date: Tue, 03 Feb 2026 16:47:55 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "Matthew Maurer" <mmaurer@...gle.com>, "Bjorn Andersson"
 <andersson@...nel.org>, "Konrad Dybcio" <konradybcio@...nel.org>, "Satya
 Durga Srinivasu Prabhala" <satyap@...cinc.com>, "Miguel Ojeda"
 <ojeda@...nel.org>, "Boqun Feng" <boqun.feng@...il.com>, "Gary Guo"
 <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, "Benno Lossin" <lossin@...nel.org>, "Andreas
 Hindborg" <a.hindborg@...nel.org>, "Alice Ryhl" <aliceryhl@...gle.com>,
 "Trevor Gross" <tmgross@...ch.edu>, "Danilo Krummrich" <dakr@...nel.org>,
 "Daniel Almeida" <daniel.almeida@...labora.com>, "Greg Kroah-Hartman"
 <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
 "David Airlie" <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>,
 "Michal Wilczynski" <m.wilczynski@...sung.com>, "Dave Ertman"
 <david.m.ertman@...el.com>, "Ira Weiny" <ira.weiny@...el.com>, "Leon
 Romanovsky" <leon@...nel.org>
Cc: "Trilok Soni" <tsoni@...cinc.com>, <linux-kernel@...r.kernel.org>,
 <linux-arm-msm@...r.kernel.org>, <rust-for-linux@...r.kernel.org>,
 <driver-core@...ts.linux.dev>, <dri-devel@...ts.freedesktop.org>,
 <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v2 5/6] rust: debugfs: Allow access to device in
 Devres-wrapped scopes

On Tue Feb 3, 2026 at 3:46 PM GMT, Matthew Maurer wrote:
> This adds support for creating a DebugFS directory which is aware that
> it is bound to a device. As a result, callbacks under that directory
> have access to a bound device which gives them efficient access to other
> Devres, ability to use dev_err! and friends, etc.
>
> Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
> ---
>  rust/kernel/debugfs.rs | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
>
> diff --git a/rust/kernel/debugfs.rs b/rust/kernel/debugfs.rs
> index d7b8014a6474698235203f2b7d8fec96f2bb43f8..ac614d693fa73929d095b669e9ba61958bec609e 100644
> --- a/rust/kernel/debugfs.rs
> +++ b/rust/kernel/debugfs.rs
> @@ -11,6 +11,11 @@
>  #[cfg(CONFIG_DEBUG_FS)]
>  use crate::sync::Arc;
>  use crate::{
> +    device::{
> +        Bound,
> +        Device, //
> +    },
> +    devres::Devres,
>      fmt,
>      prelude::*,
>      str::CStr,
> @@ -722,3 +727,38 @@ fn new(name: &CStr) -> ScopedDir<'data, 'static> {
>          }
>      }
>  }
> +
> +impl<'a, T: 'a + Send> Devres<Scope<T>> {
> +    /// Creates a new scope, which is a directory at the root of the debugfs filesystem,
> +    /// associated with some data `T`, enclosed in a [`Devres`] for the provided device.
> +    ///
> +    /// The `init` closure is called to populate the directory with files and subdirectories. These
> +    /// files can reference the data stored in the scope. Because it is stored inside a `Devres`,
> +    /// the init method is granted access to a `&Device<Bound>`.
> +    ///
> +    /// This can be used for cheaply accessing device-protected data inside DebugFS methods or
> +    /// accessing device-specific methods (e.g. [`dev_err!`]).
> +    ///
> +    /// The entire directory tree created within the scope will be removed when the returned
> +    /// `Scope` handle is dropped.
> +    pub fn dir<E: 'a, F>(
> +        dev: &'a Device<Bound>,
> +        data: impl PinInit<T, E> + 'a,
> +        name: &'a CStr,
> +        init: F,
> +    ) -> impl PinInit<Self, Error> + 'a
> +    where
> +        F: for<'data, 'dir> FnOnce(&'data T, &'data Device<Bound>, &'dir ScopedDir<'data, 'dir>)
> +            + 'a,
> +        Error: From<E>,
> +    {
> +        Devres::new(
> +            dev,
> +            Scope::new(data, |data| {
> +                let scoped = ScopedDir::new(name);
> +                init(data, dev, &scoped);
> +                scoped.into_entry()
> +            }),
> +        )
> +    }
> +}

I think it is a big strange to have this on `Devres` (in patch v6 it has `Devres::dir` doesn't make
too much sense). I would suggest that we domsomething like

    impl<'a, T: 'a + Send> Scope<T> {
        pub fn devres_dir(
            ...
        ) -> impl PinInit<Devres<Self>, Error> + 'a;
    }

To me `Devres` is just a generic container type, just like `Arc` and `ARef`, so
the assoc functions should be defined on the concrete type.

Also: is there a reason that this needs a special API, and by

    Devres::new(device, Scope::dir(data, c"name", |data| {
        // use data and device
    });

?

Best,
Gary