On Tue, Feb 3, 2026 at 8:48 AM Gary Guo [off-list ref] wrote:

On Tue Feb 3, 2026 at 3:46 PM GMT, Matthew Maurer wrote:

quoted

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 <redacted>
---
 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
    });

?

Yes - that won't work, because the function being provided to
`Scope::dir` is `for<'data, 'dir> FnOnce(&'data T, &'dir
ScopedDir<'data, 'dir>)` - this means that *intentionally*, if you
capture any non-static-lifetime variable from outside the closure, you
won't be able to use it with the methods on `ScopedDir`, because the
`'data` lifetime bound should stop you. In the general case, we
wouldn't want a reference with the same lifetime as `device` in that
example to be usable inside the debugfs callbacks. The device of a
Devres wrapped scope is a special case because we know that it will
outlive it.

Best,
Gary