Extend Rust debugfs binary support to allow exposing data stored in
common smart pointers and heap-allocated collections.

- Implement BinaryWriter for Box<T>, Pin<Box<T>>, Arc<T>, and Vec<T>.
- Introduce BinaryReaderMut for mutable binary access with outer locks.
- Implement BinaryReaderMut for Box<T>, Vec<T>, and base types.
- Update BinaryReader to delegate to BinaryReaderMut for Mutex<T>,
  Box<T>, Pin<Box<T>> and Arc<T>.

This enables debugfs files to directly expose or update data stored
inside heap-allocated, reference-counted, or lock-protected containers
without manual dereferencing or locking.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/debugfs.rs        |   2 +-
 rust/kernel/debugfs/traits.rs | 148 +++++++++++++++++++++++++++++++++-
 2 files changed, 147 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/debugfs.rs b/rust/kernel/debugfs.rs
index 95cd3376ecbe..d2bc7550d81e 100644
--- a/rust/kernel/debugfs.rs
+++ b/rust/kernel/debugfs.rs
@@ -21,7 +21,7 @@
 use core::ops::Deref;
 
 mod traits;
-pub use traits::{BinaryReader, BinaryWriter, Reader, Writer};
+pub use traits::{BinaryReader, BinaryReaderMut, BinaryWriter, Reader, Writer};
 
 mod callback_adapters;
 use callback_adapters::{FormatAdapter, NoWriter, WritableAdapter};
diff --git a/rust/kernel/debugfs/traits.rs b/rust/kernel/debugfs/traits.rs
index 5f80ce77bf17..c1adf4d9f270 100644
--- a/rust/kernel/debugfs/traits.rs
+++ b/rust/kernel/debugfs/traits.rs
@@ -3,12 +3,15 @@
 
 //! Traits for rendering or updating values exported to DebugFS.
 
+use crate::alloc::Allocator;
 use crate::fs::file;
 use crate::prelude::*;
+use crate::sync::Arc;
 use crate::sync::Mutex;
 use crate::transmute::{AsBytes, FromBytes};
 use crate::uaccess::{UserSliceReader, UserSliceWriter};
 use core::fmt::{self, Debug, Formatter};
+use core::ops::{Deref, DerefMut};
 use core::str::FromStr;
 use core::sync::atomic::{
     AtomicI16, AtomicI32, AtomicI64, AtomicI8, AtomicIsize, AtomicU16, AtomicU32, AtomicU64,
@@ -51,12 +54,14 @@ pub trait BinaryWriter {
     fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize>;
 }
 
+// Base implementation for any `T: AsBytes`.
 impl<T: AsBytes> BinaryWriter for T {
     fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
         writer.write_slice_partial(self.as_bytes(), offset)
     }
 }
 
+// Delegate for `Mutex<T>`: Support a `T` with an outer mutex.
 impl<T: BinaryWriter> BinaryWriter for Mutex<T> {
     fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
         let guard = self.lock();
@@ -65,6 +70,56 @@ fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) ->
     }
 }
 
+// Delegate for `Box<T, A>`: Support a `Box<T, A>` with no lock or an inner lock.
+impl<T, A> BinaryWriter for Box<T, A>
+where
+    T: BinaryWriter,
+    A: Allocator,
+{
+    fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
+        self.deref().write_to_slice(writer, offset)
+    }
+}
+
+// Delegate for `Pin<Box<T, A>>`: Support a `Pin<Box<T, A>>` with no lock or an inner lock.
+impl<T, A> BinaryWriter for Pin<Box<T, A>>
+where
+    T: BinaryWriter,
+    A: Allocator,
+{
+    fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
+        self.deref().write_to_slice(writer, offset)
+    }
+}
+
+// Delegate for `Arc<T>`: Support a `Arc<T>` with no lock or an inner lock.
+impl<T> BinaryWriter for Arc<T>
+where
+    T: BinaryWriter,
+{
+    fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
+        self.deref().write_to_slice(writer, offset)
+    }
+}
+
+// Delegate for `Vec<T, A>`.
+impl<T, A> BinaryWriter for Vec<T, A>
+where
+    T: AsBytes,
+    A: Allocator,
+{
+    fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
+        let slice = self.as_slice();
+
+        // SAFETY: `T: AsBytes` allows us to treat `&[T]` as `&[u8]`.
+        let buffer = unsafe {
+            core::slice::from_raw_parts(slice.as_ptr().cast(), core::mem::size_of_val(slice))
+        };
+
+        writer.write_slice_partial(buffer, offset)
+    }
+}
+
 /// A trait for types that can be updated from a user slice.
 ///
 /// This works similarly to `FromStr`, but operates on a `UserSliceReader` rather than a &str.
@@ -93,6 +148,73 @@ fn read_from_slice(&self, reader: &mut UserSliceReader) -> Result {
 }
 
 /// Trait for types that can be constructed from a binary representation.
+///
+/// See also [`BinaryReader`] for interior mutability.
+pub trait BinaryReaderMut {
+    /// Reads the binary form of `self` from `reader`.
+    ///
+    /// Same as [`BinaryReader::read_from_slice`], but takes a mutable reference.
+    ///
+    /// `offset` is the requested offset into the binary representation of `self`.
+    ///
+    /// On success, returns the number of bytes read from `reader`.
+    fn read_from_slice_mut(
+        &mut self,
+        reader: &mut UserSliceReader,
+        offset: file::Offset,
+    ) -> Result<usize>;
+}
+
+// Base implementation for any `T: AsBytes + FromBytes`.
+impl<T: AsBytes + FromBytes> BinaryReaderMut for T {
+    fn read_from_slice_mut(
+        &mut self,
+        reader: &mut UserSliceReader,
+        offset: file::Offset,
+    ) -> Result<usize> {
+        reader.read_slice_partial(self.as_bytes_mut(), offset)
+    }
+}
+
+// Delegate for `Box<T, A>`: Support a `Box<T, A>` with an outer lock.
+impl<T: ?Sized + BinaryReaderMut, A: Allocator> BinaryReaderMut for Box<T, A> {
+    fn read_from_slice_mut(
+        &mut self,
+        reader: &mut UserSliceReader,
+        offset: file::Offset,
+    ) -> Result<usize> {
+        self.deref_mut().read_from_slice_mut(reader, offset)
+    }
+}
+
+// Delegate for `Vec<T, A>`: Support a `Vec<T, A>` with an outer lock.
+impl<T, A> BinaryReaderMut for Vec<T, A>
+where
+    T: AsBytes + FromBytes,
+    A: Allocator,
+{
+    fn read_from_slice_mut(
+        &mut self,
+        reader: &mut UserSliceReader,
+        offset: file::Offset,
+    ) -> Result<usize> {
+        let slice = self.as_mut_slice();
+
+        // SAFETY: `T: AsBytes + FromBytes` allows us to treat `&mut [T]` as `&mut [u8]`.
+        let buffer = unsafe {
+            core::slice::from_raw_parts_mut(
+                slice.as_mut_ptr().cast(),
+                core::mem::size_of_val(slice),
+            )
+        };
+
+        reader.read_slice_partial(buffer, offset)
+    }
+}
+
+/// Trait for types that can be constructed from a binary representation.
+///
+/// See also [`BinaryReaderMut`] for the mutable version.
 pub trait BinaryReader {
     /// Reads the binary form of `self` from `reader`.
     ///
@@ -102,11 +224,33 @@ pub trait BinaryReader {
     fn read_from_slice(&self, reader: &mut UserSliceReader, offset: file::Offset) -> Result<usize>;
 }
 
-impl<T: AsBytes + FromBytes> BinaryReader for Mutex<T> {
+// Delegate for `Mutex<T>`: Support a `T` with an outer `Mutex`.
+impl<T: BinaryReaderMut> BinaryReader for Mutex<T> {
     fn read_from_slice(&self, reader: &mut UserSliceReader, offset: file::Offset) -> Result<usize> {
         let mut this = self.lock();
 
-        reader.read_slice_partial(this.as_bytes_mut(), offset)
+        this.read_from_slice_mut(reader, offset)
+    }
+}
+
+// Delegate for `Box<T, A>`: Support a `Box<T, A>` with an inner lock.
+impl<T: ?Sized + BinaryReader, A: Allocator> BinaryReader for Box<T, A> {
+    fn read_from_slice(&self, reader: &mut UserSliceReader, offset: file::Offset) -> Result<usize> {
+        self.deref().read_from_slice(reader, offset)
+    }
+}
+
+// Delegate for `Pin<Box<T, A>>`: Support a `Pin<Box<T, A>>` with an inner lock.
+impl<T: ?Sized + BinaryReader, A: Allocator> BinaryReader for Pin<Box<T, A>> {
+    fn read_from_slice(&self, reader: &mut UserSliceReader, offset: file::Offset) -> Result<usize> {
+        self.deref().read_from_slice(reader, offset)
+    }
+}
+
+// Delegate for `Arc<T>`: Support an `Arc<T>` with an inner lock.
+impl<T: ?Sized + BinaryReader> BinaryReader for Arc<T> {
+    fn read_from_slice(&self, reader: &mut UserSliceReader, offset: file::Offset) -> Result<usize> {
+        self.deref().read_from_slice(reader, offset)
     }
 }
 
-- 
2.51.0

On Tue Oct 21, 2025 at 7:26 AM JST, Danilo Krummrich wrote:
<snip>
> @@ -51,12 +54,14 @@ pub trait BinaryWriter {
>      fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize>;
>  }
>  
> +// Base implementation for any `T: AsBytes`.
>  impl<T: AsBytes> BinaryWriter for T {
>      fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
>          writer.write_slice_partial(self.as_bytes(), offset)
>      }
>  }
>  
> +// Delegate for `Mutex<T>`: Support a `T` with an outer mutex.

I guess these two comments belong in the previous patch?

>  impl<T: BinaryWriter> BinaryWriter for Mutex<T> {
>      fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
>          let guard = self.lock();
> @@ -65,6 +70,56 @@ fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) ->
>      }
>  }
>  
> +// Delegate for `Box<T, A>`: Support a `Box<T, A>` with no lock or an inner lock.
> +impl<T, A> BinaryWriter for Box<T, A>
> +where
> +    T: BinaryWriter,
> +    A: Allocator,
> +{
> +    fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
> +        self.deref().write_to_slice(writer, offset)
> +    }
> +}
> +
> +// Delegate for `Pin<Box<T, A>>`: Support a `Pin<Box<T, A>>` with no lock or an inner lock.
> +impl<T, A> BinaryWriter for Pin<Box<T, A>>
> +where
> +    T: BinaryWriter,
> +    A: Allocator,
> +{
> +    fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
> +        self.deref().write_to_slice(writer, offset)
> +    }
> +}
> +
> +// Delegate for `Arc<T>`: Support a `Arc<T>` with no lock or an inner lock.
> +impl<T> BinaryWriter for Arc<T>
> +where
> +    T: BinaryWriter,
> +{
> +    fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
> +        self.deref().write_to_slice(writer, offset)
> +    }
> +}

These 3 implementations are identical - can we replace some/all with
just an implementation for anything implementing `Deref<T>`?

On 10/22/25 7:57 AM, Alexandre Courbot wrote:
> On Tue Oct 21, 2025 at 7:26 AM JST, Danilo Krummrich wrote:
> <snip>
>> @@ -51,12 +54,14 @@ pub trait BinaryWriter {
>>      fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize>;
>>  }
>>  
>> +// Base implementation for any `T: AsBytes`.
>>  impl<T: AsBytes> BinaryWriter for T {
>>      fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
>>          writer.write_slice_partial(self.as_bytes(), offset)
>>      }
>>  }
>>  
>> +// Delegate for `Mutex<T>`: Support a `T` with an outer mutex.
> 
> I guess these two comments belong in the previous patch?

I added them in this patch since it is where the comments become useful, but
technically they can indeed go in the previous one.

>>  impl<T: BinaryWriter> BinaryWriter for Mutex<T> {
>>      fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
>>          let guard = self.lock();
>> @@ -65,6 +70,56 @@ fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) ->
>>      }
>>  }
>>  
>> +// Delegate for `Box<T, A>`: Support a `Box<T, A>` with no lock or an inner lock.
>> +impl<T, A> BinaryWriter for Box<T, A>
>> +where
>> +    T: BinaryWriter,
>> +    A: Allocator,
>> +{
>> +    fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
>> +        self.deref().write_to_slice(writer, offset)
>> +    }
>> +}
>> +
>> +// Delegate for `Pin<Box<T, A>>`: Support a `Pin<Box<T, A>>` with no lock or an inner lock.
>> +impl<T, A> BinaryWriter for Pin<Box<T, A>>
>> +where
>> +    T: BinaryWriter,
>> +    A: Allocator,
>> +{
>> +    fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
>> +        self.deref().write_to_slice(writer, offset)
>> +    }
>> +}
>> +
>> +// Delegate for `Arc<T>`: Support a `Arc<T>` with no lock or an inner lock.
>> +impl<T> BinaryWriter for Arc<T>
>> +where
>> +    T: BinaryWriter,
>> +{
>> +    fn write_to_slice(&self, writer: &mut UserSliceWriter, offset: file::Offset) -> Result<usize> {
>> +        self.deref().write_to_slice(writer, offset)
>> +    }
>> +}
> 
> These 3 implementations are identical - can we replace some/all with
> just an implementation for anything implementing `Deref<T>`?

Unfortunately, this would lead to some ambiguity for the compiler. A type could
match

	impl<T: AsBytes> BinaryWriter for T {}

and

	impl<T, D> BinaryWriter for T
	where
    	    T: Deref<Target = D>,
	    D: BinaryWriter,
	{}

at the same time.