[PATCH v2 1/2] rust: debugfs: migrate debugfs traits requirements to zerocopy

[Josef Ippisch via B4 Relay]

From: Josef Ippisch <josef.ippisch.dev@xxxxxxxxxxx>

Migrate `BinaryWriter` and `BinaryReaderMut`'s default implementation's
requirements on T from `kernel::transmute` traits to `zerocopy` traits.

The additional `zerocopy::Immutable` requirement on `BinaryWriter` does not
further restrict the types in practice but is rather a more explicit
requirement (that the type does not have interior mutability) and is
required by zerocopy for the `as_bytes()` function.

Suggested-by: Joshua Liebow-Feeser <joshlf@xxxxxxxxxx>
Suggested-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Link: https://github.com/Rust-for-Linux/linux/issues/975
Link: https://github.com/Rust-for-Linux/linux/issues/1241
Signed-off-by: Josef Ippisch <josef.ippisch.dev@xxxxxxxxxxx>
---
 rust/kernel/debugfs/traits.rs | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/rust/kernel/debugfs/traits.rs b/rust/kernel/debugfs/traits.rs
index 8c39524b6a99..b794f7dd7e14 100644
--- a/rust/kernel/debugfs/traits.rs
+++ b/rust/kernel/debugfs/traits.rs
@@ -18,10 +18,6 @@
         Arc,
         Mutex, //
     },
-    transmute::{
-        AsBytes,
-        FromBytes, //
-    },
     uaccess::{
         UserSliceReader,
         UserSliceWriter, //
@@ -36,6 +32,8 @@
     str::FromStr,
 };
 
+use zerocopy::Immutable;
+
 /// A trait for types that can be written into a string.
 ///
 /// This works very similarly to `Debug`, and is automatically implemented if `Debug` is
@@ -76,8 +74,8 @@ fn write_to_slice(
     ) -> Result<usize>;
 }
 
-// Base implementation for any `T: AsBytes`.
-impl<T: AsBytes> BinaryWriter for T {
+// Base implementation for any `T: Immutable + IntoBytes`.
+impl<T: Immutable + IntoBytes> BinaryWriter for T {
     fn write_to_slice(
         &self,
         writer: &mut UserSliceWriter,
@@ -147,7 +145,7 @@ fn write_to_slice(
 // Delegate for `Vec<T, A>`.
 impl<T, A> BinaryWriter for Vec<T, A>
 where
-    T: AsBytes,
+    T: Immutable + IntoBytes,
     A: Allocator,
 {
     fn write_to_slice(
@@ -157,7 +155,7 @@ fn write_to_slice(
     ) -> Result<usize> {
         let slice = self.as_slice();
 
-        // SAFETY: `T: AsBytes` allows us to treat `&[T]` as `&[u8]`.
+        // SAFETY: `T: Immutable + IntoBytes` 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))
         };
@@ -230,14 +228,14 @@ fn read_from_slice_mut(
     ) -> Result<usize>;
 }
 
-// Base implementation for any `T: AsBytes + FromBytes`.
-impl<T: AsBytes + FromBytes> BinaryReaderMut for T {
+// Base implementation for any `T: FromBytes + IntoBytes`.
+impl<T: FromBytes + IntoBytes> BinaryReaderMut for T {
     fn read_from_slice_mut(
         &mut self,
         reader: &mut UserSliceReader,
         offset: &mut file::Offset,
     ) -> Result<usize> {
-        reader.read_slice_file(self.as_bytes_mut(), offset)
+        reader.read_slice_file(self.as_mut_bytes(), offset)
     }
 }
 
@@ -255,7 +253,7 @@ fn read_from_slice_mut(
 // 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,
+    T: FromBytes + IntoBytes,
     A: Allocator,
 {
     fn read_from_slice_mut(
@@ -265,7 +263,7 @@ fn read_from_slice_mut(
     ) -> Result<usize> {
         let slice = self.as_mut_slice();
 
-        // SAFETY: `T: AsBytes + FromBytes` allows us to treat `&mut [T]` as `&mut [u8]`.
+        // SAFETY: `T: FromBytes + IntoBytes` allow us to treat `&mut [T]` as `&mut [u8]`.
         let buffer = unsafe {
             core::slice::from_raw_parts_mut(
                 slice.as_mut_ptr().cast(),

-- 
2.53.0