It is slightly more convenient to operate on mut pointers, and this also
properly conveys the desired ownership semantics of the trait.

Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
 rust/kernel/alloc/kbox.rs | 22 ++++++++++------------
 rust/kernel/sync/arc.rs   | 12 ++++++------
 rust/kernel/types.rs      | 14 +++++++-------
 3 files changed, 23 insertions(+), 25 deletions(-)

diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs
index 7a5fdf7b660fb91ca2a8e5023d69d629b0d66062..de7fadeb7fdf5cf6742c2e9749e959ac5f82359e 100644
--- a/rust/kernel/alloc/kbox.rs
+++ b/rust/kernel/alloc/kbox.rs
@@ -355,18 +355,18 @@ impl<T: 'static, A> ForeignOwnable for Box<T, A>
 {
     type Borrowed<'a> = &'a T;
 
-    fn into_foreign(self) -> *const core::ffi::c_void {
-        Box::into_raw(self).cast_const().cast()
+    fn into_foreign(self) -> *mut core::ffi::c_void {
+        Box::into_raw(self).cast()
     }
 
-    unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
-        let ptr = ptr.cast_mut().cast();
+    unsafe fn from_foreign(ptr: *mut core::ffi::c_void) -> Self {
+        let ptr = ptr.cast();
         // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
         // call to `Self::into_foreign`.
         unsafe { Box::from_raw(ptr) }
     }
 
-    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a T {
+    unsafe fn borrow<'a>(ptr: *mut core::ffi::c_void) -> &'a T {
         let ptr = ptr.cast();
         // SAFETY: The safety requirements of this method ensure that the object remains alive and
         // immutable for the duration of 'a.
@@ -380,21 +380,19 @@ impl<T: 'static, A> ForeignOwnable for Pin<Box<T, A>>
 {
     type Borrowed<'a> = Pin<&'a T>;
 
-    fn into_foreign(self) -> *const core::ffi::c_void {
+    fn into_foreign(self) -> *mut core::ffi::c_void {
         // SAFETY: We are still treating the box as pinned.
-        Box::into_raw(unsafe { Pin::into_inner_unchecked(self) })
-            .cast_const()
-            .cast()
+        Box::into_raw(unsafe { Pin::into_inner_unchecked(self) }).cast()
     }
 
-    unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
-        let ptr = ptr.cast_mut().cast();
+    unsafe fn from_foreign(ptr: *mut core::ffi::c_void) -> Self {
+        let ptr = ptr.cast();
         // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
         // call to `Self::into_foreign`.
         unsafe { Pin::new_unchecked(Box::from_raw(ptr)) }
     }
 
-    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Pin<&'a T> {
+    unsafe fn borrow<'a>(ptr: *mut core::ffi::c_void) -> Pin<&'a T> {
         let ptr = ptr.cast();
         // SAFETY: The safety requirements for this function ensure that the object is still alive,
         // so it is safe to dereference the raw pointer.
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 88e5208369e40bdeebc6f758e89f836a97790d89..26b7272424aafdd4847d9642456cab837797ac33 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -335,12 +335,12 @@ pub fn into_unique_or_drop(self) -> Option<Pin<UniqueArc<T>>> {
 impl<T: 'static> ForeignOwnable for Arc<T> {
     type Borrowed<'a> = ArcBorrow<'a, T>;
 
-    fn into_foreign(self) -> *const core::ffi::c_void {
-        ManuallyDrop::new(self).ptr.as_ptr().cast_const().cast()
+    fn into_foreign(self) -> *mut core::ffi::c_void {
+        ManuallyDrop::new(self).ptr.as_ptr().cast()
     }
 
-    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> ArcBorrow<'a, T> {
-        let ptr = ptr.cast_mut().cast();
+    unsafe fn borrow<'a>(ptr: *mut core::ffi::c_void) -> ArcBorrow<'a, T> {
+        let ptr = ptr.cast();
 
         // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
         // call to `Self::into_foreign`.
@@ -351,8 +351,8 @@ unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> ArcBorrow<'a, T> {
         unsafe { ArcBorrow::new(inner) }
     }
 
-    unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
-        let ptr = ptr.cast_mut().cast();
+    unsafe fn from_foreign(ptr: *mut core::ffi::c_void) -> Self {
+        let ptr = ptr.cast();
 
         // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
         // call to `Self::into_foreign`.
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index e8b7ff1387381e50d7963978e57b1d567113b035..04358375794dc5ba7bfebbe3cfc5885cff531f15 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -29,7 +29,7 @@ pub trait ForeignOwnable: Sized {
     /// For example, it might be invalid, dangling or pointing to uninitialized memory. Using it in
     /// any way except for [`ForeignOwnable::from_foreign`], [`ForeignOwnable::borrow`],
     /// [`ForeignOwnable::try_from_foreign`] can result in undefined behavior.
-    fn into_foreign(self) -> *const core::ffi::c_void;
+    fn into_foreign(self) -> *mut core::ffi::c_void;
 
     /// Borrows a foreign-owned object.
     ///
@@ -37,7 +37,7 @@ pub trait ForeignOwnable: Sized {
     ///
     /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
     /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
-    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Self::Borrowed<'a>;
+    unsafe fn borrow<'a>(ptr: *mut core::ffi::c_void) -> Self::Borrowed<'a>;
 
     /// Converts a foreign-owned object back to a Rust-owned one.
     ///
@@ -47,7 +47,7 @@ pub trait ForeignOwnable: Sized {
     /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
     /// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] for
     /// this object must have been dropped.
-    unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self;
+    unsafe fn from_foreign(ptr: *mut core::ffi::c_void) -> Self;
 
     /// Tries to convert a foreign-owned object back to a Rust-owned one.
     ///
@@ -58,7 +58,7 @@ pub trait ForeignOwnable: Sized {
     ///
     /// `ptr` must either be null or satisfy the safety requirements for
     /// [`ForeignOwnable::from_foreign`].
-    unsafe fn try_from_foreign(ptr: *const core::ffi::c_void) -> Option<Self> {
+    unsafe fn try_from_foreign(ptr: *mut core::ffi::c_void) -> Option<Self> {
         if ptr.is_null() {
             None
         } else {
@@ -72,13 +72,13 @@ unsafe fn try_from_foreign(ptr: *const core::ffi::c_void) -> Option<Self> {
 impl ForeignOwnable for () {
     type Borrowed<'a> = ();
 
-    fn into_foreign(self) -> *const core::ffi::c_void {
+    fn into_foreign(self) -> *mut core::ffi::c_void {
         core::ptr::NonNull::dangling().as_ptr()
     }
 
-    unsafe fn borrow<'a>(_: *const core::ffi::c_void) -> Self::Borrowed<'a> {}
+    unsafe fn borrow<'a>(_: *mut core::ffi::c_void) -> Self::Borrowed<'a> {}
 
-    unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
+    unsafe fn from_foreign(_: *mut core::ffi::c_void) -> Self {}
 }
 
 /// Runs a cleanup function/closure when dropped.

-- 
2.47.0

On Wed, Oct 30, 2024 at 9:46 PM Tamir Duberstein <tamird@gmail.com> wrote:
>
> It is slightly more convenient to operate on mut pointers, and this also
> properly conveys the desired ownership semantics of the trait.
>
> Signed-off-by: Tamir Duberstein <tamird@gmail.com>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

"Tamir Duberstein" <tamird@gmail.com> writes:

> It is slightly more convenient to operate on mut pointers, and this also
> properly conveys the desired ownership semantics of the trait.
>
> Signed-off-by: Tamir Duberstein <tamird@gmail.com>


Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>