linux-kernel - [PATCH v3 2/6] rust: types: avoid `as` casts

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Message-Id: <20241108-borrow-mut-v3-2-b7144945714e@gmail.com>
Date: Fri, 08 Nov 2024 10:46:17 -0500
From: Tamir Duberstein <tamird@...il.com>
To: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
 Benno Lossin <benno.lossin@...ton.me>, 
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
 Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Tamir Duberstein <tamird@...il.com>
Subject: [PATCH v3 2/6] rust: types: avoid `as` casts

Replace `as` casts with `cast{,_mut}` calls which are a bit safer.

In one instance, remove an unnecessary `as` cast without replacement.

Signed-off-by: Tamir Duberstein <tamird@...il.com>
---
 rust/kernel/alloc/kbox.rs | 8 ++++----
 rust/kernel/sync/arc.rs   | 9 +++++----
 rust/kernel/types.rs      | 2 +-
 3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs
index d69c32496b86a2315f81cafc8e6771ebb0cf10d1..03b7107c60344d4f03d49c51230e114d3ab38027 100644
--- a/rust/kernel/alloc/kbox.rs
+++ b/rust/kernel/alloc/kbox.rs
@@ -356,13 +356,13 @@ 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) as _
+        Box::into_raw(self).cast()
     }
 
     unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
         // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
         // call to `Self::into_foreign`.
-        unsafe { Box::from_raw(ptr as _) }
+        unsafe { Box::from_raw(ptr.cast_mut().cast()) }
     }
 
     unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a T {
@@ -380,13 +380,13 @@ impl<T: 'static, A> ForeignOwnable for Pin<Box<T, A>>
 
     fn into_foreign(self) -> *const core::ffi::c_void {
         // SAFETY: We are still treating the box as pinned.
-        Box::into_raw(unsafe { Pin::into_inner_unchecked(self) }) as _
+        Box::into_raw(unsafe { Pin::into_inner_unchecked(self) }).cast()
     }
 
     unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
         // 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 as _)) }
+        unsafe { Pin::new_unchecked(Box::from_raw(ptr.cast_mut().cast())) }
     }
 
     unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Pin<&'a T> {
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 2c9b7d4a2554278ce8608f4f4c7f9cfe87b21492..af383bcd003e1122ebe1b62a49fe40279458e379 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -201,10 +201,11 @@ pub fn new(contents: T, flags: Flags) -> Result<Self, AllocError> {
         };
 
         let inner = KBox::new(value, flags)?;
+        let inner = KBox::leak(inner).into();
 
         // SAFETY: We just created `inner` with a reference count of 1, which is owned by the new
         // `Arc` object.
-        Ok(unsafe { Self::from_inner(KBox::leak(inner).into()) })
+        Ok(unsafe { Self::from_inner(inner) })
     }
 }
 
@@ -333,13 +334,13 @@ 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() as _
+        ManuallyDrop::new(self).ptr.as_ptr().cast_const().cast()
     }
 
     unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> ArcBorrow<'a, T> {
         // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
         // call to `Self::into_foreign`.
-        let inner = unsafe { NonNull::new_unchecked(ptr as *mut ArcInner<T>) };
+        let inner = unsafe { NonNull::new_unchecked(ptr.cast_mut().cast::<ArcInner<T>>()) };
 
         // SAFETY: The safety requirements of `from_foreign` ensure that the object remains alive
         // for the lifetime of the returned value.
@@ -349,7 +350,7 @@ unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> ArcBorrow<'a, T> {
     unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
         // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
         // call to `Self::into_foreign`.
-        let inner = unsafe { NonNull::new_unchecked(ptr as *mut ArcInner<T>) };
+        let inner = unsafe { NonNull::new_unchecked(ptr.cast_mut().cast::<ArcInner<T>>()) };
 
         // SAFETY: By the safety requirement of this function, we know that `ptr` came from
         // a previous call to `Arc::into_foreign`, which guarantees that `ptr` is valid and
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index fae80814fa1c5e0f11933f2f15e173f0e3a10fe0..364dd2dc438eb7d1c4d0a4525bf2305a42297b2b 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -418,7 +418,7 @@ pub unsafe fn from_raw(ptr: NonNull<T>) -> Self {
     /// }
     ///
     /// let mut data = Empty {};
-    /// let ptr = NonNull::<Empty>::new(&mut data as *mut _).unwrap();
+    /// let ptr = NonNull::<Empty>::new(&mut data).unwrap();
     /// # // SAFETY: TODO.
     /// let data_ref: ARef<Empty> = unsafe { ARef::from_raw(ptr) };
     /// let raw_ptr: NonNull<Empty> = ARef::into_raw(data_ref);

-- 
2.47.0