[PATCH v8 6/6] rust: enable `clippy::ref_as_ptr` lint

[Tamir Duberstein <tamird@gmail.com>]

In Rust 1.78.0, Clippy introduced the `ref_as_ptr` lint [1]:

> Using `as` casts may result in silently changing mutability or type.

While this doesn't eliminate unchecked `as` conversions, it makes such
conversions easier to scrutinize.  It also has the slight benefit of
removing a degree of freedom on which to bikeshed. Thus apply the
changes and enable the lint -- no functional change intended.

Link: https://rust-lang.github.io/rust-clippy/master/index.html#ref_as_ptr [1]
Suggested-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/all/D8PGG7NTWB6U.3SS3A5LN4XWMN@proton.me/
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
 Makefile                 |  1 +
 rust/bindings/lib.rs     |  1 +
 rust/kernel/device_id.rs |  3 ++-
 rust/kernel/fs/file.rs   |  3 ++-
 rust/kernel/str.rs       |  6 ++++--
 rust/kernel/uaccess.rs   | 10 ++++------
 rust/uapi/lib.rs         |  1 +
 7 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/Makefile b/Makefile
index eb5a942241a2..2a16e02f26db 100644
--- a/Makefile
+++ b/Makefile
@@ -485,6 +485,7 @@ export rust_common_flags := --edition=2021 \
 			    -Wclippy::no_mangle_with_rust_abi \
 			    -Wclippy::ptr_as_ptr \
 			    -Wclippy::ptr_cast_constness \
+			    -Wclippy::ref_as_ptr \
 			    -Wclippy::undocumented_unsafe_blocks \
 			    -Wclippy::unnecessary_safety_comment \
 			    -Wclippy::unnecessary_safety_doc \
diff --git a/rust/bindings/lib.rs b/rust/bindings/lib.rs
index b105a0d899cc..2b69016070c6 100644
--- a/rust/bindings/lib.rs
+++ b/rust/bindings/lib.rs
@@ -27,6 +27,7 @@
 #[allow(dead_code)]
 #[allow(clippy::cast_lossless)]
 #[allow(clippy::ptr_as_ptr)]
+#[allow(clippy::ref_as_ptr)]
 #[allow(clippy::undocumented_unsafe_blocks)]
 mod bindings_raw {
     // Manual definition for blocklisted types.
diff --git a/rust/kernel/device_id.rs b/rust/kernel/device_id.rs
index 4063f09d76d9..37cc03d1df4c 100644
--- a/rust/kernel/device_id.rs
+++ b/rust/kernel/device_id.rs
@@ -136,7 +136,8 @@ impl<T: RawDeviceId, U, const N: usize> IdTable<T, U> for IdArray<T, U, N> {
     fn as_ptr(&self) -> *const T::RawType {
         // This cannot be `self.ids.as_ptr()`, as the return pointer must have correct provenance
         // to access the sentinel.
-        (self as *const Self).cast()
+        let this: *const Self = self;
+        this.cast()
     }
 
     fn id(&self, index: usize) -> &T::RawType {
diff --git a/rust/kernel/fs/file.rs b/rust/kernel/fs/file.rs
index 791f493ada10..559a4bfa123f 100644
--- a/rust/kernel/fs/file.rs
+++ b/rust/kernel/fs/file.rs
@@ -359,12 +359,13 @@ impl core::ops::Deref for File {
     type Target = LocalFile;
     #[inline]
     fn deref(&self) -> &LocalFile {
+        let this: *const Self = self;
         // SAFETY: The caller provides a `&File`, and since it is a reference, it must point at a
         // valid file for the desired duration.
         //
         // By the type invariants, there are no `fdget_pos` calls that did not take the
         // `f_pos_lock` mutex.
-        unsafe { LocalFile::from_raw_file((self as *const Self).cast()) }
+        unsafe { LocalFile::from_raw_file(this.cast()) }
     }
 }
 
diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 40034f77fc2f..75b4a18c67c4 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -28,8 +28,9 @@ pub const fn is_empty(&self) -> bool {
     /// Creates a [`BStr`] from a `[u8]`.
     #[inline]
     pub const fn from_bytes(bytes: &[u8]) -> &Self {
+        let bytes: *const [u8] = bytes;
         // SAFETY: `BStr` is transparent to `[u8]`.
-        unsafe { &*(bytes as *const [u8] as *const BStr) }
+        unsafe { &*(bytes as *const BStr) }
     }
 
     /// Strip a prefix from `self`. Delegates to [`slice::strip_prefix`].
@@ -289,8 +290,9 @@ pub const fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, CStrConvertError
     /// `NUL` byte (or the string will be truncated).
     #[inline]
     pub unsafe fn from_bytes_with_nul_unchecked_mut(bytes: &mut [u8]) -> &mut CStr {
+        let bytes: *mut [u8] = bytes;
         // SAFETY: Properties of `bytes` guaranteed by the safety precondition.
-        unsafe { &mut *(bytes as *mut [u8] as *mut CStr) }
+        unsafe { &mut *(bytes as *mut CStr) }
     }
 
     /// Returns a C pointer to the string.
diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
index 80a9782b1c6e..7a6fc78fc314 100644
--- a/rust/kernel/uaccess.rs
+++ b/rust/kernel/uaccess.rs
@@ -240,9 +240,10 @@ pub fn read_raw(&mut self, out: &mut [MaybeUninit<u8>]) -> Result {
     /// Fails with [`EFAULT`] if the read happens on a bad address, or if the read goes out of
     /// bounds of this [`UserSliceReader`]. This call may modify `out` even if it returns an error.
     pub fn read_slice(&mut self, out: &mut [u8]) -> Result {
+        let out: *mut [u8] = out;
         // SAFETY: The types are compatible and `read_raw` doesn't write uninitialized bytes to
         // `out`.
-        let out = unsafe { &mut *(out as *mut [u8] as *mut [MaybeUninit<u8>]) };
+        let out = unsafe { &mut *(out as *mut [MaybeUninit<u8>]) };
         self.read_raw(out)
     }
 
@@ -348,6 +349,7 @@ pub fn write<T: AsBytes>(&mut self, value: &T) -> Result {
         if len > self.length {
             return Err(EFAULT);
         }
+        let value: *const T = value;
         // SAFETY: The reference points to a value of type `T`, so it is valid for reading
         // `size_of::<T>()` bytes.
         //
@@ -355,11 +357,7 @@ pub fn write<T: AsBytes>(&mut self, value: &T) -> Result {
         // kernel pointer. This mirrors the logic on the C side that skips the check when the length
         // is a compile-time constant.
         let res = unsafe {
-            bindings::_copy_to_user(
-                self.ptr as *mut c_void,
-                (value as *const T).cast::<c_void>(),
-                len,
-            )
+            bindings::_copy_to_user(self.ptr as *mut c_void, value.cast::<c_void>(), len)
         };
         if res != 0 {
             return Err(EFAULT);
diff --git a/rust/uapi/lib.rs b/rust/uapi/lib.rs
index d5dab4dfabec..6230ba48201d 100644
--- a/rust/uapi/lib.rs
+++ b/rust/uapi/lib.rs
@@ -16,6 +16,7 @@
     clippy::all,
     clippy::cast_lossless,
     clippy::ptr_as_ptr,
+    clippy::ref_as_ptr,
     clippy::undocumented_unsafe_blocks,
     dead_code,
     missing_docs,

-- 
2.49.0