[PATCH v3 2/6] rust: enable `clippy::ptr_as_ptr` lint

[Tamir Duberstein <tamird@gmail.com>]

In Rust 1.51.0, Clippy introduced the `ptr_as_ptr` lint [1]:

> Though `as` casts between raw pointers are not terrible,
> `pointer::cast` is safer because it cannot accidentally change the
> pointer's mutability, nor cast the pointer to other types like `usize`.

There are a few classes of changes required:
- Modules generated by bindgen are marked
  `#[allow(clippy::ptr_as_ptr)]`.
- Inferred casts (` as _`) are replaced with `.cast()`.
- Ascribed casts (` as *... T`) are replaced with `.cast::<T>()`.
- Multistep casts from references (` as *const _ as *const T`) are
  replaced with `let x: *const _ = &x;` and `.cast()` or `.cast::<T>()`
  according to the previous rules. The intermediate `let` binding is
  required because `(x as *const _).cast::<T>()` results in inference
  failure.
- Native literal C strings are replaced with `c_str!().as_char_ptr()`.
- `*mut *mut T as _` is replaced with `let *mut *const T = (*mut *mut
  T)`.cast();` since pointer to pointer can be confusing.

Apply these changes and enable the lint -- no functional change
intended.

Link: https://rust-lang.github.io/rust-clippy/master/index.html#ptr_as_ptr [1]
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
 Makefile                               |  1 +
 rust/bindings/lib.rs                   |  1 +
 rust/kernel/alloc/allocator_test.rs    |  2 +-
 rust/kernel/alloc/kvec.rs              |  4 ++--
 rust/kernel/device.rs                  |  5 +++--
 rust/kernel/devres.rs                  |  2 +-
 rust/kernel/error.rs                   |  2 +-
 rust/kernel/firmware.rs                |  3 ++-
 rust/kernel/fs/file.rs                 |  2 +-
 rust/kernel/kunit.rs                   | 15 +++++++--------
 rust/kernel/list/impl_list_item_mod.rs |  2 +-
 rust/kernel/pci.rs                     |  2 +-
 rust/kernel/platform.rs                |  4 +++-
 rust/kernel/print.rs                   | 11 +++++------
 rust/kernel/seq_file.rs                |  3 ++-
 rust/kernel/str.rs                     |  2 +-
 rust/kernel/sync/poll.rs               |  2 +-
 rust/kernel/workqueue.rs               | 10 +++++-----
 rust/uapi/lib.rs                       |  1 +
 19 files changed, 40 insertions(+), 34 deletions(-)

diff --git a/Makefile b/Makefile
index 70bdbf2218fc..ec8efc8e23ba 100644
--- a/Makefile
+++ b/Makefile
@@ -483,6 +483,7 @@ export rust_common_flags := --edition=2021 \
 			    -Wclippy::needless_continue \
 			    -Aclippy::needless_lifetimes \
 			    -Wclippy::no_mangle_with_rust_abi \
+			    -Wclippy::ptr_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 014af0d1fc70..0486a32ed314 100644
--- a/rust/bindings/lib.rs
+++ b/rust/bindings/lib.rs
@@ -25,6 +25,7 @@
 )]
 
 #[allow(dead_code)]
+#[allow(clippy::ptr_as_ptr)]
 #[allow(clippy::undocumented_unsafe_blocks)]
 mod bindings_raw {
     // Manual definition for blocklisted types.
diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
index c37d4c0c64e9..8017aa9d5213 100644
--- a/rust/kernel/alloc/allocator_test.rs
+++ b/rust/kernel/alloc/allocator_test.rs
@@ -82,7 +82,7 @@ unsafe fn realloc(
 
         // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or
         // exceeds the given size and alignment requirements.
-        let dst = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8;
+        let dst = unsafe { libc_aligned_alloc(layout.align(), layout.size()) }.cast::<u8>();
         let dst = NonNull::new(dst).ok_or(AllocError)?;
 
         if flags.contains(__GFP_ZERO) {
diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index ae9d072741ce..c12844764671 100644
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -262,7 +262,7 @@ pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
         // - `self.len` is smaller than `self.capacity` and hence, the resulting pointer is
         //   guaranteed to be part of the same allocated object.
         // - `self.len` can not overflow `isize`.
-        let ptr = unsafe { self.as_mut_ptr().add(self.len) } as *mut MaybeUninit<T>;
+        let ptr = unsafe { self.as_mut_ptr().add(self.len) }.cast::<MaybeUninit<T>>();
 
         // SAFETY: The memory between `self.len` and `self.capacity` is guaranteed to be allocated
         // and valid, but uninitialized.
@@ -554,7 +554,7 @@ fn drop(&mut self) {
         // - `ptr` points to memory with at least a size of `size_of::<T>() * len`,
         // - all elements within `b` are initialized values of `T`,
         // - `len` does not exceed `isize::MAX`.
-        unsafe { Vec::from_raw_parts(ptr as _, len, len) }
+        unsafe { Vec::from_raw_parts(ptr.cast(), len, len) }
     }
 }
 
diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index db2d9658ba47..9e500498835d 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -168,16 +168,17 @@ pub fn pr_dbg(&self, args: fmt::Arguments<'_>) {
     /// `KERN_*`constants, for example, `KERN_CRIT`, `KERN_ALERT`, etc.
     #[cfg_attr(not(CONFIG_PRINTK), allow(unused_variables))]
     unsafe fn printk(&self, klevel: &[u8], msg: fmt::Arguments<'_>) {
+        let msg: *const _ = &msg;
         // SAFETY: `klevel` is null-terminated and one of the kernel constants. `self.as_raw`
         // is valid because `self` is valid. The "%pA" format string expects a pointer to
         // `fmt::Arguments`, which is what we're passing as the last argument.
         #[cfg(CONFIG_PRINTK)]
         unsafe {
             bindings::_dev_printk(
-                klevel as *const _ as *const crate::ffi::c_char,
+                klevel.as_ptr().cast::<crate::ffi::c_char>(),
                 self.as_raw(),
                 c_str!("%pA").as_char_ptr(),
-                &msg as *const _ as *const crate::ffi::c_void,
+                msg.cast::<crate::ffi::c_void>(),
             )
         };
     }
diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
index 942376f6f3af..3a9d998ec371 100644
--- a/rust/kernel/devres.rs
+++ b/rust/kernel/devres.rs
@@ -157,7 +157,7 @@ fn remove_action(this: &Arc<Self>) {
 
     #[allow(clippy::missing_safety_doc)]
     unsafe extern "C" fn devres_callback(ptr: *mut kernel::ffi::c_void) {
-        let ptr = ptr as *mut DevresInner<T>;
+        let ptr = ptr.cast::<DevresInner<T>>();
         // Devres owned this memory; now that we received the callback, drop the `Arc` and hence the
         // reference.
         // SAFETY: Safe, since we leaked an `Arc` reference to devm_add_action() in
diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index a194d83e6835..8c62cff8742e 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -152,7 +152,7 @@ pub(crate) fn to_blk_status(self) -> bindings::blk_status_t {
     /// Returns the error encoded as a pointer.
     pub fn to_ptr<T>(self) -> *mut T {
         // SAFETY: `self.0` is a valid error due to its invariant.
-        unsafe { bindings::ERR_PTR(self.0.get() as _) as *mut _ }
+        unsafe { bindings::ERR_PTR(self.0.get() as _).cast() }
     }
 
     /// Returns a string representing the error, if one exists.
diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
index c5162fdc95ff..74df815d2f4e 100644
--- a/rust/kernel/firmware.rs
+++ b/rust/kernel/firmware.rs
@@ -58,10 +58,11 @@ impl Firmware {
     fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Self> {
         let mut fw: *mut bindings::firmware = core::ptr::null_mut();
         let pfw: *mut *mut bindings::firmware = &mut fw;
+        let pfw: *mut *const bindings::firmware = pfw.cast();
 
         // SAFETY: `pfw` is a valid pointer to a NULL initialized `bindings::firmware` pointer.
         // `name` and `dev` are valid as by their type invariants.
-        let ret = unsafe { func.0(pfw as _, name.as_char_ptr(), dev.as_raw()) };
+        let ret = unsafe { func.0(pfw, name.as_char_ptr(), dev.as_raw()) };
         if ret != 0 {
             return Err(Error::from_errno(ret));
         }
diff --git a/rust/kernel/fs/file.rs b/rust/kernel/fs/file.rs
index e03dbe14d62a..8936afc234a4 100644
--- a/rust/kernel/fs/file.rs
+++ b/rust/kernel/fs/file.rs
@@ -364,7 +364,7 @@ fn deref(&self) -> &LocalFile {
         //
         // 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 File as *const bindings::file) }
+        unsafe { LocalFile::from_raw_file((self as *const Self).cast()) }
     }
 }
 
diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs
index 824da0e9738a..7ed2063c1af0 100644
--- a/rust/kernel/kunit.rs
+++ b/rust/kernel/kunit.rs
@@ -8,19 +8,20 @@
 
 use core::{ffi::c_void, fmt};
 
+#[cfg(CONFIG_PRINTK)]
+use crate::c_str;
+
 /// Prints a KUnit error-level message.
 ///
 /// Public but hidden since it should only be used from KUnit generated code.
 #[doc(hidden)]
 pub fn err(args: fmt::Arguments<'_>) {
+    let args: *const _ = &args;
     // SAFETY: The format string is null-terminated and the `%pA` specifier matches the argument we
     // are passing.
     #[cfg(CONFIG_PRINTK)]
     unsafe {
-        bindings::_printk(
-            c"\x013%pA".as_ptr() as _,
-            &args as *const _ as *const c_void,
-        );
+        bindings::_printk(c_str!("\x013%pA").as_char_ptr(), args.cast::<c_void>());
     }
 }
 
@@ -29,14 +30,12 @@ pub fn err(args: fmt::Arguments<'_>) {
 /// Public but hidden since it should only be used from KUnit generated code.
 #[doc(hidden)]
 pub fn info(args: fmt::Arguments<'_>) {
+    let args: *const _ = &args;
     // SAFETY: The format string is null-terminated and the `%pA` specifier matches the argument we
     // are passing.
     #[cfg(CONFIG_PRINTK)]
     unsafe {
-        bindings::_printk(
-            c"\x016%pA".as_ptr() as _,
-            &args as *const _ as *const c_void,
-        );
+        bindings::_printk(c_str!("\x016%pA").as_char_ptr(), args.cast::<c_void>());
     }
 }
 
diff --git a/rust/kernel/list/impl_list_item_mod.rs b/rust/kernel/list/impl_list_item_mod.rs
index a0438537cee1..1f9498c1458f 100644
--- a/rust/kernel/list/impl_list_item_mod.rs
+++ b/rust/kernel/list/impl_list_item_mod.rs
@@ -34,7 +34,7 @@ pub unsafe trait HasListLinks<const ID: u64 = 0> {
     unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut ListLinks<ID> {
         // SAFETY: The caller promises that the pointer is valid. The implementer promises that the
         // `OFFSET` constant is correct.
-        unsafe { (ptr as *mut u8).add(Self::OFFSET) as *mut ListLinks<ID> }
+        unsafe { ptr.cast::<u8>().add(Self::OFFSET).cast() }
     }
 }
 
diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
index c37476576f02..63218abb7a25 100644
--- a/rust/kernel/pci.rs
+++ b/rust/kernel/pci.rs
@@ -75,7 +75,7 @@ extern "C" fn probe_callback(
                 // Let the `struct pci_dev` own a reference of the driver's private data.
                 // SAFETY: By the type invariant `pdev.as_raw` returns a valid pointer to a
                 // `struct pci_dev`.
-                unsafe { bindings::pci_set_drvdata(pdev.as_raw(), data.into_foreign() as _) };
+                unsafe { bindings::pci_set_drvdata(pdev.as_raw(), data.into_foreign().cast()) };
             }
             Err(err) => return Error::to_errno(err),
         }
diff --git a/rust/kernel/platform.rs b/rust/kernel/platform.rs
index c51617569c01..d609119e8ce8 100644
--- a/rust/kernel/platform.rs
+++ b/rust/kernel/platform.rs
@@ -66,7 +66,9 @@ extern "C" fn probe_callback(pdev: *mut bindings::platform_device) -> kernel::ff
                 // Let the `struct platform_device` own a reference of the driver's private data.
                 // SAFETY: By the type invariant `pdev.as_raw` returns a valid pointer to a
                 // `struct platform_device`.
-                unsafe { bindings::platform_set_drvdata(pdev.as_raw(), data.into_foreign() as _) };
+                unsafe {
+                    bindings::platform_set_drvdata(pdev.as_raw(), data.into_foreign().cast())
+                };
             }
             Err(err) => return Error::to_errno(err),
         }
diff --git a/rust/kernel/print.rs b/rust/kernel/print.rs
index b19ee490be58..0245c145ea32 100644
--- a/rust/kernel/print.rs
+++ b/rust/kernel/print.rs
@@ -25,7 +25,7 @@
     // SAFETY: The C contract guarantees that `buf` is valid if it's less than `end`.
     let mut w = unsafe { RawFormatter::from_ptrs(buf.cast(), end.cast()) };
     // SAFETY: TODO.
-    let _ = w.write_fmt(unsafe { *(ptr as *const fmt::Arguments<'_>) });
+    let _ = w.write_fmt(unsafe { *ptr.cast::<fmt::Arguments<'_>>() });
     w.pos().cast()
 }
 
@@ -102,6 +102,7 @@ pub unsafe fn call_printk(
     module_name: &[u8],
     args: fmt::Arguments<'_>,
 ) {
+    let args: *const _ = &args;
     // `_printk` does not seem to fail in any path.
     #[cfg(CONFIG_PRINTK)]
     // SAFETY: TODO.
@@ -109,7 +110,7 @@ pub unsafe fn call_printk(
         bindings::_printk(
             format_string.as_ptr(),
             module_name.as_ptr(),
-            &args as *const _ as *const c_void,
+            args.cast::<c_void>(),
         );
     }
 }
@@ -122,15 +123,13 @@ pub unsafe fn call_printk(
 #[doc(hidden)]
 #[cfg_attr(not(CONFIG_PRINTK), allow(unused_variables))]
 pub fn call_printk_cont(args: fmt::Arguments<'_>) {
+    let args: *const _ = &args;
     // `_printk` does not seem to fail in any path.
     //
     // SAFETY: The format string is fixed.
     #[cfg(CONFIG_PRINTK)]
     unsafe {
-        bindings::_printk(
-            format_strings::CONT.as_ptr(),
-            &args as *const _ as *const c_void,
-        );
+        bindings::_printk(format_strings::CONT.as_ptr(), args.cast::<c_void>());
     }
 }
 
diff --git a/rust/kernel/seq_file.rs b/rust/kernel/seq_file.rs
index 04947c672979..90545d28e6b7 100644
--- a/rust/kernel/seq_file.rs
+++ b/rust/kernel/seq_file.rs
@@ -31,12 +31,13 @@ pub unsafe fn from_raw<'a>(ptr: *mut bindings::seq_file) -> &'a SeqFile {
 
     /// Used by the [`seq_print`] macro.
     pub fn call_printf(&self, args: core::fmt::Arguments<'_>) {
+        let args: *const _ = &args;
         // SAFETY: Passing a void pointer to `Arguments` is valid for `%pA`.
         unsafe {
             bindings::seq_printf(
                 self.inner.get(),
                 c_str!("%pA").as_char_ptr(),
-                &args as *const _ as *const crate::ffi::c_void,
+                args.cast::<crate::ffi::c_void>(),
             );
         }
     }
diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 28e2201604d6..6a1a982b946d 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -191,7 +191,7 @@ pub unsafe fn from_char_ptr<'a>(ptr: *const crate::ffi::c_char) -> &'a Self {
         // to a `NUL`-terminated C string.
         let len = unsafe { bindings::strlen(ptr) } + 1;
         // SAFETY: Lifetime guaranteed by the safety precondition.
-        let bytes = unsafe { core::slice::from_raw_parts(ptr as _, len) };
+        let bytes = unsafe { core::slice::from_raw_parts(ptr.cast(), len) };
         // SAFETY: As `len` is returned by `strlen`, `bytes` does not contain interior `NUL`.
         // As we have added 1 to `len`, the last byte is known to be `NUL`.
         unsafe { Self::from_bytes_with_nul_unchecked(bytes) }
diff --git a/rust/kernel/sync/poll.rs b/rust/kernel/sync/poll.rs
index d5f17153b424..a151f54cde91 100644
--- a/rust/kernel/sync/poll.rs
+++ b/rust/kernel/sync/poll.rs
@@ -73,7 +73,7 @@ pub fn register_wait(&mut self, file: &File, cv: &PollCondVar) {
             // be destroyed, the destructor must run. That destructor first removes all waiters,
             // and then waits for an rcu grace period. Therefore, `cv.wait_queue_head` is valid for
             // long enough.
-            unsafe { qproc(file.as_ptr() as _, cv.wait_queue_head.get(), self.0.get()) };
+            unsafe { qproc(file.as_ptr().cast(), cv.wait_queue_head.get(), self.0.get()) };
         }
     }
 }
diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
index b7be224cdf4b..51eb40d0abaa 100644
--- a/rust/kernel/workqueue.rs
+++ b/rust/kernel/workqueue.rs
@@ -170,7 +170,7 @@ impl Queue {
     pub unsafe fn from_raw<'a>(ptr: *const bindings::workqueue_struct) -> &'a Queue {
         // SAFETY: The `Queue` type is `#[repr(transparent)]`, so the pointer cast is valid. The
         // caller promises that the pointer is not dangling.
-        unsafe { &*(ptr as *const Queue) }
+        unsafe { &*ptr.cast::<Queue>() }
     }
 
     /// Enqueues a work item.
@@ -457,7 +457,7 @@ fn get_work_offset(&self) -> usize {
     #[inline]
     unsafe fn raw_get_work(ptr: *mut Self) -> *mut Work<T, ID> {
         // SAFETY: The caller promises that the pointer is valid.
-        unsafe { (ptr as *mut u8).add(Self::OFFSET) as *mut Work<T, ID> }
+        unsafe { ptr.cast::<u8>().add(Self::OFFSET).cast::<Work<T, ID>>() }
     }
 
     /// Returns a pointer to the struct containing the [`Work<T, ID>`] field.
@@ -472,7 +472,7 @@ unsafe fn work_container_of(ptr: *mut Work<T, ID>) -> *mut Self
     {
         // SAFETY: The caller promises that the pointer points at a field of the right type in the
         // right kind of struct.
-        unsafe { (ptr as *mut u8).sub(Self::OFFSET) as *mut Self }
+        unsafe { ptr.cast::<u8>().sub(Self::OFFSET).cast::<Self>() }
     }
 }
 
@@ -538,7 +538,7 @@ unsafe impl<T, const ID: u64> WorkItemPointer<ID> for Arc<T>
 {
     unsafe extern "C" fn run(ptr: *mut bindings::work_struct) {
         // The `__enqueue` method always uses a `work_struct` stored in a `Work<T, ID>`.
-        let ptr = ptr as *mut Work<T, ID>;
+        let ptr = ptr.cast::<Work<T, ID>>();
         // SAFETY: This computes the pointer that `__enqueue` got from `Arc::into_raw`.
         let ptr = unsafe { T::work_container_of(ptr) };
         // SAFETY: This pointer comes from `Arc::into_raw` and we've been given back ownership.
@@ -591,7 +591,7 @@ unsafe impl<T, const ID: u64> WorkItemPointer<ID> for Pin<KBox<T>>
 {
     unsafe extern "C" fn run(ptr: *mut bindings::work_struct) {
         // The `__enqueue` method always uses a `work_struct` stored in a `Work<T, ID>`.
-        let ptr = ptr as *mut Work<T, ID>;
+        let ptr = ptr.cast::<Work<T, ID>>();
         // SAFETY: This computes the pointer that `__enqueue` got from `Arc::into_raw`.
         let ptr = unsafe { T::work_container_of(ptr) };
         // SAFETY: This pointer comes from `Arc::into_raw` and we've been given back ownership.
diff --git a/rust/uapi/lib.rs b/rust/uapi/lib.rs
index 13495910271f..fe9bf7b5a306 100644
--- a/rust/uapi/lib.rs
+++ b/rust/uapi/lib.rs
@@ -15,6 +15,7 @@
 #![allow(
     clippy::all,
     clippy::undocumented_unsafe_blocks,
+    clippy::ptr_as_ptr,
     dead_code,
     missing_docs,
     non_camel_case_types,

-- 
2.48.1