Merge tag 'rust-6.13' of https://github.com/Rust-for-Linux/linux

Pull rust updates from Miguel Ojeda:
 "Toolchain and infrastructure:

   - Enable a series of lints, including safety-related ones, e.g. the
     compiler will now warn about missing safety comments, as well as
     unnecessary ones. How safety documentation is organized is a
     frequent source of review comments, thus having the compiler guide
     new developers on where they are expected (and where not) is very
     nice.

   - Start using '#[expect]': an interesting feature in Rust (stabilized
     in 1.81.0) that makes the compiler warn if an expected warning was
     _not_ emitted. This is useful to avoid forgetting cleaning up
     locally ignored diagnostics ('#[allow]'s).

   - Introduce '.clippy.toml' configuration file for Clippy, the Rust
     linter, which will allow us to tweak its behaviour. For instance,
     our first use cases are declaring a disallowed macro and, more
     importantly, enabling the checking of private items.

   - Lints-related fixes and cleanups related to the items above.

   - Migrate from 'receiver_trait' to 'arbitrary_self_types': to get the
     kernel into stable Rust, one of the major pieces of the puzzle is
     the support to write custom types that can be used as 'self', i.e.
     as receivers, since the kernel needs to write types such as 'Arc'
     that common userspace Rust would not. 'arbitrary_self_types' has
     been accepted to become stable, and this is one of the steps
     required to get there.

   - Remove usage of the 'new_uninit' unstable feature.

   - Use custom C FFI types. Includes a new 'ffi' crate to contain our
     custom mapping, instead of using the standard library 'core::ffi'
     one. The actual remapping will be introduced in a later cycle.

   - Map '__kernel_{size_t,ssize_t,ptrdiff_t}' to 'usize'/'isize'
     instead of 32/64-bit integers.

   - Fix 'size_t' in bindgen generated prototypes of C builtins.

   - Warn on bindgen < 0.69.5 and libclang >= 19.1 due to a double issue
     in the projects, which we managed to trigger with the upcoming
     tracepoint support. It includes a build test since some
     distributions backported the fix (e.g. Debian -- thanks!). All
     major distributions we list should be now OK except Ubuntu non-LTS.

  'macros' crate:

   - Adapt the build system to be able run the doctests there too; and
     clean up and enable the corresponding doctests.

  'kernel' crate:

   - Add 'alloc' module with generic kernel allocator support and remove
     the dependency on the Rust standard library 'alloc' and the
     extension traits we used to provide fallible methods with flags.

     Add the 'Allocator' trait and its implementations '{K,V,KV}malloc'.
     Add the 'Box' type (a heap allocation for a single value of type
     'T' that is also generic over an allocator and considers the
     kernel's GFP flags) and its shorthand aliases '{K,V,KV}Box'. Add
     'ArrayLayout' type. Add 'Vec' (a contiguous growable array type)
     and its shorthand aliases '{K,V,KV}Vec', including iterator
     support.

     For instance, now we may write code such as:

         let mut v = KVec::new();
         v.push(1, GFP_KERNEL)?;
         assert_eq!(&v, &[1]);

     Treewide, move as well old users to these new types.

   - 'sync' module: add global lock support, including the
     'GlobalLockBackend' trait; the 'Global{Lock,Guard,LockedBy}' types
     and the 'global_lock!' macro. Add the 'Lock::try_lock' method.

   - 'error' module: optimize 'Error' type to use 'NonZeroI32' and make
     conversion functions public.

   - 'page' module: add 'page_align' function.

   - Add 'transmute' module with the existing 'FromBytes' and 'AsBytes'
     traits.

   - 'block::mq::request' module: improve rendered documentation.

   - 'types' module: extend 'Opaque' type documentation and add simple
     examples for the 'Either' types.

  drm/panic:

   - Clean up a series of Clippy warnings.

  Documentation:

   - Add coding guidelines for lints and the '#[expect]' feature.

   - Add Ubuntu to the list of distributions in the Quick Start guide.

  MAINTAINERS:

   - Add Danilo Krummrich as maintainer of the new 'alloc' module.

  And a few other small cleanups and fixes"

* tag 'rust-6.13' of https://github.com/Rust-for-Linux/linux: (82 commits)
  rust: alloc: Fix `ArrayLayout` allocations
  docs: rust: remove spurious item in `expect` list
  rust: allow `clippy::needless_lifetimes`
  rust: warn on bindgen < 0.69.5 and libclang >= 19.1
  rust: use custom FFI integer types
  rust: map `__kernel_size_t` and friends also to usize/isize
  rust: fix size_t in bindgen prototypes of C builtins
  rust: sync: add global lock support
  rust: macros: enable the rest of the tests
  rust: macros: enable paste! use from macro_rules!
  rust: enable macros::module! tests
  rust: kbuild: expand rusttest target for macros
  rust: types: extend `Opaque` documentation
  rust: block: fix formatting of `kernel::block::mq::request` module
  rust: macros: fix documentation of the paste! macro
  rust: kernel: fix THIS_MODULE header path in ThisModule doc comment
  rust: page: add Rust version of PAGE_ALIGN
  rust: helpers: remove unnecessary header includes
  rust: exports: improve grammar in commentary
  drm/panic: allow verbose version check
  ...

1 files changed, 72 insertions, 124 deletions

diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 3238ffaab031..7a133d938551 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -3,13 +3,11 @@
 //! Kernel types.
 
 use crate::init::{self, PinInit};
-use alloc::boxed::Box;
 use core::{
     cell::UnsafeCell,
     marker::{PhantomData, PhantomPinned},
     mem::{ManuallyDrop, MaybeUninit},
     ops::{Deref, DerefMut},
-    pin::Pin,
     ptr::NonNull,
 };
 
@@ -31,7 +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) -> *const crate::ffi::c_void;
 
     /// Borrows a foreign-owned object.
     ///
@@ -39,7 +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: *const crate::ffi::c_void) -> Self::Borrowed<'a>;
 
     /// Converts a foreign-owned object back to a Rust-owned one.
     ///
@@ -49,7 +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: *const crate::ffi::c_void) -> Self;
 
     /// Tries to convert a foreign-owned object back to a Rust-owned one.
     ///
@@ -60,7 +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: *const crate::ffi::c_void) -> Option<Self> {
         if ptr.is_null() {
             None
         } else {
@@ -71,64 +69,16 @@ pub trait ForeignOwnable: Sized {
     }
 }
 
-impl<T: 'static> ForeignOwnable for Box<T> {
-    type Borrowed<'a> = &'a T;
-
-    fn into_foreign(self) -> *const core::ffi::c_void {
-        Box::into_raw(self) as _
-    }
-
-    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a T {
-        // SAFETY: The safety requirements for this function ensure that the object is still alive,
-        // so it is safe to dereference the raw pointer.
-        // The safety requirements of `from_foreign` also ensure that the object remains alive for
-        // the lifetime of the returned value.
-        unsafe { &*ptr.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 _) }
-    }
-}
-
-impl<T: 'static> ForeignOwnable for Pin<Box<T>> {
-    type Borrowed<'a> = Pin<&'a T>;
-
-    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 _
-    }
-
-    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Pin<&'a T> {
-        // SAFETY: The safety requirements for this function ensure that the object is still alive,
-        // so it is safe to dereference the raw pointer.
-        // The safety requirements of `from_foreign` also ensure that the object remains alive for
-        // the lifetime of the returned value.
-        let r = unsafe { &*ptr.cast() };
-
-        // SAFETY: This pointer originates from a `Pin<Box<T>>`.
-        unsafe { Pin::new_unchecked(r) }
-    }
-
-    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 _)) }
-    }
-}
-
 impl ForeignOwnable for () {
     type Borrowed<'a> = ();
 
-    fn into_foreign(self) -> *const core::ffi::c_void {
+    fn into_foreign(self) -> *const crate::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>(_: *const crate::ffi::c_void) -> Self::Borrowed<'a> {}
 
-    unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
+    unsafe fn from_foreign(_: *const crate::ffi::c_void) -> Self {}
 }
 
 /// Runs a cleanup function/closure when dropped.
@@ -185,7 +135,7 @@ impl ForeignOwnable for () {
 /// # use kernel::types::ScopeGuard;
 /// fn example3(arg: bool) -> Result {
 ///     let mut vec =
-///         ScopeGuard::new_with_data(Vec::new(), |v| pr_info!("vec had {} elements\n", v.len()));
+///         ScopeGuard::new_with_data(KVec::new(), |v| pr_info!("vec had {} elements\n", v.len()));
 ///
 ///     vec.push(10u8, GFP_KERNEL)?;
 ///     if arg {
@@ -225,7 +175,7 @@ impl<T, F: FnOnce(T)> ScopeGuard<T, F> {
 impl ScopeGuard<(), fn(())> {
     /// Creates a new guarded object with the given cleanup function.
     pub fn new(cleanup: impl FnOnce()) -> ScopeGuard<(), impl FnOnce(())> {
-        ScopeGuard::new_with_data((), move |_| cleanup())
+        ScopeGuard::new_with_data((), move |()| cleanup())
     }
 }
 
@@ -256,7 +206,58 @@ impl<T, F: FnOnce(T)> Drop for ScopeGuard<T, F> {
 
 /// Stores an opaque value.
 ///
-/// This is meant to be used with FFI objects that are never interpreted by Rust code.
+/// `Opaque<T>` is meant to be used with FFI objects that are never interpreted by Rust code.
+///
+/// It is used to wrap structs from the C side, like for example `Opaque<bindings::mutex>`.
+/// It gets rid of all the usual assumptions that Rust has for a value:
+///
+/// * The value is allowed to be uninitialized (for example have invalid bit patterns: `3` for a
+///   [`bool`]).
+/// * The value is allowed to be mutated, when a `&Opaque<T>` exists on the Rust side.
+/// * No uniqueness for mutable references: it is fine to have multiple `&mut Opaque<T>` point to
+///   the same value.
+/// * The value is not allowed to be shared with other threads (i.e. it is `!Sync`).
+///
+/// This has to be used for all values that the C side has access to, because it can't be ensured
+/// that the C side is adhering to the usual constraints that Rust needs.
+///
+/// Using `Opaque<T>` allows to continue to use references on the Rust side even for values shared
+/// with C.
+///
+/// # Examples
+///
+/// ```
+/// # #![expect(unreachable_pub, clippy::disallowed_names)]
+/// use kernel::types::Opaque;
+/// # // Emulate a C struct binding which is from C, maybe uninitialized or not, only the C side
+/// # // knows.
+/// # mod bindings {
+/// #     pub struct Foo {
+/// #         pub val: u8,
+/// #     }
+/// # }
+///
+/// // `foo.val` is assumed to be handled on the C side, so we use `Opaque` to wrap it.
+/// pub struct Foo {
+///     foo: Opaque<bindings::Foo>,
+/// }
+///
+/// impl Foo {
+///     pub fn get_val(&self) -> u8 {
+///         let ptr = Opaque::get(&self.foo);
+///
+///         // SAFETY: `Self` is valid from C side.
+///         unsafe { (*ptr).val }
+///     }
+/// }
+///
+/// // Create an instance of `Foo` with the `Opaque` wrapper.
+/// let foo = Foo {
+///     foo: Opaque::new(bindings::Foo { val: 0xdb }),
+/// };
+///
+/// assert_eq!(foo.get_val(), 0xdb);
+/// ```
 #[repr(transparent)]
 pub struct Opaque<T> {
     value: UnsafeCell<MaybeUninit<T>>,
@@ -410,6 +411,7 @@ impl<T: AlwaysRefCounted> ARef<T> {
     ///
     /// struct Empty {}
     ///
+    /// # // SAFETY: TODO.
     /// unsafe impl AlwaysRefCounted for Empty {
     ///     fn inc_ref(&self) {}
     ///     unsafe fn dec_ref(_obj: NonNull<Self>) {}
@@ -417,6 +419,7 @@ impl<T: AlwaysRefCounted> ARef<T> {
     ///
     /// let mut data = Empty {};
     /// let ptr = NonNull::<Empty>::new(&mut data as *mut _).unwrap();
+    /// # // SAFETY: TODO.
     /// let data_ref: ARef<Empty> = unsafe { ARef::from_raw(ptr) };
     /// let raw_ptr: NonNull<Empty> = ARef::into_raw(data_ref);
     ///
@@ -461,6 +464,15 @@ impl<T: AlwaysRefCounted> Drop for ARef<T> {
 }
 
 /// A sum type that always holds either a value of type `L` or `R`.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::types::Either;
+///
+/// let left_value: Either<i32, &str> = Either::Left(7);
+/// let right_value: Either<i32, &str> = Either::Right("right value");
+/// ```
 pub enum Either<L, R> {
     /// Constructs an instance of [`Either`] containing a value of type `L`.
     Left(L),
@@ -469,70 +481,6 @@ pub enum Either<L, R> {
     Right(R),
 }
 
-/// Types for which any bit pattern is valid.
-///
-/// Not all types are valid for all values. For example, a `bool` must be either zero or one, so
-/// reading arbitrary bytes into something that contains a `bool` is not okay.
-///
-/// It's okay for the type to have padding, as initializing those bytes has no effect.
-///
-/// # Safety
-///
-/// All bit-patterns must be valid for this type. This type must not have interior mutability.
-pub unsafe trait FromBytes {}
-
-// SAFETY: All bit patterns are acceptable values of the types below.
-unsafe impl FromBytes for u8 {}
-unsafe impl FromBytes for u16 {}
-unsafe impl FromBytes for u32 {}
-unsafe impl FromBytes for u64 {}
-unsafe impl FromBytes for usize {}
-unsafe impl FromBytes for i8 {}
-unsafe impl FromBytes for i16 {}
-unsafe impl FromBytes for i32 {}
-unsafe impl FromBytes for i64 {}
-unsafe impl FromBytes for isize {}
-// SAFETY: If all bit patterns are acceptable for individual values in an array, then all bit
-// patterns are also acceptable for arrays of that type.
-unsafe impl<T: FromBytes> FromBytes for [T] {}
-unsafe impl<T: FromBytes, const N: usize> FromBytes for [T; N] {}
-
-/// Types that can be viewed as an immutable slice of initialized bytes.
-///
-/// If a struct implements this trait, then it is okay to copy it byte-for-byte to userspace. This
-/// means that it should not have any padding, as padding bytes are uninitialized. Reading
-/// uninitialized memory is not just undefined behavior, it may even lead to leaking sensitive
-/// information on the stack to userspace.
-///
-/// The struct should also not hold kernel pointers, as kernel pointer addresses are also considered
-/// sensitive. However, leaking kernel pointers is not considered undefined behavior by Rust, so
-/// this is a correctness requirement, but not a safety requirement.
-///
-/// # Safety
-///
-/// Values of this type may not contain any uninitialized bytes. This type must not have interior
-/// mutability.
-pub unsafe trait AsBytes {}
-
-// SAFETY: Instances of the following types have no uninitialized portions.
-unsafe impl AsBytes for u8 {}
-unsafe impl AsBytes for u16 {}
-unsafe impl AsBytes for u32 {}
-unsafe impl AsBytes for u64 {}
-unsafe impl AsBytes for usize {}
-unsafe impl AsBytes for i8 {}
-unsafe impl AsBytes for i16 {}
-unsafe impl AsBytes for i32 {}
-unsafe impl AsBytes for i64 {}
-unsafe impl AsBytes for isize {}
-unsafe impl AsBytes for bool {}
-unsafe impl AsBytes for char {}
-unsafe impl AsBytes for str {}
-// SAFETY: If individual values in an array have no uninitialized portions, then the array itself
-// does not have any uninitialized portions either.
-unsafe impl<T: AsBytes> AsBytes for [T] {}
-unsafe impl<T: AsBytes, const N: usize> AsBytes for [T; N] {}
-
 /// Zero-sized type to mark types not [`Send`].
 ///
 /// Add this type as a field to your struct if your type should not be sent to a different task.