Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

24 files changed, 7103 insertions, 0 deletions

diff --git a/rust/kernel/allocator.rs b/rust/kernel/allocator.rs
new file mode 100644
index 0000000000..a8f3d5be1a
--- /dev/null
+++ b/rust/kernel/allocator.rs
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Allocator support.
+
+use core::alloc::{GlobalAlloc, Layout};
+use core::ptr;
+
+use crate::bindings;
+
+struct KernelAllocator;
+
+/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
+///
+/// # Safety
+///
+/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
+/// - `new_layout` must have a non-zero size.
+unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: bindings::gfp_t) -> *mut u8 {
+    // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
+    let layout = new_layout.pad_to_align();
+
+    let mut size = layout.size();
+
+    if layout.align() > bindings::BINDINGS_ARCH_SLAB_MINALIGN {
+        // The alignment requirement exceeds the slab guarantee, thus try to enlarge the size
+        // to use the "power-of-two" size/alignment guarantee (see comments in `kmalloc()` for
+        // more information).
+        //
+        // Note that `layout.size()` (after padding) is guaranteed to be a multiple of
+        // `layout.align()`, so `next_power_of_two` gives enough alignment guarantee.
+        size = size.next_power_of_two();
+    }
+
+    // SAFETY:
+    // - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the
+    //   function safety requirement.
+    // - `size` is greater than 0 since it's either a `layout.size()` (which cannot be zero
+    //    according to the function safety requirement) or a result from `next_power_of_two()`.
+    unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags) as *mut u8 }
+}
+
+unsafe impl GlobalAlloc for KernelAllocator {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
+        // requirement.
+        unsafe { krealloc_aligned(ptr::null_mut(), layout, bindings::GFP_KERNEL) }
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
+        unsafe {
+            bindings::kfree(ptr as *const core::ffi::c_void);
+        }
+    }
+
+    unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
+        // SAFETY:
+        // - `new_size`, when rounded up to the nearest multiple of `layout.align()`, will not
+        //   overflow `isize` by the function safety requirement.
+        // - `layout.align()` is a proper alignment (i.e. not zero and must be a power of two).
+        let layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
+
+        // SAFETY:
+        // - `ptr` is either null or a pointer allocated by this allocator by the function safety
+        //   requirement.
+        // - the size of `layout` is not zero because `new_size` is not zero by the function safety
+        //   requirement.
+        unsafe { krealloc_aligned(ptr, layout, bindings::GFP_KERNEL) }
+    }
+
+    unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
+        // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
+        // requirement.
+        unsafe {
+            krealloc_aligned(
+                ptr::null_mut(),
+                layout,
+                bindings::GFP_KERNEL | bindings::__GFP_ZERO,
+            )
+        }
+    }
+}
+
+#[global_allocator]
+static ALLOCATOR: KernelAllocator = KernelAllocator;
+
+// See <https://github.com/rust-lang/rust/pull/86844>.
+#[no_mangle]
+static __rust_no_alloc_shim_is_unstable: u8 = 0;
diff --git a/rust/kernel/build_assert.rs b/rust/kernel/build_assert.rs
new file mode 100644
index 0000000000..9e37120bc6
--- /dev/null
+++ b/rust/kernel/build_assert.rs
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Build-time assert.
+
+/// Fails the build if the code path calling `build_error!` can possibly be executed.
+///
+/// If the macro is executed in const context, `build_error!` will panic.
+/// If the compiler or optimizer cannot guarantee that `build_error!` can never
+/// be called, a build error will be triggered.
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::build_error;
+/// #[inline]
+/// fn foo(a: usize) -> usize {
+///     a.checked_add(1).unwrap_or_else(|| build_error!("overflow"))
+/// }
+///
+/// assert_eq!(foo(usize::MAX - 1), usize::MAX); // OK.
+/// // foo(usize::MAX); // Fails to compile.
+/// ```
+#[macro_export]
+macro_rules! build_error {
+    () => {{
+        $crate::build_error("")
+    }};
+    ($msg:expr) => {{
+        $crate::build_error($msg)
+    }};
+}
+
+/// Asserts that a boolean expression is `true` at compile time.
+///
+/// If the condition is evaluated to `false` in const context, `build_assert!`
+/// will panic. If the compiler or optimizer cannot guarantee the condition will
+/// be evaluated to `true`, a build error will be triggered.
+///
+/// [`static_assert!`] should be preferred to `build_assert!` whenever possible.
+///
+/// # Examples
+///
+/// These examples show that different types of [`assert!`] will trigger errors
+/// at different stage of compilation. It is preferred to err as early as
+/// possible, so [`static_assert!`] should be used whenever possible.
+/// ```ignore
+/// fn foo() {
+///     static_assert!(1 > 1); // Compile-time error
+///     build_assert!(1 > 1); // Build-time error
+///     assert!(1 > 1); // Run-time error
+/// }
+/// ```
+///
+/// When the condition refers to generic parameters or parameters of an inline function,
+/// [`static_assert!`] cannot be used. Use `build_assert!` in this scenario.
+/// ```
+/// fn foo<const N: usize>() {
+///     // `static_assert!(N > 1);` is not allowed
+///     build_assert!(N > 1); // Build-time check
+///     assert!(N > 1); // Run-time check
+/// }
+///
+/// #[inline]
+/// fn bar(n: usize) {
+///     // `static_assert!(n > 1);` is not allowed
+///     build_assert!(n > 1); // Build-time check
+///     assert!(n > 1); // Run-time check
+/// }
+/// ```
+///
+/// [`static_assert!`]: crate::static_assert!
+#[macro_export]
+macro_rules! build_assert {
+    ($cond:expr $(,)?) => {{
+        if !$cond {
+            $crate::build_error(concat!("assertion failed: ", stringify!($cond)));
+        }
+    }};
+    ($cond:expr, $msg:expr) => {{
+        if !$cond {
+            $crate::build_error($msg);
+        }
+    }};
+}
diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
new file mode 100644
index 0000000000..032b645439
--- /dev/null
+++ b/rust/kernel/error.rs
@@ -0,0 +1,337 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Kernel errors.
+//!
+//! C header: [`include/uapi/asm-generic/errno-base.h`](../../../include/uapi/asm-generic/errno-base.h)
+
+use crate::str::CStr;
+
+use alloc::{
+    alloc::{AllocError, LayoutError},
+    collections::TryReserveError,
+};
+
+use core::convert::From;
+use core::fmt;
+use core::num::TryFromIntError;
+use core::str::Utf8Error;
+
+/// Contains the C-compatible error codes.
+#[rustfmt::skip]
+pub mod code {
+    macro_rules! declare_err {
+        ($err:tt $(,)? $($doc:expr),+) => {
+            $(
+            #[doc = $doc]
+            )*
+            pub const $err: super::Error = super::Error(-(crate::bindings::$err as i32));
+        };
+    }
+
+    declare_err!(EPERM, "Operation not permitted.");
+    declare_err!(ENOENT, "No such file or directory.");
+    declare_err!(ESRCH, "No such process.");
+    declare_err!(EINTR, "Interrupted system call.");
+    declare_err!(EIO, "I/O error.");
+    declare_err!(ENXIO, "No such device or address.");
+    declare_err!(E2BIG, "Argument list too long.");
+    declare_err!(ENOEXEC, "Exec format error.");
+    declare_err!(EBADF, "Bad file number.");
+    declare_err!(ECHILD, "No child processes.");
+    declare_err!(EAGAIN, "Try again.");
+    declare_err!(ENOMEM, "Out of memory.");
+    declare_err!(EACCES, "Permission denied.");
+    declare_err!(EFAULT, "Bad address.");
+    declare_err!(ENOTBLK, "Block device required.");
+    declare_err!(EBUSY, "Device or resource busy.");
+    declare_err!(EEXIST, "File exists.");
+    declare_err!(EXDEV, "Cross-device link.");
+    declare_err!(ENODEV, "No such device.");
+    declare_err!(ENOTDIR, "Not a directory.");
+    declare_err!(EISDIR, "Is a directory.");
+    declare_err!(EINVAL, "Invalid argument.");
+    declare_err!(ENFILE, "File table overflow.");
+    declare_err!(EMFILE, "Too many open files.");
+    declare_err!(ENOTTY, "Not a typewriter.");
+    declare_err!(ETXTBSY, "Text file busy.");
+    declare_err!(EFBIG, "File too large.");
+    declare_err!(ENOSPC, "No space left on device.");
+    declare_err!(ESPIPE, "Illegal seek.");
+    declare_err!(EROFS, "Read-only file system.");
+    declare_err!(EMLINK, "Too many links.");
+    declare_err!(EPIPE, "Broken pipe.");
+    declare_err!(EDOM, "Math argument out of domain of func.");
+    declare_err!(ERANGE, "Math result not representable.");
+    declare_err!(ERESTARTSYS, "Restart the system call.");
+    declare_err!(ERESTARTNOINTR, "System call was interrupted by a signal and will be restarted.");
+    declare_err!(ERESTARTNOHAND, "Restart if no handler.");
+    declare_err!(ENOIOCTLCMD, "No ioctl command.");
+    declare_err!(ERESTART_RESTARTBLOCK, "Restart by calling sys_restart_syscall.");
+    declare_err!(EPROBE_DEFER, "Driver requests probe retry.");
+    declare_err!(EOPENSTALE, "Open found a stale dentry.");
+    declare_err!(ENOPARAM, "Parameter not supported.");
+    declare_err!(EBADHANDLE, "Illegal NFS file handle.");
+    declare_err!(ENOTSYNC, "Update synchronization mismatch.");
+    declare_err!(EBADCOOKIE, "Cookie is stale.");
+    declare_err!(ENOTSUPP, "Operation is not supported.");
+    declare_err!(ETOOSMALL, "Buffer or request is too small.");
+    declare_err!(ESERVERFAULT, "An untranslatable error occurred.");
+    declare_err!(EBADTYPE, "Type not supported by server.");
+    declare_err!(EJUKEBOX, "Request initiated, but will not complete before timeout.");
+    declare_err!(EIOCBQUEUED, "iocb queued, will get completion event.");
+    declare_err!(ERECALLCONFLICT, "Conflict with recalled state.");
+    declare_err!(ENOGRACE, "NFS file lock reclaim refused.");
+}
+
+/// Generic integer kernel error.
+///
+/// The kernel defines a set of integer generic error codes based on C and
+/// POSIX ones. These codes may have a more specific meaning in some contexts.
+///
+/// # Invariants
+///
+/// The value is a valid `errno` (i.e. `>= -MAX_ERRNO && < 0`).
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub struct Error(core::ffi::c_int);
+
+impl Error {
+    /// Creates an [`Error`] from a kernel error code.
+    ///
+    /// It is a bug to pass an out-of-range `errno`. `EINVAL` would
+    /// be returned in such a case.
+    pub(crate) fn from_errno(errno: core::ffi::c_int) -> Error {
+        if errno < -(bindings::MAX_ERRNO as i32) || errno >= 0 {
+            // TODO: Make it a `WARN_ONCE` once available.
+            crate::pr_warn!(
+                "attempted to create `Error` with out of range `errno`: {}",
+                errno
+            );
+            return code::EINVAL;
+        }
+
+        // INVARIANT: The check above ensures the type invariant
+        // will hold.
+        Error(errno)
+    }
+
+    /// Creates an [`Error`] from a kernel error code.
+    ///
+    /// # Safety
+    ///
+    /// `errno` must be within error code range (i.e. `>= -MAX_ERRNO && < 0`).
+    unsafe fn from_errno_unchecked(errno: core::ffi::c_int) -> Error {
+        // INVARIANT: The contract ensures the type invariant
+        // will hold.
+        Error(errno)
+    }
+
+    /// Returns the kernel error code.
+    pub fn to_errno(self) -> core::ffi::c_int {
+        self.0
+    }
+
+    /// Returns the error encoded as a pointer.
+    #[allow(dead_code)]
+    pub(crate) fn to_ptr<T>(self) -> *mut T {
+        // SAFETY: `self.0` is a valid error due to its invariant.
+        unsafe { bindings::ERR_PTR(self.0.into()) as *mut _ }
+    }
+
+    /// Returns a string representing the error, if one exists.
+    #[cfg(not(testlib))]
+    pub fn name(&self) -> Option<&'static CStr> {
+        // SAFETY: Just an FFI call, there are no extra safety requirements.
+        let ptr = unsafe { bindings::errname(-self.0) };
+        if ptr.is_null() {
+            None
+        } else {
+            // SAFETY: The string returned by `errname` is static and `NUL`-terminated.
+            Some(unsafe { CStr::from_char_ptr(ptr) })
+        }
+    }
+
+    /// Returns a string representing the error, if one exists.
+    ///
+    /// When `testlib` is configured, this always returns `None` to avoid the dependency on a
+    /// kernel function so that tests that use this (e.g., by calling [`Result::unwrap`]) can still
+    /// run in userspace.
+    #[cfg(testlib)]
+    pub fn name(&self) -> Option<&'static CStr> {
+        None
+    }
+}
+
+impl fmt::Debug for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.name() {
+            // Print out number if no name can be found.
+            None => f.debug_tuple("Error").field(&-self.0).finish(),
+            // SAFETY: These strings are ASCII-only.
+            Some(name) => f
+                .debug_tuple(unsafe { core::str::from_utf8_unchecked(name) })
+                .finish(),
+        }
+    }
+}
+
+impl From<AllocError> for Error {
+    fn from(_: AllocError) -> Error {
+        code::ENOMEM
+    }
+}
+
+impl From<TryFromIntError> for Error {
+    fn from(_: TryFromIntError) -> Error {
+        code::EINVAL
+    }
+}
+
+impl From<Utf8Error> for Error {
+    fn from(_: Utf8Error) -> Error {
+        code::EINVAL
+    }
+}
+
+impl From<TryReserveError> for Error {
+    fn from(_: TryReserveError) -> Error {
+        code::ENOMEM
+    }
+}
+
+impl From<LayoutError> for Error {
+    fn from(_: LayoutError) -> Error {
+        code::ENOMEM
+    }
+}
+
+impl From<core::fmt::Error> for Error {
+    fn from(_: core::fmt::Error) -> Error {
+        code::EINVAL
+    }
+}
+
+impl From<core::convert::Infallible> for Error {
+    fn from(e: core::convert::Infallible) -> Error {
+        match e {}
+    }
+}
+
+/// A [`Result`] with an [`Error`] error type.
+///
+/// To be used as the return type for functions that may fail.
+///
+/// # Error codes in C and Rust
+///
+/// In C, it is common that functions indicate success or failure through
+/// their return value; modifying or returning extra data through non-`const`
+/// pointer parameters. In particular, in the kernel, functions that may fail
+/// typically return an `int` that represents a generic error code. We model
+/// those as [`Error`].
+///
+/// In Rust, it is idiomatic to model functions that may fail as returning
+/// a [`Result`]. Since in the kernel many functions return an error code,
+/// [`Result`] is a type alias for a [`core::result::Result`] that uses
+/// [`Error`] as its error type.
+///
+/// Note that even if a function does not return anything when it succeeds,
+/// it should still be modeled as returning a `Result` rather than
+/// just an [`Error`].
+pub type Result<T = (), E = Error> = core::result::Result<T, E>;
+
+/// Converts an integer as returned by a C kernel function to an error if it's negative, and
+/// `Ok(())` otherwise.
+pub fn to_result(err: core::ffi::c_int) -> Result {
+    if err < 0 {
+        Err(Error::from_errno(err))
+    } else {
+        Ok(())
+    }
+}
+
+/// Transform a kernel "error pointer" to a normal pointer.
+///
+/// Some kernel C API functions return an "error pointer" which optionally
+/// embeds an `errno`. Callers are supposed to check the returned pointer
+/// for errors. This function performs the check and converts the "error pointer"
+/// to a normal pointer in an idiomatic fashion.
+///
+/// # Examples
+///
+/// ```ignore
+/// # use kernel::from_err_ptr;
+/// # use kernel::bindings;
+/// fn devm_platform_ioremap_resource(
+///     pdev: &mut PlatformDevice,
+///     index: u32,
+/// ) -> Result<*mut core::ffi::c_void> {
+///     // SAFETY: FFI call.
+///     unsafe {
+///         from_err_ptr(bindings::devm_platform_ioremap_resource(
+///             pdev.to_ptr(),
+///             index,
+///         ))
+///     }
+/// }
+/// ```
+// TODO: Remove `dead_code` marker once an in-kernel client is available.
+#[allow(dead_code)]
+pub(crate) fn from_err_ptr<T>(ptr: *mut T) -> Result<*mut T> {
+    // CAST: Casting a pointer to `*const core::ffi::c_void` is always valid.
+    let const_ptr: *const core::ffi::c_void = ptr.cast();
+    // SAFETY: The FFI function does not deref the pointer.
+    if unsafe { bindings::IS_ERR(const_ptr) } {
+        // SAFETY: The FFI function does not deref the pointer.
+        let err = unsafe { bindings::PTR_ERR(const_ptr) };
+        // CAST: If `IS_ERR()` returns `true`,
+        // then `PTR_ERR()` is guaranteed to return a
+        // negative value greater-or-equal to `-bindings::MAX_ERRNO`,
+        // which always fits in an `i16`, as per the invariant above.
+        // And an `i16` always fits in an `i32`. So casting `err` to
+        // an `i32` can never overflow, and is always valid.
+        //
+        // SAFETY: `IS_ERR()` ensures `err` is a
+        // negative value greater-or-equal to `-bindings::MAX_ERRNO`.
+        #[allow(clippy::unnecessary_cast)]
+        return Err(unsafe { Error::from_errno_unchecked(err as core::ffi::c_int) });
+    }
+    Ok(ptr)
+}
+
+/// Calls a closure returning a [`crate::error::Result<T>`] and converts the result to
+/// a C integer result.
+///
+/// This is useful when calling Rust functions that return [`crate::error::Result<T>`]
+/// from inside `extern "C"` functions that need to return an integer error result.
+///
+/// `T` should be convertible from an `i16` via `From<i16>`.
+///
+/// # Examples
+///
+/// ```ignore
+/// # use kernel::from_result;
+/// # use kernel::bindings;
+/// unsafe extern "C" fn probe_callback(
+///     pdev: *mut bindings::platform_device,
+/// ) -> core::ffi::c_int {
+///     from_result(|| {
+///         let ptr = devm_alloc(pdev)?;
+///         bindings::platform_set_drvdata(pdev, ptr);
+///         Ok(0)
+///     })
+/// }
+/// ```
+// TODO: Remove `dead_code` marker once an in-kernel client is available.
+#[allow(dead_code)]
+pub(crate) fn from_result<T, F>(f: F) -> T
+where
+    T: From<i16>,
+    F: FnOnce() -> Result<T>,
+{
+    match f() {
+        Ok(v) => v,
+        // NO-OVERFLOW: negative `errno`s are no smaller than `-bindings::MAX_ERRNO`,
+        // `-bindings::MAX_ERRNO` fits in an `i16` as per invariant above,
+        // therefore a negative `errno` always fits in an `i16` and will not overflow.
+        Err(e) => T::from(e.to_errno() as i16),
+    }
+}
diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
new file mode 100644
index 0000000000..4ebb6f23fc
--- /dev/null
+++ b/rust/kernel/init.rs
@@ -0,0 +1,1344 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! API to safely and fallibly initialize pinned `struct`s using in-place constructors.
+//!
+//! It also allows in-place initialization of big `struct`s that would otherwise produce a stack
+//! overflow.
+//!
+//! Most `struct`s from the [`sync`] module need to be pinned, because they contain self-referential
+//! `struct`s from C. [Pinning][pinning] is Rust's way of ensuring data does not move.
+//!
+//! # Overview
+//!
+//! To initialize a `struct` with an in-place constructor you will need two things:
+//! - an in-place constructor,
+//! - a memory location that can hold your `struct` (this can be the [stack], an [`Arc<T>`],
+//!   [`UniqueArc<T>`], [`Box<T>`] or any other smart pointer that implements [`InPlaceInit`]).
+//!
+//! To get an in-place constructor there are generally three options:
+//! - directly creating an in-place constructor using the [`pin_init!`] macro,
+//! - a custom function/macro returning an in-place constructor provided by someone else,
+//! - using the unsafe function [`pin_init_from_closure()`] to manually create an initializer.
+//!
+//! Aside from pinned initialization, this API also supports in-place construction without pinning,
+//! the macros/types/functions are generally named like the pinned variants without the `pin`
+//! prefix.
+//!
+//! # Examples
+//!
+//! ## Using the [`pin_init!`] macro
+//!
+//! If you want to use [`PinInit`], then you will have to annotate your `struct` with
+//! `#[`[`pin_data`]`]`. It is a macro that uses `#[pin]` as a marker for
+//! [structurally pinned fields]. After doing this, you can then create an in-place constructor via
+//! [`pin_init!`]. The syntax is almost the same as normal `struct` initializers. The difference is
+//! that you need to write `<-` instead of `:` for fields that you want to initialize in-place.
+//!
+//! ```rust
+//! # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
+//! use kernel::{prelude::*, sync::Mutex, new_mutex};
+//! # use core::pin::Pin;
+//! #[pin_data]
+//! struct Foo {
+//!     #[pin]
+//!     a: Mutex<usize>,
+//!     b: u32,
+//! }
+//!
+//! let foo = pin_init!(Foo {
+//!     a <- new_mutex!(42, "Foo::a"),
+//!     b: 24,
+//! });
+//! ```
+//!
+//! `foo` now is of the type [`impl PinInit<Foo>`]. We can now use any smart pointer that we like
+//! (or just the stack) to actually initialize a `Foo`:
+//!
+//! ```rust
+//! # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
+//! # use kernel::{prelude::*, sync::Mutex, new_mutex};
+//! # use core::pin::Pin;
+//! # #[pin_data]
+//! # struct Foo {
+//! #     #[pin]
+//! #     a: Mutex<usize>,
+//! #     b: u32,
+//! # }
+//! # let foo = pin_init!(Foo {
+//! #     a <- new_mutex!(42, "Foo::a"),
+//! #     b: 24,
+//! # });
+//! let foo: Result<Pin<Box<Foo>>> = Box::pin_init(foo);
+//! ```
+//!
+//! For more information see the [`pin_init!`] macro.
+//!
+//! ## Using a custom function/macro that returns an initializer
+//!
+//! Many types from the kernel supply a function/macro that returns an initializer, because the
+//! above method only works for types where you can access the fields.
+//!
+//! ```rust
+//! # use kernel::{new_mutex, sync::{Arc, Mutex}};
+//! let mtx: Result<Arc<Mutex<usize>>> = Arc::pin_init(new_mutex!(42, "example::mtx"));
+//! ```
+//!
+//! To declare an init macro/function you just return an [`impl PinInit<T, E>`]:
+//!
+//! ```rust
+//! # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
+//! # use kernel::{sync::Mutex, prelude::*, new_mutex, init::PinInit, try_pin_init};
+//! #[pin_data]
+//! struct DriverData {
+//!     #[pin]
+//!     status: Mutex<i32>,
+//!     buffer: Box<[u8; 1_000_000]>,
+//! }
+//!
+//! impl DriverData {
+//!     fn new() -> impl PinInit<Self, Error> {
+//!         try_pin_init!(Self {
+//!             status <- new_mutex!(0, "DriverData::status"),
+//!             buffer: Box::init(kernel::init::zeroed())?,
+//!         })
+//!     }
+//! }
+//! ```
+//!
+//! ## Manual creation of an initializer
+//!
+//! Often when working with primitives the previous approaches are not sufficient. That is where
+//! [`pin_init_from_closure()`] comes in. This `unsafe` function allows you to create a
+//! [`impl PinInit<T, E>`] directly from a closure. Of course you have to ensure that the closure
+//! actually does the initialization in the correct way. Here are the things to look out for
+//! (we are calling the parameter to the closure `slot`):
+//! - when the closure returns `Ok(())`, then it has completed the initialization successfully, so
+//!   `slot` now contains a valid bit pattern for the type `T`,
+//! - when the closure returns `Err(e)`, then the caller may deallocate the memory at `slot`, so
+//!   you need to take care to clean up anything if your initialization fails mid-way,
+//! - you may assume that `slot` will stay pinned even after the closure returns until `drop` of
+//!   `slot` gets called.
+//!
+//! ```rust
+//! # #![allow(unreachable_pub, clippy::disallowed_names)]
+//! use kernel::{prelude::*, init, types::Opaque};
+//! use core::{ptr::addr_of_mut, marker::PhantomPinned, pin::Pin};
+//! # mod bindings {
+//! #     #![allow(non_camel_case_types)]
+//! #     pub struct foo;
+//! #     pub unsafe fn init_foo(_ptr: *mut foo) {}
+//! #     pub unsafe fn destroy_foo(_ptr: *mut foo) {}
+//! #     pub unsafe fn enable_foo(_ptr: *mut foo, _flags: u32) -> i32 { 0 }
+//! # }
+//! # // `Error::from_errno` is `pub(crate)` in the `kernel` crate, thus provide a workaround.
+//! # trait FromErrno {
+//! #     fn from_errno(errno: core::ffi::c_int) -> Error {
+//! #         // Dummy error that can be constructed outside the `kernel` crate.
+//! #         Error::from(core::fmt::Error)
+//! #     }
+//! # }
+//! # impl FromErrno for Error {}
+//! /// # Invariants
+//! ///
+//! /// `foo` is always initialized
+//! #[pin_data(PinnedDrop)]
+//! pub struct RawFoo {
+//!     #[pin]
+//!     foo: Opaque<bindings::foo>,
+//!     #[pin]
+//!     _p: PhantomPinned,
+//! }
+//!
+//! impl RawFoo {
+//!     pub fn new(flags: u32) -> impl PinInit<Self, Error> {
+//!         // SAFETY:
+//!         // - when the closure returns `Ok(())`, then it has successfully initialized and
+//!         //   enabled `foo`,
+//!         // - when it returns `Err(e)`, then it has cleaned up before
+//!         unsafe {
+//!             init::pin_init_from_closure(move |slot: *mut Self| {
+//!                 // `slot` contains uninit memory, avoid creating a reference.
+//!                 let foo = addr_of_mut!((*slot).foo);
+//!
+//!                 // Initialize the `foo`
+//!                 bindings::init_foo(Opaque::raw_get(foo));
+//!
+//!                 // Try to enable it.
+//!                 let err = bindings::enable_foo(Opaque::raw_get(foo), flags);
+//!                 if err != 0 {
+//!                     // Enabling has failed, first clean up the foo and then return the error.
+//!                     bindings::destroy_foo(Opaque::raw_get(foo));
+//!                     return Err(Error::from_errno(err));
+//!                 }
+//!
+//!                 // All fields of `RawFoo` have been initialized, since `_p` is a ZST.
+//!                 Ok(())
+//!             })
+//!         }
+//!     }
+//! }
+//!
+//! #[pinned_drop]
+//! impl PinnedDrop for RawFoo {
+//!     fn drop(self: Pin<&mut Self>) {
+//!         // SAFETY: Since `foo` is initialized, destroying is safe.
+//!         unsafe { bindings::destroy_foo(self.foo.get()) };
+//!     }
+//! }
+//! ```
+//!
+//! For the special case where initializing a field is a single FFI-function call that cannot fail,
+//! there exist the helper function [`Opaque::ffi_init`]. This function initialize a single
+//! [`Opaque`] field by just delegating to the supplied closure. You can use these in combination
+//! with [`pin_init!`].
+//!
+//! For more information on how to use [`pin_init_from_closure()`], take a look at the uses inside
+//! the `kernel` crate. The [`sync`] module is a good starting point.
+//!
+//! [`sync`]: kernel::sync
+//! [pinning]: https://doc.rust-lang.org/std/pin/index.html
+//! [structurally pinned fields]:
+//!     https://doc.rust-lang.org/std/pin/index.html#pinning-is-structural-for-field
+//! [stack]: crate::stack_pin_init
+//! [`Arc<T>`]: crate::sync::Arc
+//! [`impl PinInit<Foo>`]: PinInit
+//! [`impl PinInit<T, E>`]: PinInit
+//! [`impl Init<T, E>`]: Init
+//! [`Opaque`]: kernel::types::Opaque
+//! [`Opaque::ffi_init`]: kernel::types::Opaque::ffi_init
+//! [`pin_data`]: ::macros::pin_data
+//! [`pin_init!`]: crate::pin_init!
+
+use crate::{
+    error::{self, Error},
+    sync::UniqueArc,
+    types::{Opaque, ScopeGuard},
+};
+use alloc::boxed::Box;
+use core::{
+    alloc::AllocError,
+    cell::UnsafeCell,
+    convert::Infallible,
+    marker::PhantomData,
+    mem::MaybeUninit,
+    num::*,
+    pin::Pin,
+    ptr::{self, NonNull},
+};
+
+#[doc(hidden)]
+pub mod __internal;
+#[doc(hidden)]
+pub mod macros;
+
+/// Initialize and pin a type directly on the stack.
+///
+/// # Examples
+///
+/// ```rust
+/// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
+/// # use kernel::{init, macros::pin_data, pin_init, stack_pin_init, init::*, sync::Mutex, new_mutex};
+/// # use core::pin::Pin;
+/// #[pin_data]
+/// struct Foo {
+///     #[pin]
+///     a: Mutex<usize>,
+///     b: Bar,
+/// }
+///
+/// #[pin_data]
+/// struct Bar {
+///     x: u32,
+/// }
+///
+/// stack_pin_init!(let foo = pin_init!(Foo {
+///     a <- new_mutex!(42),
+///     b: Bar {
+///         x: 64,
+///     },
+/// }));
+/// let foo: Pin<&mut Foo> = foo;
+/// pr_info!("a: {}", &*foo.a.lock());
+/// ```
+///
+/// # Syntax
+///
+/// A normal `let` binding with optional type annotation. The expression is expected to implement
+/// [`PinInit`]/[`Init`] with the error type [`Infallible`]. If you want to use a different error
+/// type, then use [`stack_try_pin_init!`].
+///
+/// [`stack_try_pin_init!`]: crate::stack_try_pin_init!
+#[macro_export]
+macro_rules! stack_pin_init {
+    (let $var:ident $(: $t:ty)? = $val:expr) => {
+        let val = $val;
+        let mut $var = ::core::pin::pin!($crate::init::__internal::StackInit$(::<$t>)?::uninit());
+        let mut $var = match $crate::init::__internal::StackInit::init($var, val) {
+            Ok(res) => res,
+            Err(x) => {
+                let x: ::core::convert::Infallible = x;
+                match x {}
+            }
+        };
+    };
+}
+
+/// Initialize and pin a type directly on the stack.
+///
+/// # Examples
+///
+/// ```rust,ignore
+/// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
+/// # use kernel::{init, pin_init, stack_try_pin_init, init::*, sync::Mutex, new_mutex};
+/// # use macros::pin_data;
+/// # use core::{alloc::AllocError, pin::Pin};
+/// #[pin_data]
+/// struct Foo {
+///     #[pin]
+///     a: Mutex<usize>,
+///     b: Box<Bar>,
+/// }
+///
+/// struct Bar {
+///     x: u32,
+/// }
+///
+/// stack_try_pin_init!(let foo: Result<Pin<&mut Foo>, AllocError> = pin_init!(Foo {
+///     a <- new_mutex!(42),
+///     b: Box::try_new(Bar {
+///         x: 64,
+///     })?,
+/// }));
+/// let foo = foo.unwrap();
+/// pr_info!("a: {}", &*foo.a.lock());
+/// ```
+///
+/// ```rust,ignore
+/// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
+/// # use kernel::{init, pin_init, stack_try_pin_init, init::*, sync::Mutex, new_mutex};
+/// # use macros::pin_data;
+/// # use core::{alloc::AllocError, pin::Pin};
+/// #[pin_data]
+/// struct Foo {
+///     #[pin]
+///     a: Mutex<usize>,
+///     b: Box<Bar>,
+/// }
+///
+/// struct Bar {
+///     x: u32,
+/// }
+///
+/// stack_try_pin_init!(let foo: Pin<&mut Foo> =? pin_init!(Foo {
+///     a <- new_mutex!(42),
+///     b: Box::try_new(Bar {
+///         x: 64,
+///     })?,
+/// }));
+/// pr_info!("a: {}", &*foo.a.lock());
+/// # Ok::<_, AllocError>(())
+/// ```
+///
+/// # Syntax
+///
+/// A normal `let` binding with optional type annotation. The expression is expected to implement
+/// [`PinInit`]/[`Init`]. This macro assigns a result to the given variable, adding a `?` after the
+/// `=` will propagate this error.
+#[macro_export]
+macro_rules! stack_try_pin_init {
+    (let $var:ident $(: $t:ty)? = $val:expr) => {
+        let val = $val;
+        let mut $var = ::core::pin::pin!($crate::init::__internal::StackInit$(::<$t>)?::uninit());
+        let mut $var = $crate::init::__internal::StackInit::init($var, val);
+    };
+    (let $var:ident $(: $t:ty)? =? $val:expr) => {
+        let val = $val;
+        let mut $var = ::core::pin::pin!($crate::init::__internal::StackInit$(::<$t>)?::uninit());
+        let mut $var = $crate::init::__internal::StackInit::init($var, val)?;
+    };
+}
+
+/// Construct an in-place, pinned initializer for `struct`s.
+///
+/// This macro defaults the error to [`Infallible`]. If you need [`Error`], then use
+/// [`try_pin_init!`].
+///
+/// The syntax is almost identical to that of a normal `struct` initializer:
+///
+/// ```rust
+/// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
+/// # use kernel::{init, pin_init, macros::pin_data, init::*};
+/// # use core::pin::Pin;
+/// #[pin_data]
+/// struct Foo {
+///     a: usize,
+///     b: Bar,
+/// }
+///
+/// #[pin_data]
+/// struct Bar {
+///     x: u32,
+/// }
+///
+/// # fn demo() -> impl PinInit<Foo> {
+/// let a = 42;
+///
+/// let initializer = pin_init!(Foo {
+///     a,
+///     b: Bar {
+///         x: 64,
+///     },
+/// });
+/// # initializer }
+/// # Box::pin_init(demo()).unwrap();
+/// ```
+///
+/// Arbitrary Rust expressions can be used to set the value of a variable.
+///
+/// The fields are initialized in the order that they appear in the initializer. So it is possible
+/// to read already initialized fields using raw pointers.
+///
+/// IMPORTANT: You are not allowed to create references to fields of the struct inside of the
+/// initializer.
+///
+/// # Init-functions
+///
+/// When working with this API it is often desired to let others construct your types without
+/// giving access to all fields. This is where you would normally write a plain function `new`
+/// that would return a new instance of your type. With this API that is also possible.
+/// However, there are a few extra things to keep in mind.
+///
+/// To create an initializer function, simply declare it like this:
+///
+/// ```rust
+/// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
+/// # use kernel::{init, pin_init, prelude::*, init::*};
+/// # use core::pin::Pin;
+/// # #[pin_data]
+/// # struct Foo {
+/// #     a: usize,
+/// #     b: Bar,
+/// # }
+/// # #[pin_data]
+/// # struct Bar {
+/// #     x: u32,
+/// # }
+/// impl Foo {
+///     fn new() -> impl PinInit<Self> {
+///         pin_init!(Self {
+///             a: 42,
+///             b: Bar {
+///                 x: 64,
+///             },
+///         })
+///     }
+/// }
+/// ```
+///
+/// Users of `Foo` can now create it like this:
+///
+/// ```rust
+/// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
+/// # use kernel::{init, pin_init, macros::pin_data, init::*};
+/// # use core::pin::Pin;
+/// # #[pin_data]
+/// # struct Foo {
+/// #     a: usize,
+/// #     b: Bar,
+/// # }
+/// # #[pin_data]
+/// # struct Bar {
+/// #     x: u32,
+/// # }
+/// # impl Foo {
+/// #     fn new() -> impl PinInit<Self> {
+/// #         pin_init!(Self {
+/// #             a: 42,
+/// #             b: Bar {
+/// #                 x: 64,
+/// #             },
+/// #         })
+/// #     }
+/// # }
+/// let foo = Box::pin_init(Foo::new());
+/// ```
+///
+/// They can also easily embed it into their own `struct`s:
+///
+/// ```rust
+/// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
+/// # use kernel::{init, pin_init, macros::pin_data, init::*};
+/// # use core::pin::Pin;
+/// # #[pin_data]
+/// # struct Foo {
+/// #     a: usize,
+/// #     b: Bar,
+/// # }
+/// # #[pin_data]
+/// # struct Bar {
+/// #     x: u32,
+/// # }
+/// # impl Foo {
+/// #     fn new() -> impl PinInit<Self> {
+/// #         pin_init!(Self {
+/// #             a: 42,
+/// #             b: Bar {
+/// #                 x: 64,
+/// #             },
+/// #         })
+/// #     }
+/// # }
+/// #[pin_data]
+/// struct FooContainer {
+///     #[pin]
+///     foo1: Foo,
+///     #[pin]
+///     foo2: Foo,
+///     other: u32,
+/// }
+///
+/// impl FooContainer {
+///     fn new(other: u32) -> impl PinInit<Self> {
+///         pin_init!(Self {
+///             foo1 <- Foo::new(),
+///             foo2 <- Foo::new(),
+///             other,
+///         })
+///     }
+/// }
+/// ```
+///
+/// Here we see that when using `pin_init!` with `PinInit`, one needs to write `<-` instead of `:`.
+/// This signifies that the given field is initialized in-place. As with `struct` initializers, just
+/// writing the field (in this case `other`) without `:` or `<-` means `other: other,`.
+///
+/// # Syntax
+///
+/// As already mentioned in the examples above, inside of `pin_init!` a `struct` initializer with
+/// the following modifications is expected:
+/// - Fields that you want to initialize in-place have to use `<-` instead of `:`.
+/// - In front of the initializer you can write `&this in` to have access to a [`NonNull<Self>`]
+///   pointer named `this` inside of the initializer.
+/// - Using struct update syntax one can place `..Zeroable::zeroed()` at the very end of the
+///   struct, this initializes every field with 0 and then runs all initializers specified in the
+///   body. This can only be done if [`Zeroable`] is implemented for the struct.
+///
+/// For instance:
+///
+/// ```rust
+/// # use kernel::{macros::{Zeroable, pin_data}, pin_init};
+/// # use core::{ptr::addr_of_mut, marker::PhantomPinned};
+/// #[pin_data]
+/// #[derive(Zeroable)]
+/// struct Buf {
+///     // `ptr` points into `buf`.
+///     ptr: *mut u8,
+///     buf: [u8; 64],
+///     #[pin]
+///     pin: PhantomPinned,
+/// }
+/// pin_init!(&this in Buf {
+///     buf: [0; 64],
+///     ptr: unsafe { addr_of_mut!((*this.as_ptr()).buf).cast() },
+///     pin: PhantomPinned,
+/// });
+/// pin_init!(Buf {
+///     buf: [1; 64],
+///     ..Zeroable::zeroed()
+/// });
+/// ```
+///
+/// [`try_pin_init!`]: kernel::try_pin_init
+/// [`NonNull<Self>`]: core::ptr::NonNull
+// For a detailed example of how this macro works, see the module documentation of the hidden
+// module `__internal` inside of `init/__internal.rs`.
+#[macro_export]
+macro_rules! pin_init {
+    ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
+        $($fields:tt)*
+    }) => {
+        $crate::__init_internal!(
+            @this($($this)?),
+            @typ($t $(::<$($generics),*>)?),
+            @fields($($fields)*),
+            @error(::core::convert::Infallible),
+            @data(PinData, use_data),
+            @has_data(HasPinData, __pin_data),
+            @construct_closure(pin_init_from_closure),
+            @munch_fields($($fields)*),
+        )
+    };
+}
+
+/// Construct an in-place, fallible pinned initializer for `struct`s.
+///
+/// If the initialization can complete without error (or [`Infallible`]), then use [`pin_init!`].
+///
+/// You can use the `?` operator or use `return Err(err)` inside the initializer to stop
+/// initialization and return the error.
+///
+/// IMPORTANT: if you have `unsafe` code inside of the initializer you have to ensure that when
+/// initialization fails, the memory can be safely deallocated without any further modifications.
+///
+/// This macro defaults the error to [`Error`].
+///
+/// The syntax is identical to [`pin_init!`] with the following exception: you can append `? $type`
+/// after the `struct` initializer to specify the error type you want to use.
+///
+/// # Examples
+///
+/// ```rust
+/// # #![feature(new_uninit)]
+/// use kernel::{init::{self, PinInit}, error::Error};
+/// #[pin_data]
+/// struct BigBuf {
+///     big: Box<[u8; 1024 * 1024 * 1024]>,
+///     small: [u8; 1024 * 1024],
+///     ptr: *mut u8,
+/// }
+///
+/// impl BigBuf {
+///     fn new() -> impl PinInit<Self, Error> {
+///         try_pin_init!(Self {
+///             big: Box::init(init::zeroed())?,
+///             small: [0; 1024 * 1024],
+///             ptr: core::ptr::null_mut(),
+///         }? Error)
+///     }
+/// }
+/// ```
+// For a detailed example of how this macro works, see the module documentation of the hidden
+// module `__internal` inside of `init/__internal.rs`.
+#[macro_export]
+macro_rules! try_pin_init {
+    ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
+        $($fields:tt)*
+    }) => {
+        $crate::__init_internal!(
+            @this($($this)?),
+            @typ($t $(::<$($generics),*>)? ),
+            @fields($($fields)*),
+            @error($crate::error::Error),
+            @data(PinData, use_data),
+            @has_data(HasPinData, __pin_data),
+            @construct_closure(pin_init_from_closure),
+            @munch_fields($($fields)*),
+        )
+    };
+    ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
+        $($fields:tt)*
+    }? $err:ty) => {
+        $crate::__init_internal!(
+            @this($($this)?),
+            @typ($t $(::<$($generics),*>)? ),
+            @fields($($fields)*),
+            @error($err),
+            @data(PinData, use_data),
+            @has_data(HasPinData, __pin_data),
+            @construct_closure(pin_init_from_closure),
+            @munch_fields($($fields)*),
+        )
+    };
+}
+
+/// Construct an in-place initializer for `struct`s.
+///
+/// This macro defaults the error to [`Infallible`]. If you need [`Error`], then use
+/// [`try_init!`].
+///
+/// The syntax is identical to [`pin_init!`] and its safety caveats also apply:
+/// - `unsafe` code must guarantee either full initialization or return an error and allow
+///   deallocation of the memory.
+/// - the fields are initialized in the order given in the initializer.
+/// - no references to fields are allowed to be created inside of the initializer.
+///
+/// This initializer is for initializing data in-place that might later be moved. If you want to
+/// pin-initialize, use [`pin_init!`].
+///
+/// [`try_init!`]: crate::try_init!
+// For a detailed example of how this macro works, see the module documentation of the hidden
+// module `__internal` inside of `init/__internal.rs`.
+#[macro_export]
+macro_rules! init {
+    ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
+        $($fields:tt)*
+    }) => {
+        $crate::__init_internal!(
+            @this($($this)?),
+            @typ($t $(::<$($generics),*>)?),
+            @fields($($fields)*),
+            @error(::core::convert::Infallible),
+            @data(InitData, /*no use_data*/),
+            @has_data(HasInitData, __init_data),
+            @construct_closure(init_from_closure),
+            @munch_fields($($fields)*),
+        )
+    }
+}
+
+/// Construct an in-place fallible initializer for `struct`s.
+///
+/// This macro defaults the error to [`Error`]. If you need [`Infallible`], then use
+/// [`init!`].
+///
+/// The syntax is identical to [`try_pin_init!`]. If you want to specify a custom error,
+/// append `? $type` after the `struct` initializer.
+/// The safety caveats from [`try_pin_init!`] also apply:
+/// - `unsafe` code must guarantee either full initialization or return an error and allow
+///   deallocation of the memory.
+/// - the fields are initialized in the order given in the initializer.
+/// - no references to fields are allowed to be created inside of the initializer.
+///
+/// # Examples
+///
+/// ```rust
+/// use kernel::{init::{PinInit, zeroed}, error::Error};
+/// struct BigBuf {
+///     big: Box<[u8; 1024 * 1024 * 1024]>,
+///     small: [u8; 1024 * 1024],
+/// }
+///
+/// impl BigBuf {
+///     fn new() -> impl Init<Self, Error> {
+///         try_init!(Self {
+///             big: Box::init(zeroed())?,
+///             small: [0; 1024 * 1024],
+///         }? Error)
+///     }
+/// }
+/// ```
+// For a detailed example of how this macro works, see the module documentation of the hidden
+// module `__internal` inside of `init/__internal.rs`.
+#[macro_export]
+macro_rules! try_init {
+    ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
+        $($fields:tt)*
+    }) => {
+        $crate::__init_internal!(
+            @this($($this)?),
+            @typ($t $(::<$($generics),*>)?),
+            @fields($($fields)*),
+            @error($crate::error::Error),
+            @data(InitData, /*no use_data*/),
+            @has_data(HasInitData, __init_data),
+            @construct_closure(init_from_closure),
+            @munch_fields($($fields)*),
+        )
+    };
+    ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
+        $($fields:tt)*
+    }? $err:ty) => {
+        $crate::__init_internal!(
+            @this($($this)?),
+            @typ($t $(::<$($generics),*>)?),
+            @fields($($fields)*),
+            @error($err),
+            @data(InitData, /*no use_data*/),
+            @has_data(HasInitData, __init_data),
+            @construct_closure(init_from_closure),
+            @munch_fields($($fields)*),
+        )
+    };
+}
+
+/// A pin-initializer for the type `T`.
+///
+/// To use this initializer, you will need a suitable memory location that can hold a `T`. This can
+/// be [`Box<T>`], [`Arc<T>`], [`UniqueArc<T>`] or even the stack (see [`stack_pin_init!`]). Use the
+/// [`InPlaceInit::pin_init`] function of a smart pointer like [`Arc<T>`] on this.
+///
+/// Also see the [module description](self).
+///
+/// # Safety
+///
+/// When implementing this type you will need to take great care. Also there are probably very few
+/// cases where a manual implementation is necessary. Use [`pin_init_from_closure`] where possible.
+///
+/// The [`PinInit::__pinned_init`] function
+/// - returns `Ok(())` if it initialized every field of `slot`,
+/// - returns `Err(err)` if it encountered an error and then cleaned `slot`, this means:
+///     - `slot` can be deallocated without UB occurring,
+///     - `slot` does not need to be dropped,
+///     - `slot` is not partially initialized.
+/// - while constructing the `T` at `slot` it upholds the pinning invariants of `T`.
+///
+/// [`Arc<T>`]: crate::sync::Arc
+/// [`Arc::pin_init`]: crate::sync::Arc::pin_init
+#[must_use = "An initializer must be used in order to create its value."]
+pub unsafe trait PinInit<T: ?Sized, E = Infallible>: Sized {
+    /// Initializes `slot`.
+    ///
+    /// # Safety
+    ///
+    /// - `slot` is a valid pointer to uninitialized memory.
+    /// - the caller does not touch `slot` when `Err` is returned, they are only permitted to
+    ///   deallocate.
+    /// - `slot` will not move until it is dropped, i.e. it will be pinned.
+    unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E>;
+
+    /// First initializes the value using `self` then calls the function `f` with the initialized
+    /// value.
+    ///
+    /// If `f` returns an error the value is dropped and the initializer will forward the error.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # #![allow(clippy::disallowed_names)]
+    /// use kernel::{types::Opaque, init::pin_init_from_closure};
+    /// #[repr(C)]
+    /// struct RawFoo([u8; 16]);
+    /// extern {
+    ///     fn init_foo(_: *mut RawFoo);
+    /// }
+    ///
+    /// #[pin_data]
+    /// struct Foo {
+    ///     #[pin]
+    ///     raw: Opaque<RawFoo>,
+    /// }
+    ///
+    /// impl Foo {
+    ///     fn setup(self: Pin<&mut Self>) {
+    ///         pr_info!("Setting up foo");
+    ///     }
+    /// }
+    ///
+    /// let foo = pin_init!(Foo {
+    ///     raw <- unsafe {
+    ///         Opaque::ffi_init(|s| {
+    ///             init_foo(s);
+    ///         })
+    ///     },
+    /// }).pin_chain(|foo| {
+    ///     foo.setup();
+    ///     Ok(())
+    /// });
+    /// ```
+    fn pin_chain<F>(self, f: F) -> ChainPinInit<Self, F, T, E>
+    where
+        F: FnOnce(Pin<&mut T>) -> Result<(), E>,
+    {
+        ChainPinInit(self, f, PhantomData)
+    }
+}
+
+/// An initializer returned by [`PinInit::pin_chain`].
+pub struct ChainPinInit<I, F, T: ?Sized, E>(I, F, __internal::Invariant<(E, Box<T>)>);
+
+// SAFETY: The `__pinned_init` function is implemented such that it
+// - returns `Ok(())` on successful initialization,
+// - returns `Err(err)` on error and in this case `slot` will be dropped.
+// - considers `slot` pinned.
+unsafe impl<T: ?Sized, E, I, F> PinInit<T, E> for ChainPinInit<I, F, T, E>
+where
+    I: PinInit<T, E>,
+    F: FnOnce(Pin<&mut T>) -> Result<(), E>,
+{
+    unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
+        // SAFETY: All requirements fulfilled since this function is `__pinned_init`.
+        unsafe { self.0.__pinned_init(slot)? };
+        // SAFETY: The above call initialized `slot` and we still have unique access.
+        let val = unsafe { &mut *slot };
+        // SAFETY: `slot` is considered pinned.
+        let val = unsafe { Pin::new_unchecked(val) };
+        (self.1)(val).map_err(|e| {
+            // SAFETY: `slot` was initialized above.
+            unsafe { core::ptr::drop_in_place(slot) };
+            e
+        })
+    }
+}
+
+/// An initializer for `T`.
+///
+/// To use this initializer, you will need a suitable memory location that can hold a `T`. This can
+/// be [`Box<T>`], [`Arc<T>`], [`UniqueArc<T>`] or even the stack (see [`stack_pin_init!`]). Use the
+/// [`InPlaceInit::init`] function of a smart pointer like [`Arc<T>`] on this. Because
+/// [`PinInit<T, E>`] is a super trait, you can use every function that takes it as well.
+///
+/// Also see the [module description](self).
+///
+/// # Safety
+///
+/// When implementing this type you will need to take great care. Also there are probably very few
+/// cases where a manual implementation is necessary. Use [`init_from_closure`] where possible.
+///
+/// The [`Init::__init`] function
+/// - returns `Ok(())` if it initialized every field of `slot`,
+/// - returns `Err(err)` if it encountered an error and then cleaned `slot`, this means:
+///     - `slot` can be deallocated without UB occurring,
+///     - `slot` does not need to be dropped,
+///     - `slot` is not partially initialized.
+/// - while constructing the `T` at `slot` it upholds the pinning invariants of `T`.
+///
+/// The `__pinned_init` function from the supertrait [`PinInit`] needs to execute the exact same
+/// code as `__init`.
+///
+/// Contrary to its supertype [`PinInit<T, E>`] the caller is allowed to
+/// move the pointee after initialization.
+///
+/// [`Arc<T>`]: crate::sync::Arc
+#[must_use = "An initializer must be used in order to create its value."]
+pub unsafe trait Init<T: ?Sized, E = Infallible>: PinInit<T, E> {
+    /// Initializes `slot`.
+    ///
+    /// # Safety
+    ///
+    /// - `slot` is a valid pointer to uninitialized memory.
+    /// - the caller does not touch `slot` when `Err` is returned, they are only permitted to
+    ///   deallocate.
+    unsafe fn __init(self, slot: *mut T) -> Result<(), E>;
+
+    /// First initializes the value using `self` then calls the function `f` with the initialized
+    /// value.
+    ///
+    /// If `f` returns an error the value is dropped and the initializer will forward the error.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # #![allow(clippy::disallowed_names)]
+    /// use kernel::{types::Opaque, init::{self, init_from_closure}};
+    /// struct Foo {
+    ///     buf: [u8; 1_000_000],
+    /// }
+    ///
+    /// impl Foo {
+    ///     fn setup(&mut self) {
+    ///         pr_info!("Setting up foo");
+    ///     }
+    /// }
+    ///
+    /// let foo = init!(Foo {
+    ///     buf <- init::zeroed()
+    /// }).chain(|foo| {
+    ///     foo.setup();
+    ///     Ok(())
+    /// });
+    /// ```
+    fn chain<F>(self, f: F) -> ChainInit<Self, F, T, E>
+    where
+        F: FnOnce(&mut T) -> Result<(), E>,
+    {
+        ChainInit(self, f, PhantomData)
+    }
+}
+
+/// An initializer returned by [`Init::chain`].
+pub struct ChainInit<I, F, T: ?Sized, E>(I, F, __internal::Invariant<(E, Box<T>)>);
+
+// SAFETY: The `__init` function is implemented such that it
+// - returns `Ok(())` on successful initialization,
+// - returns `Err(err)` on error and in this case `slot` will be dropped.
+unsafe impl<T: ?Sized, E, I, F> Init<T, E> for ChainInit<I, F, T, E>
+where
+    I: Init<T, E>,
+    F: FnOnce(&mut T) -> Result<(), E>,
+{
+    unsafe fn __init(self, slot: *mut T) -> Result<(), E> {
+        // SAFETY: All requirements fulfilled since this function is `__init`.
+        unsafe { self.0.__pinned_init(slot)? };
+        // SAFETY: The above call initialized `slot` and we still have unique access.
+        (self.1)(unsafe { &mut *slot }).map_err(|e| {
+            // SAFETY: `slot` was initialized above.
+            unsafe { core::ptr::drop_in_place(slot) };
+            e
+        })
+    }
+}
+
+// SAFETY: `__pinned_init` behaves exactly the same as `__init`.
+unsafe impl<T: ?Sized, E, I, F> PinInit<T, E> for ChainInit<I, F, T, E>
+where
+    I: Init<T, E>,
+    F: FnOnce(&mut T) -> Result<(), E>,
+{
+    unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
+        // SAFETY: `__init` has less strict requirements compared to `__pinned_init`.
+        unsafe { self.__init(slot) }
+    }
+}
+
+/// Creates a new [`PinInit<T, E>`] from the given closure.
+///
+/// # Safety
+///
+/// The closure:
+/// - returns `Ok(())` if it initialized every field of `slot`,
+/// - returns `Err(err)` if it encountered an error and then cleaned `slot`, this means:
+///     - `slot` can be deallocated without UB occurring,
+///     - `slot` does not need to be dropped,
+///     - `slot` is not partially initialized.
+/// - may assume that the `slot` does not move if `T: !Unpin`,
+/// - while constructing the `T` at `slot` it upholds the pinning invariants of `T`.
+#[inline]
+pub const unsafe fn pin_init_from_closure<T: ?Sized, E>(
+    f: impl FnOnce(*mut T) -> Result<(), E>,
+) -> impl PinInit<T, E> {
+    __internal::InitClosure(f, PhantomData)
+}
+
+/// Creates a new [`Init<T, E>`] from the given closure.
+///
+/// # Safety
+///
+/// The closure:
+/// - returns `Ok(())` if it initialized every field of `slot`,
+/// - returns `Err(err)` if it encountered an error and then cleaned `slot`, this means:
+///     - `slot` can be deallocated without UB occurring,
+///     - `slot` does not need to be dropped,
+///     - `slot` is not partially initialized.
+/// - the `slot` may move after initialization.
+/// - while constructing the `T` at `slot` it upholds the pinning invariants of `T`.
+#[inline]
+pub const unsafe fn init_from_closure<T: ?Sized, E>(
+    f: impl FnOnce(*mut T) -> Result<(), E>,
+) -> impl Init<T, E> {
+    __internal::InitClosure(f, PhantomData)
+}
+
+/// An initializer that leaves the memory uninitialized.
+///
+/// The initializer is a no-op. The `slot` memory is not changed.
+#[inline]
+pub fn uninit<T, E>() -> impl Init<MaybeUninit<T>, E> {
+    // SAFETY: The memory is allowed to be uninitialized.
+    unsafe { init_from_closure(|_| Ok(())) }
+}
+
+/// Initializes an array by initializing each element via the provided initializer.
+///
+/// # Examples
+///
+/// ```rust
+/// use kernel::{error::Error, init::init_array_from_fn};
+/// let array: Box<[usize; 1_000]>= Box::init::<Error>(init_array_from_fn(|i| i)).unwrap();
+/// assert_eq!(array.len(), 1_000);
+/// ```
+pub fn init_array_from_fn<I, const N: usize, T, E>(
+    mut make_init: impl FnMut(usize) -> I,
+) -> impl Init<[T; N], E>
+where
+    I: Init<T, E>,
+{
+    let init = move |slot: *mut [T; N]| {
+        let slot = slot.cast::<T>();
+        // Counts the number of initialized elements and when dropped drops that many elements from
+        // `slot`.
+        let mut init_count = ScopeGuard::new_with_data(0, |i| {
+            // We now free every element that has been initialized before:
+            // SAFETY: The loop initialized exactly the values from 0..i and since we
+            // return `Err` below, the caller will consider the memory at `slot` as
+            // uninitialized.
+            unsafe { ptr::drop_in_place(ptr::slice_from_raw_parts_mut(slot, i)) };
+        });
+        for i in 0..N {
+            let init = make_init(i);
+            // SAFETY: Since 0 <= `i` < N, it is still in bounds of `[T; N]`.
+            let ptr = unsafe { slot.add(i) };
+            // SAFETY: The pointer is derived from `slot` and thus satisfies the `__init`
+            // requirements.
+            unsafe { init.__init(ptr) }?;
+            *init_count += 1;
+        }
+        init_count.dismiss();
+        Ok(())
+    };
+    // SAFETY: The initializer above initializes every element of the array. On failure it drops
+    // any initialized elements and returns `Err`.
+    unsafe { init_from_closure(init) }
+}
+
+/// Initializes an array by initializing each element via the provided initializer.
+///
+/// # Examples
+///
+/// ```rust
+/// use kernel::{sync::{Arc, Mutex}, init::pin_init_array_from_fn, new_mutex};
+/// let array: Arc<[Mutex<usize>; 1_000]>=
+///     Arc::pin_init(pin_init_array_from_fn(|i| new_mutex!(i))).unwrap();
+/// assert_eq!(array.len(), 1_000);
+/// ```
+pub fn pin_init_array_from_fn<I, const N: usize, T, E>(
+    mut make_init: impl FnMut(usize) -> I,
+) -> impl PinInit<[T; N], E>
+where
+    I: PinInit<T, E>,
+{
+    let init = move |slot: *mut [T; N]| {
+        let slot = slot.cast::<T>();
+        // Counts the number of initialized elements and when dropped drops that many elements from
+        // `slot`.
+        let mut init_count = ScopeGuard::new_with_data(0, |i| {
+            // We now free every element that has been initialized before:
+            // SAFETY: The loop initialized exactly the values from 0..i and since we
+            // return `Err` below, the caller will consider the memory at `slot` as
+            // uninitialized.
+            unsafe { ptr::drop_in_place(ptr::slice_from_raw_parts_mut(slot, i)) };
+        });
+        for i in 0..N {
+            let init = make_init(i);
+            // SAFETY: Since 0 <= `i` < N, it is still in bounds of `[T; N]`.
+            let ptr = unsafe { slot.add(i) };
+            // SAFETY: The pointer is derived from `slot` and thus satisfies the `__init`
+            // requirements.
+            unsafe { init.__pinned_init(ptr) }?;
+            *init_count += 1;
+        }
+        init_count.dismiss();
+        Ok(())
+    };
+    // SAFETY: The initializer above initializes every element of the array. On failure it drops
+    // any initialized elements and returns `Err`.
+    unsafe { pin_init_from_closure(init) }
+}
+
+// SAFETY: Every type can be initialized by-value.
+unsafe impl<T, E> Init<T, E> for T {
+    unsafe fn __init(self, slot: *mut T) -> Result<(), E> {
+        unsafe { slot.write(self) };
+        Ok(())
+    }
+}
+
+// SAFETY: Every type can be initialized by-value. `__pinned_init` calls `__init`.
+unsafe impl<T, E> PinInit<T, E> for T {
+    unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
+        unsafe { self.__init(slot) }
+    }
+}
+
+/// Smart pointer that can initialize memory in-place.
+pub trait InPlaceInit<T>: Sized {
+    /// Use the given pin-initializer to pin-initialize a `T` inside of a new smart pointer of this
+    /// type.
+    ///
+    /// If `T: !Unpin` it will not be able to move afterwards.
+    fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E>
+    where
+        E: From<AllocError>;
+
+    /// Use the given pin-initializer to pin-initialize a `T` inside of a new smart pointer of this
+    /// type.
+    ///
+    /// If `T: !Unpin` it will not be able to move afterwards.
+    fn pin_init<E>(init: impl PinInit<T, E>) -> error::Result<Pin<Self>>
+    where
+        Error: From<E>,
+    {
+        // SAFETY: We delegate to `init` and only change the error type.
+        let init = unsafe {
+            pin_init_from_closure(|slot| init.__pinned_init(slot).map_err(|e| Error::from(e)))
+        };
+        Self::try_pin_init(init)
+    }
+
+    /// Use the given initializer to in-place initialize a `T`.
+    fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E>
+    where
+        E: From<AllocError>;
+
+    /// Use the given initializer to in-place initialize a `T`.
+    fn init<E>(init: impl Init<T, E>) -> error::Result<Self>
+    where
+        Error: From<E>,
+    {
+        // SAFETY: We delegate to `init` and only change the error type.
+        let init = unsafe {
+            init_from_closure(|slot| init.__pinned_init(slot).map_err(|e| Error::from(e)))
+        };
+        Self::try_init(init)
+    }
+}
+
+impl<T> InPlaceInit<T> for Box<T> {
+    #[inline]
+    fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E>
+    where
+        E: From<AllocError>,
+    {
+        let mut this = Box::try_new_uninit()?;
+        let slot = this.as_mut_ptr();
+        // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
+        // slot is valid and will not be moved, because we pin it later.
+        unsafe { init.__pinned_init(slot)? };
+        // SAFETY: All fields have been initialized.
+        Ok(unsafe { this.assume_init() }.into())
+    }
+
+    #[inline]
+    fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E>
+    where
+        E: From<AllocError>,
+    {
+        let mut this = Box::try_new_uninit()?;
+        let slot = this.as_mut_ptr();
+        // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
+        // slot is valid.
+        unsafe { init.__init(slot)? };
+        // SAFETY: All fields have been initialized.
+        Ok(unsafe { this.assume_init() })
+    }
+}
+
+impl<T> InPlaceInit<T> for UniqueArc<T> {
+    #[inline]
+    fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E>
+    where
+        E: From<AllocError>,
+    {
+        let mut this = UniqueArc::try_new_uninit()?;
+        let slot = this.as_mut_ptr();
+        // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
+        // slot is valid and will not be moved, because we pin it later.
+        unsafe { init.__pinned_init(slot)? };
+        // SAFETY: All fields have been initialized.
+        Ok(unsafe { this.assume_init() }.into())
+    }
+
+    #[inline]
+    fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E>
+    where
+        E: From<AllocError>,
+    {
+        let mut this = UniqueArc::try_new_uninit()?;
+        let slot = this.as_mut_ptr();
+        // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
+        // slot is valid.
+        unsafe { init.__init(slot)? };
+        // SAFETY: All fields have been initialized.
+        Ok(unsafe { this.assume_init() })
+    }
+}
+
+/// Trait facilitating pinned destruction.
+///
+/// Use [`pinned_drop`] to implement this trait safely:
+///
+/// ```rust
+/// # use kernel::sync::Mutex;
+/// use kernel::macros::pinned_drop;
+/// use core::pin::Pin;
+/// #[pin_data(PinnedDrop)]
+/// struct Foo {
+///     #[pin]
+///     mtx: Mutex<usize>,
+/// }
+///
+/// #[pinned_drop]
+/// impl PinnedDrop for Foo {
+///     fn drop(self: Pin<&mut Self>) {
+///         pr_info!("Foo is being dropped!");
+///     }
+/// }
+/// ```
+///
+/// # Safety
+///
+/// This trait must be implemented via the [`pinned_drop`] proc-macro attribute on the impl.
+///
+/// [`pinned_drop`]: kernel::macros::pinned_drop
+pub unsafe trait PinnedDrop: __internal::HasPinData {
+    /// Executes the pinned destructor of this type.
+    ///
+    /// While this function is marked safe, it is actually unsafe to call it manually. For this
+    /// reason it takes an additional parameter. This type can only be constructed by `unsafe` code
+    /// and thus prevents this function from being called where it should not.
+    ///
+    /// This extra parameter will be generated by the `#[pinned_drop]` proc-macro attribute
+    /// automatically.
+    fn drop(self: Pin<&mut Self>, only_call_from_drop: __internal::OnlyCallFromDrop);
+}
+
+/// Marker trait for types that can be initialized by writing just zeroes.
+///
+/// # Safety
+///
+/// The bit pattern consisting of only zeroes is a valid bit pattern for this type. In other words,
+/// this is not UB:
+///
+/// ```rust,ignore
+/// let val: Self = unsafe { core::mem::zeroed() };
+/// ```
+pub unsafe trait Zeroable {}
+
+/// Create a new zeroed T.
+///
+/// The returned initializer will write `0x00` to every byte of the given `slot`.
+#[inline]
+pub fn zeroed<T: Zeroable>() -> impl Init<T> {
+    // SAFETY: Because `T: Zeroable`, all bytes zero is a valid bit pattern for `T`
+    // and because we write all zeroes, the memory is initialized.
+    unsafe {
+        init_from_closure(|slot: *mut T| {
+            slot.write_bytes(0, 1);
+            Ok(())
+        })
+    }
+}
+
+macro_rules! impl_zeroable {
+    ($($({$($generics:tt)*})? $t:ty, )*) => {
+        $(unsafe impl$($($generics)*)? Zeroable for $t {})*
+    };
+}
+
+impl_zeroable! {
+    // SAFETY: All primitives that are allowed to be zero.
+    bool,
+    char,
+    u8, u16, u32, u64, u128, usize,
+    i8, i16, i32, i64, i128, isize,
+    f32, f64,
+
+    // SAFETY: These are ZSTs, there is nothing to zero.
+    {<T: ?Sized>} PhantomData<T>, core::marker::PhantomPinned, Infallible, (),
+
+    // SAFETY: Type is allowed to take any value, including all zeros.
+    {<T>} MaybeUninit<T>,
+    // SAFETY: Type is allowed to take any value, including all zeros.
+    {<T>} Opaque<T>,
+
+    // SAFETY: `T: Zeroable` and `UnsafeCell` is `repr(transparent)`.
+    {<T: ?Sized + Zeroable>} UnsafeCell<T>,
+
+    // SAFETY: All zeros is equivalent to `None` (option layout optimization guarantee).
+    Option<NonZeroU8>, Option<NonZeroU16>, Option<NonZeroU32>, Option<NonZeroU64>,
+    Option<NonZeroU128>, Option<NonZeroUsize>,
+    Option<NonZeroI8>, Option<NonZeroI16>, Option<NonZeroI32>, Option<NonZeroI64>,
+    Option<NonZeroI128>, Option<NonZeroIsize>,
+
+    // SAFETY: All zeros is equivalent to `None` (option layout optimization guarantee).
+    //
+    // In this case we are allowed to use `T: ?Sized`, since all zeros is the `None` variant.
+    {<T: ?Sized>} Option<NonNull<T>>,
+    {<T: ?Sized>} Option<Box<T>>,
+
+    // SAFETY: `null` pointer is valid.
+    //
+    // We cannot use `T: ?Sized`, since the VTABLE pointer part of fat pointers is not allowed to be
+    // null.
+    //
+    // When `Pointee` gets stabilized, we could use
+    // `T: ?Sized where <T as Pointee>::Metadata: Zeroable`
+    {<T>} *mut T, {<T>} *const T,
+
+    // SAFETY: `null` pointer is valid and the metadata part of these fat pointers is allowed to be
+    // zero.
+    {<T>} *mut [T], {<T>} *const [T], *mut str, *const str,
+
+    // SAFETY: `T` is `Zeroable`.
+    {<const N: usize, T: Zeroable>} [T; N], {<T: Zeroable>} Wrapping<T>,
+}
+
+macro_rules! impl_tuple_zeroable {
+    ($(,)?) => {};
+    ($first:ident, $($t:ident),* $(,)?) => {
+        // SAFETY: All elements are zeroable and padding can be zero.
+        unsafe impl<$first: Zeroable, $($t: Zeroable),*> Zeroable for ($first, $($t),*) {}
+        impl_tuple_zeroable!($($t),* ,);
+    }
+}
+
+impl_tuple_zeroable!(A, B, C, D, E, F, G, H, I, J);
diff --git a/rust/kernel/init/__internal.rs b/rust/kernel/init/__internal.rs
new file mode 100644
index 0000000000..db3372619e
--- /dev/null
+++ b/rust/kernel/init/__internal.rs
@@ -0,0 +1,230 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! This module contains API-internal items for pin-init.
+//!
+//! These items must not be used outside of
+//! - `kernel/init.rs`
+//! - `macros/pin_data.rs`
+//! - `macros/pinned_drop.rs`
+
+use super::*;
+
+/// See the [nomicon] for what subtyping is. See also [this table].
+///
+/// [nomicon]: https://doc.rust-lang.org/nomicon/subtyping.html
+/// [this table]: https://doc.rust-lang.org/nomicon/phantom-data.html#table-of-phantomdata-patterns
+pub(super) type Invariant<T> = PhantomData<fn(*mut T) -> *mut T>;
+
+/// This is the module-internal type implementing `PinInit` and `Init`. It is unsafe to create this
+/// type, since the closure needs to fulfill the same safety requirement as the
+/// `__pinned_init`/`__init` functions.
+pub(crate) struct InitClosure<F, T: ?Sized, E>(pub(crate) F, pub(crate) Invariant<(E, T)>);
+
+// SAFETY: While constructing the `InitClosure`, the user promised that it upholds the
+// `__init` invariants.
+unsafe impl<T: ?Sized, F, E> Init<T, E> for InitClosure<F, T, E>
+where
+    F: FnOnce(*mut T) -> Result<(), E>,
+{
+    #[inline]
+    unsafe fn __init(self, slot: *mut T) -> Result<(), E> {
+        (self.0)(slot)
+    }
+}
+
+// SAFETY: While constructing the `InitClosure`, the user promised that it upholds the
+// `__pinned_init` invariants.
+unsafe impl<T: ?Sized, F, E> PinInit<T, E> for InitClosure<F, T, E>
+where
+    F: FnOnce(*mut T) -> Result<(), E>,
+{
+    #[inline]
+    unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
+        (self.0)(slot)
+    }
+}
+
+/// This trait is only implemented via the `#[pin_data]` proc-macro. It is used to facilitate
+/// the pin projections within the initializers.
+///
+/// # Safety
+///
+/// Only the `init` module is allowed to use this trait.
+pub unsafe trait HasPinData {
+    type PinData: PinData;
+
+    unsafe fn __pin_data() -> Self::PinData;
+}
+
+/// Marker trait for pinning data of structs.
+///
+/// # Safety
+///
+/// Only the `init` module is allowed to use this trait.
+pub unsafe trait PinData: Copy {
+    type Datee: ?Sized + HasPinData;
+
+    /// Type inference helper function.
+    fn make_closure<F, O, E>(self, f: F) -> F
+    where
+        F: FnOnce(*mut Self::Datee) -> Result<O, E>,
+    {
+        f
+    }
+}
+
+/// This trait is automatically implemented for every type. It aims to provide the same type
+/// inference help as `HasPinData`.
+///
+/// # Safety
+///
+/// Only the `init` module is allowed to use this trait.
+pub unsafe trait HasInitData {
+    type InitData: InitData;
+
+    unsafe fn __init_data() -> Self::InitData;
+}
+
+/// Same function as `PinData`, but for arbitrary data.
+///
+/// # Safety
+///
+/// Only the `init` module is allowed to use this trait.
+pub unsafe trait InitData: Copy {
+    type Datee: ?Sized + HasInitData;
+
+    /// Type inference helper function.
+    fn make_closure<F, O, E>(self, f: F) -> F
+    where
+        F: FnOnce(*mut Self::Datee) -> Result<O, E>,
+    {
+        f
+    }
+}
+
+pub struct AllData<T: ?Sized>(PhantomData<fn(Box<T>) -> Box<T>>);
+
+impl<T: ?Sized> Clone for AllData<T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<T: ?Sized> Copy for AllData<T> {}
+
+unsafe impl<T: ?Sized> InitData for AllData<T> {
+    type Datee = T;
+}
+
+unsafe impl<T: ?Sized> HasInitData for T {
+    type InitData = AllData<T>;
+
+    unsafe fn __init_data() -> Self::InitData {
+        AllData(PhantomData)
+    }
+}
+
+/// Stack initializer helper type. Use [`stack_pin_init`] instead of this primitive.
+///
+/// # Invariants
+///
+/// If `self.is_init` is true, then `self.value` is initialized.
+///
+/// [`stack_pin_init`]: kernel::stack_pin_init
+pub struct StackInit<T> {
+    value: MaybeUninit<T>,
+    is_init: bool,
+}
+
+impl<T> Drop for StackInit<T> {
+    #[inline]
+    fn drop(&mut self) {
+        if self.is_init {
+            // SAFETY: As we are being dropped, we only call this once. And since `self.is_init` is
+            // true, `self.value` is initialized.
+            unsafe { self.value.assume_init_drop() };
+        }
+    }
+}
+
+impl<T> StackInit<T> {
+    /// Creates a new [`StackInit<T>`] that is uninitialized. Use [`stack_pin_init`] instead of this
+    /// primitive.
+    ///
+    /// [`stack_pin_init`]: kernel::stack_pin_init
+    #[inline]
+    pub fn uninit() -> Self {
+        Self {
+            value: MaybeUninit::uninit(),
+            is_init: false,
+        }
+    }
+
+    /// Initializes the contents and returns the result.
+    #[inline]
+    pub fn init<E>(self: Pin<&mut Self>, init: impl PinInit<T, E>) -> Result<Pin<&mut T>, E> {
+        // SAFETY: We never move out of `this`.
+        let this = unsafe { Pin::into_inner_unchecked(self) };
+        // The value is currently initialized, so it needs to be dropped before we can reuse
+        // the memory (this is a safety guarantee of `Pin`).
+        if this.is_init {
+            this.is_init = false;
+            // SAFETY: `this.is_init` was true and therefore `this.value` is initialized.
+            unsafe { this.value.assume_init_drop() };
+        }
+        // SAFETY: The memory slot is valid and this type ensures that it will stay pinned.
+        unsafe { init.__pinned_init(this.value.as_mut_ptr())? };
+        // INVARIANT: `this.value` is initialized above.
+        this.is_init = true;
+        // SAFETY: The slot is now pinned, since we will never give access to `&mut T`.
+        Ok(unsafe { Pin::new_unchecked(this.value.assume_init_mut()) })
+    }
+}
+
+/// When a value of this type is dropped, it drops a `T`.
+///
+/// Can be forgotten to prevent the drop.
+pub struct DropGuard<T: ?Sized> {
+    ptr: *mut T,
+}
+
+impl<T: ?Sized> DropGuard<T> {
+    /// Creates a new [`DropGuard<T>`]. It will [`ptr::drop_in_place`] `ptr` when it gets dropped.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must be a valid pointer.
+    ///
+    /// It is the callers responsibility that `self` will only get dropped if the pointee of `ptr`:
+    /// - has not been dropped,
+    /// - is not accessible by any other means,
+    /// - will not be dropped by any other means.
+    #[inline]
+    pub unsafe fn new(ptr: *mut T) -> Self {
+        Self { ptr }
+    }
+}
+
+impl<T: ?Sized> Drop for DropGuard<T> {
+    #[inline]
+    fn drop(&mut self) {
+        // SAFETY: A `DropGuard` can only be constructed using the unsafe `new` function
+        // ensuring that this operation is safe.
+        unsafe { ptr::drop_in_place(self.ptr) }
+    }
+}
+
+/// Token used by `PinnedDrop` to prevent calling the function without creating this unsafely
+/// created struct. This is needed, because the `drop` function is safe, but should not be called
+/// manually.
+pub struct OnlyCallFromDrop(());
+
+impl OnlyCallFromDrop {
+    /// # Safety
+    ///
+    /// This function should only be called from the [`Drop::drop`] function and only be used to
+    /// delegate the destruction to the pinned destructor [`PinnedDrop::drop`] of the same type.
+    pub unsafe fn new() -> Self {
+        Self(())
+    }
+}
diff --git a/rust/kernel/init/macros.rs b/rust/kernel/init/macros.rs
new file mode 100644
index 0000000000..cb6e61b6c5
--- /dev/null
+++ b/rust/kernel/init/macros.rs
@@ -0,0 +1,1383 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! This module provides the macros that actually implement the proc-macros `pin_data` and
+//! `pinned_drop`. It also contains `__init_internal` the implementation of the `{try_}{pin_}init!`
+//! macros.
+//!
+//! These macros should never be called directly, since they expect their input to be
+//! in a certain format which is internal. If used incorrectly, these macros can lead to UB even in
+//! safe code! Use the public facing macros instead.
+//!
+//! This architecture has been chosen because the kernel does not yet have access to `syn` which
+//! would make matters a lot easier for implementing these as proc-macros.
+//!
+//! # Macro expansion example
+//!
+//! This section is intended for readers trying to understand the macros in this module and the
+//! `pin_init!` macros from `init.rs`.
+//!
+//! We will look at the following example:
+//!
+//! ```rust,ignore
+//! # use kernel::init::*;
+//! # use core::pin::Pin;
+//! #[pin_data]
+//! #[repr(C)]
+//! struct Bar<T> {
+//!     #[pin]
+//!     t: T,
+//!     pub x: usize,
+//! }
+//!
+//! impl<T> Bar<T> {
+//!     fn new(t: T) -> impl PinInit<Self> {
+//!         pin_init!(Self { t, x: 0 })
+//!     }
+//! }
+//!
+//! #[pin_data(PinnedDrop)]
+//! struct Foo {
+//!     a: usize,
+//!     #[pin]
+//!     b: Bar<u32>,
+//! }
+//!
+//! #[pinned_drop]
+//! impl PinnedDrop for Foo {
+//!     fn drop(self: Pin<&mut Self>) {
+//!         pr_info!("{self:p} is getting dropped.");
+//!     }
+//! }
+//!
+//! let a = 42;
+//! let initializer = pin_init!(Foo {
+//!     a,
+//!     b <- Bar::new(36),
+//! });
+//! ```
+//!
+//! This example includes the most common and important features of the pin-init API.
+//!
+//! Below you can find individual section about the different macro invocations. Here are some
+//! general things we need to take into account when designing macros:
+//! - use global paths, similarly to file paths, these start with the separator: `::core::panic!()`
+//!   this ensures that the correct item is used, since users could define their own `mod core {}`
+//!   and then their own `panic!` inside to execute arbitrary code inside of our macro.
+//! - macro `unsafe` hygiene: we need to ensure that we do not expand arbitrary, user-supplied
+//!   expressions inside of an `unsafe` block in the macro, because this would allow users to do
+//!   `unsafe` operations without an associated `unsafe` block.
+//!
+//! ## `#[pin_data]` on `Bar`
+//!
+//! This macro is used to specify which fields are structurally pinned and which fields are not. It
+//! is placed on the struct definition and allows `#[pin]` to be placed on the fields.
+//!
+//! Here is the definition of `Bar` from our example:
+//!
+//! ```rust,ignore
+//! # use kernel::init::*;
+//! #[pin_data]
+//! #[repr(C)]
+//! struct Bar<T> {
+//!     #[pin]
+//!     t: T,
+//!     pub x: usize,
+//! }
+//! ```
+//!
+//! This expands to the following code:
+//!
+//! ```rust,ignore
+//! // Firstly the normal definition of the struct, attributes are preserved:
+//! #[repr(C)]
+//! struct Bar<T> {
+//!     t: T,
+//!     pub x: usize,
+//! }
+//! // Then an anonymous constant is defined, this is because we do not want any code to access the
+//! // types that we define inside:
+//! const _: () = {
+//!     // We define the pin-data carrying struct, it is a ZST and needs to have the same generics,
+//!     // since we need to implement access functions for each field and thus need to know its
+//!     // type.
+//!     struct __ThePinData<T> {
+//!         __phantom: ::core::marker::PhantomData<fn(Bar<T>) -> Bar<T>>,
+//!     }
+//!     // We implement `Copy` for the pin-data struct, since all functions it defines will take
+//!     // `self` by value.
+//!     impl<T> ::core::clone::Clone for __ThePinData<T> {
+//!         fn clone(&self) -> Self {
+//!             *self
+//!         }
+//!     }
+//!     impl<T> ::core::marker::Copy for __ThePinData<T> {}
+//!     // For every field of `Bar`, the pin-data struct will define a function with the same name
+//!     // and accessor (`pub` or `pub(crate)` etc.). This function will take a pointer to the
+//!     // field (`slot`) and a `PinInit` or `Init` depending on the projection kind of the field
+//!     // (if pinning is structural for the field, then `PinInit` otherwise `Init`).
+//!     #[allow(dead_code)]
+//!     impl<T> __ThePinData<T> {
+//!         unsafe fn t<E>(
+//!             self,
+//!             slot: *mut T,
+//!             // Since `t` is `#[pin]`, this is `PinInit`.
+//!             init: impl ::kernel::init::PinInit<T, E>,
+//!         ) -> ::core::result::Result<(), E> {
+//!             unsafe { ::kernel::init::PinInit::__pinned_init(init, slot) }
+//!         }
+//!         pub unsafe fn x<E>(
+//!             self,
+//!             slot: *mut usize,
+//!             // Since `x` is not `#[pin]`, this is `Init`.
+//!             init: impl ::kernel::init::Init<usize, E>,
+//!         ) -> ::core::result::Result<(), E> {
+//!             unsafe { ::kernel::init::Init::__init(init, slot) }
+//!         }
+//!     }
+//!     // Implement the internal `HasPinData` trait that associates `Bar` with the pin-data struct
+//!     // that we constructed above.
+//!     unsafe impl<T> ::kernel::init::__internal::HasPinData for Bar<T> {
+//!         type PinData = __ThePinData<T>;
+//!         unsafe fn __pin_data() -> Self::PinData {
+//!             __ThePinData {
+//!                 __phantom: ::core::marker::PhantomData,
+//!             }
+//!         }
+//!     }
+//!     // Implement the internal `PinData` trait that marks the pin-data struct as a pin-data
+//!     // struct. This is important to ensure that no user can implement a rouge `__pin_data`
+//!     // function without using `unsafe`.
+//!     unsafe impl<T> ::kernel::init::__internal::PinData for __ThePinData<T> {
+//!         type Datee = Bar<T>;
+//!     }
+//!     // Now we only want to implement `Unpin` for `Bar` when every structurally pinned field is
+//!     // `Unpin`. In other words, whether `Bar` is `Unpin` only depends on structurally pinned
+//!     // fields (those marked with `#[pin]`). These fields will be listed in this struct, in our
+//!     // case no such fields exist, hence this is almost empty. The two phantomdata fields exist
+//!     // for two reasons:
+//!     // - `__phantom`: every generic must be used, since we cannot really know which generics
+//!     //   are used, we declere all and then use everything here once.
+//!     // - `__phantom_pin`: uses the `'__pin` lifetime and ensures that this struct is invariant
+//!     //   over it. The lifetime is needed to work around the limitation that trait bounds must
+//!     //   not be trivial, e.g. the user has a `#[pin] PhantomPinned` field -- this is
+//!     //   unconditionally `!Unpin` and results in an error. The lifetime tricks the compiler
+//!     //   into accepting these bounds regardless.
+//!     #[allow(dead_code)]
+//!     struct __Unpin<'__pin, T> {
+//!         __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
+//!         __phantom: ::core::marker::PhantomData<fn(Bar<T>) -> Bar<T>>,
+//!         // Our only `#[pin]` field is `t`.
+//!         t: T,
+//!     }
+//!     #[doc(hidden)]
+//!     impl<'__pin, T> ::core::marker::Unpin for Bar<T>
+//!     where
+//!         __Unpin<'__pin, T>: ::core::marker::Unpin,
+//!     {}
+//!     // Now we need to ensure that `Bar` does not implement `Drop`, since that would give users
+//!     // access to `&mut self` inside of `drop` even if the struct was pinned. This could lead to
+//!     // UB with only safe code, so we disallow this by giving a trait implementation error using
+//!     // a direct impl and a blanket implementation.
+//!     trait MustNotImplDrop {}
+//!     // Normally `Drop` bounds do not have the correct semantics, but for this purpose they do
+//!     // (normally people want to know if a type has any kind of drop glue at all, here we want
+//!     // to know if it has any kind of custom drop glue, which is exactly what this bound does).
+//!     #[allow(drop_bounds)]
+//!     impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
+//!     impl<T> MustNotImplDrop for Bar<T> {}
+//!     // Here comes a convenience check, if one implemented `PinnedDrop`, but forgot to add it to
+//!     // `#[pin_data]`, then this will error with the same mechanic as above, this is not needed
+//!     // for safety, but a good sanity check, since no normal code calls `PinnedDrop::drop`.
+//!     #[allow(non_camel_case_types)]
+//!     trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
+//!     impl<
+//!         T: ::kernel::init::PinnedDrop,
+//!     > UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
+//!     impl<T> UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for Bar<T> {}
+//! };
+//! ```
+//!
+//! ## `pin_init!` in `impl Bar`
+//!
+//! This macro creates an pin-initializer for the given struct. It requires that the struct is
+//! annotated by `#[pin_data]`.
+//!
+//! Here is the impl on `Bar` defining the new function:
+//!
+//! ```rust,ignore
+//! impl<T> Bar<T> {
+//!     fn new(t: T) -> impl PinInit<Self> {
+//!         pin_init!(Self { t, x: 0 })
+//!     }
+//! }
+//! ```
+//!
+//! This expands to the following code:
+//!
+//! ```rust,ignore
+//! impl<T> Bar<T> {
+//!     fn new(t: T) -> impl PinInit<Self> {
+//!         {
+//!             // We do not want to allow arbitrary returns, so we declare this type as the `Ok`
+//!             // return type and shadow it later when we insert the arbitrary user code. That way
+//!             // there will be no possibility of returning without `unsafe`.
+//!             struct __InitOk;
+//!             // Get the data about fields from the supplied type.
+//!             // - the function is unsafe, hence the unsafe block
+//!             // - we `use` the `HasPinData` trait in the block, it is only available in that
+//!             //   scope.
+//!             let data = unsafe {
+//!                 use ::kernel::init::__internal::HasPinData;
+//!                 Self::__pin_data()
+//!             };
+//!             // Ensure that `data` really is of type `PinData` and help with type inference:
+//!             let init = ::kernel::init::__internal::PinData::make_closure::<
+//!                 _,
+//!                 __InitOk,
+//!                 ::core::convert::Infallible,
+//!             >(data, move |slot| {
+//!                 {
+//!                     // Shadow the structure so it cannot be used to return early. If a user
+//!                     // tries to write `return Ok(__InitOk)`, then they get a type error,
+//!                     // since that will refer to this struct instead of the one defined
+//!                     // above.
+//!                     struct __InitOk;
+//!                     // This is the expansion of `t,`, which is syntactic sugar for `t: t,`.
+//!                     {
+//!                         unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).t), t) };
+//!                     }
+//!                     // Since initialization could fail later (not in this case, since the
+//!                     // error type is `Infallible`) we will need to drop this field if there
+//!                     // is an error later. This `DropGuard` will drop the field when it gets
+//!                     // dropped and has not yet been forgotten.
+//!                     let t = unsafe {
+//!                         ::pinned_init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).t))
+//!                     };
+//!                     // Expansion of `x: 0,`:
+//!                     // Since this can be an arbitrary expression we cannot place it inside
+//!                     // of the `unsafe` block, so we bind it here.
+//!                     {
+//!                         let x = 0;
+//!                         unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).x), x) };
+//!                     }
+//!                     // We again create a `DropGuard`.
+//!                     let x = unsafe {
+//!                         ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).x))
+//!                     };
+//!                     // Since initialization has successfully completed, we can now forget
+//!                     // the guards. This is not `mem::forget`, since we only have
+//!                     // `&DropGuard`.
+//!                     ::core::mem::forget(x);
+//!                     ::core::mem::forget(t);
+//!                     // Here we use the type checker to ensure that every field has been
+//!                     // initialized exactly once, since this is `if false` it will never get
+//!                     // executed, but still type-checked.
+//!                     // Additionally we abuse `slot` to automatically infer the correct type
+//!                     // for the struct. This is also another check that every field is
+//!                     // accessible from this scope.
+//!                     #[allow(unreachable_code, clippy::diverging_sub_expression)]
+//!                     let _ = || {
+//!                         unsafe {
+//!                             ::core::ptr::write(
+//!                                 slot,
+//!                                 Self {
+//!                                     // We only care about typecheck finding every field
+//!                                     // here, the expression does not matter, just conjure
+//!                                     // one using `panic!()`:
+//!                                     t: ::core::panic!(),
+//!                                     x: ::core::panic!(),
+//!                                 },
+//!                             );
+//!                         };
+//!                     };
+//!                 }
+//!                 // We leave the scope above and gain access to the previously shadowed
+//!                 // `__InitOk` that we need to return.
+//!                 Ok(__InitOk)
+//!             });
+//!             // Change the return type from `__InitOk` to `()`.
+//!             let init = move |
+//!                 slot,
+//!             | -> ::core::result::Result<(), ::core::convert::Infallible> {
+//!                 init(slot).map(|__InitOk| ())
+//!             };
+//!             // Construct the initializer.
+//!             let init = unsafe {
+//!                 ::kernel::init::pin_init_from_closure::<
+//!                     _,
+//!                     ::core::convert::Infallible,
+//!                 >(init)
+//!             };
+//!             init
+//!         }
+//!     }
+//! }
+//! ```
+//!
+//! ## `#[pin_data]` on `Foo`
+//!
+//! Since we already took a look at `#[pin_data]` on `Bar`, this section will only explain the
+//! differences/new things in the expansion of the `Foo` definition:
+//!
+//! ```rust,ignore
+//! #[pin_data(PinnedDrop)]
+//! struct Foo {
+//!     a: usize,
+//!     #[pin]
+//!     b: Bar<u32>,
+//! }
+//! ```
+//!
+//! This expands to the following code:
+//!
+//! ```rust,ignore
+//! struct Foo {
+//!     a: usize,
+//!     b: Bar<u32>,
+//! }
+//! const _: () = {
+//!     struct __ThePinData {
+//!         __phantom: ::core::marker::PhantomData<fn(Foo) -> Foo>,
+//!     }
+//!     impl ::core::clone::Clone for __ThePinData {
+//!         fn clone(&self) -> Self {
+//!             *self
+//!         }
+//!     }
+//!     impl ::core::marker::Copy for __ThePinData {}
+//!     #[allow(dead_code)]
+//!     impl __ThePinData {
+//!         unsafe fn b<E>(
+//!             self,
+//!             slot: *mut Bar<u32>,
+//!             init: impl ::kernel::init::PinInit<Bar<u32>, E>,
+//!         ) -> ::core::result::Result<(), E> {
+//!             unsafe { ::kernel::init::PinInit::__pinned_init(init, slot) }
+//!         }
+//!         unsafe fn a<E>(
+//!             self,
+//!             slot: *mut usize,
+//!             init: impl ::kernel::init::Init<usize, E>,
+//!         ) -> ::core::result::Result<(), E> {
+//!             unsafe { ::kernel::init::Init::__init(init, slot) }
+//!         }
+//!     }
+//!     unsafe impl ::kernel::init::__internal::HasPinData for Foo {
+//!         type PinData = __ThePinData;
+//!         unsafe fn __pin_data() -> Self::PinData {
+//!             __ThePinData {
+//!                 __phantom: ::core::marker::PhantomData,
+//!             }
+//!         }
+//!     }
+//!     unsafe impl ::kernel::init::__internal::PinData for __ThePinData {
+//!         type Datee = Foo;
+//!     }
+//!     #[allow(dead_code)]
+//!     struct __Unpin<'__pin> {
+//!         __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
+//!         __phantom: ::core::marker::PhantomData<fn(Foo) -> Foo>,
+//!         b: Bar<u32>,
+//!     }
+//!     #[doc(hidden)]
+//!     impl<'__pin> ::core::marker::Unpin for Foo
+//!     where
+//!         __Unpin<'__pin>: ::core::marker::Unpin,
+//!     {}
+//!     // Since we specified `PinnedDrop` as the argument to `#[pin_data]`, we expect `Foo` to
+//!     // implement `PinnedDrop`. Thus we do not need to prevent `Drop` implementations like
+//!     // before, instead we implement `Drop` here and delegate to `PinnedDrop`.
+//!     impl ::core::ops::Drop for Foo {
+//!         fn drop(&mut self) {
+//!             // Since we are getting dropped, no one else has a reference to `self` and thus we
+//!             // can assume that we never move.
+//!             let pinned = unsafe { ::core::pin::Pin::new_unchecked(self) };
+//!             // Create the unsafe token that proves that we are inside of a destructor, this
+//!             // type is only allowed to be created in a destructor.
+//!             let token = unsafe { ::kernel::init::__internal::OnlyCallFromDrop::new() };
+//!             ::kernel::init::PinnedDrop::drop(pinned, token);
+//!         }
+//!     }
+//! };
+//! ```
+//!
+//! ## `#[pinned_drop]` on `impl PinnedDrop for Foo`
+//!
+//! This macro is used to implement the `PinnedDrop` trait, since that trait is `unsafe` and has an
+//! extra parameter that should not be used at all. The macro hides that parameter.
+//!
+//! Here is the `PinnedDrop` impl for `Foo`:
+//!
+//! ```rust,ignore
+//! #[pinned_drop]
+//! impl PinnedDrop for Foo {
+//!     fn drop(self: Pin<&mut Self>) {
+//!         pr_info!("{self:p} is getting dropped.");
+//!     }
+//! }
+//! ```
+//!
+//! This expands to the following code:
+//!
+//! ```rust,ignore
+//! // `unsafe`, full path and the token parameter are added, everything else stays the same.
+//! unsafe impl ::kernel::init::PinnedDrop for Foo {
+//!     fn drop(self: Pin<&mut Self>, _: ::kernel::init::__internal::OnlyCallFromDrop) {
+//!         pr_info!("{self:p} is getting dropped.");
+//!     }
+//! }
+//! ```
+//!
+//! ## `pin_init!` on `Foo`
+//!
+//! Since we already took a look at `pin_init!` on `Bar`, this section will only show the expansion
+//! of `pin_init!` on `Foo`:
+//!
+//! ```rust,ignore
+//! let a = 42;
+//! let initializer = pin_init!(Foo {
+//!     a,
+//!     b <- Bar::new(36),
+//! });
+//! ```
+//!
+//! This expands to the following code:
+//!
+//! ```rust,ignore
+//! let a = 42;
+//! let initializer = {
+//!     struct __InitOk;
+//!     let data = unsafe {
+//!         use ::kernel::init::__internal::HasPinData;
+//!         Foo::__pin_data()
+//!     };
+//!     let init = ::kernel::init::__internal::PinData::make_closure::<
+//!         _,
+//!         __InitOk,
+//!         ::core::convert::Infallible,
+//!     >(data, move |slot| {
+//!         {
+//!             struct __InitOk;
+//!             {
+//!                 unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).a), a) };
+//!             }
+//!             let a = unsafe {
+//!                 ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).a))
+//!             };
+//!             let init = Bar::new(36);
+//!             unsafe { data.b(::core::addr_of_mut!((*slot).b), b)? };
+//!             let b = unsafe {
+//!                 ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).b))
+//!             };
+//!             ::core::mem::forget(b);
+//!             ::core::mem::forget(a);
+//!             #[allow(unreachable_code, clippy::diverging_sub_expression)]
+//!             let _ = || {
+//!                 unsafe {
+//!                     ::core::ptr::write(
+//!                         slot,
+//!                         Foo {
+//!                             a: ::core::panic!(),
+//!                             b: ::core::panic!(),
+//!                         },
+//!                     );
+//!                 };
+//!             };
+//!         }
+//!         Ok(__InitOk)
+//!     });
+//!     let init = move |
+//!         slot,
+//!     | -> ::core::result::Result<(), ::core::convert::Infallible> {
+//!         init(slot).map(|__InitOk| ())
+//!     };
+//!     let init = unsafe {
+//!         ::kernel::init::pin_init_from_closure::<_, ::core::convert::Infallible>(init)
+//!     };
+//!     init
+//! };
+//! ```
+
+/// Creates a `unsafe impl<...> PinnedDrop for $type` block.
+///
+/// See [`PinnedDrop`] for more information.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __pinned_drop {
+    (
+        @impl_sig($($impl_sig:tt)*),
+        @impl_body(
+            $(#[$($attr:tt)*])*
+            fn drop($($sig:tt)*) {
+                $($inner:tt)*
+            }
+        ),
+    ) => {
+        unsafe $($impl_sig)* {
+            // Inherit all attributes and the type/ident tokens for the signature.
+            $(#[$($attr)*])*
+            fn drop($($sig)*, _: $crate::init::__internal::OnlyCallFromDrop) {
+                $($inner)*
+            }
+        }
+    }
+}
+
+/// This macro first parses the struct definition such that it separates pinned and not pinned
+/// fields. Afterwards it declares the struct and implement the `PinData` trait safely.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __pin_data {
+    // Proc-macro entry point, this is supplied by the proc-macro pre-parsing.
+    (parse_input:
+        @args($($pinned_drop:ident)?),
+        @sig(
+            $(#[$($struct_attr:tt)*])*
+            $vis:vis struct $name:ident
+            $(where $($whr:tt)*)?
+        ),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @body({ $($fields:tt)* }),
+    ) => {
+        // We now use token munching to iterate through all of the fields. While doing this we
+        // identify fields marked with `#[pin]`, these fields are the 'pinned fields'. The user
+        // wants these to be structurally pinned. The rest of the fields are the
+        // 'not pinned fields'. Additionally we collect all fields, since we need them in the right
+        // order to declare the struct.
+        //
+        // In this call we also put some explaining comments for the parameters.
+        $crate::__pin_data!(find_pinned_fields:
+            // Attributes on the struct itself, these will just be propagated to be put onto the
+            // struct definition.
+            @struct_attrs($(#[$($struct_attr)*])*),
+            // The visibility of the struct.
+            @vis($vis),
+            // The name of the struct.
+            @name($name),
+            // The 'impl generics', the generics that will need to be specified on the struct inside
+            // of an `impl<$ty_generics>` block.
+            @impl_generics($($impl_generics)*),
+            // The 'ty generics', the generics that will need to be specified on the impl blocks.
+            @ty_generics($($ty_generics)*),
+            // The where clause of any impl block and the declaration.
+            @where($($($whr)*)?),
+            // The remaining fields tokens that need to be processed.
+            // We add a `,` at the end to ensure correct parsing.
+            @fields_munch($($fields)* ,),
+            // The pinned fields.
+            @pinned(),
+            // The not pinned fields.
+            @not_pinned(),
+            // All fields.
+            @fields(),
+            // The accumulator containing all attributes already parsed.
+            @accum(),
+            // Contains `yes` or `` to indicate if `#[pin]` was found on the current field.
+            @is_pinned(),
+            // The proc-macro argument, this should be `PinnedDrop` or ``.
+            @pinned_drop($($pinned_drop)?),
+        );
+    };
+    (find_pinned_fields:
+        @struct_attrs($($struct_attrs:tt)*),
+        @vis($vis:vis),
+        @name($name:ident),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @where($($whr:tt)*),
+        // We found a PhantomPinned field, this should generally be pinned!
+        @fields_munch($field:ident : $($($(::)?core::)?marker::)?PhantomPinned, $($rest:tt)*),
+        @pinned($($pinned:tt)*),
+        @not_pinned($($not_pinned:tt)*),
+        @fields($($fields:tt)*),
+        @accum($($accum:tt)*),
+        // This field is not pinned.
+        @is_pinned(),
+        @pinned_drop($($pinned_drop:ident)?),
+    ) => {
+        ::core::compile_error!(concat!(
+            "The field `",
+            stringify!($field),
+            "` of type `PhantomPinned` only has an effect, if it has the `#[pin]` attribute.",
+        ));
+        $crate::__pin_data!(find_pinned_fields:
+            @struct_attrs($($struct_attrs)*),
+            @vis($vis),
+            @name($name),
+            @impl_generics($($impl_generics)*),
+            @ty_generics($($ty_generics)*),
+            @where($($whr)*),
+            @fields_munch($($rest)*),
+            @pinned($($pinned)* $($accum)* $field: ::core::marker::PhantomPinned,),
+            @not_pinned($($not_pinned)*),
+            @fields($($fields)* $($accum)* $field: ::core::marker::PhantomPinned,),
+            @accum(),
+            @is_pinned(),
+            @pinned_drop($($pinned_drop)?),
+        );
+    };
+    (find_pinned_fields:
+        @struct_attrs($($struct_attrs:tt)*),
+        @vis($vis:vis),
+        @name($name:ident),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @where($($whr:tt)*),
+        // We reached the field declaration.
+        @fields_munch($field:ident : $type:ty, $($rest:tt)*),
+        @pinned($($pinned:tt)*),
+        @not_pinned($($not_pinned:tt)*),
+        @fields($($fields:tt)*),
+        @accum($($accum:tt)*),
+        // This field is pinned.
+        @is_pinned(yes),
+        @pinned_drop($($pinned_drop:ident)?),
+    ) => {
+        $crate::__pin_data!(find_pinned_fields:
+            @struct_attrs($($struct_attrs)*),
+            @vis($vis),
+            @name($name),
+            @impl_generics($($impl_generics)*),
+            @ty_generics($($ty_generics)*),
+            @where($($whr)*),
+            @fields_munch($($rest)*),
+            @pinned($($pinned)* $($accum)* $field: $type,),
+            @not_pinned($($not_pinned)*),
+            @fields($($fields)* $($accum)* $field: $type,),
+            @accum(),
+            @is_pinned(),
+            @pinned_drop($($pinned_drop)?),
+        );
+    };
+    (find_pinned_fields:
+        @struct_attrs($($struct_attrs:tt)*),
+        @vis($vis:vis),
+        @name($name:ident),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @where($($whr:tt)*),
+        // We reached the field declaration.
+        @fields_munch($field:ident : $type:ty, $($rest:tt)*),
+        @pinned($($pinned:tt)*),
+        @not_pinned($($not_pinned:tt)*),
+        @fields($($fields:tt)*),
+        @accum($($accum:tt)*),
+        // This field is not pinned.
+        @is_pinned(),
+        @pinned_drop($($pinned_drop:ident)?),
+    ) => {
+        $crate::__pin_data!(find_pinned_fields:
+            @struct_attrs($($struct_attrs)*),
+            @vis($vis),
+            @name($name),
+            @impl_generics($($impl_generics)*),
+            @ty_generics($($ty_generics)*),
+            @where($($whr)*),
+            @fields_munch($($rest)*),
+            @pinned($($pinned)*),
+            @not_pinned($($not_pinned)* $($accum)* $field: $type,),
+            @fields($($fields)* $($accum)* $field: $type,),
+            @accum(),
+            @is_pinned(),
+            @pinned_drop($($pinned_drop)?),
+        );
+    };
+    (find_pinned_fields:
+        @struct_attrs($($struct_attrs:tt)*),
+        @vis($vis:vis),
+        @name($name:ident),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @where($($whr:tt)*),
+        // We found the `#[pin]` attr.
+        @fields_munch(#[pin] $($rest:tt)*),
+        @pinned($($pinned:tt)*),
+        @not_pinned($($not_pinned:tt)*),
+        @fields($($fields:tt)*),
+        @accum($($accum:tt)*),
+        @is_pinned($($is_pinned:ident)?),
+        @pinned_drop($($pinned_drop:ident)?),
+    ) => {
+        $crate::__pin_data!(find_pinned_fields:
+            @struct_attrs($($struct_attrs)*),
+            @vis($vis),
+            @name($name),
+            @impl_generics($($impl_generics)*),
+            @ty_generics($($ty_generics)*),
+            @where($($whr)*),
+            @fields_munch($($rest)*),
+            // We do not include `#[pin]` in the list of attributes, since it is not actually an
+            // attribute that is defined somewhere.
+            @pinned($($pinned)*),
+            @not_pinned($($not_pinned)*),
+            @fields($($fields)*),
+            @accum($($accum)*),
+            // Set this to `yes`.
+            @is_pinned(yes),
+            @pinned_drop($($pinned_drop)?),
+        );
+    };
+    (find_pinned_fields:
+        @struct_attrs($($struct_attrs:tt)*),
+        @vis($vis:vis),
+        @name($name:ident),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @where($($whr:tt)*),
+        // We reached the field declaration with visibility, for simplicity we only munch the
+        // visibility and put it into `$accum`.
+        @fields_munch($fvis:vis $field:ident $($rest:tt)*),
+        @pinned($($pinned:tt)*),
+        @not_pinned($($not_pinned:tt)*),
+        @fields($($fields:tt)*),
+        @accum($($accum:tt)*),
+        @is_pinned($($is_pinned:ident)?),
+        @pinned_drop($($pinned_drop:ident)?),
+    ) => {
+        $crate::__pin_data!(find_pinned_fields:
+            @struct_attrs($($struct_attrs)*),
+            @vis($vis),
+            @name($name),
+            @impl_generics($($impl_generics)*),
+            @ty_generics($($ty_generics)*),
+            @where($($whr)*),
+            @fields_munch($field $($rest)*),
+            @pinned($($pinned)*),
+            @not_pinned($($not_pinned)*),
+            @fields($($fields)*),
+            @accum($($accum)* $fvis),
+            @is_pinned($($is_pinned)?),
+            @pinned_drop($($pinned_drop)?),
+        );
+    };
+    (find_pinned_fields:
+        @struct_attrs($($struct_attrs:tt)*),
+        @vis($vis:vis),
+        @name($name:ident),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @where($($whr:tt)*),
+        // Some other attribute, just put it into `$accum`.
+        @fields_munch(#[$($attr:tt)*] $($rest:tt)*),
+        @pinned($($pinned:tt)*),
+        @not_pinned($($not_pinned:tt)*),
+        @fields($($fields:tt)*),
+        @accum($($accum:tt)*),
+        @is_pinned($($is_pinned:ident)?),
+        @pinned_drop($($pinned_drop:ident)?),
+    ) => {
+        $crate::__pin_data!(find_pinned_fields:
+            @struct_attrs($($struct_attrs)*),
+            @vis($vis),
+            @name($name),
+            @impl_generics($($impl_generics)*),
+            @ty_generics($($ty_generics)*),
+            @where($($whr)*),
+            @fields_munch($($rest)*),
+            @pinned($($pinned)*),
+            @not_pinned($($not_pinned)*),
+            @fields($($fields)*),
+            @accum($($accum)* #[$($attr)*]),
+            @is_pinned($($is_pinned)?),
+            @pinned_drop($($pinned_drop)?),
+        );
+    };
+    (find_pinned_fields:
+        @struct_attrs($($struct_attrs:tt)*),
+        @vis($vis:vis),
+        @name($name:ident),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @where($($whr:tt)*),
+        // We reached the end of the fields, plus an optional additional comma, since we added one
+        // before and the user is also allowed to put a trailing comma.
+        @fields_munch($(,)?),
+        @pinned($($pinned:tt)*),
+        @not_pinned($($not_pinned:tt)*),
+        @fields($($fields:tt)*),
+        @accum(),
+        @is_pinned(),
+        @pinned_drop($($pinned_drop:ident)?),
+    ) => {
+        // Declare the struct with all fields in the correct order.
+        $($struct_attrs)*
+        $vis struct $name <$($impl_generics)*>
+        where $($whr)*
+        {
+            $($fields)*
+        }
+
+        // We put the rest into this const item, because it then will not be accessible to anything
+        // outside.
+        const _: () = {
+            // We declare this struct which will host all of the projection function for our type.
+            // it will be invariant over all generic parameters which are inherited from the
+            // struct.
+            $vis struct __ThePinData<$($impl_generics)*>
+            where $($whr)*
+            {
+                __phantom: ::core::marker::PhantomData<
+                    fn($name<$($ty_generics)*>) -> $name<$($ty_generics)*>
+                >,
+            }
+
+            impl<$($impl_generics)*> ::core::clone::Clone for __ThePinData<$($ty_generics)*>
+            where $($whr)*
+            {
+                fn clone(&self) -> Self { *self }
+            }
+
+            impl<$($impl_generics)*> ::core::marker::Copy for __ThePinData<$($ty_generics)*>
+            where $($whr)*
+            {}
+
+            // Make all projection functions.
+            $crate::__pin_data!(make_pin_data:
+                @pin_data(__ThePinData),
+                @impl_generics($($impl_generics)*),
+                @ty_generics($($ty_generics)*),
+                @where($($whr)*),
+                @pinned($($pinned)*),
+                @not_pinned($($not_pinned)*),
+            );
+
+            // SAFETY: We have added the correct projection functions above to `__ThePinData` and
+            // we also use the least restrictive generics possible.
+            unsafe impl<$($impl_generics)*>
+                $crate::init::__internal::HasPinData for $name<$($ty_generics)*>
+            where $($whr)*
+            {
+                type PinData = __ThePinData<$($ty_generics)*>;
+
+                unsafe fn __pin_data() -> Self::PinData {
+                    __ThePinData { __phantom: ::core::marker::PhantomData }
+                }
+            }
+
+            unsafe impl<$($impl_generics)*>
+                $crate::init::__internal::PinData for __ThePinData<$($ty_generics)*>
+            where $($whr)*
+            {
+                type Datee = $name<$($ty_generics)*>;
+            }
+
+            // This struct will be used for the unpin analysis. Since only structurally pinned
+            // fields are relevant whether the struct should implement `Unpin`.
+            #[allow(dead_code)]
+            struct __Unpin <'__pin, $($impl_generics)*>
+            where $($whr)*
+            {
+                __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
+                __phantom: ::core::marker::PhantomData<
+                    fn($name<$($ty_generics)*>) -> $name<$($ty_generics)*>
+                >,
+                // Only the pinned fields.
+                $($pinned)*
+            }
+
+            #[doc(hidden)]
+            impl<'__pin, $($impl_generics)*> ::core::marker::Unpin for $name<$($ty_generics)*>
+            where
+                __Unpin<'__pin, $($ty_generics)*>: ::core::marker::Unpin,
+                $($whr)*
+            {}
+
+            // We need to disallow normal `Drop` implementation, the exact behavior depends on
+            // whether `PinnedDrop` was specified as the parameter.
+            $crate::__pin_data!(drop_prevention:
+                @name($name),
+                @impl_generics($($impl_generics)*),
+                @ty_generics($($ty_generics)*),
+                @where($($whr)*),
+                @pinned_drop($($pinned_drop)?),
+            );
+        };
+    };
+    // When no `PinnedDrop` was specified, then we have to prevent implementing drop.
+    (drop_prevention:
+        @name($name:ident),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @where($($whr:tt)*),
+        @pinned_drop(),
+    ) => {
+        // We prevent this by creating a trait that will be implemented for all types implementing
+        // `Drop`. Additionally we will implement this trait for the struct leading to a conflict,
+        // if it also implements `Drop`
+        trait MustNotImplDrop {}
+        #[allow(drop_bounds)]
+        impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
+        impl<$($impl_generics)*> MustNotImplDrop for $name<$($ty_generics)*>
+        where $($whr)* {}
+        // We also take care to prevent users from writing a useless `PinnedDrop` implementation.
+        // They might implement `PinnedDrop` correctly for the struct, but forget to give
+        // `PinnedDrop` as the parameter to `#[pin_data]`.
+        #[allow(non_camel_case_types)]
+        trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
+        impl<T: $crate::init::PinnedDrop>
+            UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
+        impl<$($impl_generics)*>
+            UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for $name<$($ty_generics)*>
+        where $($whr)* {}
+    };
+    // When `PinnedDrop` was specified we just implement `Drop` and delegate.
+    (drop_prevention:
+        @name($name:ident),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @where($($whr:tt)*),
+        @pinned_drop(PinnedDrop),
+    ) => {
+        impl<$($impl_generics)*> ::core::ops::Drop for $name<$($ty_generics)*>
+        where $($whr)*
+        {
+            fn drop(&mut self) {
+                // SAFETY: Since this is a destructor, `self` will not move after this function
+                // terminates, since it is inaccessible.
+                let pinned = unsafe { ::core::pin::Pin::new_unchecked(self) };
+                // SAFETY: Since this is a drop function, we can create this token to call the
+                // pinned destructor of this type.
+                let token = unsafe { $crate::init::__internal::OnlyCallFromDrop::new() };
+                $crate::init::PinnedDrop::drop(pinned, token);
+            }
+        }
+    };
+    // If some other parameter was specified, we emit a readable error.
+    (drop_prevention:
+        @name($name:ident),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @where($($whr:tt)*),
+        @pinned_drop($($rest:tt)*),
+    ) => {
+        compile_error!(
+            "Wrong parameters to `#[pin_data]`, expected nothing or `PinnedDrop`, got '{}'.",
+            stringify!($($rest)*),
+        );
+    };
+    (make_pin_data:
+        @pin_data($pin_data:ident),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @where($($whr:tt)*),
+        @pinned($($(#[$($p_attr:tt)*])* $pvis:vis $p_field:ident : $p_type:ty),* $(,)?),
+        @not_pinned($($(#[$($attr:tt)*])* $fvis:vis $field:ident : $type:ty),* $(,)?),
+    ) => {
+        // For every field, we create a projection function according to its projection type. If a
+        // field is structurally pinned, then it must be initialized via `PinInit`, if it is not
+        // structurally pinned, then it can be initialized via `Init`.
+        //
+        // The functions are `unsafe` to prevent accidentally calling them.
+        #[allow(dead_code)]
+        impl<$($impl_generics)*> $pin_data<$($ty_generics)*>
+        where $($whr)*
+        {
+            $(
+                $(#[$($p_attr)*])*
+                $pvis unsafe fn $p_field<E>(
+                    self,
+                    slot: *mut $p_type,
+                    init: impl $crate::init::PinInit<$p_type, E>,
+                ) -> ::core::result::Result<(), E> {
+                    unsafe { $crate::init::PinInit::__pinned_init(init, slot) }
+                }
+            )*
+            $(
+                $(#[$($attr)*])*
+                $fvis unsafe fn $field<E>(
+                    self,
+                    slot: *mut $type,
+                    init: impl $crate::init::Init<$type, E>,
+                ) -> ::core::result::Result<(), E> {
+                    unsafe { $crate::init::Init::__init(init, slot) }
+                }
+            )*
+        }
+    };
+}
+
+/// The internal init macro. Do not call manually!
+///
+/// This is called by the `{try_}{pin_}init!` macros with various inputs.
+///
+/// This macro has multiple internal call configurations, these are always the very first ident:
+/// - nothing: this is the base case and called by the `{try_}{pin_}init!` macros.
+/// - `with_update_parsed`: when the `..Zeroable::zeroed()` syntax has been handled.
+/// - `init_slot`: recursively creates the code that initializes all fields in `slot`.
+/// - `make_initializer`: recursively create the struct initializer that guarantees that every
+///   field has been initialized exactly once.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __init_internal {
+    (
+        @this($($this:ident)?),
+        @typ($t:path),
+        @fields($($fields:tt)*),
+        @error($err:ty),
+        // Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
+        // case.
+        @data($data:ident, $($use_data:ident)?),
+        // `HasPinData` or `HasInitData`.
+        @has_data($has_data:ident, $get_data:ident),
+        // `pin_init_from_closure` or `init_from_closure`.
+        @construct_closure($construct_closure:ident),
+        @munch_fields(),
+    ) => {
+        $crate::__init_internal!(with_update_parsed:
+            @this($($this)?),
+            @typ($t),
+            @fields($($fields)*),
+            @error($err),
+            @data($data, $($use_data)?),
+            @has_data($has_data, $get_data),
+            @construct_closure($construct_closure),
+            @zeroed(), // Nothing means default behavior.
+        )
+    };
+    (
+        @this($($this:ident)?),
+        @typ($t:path),
+        @fields($($fields:tt)*),
+        @error($err:ty),
+        // Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
+        // case.
+        @data($data:ident, $($use_data:ident)?),
+        // `HasPinData` or `HasInitData`.
+        @has_data($has_data:ident, $get_data:ident),
+        // `pin_init_from_closure` or `init_from_closure`.
+        @construct_closure($construct_closure:ident),
+        @munch_fields(..Zeroable::zeroed()),
+    ) => {
+        $crate::__init_internal!(with_update_parsed:
+            @this($($this)?),
+            @typ($t),
+            @fields($($fields)*),
+            @error($err),
+            @data($data, $($use_data)?),
+            @has_data($has_data, $get_data),
+            @construct_closure($construct_closure),
+            @zeroed(()), // `()` means zero all fields not mentioned.
+        )
+    };
+    (
+        @this($($this:ident)?),
+        @typ($t:path),
+        @fields($($fields:tt)*),
+        @error($err:ty),
+        // Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
+        // case.
+        @data($data:ident, $($use_data:ident)?),
+        // `HasPinData` or `HasInitData`.
+        @has_data($has_data:ident, $get_data:ident),
+        // `pin_init_from_closure` or `init_from_closure`.
+        @construct_closure($construct_closure:ident),
+        @munch_fields($ignore:tt $($rest:tt)*),
+    ) => {
+        $crate::__init_internal!(
+            @this($($this)?),
+            @typ($t),
+            @fields($($fields)*),
+            @error($err),
+            @data($data, $($use_data)?),
+            @has_data($has_data, $get_data),
+            @construct_closure($construct_closure),
+            @munch_fields($($rest)*),
+        )
+    };
+    (with_update_parsed:
+        @this($($this:ident)?),
+        @typ($t:path),
+        @fields($($fields:tt)*),
+        @error($err:ty),
+        // Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
+        // case.
+        @data($data:ident, $($use_data:ident)?),
+        // `HasPinData` or `HasInitData`.
+        @has_data($has_data:ident, $get_data:ident),
+        // `pin_init_from_closure` or `init_from_closure`.
+        @construct_closure($construct_closure:ident),
+        @zeroed($($init_zeroed:expr)?),
+    ) => {{
+        // We do not want to allow arbitrary returns, so we declare this type as the `Ok` return
+        // type and shadow it later when we insert the arbitrary user code. That way there will be
+        // no possibility of returning without `unsafe`.
+        struct __InitOk;
+        // Get the data about fields from the supplied type.
+        let data = unsafe {
+            use $crate::init::__internal::$has_data;
+            // Here we abuse `paste!` to retokenize `$t`. Declarative macros have some internal
+            // information that is associated to already parsed fragments, so a path fragment
+            // cannot be used in this position. Doing the retokenization results in valid rust
+            // code.
+            ::kernel::macros::paste!($t::$get_data())
+        };
+        // Ensure that `data` really is of type `$data` and help with type inference:
+        let init = $crate::init::__internal::$data::make_closure::<_, __InitOk, $err>(
+            data,
+            move |slot| {
+                {
+                    // Shadow the structure so it cannot be used to return early.
+                    struct __InitOk;
+                    // If `$init_zeroed` is present we should zero the slot now and not emit an
+                    // error when fields are missing (since they will be zeroed). We also have to
+                    // check that the type actually implements `Zeroable`.
+                    $({
+                        fn assert_zeroable<T: $crate::init::Zeroable>(_: *mut T) {}
+                        // Ensure that the struct is indeed `Zeroable`.
+                        assert_zeroable(slot);
+                        // SAFETY: The type implements `Zeroable` by the check above.
+                        unsafe { ::core::ptr::write_bytes(slot, 0, 1) };
+                        $init_zeroed // This will be `()` if set.
+                    })?
+                    // Create the `this` so it can be referenced by the user inside of the
+                    // expressions creating the individual fields.
+                    $(let $this = unsafe { ::core::ptr::NonNull::new_unchecked(slot) };)?
+                    // Initialize every field.
+                    $crate::__init_internal!(init_slot($($use_data)?):
+                        @data(data),
+                        @slot(slot),
+                        @guards(),
+                        @munch_fields($($fields)*,),
+                    );
+                    // We use unreachable code to ensure that all fields have been mentioned exactly
+                    // once, this struct initializer will still be type-checked and complain with a
+                    // very natural error message if a field is forgotten/mentioned more than once.
+                    #[allow(unreachable_code, clippy::diverging_sub_expression)]
+                    let _ = || {
+                        $crate::__init_internal!(make_initializer:
+                            @slot(slot),
+                            @type_name($t),
+                            @munch_fields($($fields)*,),
+                            @acc(),
+                        );
+                    };
+                }
+                Ok(__InitOk)
+            }
+        );
+        let init = move |slot| -> ::core::result::Result<(), $err> {
+            init(slot).map(|__InitOk| ())
+        };
+        let init = unsafe { $crate::init::$construct_closure::<_, $err>(init) };
+        init
+    }};
+    (init_slot($($use_data:ident)?):
+        @data($data:ident),
+        @slot($slot:ident),
+        @guards($($guards:ident,)*),
+        @munch_fields($(..Zeroable::zeroed())? $(,)?),
+    ) => {
+        // Endpoint of munching, no fields are left. If execution reaches this point, all fields
+        // have been initialized. Therefore we can now dismiss the guards by forgetting them.
+        $(::core::mem::forget($guards);)*
+    };
+    (init_slot($use_data:ident): // `use_data` is present, so we use the `data` to init fields.
+        @data($data:ident),
+        @slot($slot:ident),
+        @guards($($guards:ident,)*),
+        // In-place initialization syntax.
+        @munch_fields($field:ident <- $val:expr, $($rest:tt)*),
+    ) => {
+        let init = $val;
+        // Call the initializer.
+        //
+        // SAFETY: `slot` is valid, because we are inside of an initializer closure, we
+        // return when an error/panic occurs.
+        // We also use the `data` to require the correct trait (`Init` or `PinInit`) for `$field`.
+        unsafe { $data.$field(::core::ptr::addr_of_mut!((*$slot).$field), init)? };
+        // Create the drop guard:
+        //
+        // We rely on macro hygiene to make it impossible for users to access this local variable.
+        // We use `paste!` to create new hygiene for `$field`.
+        ::kernel::macros::paste! {
+            // SAFETY: We forget the guard later when initialization has succeeded.
+            let [<$field>] = unsafe {
+                $crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
+            };
+
+            $crate::__init_internal!(init_slot($use_data):
+                @data($data),
+                @slot($slot),
+                @guards([<$field>], $($guards,)*),
+                @munch_fields($($rest)*),
+            );
+        }
+    };
+    (init_slot(): // No `use_data`, so we use `Init::__init` directly.
+        @data($data:ident),
+        @slot($slot:ident),
+        @guards($($guards:ident,)*),
+        // In-place initialization syntax.
+        @munch_fields($field:ident <- $val:expr, $($rest:tt)*),
+    ) => {
+        let init = $val;
+        // Call the initializer.
+        //
+        // SAFETY: `slot` is valid, because we are inside of an initializer closure, we
+        // return when an error/panic occurs.
+        unsafe { $crate::init::Init::__init(init, ::core::ptr::addr_of_mut!((*$slot).$field))? };
+        // Create the drop guard:
+        //
+        // We rely on macro hygiene to make it impossible for users to access this local variable.
+        // We use `paste!` to create new hygiene for `$field`.
+        ::kernel::macros::paste! {
+            // SAFETY: We forget the guard later when initialization has succeeded.
+            let [<$field>] = unsafe {
+                $crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
+            };
+
+            $crate::__init_internal!(init_slot():
+                @data($data),
+                @slot($slot),
+                @guards([<$field>], $($guards,)*),
+                @munch_fields($($rest)*),
+            );
+        }
+    };
+    (init_slot($($use_data:ident)?):
+        @data($data:ident),
+        @slot($slot:ident),
+        @guards($($guards:ident,)*),
+        // Init by-value.
+        @munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
+    ) => {
+        {
+            $(let $field = $val;)?
+            // Initialize the field.
+            //
+            // SAFETY: The memory at `slot` is uninitialized.
+            unsafe { ::core::ptr::write(::core::ptr::addr_of_mut!((*$slot).$field), $field) };
+        }
+        // Create the drop guard:
+        //
+        // We rely on macro hygiene to make it impossible for users to access this local variable.
+        // We use `paste!` to create new hygiene for `$field`.
+        ::kernel::macros::paste! {
+            // SAFETY: We forget the guard later when initialization has succeeded.
+            let [<$field>] = unsafe {
+                $crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
+            };
+
+            $crate::__init_internal!(init_slot($($use_data)?):
+                @data($data),
+                @slot($slot),
+                @guards([<$field>], $($guards,)*),
+                @munch_fields($($rest)*),
+            );
+        }
+    };
+    (make_initializer:
+        @slot($slot:ident),
+        @type_name($t:path),
+        @munch_fields(..Zeroable::zeroed() $(,)?),
+        @acc($($acc:tt)*),
+    ) => {
+        // Endpoint, nothing more to munch, create the initializer. Since the users specified
+        // `..Zeroable::zeroed()`, the slot will already have been zeroed and all field that have
+        // not been overwritten are thus zero and initialized. We still check that all fields are
+        // actually accessible by using the struct update syntax ourselves.
+        // We are inside of a closure that is never executed and thus we can abuse `slot` to
+        // get the correct type inference here:
+        #[allow(unused_assignments)]
+        unsafe {
+            let mut zeroed = ::core::mem::zeroed();
+            // We have to use type inference here to make zeroed have the correct type. This does
+            // not get executed, so it has no effect.
+            ::core::ptr::write($slot, zeroed);
+            zeroed = ::core::mem::zeroed();
+            // Here we abuse `paste!` to retokenize `$t`. Declarative macros have some internal
+            // information that is associated to already parsed fragments, so a path fragment
+            // cannot be used in this position. Doing the retokenization results in valid rust
+            // code.
+            ::kernel::macros::paste!(
+                ::core::ptr::write($slot, $t {
+                    $($acc)*
+                    ..zeroed
+                });
+            );
+        }
+    };
+    (make_initializer:
+        @slot($slot:ident),
+        @type_name($t:path),
+        @munch_fields($(,)?),
+        @acc($($acc:tt)*),
+    ) => {
+        // Endpoint, nothing more to munch, create the initializer.
+        // Since we are in the closure that is never called, this will never get executed.
+        // We abuse `slot` to get the correct type inference here:
+        unsafe {
+            // Here we abuse `paste!` to retokenize `$t`. Declarative macros have some internal
+            // information that is associated to already parsed fragments, so a path fragment
+            // cannot be used in this position. Doing the retokenization results in valid rust
+            // code.
+            ::kernel::macros::paste!(
+                ::core::ptr::write($slot, $t {
+                    $($acc)*
+                });
+            );
+        }
+    };
+    (make_initializer:
+        @slot($slot:ident),
+        @type_name($t:path),
+        @munch_fields($field:ident <- $val:expr, $($rest:tt)*),
+        @acc($($acc:tt)*),
+    ) => {
+        $crate::__init_internal!(make_initializer:
+            @slot($slot),
+            @type_name($t),
+            @munch_fields($($rest)*),
+            @acc($($acc)* $field: ::core::panic!(),),
+        );
+    };
+    (make_initializer:
+        @slot($slot:ident),
+        @type_name($t:path),
+        @munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
+        @acc($($acc:tt)*),
+    ) => {
+        $crate::__init_internal!(make_initializer:
+            @slot($slot),
+            @type_name($t),
+            @munch_fields($($rest)*),
+            @acc($($acc)* $field: ::core::panic!(),),
+        );
+    };
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __derive_zeroable {
+    (parse_input:
+        @sig(
+            $(#[$($struct_attr:tt)*])*
+            $vis:vis struct $name:ident
+            $(where $($whr:tt)*)?
+        ),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @body({
+            $(
+                $(#[$($field_attr:tt)*])*
+                $field:ident : $field_ty:ty
+            ),* $(,)?
+        }),
+    ) => {
+        // SAFETY: Every field type implements `Zeroable` and padding bytes may be zero.
+        #[automatically_derived]
+        unsafe impl<$($impl_generics)*> $crate::init::Zeroable for $name<$($ty_generics)*>
+        where
+            $($($whr)*)?
+        {}
+        const _: () = {
+            fn assert_zeroable<T: ?::core::marker::Sized + $crate::init::Zeroable>() {}
+            fn ensure_zeroable<$($impl_generics)*>()
+                where $($($whr)*)?
+            {
+                $(assert_zeroable::<$field_ty>();)*
+            }
+        };
+    };
+}
diff --git a/rust/kernel/ioctl.rs b/rust/kernel/ioctl.rs
new file mode 100644
index 0000000000..c49e1a8d3f
--- /dev/null
+++ b/rust/kernel/ioctl.rs
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! ioctl() number definitions
+//!
+//! C header: [`include/asm-generic/ioctl.h`](../../../../include/asm-generic/ioctl.h)
+
+#![allow(non_snake_case)]
+
+use crate::build_assert;
+
+/// Build an ioctl number, analogous to the C macro of the same name.
+#[inline(always)]
+const fn _IOC(dir: u32, ty: u32, nr: u32, size: usize) -> u32 {
+    build_assert!(dir <= uapi::_IOC_DIRMASK);
+    build_assert!(ty <= uapi::_IOC_TYPEMASK);
+    build_assert!(nr <= uapi::_IOC_NRMASK);
+    build_assert!(size <= (uapi::_IOC_SIZEMASK as usize));
+
+    (dir << uapi::_IOC_DIRSHIFT)
+        | (ty << uapi::_IOC_TYPESHIFT)
+        | (nr << uapi::_IOC_NRSHIFT)
+        | ((size as u32) << uapi::_IOC_SIZESHIFT)
+}
+
+/// Build an ioctl number for an argumentless ioctl.
+#[inline(always)]
+pub const fn _IO(ty: u32, nr: u32) -> u32 {
+    _IOC(uapi::_IOC_NONE, ty, nr, 0)
+}
+
+/// Build an ioctl number for an read-only ioctl.
+#[inline(always)]
+pub const fn _IOR<T>(ty: u32, nr: u32) -> u32 {
+    _IOC(uapi::_IOC_READ, ty, nr, core::mem::size_of::<T>())
+}
+
+/// Build an ioctl number for an write-only ioctl.
+#[inline(always)]
+pub const fn _IOW<T>(ty: u32, nr: u32) -> u32 {
+    _IOC(uapi::_IOC_WRITE, ty, nr, core::mem::size_of::<T>())
+}
+
+/// Build an ioctl number for a read-write ioctl.
+#[inline(always)]
+pub const fn _IOWR<T>(ty: u32, nr: u32) -> u32 {
+    _IOC(
+        uapi::_IOC_READ | uapi::_IOC_WRITE,
+        ty,
+        nr,
+        core::mem::size_of::<T>(),
+    )
+}
+
+/// Get the ioctl direction from an ioctl number.
+pub const fn _IOC_DIR(nr: u32) -> u32 {
+    (nr >> uapi::_IOC_DIRSHIFT) & uapi::_IOC_DIRMASK
+}
+
+/// Get the ioctl type from an ioctl number.
+pub const fn _IOC_TYPE(nr: u32) -> u32 {
+    (nr >> uapi::_IOC_TYPESHIFT) & uapi::_IOC_TYPEMASK
+}
+
+/// Get the ioctl number from an ioctl number.
+pub const fn _IOC_NR(nr: u32) -> u32 {
+    (nr >> uapi::_IOC_NRSHIFT) & uapi::_IOC_NRMASK
+}
+
+/// Get the ioctl size from an ioctl number.
+pub const fn _IOC_SIZE(nr: u32) -> usize {
+    ((nr >> uapi::_IOC_SIZESHIFT) & uapi::_IOC_SIZEMASK) as usize
+}
diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs
new file mode 100644
index 0000000000..722655b2d6
--- /dev/null
+++ b/rust/kernel/kunit.rs
@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! KUnit-based macros for Rust unit tests.
+//!
+//! C header: [`include/kunit/test.h`](../../../../../include/kunit/test.h)
+//!
+//! Reference: <https://docs.kernel.org/dev-tools/kunit/index.html>
+
+use core::{ffi::c_void, fmt};
+
+/// 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<'_>) {
+    // SAFETY: The format string is null-terminated and the `%pA` specifier matches the argument we
+    // are passing.
+    #[cfg(CONFIG_PRINTK)]
+    unsafe {
+        bindings::_printk(
+            b"\x013%pA\0".as_ptr() as _,
+            &args as *const _ as *const c_void,
+        );
+    }
+}
+
+/// Prints a KUnit info-level message.
+///
+/// Public but hidden since it should only be used from KUnit generated code.
+#[doc(hidden)]
+pub fn info(args: fmt::Arguments<'_>) {
+    // SAFETY: The format string is null-terminated and the `%pA` specifier matches the argument we
+    // are passing.
+    #[cfg(CONFIG_PRINTK)]
+    unsafe {
+        bindings::_printk(
+            b"\x016%pA\0".as_ptr() as _,
+            &args as *const _ as *const c_void,
+        );
+    }
+}
+
+/// Asserts that a boolean expression is `true` at runtime.
+///
+/// Public but hidden since it should only be used from generated tests.
+///
+/// Unlike the one in `core`, this one does not panic; instead, it is mapped to the KUnit
+/// facilities. See [`assert!`] for more details.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! kunit_assert {
+    ($name:literal, $file:literal, $diff:expr, $condition:expr $(,)?) => {
+        'out: {
+            // Do nothing if the condition is `true`.
+            if $condition {
+                break 'out;
+            }
+
+            static FILE: &'static $crate::str::CStr = $crate::c_str!($file);
+            static LINE: i32 = core::line!() as i32 - $diff;
+            static CONDITION: &'static $crate::str::CStr = $crate::c_str!(stringify!($condition));
+
+            // SAFETY: FFI call without safety requirements.
+            let kunit_test = unsafe { $crate::bindings::kunit_get_current_test() };
+            if kunit_test.is_null() {
+                // The assertion failed but this task is not running a KUnit test, so we cannot call
+                // KUnit, but at least print an error to the kernel log. This may happen if this
+                // macro is called from an spawned thread in a test (see
+                // `scripts/rustdoc_test_gen.rs`) or if some non-test code calls this macro by
+                // mistake (it is hidden to prevent that).
+                //
+                // This mimics KUnit's failed assertion format.
+                $crate::kunit::err(format_args!(
+                    "    # {}: ASSERTION FAILED at {FILE}:{LINE}\n",
+                    $name
+                ));
+                $crate::kunit::err(format_args!(
+                    "    Expected {CONDITION} to be true, but is false\n"
+                ));
+                $crate::kunit::err(format_args!(
+                    "    Failure not reported to KUnit since this is a non-KUnit task\n"
+                ));
+                break 'out;
+            }
+
+            #[repr(transparent)]
+            struct Location($crate::bindings::kunit_loc);
+
+            #[repr(transparent)]
+            struct UnaryAssert($crate::bindings::kunit_unary_assert);
+
+            // SAFETY: There is only a static instance and in that one the pointer field points to
+            // an immutable C string.
+            unsafe impl Sync for Location {}
+
+            // SAFETY: There is only a static instance and in that one the pointer field points to
+            // an immutable C string.
+            unsafe impl Sync for UnaryAssert {}
+
+            static LOCATION: Location = Location($crate::bindings::kunit_loc {
+                file: FILE.as_char_ptr(),
+                line: LINE,
+            });
+            static ASSERTION: UnaryAssert = UnaryAssert($crate::bindings::kunit_unary_assert {
+                assert: $crate::bindings::kunit_assert {},
+                condition: CONDITION.as_char_ptr(),
+                expected_true: true,
+            });
+
+            // SAFETY:
+            //   - FFI call.
+            //   - The `kunit_test` pointer is valid because we got it from
+            //     `kunit_get_current_test()` and it was not null. This means we are in a KUnit
+            //     test, and that the pointer can be passed to KUnit functions and assertions.
+            //   - The string pointers (`file` and `condition` above) point to null-terminated
+            //     strings since they are `CStr`s.
+            //   - The function pointer (`format`) points to the proper function.
+            //   - The pointers passed will remain valid since they point to `static`s.
+            //   - The format string is allowed to be null.
+            //   - There are, however, problems with this: first of all, this will end up stopping
+            //     the thread, without running destructors. While that is problematic in itself,
+            //     it is considered UB to have what is effectively a forced foreign unwind
+            //     with `extern "C"` ABI. One could observe the stack that is now gone from
+            //     another thread. We should avoid pinning stack variables to prevent library UB,
+            //     too. For the moment, given that test failures are reported immediately before the
+            //     next test runs, that test failures should be fixed and that KUnit is explicitly
+            //     documented as not suitable for production environments, we feel it is reasonable.
+            unsafe {
+                $crate::bindings::__kunit_do_failed_assertion(
+                    kunit_test,
+                    core::ptr::addr_of!(LOCATION.0),
+                    $crate::bindings::kunit_assert_type_KUNIT_ASSERTION,
+                    core::ptr::addr_of!(ASSERTION.0.assert),
+                    Some($crate::bindings::kunit_unary_assert_format),
+                    core::ptr::null(),
+                );
+            }
+
+            // SAFETY: FFI call; the `test` pointer is valid because this hidden macro should only
+            // be called by the generated documentation tests which forward the test pointer given
+            // by KUnit.
+            unsafe {
+                $crate::bindings::__kunit_abort(kunit_test);
+            }
+        }
+    };
+}
+
+/// Asserts that two expressions are equal to each other (using [`PartialEq`]).
+///
+/// Public but hidden since it should only be used from generated tests.
+///
+/// Unlike the one in `core`, this one does not panic; instead, it is mapped to the KUnit
+/// facilities. See [`assert!`] for more details.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! kunit_assert_eq {
+    ($name:literal, $file:literal, $diff:expr, $left:expr, $right:expr $(,)?) => {{
+        // For the moment, we just forward to the expression assert because, for binary asserts,
+        // KUnit supports only a few types (e.g. integers).
+        $crate::kunit_assert!($name, $file, $diff, $left == $right);
+    }};
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
new file mode 100644
index 0000000000..e881170023
--- /dev/null
+++ b/rust/kernel/lib.rs
@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! The `kernel` crate.
+//!
+//! This crate contains the kernel APIs that have been ported or wrapped for
+//! usage by Rust code in the kernel and is shared by all of them.
+//!
+//! In other words, all the rest of the Rust code in the kernel (e.g. kernel
+//! modules written in Rust) depends on [`core`], [`alloc`] and this crate.
+//!
+//! If you need a kernel C API that is not ported or wrapped yet here, then
+//! do so first instead of bypassing this crate.
+
+#![no_std]
+#![feature(allocator_api)]
+#![feature(coerce_unsized)]
+#![feature(dispatch_from_dyn)]
+#![feature(new_uninit)]
+#![feature(receiver_trait)]
+#![feature(unsize)]
+
+// Ensure conditional compilation based on the kernel configuration works;
+// otherwise we may silently break things like initcall handling.
+#[cfg(not(CONFIG_RUST))]
+compile_error!("Missing kernel configuration for conditional compilation");
+
+// Allow proc-macros to refer to `::kernel` inside the `kernel` crate (this crate).
+extern crate self as kernel;
+
+#[cfg(not(test))]
+#[cfg(not(testlib))]
+mod allocator;
+mod build_assert;
+pub mod error;
+pub mod init;
+pub mod ioctl;
+#[cfg(CONFIG_KUNIT)]
+pub mod kunit;
+pub mod prelude;
+pub mod print;
+mod static_assert;
+#[doc(hidden)]
+pub mod std_vendor;
+pub mod str;
+pub mod sync;
+pub mod task;
+pub mod types;
+
+#[doc(hidden)]
+pub use bindings;
+pub use macros;
+pub use uapi;
+
+#[doc(hidden)]
+pub use build_error::build_error;
+
+/// Prefix to appear before log messages printed from within the `kernel` crate.
+const __LOG_PREFIX: &[u8] = b"rust_kernel\0";
+
+/// The top level entrypoint to implementing a kernel module.
+///
+/// For any teardown or cleanup operations, your type may implement [`Drop`].
+pub trait Module: Sized + Sync {
+    /// Called at module initialization time.
+    ///
+    /// Use this method to perform whatever setup or registration your module
+    /// should do.
+    ///
+    /// Equivalent to the `module_init` macro in the C API.
+    fn init(module: &'static ThisModule) -> error::Result<Self>;
+}
+
+/// Equivalent to `THIS_MODULE` in the C API.
+///
+/// C header: `include/linux/export.h`
+pub struct ThisModule(*mut bindings::module);
+
+// SAFETY: `THIS_MODULE` may be used from all threads within a module.
+unsafe impl Sync for ThisModule {}
+
+impl ThisModule {
+    /// Creates a [`ThisModule`] given the `THIS_MODULE` pointer.
+    ///
+    /// # Safety
+    ///
+    /// The pointer must be equal to the right `THIS_MODULE`.
+    pub const unsafe fn from_ptr(ptr: *mut bindings::module) -> ThisModule {
+        ThisModule(ptr)
+    }
+}
+
+#[cfg(not(any(testlib, test)))]
+#[panic_handler]
+fn panic(info: &core::panic::PanicInfo<'_>) -> ! {
+    pr_emerg!("{}\n", info);
+    // SAFETY: FFI call.
+    unsafe { bindings::BUG() };
+}
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
new file mode 100644
index 0000000000..ae21600970
--- /dev/null
+++ b/rust/kernel/prelude.rs
@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! The `kernel` prelude.
+//!
+//! These are the most common items used by Rust code in the kernel,
+//! intended to be imported by all Rust code, for convenience.
+//!
+//! # Examples
+//!
+//! ```
+//! use kernel::prelude::*;
+//! ```
+
+#[doc(no_inline)]
+pub use core::pin::Pin;
+
+#[doc(no_inline)]
+pub use alloc::{boxed::Box, vec::Vec};
+
+#[doc(no_inline)]
+pub use macros::{module, pin_data, pinned_drop, vtable, Zeroable};
+
+pub use super::build_assert;
+
+// `super::std_vendor` is hidden, which makes the macro inline for some reason.
+#[doc(no_inline)]
+pub use super::dbg;
+pub use super::{pr_alert, pr_crit, pr_debug, pr_emerg, pr_err, pr_info, pr_notice, pr_warn};
+
+pub use super::{init, pin_init, try_init, try_pin_init};
+
+pub use super::static_assert;
+
+pub use super::error::{code::*, Error, Result};
+
+pub use super::{str::CStr, ThisModule};
+
+pub use super::init::{InPlaceInit, Init, PinInit};
+
+pub use super::current;
diff --git a/rust/kernel/print.rs b/rust/kernel/print.rs
new file mode 100644
index 0000000000..8009184bf6
--- /dev/null
+++ b/rust/kernel/print.rs
@@ -0,0 +1,417 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Printing facilities.
+//!
+//! C header: [`include/linux/printk.h`](../../../../include/linux/printk.h)
+//!
+//! Reference: <https://www.kernel.org/doc/html/latest/core-api/printk-basics.html>
+
+use core::{
+    ffi::{c_char, c_void},
+    fmt,
+};
+
+use crate::str::RawFormatter;
+
+#[cfg(CONFIG_PRINTK)]
+use crate::bindings;
+
+// Called from `vsprintf` with format specifier `%pA`.
+#[no_mangle]
+unsafe extern "C" fn rust_fmt_argument(
+    buf: *mut c_char,
+    end: *mut c_char,
+    ptr: *const c_void,
+) -> *mut c_char {
+    use fmt::Write;
+    // 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()) };
+    let _ = w.write_fmt(unsafe { *(ptr as *const fmt::Arguments<'_>) });
+    w.pos().cast()
+}
+
+/// Format strings.
+///
+/// Public but hidden since it should only be used from public macros.
+#[doc(hidden)]
+pub mod format_strings {
+    use crate::bindings;
+
+    /// The length we copy from the `KERN_*` kernel prefixes.
+    const LENGTH_PREFIX: usize = 2;
+
+    /// The length of the fixed format strings.
+    pub const LENGTH: usize = 10;
+
+    /// Generates a fixed format string for the kernel's [`_printk`].
+    ///
+    /// The format string is always the same for a given level, i.e. for a
+    /// given `prefix`, which are the kernel's `KERN_*` constants.
+    ///
+    /// [`_printk`]: ../../../../include/linux/printk.h
+    const fn generate(is_cont: bool, prefix: &[u8; 3]) -> [u8; LENGTH] {
+        // Ensure the `KERN_*` macros are what we expect.
+        assert!(prefix[0] == b'\x01');
+        if is_cont {
+            assert!(prefix[1] == b'c');
+        } else {
+            assert!(prefix[1] >= b'0' && prefix[1] <= b'7');
+        }
+        assert!(prefix[2] == b'\x00');
+
+        let suffix: &[u8; LENGTH - LENGTH_PREFIX] = if is_cont {
+            b"%pA\0\0\0\0\0"
+        } else {
+            b"%s: %pA\0"
+        };
+
+        [
+            prefix[0], prefix[1], suffix[0], suffix[1], suffix[2], suffix[3], suffix[4], suffix[5],
+            suffix[6], suffix[7],
+        ]
+    }
+
+    // Generate the format strings at compile-time.
+    //
+    // This avoids the compiler generating the contents on the fly in the stack.
+    //
+    // Furthermore, `static` instead of `const` is used to share the strings
+    // for all the kernel.
+    pub static EMERG: [u8; LENGTH] = generate(false, bindings::KERN_EMERG);
+    pub static ALERT: [u8; LENGTH] = generate(false, bindings::KERN_ALERT);
+    pub static CRIT: [u8; LENGTH] = generate(false, bindings::KERN_CRIT);
+    pub static ERR: [u8; LENGTH] = generate(false, bindings::KERN_ERR);
+    pub static WARNING: [u8; LENGTH] = generate(false, bindings::KERN_WARNING);
+    pub static NOTICE: [u8; LENGTH] = generate(false, bindings::KERN_NOTICE);
+    pub static INFO: [u8; LENGTH] = generate(false, bindings::KERN_INFO);
+    pub static DEBUG: [u8; LENGTH] = generate(false, bindings::KERN_DEBUG);
+    pub static CONT: [u8; LENGTH] = generate(true, bindings::KERN_CONT);
+}
+
+/// Prints a message via the kernel's [`_printk`].
+///
+/// Public but hidden since it should only be used from public macros.
+///
+/// # Safety
+///
+/// The format string must be one of the ones in [`format_strings`], and
+/// the module name must be null-terminated.
+///
+/// [`_printk`]: ../../../../include/linux/_printk.h
+#[doc(hidden)]
+#[cfg_attr(not(CONFIG_PRINTK), allow(unused_variables))]
+pub unsafe fn call_printk(
+    format_string: &[u8; format_strings::LENGTH],
+    module_name: &[u8],
+    args: fmt::Arguments<'_>,
+) {
+    // `_printk` does not seem to fail in any path.
+    #[cfg(CONFIG_PRINTK)]
+    unsafe {
+        bindings::_printk(
+            format_string.as_ptr() as _,
+            module_name.as_ptr(),
+            &args as *const _ as *const c_void,
+        );
+    }
+}
+
+/// Prints a message via the kernel's [`_printk`] for the `CONT` level.
+///
+/// Public but hidden since it should only be used from public macros.
+///
+/// [`_printk`]: ../../../../include/linux/printk.h
+#[doc(hidden)]
+#[cfg_attr(not(CONFIG_PRINTK), allow(unused_variables))]
+pub fn call_printk_cont(args: fmt::Arguments<'_>) {
+    // `_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() as _,
+            &args as *const _ as *const c_void,
+        );
+    }
+}
+
+/// Performs formatting and forwards the string to [`call_printk`].
+///
+/// Public but hidden since it should only be used from public macros.
+#[doc(hidden)]
+#[cfg(not(testlib))]
+#[macro_export]
+#[allow(clippy::crate_in_macro_def)]
+macro_rules! print_macro (
+    // The non-continuation cases (most of them, e.g. `INFO`).
+    ($format_string:path, false, $($arg:tt)+) => (
+        // To remain sound, `arg`s must be expanded outside the `unsafe` block.
+        // Typically one would use a `let` binding for that; however, `format_args!`
+        // takes borrows on the arguments, but does not extend the scope of temporaries.
+        // Therefore, a `match` expression is used to keep them around, since
+        // the scrutinee is kept until the end of the `match`.
+        match format_args!($($arg)+) {
+            // SAFETY: This hidden macro should only be called by the documented
+            // printing macros which ensure the format string is one of the fixed
+            // ones. All `__LOG_PREFIX`s are null-terminated as they are generated
+            // by the `module!` proc macro or fixed values defined in a kernel
+            // crate.
+            args => unsafe {
+                $crate::print::call_printk(
+                    &$format_string,
+                    crate::__LOG_PREFIX,
+                    args,
+                );
+            }
+        }
+    );
+
+    // The `CONT` case.
+    ($format_string:path, true, $($arg:tt)+) => (
+        $crate::print::call_printk_cont(
+            format_args!($($arg)+),
+        );
+    );
+);
+
+/// Stub for doctests
+#[cfg(testlib)]
+#[macro_export]
+macro_rules! print_macro (
+    ($format_string:path, $e:expr, $($arg:tt)+) => (
+        ()
+    );
+);
+
+// We could use a macro to generate these macros. However, doing so ends
+// up being a bit ugly: it requires the dollar token trick to escape `$` as
+// well as playing with the `doc` attribute. Furthermore, they cannot be easily
+// imported in the prelude due to [1]. So, for the moment, we just write them
+// manually, like in the C side; while keeping most of the logic in another
+// macro, i.e. [`print_macro`].
+//
+// [1]: https://github.com/rust-lang/rust/issues/52234
+
+/// Prints an emergency-level message (level 0).
+///
+/// Use this level if the system is unusable.
+///
+/// Equivalent to the kernel's [`pr_emerg`] macro.
+///
+/// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
+/// `alloc::format!` for information about the formatting syntax.
+///
+/// [`pr_emerg`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html#c.pr_emerg
+/// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
+///
+/// # Examples
+///
+/// ```
+/// pr_emerg!("hello {}\n", "there");
+/// ```
+#[macro_export]
+macro_rules! pr_emerg (
+    ($($arg:tt)*) => (
+        $crate::print_macro!($crate::print::format_strings::EMERG, false, $($arg)*)
+    )
+);
+
+/// Prints an alert-level message (level 1).
+///
+/// Use this level if action must be taken immediately.
+///
+/// Equivalent to the kernel's [`pr_alert`] macro.
+///
+/// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
+/// `alloc::format!` for information about the formatting syntax.
+///
+/// [`pr_alert`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html#c.pr_alert
+/// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
+///
+/// # Examples
+///
+/// ```
+/// pr_alert!("hello {}\n", "there");
+/// ```
+#[macro_export]
+macro_rules! pr_alert (
+    ($($arg:tt)*) => (
+        $crate::print_macro!($crate::print::format_strings::ALERT, false, $($arg)*)
+    )
+);
+
+/// Prints a critical-level message (level 2).
+///
+/// Use this level for critical conditions.
+///
+/// Equivalent to the kernel's [`pr_crit`] macro.
+///
+/// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
+/// `alloc::format!` for information about the formatting syntax.
+///
+/// [`pr_crit`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html#c.pr_crit
+/// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
+///
+/// # Examples
+///
+/// ```
+/// pr_crit!("hello {}\n", "there");
+/// ```
+#[macro_export]
+macro_rules! pr_crit (
+    ($($arg:tt)*) => (
+        $crate::print_macro!($crate::print::format_strings::CRIT, false, $($arg)*)
+    )
+);
+
+/// Prints an error-level message (level 3).
+///
+/// Use this level for error conditions.
+///
+/// Equivalent to the kernel's [`pr_err`] macro.
+///
+/// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
+/// `alloc::format!` for information about the formatting syntax.
+///
+/// [`pr_err`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html#c.pr_err
+/// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
+///
+/// # Examples
+///
+/// ```
+/// pr_err!("hello {}\n", "there");
+/// ```
+#[macro_export]
+macro_rules! pr_err (
+    ($($arg:tt)*) => (
+        $crate::print_macro!($crate::print::format_strings::ERR, false, $($arg)*)
+    )
+);
+
+/// Prints a warning-level message (level 4).
+///
+/// Use this level for warning conditions.
+///
+/// Equivalent to the kernel's [`pr_warn`] macro.
+///
+/// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
+/// `alloc::format!` for information about the formatting syntax.
+///
+/// [`pr_warn`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html#c.pr_warn
+/// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
+///
+/// # Examples
+///
+/// ```
+/// pr_warn!("hello {}\n", "there");
+/// ```
+#[macro_export]
+macro_rules! pr_warn (
+    ($($arg:tt)*) => (
+        $crate::print_macro!($crate::print::format_strings::WARNING, false, $($arg)*)
+    )
+);
+
+/// Prints a notice-level message (level 5).
+///
+/// Use this level for normal but significant conditions.
+///
+/// Equivalent to the kernel's [`pr_notice`] macro.
+///
+/// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
+/// `alloc::format!` for information about the formatting syntax.
+///
+/// [`pr_notice`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html#c.pr_notice
+/// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
+///
+/// # Examples
+///
+/// ```
+/// pr_notice!("hello {}\n", "there");
+/// ```
+#[macro_export]
+macro_rules! pr_notice (
+    ($($arg:tt)*) => (
+        $crate::print_macro!($crate::print::format_strings::NOTICE, false, $($arg)*)
+    )
+);
+
+/// Prints an info-level message (level 6).
+///
+/// Use this level for informational messages.
+///
+/// Equivalent to the kernel's [`pr_info`] macro.
+///
+/// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
+/// `alloc::format!` for information about the formatting syntax.
+///
+/// [`pr_info`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html#c.pr_info
+/// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
+///
+/// # Examples
+///
+/// ```
+/// pr_info!("hello {}\n", "there");
+/// ```
+#[macro_export]
+#[doc(alias = "print")]
+macro_rules! pr_info (
+    ($($arg:tt)*) => (
+        $crate::print_macro!($crate::print::format_strings::INFO, false, $($arg)*)
+    )
+);
+
+/// Prints a debug-level message (level 7).
+///
+/// Use this level for debug messages.
+///
+/// Equivalent to the kernel's [`pr_debug`] macro, except that it doesn't support dynamic debug
+/// yet.
+///
+/// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
+/// `alloc::format!` for information about the formatting syntax.
+///
+/// [`pr_debug`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html#c.pr_debug
+/// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
+///
+/// # Examples
+///
+/// ```
+/// pr_debug!("hello {}\n", "there");
+/// ```
+#[macro_export]
+#[doc(alias = "print")]
+macro_rules! pr_debug (
+    ($($arg:tt)*) => (
+        if cfg!(debug_assertions) {
+            $crate::print_macro!($crate::print::format_strings::DEBUG, false, $($arg)*)
+        }
+    )
+);
+
+/// Continues a previous log message in the same line.
+///
+/// Use only when continuing a previous `pr_*!` macro (e.g. [`pr_info!`]).
+///
+/// Equivalent to the kernel's [`pr_cont`] macro.
+///
+/// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
+/// `alloc::format!` for information about the formatting syntax.
+///
+/// [`pr_cont`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html#c.pr_cont
+/// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::pr_cont;
+/// pr_info!("hello");
+/// pr_cont!(" {}\n", "there");
+/// ```
+#[macro_export]
+macro_rules! pr_cont (
+    ($($arg:tt)*) => (
+        $crate::print_macro!($crate::print::format_strings::CONT, true, $($arg)*)
+    )
+);
diff --git a/rust/kernel/static_assert.rs b/rust/kernel/static_assert.rs
new file mode 100644
index 0000000000..3115ee0ba8
--- /dev/null
+++ b/rust/kernel/static_assert.rs
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Static assert.
+
+/// Static assert (i.e. compile-time assert).
+///
+/// Similar to C11 [`_Static_assert`] and C++11 [`static_assert`].
+///
+/// The feature may be added to Rust in the future: see [RFC 2790].
+///
+/// [`_Static_assert`]: https://en.cppreference.com/w/c/language/_Static_assert
+/// [`static_assert`]: https://en.cppreference.com/w/cpp/language/static_assert
+/// [RFC 2790]: https://github.com/rust-lang/rfcs/issues/2790
+///
+/// # Examples
+///
+/// ```
+/// static_assert!(42 > 24);
+/// static_assert!(core::mem::size_of::<u8>() == 1);
+///
+/// const X: &[u8] = b"bar";
+/// static_assert!(X[1] == b'a');
+///
+/// const fn f(x: i32) -> i32 {
+///     x + 2
+/// }
+/// static_assert!(f(40) == 42);
+/// ```
+#[macro_export]
+macro_rules! static_assert {
+    ($condition:expr) => {
+        const _: () = core::assert!($condition);
+    };
+}
diff --git a/rust/kernel/std_vendor.rs b/rust/kernel/std_vendor.rs
new file mode 100644
index 0000000000..388d6a5147
--- /dev/null
+++ b/rust/kernel/std_vendor.rs
@@ -0,0 +1,165 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! The contents of this file come from the Rust standard library, hosted in
+//! the <https://github.com/rust-lang/rust> repository, licensed under
+//! "Apache-2.0 OR MIT" and adapted for kernel use. For copyright details,
+//! see <https://github.com/rust-lang/rust/blob/master/COPYRIGHT>.
+
+/// [`std::dbg`], but using [`pr_info`] instead of [`eprintln`].
+///
+/// Prints and returns the value of a given expression for quick and dirty
+/// debugging.
+///
+/// An example:
+///
+/// ```rust
+/// let a = 2;
+/// # #[allow(clippy::dbg_macro)]
+/// let b = dbg!(a * 2) + 1;
+/// //      ^-- prints: [src/main.rs:2] a * 2 = 4
+/// assert_eq!(b, 5);
+/// ```
+///
+/// The macro works by using the `Debug` implementation of the type of
+/// the given expression to print the value with [`printk`] along with the
+/// source location of the macro invocation as well as the source code
+/// of the expression.
+///
+/// Invoking the macro on an expression moves and takes ownership of it
+/// before returning the evaluated expression unchanged. If the type
+/// of the expression does not implement `Copy` and you don't want
+/// to give up ownership, you can instead borrow with `dbg!(&expr)`
+/// for some expression `expr`.
+///
+/// The `dbg!` macro works exactly the same in release builds.
+/// This is useful when debugging issues that only occur in release
+/// builds or when debugging in release mode is significantly faster.
+///
+/// Note that the macro is intended as a temporary debugging tool to be
+/// used during development. Therefore, avoid committing `dbg!` macro
+/// invocations into the kernel tree.
+///
+/// For debug output that is intended to be kept in the kernel tree,
+/// use [`pr_debug`] and similar facilities instead.
+///
+/// # Stability
+///
+/// The exact output printed by this macro should not be relied upon
+/// and is subject to future changes.
+///
+/// # Further examples
+///
+/// With a method call:
+///
+/// ```rust
+/// # #[allow(clippy::dbg_macro)]
+/// fn foo(n: usize) {
+///     if dbg!(n.checked_sub(4)).is_some() {
+///         // ...
+///     }
+/// }
+///
+/// foo(3)
+/// ```
+///
+/// This prints to the kernel log:
+///
+/// ```text,ignore
+/// [src/main.rs:4] n.checked_sub(4) = None
+/// ```
+///
+/// Naive factorial implementation:
+///
+/// ```rust
+/// # #[allow(clippy::dbg_macro)]
+/// # {
+/// fn factorial(n: u32) -> u32 {
+///     if dbg!(n <= 1) {
+///         dbg!(1)
+///     } else {
+///         dbg!(n * factorial(n - 1))
+///     }
+/// }
+///
+/// dbg!(factorial(4));
+/// # }
+/// ```
+///
+/// This prints to the kernel log:
+///
+/// ```text,ignore
+/// [src/main.rs:3] n <= 1 = false
+/// [src/main.rs:3] n <= 1 = false
+/// [src/main.rs:3] n <= 1 = false
+/// [src/main.rs:3] n <= 1 = true
+/// [src/main.rs:4] 1 = 1
+/// [src/main.rs:5] n * factorial(n - 1) = 2
+/// [src/main.rs:5] n * factorial(n - 1) = 6
+/// [src/main.rs:5] n * factorial(n - 1) = 24
+/// [src/main.rs:11] factorial(4) = 24
+/// ```
+///
+/// The `dbg!(..)` macro moves the input:
+///
+/// ```ignore
+/// /// A wrapper around `usize` which importantly is not Copyable.
+/// #[derive(Debug)]
+/// struct NoCopy(usize);
+///
+/// let a = NoCopy(42);
+/// let _ = dbg!(a); // <-- `a` is moved here.
+/// let _ = dbg!(a); // <-- `a` is moved again; error!
+/// ```
+///
+/// You can also use `dbg!()` without a value to just print the
+/// file and line whenever it's reached.
+///
+/// Finally, if you want to `dbg!(..)` multiple values, it will treat them as
+/// a tuple (and return it, too):
+///
+/// ```
+/// # #[allow(clippy::dbg_macro)]
+/// assert_eq!(dbg!(1usize, 2u32), (1, 2));
+/// ```
+///
+/// However, a single argument with a trailing comma will still not be treated
+/// as a tuple, following the convention of ignoring trailing commas in macro
+/// invocations. You can use a 1-tuple directly if you need one:
+///
+/// ```
+/// # #[allow(clippy::dbg_macro)]
+/// # {
+/// assert_eq!(1, dbg!(1u32,)); // trailing comma ignored
+/// assert_eq!((1,), dbg!((1u32,))); // 1-tuple
+/// # }
+/// ```
+///
+/// [`std::dbg`]: https://doc.rust-lang.org/std/macro.dbg.html
+/// [`eprintln`]: https://doc.rust-lang.org/std/macro.eprintln.html
+/// [`printk`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html
+/// [`pr_info`]: crate::pr_info!
+/// [`pr_debug`]: crate::pr_debug!
+#[macro_export]
+macro_rules! dbg {
+    // NOTE: We cannot use `concat!` to make a static string as a format argument
+    // of `pr_info!` because `file!` could contain a `{` or
+    // `$val` expression could be a block (`{ .. }`), in which case the `pr_info!`
+    // will be malformed.
+    () => {
+        $crate::pr_info!("[{}:{}]\n", ::core::file!(), ::core::line!())
+    };
+    ($val:expr $(,)?) => {
+        // Use of `match` here is intentional because it affects the lifetimes
+        // of temporaries - https://stackoverflow.com/a/48732525/1063961
+        match $val {
+            tmp => {
+                $crate::pr_info!("[{}:{}] {} = {:#?}\n",
+                    ::core::file!(), ::core::line!(), ::core::stringify!($val), &tmp);
+                tmp
+            }
+        }
+    };
+    ($($val:expr),+ $(,)?) => {
+        ($($crate::dbg!($val)),+,)
+    };
+}
diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
new file mode 100644
index 0000000000..c41607b2e4
--- /dev/null
+++ b/rust/kernel/str.rs
@@ -0,0 +1,615 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! String representations.
+
+use alloc::alloc::AllocError;
+use alloc::vec::Vec;
+use core::fmt::{self, Write};
+use core::ops::{self, Deref, Index};
+
+use crate::{
+    bindings,
+    error::{code::*, Error},
+};
+
+/// Byte string without UTF-8 validity guarantee.
+///
+/// `BStr` is simply an alias to `[u8]`, but has a more evident semantical meaning.
+pub type BStr = [u8];
+
+/// Creates a new [`BStr`] from a string literal.
+///
+/// `b_str!` converts the supplied string literal to byte string, so non-ASCII
+/// characters can be included.
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::b_str;
+/// # use kernel::str::BStr;
+/// const MY_BSTR: &BStr = b_str!("My awesome BStr!");
+/// ```
+#[macro_export]
+macro_rules! b_str {
+    ($str:literal) => {{
+        const S: &'static str = $str;
+        const C: &'static $crate::str::BStr = S.as_bytes();
+        C
+    }};
+}
+
+/// Possible errors when using conversion functions in [`CStr`].
+#[derive(Debug, Clone, Copy)]
+pub enum CStrConvertError {
+    /// Supplied bytes contain an interior `NUL`.
+    InteriorNul,
+
+    /// Supplied bytes are not terminated by `NUL`.
+    NotNulTerminated,
+}
+
+impl From<CStrConvertError> for Error {
+    #[inline]
+    fn from(_: CStrConvertError) -> Error {
+        EINVAL
+    }
+}
+
+/// A string that is guaranteed to have exactly one `NUL` byte, which is at the
+/// end.
+///
+/// Used for interoperability with kernel APIs that take C strings.
+#[repr(transparent)]
+pub struct CStr([u8]);
+
+impl CStr {
+    /// Returns the length of this string excluding `NUL`.
+    #[inline]
+    pub const fn len(&self) -> usize {
+        self.len_with_nul() - 1
+    }
+
+    /// Returns the length of this string with `NUL`.
+    #[inline]
+    pub const fn len_with_nul(&self) -> usize {
+        // SAFETY: This is one of the invariant of `CStr`.
+        // We add a `unreachable_unchecked` here to hint the optimizer that
+        // the value returned from this function is non-zero.
+        if self.0.is_empty() {
+            unsafe { core::hint::unreachable_unchecked() };
+        }
+        self.0.len()
+    }
+
+    /// Returns `true` if the string only includes `NUL`.
+    #[inline]
+    pub const fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Wraps a raw C string pointer.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must be a valid pointer to a `NUL`-terminated C string, and it must
+    /// last at least `'a`. When `CStr` is alive, the memory pointed by `ptr`
+    /// must not be mutated.
+    #[inline]
+    pub unsafe fn from_char_ptr<'a>(ptr: *const core::ffi::c_char) -> &'a Self {
+        // SAFETY: The safety precondition guarantees `ptr` is a valid pointer
+        // 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 as _) };
+        // 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) }
+    }
+
+    /// Creates a [`CStr`] from a `[u8]`.
+    ///
+    /// The provided slice must be `NUL`-terminated, does not contain any
+    /// interior `NUL` bytes.
+    pub const fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, CStrConvertError> {
+        if bytes.is_empty() {
+            return Err(CStrConvertError::NotNulTerminated);
+        }
+        if bytes[bytes.len() - 1] != 0 {
+            return Err(CStrConvertError::NotNulTerminated);
+        }
+        let mut i = 0;
+        // `i + 1 < bytes.len()` allows LLVM to optimize away bounds checking,
+        // while it couldn't optimize away bounds checks for `i < bytes.len() - 1`.
+        while i + 1 < bytes.len() {
+            if bytes[i] == 0 {
+                return Err(CStrConvertError::InteriorNul);
+            }
+            i += 1;
+        }
+        // SAFETY: We just checked that all properties hold.
+        Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
+    }
+
+    /// Creates a [`CStr`] from a `[u8]` without performing any additional
+    /// checks.
+    ///
+    /// # Safety
+    ///
+    /// `bytes` *must* end with a `NUL` byte, and should only have a single
+    /// `NUL` byte (or the string will be truncated).
+    #[inline]
+    pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
+        // SAFETY: Properties of `bytes` guaranteed by the safety precondition.
+        unsafe { core::mem::transmute(bytes) }
+    }
+
+    /// Returns a C pointer to the string.
+    #[inline]
+    pub const fn as_char_ptr(&self) -> *const core::ffi::c_char {
+        self.0.as_ptr() as _
+    }
+
+    /// Convert the string to a byte slice without the trailing 0 byte.
+    #[inline]
+    pub fn as_bytes(&self) -> &[u8] {
+        &self.0[..self.len()]
+    }
+
+    /// Convert the string to a byte slice containing the trailing 0 byte.
+    #[inline]
+    pub const fn as_bytes_with_nul(&self) -> &[u8] {
+        &self.0
+    }
+
+    /// Yields a [`&str`] slice if the [`CStr`] contains valid UTF-8.
+    ///
+    /// If the contents of the [`CStr`] are valid UTF-8 data, this
+    /// function will return the corresponding [`&str`] slice. Otherwise,
+    /// it will return an error with details of where UTF-8 validation failed.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use kernel::str::CStr;
+    /// let cstr = CStr::from_bytes_with_nul(b"foo\0").unwrap();
+    /// assert_eq!(cstr.to_str(), Ok("foo"));
+    /// ```
+    #[inline]
+    pub fn to_str(&self) -> Result<&str, core::str::Utf8Error> {
+        core::str::from_utf8(self.as_bytes())
+    }
+
+    /// Unsafely convert this [`CStr`] into a [`&str`], without checking for
+    /// valid UTF-8.
+    ///
+    /// # Safety
+    ///
+    /// The contents must be valid UTF-8.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use kernel::c_str;
+    /// # use kernel::str::CStr;
+    /// // SAFETY: String literals are guaranteed to be valid UTF-8
+    /// // by the Rust compiler.
+    /// let bar = c_str!("ツ");
+    /// assert_eq!(unsafe { bar.as_str_unchecked() }, "ツ");
+    /// ```
+    #[inline]
+    pub unsafe fn as_str_unchecked(&self) -> &str {
+        unsafe { core::str::from_utf8_unchecked(self.as_bytes()) }
+    }
+
+    /// Convert this [`CStr`] into a [`CString`] by allocating memory and
+    /// copying over the string data.
+    pub fn to_cstring(&self) -> Result<CString, AllocError> {
+        CString::try_from(self)
+    }
+}
+
+impl fmt::Display for CStr {
+    /// Formats printable ASCII characters, escaping the rest.
+    ///
+    /// ```
+    /// # use kernel::c_str;
+    /// # use kernel::fmt;
+    /// # use kernel::str::CStr;
+    /// # use kernel::str::CString;
+    /// let penguin = c_str!("🐧");
+    /// let s = CString::try_from_fmt(fmt!("{}", penguin)).unwrap();
+    /// assert_eq!(s.as_bytes_with_nul(), "\\xf0\\x9f\\x90\\xa7\0".as_bytes());
+    ///
+    /// let ascii = c_str!("so \"cool\"");
+    /// let s = CString::try_from_fmt(fmt!("{}", ascii)).unwrap();
+    /// assert_eq!(s.as_bytes_with_nul(), "so \"cool\"\0".as_bytes());
+    /// ```
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        for &c in self.as_bytes() {
+            if (0x20..0x7f).contains(&c) {
+                // Printable character.
+                f.write_char(c as char)?;
+            } else {
+                write!(f, "\\x{:02x}", c)?;
+            }
+        }
+        Ok(())
+    }
+}
+
+impl fmt::Debug for CStr {
+    /// Formats printable ASCII characters with a double quote on either end, escaping the rest.
+    ///
+    /// ```
+    /// # use kernel::c_str;
+    /// # use kernel::fmt;
+    /// # use kernel::str::CStr;
+    /// # use kernel::str::CString;
+    /// let penguin = c_str!("🐧");
+    /// let s = CString::try_from_fmt(fmt!("{:?}", penguin)).unwrap();
+    /// assert_eq!(s.as_bytes_with_nul(), "\"\\xf0\\x9f\\x90\\xa7\"\0".as_bytes());
+    ///
+    /// // Embedded double quotes are escaped.
+    /// let ascii = c_str!("so \"cool\"");
+    /// let s = CString::try_from_fmt(fmt!("{:?}", ascii)).unwrap();
+    /// assert_eq!(s.as_bytes_with_nul(), "\"so \\\"cool\\\"\"\0".as_bytes());
+    /// ```
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("\"")?;
+        for &c in self.as_bytes() {
+            match c {
+                // Printable characters.
+                b'\"' => f.write_str("\\\"")?,
+                0x20..=0x7e => f.write_char(c as char)?,
+                _ => write!(f, "\\x{:02x}", c)?,
+            }
+        }
+        f.write_str("\"")
+    }
+}
+
+impl AsRef<BStr> for CStr {
+    #[inline]
+    fn as_ref(&self) -> &BStr {
+        self.as_bytes()
+    }
+}
+
+impl Deref for CStr {
+    type Target = BStr;
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        self.as_bytes()
+    }
+}
+
+impl Index<ops::RangeFrom<usize>> for CStr {
+    type Output = CStr;
+
+    #[inline]
+    fn index(&self, index: ops::RangeFrom<usize>) -> &Self::Output {
+        // Delegate bounds checking to slice.
+        // Assign to _ to mute clippy's unnecessary operation warning.
+        let _ = &self.as_bytes()[index.start..];
+        // SAFETY: We just checked the bounds.
+        unsafe { Self::from_bytes_with_nul_unchecked(&self.0[index.start..]) }
+    }
+}
+
+impl Index<ops::RangeFull> for CStr {
+    type Output = CStr;
+
+    #[inline]
+    fn index(&self, _index: ops::RangeFull) -> &Self::Output {
+        self
+    }
+}
+
+mod private {
+    use core::ops;
+
+    // Marker trait for index types that can be forward to `BStr`.
+    pub trait CStrIndex {}
+
+    impl CStrIndex for usize {}
+    impl CStrIndex for ops::Range<usize> {}
+    impl CStrIndex for ops::RangeInclusive<usize> {}
+    impl CStrIndex for ops::RangeToInclusive<usize> {}
+}
+
+impl<Idx> Index<Idx> for CStr
+where
+    Idx: private::CStrIndex,
+    BStr: Index<Idx>,
+{
+    type Output = <BStr as Index<Idx>>::Output;
+
+    #[inline]
+    fn index(&self, index: Idx) -> &Self::Output {
+        &self.as_bytes()[index]
+    }
+}
+
+/// Creates a new [`CStr`] from a string literal.
+///
+/// The string literal should not contain any `NUL` bytes.
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::c_str;
+/// # use kernel::str::CStr;
+/// const MY_CSTR: &CStr = c_str!("My awesome CStr!");
+/// ```
+#[macro_export]
+macro_rules! c_str {
+    ($str:expr) => {{
+        const S: &str = concat!($str, "\0");
+        const C: &$crate::str::CStr = match $crate::str::CStr::from_bytes_with_nul(S.as_bytes()) {
+            Ok(v) => v,
+            Err(_) => panic!("string contains interior NUL"),
+        };
+        C
+    }};
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_cstr_to_str() {
+        let good_bytes = b"\xf0\x9f\xa6\x80\0";
+        let checked_cstr = CStr::from_bytes_with_nul(good_bytes).unwrap();
+        let checked_str = checked_cstr.to_str().unwrap();
+        assert_eq!(checked_str, "🦀");
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_cstr_to_str_panic() {
+        let bad_bytes = b"\xc3\x28\0";
+        let checked_cstr = CStr::from_bytes_with_nul(bad_bytes).unwrap();
+        checked_cstr.to_str().unwrap();
+    }
+
+    #[test]
+    fn test_cstr_as_str_unchecked() {
+        let good_bytes = b"\xf0\x9f\x90\xA7\0";
+        let checked_cstr = CStr::from_bytes_with_nul(good_bytes).unwrap();
+        let unchecked_str = unsafe { checked_cstr.as_str_unchecked() };
+        assert_eq!(unchecked_str, "🐧");
+    }
+}
+
+/// Allows formatting of [`fmt::Arguments`] into a raw buffer.
+///
+/// It does not fail if callers write past the end of the buffer so that they can calculate the
+/// size required to fit everything.
+///
+/// # Invariants
+///
+/// The memory region between `pos` (inclusive) and `end` (exclusive) is valid for writes if `pos`
+/// is less than `end`.
+pub(crate) struct RawFormatter {
+    // Use `usize` to use `saturating_*` functions.
+    beg: usize,
+    pos: usize,
+    end: usize,
+}
+
+impl RawFormatter {
+    /// Creates a new instance of [`RawFormatter`] with an empty buffer.
+    fn new() -> Self {
+        // INVARIANT: The buffer is empty, so the region that needs to be writable is empty.
+        Self {
+            beg: 0,
+            pos: 0,
+            end: 0,
+        }
+    }
+
+    /// Creates a new instance of [`RawFormatter`] with the given buffer pointers.
+    ///
+    /// # Safety
+    ///
+    /// If `pos` is less than `end`, then the region between `pos` (inclusive) and `end`
+    /// (exclusive) must be valid for writes for the lifetime of the returned [`RawFormatter`].
+    pub(crate) unsafe fn from_ptrs(pos: *mut u8, end: *mut u8) -> Self {
+        // INVARIANT: The safety requirements guarantee the type invariants.
+        Self {
+            beg: pos as _,
+            pos: pos as _,
+            end: end as _,
+        }
+    }
+
+    /// Creates a new instance of [`RawFormatter`] with the given buffer.
+    ///
+    /// # Safety
+    ///
+    /// The memory region starting at `buf` and extending for `len` bytes must be valid for writes
+    /// for the lifetime of the returned [`RawFormatter`].
+    pub(crate) unsafe fn from_buffer(buf: *mut u8, len: usize) -> Self {
+        let pos = buf as usize;
+        // INVARIANT: We ensure that `end` is never less then `buf`, and the safety requirements
+        // guarantees that the memory region is valid for writes.
+        Self {
+            pos,
+            beg: pos,
+            end: pos.saturating_add(len),
+        }
+    }
+
+    /// Returns the current insert position.
+    ///
+    /// N.B. It may point to invalid memory.
+    pub(crate) fn pos(&self) -> *mut u8 {
+        self.pos as _
+    }
+
+    /// Return the number of bytes written to the formatter.
+    pub(crate) fn bytes_written(&self) -> usize {
+        self.pos - self.beg
+    }
+}
+
+impl fmt::Write for RawFormatter {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        // `pos` value after writing `len` bytes. This does not have to be bounded by `end`, but we
+        // don't want it to wrap around to 0.
+        let pos_new = self.pos.saturating_add(s.len());
+
+        // Amount that we can copy. `saturating_sub` ensures we get 0 if `pos` goes past `end`.
+        let len_to_copy = core::cmp::min(pos_new, self.end).saturating_sub(self.pos);
+
+        if len_to_copy > 0 {
+            // SAFETY: If `len_to_copy` is non-zero, then we know `pos` has not gone past `end`
+            // yet, so it is valid for write per the type invariants.
+            unsafe {
+                core::ptr::copy_nonoverlapping(
+                    s.as_bytes().as_ptr(),
+                    self.pos as *mut u8,
+                    len_to_copy,
+                )
+            };
+        }
+
+        self.pos = pos_new;
+        Ok(())
+    }
+}
+
+/// Allows formatting of [`fmt::Arguments`] into a raw buffer.
+///
+/// Fails if callers attempt to write more than will fit in the buffer.
+pub(crate) struct Formatter(RawFormatter);
+
+impl Formatter {
+    /// Creates a new instance of [`Formatter`] with the given buffer.
+    ///
+    /// # Safety
+    ///
+    /// The memory region starting at `buf` and extending for `len` bytes must be valid for writes
+    /// for the lifetime of the returned [`Formatter`].
+    pub(crate) unsafe fn from_buffer(buf: *mut u8, len: usize) -> Self {
+        // SAFETY: The safety requirements of this function satisfy those of the callee.
+        Self(unsafe { RawFormatter::from_buffer(buf, len) })
+    }
+}
+
+impl Deref for Formatter {
+    type Target = RawFormatter;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl fmt::Write for Formatter {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        self.0.write_str(s)?;
+
+        // Fail the request if we go past the end of the buffer.
+        if self.0.pos > self.0.end {
+            Err(fmt::Error)
+        } else {
+            Ok(())
+        }
+    }
+}
+
+/// An owned string that is guaranteed to have exactly one `NUL` byte, which is at the end.
+///
+/// Used for interoperability with kernel APIs that take C strings.
+///
+/// # Invariants
+///
+/// The string is always `NUL`-terminated and contains no other `NUL` bytes.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::{str::CString, fmt};
+///
+/// let s = CString::try_from_fmt(fmt!("{}{}{}", "abc", 10, 20)).unwrap();
+/// assert_eq!(s.as_bytes_with_nul(), "abc1020\0".as_bytes());
+///
+/// let tmp = "testing";
+/// let s = CString::try_from_fmt(fmt!("{tmp}{}", 123)).unwrap();
+/// assert_eq!(s.as_bytes_with_nul(), "testing123\0".as_bytes());
+///
+/// // This fails because it has an embedded `NUL` byte.
+/// let s = CString::try_from_fmt(fmt!("a\0b{}", 123));
+/// assert_eq!(s.is_ok(), false);
+/// ```
+pub struct CString {
+    buf: Vec<u8>,
+}
+
+impl CString {
+    /// Creates an instance of [`CString`] from the given formatted arguments.
+    pub fn try_from_fmt(args: fmt::Arguments<'_>) -> Result<Self, Error> {
+        // Calculate the size needed (formatted string plus `NUL` terminator).
+        let mut f = RawFormatter::new();
+        f.write_fmt(args)?;
+        f.write_str("\0")?;
+        let size = f.bytes_written();
+
+        // Allocate a vector with the required number of bytes, and write to it.
+        let mut buf = Vec::try_with_capacity(size)?;
+        // SAFETY: The buffer stored in `buf` is at least of size `size` and is valid for writes.
+        let mut f = unsafe { Formatter::from_buffer(buf.as_mut_ptr(), size) };
+        f.write_fmt(args)?;
+        f.write_str("\0")?;
+
+        // SAFETY: The number of bytes that can be written to `f` is bounded by `size`, which is
+        // `buf`'s capacity. The contents of the buffer have been initialised by writes to `f`.
+        unsafe { buf.set_len(f.bytes_written()) };
+
+        // Check that there are no `NUL` bytes before the end.
+        // SAFETY: The buffer is valid for read because `f.bytes_written()` is bounded by `size`
+        // (which the minimum buffer size) and is non-zero (we wrote at least the `NUL` terminator)
+        // so `f.bytes_written() - 1` doesn't underflow.
+        let ptr = unsafe { bindings::memchr(buf.as_ptr().cast(), 0, (f.bytes_written() - 1) as _) };
+        if !ptr.is_null() {
+            return Err(EINVAL);
+        }
+
+        // INVARIANT: We wrote the `NUL` terminator and checked above that no other `NUL` bytes
+        // exist in the buffer.
+        Ok(Self { buf })
+    }
+}
+
+impl Deref for CString {
+    type Target = CStr;
+
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: The type invariants guarantee that the string is `NUL`-terminated and that no
+        // other `NUL` bytes exist.
+        unsafe { CStr::from_bytes_with_nul_unchecked(self.buf.as_slice()) }
+    }
+}
+
+impl<'a> TryFrom<&'a CStr> for CString {
+    type Error = AllocError;
+
+    fn try_from(cstr: &'a CStr) -> Result<CString, AllocError> {
+        let mut buf = Vec::new();
+
+        buf.try_extend_from_slice(cstr.as_bytes_with_nul())
+            .map_err(|_| AllocError)?;
+
+        // INVARIANT: The `CStr` and `CString` types have the same invariants for
+        // the string data, and we copied it over without changes.
+        Ok(CString { buf })
+    }
+}
+
+/// A convenience alias for [`core::format_args`].
+#[macro_export]
+macro_rules! fmt {
+    ($($f:tt)*) => ( core::format_args!($($f)*) )
+}
diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
new file mode 100644
index 0000000000..d219ee518e
--- /dev/null
+++ b/rust/kernel/sync.rs
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Synchronisation primitives.
+//!
+//! This module contains the kernel APIs related to synchronisation that have been ported or
+//! wrapped for usage by Rust code in the kernel.
+
+use crate::types::Opaque;
+
+mod arc;
+mod condvar;
+pub mod lock;
+mod locked_by;
+
+pub use arc::{Arc, ArcBorrow, UniqueArc};
+pub use condvar::CondVar;
+pub use lock::{mutex::Mutex, spinlock::SpinLock};
+pub use locked_by::LockedBy;
+
+/// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
+#[repr(transparent)]
+pub struct LockClassKey(Opaque<bindings::lock_class_key>);
+
+// SAFETY: `bindings::lock_class_key` is designed to be used concurrently from multiple threads and
+// provides its own synchronization.
+unsafe impl Sync for LockClassKey {}
+
+impl LockClassKey {
+    /// Creates a new lock class key.
+    pub const fn new() -> Self {
+        Self(Opaque::uninit())
+    }
+
+    pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key {
+        self.0.get()
+    }
+}
+
+/// Defines a new static lock class and returns a pointer to it.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! static_lock_class {
+    () => {{
+        static CLASS: $crate::sync::LockClassKey = $crate::sync::LockClassKey::new();
+        &CLASS
+    }};
+}
+
+/// Returns the given string, if one is provided, otherwise generates one based on the source code
+/// location.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! optional_name {
+    () => {
+        $crate::c_str!(::core::concat!(::core::file!(), ":", ::core::line!()))
+    };
+    ($name:literal) => {
+        $crate::c_str!($name)
+    };
+}
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
new file mode 100644
index 0000000000..3d496391a9
--- /dev/null
+++ b/rust/kernel/sync/arc.rs
@@ -0,0 +1,637 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! A reference-counted pointer.
+//!
+//! This module implements a way for users to create reference-counted objects and pointers to
+//! them. Such a pointer automatically increments and decrements the count, and drops the
+//! underlying object when it reaches zero. It is also safe to use concurrently from multiple
+//! threads.
+//!
+//! It is different from the standard library's [`Arc`] in a few ways:
+//! 1. It is backed by the kernel's `refcount_t` type.
+//! 2. It does not support weak references, which allows it to be half the size.
+//! 3. It saturates the reference count instead of aborting when it goes over a threshold.
+//! 4. It does not provide a `get_mut` method, so the ref counted object is pinned.
+//!
+//! [`Arc`]: https://doc.rust-lang.org/std/sync/struct.Arc.html
+
+use crate::{
+    bindings,
+    error::{self, Error},
+    init::{self, InPlaceInit, Init, PinInit},
+    try_init,
+    types::{ForeignOwnable, Opaque},
+};
+use alloc::boxed::Box;
+use core::{
+    alloc::AllocError,
+    fmt,
+    marker::{PhantomData, Unsize},
+    mem::{ManuallyDrop, MaybeUninit},
+    ops::{Deref, DerefMut},
+    pin::Pin,
+    ptr::NonNull,
+};
+use macros::pin_data;
+
+mod std_vendor;
+
+/// A reference-counted pointer to an instance of `T`.
+///
+/// The reference count is incremented when new instances of [`Arc`] are created, and decremented
+/// when they are dropped. When the count reaches zero, the underlying `T` is also dropped.
+///
+/// # Invariants
+///
+/// The reference count on an instance of [`Arc`] is always non-zero.
+/// The object pointed to by [`Arc`] is always pinned.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::sync::Arc;
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// // Create a ref-counted instance of `Example`.
+/// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
+///
+/// // Get a new pointer to `obj` and increment the refcount.
+/// let cloned = obj.clone();
+///
+/// // Assert that both `obj` and `cloned` point to the same underlying object.
+/// assert!(core::ptr::eq(&*obj, &*cloned));
+///
+/// // Destroy `obj` and decrement its refcount.
+/// drop(obj);
+///
+/// // Check that the values are still accessible through `cloned`.
+/// assert_eq!(cloned.a, 10);
+/// assert_eq!(cloned.b, 20);
+///
+/// // The refcount drops to zero when `cloned` goes out of scope, and the memory is freed.
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// Using `Arc<T>` as the type of `self`:
+///
+/// ```
+/// use kernel::sync::Arc;
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// impl Example {
+///     fn take_over(self: Arc<Self>) {
+///         // ...
+///     }
+///
+///     fn use_reference(self: &Arc<Self>) {
+///         // ...
+///     }
+/// }
+///
+/// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
+/// obj.use_reference();
+/// obj.take_over();
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// Coercion from `Arc<Example>` to `Arc<dyn MyTrait>`:
+///
+/// ```
+/// use kernel::sync::{Arc, ArcBorrow};
+///
+/// trait MyTrait {
+///     // Trait has a function whose `self` type is `Arc<Self>`.
+///     fn example1(self: Arc<Self>) {}
+///
+///     // Trait has a function whose `self` type is `ArcBorrow<'_, Self>`.
+///     fn example2(self: ArcBorrow<'_, Self>) {}
+/// }
+///
+/// struct Example;
+/// impl MyTrait for Example {}
+///
+/// // `obj` has type `Arc<Example>`.
+/// let obj: Arc<Example> = Arc::try_new(Example)?;
+///
+/// // `coerced` has type `Arc<dyn MyTrait>`.
+/// let coerced: Arc<dyn MyTrait> = obj;
+/// # Ok::<(), Error>(())
+/// ```
+pub struct Arc<T: ?Sized> {
+    ptr: NonNull<ArcInner<T>>,
+    _p: PhantomData<ArcInner<T>>,
+}
+
+#[pin_data]
+#[repr(C)]
+struct ArcInner<T: ?Sized> {
+    refcount: Opaque<bindings::refcount_t>,
+    data: T,
+}
+
+// This is to allow [`Arc`] (and variants) to be used as the type of `self`.
+impl<T: ?Sized> core::ops::Receiver for Arc<T> {}
+
+// This is to allow coercion from `Arc<T>` to `Arc<U>` if `T` can be converted to the
+// dynamically-sized type (DST) `U`.
+impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::CoerceUnsized<Arc<U>> for Arc<T> {}
+
+// This is to allow `Arc<U>` to be dispatched on when `Arc<T>` can be coerced into `Arc<U>`.
+impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<Arc<U>> for Arc<T> {}
+
+// SAFETY: It is safe to send `Arc<T>` to another thread when the underlying `T` is `Sync` because
+// it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs
+// `T` to be `Send` because any thread that has an `Arc<T>` may ultimately access `T` using a
+// mutable reference when the reference count reaches zero and `T` is dropped.
+unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
+
+// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync`
+// because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
+// it needs `T` to be `Send` because any thread that has a `&Arc<T>` may clone it and get an
+// `Arc<T>` on that thread, so the thread may ultimately access `T` using a mutable reference when
+// the reference count reaches zero and `T` is dropped.
+unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
+
+impl<T> Arc<T> {
+    /// Constructs a new reference counted instance of `T`.
+    pub fn try_new(contents: T) -> Result<Self, AllocError> {
+        // INVARIANT: The refcount is initialised to a non-zero value.
+        let value = ArcInner {
+            // SAFETY: There are no safety requirements for this FFI call.
+            refcount: Opaque::new(unsafe { bindings::REFCOUNT_INIT(1) }),
+            data: contents,
+        };
+
+        let inner = Box::try_new(value)?;
+
+        // SAFETY: We just created `inner` with a reference count of 1, which is owned by the new
+        // `Arc` object.
+        Ok(unsafe { Self::from_inner(Box::leak(inner).into()) })
+    }
+
+    /// Use the given initializer to in-place initialize a `T`.
+    ///
+    /// If `T: !Unpin` it will not be able to move afterwards.
+    #[inline]
+    pub fn pin_init<E>(init: impl PinInit<T, E>) -> error::Result<Self>
+    where
+        Error: From<E>,
+    {
+        UniqueArc::pin_init(init).map(|u| u.into())
+    }
+
+    /// Use the given initializer to in-place initialize a `T`.
+    ///
+    /// This is equivalent to [`Arc<T>::pin_init`], since an [`Arc`] is always pinned.
+    #[inline]
+    pub fn init<E>(init: impl Init<T, E>) -> error::Result<Self>
+    where
+        Error: From<E>,
+    {
+        UniqueArc::init(init).map(|u| u.into())
+    }
+}
+
+impl<T: ?Sized> Arc<T> {
+    /// Constructs a new [`Arc`] from an existing [`ArcInner`].
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `inner` points to a valid location and has a non-zero reference
+    /// count, one of which will be owned by the new [`Arc`] instance.
+    unsafe fn from_inner(inner: NonNull<ArcInner<T>>) -> Self {
+        // INVARIANT: By the safety requirements, the invariants hold.
+        Arc {
+            ptr: inner,
+            _p: PhantomData,
+        }
+    }
+
+    /// Returns an [`ArcBorrow`] from the given [`Arc`].
+    ///
+    /// This is useful when the argument of a function call is an [`ArcBorrow`] (e.g., in a method
+    /// receiver), but we have an [`Arc`] instead. Getting an [`ArcBorrow`] is free when optimised.
+    #[inline]
+    pub fn as_arc_borrow(&self) -> ArcBorrow<'_, T> {
+        // SAFETY: The constraint that the lifetime of the shared reference must outlive that of
+        // the returned `ArcBorrow` ensures that the object remains alive and that no mutable
+        // reference can be created.
+        unsafe { ArcBorrow::new(self.ptr) }
+    }
+
+    /// Compare whether two [`Arc`] pointers reference the same underlying object.
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        core::ptr::eq(this.ptr.as_ptr(), other.ptr.as_ptr())
+    }
+}
+
+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 _
+    }
+
+    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> ArcBorrow<'a, T> {
+        // SAFETY: By the safety requirement of this function, we know that `ptr` came from
+        // a previous call to `Arc::into_foreign`.
+        let inner = NonNull::new(ptr as *mut ArcInner<T>).unwrap();
+
+        // SAFETY: The safety requirements of `from_foreign` ensure that the object remains alive
+        // for the lifetime of the returned value.
+        unsafe { ArcBorrow::new(inner) }
+    }
+
+    unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
+        // 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
+        // holds a reference count increment that is transferrable to us.
+        unsafe { Self::from_inner(NonNull::new(ptr as _).unwrap()) }
+    }
+}
+
+impl<T: ?Sized> Deref for Arc<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is
+        // safe to dereference it.
+        unsafe { &self.ptr.as_ref().data }
+    }
+}
+
+impl<T: ?Sized> AsRef<T> for Arc<T> {
+    fn as_ref(&self) -> &T {
+        self.deref()
+    }
+}
+
+impl<T: ?Sized> Clone for Arc<T> {
+    fn clone(&self) -> Self {
+        // INVARIANT: C `refcount_inc` saturates the refcount, so it cannot overflow to zero.
+        // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is
+        // safe to increment the refcount.
+        unsafe { bindings::refcount_inc(self.ptr.as_ref().refcount.get()) };
+
+        // SAFETY: We just incremented the refcount. This increment is now owned by the new `Arc`.
+        unsafe { Self::from_inner(self.ptr) }
+    }
+}
+
+impl<T: ?Sized> Drop for Arc<T> {
+    fn drop(&mut self) {
+        // SAFETY: By the type invariant, there is necessarily a reference to the object. We cannot
+        // touch `refcount` after it's decremented to a non-zero value because another thread/CPU
+        // may concurrently decrement it to zero and free it. It is ok to have a raw pointer to
+        // freed/invalid memory as long as it is never dereferenced.
+        let refcount = unsafe { self.ptr.as_ref() }.refcount.get();
+
+        // INVARIANT: If the refcount reaches zero, there are no other instances of `Arc`, and
+        // this instance is being dropped, so the broken invariant is not observable.
+        // SAFETY: Also by the type invariant, we are allowed to decrement the refcount.
+        let is_zero = unsafe { bindings::refcount_dec_and_test(refcount) };
+        if is_zero {
+            // The count reached zero, we must free the memory.
+            //
+            // SAFETY: The pointer was initialised from the result of `Box::leak`.
+            unsafe { Box::from_raw(self.ptr.as_ptr()) };
+        }
+    }
+}
+
+impl<T: ?Sized> From<UniqueArc<T>> for Arc<T> {
+    fn from(item: UniqueArc<T>) -> Self {
+        item.inner
+    }
+}
+
+impl<T: ?Sized> From<Pin<UniqueArc<T>>> for Arc<T> {
+    fn from(item: Pin<UniqueArc<T>>) -> Self {
+        // SAFETY: The type invariants of `Arc` guarantee that the data is pinned.
+        unsafe { Pin::into_inner_unchecked(item).inner }
+    }
+}
+
+/// A borrowed reference to an [`Arc`] instance.
+///
+/// For cases when one doesn't ever need to increment the refcount on the allocation, it is simpler
+/// to use just `&T`, which we can trivially get from an `Arc<T>` instance.
+///
+/// However, when one may need to increment the refcount, it is preferable to use an `ArcBorrow<T>`
+/// over `&Arc<T>` because the latter results in a double-indirection: a pointer (shared reference)
+/// to a pointer (`Arc<T>`) to the object (`T`). An [`ArcBorrow`] eliminates this double
+/// indirection while still allowing one to increment the refcount and getting an `Arc<T>` when/if
+/// needed.
+///
+/// # Invariants
+///
+/// There are no mutable references to the underlying [`Arc`], and it remains valid for the
+/// lifetime of the [`ArcBorrow`] instance.
+///
+/// # Example
+///
+/// ```
+/// use kernel::sync::{Arc, ArcBorrow};
+///
+/// struct Example;
+///
+/// fn do_something(e: ArcBorrow<'_, Example>) -> Arc<Example> {
+///     e.into()
+/// }
+///
+/// let obj = Arc::try_new(Example)?;
+/// let cloned = do_something(obj.as_arc_borrow());
+///
+/// // Assert that both `obj` and `cloned` point to the same underlying object.
+/// assert!(core::ptr::eq(&*obj, &*cloned));
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// Using `ArcBorrow<T>` as the type of `self`:
+///
+/// ```
+/// use kernel::sync::{Arc, ArcBorrow};
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// impl Example {
+///     fn use_reference(self: ArcBorrow<'_, Self>) {
+///         // ...
+///     }
+/// }
+///
+/// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
+/// obj.as_arc_borrow().use_reference();
+/// # Ok::<(), Error>(())
+/// ```
+pub struct ArcBorrow<'a, T: ?Sized + 'a> {
+    inner: NonNull<ArcInner<T>>,
+    _p: PhantomData<&'a ()>,
+}
+
+// This is to allow [`ArcBorrow`] (and variants) to be used as the type of `self`.
+impl<T: ?Sized> core::ops::Receiver for ArcBorrow<'_, T> {}
+
+// This is to allow `ArcBorrow<U>` to be dispatched on when `ArcBorrow<T>` can be coerced into
+// `ArcBorrow<U>`.
+impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<ArcBorrow<'_, U>>
+    for ArcBorrow<'_, T>
+{
+}
+
+impl<T: ?Sized> Clone for ArcBorrow<'_, T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<T: ?Sized> Copy for ArcBorrow<'_, T> {}
+
+impl<T: ?Sized> ArcBorrow<'_, T> {
+    /// Creates a new [`ArcBorrow`] instance.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure the following for the lifetime of the returned [`ArcBorrow`] instance:
+    /// 1. That `inner` remains valid;
+    /// 2. That no mutable references to `inner` are created.
+    unsafe fn new(inner: NonNull<ArcInner<T>>) -> Self {
+        // INVARIANT: The safety requirements guarantee the invariants.
+        Self {
+            inner,
+            _p: PhantomData,
+        }
+    }
+}
+
+impl<T: ?Sized> From<ArcBorrow<'_, T>> for Arc<T> {
+    fn from(b: ArcBorrow<'_, T>) -> Self {
+        // SAFETY: The existence of `b` guarantees that the refcount is non-zero. `ManuallyDrop`
+        // guarantees that `drop` isn't called, so it's ok that the temporary `Arc` doesn't own the
+        // increment.
+        ManuallyDrop::new(unsafe { Arc::from_inner(b.inner) })
+            .deref()
+            .clone()
+    }
+}
+
+impl<T: ?Sized> Deref for ArcBorrow<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: By the type invariant, the underlying object is still alive with no mutable
+        // references to it, so it is safe to create a shared reference.
+        unsafe { &self.inner.as_ref().data }
+    }
+}
+
+/// A refcounted object that is known to have a refcount of 1.
+///
+/// It is mutable and can be converted to an [`Arc`] so that it can be shared.
+///
+/// # Invariants
+///
+/// `inner` always has a reference count of 1.
+///
+/// # Examples
+///
+/// In the following example, we make changes to the inner object before turning it into an
+/// `Arc<Test>` object (after which point, it cannot be mutated directly). Note that `x.into()`
+/// cannot fail.
+///
+/// ```
+/// use kernel::sync::{Arc, UniqueArc};
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// fn test() -> Result<Arc<Example>> {
+///     let mut x = UniqueArc::try_new(Example { a: 10, b: 20 })?;
+///     x.a += 1;
+///     x.b += 1;
+///     Ok(x.into())
+/// }
+///
+/// # test().unwrap();
+/// ```
+///
+/// In the following example we first allocate memory for a ref-counted `Example` but we don't
+/// initialise it on allocation. We do initialise it later with a call to [`UniqueArc::write`],
+/// followed by a conversion to `Arc<Example>`. This is particularly useful when allocation happens
+/// in one context (e.g., sleepable) and initialisation in another (e.g., atomic):
+///
+/// ```
+/// use kernel::sync::{Arc, UniqueArc};
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// fn test() -> Result<Arc<Example>> {
+///     let x = UniqueArc::try_new_uninit()?;
+///     Ok(x.write(Example { a: 10, b: 20 }).into())
+/// }
+///
+/// # test().unwrap();
+/// ```
+///
+/// In the last example below, the caller gets a pinned instance of `Example` while converting to
+/// `Arc<Example>`; this is useful in scenarios where one needs a pinned reference during
+/// initialisation, for example, when initialising fields that are wrapped in locks.
+///
+/// ```
+/// use kernel::sync::{Arc, UniqueArc};
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// fn test() -> Result<Arc<Example>> {
+///     let mut pinned = Pin::from(UniqueArc::try_new(Example { a: 10, b: 20 })?);
+///     // We can modify `pinned` because it is `Unpin`.
+///     pinned.as_mut().a += 1;
+///     Ok(pinned.into())
+/// }
+///
+/// # test().unwrap();
+/// ```
+pub struct UniqueArc<T: ?Sized> {
+    inner: Arc<T>,
+}
+
+impl<T> UniqueArc<T> {
+    /// Tries to allocate a new [`UniqueArc`] instance.
+    pub fn try_new(value: T) -> Result<Self, AllocError> {
+        Ok(Self {
+            // INVARIANT: The newly-created object has a ref-count of 1.
+            inner: Arc::try_new(value)?,
+        })
+    }
+
+    /// Tries to allocate a new [`UniqueArc`] instance whose contents are not initialised yet.
+    pub fn try_new_uninit() -> Result<UniqueArc<MaybeUninit<T>>, AllocError> {
+        // INVARIANT: The refcount is initialised to a non-zero value.
+        let inner = Box::try_init::<AllocError>(try_init!(ArcInner {
+            // SAFETY: There are no safety requirements for this FFI call.
+            refcount: Opaque::new(unsafe { bindings::REFCOUNT_INIT(1) }),
+            data <- init::uninit::<T, AllocError>(),
+        }? AllocError))?;
+        Ok(UniqueArc {
+            // INVARIANT: The newly-created object has a ref-count of 1.
+            // SAFETY: The pointer from the `Box` is valid.
+            inner: unsafe { Arc::from_inner(Box::leak(inner).into()) },
+        })
+    }
+}
+
+impl<T> UniqueArc<MaybeUninit<T>> {
+    /// Converts a `UniqueArc<MaybeUninit<T>>` into a `UniqueArc<T>` by writing a value into it.
+    pub fn write(mut self, value: T) -> UniqueArc<T> {
+        self.deref_mut().write(value);
+        // SAFETY: We just wrote the value to be initialized.
+        unsafe { self.assume_init() }
+    }
+
+    /// Unsafely assume that `self` is initialized.
+    ///
+    /// # Safety
+    ///
+    /// The caller guarantees that the value behind this pointer has been initialized. It is
+    /// *immediate* UB to call this when the value is not initialized.
+    pub unsafe fn assume_init(self) -> UniqueArc<T> {
+        let inner = ManuallyDrop::new(self).inner.ptr;
+        UniqueArc {
+            // SAFETY: The new `Arc` is taking over `ptr` from `self.inner` (which won't be
+            // dropped). The types are compatible because `MaybeUninit<T>` is compatible with `T`.
+            inner: unsafe { Arc::from_inner(inner.cast()) },
+        }
+    }
+
+    /// Initialize `self` using the given initializer.
+    pub fn init_with<E>(mut self, init: impl Init<T, E>) -> core::result::Result<UniqueArc<T>, E> {
+        // SAFETY: The supplied pointer is valid for initialization.
+        match unsafe { init.__init(self.as_mut_ptr()) } {
+            // SAFETY: Initialization completed successfully.
+            Ok(()) => Ok(unsafe { self.assume_init() }),
+            Err(err) => Err(err),
+        }
+    }
+
+    /// Pin-initialize `self` using the given pin-initializer.
+    pub fn pin_init_with<E>(
+        mut self,
+        init: impl PinInit<T, E>,
+    ) -> core::result::Result<Pin<UniqueArc<T>>, E> {
+        // SAFETY: The supplied pointer is valid for initialization and we will later pin the value
+        // to ensure it does not move.
+        match unsafe { init.__pinned_init(self.as_mut_ptr()) } {
+            // SAFETY: Initialization completed successfully.
+            Ok(()) => Ok(unsafe { self.assume_init() }.into()),
+            Err(err) => Err(err),
+        }
+    }
+}
+
+impl<T: ?Sized> From<UniqueArc<T>> for Pin<UniqueArc<T>> {
+    fn from(obj: UniqueArc<T>) -> Self {
+        // SAFETY: It is not possible to move/replace `T` inside a `Pin<UniqueArc<T>>` (unless `T`
+        // is `Unpin`), so it is ok to convert it to `Pin<UniqueArc<T>>`.
+        unsafe { Pin::new_unchecked(obj) }
+    }
+}
+
+impl<T: ?Sized> Deref for UniqueArc<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        self.inner.deref()
+    }
+}
+
+impl<T: ?Sized> DerefMut for UniqueArc<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        // SAFETY: By the `Arc` type invariant, there is necessarily a reference to the object, so
+        // it is safe to dereference it. Additionally, we know there is only one reference when
+        // it's inside a `UniqueArc`, so it is safe to get a mutable reference.
+        unsafe { &mut self.inner.ptr.as_mut().data }
+    }
+}
+
+impl<T: fmt::Display + ?Sized> fmt::Display for UniqueArc<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self.deref(), f)
+    }
+}
+
+impl<T: fmt::Display + ?Sized> fmt::Display for Arc<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self.deref(), f)
+    }
+}
+
+impl<T: fmt::Debug + ?Sized> fmt::Debug for UniqueArc<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(self.deref(), f)
+    }
+}
+
+impl<T: fmt::Debug + ?Sized> fmt::Debug for Arc<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(self.deref(), f)
+    }
+}
diff --git a/rust/kernel/sync/arc/std_vendor.rs b/rust/kernel/sync/arc/std_vendor.rs
new file mode 100644
index 0000000000..a66a0c2831
--- /dev/null
+++ b/rust/kernel/sync/arc/std_vendor.rs
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! The contents of this file come from the Rust standard library, hosted in
+//! the <https://github.com/rust-lang/rust> repository, licensed under
+//! "Apache-2.0 OR MIT" and adapted for kernel use. For copyright details,
+//! see <https://github.com/rust-lang/rust/blob/master/COPYRIGHT>.
+
+use crate::sync::{arc::ArcInner, Arc};
+use core::any::Any;
+
+impl Arc<dyn Any + Send + Sync> {
+    /// Attempt to downcast the `Arc<dyn Any + Send + Sync>` to a concrete type.
+    pub fn downcast<T>(self) -> core::result::Result<Arc<T>, Self>
+    where
+        T: Any + Send + Sync,
+    {
+        if (*self).is::<T>() {
+            // SAFETY: We have just checked that the type is correct, so we can cast the pointer.
+            unsafe {
+                let ptr = self.ptr.cast::<ArcInner<T>>();
+                core::mem::forget(self);
+                Ok(Arc::from_inner(ptr))
+            }
+        } else {
+            Err(self)
+        }
+    }
+}
diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
new file mode 100644
index 0000000000..ed353399c4
--- /dev/null
+++ b/rust/kernel/sync/condvar.rs
@@ -0,0 +1,174 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! A condition variable.
+//!
+//! This module allows Rust code to use the kernel's [`struct wait_queue_head`] as a condition
+//! variable.
+
+use super::{lock::Backend, lock::Guard, LockClassKey};
+use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque};
+use core::marker::PhantomPinned;
+use macros::pin_data;
+
+/// Creates a [`CondVar`] initialiser with the given name and a newly-created lock class.
+#[macro_export]
+macro_rules! new_condvar {
+    ($($name:literal)?) => {
+        $crate::sync::CondVar::new($crate::optional_name!($($name)?), $crate::static_lock_class!())
+    };
+}
+
+/// A conditional variable.
+///
+/// Exposes the kernel's [`struct wait_queue_head`] as a condition variable. It allows the caller to
+/// atomically release the given lock and go to sleep. It reacquires the lock when it wakes up. And
+/// it wakes up when notified by another thread (via [`CondVar::notify_one`] or
+/// [`CondVar::notify_all`]) or because the thread received a signal. It may also wake up
+/// spuriously.
+///
+/// Instances of [`CondVar`] need a lock class and to be pinned. The recommended way to create such
+/// instances is with the [`pin_init`](crate::pin_init) and [`new_condvar`] macros.
+///
+/// # Examples
+///
+/// The following is an example of using a condvar with a mutex:
+///
+/// ```
+/// use kernel::sync::{CondVar, Mutex};
+/// use kernel::{new_condvar, new_mutex};
+///
+/// #[pin_data]
+/// pub struct Example {
+///     #[pin]
+///     value: Mutex<u32>,
+///
+///     #[pin]
+///     value_changed: CondVar,
+/// }
+///
+/// /// Waits for `e.value` to become `v`.
+/// fn wait_for_value(e: &Example, v: u32) {
+///     let mut guard = e.value.lock();
+///     while *guard != v {
+///         e.value_changed.wait_uninterruptible(&mut guard);
+///     }
+/// }
+///
+/// /// Increments `e.value` and notifies all potential waiters.
+/// fn increment(e: &Example) {
+///     *e.value.lock() += 1;
+///     e.value_changed.notify_all();
+/// }
+///
+/// /// Allocates a new boxed `Example`.
+/// fn new_example() -> Result<Pin<Box<Example>>> {
+///     Box::pin_init(pin_init!(Example {
+///         value <- new_mutex!(0),
+///         value_changed <- new_condvar!(),
+///     }))
+/// }
+/// ```
+///
+/// [`struct wait_queue_head`]: ../../../include/linux/wait.h
+#[pin_data]
+pub struct CondVar {
+    #[pin]
+    pub(crate) wait_list: Opaque<bindings::wait_queue_head>,
+
+    /// A condvar needs to be pinned because it contains a [`struct list_head`] that is
+    /// self-referential, so it cannot be safely moved once it is initialised.
+    #[pin]
+    _pin: PhantomPinned,
+}
+
+// SAFETY: `CondVar` only uses a `struct wait_queue_head`, which is safe to use on any thread.
+#[allow(clippy::non_send_fields_in_send_ty)]
+unsafe impl Send for CondVar {}
+
+// SAFETY: `CondVar` only uses a `struct wait_queue_head`, which is safe to use on multiple threads
+// concurrently.
+unsafe impl Sync for CondVar {}
+
+impl CondVar {
+    /// Constructs a new condvar initialiser.
+    #[allow(clippy::new_ret_no_self)]
+    pub fn new(name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self> {
+        pin_init!(Self {
+            _pin: PhantomPinned,
+            // SAFETY: `slot` is valid while the closure is called and both `name` and `key` have
+            // static lifetimes so they live indefinitely.
+            wait_list <- Opaque::ffi_init(|slot| unsafe {
+                bindings::__init_waitqueue_head(slot, name.as_char_ptr(), key.as_ptr())
+            }),
+        })
+    }
+
+    fn wait_internal<T: ?Sized, B: Backend>(&self, wait_state: u32, guard: &mut Guard<'_, T, B>) {
+        let wait = Opaque::<bindings::wait_queue_entry>::uninit();
+
+        // SAFETY: `wait` points to valid memory.
+        unsafe { bindings::init_wait(wait.get()) };
+
+        // SAFETY: Both `wait` and `wait_list` point to valid memory.
+        unsafe {
+            bindings::prepare_to_wait_exclusive(self.wait_list.get(), wait.get(), wait_state as _)
+        };
+
+        // SAFETY: No arguments, switches to another thread.
+        guard.do_unlocked(|| unsafe { bindings::schedule() });
+
+        // SAFETY: Both `wait` and `wait_list` point to valid memory.
+        unsafe { bindings::finish_wait(self.wait_list.get(), wait.get()) };
+    }
+
+    /// Releases the lock and waits for a notification in interruptible mode.
+    ///
+    /// Atomically releases the given lock (whose ownership is proven by the guard) and puts the
+    /// thread to sleep, reacquiring the lock on wake up. It wakes up when notified by
+    /// [`CondVar::notify_one`] or [`CondVar::notify_all`], or when the thread receives a signal.
+    /// It may also wake up spuriously.
+    ///
+    /// Returns whether there is a signal pending.
+    #[must_use = "wait returns if a signal is pending, so the caller must check the return value"]
+    pub fn wait<T: ?Sized, B: Backend>(&self, guard: &mut Guard<'_, T, B>) -> bool {
+        self.wait_internal(bindings::TASK_INTERRUPTIBLE, guard);
+        crate::current!().signal_pending()
+    }
+
+    /// Releases the lock and waits for a notification in uninterruptible mode.
+    ///
+    /// Similar to [`CondVar::wait`], except that the wait is not interruptible. That is, the
+    /// thread won't wake up due to signals. It may, however, wake up supirously.
+    pub fn wait_uninterruptible<T: ?Sized, B: Backend>(&self, guard: &mut Guard<'_, T, B>) {
+        self.wait_internal(bindings::TASK_UNINTERRUPTIBLE, guard)
+    }
+
+    /// Calls the kernel function to notify the appropriate number of threads with the given flags.
+    fn notify(&self, count: i32, flags: u32) {
+        // SAFETY: `wait_list` points to valid memory.
+        unsafe {
+            bindings::__wake_up(
+                self.wait_list.get(),
+                bindings::TASK_NORMAL,
+                count,
+                flags as _,
+            )
+        };
+    }
+
+    /// Wakes a single waiter up, if any.
+    ///
+    /// This is not 'sticky' in the sense that if no thread is waiting, the notification is lost
+    /// completely (as opposed to automatically waking up the next waiter).
+    pub fn notify_one(&self) {
+        self.notify(1, 0);
+    }
+
+    /// Wakes all waiters up, if any.
+    ///
+    /// This is not 'sticky' in the sense that if no thread is waiting, the notification is lost
+    /// completely (as opposed to automatically waking up the next waiter).
+    pub fn notify_all(&self) {
+        self.notify(0, 0);
+    }
+}
diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
new file mode 100644
index 0000000000..70a785f047
--- /dev/null
+++ b/rust/kernel/sync/lock.rs
@@ -0,0 +1,191 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Generic kernel lock and guard.
+//!
+//! It contains a generic Rust lock and guard that allow for different backends (e.g., mutexes,
+//! spinlocks, raw spinlocks) to be provided with minimal effort.
+
+use super::LockClassKey;
+use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque, types::ScopeGuard};
+use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned};
+use macros::pin_data;
+
+pub mod mutex;
+pub mod spinlock;
+
+/// The "backend" of a lock.
+///
+/// It is the actual implementation of the lock, without the need to repeat patterns used in all
+/// locks.
+///
+/// # Safety
+///
+/// - Implementers must ensure that only one thread/CPU may access the protected data once the lock
+/// is owned, that is, between calls to `lock` and `unlock`.
+/// - Implementers must also ensure that `relock` uses the same locking method as the original
+/// lock operation.
+pub unsafe trait Backend {
+    /// The state required by the lock.
+    type State;
+
+    /// The state required to be kept between lock and unlock.
+    type GuardState;
+
+    /// Initialises the lock.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must be valid for write for the duration of the call, while `name` and `key` must
+    /// remain valid for read indefinitely.
+    unsafe fn init(
+        ptr: *mut Self::State,
+        name: *const core::ffi::c_char,
+        key: *mut bindings::lock_class_key,
+    );
+
+    /// Acquires the lock, making the caller its owner.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that [`Backend::init`] has been previously called.
+    #[must_use]
+    unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState;
+
+    /// Releases the lock, giving up its ownership.
+    ///
+    /// # Safety
+    ///
+    /// It must only be called by the current owner of the lock.
+    unsafe fn unlock(ptr: *mut Self::State, guard_state: &Self::GuardState);
+
+    /// Reacquires the lock, making the caller its owner.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that `guard_state` comes from a previous call to [`Backend::lock`] (or
+    /// variant) that has been unlocked with [`Backend::unlock`] and will be relocked now.
+    unsafe fn relock(ptr: *mut Self::State, guard_state: &mut Self::GuardState) {
+        // SAFETY: The safety requirements ensure that the lock is initialised.
+        *guard_state = unsafe { Self::lock(ptr) };
+    }
+}
+
+/// A mutual exclusion primitive.
+///
+/// Exposes one of the kernel locking primitives. Which one is exposed depends on the lock
+/// [`Backend`] specified as the generic parameter `B`.
+#[pin_data]
+pub struct Lock<T: ?Sized, B: Backend> {
+    /// The kernel lock object.
+    #[pin]
+    state: Opaque<B::State>,
+
+    /// Some locks are known to be self-referential (e.g., mutexes), while others are architecture
+    /// or config defined (e.g., spinlocks). So we conservatively require them to be pinned in case
+    /// some architecture uses self-references now or in the future.
+    #[pin]
+    _pin: PhantomPinned,
+
+    /// The data protected by the lock.
+    pub(crate) data: UnsafeCell<T>,
+}
+
+// SAFETY: `Lock` can be transferred across thread boundaries iff the data it protects can.
+unsafe impl<T: ?Sized + Send, B: Backend> Send for Lock<T, B> {}
+
+// SAFETY: `Lock` serialises the interior mutability it provides, so it is `Sync` as long as the
+// data it protects is `Send`.
+unsafe impl<T: ?Sized + Send, B: Backend> Sync for Lock<T, B> {}
+
+impl<T, B: Backend> Lock<T, B> {
+    /// Constructs a new lock initialiser.
+    #[allow(clippy::new_ret_no_self)]
+    pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self> {
+        pin_init!(Self {
+            data: UnsafeCell::new(t),
+            _pin: PhantomPinned,
+            // SAFETY: `slot` is valid while the closure is called and both `name` and `key` have
+            // static lifetimes so they live indefinitely.
+            state <- Opaque::ffi_init(|slot| unsafe {
+                B::init(slot, name.as_char_ptr(), key.as_ptr())
+            }),
+        })
+    }
+}
+
+impl<T: ?Sized, B: Backend> Lock<T, B> {
+    /// Acquires the lock and gives the caller access to the data protected by it.
+    pub fn lock(&self) -> Guard<'_, T, B> {
+        // SAFETY: The constructor of the type calls `init`, so the existence of the object proves
+        // that `init` was called.
+        let state = unsafe { B::lock(self.state.get()) };
+        // SAFETY: The lock was just acquired.
+        unsafe { Guard::new(self, state) }
+    }
+}
+
+/// A lock guard.
+///
+/// Allows mutual exclusion primitives that implement the [`Backend`] trait to automatically unlock
+/// when a guard goes out of scope. It also provides a safe and convenient way to access the data
+/// protected by the lock.
+#[must_use = "the lock unlocks immediately when the guard is unused"]
+pub struct Guard<'a, T: ?Sized, B: Backend> {
+    pub(crate) lock: &'a Lock<T, B>,
+    pub(crate) state: B::GuardState,
+    _not_send: PhantomData<*mut ()>,
+}
+
+// SAFETY: `Guard` is sync when the data protected by the lock is also sync.
+unsafe impl<T: Sync + ?Sized, B: Backend> Sync for Guard<'_, T, B> {}
+
+impl<T: ?Sized, B: Backend> Guard<'_, T, B> {
+    pub(crate) fn do_unlocked(&mut self, cb: impl FnOnce()) {
+        // SAFETY: The caller owns the lock, so it is safe to unlock it.
+        unsafe { B::unlock(self.lock.state.get(), &self.state) };
+
+        // SAFETY: The lock was just unlocked above and is being relocked now.
+        let _relock =
+            ScopeGuard::new(|| unsafe { B::relock(self.lock.state.get(), &mut self.state) });
+
+        cb();
+    }
+}
+
+impl<T: ?Sized, B: Backend> core::ops::Deref for Guard<'_, T, B> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: The caller owns the lock, so it is safe to deref the protected data.
+        unsafe { &*self.lock.data.get() }
+    }
+}
+
+impl<T: ?Sized, B: Backend> core::ops::DerefMut for Guard<'_, T, B> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        // SAFETY: The caller owns the lock, so it is safe to deref the protected data.
+        unsafe { &mut *self.lock.data.get() }
+    }
+}
+
+impl<T: ?Sized, B: Backend> Drop for Guard<'_, T, B> {
+    fn drop(&mut self) {
+        // SAFETY: The caller owns the lock, so it is safe to unlock it.
+        unsafe { B::unlock(self.lock.state.get(), &self.state) };
+    }
+}
+
+impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> {
+    /// Constructs a new immutable lock guard.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that it owns the lock.
+    pub(crate) unsafe fn new(lock: &'a Lock<T, B>, state: B::GuardState) -> Self {
+        Self {
+            lock,
+            state,
+            _not_send: PhantomData,
+        }
+    }
+}
diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs
new file mode 100644
index 0000000000..09276fedc0
--- /dev/null
+++ b/rust/kernel/sync/lock/mutex.rs
@@ -0,0 +1,119 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! A kernel mutex.
+//!
+//! This module allows Rust code to use the kernel's `struct mutex`.
+
+use crate::bindings;
+
+/// Creates a [`Mutex`] initialiser with the given name and a newly-created lock class.
+///
+/// It uses the name if one is given, otherwise it generates one based on the file name and line
+/// number.
+#[macro_export]
+macro_rules! new_mutex {
+    ($inner:expr $(, $name:literal)? $(,)?) => {
+        $crate::sync::Mutex::new(
+            $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!())
+    };
+}
+
+/// A mutual exclusion primitive.
+///
+/// Exposes the kernel's [`struct mutex`]. When multiple threads attempt to lock the same mutex,
+/// only one at a time is allowed to progress, the others will block (sleep) until the mutex is
+/// unlocked, at which point another thread will be allowed to wake up and make progress.
+///
+/// Since it may block, [`Mutex`] needs to be used with care in atomic contexts.
+///
+/// Instances of [`Mutex`] need a lock class and to be pinned. The recommended way to create such
+/// instances is with the [`pin_init`](crate::pin_init) and [`new_mutex`] macros.
+///
+/// # Examples
+///
+/// The following example shows how to declare, allocate and initialise a struct (`Example`) that
+/// contains an inner struct (`Inner`) that is protected by a mutex.
+///
+/// ```
+/// use kernel::{init::InPlaceInit, init::PinInit, new_mutex, pin_init, sync::Mutex};
+///
+/// struct Inner {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// #[pin_data]
+/// struct Example {
+///     c: u32,
+///     #[pin]
+///     d: Mutex<Inner>,
+/// }
+///
+/// impl Example {
+///     fn new() -> impl PinInit<Self> {
+///         pin_init!(Self {
+///             c: 10,
+///             d <- new_mutex!(Inner { a: 20, b: 30 }),
+///         })
+///     }
+/// }
+///
+/// // Allocate a boxed `Example`.
+/// let e = Box::pin_init(Example::new())?;
+/// assert_eq!(e.c, 10);
+/// assert_eq!(e.d.lock().a, 20);
+/// assert_eq!(e.d.lock().b, 30);
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// The following example shows how to use interior mutability to modify the contents of a struct
+/// protected by a mutex despite only having a shared reference:
+///
+/// ```
+/// use kernel::sync::Mutex;
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// fn example(m: &Mutex<Example>) {
+///     let mut guard = m.lock();
+///     guard.a += 10;
+///     guard.b += 20;
+/// }
+/// ```
+///
+/// [`struct mutex`]: ../../../../include/linux/mutex.h
+pub type Mutex<T> = super::Lock<T, MutexBackend>;
+
+/// A kernel `struct mutex` lock backend.
+pub struct MutexBackend;
+
+// SAFETY: The underlying kernel `struct mutex` object ensures mutual exclusion.
+unsafe impl super::Backend for MutexBackend {
+    type State = bindings::mutex;
+    type GuardState = ();
+
+    unsafe fn init(
+        ptr: *mut Self::State,
+        name: *const core::ffi::c_char,
+        key: *mut bindings::lock_class_key,
+    ) {
+        // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and
+        // `key` are valid for read indefinitely.
+        unsafe { bindings::__mutex_init(ptr, name, key) }
+    }
+
+    unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {
+        // SAFETY: The safety requirements of this function ensure that `ptr` points to valid
+        // memory, and that it has been initialised before.
+        unsafe { bindings::mutex_lock(ptr) };
+    }
+
+    unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
+        // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the
+        // caller is the owner of the mutex.
+        unsafe { bindings::mutex_unlock(ptr) };
+    }
+}
diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
new file mode 100644
index 0000000000..91eb2c9e91
--- /dev/null
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -0,0 +1,118 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! A kernel spinlock.
+//!
+//! This module allows Rust code to use the kernel's `spinlock_t`.
+
+use crate::bindings;
+
+/// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
+///
+/// It uses the name if one is given, otherwise it generates one based on the file name and line
+/// number.
+#[macro_export]
+macro_rules! new_spinlock {
+    ($inner:expr $(, $name:literal)? $(,)?) => {
+        $crate::sync::SpinLock::new(
+            $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!())
+    };
+}
+
+/// A spinlock.
+///
+/// Exposes the kernel's [`spinlock_t`]. When multiple CPUs attempt to lock the same spinlock, only
+/// one at a time is allowed to progress, the others will block (spinning) until the spinlock is
+/// unlocked, at which point another CPU will be allowed to make progress.
+///
+/// Instances of [`SpinLock`] need a lock class and to be pinned. The recommended way to create such
+/// instances is with the [`pin_init`](crate::pin_init) and [`new_spinlock`] macros.
+///
+/// # Examples
+///
+/// The following example shows how to declare, allocate and initialise a struct (`Example`) that
+/// contains an inner struct (`Inner`) that is protected by a spinlock.
+///
+/// ```
+/// use kernel::{init::InPlaceInit, init::PinInit, new_spinlock, pin_init, sync::SpinLock};
+///
+/// struct Inner {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// #[pin_data]
+/// struct Example {
+///     c: u32,
+///     #[pin]
+///     d: SpinLock<Inner>,
+/// }
+///
+/// impl Example {
+///     fn new() -> impl PinInit<Self> {
+///         pin_init!(Self {
+///             c: 10,
+///             d <- new_spinlock!(Inner { a: 20, b: 30 }),
+///         })
+///     }
+/// }
+///
+/// // Allocate a boxed `Example`.
+/// let e = Box::pin_init(Example::new())?;
+/// assert_eq!(e.c, 10);
+/// assert_eq!(e.d.lock().a, 20);
+/// assert_eq!(e.d.lock().b, 30);
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// The following example shows how to use interior mutability to modify the contents of a struct
+/// protected by a spinlock despite only having a shared reference:
+///
+/// ```
+/// use kernel::sync::SpinLock;
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// fn example(m: &SpinLock<Example>) {
+///     let mut guard = m.lock();
+///     guard.a += 10;
+///     guard.b += 20;
+/// }
+/// ```
+///
+/// [`spinlock_t`]: ../../../../include/linux/spinlock.h
+pub type SpinLock<T> = super::Lock<T, SpinLockBackend>;
+
+/// A kernel `spinlock_t` lock backend.
+pub struct SpinLockBackend;
+
+// SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. `relock` uses the
+// default implementation that always calls the same locking method.
+unsafe impl super::Backend for SpinLockBackend {
+    type State = bindings::spinlock_t;
+    type GuardState = ();
+
+    unsafe fn init(
+        ptr: *mut Self::State,
+        name: *const core::ffi::c_char,
+        key: *mut bindings::lock_class_key,
+    ) {
+        // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and
+        // `key` are valid for read indefinitely.
+        unsafe { bindings::__spin_lock_init(ptr, name, key) }
+    }
+
+    unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {
+        // SAFETY: The safety requirements of this function ensure that `ptr` points to valid
+        // memory, and that it has been initialised before.
+        unsafe { bindings::spin_lock(ptr) }
+    }
+
+    unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
+        // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the
+        // caller is the owner of the mutex.
+        unsafe { bindings::spin_unlock(ptr) }
+    }
+}
diff --git a/rust/kernel/sync/locked_by.rs b/rust/kernel/sync/locked_by.rs
new file mode 100644
index 0000000000..b17ee5cd98
--- /dev/null
+++ b/rust/kernel/sync/locked_by.rs
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! A wrapper for data protected by a lock that does not wrap it.
+
+use super::{lock::Backend, lock::Lock};
+use crate::build_assert;
+use core::{cell::UnsafeCell, mem::size_of, ptr};
+
+/// Allows access to some data to be serialised by a lock that does not wrap it.
+///
+/// In most cases, data protected by a lock is wrapped by the appropriate lock type, e.g.,
+/// [`super::Mutex`] or [`super::SpinLock`]. [`LockedBy`] is meant for cases when this is not
+/// possible. For example, if a container has a lock and some data in the contained elements needs
+/// to be protected by the same lock.
+///
+/// [`LockedBy`] wraps the data in lieu of another locking primitive, and only allows access to it
+/// when the caller shows evidence that the 'external' lock is locked. It panics if the evidence
+/// refers to the wrong instance of the lock.
+///
+/// # Examples
+///
+/// The following is an example for illustrative purposes: `InnerDirectory::bytes_used` is an
+/// aggregate of all `InnerFile::bytes_used` and must be kept consistent; so we wrap `InnerFile` in
+/// a `LockedBy` so that it shares a lock with `InnerDirectory`. This allows us to enforce at
+/// compile-time that access to `InnerFile` is only granted when an `InnerDirectory` is also
+/// locked; we enforce at run time that the right `InnerDirectory` is locked.
+///
+/// ```
+/// use kernel::sync::{LockedBy, Mutex};
+///
+/// struct InnerFile {
+///     bytes_used: u64,
+/// }
+///
+/// struct File {
+///     _ino: u32,
+///     inner: LockedBy<InnerFile, InnerDirectory>,
+/// }
+///
+/// struct InnerDirectory {
+///     /// The sum of the bytes used by all files.
+///     bytes_used: u64,
+///     _files: Vec<File>,
+/// }
+///
+/// struct Directory {
+///     _ino: u32,
+///     inner: Mutex<InnerDirectory>,
+/// }
+///
+/// /// Prints `bytes_used` from both the directory and file.
+/// fn print_bytes_used(dir: &Directory, file: &File) {
+///     let guard = dir.inner.lock();
+///     let inner_file = file.inner.access(&guard);
+///     pr_info!("{} {}", guard.bytes_used, inner_file.bytes_used);
+/// }
+///
+/// /// Increments `bytes_used` for both the directory and file.
+/// fn inc_bytes_used(dir: &Directory, file: &File) {
+///     let mut guard = dir.inner.lock();
+///     guard.bytes_used += 10;
+///
+///     let file_inner = file.inner.access_mut(&mut guard);
+///     file_inner.bytes_used += 10;
+/// }
+///
+/// /// Creates a new file.
+/// fn new_file(ino: u32, dir: &Directory) -> File {
+///     File {
+///         _ino: ino,
+///         inner: LockedBy::new(&dir.inner, InnerFile { bytes_used: 0 }),
+///     }
+/// }
+/// ```
+pub struct LockedBy<T: ?Sized, U: ?Sized> {
+    owner: *const U,
+    data: UnsafeCell<T>,
+}
+
+// SAFETY: `LockedBy` can be transferred across thread boundaries iff the data it protects can.
+unsafe impl<T: ?Sized + Send, U: ?Sized> Send for LockedBy<T, U> {}
+
+// SAFETY: `LockedBy` serialises the interior mutability it provides, so it is `Sync` as long as the
+// data it protects is `Send`.
+unsafe impl<T: ?Sized + Send, U: ?Sized> Sync for LockedBy<T, U> {}
+
+impl<T, U> LockedBy<T, U> {
+    /// Constructs a new instance of [`LockedBy`].
+    ///
+    /// It stores a raw pointer to the owner that is never dereferenced. It is only used to ensure
+    /// that the right owner is being used to access the protected data. If the owner is freed, the
+    /// data becomes inaccessible; if another instance of the owner is allocated *on the same
+    /// memory location*, the data becomes accessible again: none of this affects memory safety
+    /// because in any case at most one thread (or CPU) can access the protected data at a time.
+    pub fn new<B: Backend>(owner: &Lock<U, B>, data: T) -> Self {
+        build_assert!(
+            size_of::<Lock<U, B>>() > 0,
+            "The lock type cannot be a ZST because it may be impossible to distinguish instances"
+        );
+        Self {
+            owner: owner.data.get(),
+            data: UnsafeCell::new(data),
+        }
+    }
+}
+
+impl<T: ?Sized, U> LockedBy<T, U> {
+    /// Returns a reference to the protected data when the caller provides evidence (via a
+    /// reference) that the owner is locked.
+    ///
+    /// `U` cannot be a zero-sized type (ZST) because there are ways to get an `&U` that matches
+    /// the data protected by the lock without actually holding it.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `owner` is different from the data protected by the lock used in
+    /// [`new`](LockedBy::new).
+    pub fn access<'a>(&'a self, owner: &'a U) -> &'a T {
+        build_assert!(
+            size_of::<U>() > 0,
+            "`U` cannot be a ZST because `owner` wouldn't be unique"
+        );
+        if !ptr::eq(owner, self.owner) {
+            panic!("mismatched owners");
+        }
+
+        // SAFETY: `owner` is evidence that the owner is locked.
+        unsafe { &*self.data.get() }
+    }
+
+    /// Returns a mutable reference to the protected data when the caller provides evidence (via a
+    /// mutable owner) that the owner is locked mutably.
+    ///
+    /// `U` cannot be a zero-sized type (ZST) because there are ways to get an `&mut U` that
+    /// matches the data protected by the lock without actually holding it.
+    ///
+    /// Showing a mutable reference to the owner is sufficient because we know no other references
+    /// can exist to it.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `owner` is different from the data protected by the lock used in
+    /// [`new`](LockedBy::new).
+    pub fn access_mut<'a>(&'a self, owner: &'a mut U) -> &'a mut T {
+        build_assert!(
+            size_of::<U>() > 0,
+            "`U` cannot be a ZST because `owner` wouldn't be unique"
+        );
+        if !ptr::eq(owner, self.owner) {
+            panic!("mismatched owners");
+        }
+
+        // SAFETY: `owner` is evidence that there is only one reference to the owner.
+        unsafe { &mut *self.data.get() }
+    }
+}
diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
new file mode 100644
index 0000000000..7eda15e5f1
--- /dev/null
+++ b/rust/kernel/task.rs
@@ -0,0 +1,161 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Tasks (threads and processes).
+//!
+//! C header: [`include/linux/sched.h`](../../../../include/linux/sched.h).
+
+use crate::{bindings, types::Opaque};
+use core::{marker::PhantomData, ops::Deref, ptr};
+
+/// Returns the currently running task.
+#[macro_export]
+macro_rules! current {
+    () => {
+        // SAFETY: Deref + addr-of below create a temporary `TaskRef` that cannot outlive the
+        // caller.
+        unsafe { &*$crate::task::Task::current() }
+    };
+}
+
+/// Wraps the kernel's `struct task_struct`.
+///
+/// # Invariants
+///
+/// All instances are valid tasks created by the C portion of the kernel.
+///
+/// Instances of this type are always ref-counted, that is, a call to `get_task_struct` ensures
+/// that the allocation remains valid at least until the matching call to `put_task_struct`.
+///
+/// # Examples
+///
+/// The following is an example of getting the PID of the current thread with zero additional cost
+/// when compared to the C version:
+///
+/// ```
+/// let pid = current!().pid();
+/// ```
+///
+/// Getting the PID of the current process, also zero additional cost:
+///
+/// ```
+/// let pid = current!().group_leader().pid();
+/// ```
+///
+/// Getting the current task and storing it in some struct. The reference count is automatically
+/// incremented when creating `State` and decremented when it is dropped:
+///
+/// ```
+/// use kernel::{task::Task, types::ARef};
+///
+/// struct State {
+///     creator: ARef<Task>,
+///     index: u32,
+/// }
+///
+/// impl State {
+///     fn new() -> Self {
+///         Self {
+///             creator: current!().into(),
+///             index: 0,
+///         }
+///     }
+/// }
+/// ```
+#[repr(transparent)]
+pub struct Task(pub(crate) Opaque<bindings::task_struct>);
+
+// SAFETY: By design, the only way to access a `Task` is via the `current` function or via an
+// `ARef<Task>` obtained through the `AlwaysRefCounted` impl. This means that the only situation in
+// which a `Task` can be accessed mutably is when the refcount drops to zero and the destructor
+// runs. It is safe for that to happen on any thread, so it is ok for this type to be `Send`.
+unsafe impl Send for Task {}
+
+// SAFETY: It's OK to access `Task` through shared references from other threads because we're
+// either accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
+// synchronised by C code (e.g., `signal_pending`).
+unsafe impl Sync for Task {}
+
+/// The type of process identifiers (PIDs).
+type Pid = bindings::pid_t;
+
+impl Task {
+    /// Returns a task reference for the currently executing task/thread.
+    ///
+    /// The recommended way to get the current task/thread is to use the
+    /// [`current`](crate::current) macro because it is safe.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that the returned object doesn't outlive the current task/thread.
+    pub unsafe fn current() -> impl Deref<Target = Task> {
+        struct TaskRef<'a> {
+            task: &'a Task,
+            _not_send: PhantomData<*mut ()>,
+        }
+
+        impl Deref for TaskRef<'_> {
+            type Target = Task;
+
+            fn deref(&self) -> &Self::Target {
+                self.task
+            }
+        }
+
+        // SAFETY: Just an FFI call with no additional safety requirements.
+        let ptr = unsafe { bindings::get_current() };
+
+        TaskRef {
+            // SAFETY: If the current thread is still running, the current task is valid. Given
+            // that `TaskRef` is not `Send`, we know it cannot be transferred to another thread
+            // (where it could potentially outlive the caller).
+            task: unsafe { &*ptr.cast() },
+            _not_send: PhantomData,
+        }
+    }
+
+    /// Returns the group leader of the given task.
+    pub fn group_leader(&self) -> &Task {
+        // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always
+        // have a valid group_leader.
+        let ptr = unsafe { *ptr::addr_of!((*self.0.get()).group_leader) };
+
+        // SAFETY: The lifetime of the returned task reference is tied to the lifetime of `self`,
+        // and given that a task has a reference to its group leader, we know it must be valid for
+        // the lifetime of the returned task reference.
+        unsafe { &*ptr.cast() }
+    }
+
+    /// Returns the PID of the given task.
+    pub fn pid(&self) -> Pid {
+        // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always
+        // have a valid pid.
+        unsafe { *ptr::addr_of!((*self.0.get()).pid) }
+    }
+
+    /// Determines whether the given task has pending signals.
+    pub fn signal_pending(&self) -> bool {
+        // SAFETY: By the type invariant, we know that `self.0` is valid.
+        unsafe { bindings::signal_pending(self.0.get()) != 0 }
+    }
+
+    /// Wakes up the task.
+    pub fn wake_up(&self) {
+        // SAFETY: By the type invariant, we know that `self.0.get()` is non-null and valid.
+        // And `wake_up_process` is safe to be called for any valid task, even if the task is
+        // running.
+        unsafe { bindings::wake_up_process(self.0.get()) };
+    }
+}
+
+// SAFETY: The type invariants guarantee that `Task` is always ref-counted.
+unsafe impl crate::types::AlwaysRefCounted for Task {
+    fn inc_ref(&self) {
+        // SAFETY: The existence of a shared reference means that the refcount is nonzero.
+        unsafe { bindings::get_task_struct(self.0.get()) };
+    }
+
+    unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
+        // SAFETY: The safety requirements guarantee that the refcount is nonzero.
+        unsafe { bindings::put_task_struct(obj.cast().as_ptr()) }
+    }
+}
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
new file mode 100644
index 0000000000..fdb778e65d
--- /dev/null
+++ b/rust/kernel/types.rs
@@ -0,0 +1,389 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Kernel types.
+
+use crate::init::{self, PinInit};
+use alloc::boxed::Box;
+use core::{
+    cell::UnsafeCell,
+    marker::{PhantomData, PhantomPinned},
+    mem::MaybeUninit,
+    ops::{Deref, DerefMut},
+    ptr::NonNull,
+};
+
+/// Used to transfer ownership to and from foreign (non-Rust) languages.
+///
+/// Ownership is transferred from Rust to a foreign language by calling [`Self::into_foreign`] and
+/// later may be transferred back to Rust by calling [`Self::from_foreign`].
+///
+/// This trait is meant to be used in cases when Rust objects are stored in C objects and
+/// eventually "freed" back to Rust.
+pub trait ForeignOwnable: Sized {
+    /// Type of values borrowed between calls to [`ForeignOwnable::into_foreign`] and
+    /// [`ForeignOwnable::from_foreign`].
+    type Borrowed<'a>;
+
+    /// Converts a Rust-owned object to a foreign-owned one.
+    ///
+    /// The foreign representation is a pointer to void.
+    fn into_foreign(self) -> *const core::ffi::c_void;
+
+    /// Borrows a foreign-owned object.
+    ///
+    /// # Safety
+    ///
+    /// `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>;
+
+    /// Converts a foreign-owned object back to a Rust-owned one.
+    ///
+    /// # Safety
+    ///
+    /// `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.
+    /// 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;
+}
+
+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 ForeignOwnable for () {
+    type Borrowed<'a> = ();
+
+    fn into_foreign(self) -> *const core::ffi::c_void {
+        core::ptr::NonNull::dangling().as_ptr()
+    }
+
+    unsafe fn borrow<'a>(_: *const core::ffi::c_void) -> Self::Borrowed<'a> {}
+
+    unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
+}
+
+/// Runs a cleanup function/closure when dropped.
+///
+/// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running.
+///
+/// # Examples
+///
+/// In the example below, we have multiple exit paths and we want to log regardless of which one is
+/// taken:
+/// ```
+/// # use kernel::types::ScopeGuard;
+/// fn example1(arg: bool) {
+///     let _log = ScopeGuard::new(|| pr_info!("example1 completed\n"));
+///
+///     if arg {
+///         return;
+///     }
+///
+///     pr_info!("Do something...\n");
+/// }
+///
+/// # example1(false);
+/// # example1(true);
+/// ```
+///
+/// In the example below, we want to log the same message on all early exits but a different one on
+/// the main exit path:
+/// ```
+/// # use kernel::types::ScopeGuard;
+/// fn example2(arg: bool) {
+///     let log = ScopeGuard::new(|| pr_info!("example2 returned early\n"));
+///
+///     if arg {
+///         return;
+///     }
+///
+///     // (Other early returns...)
+///
+///     log.dismiss();
+///     pr_info!("example2 no early return\n");
+/// }
+///
+/// # example2(false);
+/// # example2(true);
+/// ```
+///
+/// In the example below, we need a mutable object (the vector) to be accessible within the log
+/// function, so we wrap it in the [`ScopeGuard`]:
+/// ```
+/// # 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()));
+///
+///     vec.try_push(10u8)?;
+///     if arg {
+///         return Ok(());
+///     }
+///     vec.try_push(20u8)?;
+///     Ok(())
+/// }
+///
+/// # assert_eq!(example3(false), Ok(()));
+/// # assert_eq!(example3(true), Ok(()));
+/// ```
+///
+/// # Invariants
+///
+/// The value stored in the struct is nearly always `Some(_)`, except between
+/// [`ScopeGuard::dismiss`] and [`ScopeGuard::drop`]: in this case, it will be `None` as the value
+/// will have been returned to the caller. Since  [`ScopeGuard::dismiss`] consumes the guard,
+/// callers won't be able to use it anymore.
+pub struct ScopeGuard<T, F: FnOnce(T)>(Option<(T, F)>);
+
+impl<T, F: FnOnce(T)> ScopeGuard<T, F> {
+    /// Creates a new guarded object wrapping the given data and with the given cleanup function.
+    pub fn new_with_data(data: T, cleanup_func: F) -> Self {
+        // INVARIANT: The struct is being initialised with `Some(_)`.
+        Self(Some((data, cleanup_func)))
+    }
+
+    /// Prevents the cleanup function from running and returns the guarded data.
+    pub fn dismiss(mut self) -> T {
+        // INVARIANT: This is the exception case in the invariant; it is not visible to callers
+        // because this function consumes `self`.
+        self.0.take().unwrap().0
+    }
+}
+
+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())
+    }
+}
+
+impl<T, F: FnOnce(T)> Deref for ScopeGuard<T, F> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        // The type invariants guarantee that `unwrap` will succeed.
+        &self.0.as_ref().unwrap().0
+    }
+}
+
+impl<T, F: FnOnce(T)> DerefMut for ScopeGuard<T, F> {
+    fn deref_mut(&mut self) -> &mut T {
+        // The type invariants guarantee that `unwrap` will succeed.
+        &mut self.0.as_mut().unwrap().0
+    }
+}
+
+impl<T, F: FnOnce(T)> Drop for ScopeGuard<T, F> {
+    fn drop(&mut self) {
+        // Run the cleanup function if one is still present.
+        if let Some((data, cleanup)) = self.0.take() {
+            cleanup(data)
+        }
+    }
+}
+
+/// Stores an opaque value.
+///
+/// This is meant to be used with FFI objects that are never interpreted by Rust code.
+#[repr(transparent)]
+pub struct Opaque<T> {
+    value: UnsafeCell<MaybeUninit<T>>,
+    _pin: PhantomPinned,
+}
+
+impl<T> Opaque<T> {
+    /// Creates a new opaque value.
+    pub const fn new(value: T) -> Self {
+        Self {
+            value: UnsafeCell::new(MaybeUninit::new(value)),
+            _pin: PhantomPinned,
+        }
+    }
+
+    /// Creates an uninitialised value.
+    pub const fn uninit() -> Self {
+        Self {
+            value: UnsafeCell::new(MaybeUninit::uninit()),
+            _pin: PhantomPinned,
+        }
+    }
+
+    /// Creates a pin-initializer from the given initializer closure.
+    ///
+    /// The returned initializer calls the given closure with the pointer to the inner `T` of this
+    /// `Opaque`. Since this memory is uninitialized, the closure is not allowed to read from it.
+    ///
+    /// This function is safe, because the `T` inside of an `Opaque` is allowed to be
+    /// uninitialized. Additionally, access to the inner `T` requires `unsafe`, so the caller needs
+    /// to verify at that point that the inner value is valid.
+    pub fn ffi_init(init_func: impl FnOnce(*mut T)) -> impl PinInit<Self> {
+        // SAFETY: We contain a `MaybeUninit`, so it is OK for the `init_func` to not fully
+        // initialize the `T`.
+        unsafe {
+            init::pin_init_from_closure::<_, ::core::convert::Infallible>(move |slot| {
+                init_func(Self::raw_get(slot));
+                Ok(())
+            })
+        }
+    }
+
+    /// Returns a raw pointer to the opaque data.
+    pub fn get(&self) -> *mut T {
+        UnsafeCell::get(&self.value).cast::<T>()
+    }
+
+    /// Gets the value behind `this`.
+    ///
+    /// This function is useful to get access to the value without creating intermediate
+    /// references.
+    pub const fn raw_get(this: *const Self) -> *mut T {
+        UnsafeCell::raw_get(this.cast::<UnsafeCell<MaybeUninit<T>>>()).cast::<T>()
+    }
+}
+
+/// Types that are _always_ reference counted.
+///
+/// It allows such types to define their own custom ref increment and decrement functions.
+/// Additionally, it allows users to convert from a shared reference `&T` to an owned reference
+/// [`ARef<T>`].
+///
+/// This is usually implemented by wrappers to existing structures on the C side of the code. For
+/// Rust code, the recommendation is to use [`Arc`](crate::sync::Arc) to create reference-counted
+/// instances of a type.
+///
+/// # Safety
+///
+/// Implementers must ensure that increments to the reference count keep the object alive in memory
+/// at least until matching decrements are performed.
+///
+/// Implementers must also ensure that all instances are reference-counted. (Otherwise they
+/// won't be able to honour the requirement that [`AlwaysRefCounted::inc_ref`] keep the object
+/// alive.)
+pub unsafe trait AlwaysRefCounted {
+    /// Increments the reference count on the object.
+    fn inc_ref(&self);
+
+    /// Decrements the reference count on the object.
+    ///
+    /// Frees the object when the count reaches zero.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that there was a previous matching increment to the reference count,
+    /// and that the object is no longer used after its reference count is decremented (as it may
+    /// result in the object being freed), unless the caller owns another increment on the refcount
+    /// (e.g., it calls [`AlwaysRefCounted::inc_ref`] twice, then calls
+    /// [`AlwaysRefCounted::dec_ref`] once).
+    unsafe fn dec_ref(obj: NonNull<Self>);
+}
+
+/// An owned reference to an always-reference-counted object.
+///
+/// The object's reference count is automatically decremented when an instance of [`ARef`] is
+/// dropped. It is also automatically incremented when a new instance is created via
+/// [`ARef::clone`].
+///
+/// # Invariants
+///
+/// The pointer stored in `ptr` is non-null and valid for the lifetime of the [`ARef`] instance. In
+/// particular, the [`ARef`] instance owns an increment on the underlying object's reference count.
+pub struct ARef<T: AlwaysRefCounted> {
+    ptr: NonNull<T>,
+    _p: PhantomData<T>,
+}
+
+// SAFETY: It is safe to send `ARef<T>` to another thread when the underlying `T` is `Sync` because
+// it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs
+// `T` to be `Send` because any thread that has an `ARef<T>` may ultimately access `T` using a
+// mutable reference, for example, when the reference count reaches zero and `T` is dropped.
+unsafe impl<T: AlwaysRefCounted + Sync + Send> Send for ARef<T> {}
+
+// SAFETY: It is safe to send `&ARef<T>` to another thread when the underlying `T` is `Sync`
+// because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
+// it needs `T` to be `Send` because any thread that has a `&ARef<T>` may clone it and get an
+// `ARef<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for
+// example, when the reference count reaches zero and `T` is dropped.
+unsafe impl<T: AlwaysRefCounted + Sync + Send> Sync for ARef<T> {}
+
+impl<T: AlwaysRefCounted> ARef<T> {
+    /// Creates a new instance of [`ARef`].
+    ///
+    /// It takes over an increment of the reference count on the underlying object.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that the reference count was incremented at least once, and that they
+    /// are properly relinquishing one increment. That is, if there is only one increment, callers
+    /// must not use the underlying object anymore -- it is only safe to do so via the newly
+    /// created [`ARef`].
+    pub unsafe fn from_raw(ptr: NonNull<T>) -> Self {
+        // INVARIANT: The safety requirements guarantee that the new instance now owns the
+        // increment on the refcount.
+        Self {
+            ptr,
+            _p: PhantomData,
+        }
+    }
+}
+
+impl<T: AlwaysRefCounted> Clone for ARef<T> {
+    fn clone(&self) -> Self {
+        self.inc_ref();
+        // SAFETY: We just incremented the refcount above.
+        unsafe { Self::from_raw(self.ptr) }
+    }
+}
+
+impl<T: AlwaysRefCounted> Deref for ARef<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: The type invariants guarantee that the object is valid.
+        unsafe { self.ptr.as_ref() }
+    }
+}
+
+impl<T: AlwaysRefCounted> From<&T> for ARef<T> {
+    fn from(b: &T) -> Self {
+        b.inc_ref();
+        // SAFETY: We just incremented the refcount above.
+        unsafe { Self::from_raw(NonNull::from(b)) }
+    }
+}
+
+impl<T: AlwaysRefCounted> Drop for ARef<T> {
+    fn drop(&mut self) {
+        // SAFETY: The type invariants guarantee that the `ARef` owns the reference we're about to
+        // decrement.
+        unsafe { T::dec_ref(self.ptr) };
+    }
+}
+
+/// A sum type that always holds either a value of type `L` or `R`.
+pub enum Either<L, R> {
+    /// Constructs an instance of [`Either`] containing a value of type `L`.
+    Left(L),
+
+    /// Constructs an instance of [`Either`] containing a value of type `R`.
+    Right(R),
+}