Merge tag 'rust-6.4' of https://github.com/Rust-for-Linux/linux

Pull rust updates from Miguel Ojeda
 "More additions to the Rust core. Importantly, this adds the pin-init
  API, which will be used by other abstractions, such as the
  synchronization ones added here too:

   - pin-init API: a solution for the safe pinned initialization
     problem.

     This allows to reduce the need for 'unsafe' code in the kernel when
     dealing with data structures that require a stable address. Commit
     90e53c5e70a6 ("rust: add pin-init API core") contains a nice
     introduction -- here is an example of how it looks like:

        #[pin_data]
        struct Example {
            #[pin]
            value: Mutex<u32>,

            #[pin]
            value_changed: CondVar,
        }

        impl Example {
            fn new() -> impl PinInit<Self> {
                pin_init!(Self {
                    value <- new_mutex!(0),
                    value_changed <- new_condvar!(),
                })
            }
        }

        // In a `Box`.
        let b = Box::pin_init(Example::new())?;

        // In the stack.
        stack_pin_init!(let s = Example::new());

   - 'sync' module:

     New types 'LockClassKey' ('struct lock_class_key'), 'Lock',
     'Guard', 'Mutex' ('struct mutex'), 'SpinLock' ('spinlock_t'),
     'LockedBy' and 'CondVar' (uses 'wait_queue_head_t'), plus macros
     such as 'static_lock_class!' and 'new_spinlock!'.

     In particular, 'Lock' and 'Guard' are generic implementations that
     contain code that is common to all locks. Then, different backends
     (the new 'Backend' trait) are implemented and used to define types
     like 'Mutex':

        type Mutex<T> = Lock<T, MutexBackend>;

     In addition, new methods 'assume_init()', 'init_with()' and
     'pin_init_with()' for 'UniqueArc<MaybeUninit<T>>' and 'downcast()'
     for 'Arc<dyn Any + Send + Sync>'; as well as 'Debug' and 'Display'
     implementations for 'Arc' and 'UniqueArc'. Reduced stack usage of
     'UniqueArc::try_new_uninit()', too.

   - 'types' module:

     New trait 'AlwaysRefCounted' and new type 'ARef' (an owned
     reference to an always-reference-counted object, meant to be used
     in wrappers for C types that have their own ref counting
     functions).

     Moreover, new associated functions 'raw_get()' and 'ffi_init()' for
     'Opaque'.

   - New 'task' module with a new type 'Task' ('struct task_struct'),
     and a new macro 'current!' to safely get a reference to the current
     one.

   - New 'ioctl' module with new '_IOC*' const functions (equivalent to
     the C macros).

   - New 'uapi' crate, intended to be accessible by drivers directly.

   - 'macros' crate: new 'quote!' macro (similar to the one provided in
     userspace by the 'quote' crate); and the 'module!' macro now allows
     specifying multiple module aliases.

   - 'error' module:

     New associated functions for the 'Error' type, such as
     'from_errno()' and new functions such as 'to_result()'.

   - 'alloc' crate:

     More fallible 'Vec' methods: 'try_resize` and
     'try_extend_from_slice' and the infrastructure (imported from the
     Rust standard library) they need"

* tag 'rust-6.4' of https://github.com/Rust-for-Linux/linux: (44 commits)
  rust: ioctl: Add ioctl number manipulation functions
  rust: uapi: Add UAPI crate
  rust: sync: introduce `CondVar`
  rust: lock: add `Guard::do_unlocked`
  rust: sync: introduce `LockedBy`
  rust: introduce `current`
  rust: add basic `Task`
  rust: introduce `ARef`
  rust: lock: introduce `SpinLock`
  rust: lock: introduce `Mutex`
  rust: sync: introduce `Lock` and `Guard`
  rust: sync: introduce `LockClassKey`
  MAINTAINERS: add Benno Lossin as Rust reviewer
  rust: init: broaden the blanket impl of `Init`
  rust: sync: add functions for initializing `UniqueArc<MaybeUninit<T>>`
  rust: sync: reduce stack usage of `UniqueArc::try_new_uninit`
  rust: types: add `Opaque::ffi_init`
  rust: prelude: add `pin-init` API items to prelude
  rust: init: add `Zeroable` trait and `init::zeroed` function
  rust: init: add `stack_pin_init!` macro
  ...

1 files changed, 155 insertions, 0 deletions

diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
new file mode 100644
index 0000000000000..526d29a0ae278
--- /dev/null
+++ b/rust/kernel/task.rs
@@ -0,0 +1,155 @@
+// 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: It's OK to access `Task` through 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()) }
+    }
+}