rust: kernel: lock: Add Lock::pin_init()

This allows initializing a lock using pin_init!(), instead of requiring
the inner data to be passed through the stack.

Signed-off-by: Asahi Lina <lina@asahilina.net>

Author: hoshinolina

rust/kernel/sync/lock.rs

@@ -8,6 +8,7 @@
 use super::LockClassKey;
 use crate::{
     str::CStr,
+    try_pin_init,
     types::{NotThreadSafe, Opaque, ScopeGuard},
 };
 use core::{cell::UnsafeCell, marker::PhantomPinned, pin::Pin};
@@ -115,6 +116,7 @@ pub struct Lock<T: ?Sized, B: Backend> {
     _pin: PhantomPinned,
 
     /// The data protected by the lock.
+    #[pin]
     pub(crate) data: UnsafeCell<T>,
 }
 
@@ -138,6 +140,31 @@ impl<T, B: Backend> Lock<T, B> {
             }),
         })
     }
+
+    /// Constructs a new lock initialiser taking an initialiser.
+    pub fn pin_init<E>(
+        t: impl PinInit<T, E>,
+        name: &'static CStr,
+        key: &'static LockClassKey,
+    ) -> impl PinInit<Self, E>
+    where
+        E: core::convert::From<core::convert::Infallible>,
+    {
+        try_pin_init!(Self {
+            // SAFETY: We are just forwarding the initialization across a
+            // cast away from UnsafeCell, so the pin_init_from_closure and
+            // __pinned_init() requirements are in sync.
+            data <- unsafe { pin_init::pin_init_from_closure(move |slot: *mut UnsafeCell<T>| {
+                t.__pinned_init(slot as *mut 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())
+            }),
+        }? E)
+    }
 }
 
 impl<B: Backend> Lock<(), B> {

rust/kernel/sync/lock/mutex.rs

@@ -17,6 +17,19 @@ macro_rules! new_mutex {
 }
 pub use new_mutex;
 
+/// Creates a [`Mutex`] initialiser with the given name and a newly-created lock class,
+/// given an initialiser for the inner type.
+///
+/// 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_pinned {
+    ($inner:expr $(, $name:literal)? $(,)?) => {
+        $crate::sync::Mutex::pin_init(
+            $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,