[PATCH RFC 02/11] rust: lock: Add Lock::pin_init()

[Asahi Lina <lina@xxxxxxxxxxxxx>]

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

Signed-off-by: Asahi Lina <lina@xxxxxxxxxxxxx>
---
 rust/kernel/sync/lock.rs       | 30 +++++++++++++++++++++++++++++-
 rust/kernel/sync/lock/mutex.rs | 13 +++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index a2216325632d..d493c5d19104 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -6,7 +6,9 @@
 //! 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 crate::{
+    bindings, init::PinInit, pin_init, str::CStr, try_pin_init, types::Opaque, types::ScopeGuard,
+};
 use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned};
 use macros::pin_data;
 
@@ -87,6 +89,7 @@ pub struct Lock<T: ?Sized, B: Backend> {
     _pin: PhantomPinned,
 
     /// The data protected by the lock.
+    #[pin]
     pub(crate) data: UnsafeCell<T>,
 }
 
@@ -111,6 +114,31 @@ pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinIni
             }),
         })
     }
+
+    /// 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 { crate::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<T: ?Sized, B: Backend> Lock<T, B> {
diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs
index 923472f04af4..06fe685501b4 100644
--- a/rust/kernel/sync/lock/mutex.rs
+++ b/rust/kernel/sync/lock/mutex.rs
@@ -18,6 +18,19 @@ macro_rules! 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,

-- 
2.40.1