[PATCH v3 06/13] rust: lock: add support for `Lock::lock_irqsave`

[Wedson Almeida Filho <wedsonaf@gmail.com>]

From: Wedson Almeida Filho <walmeida@microsoft.com>

This allows locks like spinlocks and raw spinlocks to expose a
`lock_irqsave` variant in Rust that corresponds to the C version.

Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
---
v1 -> v2: No changes
v2 -> v3: No changes

 rust/kernel/sync/lock.rs | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index df43dff5af5c..690429561f0e 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -57,6 +57,29 @@ pub unsafe trait Backend {
     unsafe fn unlock(ptr: *mut Self::State, guard_state: &Self::GuardState);
 }
 
+/// The "backend" of a lock that supports the irq-save variant.
+///
+/// # Safety
+///
+/// The same requirements wrt mutual exclusion in [`Backend`] apply for acquiring the lock via
+/// [`IrqSaveBackend::lock_irqsave`].
+///
+/// Additionally, when [`IrqSaveBackend::lock_irqsave`] is used to acquire the lock, implementers
+/// must disable interrupts on lock, and restore interrupt state on unlock. Implementers may use
+/// [`Backend::GuardState`] to store state needed to keep track of the interrupt state.
+pub unsafe trait IrqSaveBackend: Backend {
+    /// Acquires the lock, making the caller its owner.
+    ///
+    /// Before acquiring the lock, it disables interrupts, and returns the previous interrupt state
+    /// as its guard state so that the guard can restore it when it is dropped.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that [`Backend::init`] has been previously called.
+    #[must_use]
+    unsafe fn lock_irqsave(ptr: *mut Self::State) -> Self::GuardState;
+}
+
 /// A mutual exclusion primitive.
 ///
 /// Exposes one of the kernel locking primitives. Which one is exposed depends on the lock banckend
@@ -111,6 +134,21 @@ impl<T: ?Sized, B: Backend> Lock<T, B> {
     }
 }
 
+impl<T: ?Sized, B: IrqSaveBackend> Lock<T, B> {
+    /// Acquires the lock and gives the caller access to the data protected by it.
+    ///
+    /// Before acquiring the lock, it disables interrupts. When the guard is dropped, the interrupt
+    /// state (either enabled or disabled) is restored to its state before
+    /// [`lock_irqsave`](Self::lock_irqsave) was called.
+    pub fn lock_irqsave(&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_irqsave(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
-- 
2.34.1