[PATCH v2 4/5] rust: init: add common init-helper functions for `Opaque`

[Benno Lossin <y86-dev@protonmail.com>]

Add helper functions to more easily initialize `Opaque<T>` via FFI.
These functions take a function pointer to the FFI-initialization
function and take between 0-4 other arguments. It then returns an
initializer that uses the FFI function along with the given arguments to
initialize an `Opaque<T>`.

Signed-off-by: Benno Lossin <y86-dev@protonmail.com>
---
 rust/kernel/init.rs        |  1 +
 rust/kernel/init/common.rs | 42 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)
 create mode 100644 rust/kernel/init/common.rs

diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
index 895845db6f2b..5b8adb8727b2 100644
--- a/rust/kernel/init.rs
+++ b/rust/kernel/init.rs
@@ -207,6 +207,7 @@ use core::{
     ptr,
 };

+pub mod common;
 #[doc(hidden)]
 pub mod macros;

diff --git a/rust/kernel/init/common.rs b/rust/kernel/init/common.rs
new file mode 100644
index 000000000000..f8c6e9dff786
--- /dev/null
+++ b/rust/kernel/init/common.rs
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! Module containing common kernel initializer functions.
+
+use crate::{
+    init::{self, PinInit},
+    types::Opaque,
+};
+
+macro_rules! create_func {
+    ($name:ident $(, $arg_name:ident: $arg_typ:ident)*) => {
+        /// Create an initializer using the given initializer function from C.
+        ///
+        /// # Safety
+        ///
+        /// The given function **must** under all circumstances initialize the memory location to a
+        /// valid `T`. If it fails to do so it results in UB.
+        ///
+        /// If any parameters are given, those need to be valid for the function. Valid means that
+        /// calling the function with those parameters complies with the above requirement **and**
+        /// every other requirement on the function itself.
+        pub unsafe fn $name<T $(, $arg_typ)*>(
+            init_func: unsafe extern "C" fn(*mut T $(, $arg_name: $arg_typ)*),
+            $($arg_name: $arg_typ,)*
+        ) -> impl PinInit<Opaque<T>> {
+            // SAFETY: The safety contract of this function ensures that `init_func` fully
+            // initializes `slot`.
+            unsafe {
+                init::pin_init_from_closure(move |slot| {
+                    init_func(Opaque::raw_get(slot) $(, $arg_name)*);
+                    Ok(())
+                })
+            }
+        }
+    }
+}
+
+create_func!(ffi_init);
+create_func!(ffi_init1, arg1: A1);
+create_func!(ffi_init2, arg1: A1, arg2: A2);
+create_func!(ffi_init3, arg1: A1, arg2: A2, arg3: A3);
+create_func!(ffi_init4, arg1: A1, arg2: A2, arg3: A3, arg4: A4);
--
2.39.2