[PATCH v6 13/15] rust: types: add common init-helper functions for `Opaque`

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

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

Signed-off-by: Benno Lossin <y86-dev@protonmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Cc: Gary Guo <gary@garyguo.net>
---
 rust/kernel/init.rs  |  9 +++++++++
 rust/kernel/types.rs | 47 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
index ffd539e2f5ef..a501fb823ae9 100644
--- a/rust/kernel/init.rs
+++ b/rust/kernel/init.rs
@@ -177,6 +177,14 @@
 //! }
 //! ```
 //!
+//! For the special case where initializing a field is a single FFI-function call that cannot fail,
+//! there exist helper functions [`Opaque::ffi_init`]. These functions initialize a single
+//! [`Opaque`] field by just delegating to the FFI-function. You can use these in combination with
+//! [`pin_init!`].
+//!
+//! For more information on how to use [`pin_init_from_closure()`], take a look at the uses inside
+//! the `kernel` crate. The [`sync`] module is a good starting point.
+//!
 //! [`sync`]: kernel::sync
 //! [pinning]: https://doc.rust-lang.org/std/pin/index.html
 //! [structurally pinned fields]:
@@ -187,6 +195,7 @@
 //! [`impl PinInit<T, E>`]: PinInit
 //! [`impl Init<T, E>`]: Init
 //! [`Opaque`]: kernel::types::Opaque
+//! [`Opaque::ffi_init`]: kernel::types::Opaque::ffi_init
 //! [`pin_data`]: ::macros::pin_data

 use crate::{
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index ff2b2fac951d..dbfae9bb97ce 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -2,6 +2,7 @@

 //! Kernel types.

+use crate::init::{self, PinInit};
 use alloc::boxed::Box;
 use core::{
     cell::UnsafeCell,
@@ -248,6 +249,52 @@ impl<T> Opaque<T> {
     }
 }

+macro_rules! opaque_init_funcs {
+    ($($abi:literal $name:ident($($arg_name:ident: $arg_typ:ident),*);)*) => {
+        impl<T> Opaque<T> {
+            $(
+                /// Create an initializer using the given initializer function.
+                ///
+                /// # 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 $name<$($arg_typ),*>(
+                    init_func: unsafe extern $abi fn(*mut T $(, $arg_typ)*),
+                    $($arg_name: $arg_typ,)*
+                ) -> impl PinInit<Self> {
+                    // SAFETY: The safety contract of this function ensures that `init_func` fully
+                    // initializes `slot`.
+                    unsafe {
+                        init::pin_init_from_closure(move |slot| {
+                            init_func(Self::raw_get(slot) $(, $arg_name)*);
+                            Ok(())
+                        })
+                    }
+                }
+            )*
+        }
+    }
+}
+
+opaque_init_funcs! {
+    "C" ffi_init();
+    "C" ffi_init1(arg1: A1);
+    "C" ffi_init2(arg1: A1, arg2: A2);
+    "C" ffi_init3(arg1: A1, arg2: A2, arg3: A3);
+    "C" ffi_init4(arg1: A1, arg2: A2, arg3: A3, arg4: A4);
+
+    "Rust" manual_init();
+    "Rust" manual_init1(arg1: A1);
+    "Rust" manual_init2(arg1: A1, arg2: A2);
+    "Rust" manual_init3(arg1: A1, arg2: A2, arg3: A3);
+    "Rust" manual_init4(arg1: A1, arg2: A2, arg3: A3, arg4: A4);
+}
+
 /// A sum type that always holds either a value of type `L` or `R`.
 pub enum Either<L, R> {
     /// Constructs an instance of [`Either`] containing a value of type `L`.
--
2.39.2