rust: init: add initialization macros

Add the following initializer macros:
- `#[pin_data]` to annotate structurally pinned fields of structs,
  needed for `pin_init!` and `try_pin_init!` to select the correct
  initializer of fields.
- `pin_init!` create a pin-initializer for a struct with the
  `Infallible` error type.
- `try_pin_init!` create a pin-initializer for a struct with a custom
  error type (`kernel::error::Error` is the default).
- `init!` create an in-place-initializer for a struct with the
  `Infallible` error type.
- `try_init!` create an in-place-initializer for a struct with a custom
  error type (`kernel::error::Error` is the default).

Also add their needed internal helper traits and structs.

Co-developed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Link: https://lore.kernel.org/r/20230408122429.1103522-8-y86-dev@protonmail.com
[ Fixed three typos. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 29 insertions, 0 deletions

diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
index 82b520f024dd..6d84f2fd0d77 100644
--- a/rust/macros/lib.rs
+++ b/rust/macros/lib.rs
@@ -7,6 +7,7 @@ mod quote;
 mod concat_idents;
 mod helpers;
 mod module;
+mod pin_data;
 mod vtable;
 
 use proc_macro::TokenStream;
@@ -168,3 +169,31 @@ pub fn vtable(attr: TokenStream, ts: TokenStream) -> TokenStream {
 pub fn concat_idents(ts: TokenStream) -> TokenStream {
     concat_idents::concat_idents(ts)
 }
+
+/// Used to specify the pinning information of the fields of a struct.
+///
+/// This is somewhat similar in purpose as
+/// [pin-project-lite](https://crates.io/crates/pin-project-lite).
+/// Place this macro on a struct definition and then `#[pin]` in front of the attributes of each
+/// field you want to structurally pin.
+///
+/// This macro enables the use of the [`pin_init!`] macro. When pin-initializing a `struct`,
+/// then `#[pin]` directs the type of initializer that is required.
+///
+/// # Examples
+///
+/// ```rust,ignore
+/// #[pin_data]
+/// struct DriverData {
+///     #[pin]
+///     queue: Mutex<Vec<Command>>,
+///     buf: Box<[u8; 1024 * 1024]>,
+/// }
+/// ```
+///
+/// [`pin_init!`]: ../kernel/macro.pin_init.html
+//  ^ cannot use direct link, since `kernel` is not a dependency of `macros`.
+#[proc_macro_attribute]
+pub fn pin_data(inner: TokenStream, item: TokenStream) -> TokenStream {
+    pin_data::pin_data(inner, item)
+}