rust: pin-init: add `MaybeZeroable` derive macro

This derive macro implements `Zeroable` for structs & unions precisely
if all fields also implement `Zeroable` and does nothing otherwise. The
plain `Zeroable` derive macro instead errors when it cannot derive
`Zeroable` safely. The `MaybeZeroable` derive macro is useful in cases
where manual checking is infeasible such as with the bindings crate.

Move the zeroable generics parsing into a standalone function in order
to avoid code duplication between the two derive macros.

Link: https://github.com/Rust-for-Linux/pin-init/pull/42/commits/1165cdad1a391b923efaf30cf76bc61e38da022e
Signed-off-by: Benno Lossin <benno.lossin@proton.me>

1 files changed, 30 insertions, 0 deletions

diff --git a/rust/pin-init/src/lib.rs b/rust/pin-init/src/lib.rs
index 774f8ca033bc..05a0cd6ad8f4 100644
--- a/rust/pin-init/src/lib.rs
+++ b/rust/pin-init/src/lib.rs
@@ -413,6 +413,36 @@ pub use ::pin_init_internal::pinned_drop;
 /// ```
 pub use ::pin_init_internal::Zeroable;
 
+/// Derives the [`Zeroable`] trait for the given struct if all fields implement [`Zeroable`].
+///
+/// Contrary to the derive macro named [`macro@Zeroable`], this one silently fails when a field
+/// doesn't implement [`Zeroable`].
+///
+/// # Examples
+///
+/// ```
+/// use pin_init::MaybeZeroable;
+///
+/// // implmements `Zeroable`
+/// #[derive(MaybeZeroable)]
+/// pub struct DriverData {
+///     id: i64,
+///     buf_ptr: *mut u8,
+///     len: usize,
+/// }
+///
+/// // does not implmement `Zeroable`
+/// #[derive(MaybeZeroable)]
+/// pub struct DriverData2 {
+///     id: i64,
+///     buf_ptr: *mut u8,
+///     len: usize,
+///     // this field doesn't implement `Zeroable`
+///     other_data: &'static i32,
+/// }
+/// ```
+pub use ::pin_init_internal::MaybeZeroable;
+
 /// Initialize and pin a type directly on the stack.
 ///
 /// # Examples