[PATCH v3 02/11] rust: derive `Zeroable` for all structs & unions generated by bindgen where possible

[Benno Lossin <lossin@kernel.org>]

Using the `--with-derive-custom-{struct,union}` option of bindgen, add
`#[derive(MaybeZeroable)]` to every struct & union. This makes those
types implement `Zeroable` if all their fields implement it.

Sadly bindgen doesn't add custom derives to the `__BindgenBitfieldUnit`
struct. So manually implement `Zeroable` for that.

Signed-off-by: Benno Lossin <lossin@kernel.org>
---
 rust/bindgen_parameters | 4 ++++
 rust/bindings/lib.rs    | 8 ++++++++
 rust/uapi/lib.rs        | 2 ++
 3 files changed, 14 insertions(+)

diff --git a/rust/bindgen_parameters b/rust/bindgen_parameters
index 0f96af8b9a7f..307545cf7363 100644
--- a/rust/bindgen_parameters
+++ b/rust/bindgen_parameters
@@ -34,3 +34,7 @@
 # We use const helpers to aid bindgen, to avoid conflicts when constants are
 # recognized, block generation of the non-helper constants.
 --blocklist-item ARCH_SLAB_MINALIGN
+
+# Structs should implement Zeroable when all of their fields do.
+--with-derive-custom-struct .*=MaybeZeroable
+--with-derive-custom-union .*=MaybeZeroable
diff --git a/rust/bindings/lib.rs b/rust/bindings/lib.rs
index 474cc98c48a3..0c57cf9b4004 100644
--- a/rust/bindings/lib.rs
+++ b/rust/bindings/lib.rs
@@ -31,11 +31,19 @@
 #[allow(clippy::undocumented_unsafe_blocks)]
 #[cfg_attr(CONFIG_RUSTC_HAS_UNNECESSARY_TRANSMUTES, allow(unnecessary_transmutes))]
 mod bindings_raw {
+    use pin_init::{MaybeZeroable, Zeroable};
+
     // Manual definition for blocklisted types.
     type __kernel_size_t = usize;
     type __kernel_ssize_t = isize;
     type __kernel_ptrdiff_t = isize;
 
+    // `bindgen` doesn't automatically do this, see
+    // <https://github.com/rust-lang/rust-bindgen/issues/3196>
+    //
+    // SAFETY: `__BindgenBitfieldUnit<Storage>` is a newtype around `Storage`.
+    unsafe impl<Storage> Zeroable for __BindgenBitfieldUnit<Storage> where Storage: Zeroable {}
+
     // Use glob import here to expose all helpers.
     // Symbols defined within the module will take precedence to the glob import.
     pub use super::bindings_helper::*;
diff --git a/rust/uapi/lib.rs b/rust/uapi/lib.rs
index 31c2f713313f..1d5fd9efb93e 100644
--- a/rust/uapi/lib.rs
+++ b/rust/uapi/lib.rs
@@ -34,4 +34,6 @@
 type __kernel_ssize_t = isize;
 type __kernel_ptrdiff_t = isize;
 
+use pin_init::MaybeZeroable;
+
 include!(concat!(env!("OBJTREE"), "/rust/uapi/uapi_generated.rs"));
-- 
2.50.1