rust: add `ZeroableOption` and implement it instead of `Zeroable` for `Option<Box<T, A>>`

When making pin-init its own crate, `Zeroable` will no longer be defined
by the kernel crate and thus implementing it for `Option<Box<T, A>>` is
no longer possible due to the orphan rule.
For this reason introduce a new `ZeroableOption` trait that circumvents
this problem.

Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Fiona Behrens <me@kloenk.dev>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Tested-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250308110339.2997091-11-benno.lossin@proton.me
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs
index 9861433559dc..07150c038e3f 100644
--- a/rust/kernel/alloc/kbox.rs
+++ b/rust/kernel/alloc/kbox.rs
@@ -15,7 +15,7 @@ use core::pin::Pin;
 use core::ptr::NonNull;
 use core::result::Result;
 
-use crate::init::{InPlaceWrite, Init, PinInit, Zeroable};
+use crate::init::{InPlaceWrite, Init, PinInit, ZeroableOption};
 use crate::init_ext::InPlaceInit;
 use crate::types::ForeignOwnable;
 
@@ -104,7 +104,7 @@ pub type KVBox<T> = Box<T, super::allocator::KVmalloc>;
 //
 // In this case we are allowed to use `T: ?Sized`, since all zeros is the `None` variant and there
 // is no problem with a VTABLE pointer being null.
-unsafe impl<T: ?Sized, A: Allocator> Zeroable for Option<Box<T, A>> {}
+unsafe impl<T: ?Sized, A: Allocator> ZeroableOption for Box<T, A> {}
 
 // SAFETY: `Box` is `Send` if `T` is `Send` because the `Box` owns a `T`.
 unsafe impl<T, A> Send for Box<T, A>