[PATCH] rust: transmute: implement FromBytes and AsBytes for ()

Alexandre Courbot
2025-12-08T04:15:24Z

This is useful when using types that may or may not be empty in generic
code relying on these traits. It is also safe because technically a
no-op.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
---
This is going to be useful in Nova's GSP message handling, as some
messages are empty and we need to explicitly use an empty structure for
them.

If accepted, I would like to merge it through `drm-rust-next` so Nova
code can start using this feature quickly.
---
rust/kernel/transmute.rs | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/rust/kernel/transmute.rs b/rust/kernel/transmute.rs
index be5dbf3829e2..8d78c81e3749 100644
--- a/rust/kernel/transmute.rs
+++ b/rust/kernel/transmute.rs
@@ -170,6 +170,9 @@ macro_rules! impl_frombytes {
}

impl_frombytes! {
+ // SAFETY: This type is empty and thus does not consume any data.
+ (),
+
// SAFETY: All bit patterns are acceptable values of the types below.
u8, u16, u32, u64, usize,
i8, i16, i32, i64, isize,
@@ -230,6 +233,9 @@ macro_rules! impl_asbytes {
}

impl_asbytes! {
+ // SAFETY: This type is empty and thus returns an empty slice.
+ (),
+
// SAFETY: Instances of the following types have no uninitialized portions.
u8, u16, u32, u64, usize,
i8, i16, i32, i64, isize,

---
base-commit: ba65a4e7120a616d9c592750d9147f6dcafedffa
change-id: 20251208-transmute_unit-78ab58ba9e6e

Best regards,
--
Alexandre Courbot <acourbot@nvidia.com>