[PATCH 03/19] rust: types: avoid repetition in `{As,From}Bytes` impls

Miguel Ojeda
2024-09-04T20:44:53Z

In order to provide `// SAFETY` comments for every `unsafe impl`, we would
need to repeat them, which is not very useful and would be harder to read.

We could perhaps allow the lint (ideally within a small module), but we
can take the chance to avoid the repetition of the `impl`s themselves
too by using a small local macro, like in other places where we have
had to do this sort of thing.

Thus add the straightforward `impl_{from,as}bytes!` macros and use them
to implement `FromBytes`.

This, in turn, will allow us in the next patch to place a `// SAFETY`
comment that defers to the actual invocation of the macro.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
rust/kernel/types.rs | 68 +++++++++++++++++++++++---------------------
1 file changed, 35 insertions(+), 33 deletions(-)

diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 9e7ca066355c..70e173f15d87 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -481,21 +481,22 @@ pub enum Either<L, R> {
/// All bit-patterns must be valid for this type. This type must not have interior mutability.
pub unsafe trait FromBytes {}

-// SAFETY: All bit patterns are acceptable values of the types below.
-unsafe impl FromBytes for u8 {}
-unsafe impl FromBytes for u16 {}
-unsafe impl FromBytes for u32 {}
-unsafe impl FromBytes for u64 {}
-unsafe impl FromBytes for usize {}
-unsafe impl FromBytes for i8 {}
-unsafe impl FromBytes for i16 {}
-unsafe impl FromBytes for i32 {}
-unsafe impl FromBytes for i64 {}
-unsafe impl FromBytes for isize {}
-// SAFETY: If all bit patterns are acceptable for individual values in an array, then all bit
-// patterns are also acceptable for arrays of that type.
-unsafe impl<T: FromBytes> FromBytes for [T] {}
-unsafe impl<T: FromBytes, const N: usize> FromBytes for [T; N] {}
+macro_rules! impl_frombytes {
+ ($($({$($generics:tt)*})? $t:ty, )*) => {
+ $(unsafe impl$($($generics)*)? FromBytes for $t {})*
+ };
+}
+
+impl_frombytes! {
+ // SAFETY: All bit patterns are acceptable values of the types below.
+ u8, u16, u32, u64, usize,
+ i8, i16, i32, i64, isize,
+
+ // SAFETY: If all bit patterns are acceptable for individual values in an array, then all bit
+ // patterns are also acceptable for arrays of that type.
+ {<T: FromBytes>} [T],
+ {<T: FromBytes, const N: usize>} [T; N],
+}

/// Types that can be viewed as an immutable slice of initialized bytes.
///
@@ -514,21 +515,22 @@ unsafe impl<T: FromBytes> FromBytes for [T] {}
/// mutability.
pub unsafe trait AsBytes {}

-// SAFETY: Instances of the following types have no uninitialized portions.
-unsafe impl AsBytes for u8 {}
-unsafe impl AsBytes for u16 {}
-unsafe impl AsBytes for u32 {}
-unsafe impl AsBytes for u64 {}
-unsafe impl AsBytes for usize {}
-unsafe impl AsBytes for i8 {}
-unsafe impl AsBytes for i16 {}
-unsafe impl AsBytes for i32 {}
-unsafe impl AsBytes for i64 {}
-unsafe impl AsBytes for isize {}
-unsafe impl AsBytes for bool {}
-unsafe impl AsBytes for char {}
-unsafe impl AsBytes for str {}
-// SAFETY: If individual values in an array have no uninitialized portions, then the array itself
-// does not have any uninitialized portions either.
-unsafe impl<T: AsBytes> AsBytes for [T] {}
-unsafe impl<T: AsBytes, const N: usize> AsBytes for [T; N] {}
+macro_rules! impl_asbytes {
+ ($($({$($generics:tt)*})? $t:ty, )*) => {
+ $(unsafe impl$($($generics)*)? AsBytes for $t {})*
+ };
+}
+
+impl_asbytes! {
+ // SAFETY: Instances of the following types have no uninitialized portions.
+ u8, u16, u32, u64, usize,
+ i8, i16, i32, i64, isize,
+ bool,
+ char,
+ str,
+
+ // SAFETY: If individual values in an array have no uninitialized portions, then the array
+ // itself does not have any uninitialized portions either.
+ {<T: AsBytes>} [T],
+ {<T: AsBytes, const N: usize>} [T; N],
+}
--
2.46.0