diff mbox series

[v3,10/13] rust: init: implement `Zeroable` for `UnsafeCell<T>` and `Opaque<T>`

Message ID 20230729090838.225225-11-benno.lossin@proton.me
State New
Headers
Series Quality of life improvements for pin-init |

Commit Message

Benno Lossin July 29, 2023, 9:10 a.m. UTC 
  `UnsafeCell<T>` and `T` have the same layout so if `T` is `Zeroable`
then so should `UnsafeCell<T>` be. This allows using the derive macro
for `Zeroable` on types that contain an `UnsafeCell<T>`.
Since `Opaque<T>` contains a `MaybeUninit<T>`, all bytes zero is a valid
bit pattern for that type.

Signed-off-by: Benno Lossin <benno.lossin@proton.me>
---
v2 -> v3:
- also implement Zeroable for `UnsafeCell<T>` when `T: Zeroable`,
- use `impl_zeroable!` instead of `derive(Zeroable)`.

 rust/kernel/init.rs | 7 +++++++
 1 file changed, 7 insertions(+)

Comments

Martin Rodriguez Reboredo Aug. 5, 2023, 5:12 p.m. UTC | #1 
On 7/29/23 06:10, Benno Lossin wrote:
> `UnsafeCell<T>` and `T` have the same layout so if `T` is `Zeroable`
> then so should `UnsafeCell<T>` be. This allows using the derive macro
> for `Zeroable` on types that contain an `UnsafeCell<T>`.
> Since `Opaque<T>` contains a `MaybeUninit<T>`, all bytes zero is a valid
> bit pattern for that type.
> 
> Signed-off-by: Benno Lossin <benno.lossin@proton.me>
> ---
> [...]
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Gary Guo Aug. 6, 2023, 4:08 p.m. UTC | #2 
On Sat, 29 Jul 2023 09:10:19 +0000
Benno Lossin <benno.lossin@proton.me> wrote:

> `UnsafeCell<T>` and `T` have the same layout so if `T` is `Zeroable`
> then so should `UnsafeCell<T>` be. This allows using the derive macro
> for `Zeroable` on types that contain an `UnsafeCell<T>`.
> Since `Opaque<T>` contains a `MaybeUninit<T>`, all bytes zero is a valid
> bit pattern for that type.
> 
> Signed-off-by: Benno Lossin <benno.lossin@proton.me>

Reviewed-by: Gary Guo <gary@garyguo.net>

> ---
> v2 -> v3:
> - also implement Zeroable for `UnsafeCell<T>` when `T: Zeroable`,
> - use `impl_zeroable!` instead of `derive(Zeroable)`.
> 
>  rust/kernel/init.rs | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
> index af96d4acc26b..06ecab4901f2 100644
> --- a/rust/kernel/init.rs
> +++ b/rust/kernel/init.rs
> @@ -212,10 +212,12 @@
>  use crate::{
>      error::{self, Error},
>      sync::UniqueArc,
> +    types::Opaque,
>  };
>  use alloc::boxed::Box;
>  use core::{
>      alloc::AllocError,
> +    cell::UnsafeCell,
>      convert::Infallible,
>      marker::PhantomData,
>      mem::MaybeUninit,
> @@ -1157,6 +1159,11 @@ macro_rules! impl_zeroable {
>  
>      // SAFETY: Type is allowed to take any value, including all zeros.
>      {<T>} MaybeUninit<T>,
> +    // SAFETY: Type is allowed to take any value, including all zeros.
> +    {<T>} Opaque<T>,
> +
> +    // SAFETY: `T: Zeroable` and `UnsafeCell` is `repr(transparent)`.
> +    {<T: ?Sized + Zeroable>} UnsafeCell<T>,
>  
>      // SAFETY: All zeros is equivalent to `None` (option layout optimization guarantee).
>      Option<NonZeroU8>, Option<NonZeroU16>, Option<NonZeroU32>, Option<NonZeroU64>,
diff mbox series

Patch

diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
index af96d4acc26b..06ecab4901f2 100644
--- a/rust/kernel/init.rs
+++ b/rust/kernel/init.rs
@@ -212,10 +212,12 @@ 
 use crate::{
     error::{self, Error},
     sync::UniqueArc,
+    types::Opaque,
 };
 use alloc::boxed::Box;
 use core::{
     alloc::AllocError,
+    cell::UnsafeCell,
     convert::Infallible,
     marker::PhantomData,
     mem::MaybeUninit,
@@ -1157,6 +1159,11 @@  macro_rules! impl_zeroable {
 
     // SAFETY: Type is allowed to take any value, including all zeros.
     {<T>} MaybeUninit<T>,
+    // SAFETY: Type is allowed to take any value, including all zeros.
+    {<T>} Opaque<T>,
+
+    // SAFETY: `T: Zeroable` and `UnsafeCell` is `repr(transparent)`.
+    {<T: ?Sized + Zeroable>} UnsafeCell<T>,
 
     // SAFETY: All zeros is equivalent to `None` (option layout optimization guarantee).
     Option<NonZeroU8>, Option<NonZeroU16>, Option<NonZeroU32>, Option<NonZeroU64>,