[PATCH v3] rust: Implement the smart pointer `InPlaceInit` for `Arc`
From: Alex Mantel
Date: Sat Jul 27 2024 - 00:25:14 EST
For pinned and unpinned initialization of structs, a trait named
`InPlaceInit` exists for uniform access. `Arc` did not implement
`InPlaceInit` yet, although the functions already existed. The main
reason for that, was that the trait itself returned a `Pin<Self>`. The
`Arc` implementation of the kernel is already implicitly pinned.
To enable `Arc` to implement `InPlaceInit` and to have uniform access,
for in-place and pinned in-place initialization, an associated type is
introduced for `InPlaceInit`. The new implementation of `InPlaceInit`
for `Arc` sets `Arc` as the associated type. Older implementations use
an explicit `Pin<T>` as the associated type. The implemented methods for
`Arc` are mostly moved from a direct implementation on `Arc`. There
should be no user impact. The implementation for `ListArc` is omitted,
because it is not merged yet.
Link: https://github.com/Rust-for-Linux/linux/issues/1079
Signed-off-by: Alex Mantel <alexmantel93@xxxxxxxxxxx>
---
Hello again!
This is the 3rd version of my very first patch. I applied the
suggestions on the 2nd submission. Thank you again for your feedback,
looking for more!
v1:
* https://lore.kernel.org/rust-for-linux/20240717034801.262343-2-alexmantel93@xxxxxxxxxxx/
v2:
* remove the `From:` from the patch.
* add the prefix `rust: ` to the subject.
* Remove the empty line between `Link` and `Signed-off-by`.
* https://lore.kernel.org/all/20240719192234.330341-1-alexmantel93@xxxxxxxxxxx/
v3:
* Rename PinnedResult to PinnedSelf
* Adjust documentation for PinnedSelf
rust/kernel/init.rs | 39 +++++++++++++++++++++++++++++++++++----
rust/kernel/sync/arc.rs | 25 ++-----------------------
2 files changed, 37 insertions(+), 27 deletions(-)
diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
index 68605b633..fa5f182fe 100644
--- a/rust/kernel/init.rs
+++ b/rust/kernel/init.rs
@@ -213,6 +213,7 @@
use crate::{
alloc::{box_ext::BoxExt, AllocError, Flags},
error::{self, Error},
+ sync::Arc,
sync::UniqueArc,
types::{Opaque, ScopeGuard},
};
@@ -1112,11 +1113,17 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
/// Smart pointer that can initialize memory in-place.
pub trait InPlaceInit<T>: Sized {
+ /// Pinned version of Rusts `Self`.
+ ///
+ /// If a type already implicitly pins its pointee, `Pin<Self>` is unnecessary. In this case use
+ /// `Self`, otherwise just use `Pin<Self>`.
+ type PinnedSelf;
+
/// Use the given pin-initializer to pin-initialize a `T` inside of a new smart pointer of this
/// type.
///
/// If `T: !Unpin` it will not be able to move afterwards.
- fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Pin<Self>, E>
+ fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Self::PinnedSelf, E>
where
E: From<AllocError>;
@@ -1124,7 +1131,7 @@ fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Pin<Self>,
/// type.
///
/// If `T: !Unpin` it will not be able to move afterwards.
- fn pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> error::Result<Pin<Self>>
+ fn pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> error::Result<Self::PinnedSelf>
where
Error: From<E>,
{
@@ -1153,9 +1160,31 @@ fn init<E>(init: impl Init<T, E>, flags: Flags) -> error::Result<Self>
}
}
+impl<T> InPlaceInit<T> for Arc<T> {
+ type PinnedSelf = Self;
+
+ #[inline]
+ fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Self::PinnedSelf, E>
+ where
+ E: From<AllocError>,
+ {
+ UniqueArc::try_pin_init(init, flags).map(|u| u.into())
+ }
+
+ #[inline]
+ fn try_init<E>(init: impl Init<T, E>, flags: Flags) -> Result<Self, E>
+ where
+ E: From<AllocError>,
+ {
+ UniqueArc::try_init(init, flags).map(|u| u.into())
+ }
+}
+
impl<T> InPlaceInit<T> for Box<T> {
+ type PinnedSelf = Pin<Self>;
+
#[inline]
- fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Pin<Self>, E>
+ fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Self::PinnedSelf, E>
where
E: From<AllocError>,
{
@@ -1184,8 +1213,10 @@ fn try_init<E>(init: impl Init<T, E>, flags: Flags) -> Result<Self, E>
}
impl<T> InPlaceInit<T> for UniqueArc<T> {
+ type PinnedSelf = Pin<Self>;
+
#[inline]
- fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Pin<Self>, E>
+ fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Self::PinnedSelf, E>
where
E: From<AllocError>,
{
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 3673496c2..3021f30fd 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -12,12 +12,13 @@
//! 2. It does not support weak references, which allows it to be half the size.
//! 3. It saturates the reference count instead of aborting when it goes over a threshold.
//! 4. It does not provide a `get_mut` method, so the ref counted object is pinned.
+//! 5. The object in [`Arc`] is pinned implicitly.
//!
//! [`Arc`]: https://doc.rust-lang.org/std/sync/struct.Arc.html
use crate::{
alloc::{box_ext::BoxExt, AllocError, Flags},
- error::{self, Error},
+ bindings,
init::{self, InPlaceInit, Init, PinInit},
try_init,
types::{ForeignOwnable, Opaque},
@@ -209,28 +210,6 @@ pub fn new(contents: T, flags: Flags) -> Result<Self, AllocError> {
// `Arc` object.
Ok(unsafe { Self::from_inner(Box::leak(inner).into()) })
}
-
- /// Use the given initializer to in-place initialize a `T`.
- ///
- /// If `T: !Unpin` it will not be able to move afterwards.
- #[inline]
- pub fn pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> error::Result<Self>
- where
- Error: From<E>,
- {
- UniqueArc::pin_init(init, flags).map(|u| u.into())
- }
-
- /// Use the given initializer to in-place initialize a `T`.
- ///
- /// This is equivalent to [`Arc<T>::pin_init`], since an [`Arc`] is always pinned.
- #[inline]
- pub fn init<E>(init: impl Init<T, E>, flags: Flags) -> error::Result<Self>
- where
- Error: From<E>,
- {
- UniqueArc::init(init, flags).map(|u| u.into())
- }
}
impl<T: ?Sized> Arc<T> {
--
2.39.2