[PATCH v5 08/15] rust: init/sync: add `InPlaceInit` trait to pin-initialize smart pointers

Benno Lossin
2023-04-03T16:05:56Z

The `InPlaceInit` trait that provides two functions, for initializing
using `PinInit<T, E>` and `Init<T>`. It is implemented by `Arc<T>`,
`UniqueArc<T>` and `Box<T>`.

Signed-off-by: Benno Lossin <y86-dev@protonmail.com>
Cc: Andreas Hindborg <a.hindborg@samsung.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Gary Guo <gary@garyguo.net>
---
rust/kernel/init.rs | 128 ++++++++++++++++++++++++++++++++++++----
rust/kernel/sync/arc.rs | 24 ++++++++
2 files changed, 139 insertions(+), 13 deletions(-)

diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
index ecef0376d726..6499cf5c9c20 100644
--- a/rust/kernel/init.rs
+++ b/rust/kernel/init.rs
@@ -114,10 +114,16 @@
//! [`impl Init<T, E>`]: Init
//! [`Opaque`]: kernel::types::Opaque
//! [`pin_data`]: ::macros::pin_data
-//! [`UniqueArc<T>`]: kernel::sync::UniqueArc

+use crate::{
+ error::{self, Error},
+ sync::UniqueArc,
+};
use alloc::boxed::Box;
-use core::{cell::Cell, convert::Infallible, marker::PhantomData, mem::MaybeUninit, ptr};
+use core::{
+ alloc::AllocError, cell::Cell, convert::Infallible, marker::PhantomData, mem::MaybeUninit,
+ pin::Pin, ptr,
+};

#[doc(hidden)]
pub mod __internal;
@@ -309,7 +315,6 @@ pub mod macros;
///
/// [`try_pin_init!`]: kernel::try_pin_init
/// [`NonNull<Self>`]: core::ptr::NonNull
-/// [`Error`]: kernel::error::Error
// For a detailed example of how this macro works, see the module documentation of the hidden
// module `__internal` inside of `init/__internal.rs`.
#[macro_export]
@@ -363,8 +368,6 @@ macro_rules! pin_init {
/// }
/// }
/// ```
-///
-/// [`Error`]: kernel::error::Error
// For a detailed example of how this macro works, see the module documentation of the hidden
// module `__internal` inside of `init/__internal.rs`.
#[macro_export]
@@ -586,8 +589,6 @@ macro_rules! try_pin_init {
///
/// This initializer is for initializing data in-place that might later be moved. If you want to
/// pin-initialize, use [`pin_init!`].
-///
-/// [`Error`]: kernel::error::Error
// For a detailed example of how this macro works, see the module documentation of the hidden
// module `__internal` inside of `init/__internal.rs`.
#[macro_export]
@@ -635,8 +636,6 @@ macro_rules! init {
/// }
/// }
/// ```
-///
-/// [`Error`]: kernel::error::Error
// For a detailed example of how this macro works, see the module documentation of the hidden
// module `__internal` inside of `init/__internal.rs`.
#[macro_export]
@@ -842,7 +841,8 @@ macro_rules! try_init {
/// A pin-initializer for the type `T`.
///
/// To use this initializer, you will need a suitable memory location that can hold a `T`. This can
-/// be [`Box<T>`], [`Arc<T>`], [`UniqueArc<T>`].
+/// be [`Box<T>`], [`Arc<T>`], [`UniqueArc<T>`]. Use the [`InPlaceInit::pin_init`] function of a
+/// smart pointer like [`Arc<T>`] on this.
///
/// Also see the [module description](self).
///
@@ -861,7 +861,6 @@ macro_rules! try_init {
///
/// [`Arc<T>`]: crate::sync::Arc
/// [`Arc::pin_init`]: crate::sync::Arc::pin_init
-/// [`UniqueArc<T>`]: kernel::sync::UniqueArc
#[must_use = "An initializer must be used in order to create its value."]
pub unsafe trait PinInit<T: ?Sized, E = Infallible>: Sized {
/// Initializes `slot`.
@@ -878,7 +877,8 @@ pub unsafe trait PinInit<T: ?Sized, E = Infallible>: Sized {
/// An initializer for `T`.
///
/// To use this initializer, you will need a suitable memory location that can hold a `T`. This can
-/// be [`Box<T>`], [`Arc<T>`], [`UniqueArc<T>`]. Because [`PinInit<T, E>`] is a super trait, you can
+/// be [`Box<T>`], [`Arc<T>`], [`UniqueArc<T>`]. Use the [`InPlaceInit::init`] function of a smart
+/// pointer like [`Arc<T>`] on this. Because [`PinInit<T, E>`] is a super trait, you can
/// use every function that takes it as well.
///
/// Also see the [module description](self).
@@ -903,7 +903,6 @@ pub unsafe trait PinInit<T: ?Sized, E = Infallible>: Sized {
/// move the pointee after initialization.
///
/// [`Arc<T>`]: crate::sync::Arc
-/// [`UniqueArc<T>`]: kernel::sync::UniqueArc
#[must_use = "An initializer must be used in order to create its value."]
pub unsafe trait Init<T: ?Sized, E = Infallible>: Sized {
/// Initializes `slot`.
@@ -982,3 +981,106 @@ unsafe impl<T> Init<T> for T {
Ok(())
}
}
+
+/// Smart pointer that can initialize memory in-place.
+pub trait InPlaceInit<T>: Sized {
+ /// 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>) -> Result<Pin<Self>, E>
+ where
+ E: From<AllocError>;
+
+ /// 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 pin_init<E>(init: impl PinInit<T, E>) -> error::Result<Pin<Self>>
+ where
+ Error: From<E>,
+ {
+ // SAFETY: We delegate to `init` and only change the error type.
+ let init = unsafe {
+ pin_init_from_closure(|slot| init.__pinned_init(slot).map_err(|e| Error::from(e)))
+ };
+ Self::try_pin_init(init)
+ }
+
+ /// Use the given initializer to in-place initialize a `T`.
+ fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E>
+ where
+ E: From<AllocError>;
+
+ /// Use the given initializer to in-place initialize a `T`.
+ fn init<E>(init: impl Init<T, E>) -> error::Result<Self>
+ where
+ Error: From<E>,
+ {
+ // SAFETY: We delegate to `init` and only change the error type.
+ let init = unsafe {
+ init_from_closure(|slot| init.__pinned_init(slot).map_err(|e| Error::from(e)))
+ };
+ Self::try_init(init)
+ }
+}
+
+impl<T> InPlaceInit<T> for Box<T> {
+ #[inline]
+ fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E>
+ where
+ E: From<AllocError>,
+ {
+ let mut this = Box::try_new_uninit()?;
+ let slot = this.as_mut_ptr();
+ // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
+ // slot is valid and will not be moved, because we pin it later.
+ unsafe { init.__pinned_init(slot)? };
+ // SAFETY: All fields have been initialized.
+ Ok(unsafe { this.assume_init() }.into())
+ }
+
+ #[inline]
+ fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E>
+ where
+ E: From<AllocError>,
+ {
+ let mut this = Box::try_new_uninit()?;
+ let slot = this.as_mut_ptr();
+ // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
+ // slot is valid.
+ unsafe { init.__init(slot)? };
+ // SAFETY: All fields have been initialized.
+ Ok(unsafe { this.assume_init() })
+ }
+}
+
+impl<T> InPlaceInit<T> for UniqueArc<T> {
+ #[inline]
+ fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E>
+ where
+ E: From<AllocError>,
+ {
+ let mut this = UniqueArc::try_new_uninit()?;
+ let slot = this.as_mut_ptr();
+ // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
+ // slot is valid and will not be moved, because we pin it later.
+ unsafe { init.__pinned_init(slot)? };
+ // SAFETY: All fields have been initialized.
+ Ok(unsafe { this.assume_init() }.into())
+ }
+
+ #[inline]
+ fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E>
+ where
+ E: From<AllocError>,
+ {
+ let mut this = UniqueArc::try_new_uninit()?;
+ let slot = this.as_mut_ptr();
+ // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
+ // slot is valid.
+ unsafe { init.__init(slot)? };
+ // SAFETY: All fields have been initialized.
+ Ok(unsafe { this.assume_init() })
+ }
+}
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index eee7008e5e3e..43a53fbe175d 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -17,6 +17,8 @@

use crate::{
bindings,
+ error::{self, Error},
+ init::{InPlaceInit, Init, PinInit},
types::{ForeignOwnable, Opaque},
};
use alloc::boxed::Box;
@@ -163,6 +165,28 @@ impl<T> Arc<T> {
// `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>) -> error::Result<Self>
+ where
+ Error: From<E>,
+ {
+ UniqueArc::pin_init(init).map(|u| u.into())
+ }
+
+ /// Use the given initializer to in-place initialize a `T`.
+ ///
+ /// This is equivalent to [`pin_init`], since an [`Arc`] is always pinned.
+ #[inline]
+ pub fn init<E>(init: impl Init<T, E>) -> error::Result<Self>
+ where
+ Error: From<E>,
+ {
+ UniqueArc::init(init).map(|u| u.into())
+ }
}

impl<T: ?Sized> Arc<T> {
--
2.39.2