[PATCH 06/10] rust: alloc: introduce the `BoxExt` trait

Wedson Almeida Filho
2024-03-25T19:55:22Z

From: Wedson Almeida Filho <walmeida@microsoft.com>

Make fallible versions of `new` and `new_uninit` methods available in
`Box` even though it doesn't implement them because we build `alloc`
with the `no_global_oom_handling` config.

They also have an extra `flags` parameter that allows callers to pass
flags to the allocator.

Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
---
rust/kernel/alloc.rs | 1 +
rust/kernel/alloc/allocator.rs | 6 +++-
rust/kernel/alloc/boxext.rs | 61 ++++++++++++++++++++++++++++++++++
rust/kernel/init.rs | 13 ++++----
rust/kernel/prelude.rs | 2 +-
rust/kernel/sync/arc.rs | 3 +-
6 files changed, 77 insertions(+), 9 deletions(-)
create mode 100644 rust/kernel/alloc/boxext.rs

diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index ad48ac8dc13d..5712c81b1308 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -5,6 +5,7 @@
#[cfg(not(test))]
#[cfg(not(testlib))]
mod allocator;
+pub mod boxext;
pub mod vecext;

/// Flags to be used when allocating memory.
diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index 01ad139e19bc..fc0439455faa 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -15,7 +15,11 @@
///
/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
/// - `new_layout` must have a non-zero size.
-unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: bindings::gfp_t) -> *mut u8 {
+pub(crate) unsafe fn krealloc_aligned(
+ ptr: *mut u8,
+ new_layout: Layout,
+ flags: bindings::gfp_t,
+) -> *mut u8 {
// Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
let layout = new_layout.pad_to_align();

diff --git a/rust/kernel/alloc/boxext.rs b/rust/kernel/alloc/boxext.rs
new file mode 100644
index 000000000000..26a918df7acf
--- /dev/null
+++ b/rust/kernel/alloc/boxext.rs
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Extensions to [`Box`] for fallible allocations.
+
+use super::Flags;
+use alloc::boxed::Box;
+use core::alloc::AllocError;
+use core::mem::MaybeUninit;
+use core::result::Result;
+
+/// Extensions to [`Box`].
+pub trait BoxExt<T>: Sized {
+ /// Allocates a new box.
+ ///
+ /// The allocation may fail, in which case an error is returned.
+ fn new(x: T, flags: Flags) -> Result<Self, AllocError>;
+
+ /// Allocates a new uninitialised box.
+ ///
+ /// The allocation may fail, in which case an error is returned.
+ fn new_uninit(flags: Flags) -> Result<Box<MaybeUninit<T>>, AllocError>;
+}
+
+impl<T> BoxExt<T> for Box<T> {
+ #[cfg(any(test, testlib))]
+ fn new(x: T, _flags: Flags) -> Result<Self, AllocError> {
+ Ok(Box::new(x))
+ }
+
+ #[cfg(not(any(test, testlib)))]
+ fn new(x: T, flags: Flags) -> Result<Self, AllocError> {
+ let ptr = if core::mem::size_of::<T>() == 0 {
+ core::ptr::NonNull::<T>::dangling().as_ptr()
+ } else {
+ let layout = core::alloc::Layout::new::<T>();
+
+ // SAFETY: Memory is being allocated (first arg is null). The only other source of
+ // safety issues is sleeping on atomic context, which is addressed by klint.
+ let ptr = unsafe {
+ super::allocator::krealloc_aligned(core::ptr::null_mut(), layout, flags.0)
+ };
+ if ptr.is_null() {
+ return Err(AllocError);
+ }
+
+ let ptr = ptr.cast::<T>();
+
+ // SAFETY: We just allocated the memory above, it is valid for write.
+ unsafe { ptr.write(x) };
+ ptr
+ };
+
+ // SAFETY: For non-zero-sized types, we allocate above using the global allocator. For
+ // zero-sized types, we use `NonNull::dangling`.
+ Ok(unsafe { Box::from_raw(ptr) })
+ }
+
+ fn new_uninit(flags: Flags) -> Result<Box<MaybeUninit<T>>, AllocError> {
+ <Box<_> as BoxExt<_>>::new(MaybeUninit::<T>::uninit(), flags)
+ }
+}
diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
index 424257284d16..0d956934eaa4 100644
--- a/rust/kernel/init.rs
+++ b/rust/kernel/init.rs
@@ -210,6 +210,7 @@
//! [`pin_init!`]: crate::pin_init!

use crate::{
+ alloc::{boxext::BoxExt, flags::*},
error::{self, Error},
sync::UniqueArc,
types::{Opaque, ScopeGuard},
@@ -305,9 +306,9 @@ macro_rules! stack_pin_init {
///
/// stack_try_pin_init!(let foo: Result<Pin<&mut Foo>, AllocError> = pin_init!(Foo {
/// a <- new_mutex!(42),
-/// b: Box::try_new(Bar {
+/// b: Box::new(Bar {
/// x: 64,
-/// })?,
+/// }, GFP_KERNEL)?,
/// }));
/// let foo = foo.unwrap();
/// pr_info!("a: {}", &*foo.a.lock());
@@ -331,9 +332,9 @@ macro_rules! stack_pin_init {
///
/// stack_try_pin_init!(let foo: Pin<&mut Foo> =? pin_init!(Foo {
/// a <- new_mutex!(42),
-/// b: Box::try_new(Bar {
+/// b: Box::new(Bar {
/// x: 64,
-/// })?,
+/// }, GFP_KERNEL)?,
/// }));
/// pr_info!("a: {}", &*foo.a.lock());
/// # Ok::<_, AllocError>(())
@@ -1158,7 +1159,7 @@ 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 mut this = <Box<_> as BoxExt<_>>::new_uninit(GFP_KERNEL)?;
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.
@@ -1172,7 +1173,7 @@ fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E>
where
E: From<AllocError>,
{
- let mut this = Box::try_new_uninit()?;
+ let mut this = <Box<_> as BoxExt<_>>::new_uninit(GFP_KERNEL)?;
let slot = this.as_mut_ptr();
// SAFETY: When init errors/panics, slot will get deallocated but not dropped,
// slot is valid.
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index a7b203f87aa1..f73b4285168c 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -14,7 +14,7 @@
#[doc(no_inline)]
pub use core::pin::Pin;

-pub use crate::alloc::{flags::*, vecext::VecExt};
+pub use crate::alloc::{boxext::BoxExt, flags::*, vecext::VecExt};

#[doc(no_inline)]
pub use alloc::{boxed::Box, vec::Vec};
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 7d4c4bf58388..f0a5aed69693 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -16,6 +16,7 @@
//! [`Arc`]: https://doc.rust-lang.org/std/sync/struct.Arc.html

use crate::{
+ alloc::{boxext::BoxExt, flags::*},
bindings,
error::{self, Error},
init::{self, InPlaceInit, Init, PinInit},
@@ -170,7 +171,7 @@ pub fn try_new(contents: T) -> Result<Self, AllocError> {
data: contents,
};

- let inner = Box::try_new(value)?;
+ let inner = <Box<_> as BoxExt<_>>::new(value, GFP_KERNEL)?;

// SAFETY: We just created `inner` with a reference count of 1, which is owned by the new
// `Arc` object.
--
2.34.1