From: Benno Lossin <benno.lossin@xxxxxxxxx>
When allocating memory for arrays using allocators, the `Layout::array`
function is typically used. It returns a result, since the given size
might be too big. However, `Vec` and its iterators store their allocated
capacity and thus they already did check that the size is not too big.
The `ArrayLayout` type provides this exact behavior, as it can be
infallibly converted into a `Layout`. Instead of a `usize` capacity,
`Vec` and other similar array-storing types can use `ArrayLayout`
instead.
Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>
Signed-off-by: Benno Lossin <benno.lossin@xxxxxxxxx>
Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
---
rust/kernel/alloc.rs | 1 +
rust/kernel/alloc/layout.rs | 91 +++++++++++++++++++++++++++++++++++++
2 files changed, 92 insertions(+)
create mode 100644 rust/kernel/alloc/layout.rs
diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index ebe58247504f..bf143a71d53d 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -5,6 +5,7 @@
#[cfg(not(any(test, testlib)))]
pub mod allocator;
pub mod kbox;
+pub mod layout;
pub mod vec_ext;
#[cfg(any(test, testlib))]
diff --git a/rust/kernel/alloc/layout.rs b/rust/kernel/alloc/layout.rs
new file mode 100644
index 000000000000..7f0427a4d3d8
--- /dev/null
+++ b/rust/kernel/alloc/layout.rs
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Memory layout.
+//!
+//! Custom layout types extending or improving [`Layout`].
+
+use core::{alloc::Layout, marker::PhantomData};
+
+/// Error when constructing an [`ArrayLayout`].
+pub struct LayoutError;
+
+/// A layout for an array `[T; n]`.
+///
+/// # Invariants
+///
+/// - `len * size_of::<T>() <= isize::MAX`
+pub struct ArrayLayout<T> {
+ len: usize,
+ _phantom: PhantomData<fn() -> T>,
+}
+
+impl<T> Clone for ArrayLayout<T> {
+ fn clone(&self) -> Self {
+ *self
+ }
+}
+impl<T> Copy for ArrayLayout<T> {}
+
+const ISIZE_MAX: usize = isize::MAX as usize;
+
+impl<T> ArrayLayout<T> {
+ /// Creates a new layout for `[T; 0]`.
+ pub const fn empty() -> Self {
+ // INVARIANT: `0 * size_of::<T>() <= isize::MAX`
+ Self {
+ len: 0,
+ _phantom: PhantomData,
+ }
+ }
+
+ /// Creates a new layout for `[T; len]`.
+ ///
+ /// # Errors
+ ///
+ /// When `len * size_of::<T>()` overflows or when `len * size_of::<T>() > isize::MAX`.
+ pub const fn new(len: usize) -> Result<Self, LayoutError> {
+ match len.checked_mul(core::mem::size_of::<T>()) {
+ Some(len) if len <= ISIZE_MAX => {
+ // INVARIANT: we checked above that `len * size_of::<T>() <= isize::MAX`
+ Ok(Self {
+ len,
+ _phantom: PhantomData,
+ })
+ }
+ _ => Err(LayoutError),
+ }
+ }
+
+ /// Creates a new layout for `[T; len]`.
+ ///
+ /// # Safety
+ ///
+ /// `len` must be a value, for which `len * size_of::<T>() <= isize::MAX` is true.
+ pub unsafe fn new_unchecked(len: usize) -> Self {
+ // INVARIANT: By the safety requirements of this function
+ // `len * size_of::<T>() <= isize::MAX`.
+ Self {
+ len,
+ _phantom: PhantomData,
+ }
+ }
+
+ /// Returns the number of array elements represented by this layout.
+ pub const fn len(&self) -> usize {
+ self.len
+ }
+
+ /// Returns `true` when no array elements are represented by this layout.
+ pub const fn is_empty(&self) -> bool {
+ self.len == 0
+ }
+}
+
+impl<T> From<ArrayLayout<T>> for Layout {
+ fn from(value: ArrayLayout<T>) -> Self {
+ let res = Layout::array::<T>(value.len);
+ // SAFETY: by the type invariant of `ArrayLayout` we have
+ // `len * size_of::<T>() <= isize::MAX` and thus the result must be `Ok`.
+ unsafe { res.unwrap_unchecked() }
+ }
+}
--
2.46.1
