Implement `Allocator` for `Kmalloc`, the kernel's default allocator,
typically used for objects smaller than page size.
All memory allocations made with `Kmalloc` end up in `krealloc()`.
It serves as allocator for the subsequently introduced types `KBox` and
`KVec`.
Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx>
Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>
Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
---
rust/kernel/alloc/allocator.rs | 31 ++++++++++++++++++++++++++++---
1 file changed, 28 insertions(+), 3 deletions(-)
diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index e5bac90046a4..b1894c800448 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -13,10 +13,16 @@
use core::ptr;
use core::ptr::NonNull;
-use crate::alloc::AllocError;
+use crate::alloc::{AllocError, Allocator};
use crate::bindings;
-struct Kmalloc;
+/// The contiguous kernel allocator.
+///
+/// `Kmalloc` is typically used for physically contiguous allocations up to page size, but also
+/// supports larger allocations up to `bindings::KMALLOC_MAX_SIZE`, which is hardware specific.
+///
+/// For more details see [self].
+pub struct Kmalloc;
/// Returns a proper size to alloc a new object aligned to `new_layout`'s alignment.
fn aligned_size(new_layout: Layout) -> usize {
@@ -53,8 +59,10 @@ struct ReallocFunc(
unsafe extern "C" fn(*const core::ffi::c_void, usize, u32) -> *mut core::ffi::c_void,
);
-#[expect(dead_code)]
impl ReallocFunc {
+ // INVARIANT: `krealloc` satisfies the type invariants.
+ const KREALLOC: Self = Self(bindings::krealloc);
+
/// # Safety
///
/// This method has the same safety requirements as [`Allocator::realloc`].
@@ -106,6 +114,23 @@ unsafe fn call(
}
}
+// SAFETY: `realloc` delegates to `ReallocFunc::call`, which guarantees that
+// - memory remains valid until it is explicitly freed,
+// - passing a pointer to a valid memory allocation is OK,
+// - `realloc` satisfies the guarantees, since `ReallocFunc::call` has the same.
+unsafe impl Allocator for Kmalloc {
+ #[inline]
+ unsafe fn realloc(
+ ptr: Option<NonNull<u8>>,
+ layout: Layout,
+ old_layout: Layout,
+ flags: Flags,
+ ) -> Result<NonNull<[u8]>, AllocError> {
+ // SAFETY: `ReallocFunc::call` has the same safety requirements as `Allocator::realloc`.
+ unsafe { ReallocFunc::KREALLOC.call(ptr, layout, old_layout, flags) }
+ }
+}
+
// SAFETY: TODO.
unsafe impl GlobalAlloc for Kmalloc {
unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
--
2.46.1
