[PATCH v4 02/28] rust: alloc: separate `aligned_size` from `krealloc_aligned`

Danilo Krummrich
2024-08-05T15:20:24Z

Separate `aligned_size` from `krealloc_aligned`.

Subsequent patches implement `Allocator` derivates, such as `Kmalloc`,
that require `aligned_size` and replace the original `krealloc_aligned`.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
rust/kernel/alloc/allocator.rs | 27 ++++++++++++++++++---------
1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index e6ea601f38c6..e7b7eba84acb 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -8,27 +8,36 @@

struct KernelAllocator;

-/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
-///
-/// # Safety
-///
-/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
-/// - `new_layout` must have a non-zero size.
-pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: Flags) -> *mut u8 {
+/// Returns a proper size to alloc a new object aligned to `new_layout`'s alignment.
+fn aligned_size(new_layout: Layout) -> usize {
// Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
let layout = new_layout.pad_to_align();

// Note that `layout.size()` (after padding) is guaranteed to be a multiple of `layout.align()`
// which together with the slab guarantees means the `krealloc` will return a properly aligned
// object (see comments in `kmalloc()` for more information).
- let size = layout.size();
+ layout.size()
+}

+/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
+///
+/// # Safety
+///
+/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
+/// - `new_layout` must have a non-zero size.
+pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: Flags) -> *mut u8 {
// SAFETY:
// - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the
// function safety requirement.
// - `size` is greater than 0 since it's from `layout.size()` (which cannot be zero according
// to the function safety requirement)
- unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags.0) as *mut u8 }
+ unsafe {
+ bindings::krealloc(
+ ptr as *const core::ffi::c_void,
+ aligned_size(new_layout),
+ flags.0,
+ ) as *mut u8
+ }
}

unsafe impl GlobalAlloc for KernelAllocator {
--
2.45.2