Re: [PATCH v6 02/26] rust: alloc: separate `aligned_size` from `krealloc_aligned`

[Gary Guo]

On Fri, 16 Aug 2024 02:10:44 +0200
Danilo Krummrich <dakr@xxxxxxxxxx> wrote:

> 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@xxxxxxxxxx>
> Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx>
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>

Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>

> ---
>  rust/kernel/alloc/allocator.rs | 19 ++++++++++++-------
>  1 file changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
> index e6ea601f38c6..c83b6dff896d 100644
> --- a/rust/kernel/alloc/allocator.rs
> +++ b/rust/kernel/alloc/allocator.rs
> @@ -8,6 +8,17 @@
>  
>  struct KernelAllocator;
>  
> +/// 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).
> +    layout.size()
> +}
> +
>  /// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
>  ///
>  /// # Safety
> @@ -15,13 +26,7 @@
>  /// - `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 {
> -    // 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();
> +    let size = aligned_size(new_layout);
>  
>      // SAFETY:
>      // - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the