Re: [PATCH v5 04/26] rust: alloc: implement `Allocator` for `Kmalloc`

Danilo Krummrich
2024-08-14T17:15:08Z

On Wed, Aug 14, 2024 at 05:02:53PM +0000, Benno Lossin wrote:
> On 14.08.24 18:59, Danilo Krummrich wrote:
> > On Wed, Aug 14, 2024 at 04:21:38PM +0000, Benno Lossin wrote:
> >> On 12.08.24 20:22, Danilo Krummrich wrote:
> >>> + unsafe fn call(
> >>> + &self,
> >>> + ptr: Option<NonNull<u8>>,
> >>> + layout: Layout,
> >>> + flags: Flags,
> >>> + ) -> Result<NonNull<[u8]>, AllocError> {
> >>> + let size = aligned_size(layout);
> >>> + let ptr = match ptr {
> >>> + Some(ptr) => ptr.as_ptr(),
> >>> + None => ptr::null(),
> >>> + };
> >>> +
> >>> + // SAFETY: `ptr` is either NULL or valid by the safety requirements of this function.
> >>> + let raw_ptr = unsafe {
> >>> + // If `size == 0` and `ptr != NULL` the memory behind the pointer is freed.
> >>> + self.0(ptr.cast(), size, flags.0).cast()
> >>> + };
> >>> +
> >>> + let ptr = if size == 0 {
> >>
> >> Why do you do this check *after* calling `self.0`?
> >
> > Because I need `raw_ptr` in the else case below.
>
> But you can just return early above? I would prefer the check be done
> before `self.0` is called.

No, we can't return early, we need `self.0` to be called, because if `size == 0`
we free the given allocation, if any.

>
> ---
> Cheers,
> Benno
>