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

Benno Lossin
2024-08-14T21:08:05Z

On 14.08.24 19:15, Danilo Krummrich wrote:
> 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.

Oh yeah of course... I don't know how I arrived at that comment...

---
Cheers,
Benno