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

Benno Lossin
2024-08-14T21:10:24Z

On 14.08.24 19:13, Danilo Krummrich wrote:
> On Wed, Aug 14, 2024 at 04:28:04PM +0000, Benno Lossin wrote:
>> On 12.08.24 20:22, Danilo Krummrich wrote:
>>> +unsafe impl Allocator for Kmalloc {
>>
>> There is a missing SAFETY comment here (and also for Vmalloc, probably
>> also for VKmalloc then).
>
> Any suggestion on what to write here?
>
> I'd probably come up with something like:
>
> --
> Memory returned from `Kmalloc` remains valid until explicitly freed.
>
> It is valid to pass any pointer to an allocated memory buffer obtained with any
> function of `Kmalloc` to any other function of `Kmalloc`.
>
> If `Kmalloc::realloc` is called with a size of zero, the given memory
> allocation, if any, is freed.
>
> If `Kmalloc::realloc` is called with `None` it behaves like `Kmalloc::alloc`,
> i.e. a new memory allocation is created.
> --
>
> and repeat that for `Vmalloc` and `KVmalloc`.
>
> I'm not sure how useful that is though.

Ideally you would write down how the guarantees are satisfied in
addition to the invariants. But I guess this is only guaranteed by the
`ReallocFunc::call`, since that handles the ZSTs... Maybe this is a bit
excessive. If I come up with something better I will let you know.

---
Cheers,
Benno