linux-kernel - Re: [PATCH v5 00/26] Generic `Allocator` support for Rust

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Message-ID: <e0b0bffb-c240-4d23-bf4d-0c1c19608f60@proton.me>
Date: Thu, 15 Aug 2024 13:39:05 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Danilo Krummrich <dakr@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>
Cc: Boqun Feng <boqun.feng@...il.com>, ojeda@...nel.org, alex.gaynor@...il.com, wedsonaf@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, a.hindborg@...sung.com, akpm@...ux-foundation.org, daniel.almeida@...labora.com, faith.ekstrand@...labora.com, boris.brezillon@...labora.com, lina@...hilina.net, mcanal@...lia.com, zhiw@...dia.com, cjia@...dia.com, jhubbard@...dia.com, airlied@...hat.com, ajanulgu@...hat.com, lyude@...hat.com, linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v5 00/26] Generic `Allocator` support for Rust

On 15.08.24 15:33, Danilo Krummrich wrote:
> On Thu, Aug 15, 2024 at 02:34:50PM +0200, Alice Ryhl wrote:
>> On Thu, Aug 15, 2024 at 2:33 PM Danilo Krummrich <dakr@...nel.org> wrote:
>>>
>>> On Thu, Aug 15, 2024 at 11:20:32AM +0200, Alice Ryhl wrote:
>>>> On Thu, Aug 15, 2024 at 4:52 AM Danilo Krummrich <dakr@...nel.org> wrote:
>>>>>
>>>>> On Wed, Aug 14, 2024 at 12:32:15PM -0700, Boqun Feng wrote:
>>>>>> Hi Danilo,
>>>>>>
>>>>>> I'm trying to put your series on rust-dev, but I hit a few conflicts due
>>>>>> to the conflict with `Box::drop_contents`, which has been in rust-dev
>>>>>> for a while. And the conflict is not that trivial for me to resolve.
>>>>>> So just a head-up, that's a requirement for me to put it on rust-dev for
>>>>>> more tests from my end ;-)
>>>>>
>>>>> I rebased everything and you can fetch them from [1].
>>>>>
>>>>> I resolved the following conflicts:
>>>>>
>>>>>   - for `Box`, implement
>>>>>     - `drop_contents`
>>>>>     - `manually_drop_contents` [2]
>>>>
>>>> Not sure I like this name. It sounds like something that runs the
>>>> destructor, but it does the exact opposite.
>>>
>>> I thought it kinda makes sense, since it's analogous to `ManuallyDrop::new`.
>>>
>>> What about `Box::forget_contents` instead?
>>
>> One option is `into_manually_drop`. This uses the convention of using
>> the `into_*` prefix for conversions that take ownership of the
>> original value.
> 
> The signature of the current `Box::manually_drop_contents` is the same as for
> `Box::drop_contents`, namely
> `fn manually_drop_contents(this: Self) -> Box<MaybeUninit<T>, A>`.
> 
> `into_manually_drop` seems misleading for for returning a
> `Box<MaybeUninit<T>, A>`.
> 
> I still think `forget_contents` hits it quite well. Just as `drop_contents`
> drops the value, `forget_contents` makes the `Box` forget the value.

I think `forget_contents` sounds good. Can you please add some more docs
to that function though? Like an example and change "Manually drops the
contents, but keeps the allocation" to "Forgets the contents (does not
run the destructor), but keeps the allocation.".

Another thing that I spotted while looking at the patch, `move_out`
doesn't need the `transmute_copy`, you should be able to just call
`read` on the pointer.

---
Cheers,
Benno