linux-kernel - Re: [PATCH v9 00/29] Generic `Allocator` support for Rust

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Message-ID: <CAH5fLgg68b-pfGhDubJMzGA8w4dywviMv+ghw0KV1emFvNKe9Q@mail.gmail.com>
Date: Fri, 15 Nov 2024 15:00:43 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Asahi Lina <lina@...hilina.net>
Cc: Danilo Krummrich <dakr@...nel.org>, ojeda@...nel.org, alex.gaynor@...il.com, 
	wedsonaf@...il.com, boqun.feng@...il.com, gary@...yguo.net, 
	bjorn3_gh@...tonmail.com, benno.lossin@...ton.me, a.hindborg@...sung.com, 
	akpm@...ux-foundation.org, daniel.almeida@...labora.com, 
	faith.ekstrand@...labora.com, boris.brezillon@...labora.com, 
	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, asahi@...ts.linux.dev
Subject: Re: [PATCH v9 00/29] Generic `Allocator` support for Rust

On Fri, Nov 15, 2024 at 12:33 PM Asahi Lina <lina@...hilina.net> wrote:
>
> We (Asahi Linux) noticed that this doesn't support unsized types, which
> is a regression from the alloc Box. drm/asahi uses boxed trait objects
> to generalize across certain object types like render commands, so this
> breaks the driver.
>
> Is there a plan to add this back in? AIUI this would need the
> coerce_unsized unstable feature, but is there any other blocker?

We're already using coerce_unsized for Arc, so I see no reason we
can't just add that for KBox too. Soon, we should be able to use the
derive macro [1] I proposed to do this without unstable language
features. The limitation that the RFC mentions for custom allocators
does not apply to KBox because it uses PhantomData<A> instead of A for
the allocator field.

Alice

[1]: https://rust-lang.github.io/rfcs/3621-derive-smart-pointer.html