linux-kernel - Re: [PATCH v6 09/26] rust: alloc: implement kernel `Box`

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Message-ID: <ZsS1njIt0Mp9pWok@pollux>
Date: Tue, 20 Aug 2024 17:26:22 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: 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,
	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 v6 09/26] rust: alloc: implement kernel `Box`

On Tue, Aug 20, 2024 at 11:47:45AM +0200, Alice Ryhl wrote:
> On Fri, Aug 16, 2024 at 2:13 AM Danilo Krummrich <dakr@...nel.org> wrote:
> >
> > `Box` provides the simplest way to allocate memory for a generic type
> > with one of the kernel's allocators, e.g. `Kmalloc`, `Vmalloc` or
> > `KVmalloc`.
> >
> > In contrast to Rust's `Box` type, the kernel `Box` type considers the
> > kernel's GFP flags for all appropriate functions, always reports
> > allocation failures through `Result<_, AllocError>` and remains
> > independent from unstable features.
> >
> > Signed-off-by: Danilo Krummrich <dakr@...nel.org>
> 
> Overall looks good to me, but I have a question:
> 
> > +impl<T: 'static, A> ForeignOwnable for Box<T, A>
> > +where
> > +    A: Allocator,
> > +{
> > +    type Borrowed<'a> = &'a T;
> > +    type BorrowedMut<'a> = &'a mut T;
> > [..]
> > +    unsafe fn borrow_mut<'a>(ptr: *const core::ffi::c_void) -> &'a mut T {
> > +        // SAFETY: The safety requirements of this method ensure that the pointer is valid and that
> > +        // nothing else will access the value for the duration of 'a.
> > +        unsafe { &mut *ptr.cast_mut().cast() }
> > +    }
> 
> Where does this come from? It looks like you've based the series on
> top of [1], but I dropped that patch a long time ago, and I don't see
> it in rust-dev anymore.

I comes from me rebasing onto rust-dev. When Boqun asked me to resolve the merge
conflicts a few days ago, this patch was in rust-dev. I think it disappeared two
days ago or so.

@Bonqun: Need to me to rebase again?

- Danilo

> 
> Alice
> 
> [1]: https://lore.kernel.org/all/20230710074642.683831-1-aliceryhl@google.com/
>