linux-kernel - Re: [PATCH 3/3] rust: add abstraction for `struct page`

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Date: Thu, 8 Feb 2024 14:02:43 +0000
From: Andreas Hindborg <a.hindborg@...sung.com>
To: Alice Ryhl <aliceryhl@...gle.com>
CC: Trevor Gross <tmgross@...ch.edu>, Miguel Ojeda <ojeda@...nel.org>, "Alex
 Gaynor" <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, Benno
	Lossin <benno.lossin@...ton.me>, Kees Cook <keescook@...omium.org>, Al Viro
	<viro@...iv.linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, "Greg
 Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>, Todd Kjos
	<tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>, Joel Fernandes
	<joel@...lfernandes.org>, Carlos Llamas <cmllamas@...gle.com>, "Suren
 Baghdasaryan" <surenb@...gle.com>, Arnd Bergmann <arnd@...db.de>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "rust-for-linux@...r.kernel.org"
	<rust-for-linux@...r.kernel.org>, Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH 3/3] rust: add abstraction for `struct page`


Alice Ryhl <aliceryhl@...gle.com> writes:

> On Thu, Feb 1, 2024 at 7:02 AM Trevor Gross <tmgross@...ch.edu> wrote:
>>
>> On Wed, Jan 24, 2024 at 6:22 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
>> > +/// A pointer to a page that owns the page allocation.
>> > +///
>> > +/// # Invariants
>> > +///
>> > +/// The pointer points at a page, and has ownership over the page.
>> > +pub struct Page {
>> > +    page: NonNull<bindings::page>,
>> > +}
>>
>> Shouldn't this be UnsafeCell / Opaque? Since `struct page` contains locks.
>
> That only matters when we use a reference. Here, it's behind a raw pointer.

Why is it behind a pointer rather than being transparent over
`Opaque<bindings::page>` and using a `&Page` instead?

BR Andreas