linux-kernel - Re: [PATCH 1/2] nova-core: Add a library for bitfields in Rust structs

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Message-Id: <8498F151-B4DF-43D3-981E-FAE598964CA2@collabora.com>
Date: Thu, 4 Sep 2025 08:02:16 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Alexandre Courbot <acourbot@...dia.com>
Cc: Joel Fernandes <joelagnelf@...dia.com>,
 linux-kernel@...r.kernel.org,
 Danilo Krummrich <dakr@...nel.org>,
 David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>,
 Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <lossin@...nel.org>,
 Andreas Hindborg <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>,
 John Hubbard <jhubbard@...dia.com>,
 Alistair Popple <apopple@...dia.com>,
 nouveau@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 1/2] nova-core: Add a library for bitfields in Rust
 structs



> On 4 Sep 2025, at 00:16, Alexandre Courbot <acourbot@...dia.com> wrote:
> 
> On Thu Sep 4, 2025 at 12:15 AM JST, Joel Fernandes wrote:
> <snip>
>>>> +use kernel::prelude::*;
>>>> +
>>>> +/// Macro for defining bitfield-packed structures in Rust.
>>>> +/// The size of the underlying storage type is specified with #[repr(TYPE)].
>>>> +///
>>>> +/// # Example (just for illustration)
>>>> +/// ```rust
>>>> +/// bitstruct! {
>>>> +///     #[repr(u64)]
>>>> +///     pub struct PageTableEntry {
>>>> +///         0:0       present     as bool,
>>>> +///         1:1       writable    as bool,
>>>> +///         11:9      available   as u8,
>>>> +///         51:12     pfn         as u64,
>>>> +///         62:52     available2  as u16,
>>>> +///         63:63     nx          as bool,
>>> 
>>> A note on syntax: for nova-core, we may want to use the `H:L` notation,
>>> as this is what OpenRM uses, but in the larger kernel we might want to
>>> use inclusive ranges (`L..=H`) as it will look more natural in Rust
>>> code (and is the notation the `bits` module already uses).
>> 
>> Perhaps future add-on enhancement to have both syntax? I'd like to initially
>> keep H:L and stabilize the code first, what do you think?
> 
> Let's have the discussion with the other stakeholders (Daniel?). I think
> in Nova we want to keep the `H:L` syntax, as it matches what the OpenRM
> headers do (so Nova would have its own `register` macro that calls into
> the common one, tweaking things as it needs). But in the kernel crate we
> should use something intuitive for everyone.
> 

I don’t specifically care which syntax is used. We will adapt to it.

— Daniel