linux-kernel - Re: [PATCH v3 04/12] rust: xarray: add `XArrayState`

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Message-ID: <aYtcdGk8zcwaHfsd@macos>
Date: Tue, 10 Feb 2026 17:48:18 +0100
From: Daniel Gomez <da.gomez@...nel.org>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: Tamir Duberstein <tamird@...il.com>, 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>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...two.org>, 
	David Rientjes <rientjes@...gle.com>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Harry Yoo <harry.yoo@...cle.com>, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCH v3 04/12] rust: xarray: add `XArrayState`

On 2026-02-09 15:38, Andreas Hindborg wrote:
> Add `XArrayState` as internal state for XArray iteration and entry
> operations. This struct wraps the C `xa_state` structure and holds a
> reference to a `Guard` to ensure exclusive access to the XArray for the
> lifetime of the state object.
> 
> The `XAS_RESTART` constant is also exposed through the bindings helper
> to properly initialize the `xa_node` field.
> 
> The struct and its constructor are marked with `#[expect(dead_code)]` as
> there are no users yet. We will remove this annotation in a later patch.

It makes sense to me to merge patch 4 and 5 to avoid this.

> 
> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
> ---
>  rust/bindings/bindings_helper.h |  1 +
>  rust/kernel/xarray.rs           | 41 ++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index a067038b4b422..58605c32e8102 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
...
> @@ -319,6 +322,42 @@ pub fn store(
...
> +impl<'a, 'b, T: ForeignOwnable> XArrayState<'a, 'b, T> {
> +    #[expect(dead_code)]
> +    fn new(access: &'b Guard<'a, T>, index: usize) -> Self {
> +        let ptr = access.xa.xa.get();
> +        // INVARIANT: We initialize `self.state` to a valid value below.
> +        Self {
> +            _access: PhantomData,
> +            state: bindings::xa_state {
> +                xa: ptr,
> +                xa_index: index,
> +                xa_shift: 0,
> +                xa_sibs: 0,
> +                xa_offset: 0,

To match C XArray __XA_STATE() we should also pass shift and sibs. Even if the
only use case we have currently is setting these to 0 (XA_STATE()).