linux-kernel - Re: [PATCH 1/3] rust: xarray: use the prelude

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Message-ID: <aGQORK02N8jMOhy6@Mac.home>
Date: Tue, 1 Jul 2025 09:35:16 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Tamir Duberstein <tamird@...il.com>
Cc: Andreas Hindborg <a.hindborg@...nel.org>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...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>,
	Matthew Wilcox <willy@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	Daniel Almeida <daniel.almeida@...labora.com>
Subject: Re: [PATCH 1/3] rust: xarray: use the prelude

On Tue, Jul 01, 2025 at 12:27:17PM -0400, Tamir Duberstein wrote:
> Using the prelude is customary in the kernel crate.
> 
> Signed-off-by: Tamir Duberstein <tamird@...il.com>
> ---
>  rust/kernel/xarray.rs | 34 ++++++++++++++++++++--------------
>  1 file changed, 20 insertions(+), 14 deletions(-)
> 
> diff --git a/rust/kernel/xarray.rs b/rust/kernel/xarray.rs
> index 75719e7bb491..436faad99c89 100644
> --- a/rust/kernel/xarray.rs
> +++ b/rust/kernel/xarray.rs
> @@ -5,16 +5,15 @@
>  //! C header: [`include/linux/xarray.h`](srctree/include/linux/xarray.h)
>  
>  use crate::{
> -    alloc, bindings, build_assert,
> -    error::{Error, Result},
> +    alloc,
> +    prelude::*,
>      types::{ForeignOwnable, NotThreadSafe, Opaque},
>  };
> -use core::{iter, marker::PhantomData, mem, pin::Pin, ptr::NonNull};
> -use pin_init::{pin_data, pin_init, pinned_drop, PinInit};
> +use core::{iter, marker::PhantomData, mem, ptr::NonNull};
>  
>  /// An array which efficiently maps sparse integer indices to owned objects.
>  ///
> -/// This is similar to a [`crate::alloc::kvec::Vec<Option<T>>`], but more efficient when there are
> +/// This is similar to a [`Vec<Option<T>>`], but more efficient when there are
>  /// holes in the index space, and can be efficiently grown.
>  ///
>  /// # Invariants
> @@ -104,16 +103,23 @@ pub fn new(kind: AllocKind) -> impl PinInit<Self> {
>      fn iter(&self) -> impl Iterator<Item = NonNull<T::PointedTo>> + '_ {
>          let mut index = 0;
>  
> -        // SAFETY: `self.xa` is always valid by the type invariant.
> -        iter::once(unsafe {
> -            bindings::xa_find(self.xa.get(), &mut index, usize::MAX, bindings::XA_PRESENT)
> -        })
> -        .chain(iter::from_fn(move || {
> +        core::iter::Iterator::chain(

Does this part come from using the prelude? If not, either we need to
split the patch or we need to mention it in the changelog at least.

Also since we `use core::iter` above, we can avoid the `core::` here.

Regards,
Boqun

>              // SAFETY: `self.xa` is always valid by the type invariant.
> -            Some(unsafe {
> -                bindings::xa_find_after(self.xa.get(), &mut index, usize::MAX, bindings::XA_PRESENT)
> -            })
> -        }))
> +            iter::once(unsafe {
> +                bindings::xa_find(self.xa.get(), &mut index, usize::MAX, bindings::XA_PRESENT)
> +            }),
> +            iter::from_fn(move || {
> +                // SAFETY: `self.xa` is always valid by the type invariant.
> +                Some(unsafe {
> +                    bindings::xa_find_after(
> +                        self.xa.get(),
> +                        &mut index,
> +                        usize::MAX,
> +                        bindings::XA_PRESENT,
> +                    )
> +                })
> +            }),
> +        )
>          .map_while(|ptr| NonNull::new(ptr.cast()))
>      }
>  
> 
> -- 
> 2.50.0
>