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

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Message-ID: <CAJ-ks9nqWHSJjjeg=QReVh3pq87LSLE-+NDOD5scp1axYV7k7Q@mail.gmail.com>
Date: Tue, 1 Jul 2025 12:36:20 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Boqun Feng <boqun.feng@...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 1, 2025 at 12:35 PM Boqun Feng <boqun.feng@...il.com> wrote:
>
> 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.

Yes, it's from using the prelude - PinInit also has a chain method
that causes ambiguity here.

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

Good point.