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

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Message-ID: <aGQUuuCpaBFrWrSe@Mac.home>
Date: Tue, 1 Jul 2025 10:02:50 -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 12:36:20PM -0400, Tamir Duberstein wrote:
> 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.

Maybe you can mention this in the change log as well. Like "Calling
iter::chain() with the associated function style to disambiguate with
PinInit::chain()". Make it easier to review (and remember) why.

Regards,
Boqun

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