linux-kernel - Re: [PATCH v2 2/4] rust: xarray: abstract `xa

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Message-ID: <CAH5fLghoDEKnpq6WaD3zzV9UHm6gYzYXCOG_Q=pOUomcNcQhPg@mail.gmail.com>
Date: Wed, 8 Oct 2025 16:05:05 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Onur Özkan <work@...rozkan.dev>, 
	rust-for-linux@...r.kernel.org, ojeda@...nel.org, alex.gaynor@...il.com, 
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	lossin@...nel.org, tmgross@...ch.edu, dakr@...nel.org, 
	linux-kernel@...r.kernel.org, acourbot@...dia.com, airlied@...il.com, 
	simona@...ll.ch, maarten.lankhorst@...ux.intel.com, mripard@...nel.org, 
	tzimmermann@...e.de, corbet@....net, lyude@...hat.com, 
	linux-doc@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 2/4] rust: xarray: abstract `xa_alloc`

On Wed, Oct 8, 2025 at 3:40 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Wed, Oct 08, 2025 at 01:04:11PM +0000, Alice Ryhl wrote:
> > > +        limit: Range<u32>,
> >
> > The Range type is inclusive/exclusive but xa_limit is
> > inclusive/inclusive. They should match to avoid confusion.
>
> ... and xa_limit is inclusive at the top end to be sure that we can
> actually allocate 2^32-1.  Or does Range handle that by using 0 to mean
> that 2^32-1 is allowed?

Rust has multiple range types for inclusive and exclusive cases. The
Range type is usually used for indexing arrays where the length fits
in the integer type. To include 2^32-1, you have to use RangeInclusive
instead of Range. It should be possible to write code that handles all
of the range types without repetition.

Alice