linux-kernel - Re: [PATCH 0/2] rust: cpumask: Bindings for core cpumasks and cpumask iterators

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Message-ID: <690e8748.050a0220.22e404.3a1d@mx.google.com>
Date: Fri, 7 Nov 2025 15:56:54 -0800
From: Mitchell Levy <levymitchell0@...il.com>
To: Yury Norov <yury.norov@...il.com>
Cc: John Hubbard <jhubbard@...dia.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>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] rust: cpumask: Bindings for core cpumasks and
 cpumask iterators

On Thu, Nov 06, 2025 at 08:38:54PM -0500, Yury Norov wrote:
> On Wed, Nov 05, 2025 at 04:19:36PM -0800, John Hubbard wrote:
> > On 11/5/25 3:16 PM, Mitchell Levy wrote:
> > > The kernel provides a number of very useful CPU masks from the C side,
> > > including CPU masks for possible and online CPUs. In particular, these
> > > are very useful when some operation must be done on each CPU (either
> > > each possible CPU or each online CPU, etc). Therefore, it seems to make
> > > sense to add both of these functionalities at once.
> > > 
> > > Signed-off-by: Mitchell Levy <levymitchell0@...il.com>
> > > ---
> > > These patches originated as part of my work on a Rust per-CPU API [1].
> > > Boqun suggested to me that these may make sense to merge separately, and
> > > it does seem like these might be useful beyond the per-CPU work.
> > > 
> > > [1]: https://lore.kernel.org/rust-for-linux/20251105-rust-percpu-v4-0-984b1470adcb@gmail.com/
> > 
> > Even though you are trying to get these two patches merged separately,
> > I think it's best (for reviewers) if you post a patchset that shows
> > these things being used. Otherwise it is potentially too unmoored from 
> > reality, and hard to be sure that it's exactly right from a caller's
> > point of view.
> > 
> > In this case, just posting that 9-patch series might work, and just
> > say in the cover letter that patches 3 through 9 are not ready for
> > merging.
> > 
> > Something like that.
> > 
> > I realize that Rust for Linux is being built from scratch right
> > now, but including calling code in a patchset is a really valuable
> > kernel convention that helps validate the code.
> > 
> > I say this for the benefit of others who may be reading. :)
> 
> Not a big deal. Those two patches are self-consistent enough to take
> them separately. But I agree that examples are always welcome.
> 
> Mitchell, can you resend this small series after addressing my
> comments to the big one, and also can you illustrate it with the
> usage examples?
> 
> Maybe a small test doing:
>         
>         for cpu in CpuMask::possible_cpus().iter()
>                 ncpus++;
> 
>         assert_eq!(ncpus == CpuMask::num_possible_cpus());

Sure, will do. My current plan is to do rustdoc tests that will double
as examples in the generated documentation. However, if you'd prefer
something in `samples/rust` instead (or in addition), please let me
know.

Thanks,
Mitchell

> Thanks,
> Yury