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

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Message-ID: <aQ1NpPIcVIUXqgQS@yury>
Date: Thu, 6 Nov 2025 20:38:54 -0500
From: Yury Norov <yury.norov@...il.com>
To: John Hubbard <jhubbard@...dia.com>
Cc: Mitchell Levy <levymitchell0@...il.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 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());

Thanks,
Yury