linux-kernel - Re: [PATCH 1/2] rust: Add cpumask helpers

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Message-ID: <20250224085613.ksburgsarl35tvnh@vireshk-i7>
Date: Mon, 24 Feb 2025 14:26:13 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Yury Norov <yury.norov@...il.com>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
	Danilo Krummrich <dakr@...hat.com>,
	"Rafael J. Wysocki" <rafael@...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 <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Stephen Boyd <sboyd@...nel.org>, Nishanth Menon <nm@...com>,
	Manos Pitsidianakis <manos.pitsidianakis@...aro.org>,
	Erik Schilling <erik.schilling@...aro.org>,
	Alex Bennée <alex.bennee@...aro.org>,
	Joakim Bech <joakim.bech@...aro.org>, Rob Herring <robh@...nel.org>,
	Christoph Hellwig <hch@....de>, Jason Gunthorpe <jgg@...dia.com>,
	John Hubbard <jhubbard@...dia.com>, linux-pm@...r.kernel.org,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] rust: Add cpumask helpers

Hi Yury,

On 21-02-25, 15:56, Yury Norov wrote:
> Question: zalloc_cpumask_war() is a convenient wrapper around
> alloc_cpumask_var_node(). Maybe rust can use the latter directly as it's
> a true outlined function? There's more flexibility, if you need it, but
> also a higher risk that the API will change: ~40 users vs 180 for zalloc
> thing. Up to you guys. I can send v2 if needed.

I looked at the APIs again and here is what I feel:

- I am not sure if the Rust code will have any users of the *_node()
  APIs in the near future. i.e. There is no need for the Rust code to
  implement Cpumask::new_node() version for now.

- I have missed implementing the uninitialized version earlier,
  alloc_cpumask_var(), which I think should be implemented right away.
  Bindings for alloc_cpumask_var() are required to be added for this
  though.

- One advantage of using zalloc_cpumask_var() instead of
  alloc_cpumask_var() is that we don't need to open code it in the
  Rust code, specifically for the !CONFIG_CPUMASK_OFFSTACK case where
  we need to call cpumask_clear() separately.

- The Rust side can have following abstractions for now:

  pub fn new() -> Result<Self>;
  pub fn new_zeroed() -> Result<Self>;

-- 
viresh