linux-kernel - Re: [PATCH v5 05/23] rust: num: add the `fls` operation

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Message-Id: <DAQJLYKS5AV3.62SL1IRSQE4B@nvidia.com>
Date: Thu, 19 Jun 2025 22:26:55 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Benno Lossin" <lossin@...nel.org>, "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>, "Andreas Hindborg" <a.hindborg@...nel.org>,
 "Alice Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>,
 "Danilo Krummrich" <dakr@...nel.org>, "David Airlie" <airlied@...il.com>,
 "Simona Vetter" <simona@...ll.ch>, "Maarten Lankhorst"
 <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>
Cc: "John Hubbard" <jhubbard@...dia.com>, "Ben Skeggs" <bskeggs@...dia.com>,
 "Joel Fernandes" <joelagnelf@...dia.com>, "Timur Tabi" <ttabi@...dia.com>,
 "Alistair Popple" <apopple@...dia.com>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>, <nouveau@...ts.freedesktop.org>,
 <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v5 05/23] rust: num: add the `fls` operation

On Thu Jun 19, 2025 at 4:24 AM JST, Benno Lossin wrote:
> On Mon Jun 16, 2025 at 8:41 AM CEST, Alexandre Courbot wrote:
>> On Sun Jun 15, 2025 at 4:16 AM JST, Benno Lossin wrote:
>>> On Thu Jun 12, 2025 at 4:01 PM CEST, Alexandre Courbot wrote:
>>>> +            #[inline(always)]
>>>> +            pub const fn [<fls_ $t>](v: $t) -> u32 {
>>>
>>> Can we name this `find_last_set_bit_ $t`? When the upstream function
>>> lands, we should also rename this one.
>>
>> We can - but as for `align_up`/`next_multiple_of`, I am not sure which
>> naming scheme (kernel-like or closer to Rust conventions) is favored in
>> such cases, and so far it seems to come down to personal preference. I
>> tend to think that staying close to kernel conventions make it easier to
>> understand when a function is the equivalent of a C one, but whichever
>> policy we adopt it would be nice to codify it somewhere (apologies if it
>> is already and I missed it).
>
> I don't think we have it written down anywhere. I don't think that we
> should have a global rule for this. Certain things are more in the
> purview of the kernel and others are more on the Rust side.
>
> My opinion is that this, since it will hopefully be in `core` at some
> point, should go with the Rust naming.

I guess in that case we should go with `last_set_bit`, as `find_` is not
really used as a prefix for this kind of operations (e.g.
`leading_zeros` and friends).