linux-kernel - Re: [PATCH v6] rust: kernel: add support for bits/genmask macros

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Message-Id: <DAO1RRSIUW6F.2FUMJ00GSXUIQ@nvidia.com>
Date: Tue, 17 Jun 2025 00:02:50 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Daniel Almeida" <daniel.almeida@...labora.com>
Cc: "Boqun Feng" <boqun.feng@...il.com>, "Miguel Ojeda" <ojeda@...nel.org>,
 "Alex Gaynor" <alex.gaynor@...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>,
 "Danilo Krummrich" <dakr@...nel.org>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v6] rust: kernel: add support for bits/genmask macros

On Mon Jun 16, 2025 at 11:56 PM JST, Daniel Almeida wrote:
> Hi Alex,
>
>> On 16 Jun 2025, at 11:52, Alexandre Courbot <acourbot@...dia.com> wrote:
>> 
>> On Mon Jun 16, 2025 at 11:45 PM JST, Daniel Almeida wrote:
>>> 
>>> 
>>>> On 16 Jun 2025, at 11:42, Daniel Almeida <daniel.almeida@...labora.com> wrote:
>>>> 
>>>> Hi Boqun,
>>>> 
>>>>> 
>>>>> We should tell/educate people to do the right thing, if a..b is not
>>>>> inclusive in Rust, then we should treat them as non-inclusive in Rust
>>>>> kernel code. Otherwise you create confusion for no reason. My assumption
>>>>> is that most people will ask "what's the right way to do this" first
>>>>> instead of replicating the old way.
>>>>> 
>>>>> Regards,
>>>>> Boqun
>>>>> 
>>>> 
>>>> This is just my opinion, of course:
>>>> 
>>>> I _hardly_ believe this will be the case. When people see genmask and two
>>>> numbers, they expect the range to be inclusive, full stop (at least IMHO). That's how it has
>>>> worked for decades, so it’s only natural to expect this behavior to transfer over.
>>>> 
>>>> However, I do understand and agree with your point, and I will change the
>>>> implementation here to comply. Perhaps we can use some markdown to alert users?
>>>> 
>>>> — Daniel
>>> 
>>> Or better yet, perhaps we should only support a..=b.
>> 
>> ... or just drop the ranges and do as Daniel initially did, using two
>> arguments. But I agree with Boqun that we should not deviate from the
>> official interpretation of ranges if we use them - the fact that `Range`
>> is exclusive on its upper bound is documented and a property of the type
>> itself.
>
> By the same token, I agree that we should use ranges instead of two arguments,
> if said two arguments represent a range anyways. So my vote is for a..=b JFYI.

That works for me, it has the benefit of being absolutely clear that the
range is inclusive.