linux-kernel - Re: [PATCH] gpu: nova-core: bitfield: use &mut self setters instead of builder pattern

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CE6A313F-9DF3-4944-A5AE-F26464D89C17@nvidia.com>
Date: Thu, 1 Jan 2026 00:15:52 +0000
From: Joel Fernandes <joelagnelf@...dia.com>
To: John Hubbard <jhubbard@...dia.com>
CC: Timur Tabi <ttabi@...dia.com>, "dakr@...nel.org" <dakr@...nel.org>,
	Alexandre Courbot <acourbot@...dia.com>, "lossin@...nel.org"
	<lossin@...nel.org>, "a.hindborg@...nel.org" <a.hindborg@...nel.org>,
	"boqun.feng@...il.com" <boqun.feng@...il.com>, "aliceryhl@...gle.com"
	<aliceryhl@...gle.com>, Zhi Wang <zhiw@...dia.com>, "simona@...ll.ch"
	<simona@...ll.ch>, "alex.gaynor@...il.com" <alex.gaynor@...il.com>,
	"ojeda@...nel.org" <ojeda@...nel.org>, "tmgross@...ch.edu"
	<tmgross@...ch.edu>, "nouveau@...ts.freedesktop.org"
	<nouveau@...ts.freedesktop.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "rust-for-linux@...r.kernel.org"
	<rust-for-linux@...r.kernel.org>, "bjorn3_gh@...tonmail.com"
	<bjorn3_gh@...tonmail.com>, Edwin Peer <epeer@...dia.com>,
	"airlied@...il.com" <airlied@...il.com>, "bhelgaas@...gle.com"
	<bhelgaas@...gle.com>, "gary@...yguo.net" <gary@...yguo.net>, Alistair Popple
	<apopple@...dia.com>
Subject: Re: [PATCH] gpu: nova-core: bitfield: use &mut self setters instead
 of builder pattern



> On Dec 31, 2025, at 5:47 PM, John Hubbard <jhubbard@...dia.com> wrote:
> 
> On 12/31/25 2:33 PM, Timur Tabi wrote:
>>> On Wed, 2025-12-31 at 13:47 -0800, John Hubbard wrote:
>>> The builder-pattern setters (self -> Self) enabled method chaining like:
>>> 
>>>     reg.set_foo(x).set_sec(y).write(bar);
>>> 
>>> This made separate operations appear as a single expression, obscuring
>>> that each setter is a distinct mutation. 
>> 
>> So you're concerned about the fact that the compiler is not merging the set_foo(x) and the
>> set_sec(y) into a single read-modify-write?
> 
> No, I don't care about that aspect.
> 
>> 
>>> These setters are infallible,
>>> so the chaining provides no error-propagation benefit—it just obscures
>>> what are simple, independent assignments.
>>> 
>>> Change the bitfield!() macro to generate `&mut self` setters, so each
>>> operation is a distinct statement:
>>> 
>>>     reg.set_foo(x);
>>>     reg.set_sec(y);
>>>     reg.write(bar);
>> 
>> Are you sure about this?  It just seems like you're throwing out a neat little feature of Rust and
>> replacing it with something that's very C-like.  This breaks compatible with all users of the regs
>> macros.  Seems really disruptive for what seems to me like a cosmetic change.
>> 
> 
> It's only a neat feature if it *does* something. In this case, it *looks*
> like a neat Rust feature, but under the covers it really is just handing
> around copies unnecessarily, when really, it *is* doing the C-like thing
> in the end.
> 
> I object to the fake Rust-ness that's being done here. It's like putting
> hubcabs on a car.

But IMO there is only one operation here, the IO write. The setter is just mutations. Builder pattern chaining is idiomatic to Rust.

I would not call it fake Rustness since it is Rustness in the Rust language. Afair, similar arguments were made before and conclusion was, well, this is Rust.

Regarding the copies, I am intrigued - have you verified that the code generation actually results in copies? I would be surprised if the compiler did not optimize.

 - Joel





> 
> thanks,
> --
> John Hubbard
>