linux-kernel - Re: [PATCH v6 2/6] rust: irq: add flags module

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Message-ID: <CAH5fLgggM7ZCX7nRz7M=hkxwzcp8UA1=2BQqRFA2CgN9eEUmsA@mail.gmail.com>
Date: Sat, 12 Jul 2025 22:03:48 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: Daniel Sedlak <daniel@...lak.dev>, 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>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Benno Lossin <lossin@...nel.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Krzysztof Wilczyński <kwilczynski@...nel.org>, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	linux-pci@...r.kernel.org
Subject: Re: [PATCH v6 2/6] rust: irq: add flags module

On Sat, Jul 12, 2025 at 6:27 PM Daniel Almeida
<daniel.almeida@...labora.com> wrote:
>
> Hi Alice,
>
> > On 4 Jul 2025, at 04:42, Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > On Fri, Jul 04, 2025 at 08:14:11AM +0200, Daniel Sedlak wrote:
> >> Hi Daniel,
> >>
> >> On 7/3/25 9:30 PM, Daniel Almeida wrote:
> >>> +/// Flags to be used when registering IRQ handlers.
> >>> +///
> >>> +/// They can be combined with the operators `|`, `&`, and `!`.
> >>> +#[derive(Clone, Copy, PartialEq, Eq)]
> >>> +pub struct Flags(u64);
> >>
> >> Why not Flags(u32)? You may get rid of all unnecessary casts later, plus
> >> save some extra bytes.
> >
> > It looks like the C methods take an `unsigned long`. In that case, I'd
> > probably write the code to match that.
> >
> > pub struct Flags(c_ulong);
> >
> > and git rid of the cast when calling bindings::request_irq.
> >
> > As for all the constants in this file, maybe it would be nice with a
> > private constructor that uses the same type as bindings to avoid the
> > casts?
> >
> > impl Flags {
> >    const fn new(value: u32) -> Flags {
> >     ...
> >    }
> > }
>
>
> Sure, but what goes here? This has to be "value as c_ulong” anyways so it
> doesn’t really reduce the number of casts.
>
> We should probably switch to Flags(u32) as Daniel Sedlak suggested. Then
> it’s a matter of casting once for bindings::request_irq().

IMO the advantage of doing it here is that we can fail compilation if
the cast is out of bounds, whereas the other cast is at runtime so we
can't do that.

Alice