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Message-ID: <aLzoyWpOr6eg-3yB@tardis-2.local>
Date: Sat, 6 Sep 2025 19:07:05 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Benno Lossin <lossin@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...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>,
Fiona Behrens <me@...enk.dev>, Alban Kurti <kurti@...icto.ai>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Krzysztof Wilczy´nski <kwilczynski@...nel.org>,
rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: pin-init: add references to previously initialized
fields
On Sat, Sep 06, 2025 at 06:57:04PM -0700, Boqun Feng wrote:
> On Sat, Sep 06, 2025 at 12:52:22PM +0200, Danilo Krummrich wrote:
> > On Fri Sep 5, 2025 at 7:44 PM CEST, Boqun Feng wrote:
> > > On Fri, Sep 05, 2025 at 07:18:25PM +0200, Benno Lossin wrote:
> > > [...]
> > >> index 606946ff4d7f..1ac0b06fa3b3 100644
> > >> --- a/samples/rust/rust_driver_pci.rs
> > >> +++ b/samples/rust/rust_driver_pci.rs
> > >> @@ -78,8 +78,8 @@ fn probe(pdev: &pci::Device<Core>, info: &Self::IdInfo) -> Result<Pin<KBox<Self>
> > >>
> > >> let drvdata = KBox::pin_init(
> > >> try_pin_init!(Self {
> > >> - pdev: pdev.into(),
> > >> bar <- pdev.iomap_region_sized::<{ Regs::END }>(0, c_str!("rust_driver_pci")),
> > >> + pdev: pdev.into(),
> > >
> > > Ok, this example is good enough for me to express the concern here: the
> > > variable shadowing behavior seems not straightforward (maybe because in
> > > normal Rust initalization expression, no binding is created for
> > > previous variables, neither do we have a `let` here).
> > >
> > > Would the future inplace initialization have the similar behavior? I
> > > asked because a natural resolution is adding a special syntax like:
> > >
> > > let a = ..;
> > >
> > > try_pin_init!(Self {
> > > b: a,
> > > let a = a.into(); // create the new binding here.
> > > c: a, // <- use the previous initalized `a`.
> > > }
> >
> > Can you please clarify the example? I'm a bit confused that this is not a field
> > of Self, so currently this can just be written as:
> >
>
> Oh, I could have been more clear: `a` is a field of `Self`, and the
> `let` part initalizes it.
>
> > try_pin_init!(Self {
> > b: a,
> > c: a.into,
> > })
> >
> > Of course assuming that a is Clone, as the code above does as well.
> >
> > So, if we are concerned by the variable shadowing, which I'm less concerned
> > about, maybe we can do this:
>
> I'm not that concerned to block this, but it does look to me like we are
> inventing a new way (and even a different syntax because normal Rust
> initialization doesn't create new bindings) to create binding, so I
> think I should bring it up.
>
> >
> > // The "original" `a` and `b`.
> > let a: A = ...;
> > let b: B = ...;
> >
> > try_pin_init!(Self {
> > a, // Initialize the field only.
> > let b <- b, // Initialize the field and create a `&B` named `b`.
> > c: a.into(), // That's the "original" `a`.
> > d <- D::new(b), // Not the original `b`, but the pin-init one.
> > })
Another idea is using `&this`:
try_pin_init!(&this in Self {
a, // Initialize the field only.
b <- b, // Initialize the field only.
c: a.into(), // That's the "original" `a`.
d <- D::new(this->b), // Not the original `b`, but the pin-init one.
})
, like a special field projection during initialization.
Regards,
Boqun
>
> This looks good to me as well. But I'm curious what the syntax would be
> like in the in-place placement language feature in the future.
>
> Regards,
> Boqun
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