linux-kernel - Re: [PATCH v4 3/6] rust: irq: add support for non-threaded IRQs and handlers

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Message-ID: <CAH5fLghDbrgO2PiKyKZ87UrtouG25xWhVP_YmcgO0fFcnvZRkQ@mail.gmail.com>
Date: Mon, 23 Jun 2025 16:10:50 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Daniel Almeida <daniel.almeida@...labora.com>, 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>, 
	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 v4 3/6] rust: irq: add support for non-threaded IRQs and handlers

On Mon, Jun 9, 2025 at 12:47 PM Danilo Krummrich <dakr@...nel.org> wrote:
>
> On Sun, Jun 08, 2025 at 07:51:08PM -0300, Daniel Almeida wrote:
> > +        dev: &'a Device<Bound>,
> > +        irq: u32,
> > +        flags: Flags,
> > +        name: &'static CStr,
> > +        handler: T,
> > +    ) -> impl PinInit<Self, Error> + 'a {
> > +        let closure = move |slot: *mut Self| {
> > +            // SAFETY: The slot passed to pin initializer is valid for writing.
> > +            unsafe {
> > +                slot.write(Self {
> > +                    inner: Devres::new(
> > +                        dev,
> > +                        RegistrationInner {
> > +                            irq,
> > +                            cookie: slot.cast(),
> > +                        },
> > +                        GFP_KERNEL,
> > +                    )?,
> > +                    handler,
> > +                    _pin: PhantomPinned,
> > +                })
> > +            };
> > +
> > +            // SAFETY:
> > +            // - The callbacks are valid for use with request_irq.
> > +            // - If this succeeds, the slot is guaranteed to be valid until the
> > +            // destructor of Self runs, which will deregister the callbacks
> > +            // before the memory location becomes invalid.
> > +            let res = to_result(unsafe {
> > +                bindings::request_irq(
> > +                    irq,
> > +                    Some(handle_irq_callback::<T>),
> > +                    flags.into_inner() as usize,
> > +                    name.as_char_ptr(),
> > +                    slot.cast(),
> > +                )
> > +            });
> > +
> > +            if res.is_err() {
> > +                // SAFETY: We are returning an error, so we can destroy the slot.
> > +                unsafe { core::ptr::drop_in_place(&raw mut (*slot).handler) };
> > +            }
> > +
> > +            res
> > +        };
> > +
> > +        // SAFETY:
> > +        // - if this returns Ok, then every field of `slot` is fully
> > +        // initialized.
> > +        // - if this returns an error, then the slot does not need to remain
> > +        // valid.
> > +        unsafe { pin_init_from_closure(closure) }
>
> Can't we use try_pin_init!() instead, move request_irq() into the initializer of
> RegistrationInner and initialize inner last?

We need a pointer to the entire struct when calling
bindings::request_irq. I'm not sure this allows you to easily get one?
I don't think using container_of! here is worth it.

Alice