linux-kernel - Re: [PATCH] rust: irq: add support for request

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Message-ID: <CAH5fLgiaVg1+PZxGr0Y_oyu9pJfTSRuN9n4EomFGhnvnZXC4cg@mail.gmail.com>
Date: Tue, 14 Jan 2025 19:36:57 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: 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>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH] rust: irq: add support for request_irq()

On Tue, Jan 14, 2025 at 7:35 PM Daniel Almeida
<daniel.almeida@...labora.com> wrote:
>
> Hi Alice,
>
> > On 13 Jan 2025, at 11:42, Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > On Thu, Oct 24, 2024 at 4:20 PM Daniel Almeida
> > <daniel.almeida@...labora.com> wrote:
> >>
> >> +impl<T: Handler> Registration<T> {
> >> +    /// Registers the IRQ handler with the system for the given IRQ number. The
> >> +    /// handler must be able to be called as soon as this function returns.
> >> +    pub fn register(
> >> +        irq: u32,
> >> +        flags: Flags,
> >> +        name: &'static CStr,
> >> +        handler: T,
> >> +    ) -> impl PinInit<Self, Error> {
> >> +        try_pin_init!(Self {
> >> +            irq,
> >> +            handler: Opaque::new(handler)
> >> +        })
> >> +        .pin_chain(move |slot| {
> >> +            // SAFETY:
> >> +            // - `handler` points to a valid function defined below.
> >> +            // - only valid flags can be constructed using the `flags` module.
> >> +            // - `devname` is a nul-terminated string with a 'static lifetime.
> >> +            // - `ptr` is a cookie used to identify the handler. The same cookie is
> >> +            // passed back when the system calls the handler.
> >> +            to_result(unsafe {
> >> +                bindings::request_irq(
> >> +                    irq,
> >> +                    Some(handle_irq_callback::<T>),
> >> +                    flags.0,
> >> +                    name.as_char_ptr(),
> >> +                    &*slot as *const _ as *mut core::ffi::c_void,
> >> +                )
> >> +            })?;
> >> +
> >> +            Ok(())
> >> +        })
> >
> > I think this does not run the destructor of `handler` when
> > `request_irq` returns an error.
> >
> > Alice
>
> How? T is passed by value, so if request_irq() fails and thus Registration::register() returns Err,
> I assume T is dropped.
>
> Or is the pin_init! stuff somehow special here?

It's not the pin_init! stuff, but the Opaque stuff. If it fails, then
it runs the destructor of Opaque<T>, which does *not* run the
destructor of T.

Alice