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

[Danilo Krummrich <dakr@kernel.org>]

On Mon, Jun 23, 2025 at 04:10:50PM +0100, Alice Ryhl wrote:
> On Mon, Jun 9, 2025 at 12:47 PM Danilo Krummrich <dakr@kernel.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.

Would `try_pin_init!(&this in Self { ...` work?