Re: [PATCH v3 1/2] rust: irq: add support for request_irq()

[Benno Lossin]

On Mon Jun 2, 2025 at 5:20 PM CEST, Alice Ryhl wrote:
> On Wed, May 14, 2025 at 10:04:43PM +0200, Benno Lossin wrote:
>> On Wed May 14, 2025 at 9:20 PM CEST, Daniel Almeida wrote:
>> > +                )
>> > +            });
>> > +
>> > +            if res.is_err() {
>> > +                // SAFETY: We are returning an error, so we can destroy the slot.
>> > +                unsafe { core::ptr::drop_in_place(addr_of_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) }
>> 
>> Please don't use `pin_init_from_closure`, instead do this:
>> 
>>     pin_init!(Self {
>>         irq,
>>         handler,
>>         _pin: PhantomPinned
>>     })
>>     .pin_chain(|this| {
>>         // SAFETY: TODO: correct FFI safety requirements
>>         to_result(unsafe {
>>             bindings::request_irq(...)
>>         })
>>     })
>> 
>> The `pin_chain` function is exactly for this use-case, doing some
>> operation that might fail after initializing & it will drop the value
>> when the closure fails.
>
> No, that doesn't work. Using pin_chain will call free_irq if the call to
> request_irq fails, which is incorrect.

Good catch. That's a bit annoying then... I wonder if there is a
primitive missing in pin-init that could help with this... Any ideas?

---
Cheers,
Benno