On Mon, Jun 23, 2025 at 05:26:14PM +0200, Benno Lossin wrote:
> On Mon Jun 23, 2025 at 5:10 PM CEST, Alice Ryhl wrote:
> > On Mon, Jun 9, 2025 at 12:47 PM Danilo Krummrich <dakr@xxxxxxxxxx> 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.
>
> There is the `&this in` syntax (`this` is of type `NonNull<Self>`):
>
> try_pin_init!(&this in Self {
> inner: Devres::new(
> dev,
> RegistrationInner {
> irq,
> cookie: this.as_ptr().cast(),
> },
> GFP_KERNEL,
> )?,
> handler,
> _pin: {
> to_result(unsafe {
> bindings::request_irq(
> irq,
> Some(handle_irq_callback::<T>),
> flags.into_inner() as usize,
> name.as_char_ptr(),
> slot.as_ptr().cast(),
this is "this" instead of "slot", right?
> )
> })?;
> PhantomPinned
> },
> })
>
> Last time around, I also asked this question and you replied with that
> we need to abort the initializer when `request_irq` returns false and
> avoid running `Self::drop` (thus we can't do it using `pin_chain`).
>
> I asked what we could do instead and you mentioned the `_: {}`
> initializers and those would indeed solve it, but we can abuse the
> `_pin` field for that :)
>
Hmm.. but if request_irq() fails, aren't we going to call `drop` on
`inner`, which drops the `Devres` which will eventually call
`RegistrationInner::drop()`? And that's a `free_irq()` without
`request_irq()` succeeded.
Regards,
Boqun
> ---
> Cheers,
> Benno
