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Date:   Sun, 11 Jun 2023 16:10:20 +0000
To:     Alice Ryhl <aliceryhl@google.com>
From:   Benno Lossin <benno.lossin@proton.me>
Cc:     rust-for-linux@vger.kernel.org, Miguel Ojeda <ojeda@kernel.org>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Tejun Heo <tj@kernel.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        linux-kernel@vger.kernel.org, patches@lists.linux.dev
Subject: Re: [PATCH v2 7/8] rust: workqueue: add `try_spawn` helper method
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On 01.06.23 15:49, Alice Ryhl wrote:
> This adds a convenience method that lets you spawn a closure for
> execution on a workqueue. This will be the most convenient way to use
> workqueues, but it is fallible because it needs to allocate memory.
>=20
> Co-developed-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>

Reviewed-by: Benno Lossin <benno.lossin@proton.me>

--=20
Cheers,
Benno

> ---
>   rust/kernel/workqueue.rs | 43 ++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 43 insertions(+)
>=20
> diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
> index f06a2f036d8b..c302e8b8624b 100644
> --- a/rust/kernel/workqueue.rs
> +++ b/rust/kernel/workqueue.rs
> @@ -29,6 +29,7 @@
>   //! C header: [`include/linux/workqueue.h`](../../../../include/linux/w=
orkqueue.h)
>=20
>   use crate::{bindings, prelude::*, sync::Arc, types::Opaque};
> +use alloc::alloc::AllocError;
>   use alloc::boxed::Box;
>   use core::marker::{PhantomData, PhantomPinned};
>   use core::pin::Pin;
> @@ -87,6 +88,44 @@ pub fn enqueue<W, const ID: u64>(&self, w: W) -> W::En=
queueOutput
>               })
>           }
>       }
> +
> +    /// Tries to spawn the given function or closure as a work item.
> +    ///
> +    /// This method can fail because it allocates memory to store the wo=
rk item.
> +    pub fn try_spawn<T: 'static + Send + FnOnce()>(&self, func: T) -> Re=
sult<(), AllocError> {
> +        let init =3D pin_init!(ClosureWork {
> +            work <- Work::new(),
> +            func: Some(func),
> +        });
> +
> +        self.enqueue(Box::pin_init(init).map_err(|_| AllocError)?);
> +        Ok(())
> +    }
> +}
> +
> +/// A helper type used in `try_spawn`.
> +#[pin_data]
> +struct ClosureWork<T> {
> +    #[pin]
> +    work: Work<ClosureWork<T>>,
> +    func: Option<T>,
> +}
> +
> +impl<T> ClosureWork<T> {
> +    fn project(self: Pin<&mut Self>) -> &mut Option<T> {
> +        // SAFETY: The `func` field is not structurally pinned.
> +        unsafe { &mut self.get_unchecked_mut().func }
> +    }
> +}
> +
> +impl<T: FnOnce()> WorkItem for ClosureWork<T> {
> +    type Pointer =3D Pin<Box<Self>>;
> +
> +    fn run(mut this: Pin<Box<Self>>) {
> +        if let Some(func) =3D this.as_mut().project().take() {
> +            (func)()
> +        }
> +    }
>   }
>=20
>   /// A raw work item.
> @@ -325,6 +364,10 @@ unsafe fn raw_get_work(ptr: *mut Self) -> *mut $crat=
e::workqueue::Work<$work_typ
>       )*};
>   }
>=20
> +impl_has_work! {
> +    impl<T> HasWork<Self> for ClosureWork<T> { self.work }
> +}
> +
>   unsafe impl<T, const ID: u64> WorkItemPointer<ID> for Arc<T>
>   where
>       T: WorkItem<ID, Pointer =3D Self>,
> --
> 2.41.0.rc0.172.g3f132b7071-goog
>=20