linux-kernel - Re: [PATCH 2/2] rust: workqueue: remove HasWork::OFFSET

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Message-ID: <CAJ-ks9m-ab9Y5RD01higxZxbowZi_0tsSmCCw2umJLxBLH4dEw@mail.gmail.com>
Date: Sat, 15 Mar 2025 14:12:48 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Benno Lossin <benno.lossin@...ton.me>
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>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 2/2] rust: workqueue: remove HasWork::OFFSET

On Sat, Mar 15, 2025 at 2:06 PM Benno Lossin <benno.lossin@...ton.me> wrote:
>
> On Sat Mar 15, 2025 at 4:37 PM CET, Tamir Duberstein wrote:
> > On Sat, Mar 15, 2025 at 5:30 AM Benno Lossin <benno.lossin@...ton.me> wrote:
> >>
> >> On Fri Mar 14, 2025 at 9:44 PM CET, Tamir Duberstein wrote:
> >> > On Fri, Mar 14, 2025 at 3:20 PM Benno Lossin <benno.lossin@...ton.me> wrote:
> >> >>
> >> >> On Fri Mar 7, 2025 at 10:58 PM CET, Tamir Duberstein wrote:
> >> >> >      /// Returns a pointer to the struct containing the [`Work<T, ID>`] field.
> >> >> >      ///
> >> >> >      /// # Safety
> >> >> >      ///
> >> >> >      /// The pointer must point at a [`Work<T, ID>`] field in a struct of type `Self`.
> >> >> > -    #[inline]
> >> >> > -    unsafe fn work_container_of(ptr: *mut Work<T, ID>) -> *mut Self
> >> >> > -    where
> >> >> > -        Self: Sized,
> >> >>
> >> >> This bound is required in order to allow the usage of `dyn HasWork` (ie
> >> >> object safety), so it should stay.
> >> >>
> >> >> Maybe add a comment explaining why it's there.
> >> >
> >> > I guess a doctest would be better, but I still don't understand why
> >> > the bound is needed. Sorry, can you cite something or explain in more
> >> > detail please?
> >>
> >> Here is a link: https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility
> >>
> >> But I realized that the trait wasn't object safe to begin with due to
> >> the `OFFSET` associated constant. So I'm not sure we need this. Alice,
> >> do you need `dyn HasWork`?
> >
> > I wrote a simple test:
>
> [...]
>
> > so I don't think adding the Sized bound makes sense - we'd end up
> > adding it on every item in the trait.
>
> Yeah the `Sized` bound was probably to make the cast work, so let's
> remove it.

It's already removed, right?