linux-kernel - Re: [PATCH v2 2/2] rust: workqueue: remove HasWork::OFFSET

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Message-ID: <CAH5fLghSWJKDYae+oDsbkQHSWLVyAS6fqGYt7whHWaA6PXox_w@mail.gmail.com>
Date: Fri, 11 Apr 2025 16:03:55 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Tamir Duberstein <tamird@...il.com>
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>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	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>, Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pci@...r.kernel.org
Subject: Re: [PATCH v2 2/2] rust: workqueue: remove HasWork::OFFSET

On Fri, Apr 11, 2025 at 3:57 PM Tamir Duberstein <tamird@...il.com> wrote:
>
> On Fri, Apr 11, 2025 at 5:10 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > On Thu, Apr 10, 2025 at 10:15:53AM -0400, Tamir Duberstein wrote:
> > > On Thu, Apr 10, 2025 at 5:16 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
> > > >
> > > > On Wed, Apr 09, 2025 at 06:03:22AM -0400, Tamir Duberstein wrote:
> > > > > Implement `HasWork::work_container_of` in `impl_has_work!`, narrowing
> > > > > the interface of `HasWork` and replacing pointer arithmetic with
> > > > > `container_of!`. Remove the provided implementation of
> > > > > `HasWork::get_work_offset` without replacement; an implementation is
> > > > > already generated in `impl_has_work!`. Remove the `Self: Sized` bound on
> > > > > `HasWork::work_container_of` which was apparently necessary to access
> > > > > `OFFSET` as `OFFSET` no longer exists.
> > > > >
> > > > > A similar API change was discussed on the hrtimer series[1].
> > > > >
> > > > > Link: https://lore.kernel.org/all/20250224-hrtimer-v3-v6-12-rc2-v9-1-5bd3bf0ce6cc@kernel.org/ [1]
> > > > > Reviewed-by: Benno Lossin <benno.lossin@...ton.me>
> > > > > Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> > > > > Tested-by: Alice Ryhl <aliceryhl@...gle.com>
> > > > > Signed-off-by: Tamir Duberstein <tamird@...il.com>
> > > > > ---
> > > > >  rust/kernel/workqueue.rs | 45 ++++++++++++---------------------------------
> > > > >  1 file changed, 12 insertions(+), 33 deletions(-)
> > > > >
> > > > > diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
> > > > > index f98bd02b838f..1d640dbdc6ad 100644
> > > > > --- a/rust/kernel/workqueue.rs
> > > > > +++ b/rust/kernel/workqueue.rs
> > > > > @@ -429,51 +429,23 @@ pub unsafe fn raw_get(ptr: *const Self) -> *mut bindings::work_struct {
> > > > >  ///
> > > > >  /// # Safety
> > > > >  ///
> > > > > -/// The [`OFFSET`] constant must be the offset of a field in `Self` of type [`Work<T, ID>`]. The
> > > > > -/// methods on this trait must have exactly the behavior that the definitions given below have.
> > > > > +/// The methods on this trait must have exactly the behavior that the definitions given below have.
> > > >
> > > > This wording probably needs to be rephrased. You got rid of the
> > > > definitions that sentence refers to.
> > >
> > > I don't follow. What definitions was it referring to? I interpreted it
> > > as having referred to all the items: constants *and* methods.
> >
> > I meant for it to refer to the default implementations of the methods.
> >
> > > Could you propose an alternate phrasing?
> >
> > I guess the requirements are something along the lines of raw_get_work
> > must return a value pointer, and it must roundtrip with
> > raw_container_of.
>
> What is a value pointer?

Sorry, I meant "valid".