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Message-ID: <CAH5fLgg6_U4OAnDXy1eM98ur=MZonnDq3tk2o=KAf+YXNPtBbQ@mail.gmail.com>
Date: Fri, 11 Apr 2025 16:14:35 +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 v3] rust: workqueue: remove HasWork::OFFSET
On Fri, Apr 11, 2025 at 4:08 PM Tamir Duberstein <tamird@...il.com> 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>
> Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>
> Signed-off-by: Tamir Duberstein <tamird@...il.com>
Seems reasonable enough.
Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
> Changes in v3:
> - Extract first commit to its own series as it is shared with other
> series.
> - Reword `HasWork` safety comment.
> - Link to v2: https://lore.kernel.org/r/20250409-no-offset-v2-0-dda8e141a909@gmail.com
>
> Changes in v2:
> - Rebase on v6.15-rc1.
> - Add WORKQUEUE maintainers to cc.
> - Link to v1: https://lore.kernel.org/r/20250307-no-offset-v1-0-0c728f63b69c@gmail.com
> ---
> rust/kernel/workqueue.rs | 50 ++++++++++++++++--------------------------------
> 1 file changed, 17 insertions(+), 33 deletions(-)
>
> diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
> index f98bd02b838f..d092112d843f 100644
> --- a/rust/kernel/workqueue.rs
> +++ b/rust/kernel/workqueue.rs
> @@ -429,51 +429,28 @@ 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 [`raw_get_work`] and [`work_container_of`] must return valid pointers and must be
> +/// true inverses of each other; that is, they must satisfy the following invariants:
> +/// - `work_container_of(raw_get_work(ptr)) == ptr` for any `ptr: *mut Self`.
> +/// - `raw_get_work(work_container_of(ptr)) == ptr` for any `ptr: *mut Work<T, ID>`.
> ///
> /// [`impl_has_work!`]: crate::impl_has_work
> -/// [`OFFSET`]: HasWork::OFFSET
> +/// [`raw_get_work`]: HasWork::raw_get_work
> +/// [`work_container_of`]: HasWork::work_container_of
> pub unsafe trait HasWork<T, const ID: u64 = 0> {
> - /// The offset of the [`Work<T, ID>`] field.
> - const OFFSET: usize;
> -
> - /// Returns the offset of the [`Work<T, ID>`] field.
> - ///
> - /// This method exists because the [`OFFSET`] constant cannot be accessed if the type is not
> - /// [`Sized`].
> - ///
> - /// [`OFFSET`]: HasWork::OFFSET
> - #[inline]
> - fn get_work_offset(&self) -> usize {
> - Self::OFFSET
> - }
> -
> /// Returns a pointer to the [`Work<T, ID>`] field.
> ///
> /// # Safety
> ///
> /// The provided pointer must point at a valid struct of type `Self`.
> - #[inline]
> - unsafe fn raw_get_work(ptr: *mut Self) -> *mut Work<T, ID> {
> - // SAFETY: The caller promises that the pointer is valid.
> - unsafe { (ptr as *mut u8).add(Self::OFFSET) as *mut Work<T, ID> }
> - }
> + unsafe fn raw_get_work(ptr: *mut Self) -> *mut Work<T, ID>;
>
> /// 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,
> - {
> - // SAFETY: The caller promises that the pointer points at a field of the right type in the
> - // right kind of struct.
> - unsafe { (ptr as *mut u8).sub(Self::OFFSET) as *mut Self }
> - }
> + unsafe fn work_container_of(ptr: *mut Work<T, ID>) -> *mut Self;
> }
>
> /// Used to safely implement the [`HasWork<T, ID>`] trait.
> @@ -504,8 +481,6 @@ macro_rules! impl_has_work {
> // SAFETY: The implementation of `raw_get_work` only compiles if the field has the right
> // type.
> unsafe impl$(<$($generics)+>)? $crate::workqueue::HasWork<$work_type $(, $id)?> for $self {
> - const OFFSET: usize = ::core::mem::offset_of!(Self, $field) as usize;
> -
> #[inline]
> unsafe fn raw_get_work(ptr: *mut Self) -> *mut $crate::workqueue::Work<$work_type $(, $id)?> {
> // SAFETY: The caller promises that the pointer is not dangling.
> @@ -513,6 +488,15 @@ unsafe fn raw_get_work(ptr: *mut Self) -> *mut $crate::workqueue::Work<$work_typ
> ::core::ptr::addr_of_mut!((*ptr).$field)
> }
> }
> +
> + #[inline]
> + unsafe fn work_container_of(
> + ptr: *mut $crate::workqueue::Work<$work_type $(, $id)?>,
> + ) -> *mut Self {
> + // SAFETY: The caller promises that the pointer points at a field of the right type
> + // in the right kind of struct.
> + unsafe { $crate::container_of!(ptr, Self, $field) }
> + }
> }
> )*};
> }
>
> ---
> base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
> change-id: 20250307-no-offset-e463667a72fb
> prerequisite-change-id: 20250409-container-of-mutness-b153dab4388d:v1
> prerequisite-patch-id: 53d5889db599267f87642bb0ae3063c29bc24863
>
> Best regards,
> --
> Tamir Duberstein <tamird@...il.com>
>
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