[PATCH 2/2] rust: workqueue: remove HasWork::OFFSET

[Tamir Duberstein <tamird@gmail.com>]

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]
Signed-off-by: Tamir Duberstein <tamird@gmail.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 0cd100d2aefb..0e2e0ecc58a6 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.
 ///
 /// [`impl_has_work!`]: crate::impl_has_work
-/// [`OFFSET`]: HasWork::OFFSET
 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 +476,6 @@ 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 +483,15 @@ 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) }
+            }
         }
     )*};
 }

-- 
2.48.1