(This is more an RFC) Add arithmetic operations support for `Atomic<*mut T>`. Currently the semantics of arithmetic atomic operation is the same as pointer arithmetic, that is, e.g. `Atomic<*mut u64>::add(1)` is adding 8 (`size_of::<u64>`) to the pointer value.
In Rust std library, there are two sets of pointer arithmetic for `AtomicPtr`: * ptr_add() and ptr_sub(), which is the same as Atomic<*mut T>::add(), pointer arithmetic. * byte_add() and byte_sub(), which use the input as byte offset to change the pointer value, e.g. byte_add(1) means adding 1 to the pointer value. We can either take the approach in the current patch and add byte_add() later on if needed, or start with ptr_add() and byte_add() naming. Signed-off-by: Boqun Feng <boqun.f...@gmail.com> --- rust/kernel/sync/atomic.rs | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index e62c3cd1d3ca..cbe5d40d9e36 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -197,3 +197,32 @@ fn from_repr(repr: Self::Repr) -> Self { repr as _ } } + +/// ```rust +/// use kernel::sync::atomic::{Atomic, Relaxed}; +/// +/// let s: &mut [i32] = &mut [1, 3, 2, 4]; +/// +/// let x = Atomic::new(s.as_mut_ptr()); +/// +/// x.add(1, Relaxed); +/// +/// let ptr = x.fetch_add(1, Relaxed); // points to the 2nd element. +/// let ptr2 = x.load(Relaxed); // points to the 3rd element. +/// +/// // SAFETY: `ptr` and `ptr2` are valid pointers to the 2nd and 3rd elements of `s` with writing +/// // provenance, and no other thread is accessing these elements. +/// unsafe { core::ptr::swap(ptr, ptr2); } +/// +/// assert_eq!(s, &mut [1, 2, 3, 4]); +/// ``` +impl<T> generic::AllowAtomicArithmetic for *mut T { + type Delta = isize; + + /// The behavior of arithmetic operations + fn delta_into_repr(d: Self::Delta) -> Self::Repr { + // Since atomic arithmetic operations are wrapping, so a wrapping_mul() here suffices even + // if overflow may happen. + d.wrapping_mul(core::mem::size_of::<T>() as _) as _ + } +} -- 2.45.2