[PATCH] rust: alloc: use `spare_capacity_mut` to reduce unsafe

Tamir Duberstein
2025-03-17T11:42:33Z

Use `spare_capacity_mut` in the implementation of `push` to reduce the
use of `unsafe`. Both methods were added in commit 2aac4cd7dae3 ("rust:
alloc: implement kernel `Vec` type").

Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
rust/kernel/alloc/kvec.rs | 11 ++---------
1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index ae9d072741ce..d2bc3d02179e 100644
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -285,15 +285,8 @@ pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
pub fn push(&mut self, v: T, flags: Flags) -> Result<(), AllocError> {
self.reserve(1, flags)?;

- // SAFETY:
- // - `self.len` is smaller than `self.capacity` and hence, the resulting pointer is
- // guaranteed to be part of the same allocated object.
- // - `self.len` can not overflow `isize`.
- let ptr = unsafe { self.as_mut_ptr().add(self.len) };
-
- // SAFETY:
- // - `ptr` is properly aligned and valid for writes.
- unsafe { core::ptr::write(ptr, v) };
+ // The call to `reserve` was successful so the spare capacity is at least 1.
+ self.spare_capacity_mut()[0].write(v);

// SAFETY: We just initialised the first spare entry, so it is safe to increase the length
// by 1. We also know that the new length is <= capacity because of the previous call to

---
base-commit: cf25bc61f8aecad9b0c45fe32697e35ea4b13378
change-id: 20250317-vec-push-use-spare-27484fd016a9

Best regards,
--
Tamir Duberstein <tamird@gmail.com>