[PATCH v2 1/3] rust: alloc: add Box::zeroed()

Danilo Krummrich
2026-05-05T15:24:11Z

Add Box::zeroed() for T: Zeroable types.

This allocates with __GFP_ZERO directly, letting the underlying
allocator deal with zeroing out the memory compared to
Box::new(T::zeroed(), flags).

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
rust/kernel/alloc/kbox.rs | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)

diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs
index bd6da02c7ab8..c824ed6e1523 100644
--- a/rust/kernel/alloc/kbox.rs
+++ b/rust/kernel/alloc/kbox.rs
@@ -19,6 +19,7 @@
use crate::fmt;
use crate::init::InPlaceInit;
use crate::page::AsPageIter;
+use crate::prelude::*;
use crate::types::ForeignOwnable;
use pin_init::{InPlaceWrite, Init, PinInit, ZeroableOption};

@@ -256,6 +257,27 @@ pub fn new_uninit(flags: Flags) -> Result<Box<MaybeUninit<T>, A>, AllocError> {
Ok(Box(ptr.cast(), PhantomData))
}

+ /// Creates a new zero-initialized `Box<T, A>`.
+ ///
+ /// New memory is allocated with `A` and the [`__GFP_ZERO`] flag. The allocation may fail, in
+ /// which case an error is returned. For ZSTs no memory is allocated.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let b = KBox::<[u8; 128]>::zeroed(GFP_KERNEL)?;
+ /// assert_eq!(*b, [0; 128]);
+ /// # Ok::<(), Error>(())
+ /// ```
+ pub fn zeroed(flags: Flags) -> Result<Self, AllocError>
+ where
+ T: Zeroable,
+ {
+ // SAFETY: `__GFP_ZERO` guarantees the memory is zeroed; `T: Zeroable` guarantees that
+ // all-zeroes is a valid bit pattern for `T`.
+ Ok(unsafe { Self::new_uninit(flags | __GFP_ZERO)?.assume_init() })
+ }
+
/// Constructs a new `Pin<Box<T, A>>`. If `T` does not implement [`Unpin`], then `x` will be
/// pinned in memory and can't be moved.
#[inline]
--
2.54.0