diff options
| -rw-r--r-- | rust/kernel/alloc/box_ext.rs | 31 |
1 files changed, 30 insertions, 1 deletions
diff --git a/rust/kernel/alloc/box_ext.rs b/rust/kernel/alloc/box_ext.rs index 829cb1c1cf9e..b68ade26a42d 100644 --- a/rust/kernel/alloc/box_ext.rs +++ b/rust/kernel/alloc/box_ext.rs @@ -4,7 +4,7 @@ use super::{AllocError, Flags}; use alloc::boxed::Box; -use core::mem::MaybeUninit; +use core::{mem::MaybeUninit, ptr, result::Result}; /// Extensions to [`Box`]. pub trait BoxExt<T>: Sized { @@ -17,6 +17,22 @@ pub trait BoxExt<T>: Sized { /// /// The allocation may fail, in which case an error is returned. fn new_uninit(flags: Flags) -> Result<Box<MaybeUninit<T>>, AllocError>; + + /// Drops the contents, but keeps the allocation. + /// + /// # Examples + /// + /// ``` + /// use kernel::alloc::{flags, box_ext::BoxExt}; + /// let value = Box::new([0; 32], flags::GFP_KERNEL)?; + /// assert_eq!(*value, [0; 32]); + /// let value = Box::drop_contents(value); + /// // Now we can re-use `value`: + /// let value = Box::write(value, [1; 32]); + /// assert_eq!(*value, [1; 32]); + /// # Ok::<(), Error>(()) + /// ``` + fn drop_contents(this: Self) -> Box<MaybeUninit<T>>; } impl<T> BoxExt<T> for Box<T> { @@ -53,4 +69,17 @@ impl<T> BoxExt<T> for Box<T> { // zero-sized types, we use `NonNull::dangling`. Ok(unsafe { Box::from_raw(ptr) }) } + + fn drop_contents(this: Self) -> Box<MaybeUninit<T>> { + let ptr = Box::into_raw(this); + // SAFETY: `ptr` is valid, because it came from `Box::into_raw`. + unsafe { ptr::drop_in_place(ptr) }; + + // CAST: `MaybeUninit<T>` is a transparent wrapper of `T`. + let ptr = ptr.cast::<MaybeUninit<T>>(); + + // SAFETY: `ptr` is valid for writes, because it came from `Box::into_raw` and it is valid for + // reads, since the pointer came from `Box::into_raw` and the type is `MaybeUninit<T>`. + unsafe { Box::from_raw(ptr) } + } } |