Re: [PATCH RFC 3/4] rust: drm: Add DRM buddy allocator bindings

Danilo Krummrich
2025-10-30T21:27:52Z

On Thu Oct 30, 2025 at 8:06 PM CET, Joel Fernandes wrote:
> + ///
> + /// Returns an [`AllocatedBlocks`] structure that owns the allocated blocks and automatically
> + /// frees them when dropped. Allocation of `list_head` uses the `gfp` flags passed.
> + pub fn alloc_blocks(
> + &self,
> + start: usize,
> + end: usize,
> + size: usize,
> + min_block_size: usize,
> + flags: BuddyFlags,
> + gfp: Flags,
> + ) -> Result<AllocatedBlocks<'_>> {
> + // Allocate list_head on the heap.
> + let mut list_head = KBox::new(bindings::list_head::default(), gfp)?;
> +
> + // SAFETY: list_head is valid and heap-allocated.
> + unsafe {
> + bindings::INIT_LIST_HEAD(&mut *list_head as *mut _);
> + }

Not a full review, but a quick drive-by comment:

bindings::list_head has to be pinned in memory it should be

let list_head = KBox::pin_init(Opaque::ffi_init(|slot: *mut bindings::list_head| {
// SAFETY: `slot` is a valid pointer to uninitialized memory.
unsafe { bindings::INIT_LIST_HEAD(slot) };
}), gfp)?;

if you're doing it by hand, but as mentioned in a previous patch, I think it
would be nice to have a transparent wrapper type, CListHead, for this.