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

["Alexandre Courbot" <acourbot@nvidia.com>]

On Fri Oct 31, 2025 at 4:06 AM JST, Joel Fernandes wrote:
<snip>
> +    /// Allocate blocks from the buddy allocator.
> +    ///
> +    /// 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<'_>> {

It looks like some of the flags heavily modify the behavior of the
allocator, and make some of the parameters irrelevant (for instance,
IIUC `start` and `end` only make sense if `RANGE_ALLOCATION` is
passed?).

In that case, we should either have several allocation methods, or have
an `AllocationRequest` enum which variants are the allocation type and its
relevant parameters. E.g (very naively):

enum AllocationRange {
    Whole,
    Ranged(Range<u64>),
    ...
}

struct AllocationRequest {
    range: AllocationRange,
    top_down: bool,
    contiguous: bool,
    clear: bool,
}

I.e. use the type system to make sure we can only express things that
make sense, and never pass data that will end up being ignored.

If we do that well, I think we can drop the `BuddyFlags` type
altogether, which is great as it seems to serve several different
purposes.