Re: [PATCH RFC v6 01/26] rust: clist: Add support to interface with C linked lists

Joel Fernandes
2026-01-25T01:51:35Z

On Wed, Jan 21, 2026 at 08:36:05PM +0000, Gary Guo wrote:
>>> Why is this callback necessary? The user can just create the list head and
>>> then reference it later? I don't see what this specifically gains over just
>>> doing
>>>
>>> fn new() -> impl PinInit<Self>;
>>>
>>> and have user-side
>>>
>>> list <- CListHead::new(),
>>> _: {
>>> do_want_ever(&list)
>>> }
>>
>> The list initialization can fail, see the GPU buddy patch:
>>
>> // Create pin-initializer that initializes list and allocates blocks.
>> let init = try_pin_init!(AllocatedBlocks {
>> list <- CListHead::try_init(|list| {
>> // Lock while allocating to serialize with concurrent frees.
>> let guard = buddy_arc.lock();
>>
>> // SAFETY: guard provides exclusive access, list is initialized.
>> to_result(unsafe {
>> bindings::gpu_buddy_alloc_blocks(
>> guard.as_raw(),
>> params.start_range_address,
>> params.end_range_address,
>> params.size_bytes,
>> params.min_block_size_bytes,
>> list.as_raw(),
>> params.buddy_flags.as_raw(),
>> )
>> })
>> }),
>> buddy: Arc::clone(&buddy_arc),
>> flags: params.buddy_flags,
>> });
>
> The list initialization doesn't fail? It's the subsequent action you did that
> failed.
>
> You can put failing things in the `_: { ... }` block too.

This worked out well, thanks for the suggestion! I've updated the code
to use `CListHead::new()` with the failable allocation in a `_: { ... }` block:

let init = try_pin_init!(AllocatedBlocks {
buddy: Arc::clone(&buddy_arc),
list <- CListHead::new(),
flags: params.buddy_flags,
_: {
// Lock while allocating to serialize with concurrent frees.
let guard = buddy.lock();

// SAFETY: `guard` provides exclusive access to the buddy allocator.
to_result(unsafe {
bindings::gpu_buddy_alloc_blocks(
guard.as_raw(),
params.start_range_address,
params.end_range_address,
params.size_bytes,
params.min_block_size_bytes,
list.as_raw(),
params.buddy_flags.as_raw(),
)
})?
}
});

I'll remove the try_init() method from CListHead since new() is sufficient.

--
Joel Fernandes