Re: [PATCH bpf-next v1 08/10] bpf: Add bpf_task_work_schedule_* kfuncs with KF_IMPLICIT_ARGS

[Ihor Solodrai <ihor.solodrai@linux.dev>]

On 1/9/26 1:56 PM, Ihor Solodrai wrote:
> On 1/9/26 1:49 PM, Alexei Starovoitov wrote:
>> On Fri, Jan 9, 2026 at 1:39 PM Ihor Solodrai <ihor.solodrai@linux.dev> wrote:
>>>
>>> [...]
>>>
>>>> I feel bpf_task_work_schedule_resume() is ok to break, since it's so new.
>>>> We can remove bpf_task_work_schedule_[resume|singal]_impl()
>>>> to avoid carrying forward forever.
>>>>
>>>> bpf_stream_vprintk_impl() is not that clear. I would remove it too.
>>>
>>> That leaves only bpf_wq_set_callback_impl(). Can we break that too?
>>
>> Sounds like Benjamin is ok removing it.
>> So I think we can indeed remove them all.
>>
>>> Then there won't be legacy cases at all. It was introduced in v6.16
>>> along the with __prog suffix [1][2].
>>>
>>> If we go this route, we could clean up __prog support/docs too.
>>>
>>> I think it's worth it to make an "all or nothing" decision here:
>>> either break all 4 existing kfuncs, or backwards-support all of them.
>>
>> I don't see why "all or nothing" is a good thing.
>> It won't be "all" anyway.
>> We have bpf_rbtree_add_impl(), bpf_list_push_front_impl(), etc.
>> And those we cannot remove. sched-ext is using them.
>> Another few categories are bpf_obj_new_impl(), bpf_obj_drop_impl().
>> There are not __prog type, but conceptually the same thing and
>> KF_IMPLICIT_ARGS should support them too eventually.
> 
> I was thinking we could remove/simplify code relevant to backwards
> compat of existing _impl kfuncs. But you're right, if we start using
> implicit args for other types/kfuncs, the "legacy" case still has to
> work.
> 
> Ok, in the next revision I'll remove all the __prog users, but leave
> the "legacy" case support in place for future use.

I just had an off-list chat with Andrii, and we agreed that leaving
the existing _impl kfuncs supported may be a good idea.

It doesn't cost us much: we keep the mechanism for legacy functions
anyways, so supporting bpf_wq_set_callback_impl() and co only requires
keeping definitions in the kernel.

The only benefit of *removing* these _impl functions is that we could
clean up __prog support.

But having backwards compat seems like a better deal.
What do you think?


> 
>>
>>
>>> git tag --contains bc049387b41f | grep -v rc
>>> v6.16
>>> v6.17
>>> v6.18
>>>
>>> [1] https://lore.kernel.org/all/20250513142812.1021591-1-memxor@gmail.com/
>>> [2] https://lore.kernel.org/all/20240420-bpf_wq-v2-13-6c986a5a741f@kernel.org/
>>>
>>>
>