Re: [PATCH v1 1/4] bpf: Add netpoll kfuncs for sending UDP packets

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Mon May 11, 2026 at 6:20 PM PDT, Jakub Kicinski wrote:
> On Mon, 11 May 2026 08:53:41 +0000 Mahe Tardy wrote:
>> Add BPF kfuncs that allow BPF programs to send UDP packets via the
>> netpoll infrastructure. This provides a mechanism for BPF programs
>> (e.g., LSM hooks) to emit telemetry over UDP without depending on
>> the regular networking stack.
>> 
>> The API consists of four kfuncs:
>> 
>>   bpf_netpoll_create()   - Allocate and set up a netpoll context
>>                            (sleepable, SYSCALL prog type only)
>>   bpf_netpoll_acquire()  - Acquire a reference to a netpoll context
>>   bpf_netpoll_release()  - Release a reference (cleanup via
>>                            queue_rcu_work since netpoll_cleanup sleeps)
>>   bpf_netpoll_send_udp() - Send a UDP packet (any context, LSM prog
>>                            type only for now)
>> 
>> The implementation follows the established kfunc lifecycle pattern
>> (create/acquire/release with refcounting, kptr map storage, dtor
>> registration). The netpoll context is wrapped in a refcounted
>> bpf_netpoll struct. Cleanup is deferred via queue_rcu_work() because
>> netpoll_cleanup() takes rtnl_lock.
>
> We have enough bug reports as is, let's not merge unusable toys.
> For any use of netpoll by BPF:
>
> Nacked-by: Jakub Kicinski <kuba@kernel.org>

unusable toys? What are you talking about?
netpoll is already called from everywhere.
bpf_netpoll_send_udp() won't add any more bugs.

I like this netpoll approach way more then creating and keeping proper socket
within bpf and all head aches of keeping it around and doing send from
good context. With netpoll all of these issues are gone.
Just bpf_netpoll_send_udp() from anywhere and it works just like it does
for dmesg.