Re: Should I add BPF kfuncs for userspace apps? And how?

[Akihiko Odaki <akihiko.odaki@daynix.com>]

On 2023/12/19 4:56, Song Liu wrote:
> Hi Akihiko,
> 
> On Tue, Dec 12, 2023 at 12:05 AM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>>
> [...]
>> ---
>>
>> I'm working on a new feature that aids virtio-net implementations using
>> tuntap virtual network device. You can see [1] for details, but
>> basically it's to extend BPF_PROG_TYPE_SOCKET_FILTER to report four more
>> bytes.
> 
> AFAICT, [1] adds a new program type, which is really hard to ship. However,
> you mentioned it is basically "extend BPF_PROG_TYPE_SOCKET_FILTER to
> report four more bytes", which confuses me.
> 
> Can we achieve the same goal by extending BPF_PROG_TYPE_SOCKET_FILTER
> (without adding a new program type)? Does this require extending
> __sk_buff, which
> is also not an option any more?

It is certainly possible to achieve the same result by extending 
BPF_PROG_TYPE_SOCKET_FILTER.

It is not required to extend __sk_buff; we can repurpose the cb member. 
But I think such an API will be error-prone than new members dedicated 
for this particular purpose.

Regards,
Akihiko Odaki