RE: [Bpf] Re: Writing into a ring buffer map from user space

[dthaler1968@googlemail.com]

Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:

> On Tue, May 28, 2024 at 9:32 AM Shankar Seal
> <Shankar.Seal=40microsoft.com@dmarc.ietf.org> wrote:
> >
> > Adding bpf@vger.kernel.org
> >
> > A common use case of an BPF ring buffer map to use as a queue of
> > events generated by BPF programs that can be read in-order by user
> > space applications. I have a scenario requirement for a user space
> > application to write into a ring buffer (or similar) map, such that
> > events by BPF programs in kernel and user space applications are
> > interleaved in the order they were generated, that can be consumed by
> > another user space application
> >
> > I would like to implement this new feature in the
> https://github.com/microsoft/ebpf-for-windows project. But before I go ahead with
> the implementation, I wanted to check if there is any way to accomplish this in
> Linux today? If not, is there any reason why this should not be done?
> 
> Yes, there is. See user_ring_buffer ([0], [1]).
> 
>   [0]
> https://github.com/torvalds/linux/blob/master/tools/testing/selftests/bpf/prog_tests/
> user_ringbuf.c
>   [1]
> https://github.com/torvalds/linux/blob/master/tools/testing/selftests/bpf/progs/user_
> ringbuf_success.c

Both of those links go to GPL code so I suspect Shankar cannot use those links.
I think the answer is that BPF_MAP_TYPE_USER_RINGBUF is defined for this
purpose and Shankar can read https://lwn.net/Articles/907056/

Thanks,
Dave