netdev - Re: [PATCH bpf-next] libbpf: Add '_wait()' and '_nowait()' macros for 'bpf_ring_buffer_

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Date:   Wed, 31 Mar 2021 11:59:27 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     Pedro Tammela <pctammela@...il.com>,
        Pedro Tammela <pctammela@...atatu.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Joe Stringer <joe@...ium.io>,
        Quentin Monnet <quentin@...valent.com>,
        Yang Li <yang.lee@...ux.alibaba.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next] libbpf: Add '_wait()' and '_nowait()' macros for 'bpf_ring_buffer__poll()'

On Mon, Mar 29, 2021 at 9:28 AM Song Liu <songliubraving@...com> wrote:
>
>
>
> > On Mar 28, 2021, at 9:10 AM, Pedro Tammela <pctammela@...il.com> wrote:
> >
> > 'bpf_ring_buffer__poll()' abstracts the polling method, so abstract the
> > constants that make the implementation don't wait or wait indefinetly
> > for data.
> >
> > Signed-off-by: Pedro Tammela <pctammela@...atatu.com>
> > ---
> > tools/lib/bpf/libbpf.h                                 | 3 +++
> > tools/testing/selftests/bpf/benchs/bench_ringbufs.c    | 2 +-
> > tools/testing/selftests/bpf/prog_tests/ringbuf.c       | 6 +++---
> > tools/testing/selftests/bpf/prog_tests/ringbuf_multi.c | 4 ++--
> > 4 files changed, 9 insertions(+), 6 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> > index f500621d28e5..3817d84f91c6 100644
> > --- a/tools/lib/bpf/libbpf.h
> > +++ b/tools/lib/bpf/libbpf.h
> > @@ -540,6 +540,9 @@ LIBBPF_API int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms);
> > LIBBPF_API int ring_buffer__consume(struct ring_buffer *rb);
> > LIBBPF_API int ring_buffer__epoll_fd(const struct ring_buffer *rb);
> >
> > +#define ring_buffer__poll_wait(rb) ring_buffer__poll(rb, -1)
> > +#define ring_buffer__poll_nowait(rb) ring_buffer__poll(rb, 0)
>
> I think we don't need ring_buffer__poll_wait() as ring_buffer__poll() already
> means "wait for timeout_ms".
>
> Actually, I think ring_buffer__poll() is enough. ring_buffer__poll_nowait()
> is not that useful either.
>

I agree. I think adding a comment to the API itself might be useful
specifying 0 and -1 as somewhat special cases.

> Thanks,
> Song
>