linux-kernel - Re: [PATCH bpf-next v4] libbpf: Expose API to consume one ring at a time

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Date:   Thu, 27 Jul 2023 15:11:00 -0700
From:   Yonghong Song <yonghong.song@...ux.dev>
To:     Adam Sindelar <adam@...signal.io>, bpf@...r.kernel.org
Cc:     Adam Sindelar <ats@...com>, David Vernet <void@...ifault.com>,
        Brendan Jackman <jackmanb@...gle.com>,
        KP Singh <kpsingh@...omium.org>, linux-kernel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Florent Revest <revest@...omium.org>
Subject: Re: [PATCH bpf-next v4] libbpf: Expose API to consume one ring at a
 time



On 7/27/23 1:34 AM, Adam Sindelar wrote:
> We already provide ring_buffer__epoll_fd to enable use of external
> polling systems. However, the only API available to consume the ring
> buffer is ring_buffer__consume, which always checks all rings. When
> polling for many events, this can be wasteful.
> 
> Signed-off-by: Adam Sindelar <adam@...signal.io>
> ---
> v1->v2: Added entry to libbpf.map
> v2->v3: Correctly set errno and handle overflow
> v3->v4: Fixed an embarrasing typo from zealous autocomplete
> 
>   tools/lib/bpf/libbpf.h   |  1 +
>   tools/lib/bpf/libbpf.map |  1 +
>   tools/lib/bpf/ringbuf.c  | 22 ++++++++++++++++++++++
>   3 files changed, 24 insertions(+)

Could you add a selftest to exercise ring_buffer__consume_ring()?
This way, people can better understand how this API could be used.

> 
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 55b97b2087540..20ccc65eb3f9d 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -1195,6 +1195,7 @@ LIBBPF_API int ring_buffer__add(struct ring_buffer *rb, int map_fd,
>   				ring_buffer_sample_fn sample_cb, void *ctx);
>   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__consume_ring(struct ring_buffer *rb, uint32_t ring_id);
>   LIBBPF_API int ring_buffer__epoll_fd(const struct ring_buffer *rb);
>   
[...]