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

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Date:   Thu, 27 Jul 2023 09:06:20 +0800
From:   Hou Tao <houtao@...weicloud.com>
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] libbpf: Expose API to consume one ring at a time

Hi,

On 7/26/2023 12:26 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>
> ---
>  tools/lib/bpf/libbpf.h  |  1 +
>  tools/lib/bpf/ringbuf.c | 15 +++++++++++++++
>  2 files changed, 16 insertions(+)
>
> 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);
>  
>  struct user_ring_buffer_opts {
> diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
> index 02199364db136..8d087bfc7d005 100644
> --- a/tools/lib/bpf/ringbuf.c
> +++ b/tools/lib/bpf/ringbuf.c
> @@ -290,6 +290,21 @@ int ring_buffer__consume(struct ring_buffer *rb)
>  	return res;
>  }
>  
> +/* Consume available data from a single RINGBUF map identified by its ID.
> + * The ring ID is returned in epoll_data by epoll_wait when called with
> + * ring_buffer__epoll_fd.
> + */
> +int ring_buffer__consume_ring(struct ring_buffer *rb, uint32_t ring_id)
> +{
> +	struct ring *ring;
> +
> +	if (ring_id >= rb->ring_cnt)
> +		return libbpf_err(-EINVAL);
> +
> +	ring = &rb->rings[ring_id];
> +	return ringbuf_process_ring(ring);

When ringbuf_process_ring() returns an error, we need to use
libbpf_err() to set the errno accordingly.
> +}
> +
>  /* Poll for available data and consume records, if any are available.
>   * Returns number of records consumed (or INT_MAX, whichever is less), or
>   * negative number, if any of the registered callbacks returned error.