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

Hou Tao
2023-07-27T01:06:28Z

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@wowsignal.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.