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

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Message-ID: <ZMIrU0kQZElkUhAg@debian>
Date:   Thu, 27 Jul 2023 10:31:15 +0200
From:   Adam Sindelar <adam@...signal.io>
To:     Hou Tao <houtao@...weicloud.com>
Cc:     bpf@...r.kernel.org, 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>,
        Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH] libbpf: Expose API to consume one ring at a time

On Thu, Jul 27, 2023 at 02:17:12PM +0800, Hou Tao wrote:
> Hi,
> 
> On 7/27/2023 9:06 AM, Hou Tao wrote:
> > 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.
> 
> It seems that even when ringbuf_process_ring() returns a positive
> result, we also need to cap it under INT_MAX, otherwise it may be cast
> into a negative error.

Ah, sorry I missed that. Fixed in v3, going out in a few moments.

> >> +}
> >> +
> >>  /* 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.
> >
> >
> > .
> 

Thanks!