netdev - Re: [PATCH bpf-next] libbpf: clarify flags in ringbuf helpers

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Date:   Wed, 7 Apr 2021 11:42:33 -0700
From:   Joe Stringer <joe@...ium.io>
To:     Pedro Tammela <pctammela@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Quentin Monnet <quentin@...valent.com>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <netdev@...r.kernel.org>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <bpf@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>,
        Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH bpf-next] libbpf: clarify flags in ringbuf helpers

Hi Pedro,

On Tue, Apr 6, 2021 at 11:58 AM Pedro Tammela <pctammela@...il.com> wrote:
>
> In 'bpf_ringbuf_reserve()' we require the flag to '0' at the moment.
>
> For 'bpf_ringbuf_{discard,submit,output}' a flag of '0' might send a
> notification to the process if needed.
>
> Signed-off-by: Pedro Tammela <pctammela@...atatu.com>
> ---
>  include/uapi/linux/bpf.h       | 7 +++++++
>  tools/include/uapi/linux/bpf.h | 7 +++++++
>  2 files changed, 14 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 49371eba98ba..8c5c7a893b87 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -4061,12 +4061,15 @@ union bpf_attr {
>   *             of new data availability is sent.
>   *             If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
>   *             of new data availability is sent unconditionally.
> + *             If **0** is specified in *flags*, notification
> + *             of new data availability is sent if needed.

Maybe a trivial question, but what does "if needed" mean? Does that
mean "when the buffer is full"?