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

[Joe Stringer]

Hi Pedro,

On Tue, Apr 6, 2021 at 11:58 AM Pedro Tammela <pctammela@xxxxxxxxx> 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@xxxxxxxxxxxx>
> ---
>  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"?