netdev - Re: [PATCH v2 bpf-next 0/3] libbpf: add perf buffer abstraction and API

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Date:   Wed, 26 Jun 2019 11:41:53 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Andrii Nakryiko <andriin@...com>, Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 0/3] libbpf: add perf buffer abstraction and API

On Wed, Jun 26, 2019 at 4:55 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> Andrii Nakryiko <andriin@...com> writes:
>
> > This patchset adds a high-level API for setting up and polling perf buffers
> > associated with BPF_MAP_TYPE_PERF_EVENT_ARRAY map. Details of APIs are
> > described in corresponding commit.
> >
> > Patch #1 adds a set of APIs to set up and work with perf buffer.
> > Patch #2 enhances libbpf to supprot auto-setting PERF_EVENT_ARRAY map size.
> > Patch #3 adds test.
>
> Having this in libbpf is great! Do you have a usage example of how a
> program is supposed to read events from the buffer? This is something we
> would probably want to add to the XDP tutorial

Did you check patch #3 with selftest? It's essentially an end-to-end
example of how to set everything up and process data (in my case it's
just simple int being sent as a sample, but it's exactly the same with
more complicated structs). I didn't bother to handle lost samples
notification, but it's just another optional callback with a single
counter denoting how many samples were dropped.

Let me know if it's still unclear.

>
> -Toke