linux-kernel - Re: [PATCH bpf-next] bpf: Add bpf_read_raw

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Message-ID: <CAM9d7cijLEKmBMs5M6A02GpsEPJoqxOj6+VCuaE=ae8R4VseWQ@mail.gmail.com>
Date:   Thu, 25 Aug 2022 10:21:36 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Song Liu <songliubraving@...com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Yonghong Song <yhs@...com>, KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next] bpf: Add bpf_read_raw_record() helper

On Thu, Aug 25, 2022 at 10:05 AM Song Liu <songliubraving@...com> wrote:
>
> > On Aug 25, 2022, at 9:57 AM, Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > On Tue, Aug 23, 2022 at 10:32 PM John Fastabend
> > <john.fastabend@...il.com> wrote:
> >> Namhyung Kim wrote:
> >>> Ok, now I think that I can use a bpf-output sw event.  It would need
> >>> another BPF program to write data to the event and the test program
> >>> can read it from BPF using this helper. :)
> >>
> >> Ah good idea. Feel free to carry my ACK to the v2 with the test.
> >
> > Hmm.. it seems not to work because
> > 1. bpf_output sw event doesn't have the overflow mechanism and it
> >   doesn't call the bpf program.
> > 2. even if I added it, it couldn't run due to the recursion protection by
> >   bpf_prog_active.
>
> How about we enable some raw record for a software event? Something not
> controlled by BPF?

Only for the test?  It'd be nice if we could have meaningful data from software
events but I don't have an idea what data it could carry on which event.

Peter, what do you think?

>
> If this doesn't work, a self test that only runs on some hardware is also
> helpful.

Yep, makes sense.

Thanks,
Namhyung