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

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Message-ID: <E6872BF2-8DB9-4D42-957B-E57EAE28AA65@fb.com>
Date:   Thu, 25 Aug 2022 17:04:50 +0000
From:   Song Liu <songliubraving@...com>
To:     Namhyung Kim <namhyung@...nel.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>,
        Peter Zijlstra <peterz@...radead.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 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?

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

Thanks,
Song