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From:   Song Liu <songliubraving@fb.com>
To:     Peter Zijlstra <peterz@infradead.org>
CC:     Yonghong Song <yhs@fb.com>, Daniel Xu <dxu@dxuuu.xyz>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
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        "Arnaldo Carvalho de Melo" <acme@redhat.com>
Subject: Re: [PATCH v3 bpf-next 1/4] tracing/probe: Add
 PERF_EVENT_IOC_QUERY_PROBE ioctl
Thread-Topic: [PATCH v3 bpf-next 1/4] tracing/probe: Add
 PERF_EVENT_IOC_QUERY_PROBE ioctl
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Date:   Thu, 22 Aug 2019 07:54:16 +0000
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Hi Peter,=20

> On Aug 22, 2019, at 12:47 AM, Peter Zijlstra <peterz@infradead.org> wrote=
:
>=20
> On Wed, Aug 21, 2019 at 06:43:49PM +0000, Yonghong Song wrote:
>> On 8/21/19 11:31 AM, Peter Zijlstra wrote:
>=20
>>> So extending PERF_RECORD_LOST doesn't work. But PERF_FORMAT_LOST might
>>> still work fine; but you get to implement it for all software events.
>>=20
>> Could you give more specifics about PERF_FORMAT_LOST? Googling=20
>> "PERF_FORMAT_LOST" only yields two emails which we are discussing here :=
-(
>=20
> Look at what the other PERF_FORMAT_ flags do? Basically it is adding a
> field to the read(2) output.

Do we need to implement PERF_FORMAT_LOST for all software events? If user
space asks for PERF_FORMAT_LOST for events that do not support it, can we
just fail sys_perf_event_open()?

Thanks,
Song