Re: [PATCH bpf,perf]] bpf,perf: return EOPNOTSUPP for attaching bpf handler on PERF_COUNT_SW_DUMMY

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Florian Lehner <dev@der-flo.net>
Cc: bpf <bpf@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: [PATCH bpf,perf]] bpf,perf: return EOPNOTSUPP for attaching bpf handler on PERF_COUNT_SW_DUMMY
Date: Sat, 14 Nov 2020 08:07:29 -0800	[thread overview]
Message-ID: <CAADnVQL4zBmS5Yo3skoA32YjFXz5qu0q9LuJ5Z-61EGwZzgD6Q@mail.gmail.com> (raw)
In-Reply-To: <20201114135126.29462-1-dev@der-flo.net>

On Sat, Nov 14, 2020 at 5:53 AM Florian Lehner <dev@der-flo.net> wrote:
>
> At the moment it is not possible to attach a bpf handler to a perf event
> of type PERF_TYPE_SOFTWARE with a configuration of PERF_COUNT_SW_DUMMY.

It is possible or it is not possible?

Such "commit log as an abstract statement" patches are a mystery to a reader.
Please explain what problem you're trying to solve and how it's being addressed.

> Signed-off-by: Florian Lehner <dev@der-flo.net>
> ---
>  kernel/events/core.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index da467e1dd49a..4e8846b7ceda 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9668,6 +9668,10 @@ static int perf_event_set_bpf_handler(struct perf_event *event, u32 prog_fd)
>         if (event->prog)
>                 return -EEXIST;
>
> +       if (event->attr.type == PERF_TYPE_SOFTWARE &&
> +           event->attr.config == PERF_COUNT_SW_DUMMY)
> +               return -EOPNOTSUPP;

Is it a fix or a feature?
If it is a fix please add 'Fixes:' tag.