Date: Mon, 18 Apr 2016 12:13:11 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Alexei Starovoitov <ast@fb.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
        "David S . Miller" <davem@davemloft.net>,
        Ingo Molnar <mingo@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Wang Nan <wangnan0@huawei.com>, Josef Bacik <jbacik@fb.com>,
        Brendan Gregg <brendan.d.gregg@gmail.com>, <netdev@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <kernel-team@fb.com>
Subject: Re: [PATCH net-next 0/8] allow bpf attach to tracepoints
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On Mon, 4 Apr 2016 21:52:46 -0700
Alexei Starovoitov <ast@fb.com> wrote:

> Hi Steven, Peter,
> 
> last time we discussed bpf+tracepoints it was a year ago [1] and the reason
> we didn't proceed with that approach was that bpf would make arguments
> arg1, arg2 to trace_xx(arg1, arg2) call to be exposed to bpf program
> and that was considered unnecessary extension of abi. Back then I wanted
> to avoid the cost of buffer alloc and field assign part in all
> of the tracepoints, but looks like when optimized the cost is acceptable.
> So this new apporach doesn't expose any new abi to bpf program.
> The program is looking at tracepoint fields after they were copied
> by perf_trace_xx() and described in /sys/kernel/debug/tracing/events/xxx/format

Does this mean that ftrace could use this ability as well? As all the
current filtering of ftrace was done after it was copied to the buffer,
and that was what you wanted to avoid.

-- Steve