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Date:   Tue, 12 Mar 2019 16:19:41 +0000
From:   Qais Yousef <qais.yousef@arm.com>
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>
Subject: Re: [RFC][PATCH] Export supported trace features in debugfs
Message-ID: <20190312161941.6vlxp3qvad5oy4fs@e107158-lin.cambridge.arm.com>
References: <20190312110437.5977-1-qais.yousef@arm.com>
 <20190312152703.dulqcnhkknklxihq@ast-mbp>
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On 03/12/19 08:27, Alexei Starovoitov wrote:
> On Tue, Mar 12, 2019 at 11:07:14AM +0000, Qais Yousef wrote:
> > eBPF tools like bcc-tools have hard time figuring out when features like
> > raw_tracepoint are supported in the kernel on which we are running. At
> > the moment a fragile mechanism of matching bpf_find_raw_tracepoint()
> > function in /proc/kallsyms is used to find out whether raw tracepoints
> > can be used or not. But when this function was renamed recently to
> > bpf_get_raw_tracepoint() the tool started to fail to use raw
> > tracepoints.
> > 
> > To help in providing a more reliable way to detect features like
> > RAW_TRACEPOINT, add a new file in trace debugfs to export the supported
> > features.
> > 
> > $cat /sys/kernel/debug/tracing/supported_features
> > RAW_TRACEPOINT
> > EXAMPLE_FEATURE_1
> > EXAMPLE_FEATURE_2
> > 
> > Signed-off-by: Qais Yousef <qais.yousef@arm.com>
> 
> this type of attempts have been made in the past and we always rejected them.
> Please use 'bpftool' instead that detects numerous bpf related features including raw_tp.
> # bpftool feature probe|grep raw_tracepoint
> eBPF program_type raw_tracepoint is available
> 

I see. I should have looked harder. I'll have a look at what bpftool does then.

Thanks

--
Qais Yousef