netdev - Re: [RFC][PATCH] Export supported trace features in debugfs

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Message-ID: <20190312152703.dulqcnhkknklxihq@ast-mbp>
Date:   Tue, 12 Mar 2019 08:27:06 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Qais Yousef <Qais.Yousef@....com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: Re: [RFC][PATCH] Export supported trace features in debugfs

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@....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