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Subject: Re: [PATCH bpf] libbpf: Return btf_fd in libbpf__probe_raw_btf
To:     Michal Rostecki <mrostecki@opensuse.org>
Cc:     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>,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20190529082941.9440-1-mrostecki@opensuse.org>
From:   Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Message-ID: <e28170e1-cf06-87ef-812b-9b9e6185d925@cogentembedded.com>
Date:   Wed, 29 May 2019 12:53:42 +0300
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Hello!

On 29.05.2019 11:29, Michal Rostecki wrote:

> Function load_sk_storage_btf expects that libbpf__probe_raw_btf is
> returning a btf descriptor, but before this change it was returning
> an information about whether the probe was successful (0 or 1).
> load_sk_storage_btf was using that value as an argument to the close
> function, which was resulting in closing stdout and thus terminating the
> process which used that dunction.

    Function? :-)

> That bug was visible in bpftool. `bpftool feature` subcommand was always
> exiting too early (because of closed stdout) and it didn't display all
> requested probes. `bpftool -j feature` or `bpftool -p feature` were not
> returning a valid json object.
> 
> Fixes: d7c4b3980c18 ("libbpf: detect supported kernel BTF features and sanitize BTF")
> Signed-off-by: Michal Rostecki <mrostecki@opensuse.org>
[...]

MBR, Sergei