linux-kernel - Re: [PATCH bpf] libbpf: Return btf_fd in libbpf__probe_raw

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Date:   Wed, 29 May 2019 12:53:42 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Michal Rostecki <mrostecki@...nsuse.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf] libbpf: Return btf_fd in libbpf__probe_raw_btf

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@...nsuse.org>
[...]

MBR, Sergei