netdev - Re: [PATCH bpf-next v2 3/3] tools: bpftool: make -d option print debug output from verifier

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Message-ID: <e97e5b03-2bc5-a3c6-ad40-812b864fc425@netronome.com>
Date:   Fri, 24 May 2019 10:47:07 +0100
From:   Quentin Monnet <quentin.monnet@...ronome.com>
To:     Yonghong Song <yhs@...com>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "oss-drivers@...ronome.com" <oss-drivers@...ronome.com>
Subject: Re: [PATCH bpf-next v2 3/3] tools: bpftool: make -d option print
 debug output from verifier

2019-05-23 16:38 UTC+0000 ~ Yonghong Song <yhs@...com>
> 
> 
> On 5/23/19 3:54 AM, Quentin Monnet wrote:
>> The "-d" option is used to require all logs available for bpftool. So
>> far it meant telling libbpf to print even debug-level information. But
>> there is another source of info that can be made more verbose: when we
>> attemt to load programs with bpftool, we can pass a log_level parameter
>> to the verifier in order to control the amount of information that is
>> printed to the console.
>>
>> Reuse the "-d" option to print all information the verifier can tell. At
>> this time, this means logs related to BPF_LOG_LEVEL1, BPF_LOG_LEVEL2 and
>> BPF_LOG_STATS. As mentioned in the discussion on the first version of
>> this set, these macros are internal to the kernel
>> (include/linux/bpf_verifier.h) and are not meant to be part of the
>> stable user API, therefore we simply use the related constants to print
>> whatever we can at this time, without trying to tell users what is
>> log_level1 or what is statistics.
>>
>> Verifier logs are only used when loading programs for now (in the
>> future: for loading BTF objects with bpftool?), so bpftool.rst and
>> bpftool-prog.rst are the only man pages to get the update.
> 
> The current BTF error log print out at warning level. So by default,
> it should print out error logs unless it is suppressed explicitly.

Understood, thanks! This is probably something we could change in
libbpf, to have it printed for debug log-level even when no error
occurred. But bpftool does not support loading BTF just yet anyway, so I
suppose it can wait.

Thanks for the review!
Quentin