linux-kernel - Re: [PATCH 03/31] perf tools: Enable passing bpf object file to --event

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Date:	Wed, 21 Oct 2015 09:55:43 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	<ast@...mgrid.com>, <brendan.d.gregg@...il.com>,
	<a.p.zijlstra@...llo.nl>, <daniel@...earbox.net>,
	<dsahern@...il.com>, <hekuang@...wei.com>, <jolsa@...nel.org>,
	<lizefan@...wei.com>, <masami.hiramatsu.pt@...achi.com>,
	<namhyung@...nel.org>, <paulus@...ba.org>,
	<linux-kernel@...r.kernel.org>, <pi3orama@....com>,
	<xiakaixu@...wei.com>
Subject: Re: [PATCH 03/31] perf tools: Enable passing bpf object file to --event



On 2015/10/20 23:15, Arnaldo Carvalho de Melo wrote:
> Em Tue, Oct 20, 2015 at 12:12:55PM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Wed, Oct 14, 2015 at 12:41:14PM +0000, Wang Nan escreveu:
>>> By introducing new rules in tools/perf/util/parse-events.[ly], this
>>> patch enables 'perf record --event bpf_file.o' to select events by an
>>> eBPF object file. It calls parse_events_load_bpf() to load that file,
>>> which uses bpf__prepare_load() and finally calls bpf_object__open() for
>>> the object files.
>>>
>>> After applying this patch, commands like:
>>>
>>>   # perf record --event foo.o sleep
>>>
>>> become possible.
>> So, trying the above command I get almost perfect output:
>>
>>    [root@...icio ~]# perf record --event foo.o sleep
>>    libbpf: failed to open foo.o: No such file or directory
>>    event syntax error: 'foo.o'
>>                         \___ BPF object file 'foo.o' is invalid
>>
>>    (add -v to see detail)
>>    Run 'perf list' for a list of valid events
>>
>>     Usage: perf record [<options>] [<command>]
>>        or: perf record [<options>] -- <command> [<options>]
>>
>>        -e, --event <event>   event selector. use 'perf list' to list available events
>>    [root@...icio ~]#
>>
>>
>> Good thing would be to not have any message from libbpf and the right error
>> message from the parser, i.e. the first three lines become these two:
>>
>>
>>    event syntax error: 'foo.o'
>>                         \___ BPF object file 'foo.o' not found.o
>>
>> But that can be fixed up in an upcoming patch, so I am applying this one now in
>> my new attempt at processing this patchkit.

I think fixing that is not very hard. When designing libbpf, I thought
the problem like this so makes libbpf output controled by caller using
'libbpf_set_print()'. What we need to do is to pass different output
functions to libbpf. We can easily disable all output from libbpf if
verbose is set 0. The only question is: do you want me to provide a new
version of patch 'perf ebpf: Add the libbpf glue' or you prefer another
patch to adjust the output functions?

Thank you.

> Ditto for:
>
>    [acme@...icio linux]$ perf record --event /tmp/build/perf/perf.o sleep
>    libbpf: /tmp/build/perf/perf.o is not an eBPF object file
>    event syntax error: '/tmp/build/perf/perf.o'
>                         \___ BPF object file '/tmp/build/perf/perf.o' is invalid
>    
>    (add -v to see detail)
>    Run 'perf list' for a list of valid events
>
>     Usage: perf record [<options>] [<command>]
>        or: perf record [<options>] -- <command> [<options>]
>
>        -e, --event <event>   event selector. use 'perf list' to list available events
>    [acme@...icio linux]$
>
> Now trying to find a _valid_ ebpf object file to test with.
>
> - Arnaldo


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