linux-kernel - Re: [PATCH 1/2] SDT markers listing by perf

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Date:	Sun, 15 Sep 2013 16:58:02 +0530
From:	Hemant <hkshaw@...ux.vnet.ibm.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
CC:	Namhyung Kim <namhyung@...nel.org>, linux-kernel@...r.kernel.org,
	srikar@...ux.vnet.ibm.com, peterz@...radead.org, oleg@...hat.com,
	mingo@...hat.com, anton@...hat.com, systemtap@...rceware.org
Subject: Re: [PATCH 1/2] SDT markers listing by perf

Hi Masami,

On 09/04/2013 01:31 PM, Masami Hiramatsu wrote:
> (2013/09/04 15:42), Namhyung Kim wrote:
>> On Tue, 03 Sep 2013 13:06:55 +0530, Hemant Kumar wrote:
>>
>> [SNIP]
>>
>>> diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
>>> index e8a66f9..3d8dcdf 100644
>>> --- a/tools/perf/builtin-probe.c
>>> +++ b/tools/perf/builtin-probe.c
>>> @@ -55,6 +55,7 @@ static struct {
>>>  	bool show_funcs;
>>>  	bool mod_events;
>>>  	bool uprobes;
>>> +	bool sdt;
>>>  	int nevents;
>>>  	struct perf_probe_event events[MAX_PROBES];
>>>  	struct strlist *dellist;
>>> @@ -325,6 +326,8 @@ int cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
>>>  		     opt_set_filter),
>>>  	OPT_CALLBACK('x', "exec", NULL, "executable|path",
>>>  			"target executable name or path", opt_set_target),
>>> +	OPT_BOOLEAN('S', "sdt", &params.sdt,
>>> +		    "Show and probe on the SDT markers"),
>> You need to add it to Documentation/perf-probe.txt too.  In addition if
>> the --sdt option is only able to work with libelf, it should be wrapped
>> into the #ifdef LIBELF_SUPPORT pair.
>>
>> And I'm not sure that it's a good idea to have two behavior on a single
>> option (S) - show and probe (add).  Maybe it can be separated into two
>> or the S option can be used as a flag with existing --list and --add
>> option?
>>
> Good catch! :)
> No, that is really bad idea. All probes must be added by "--add" action.
> So we need a new probe syntax for specifying sdt marker.
>
> How about the below syntax?
>
> [EVENT=]%PROVIDER:MARKER [ARG ...]
>
> Of course, this will require to list up all markers with "%" prefix for
> continuity.
>
> And since --list option is to list up all existing(defined) probe events,
> I think --markers (as like as --funcs) is better for listing it up.
>
> Thank you!
>

I have one doubt here. Why do we need [ARG ...] in the syntax you
specified? I believe these args are to fetched from the sdt notes'
section of the elf of the executable/library. Or am I taking this in a
wrong way and this suggested syntax is actually for the uprobe_events
file in the tracing directory?

-- 
Thanks
Hemant

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