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Message-ID: <4B4E4551.2010302@redhat.com>
Date: Wed, 13 Jan 2010 17:12:33 -0500
From: Masami Hiramatsu <mhiramat@redhat.com>
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To: rostedt@goodmis.org
CC: Frederic Weisbecker <fweisbec@gmail.com>,
       Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
       Ingo Molnar <mingo@elte.hu>,
       Arnaldo Carvalho de Melo <acme@infradead.org>,
       Peter Zijlstra <peterz@infradead.org>,
       Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
       utrace-devel <utrace-devel@redhat.com>,
       Jim Keniston <jkenisto@us.ibm.com>, Maneesh Soni <maneesh@in.ibm.com>,
       Mark Wielaard <mjw@redhat.com>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] [PATCH 7/7] Ftrace plugin for Uprobes
References: <20100111122521.22050.3654.sendpatchset@srikar.in.ibm.com>	 <20100111122608.22050.94088.sendpatchset@srikar.in.ibm.com>	 <20100112045454.GJ5243@nowhere> <1263272933.28171.3804.camel@gandalf.stny.rr.com> <4B4E41FF.4020800@redhat.com>
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Masami Hiramatsu wrote:
> Steven Rostedt wrote:
>> On Tue, 2010-01-12 at 05:54 +0100, Frederic Weisbecker wrote:
>>
>>> Now what if I want to launch ls and want to profile a function
>>> inside. What can I do with a trace event. I can't create the
>>> probe event based on a pid as I don't know it in advance.
>>> I could give it the ls cmdline and it manages to activate
>>> on the next ls launched. This is racy as another ls can
>>> be launched concurrently.
>>
>> You make a wrapper script:
>>
>> #!/bin/sh
>> <add probe to ls with pid> $$
>> exec $*
>>
>> I do this all the time to limit the function tracer to a specific app.
>>
>> #!/bin/sh
>> echo $$ > /debug/tracing/set_ftrace_pid
>> echo function > /debug/tracing/current_tracer
>> exec $*
> 
> I recommend you to add below line at the end of the script,
> from my experience. :)
> 
> echo nop > /debug/tracing/current_tracer

Oops, my bad, it doesn't work after exec...
But, it is very important to disable function tracer after
tracing target process.

So, perhaps, below script may work.

#!/bin/sh
(echo $BASHPID > /debug/tracing/set_ftrace_pid
 echo function > /debug/tracing/current_tracer
 exec $*)
echo nop > /debug/tracing/current_tracer

Thanks,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com

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