linux-kernel - Re: [PATCH 2/2] trace-cmd: [BUGFIX] Don't die if an instance does not have 'current

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Date:	Fri, 27 Jun 2014 15:17:18 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
Cc:	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org, yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH 2/2] trace-cmd: [BUGFIX] Don't die if an instance does
 not have 'current_tracer' file

On Tue, 24 Jun 2014 02:23:45 +0000
Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com> wrote:

> Current trace-cmd requires 'current_tracer' file for an instance, and if
> the file is nothing, trace-cmd dies. However, current_tracer file was
> introduced from 607e2ea167e patch in Linux kernel 3.14-rc3, so current
> trace-cmd cannot use multiple buffers for old kernels.
> 
> This patch avoids to die if current_tracer file is nothing in an instance
> and the plugin name is "nop". This is because old kernels always trace
> as nop mode in an instance.
> 
> <How to test>
> 1) # ./trace-cmd record -B foo -e sched
> 
> Before introducing this patch, following error message is output in an old
> kernel:
> 
>  trace-cmd: Permission denied
>    writing to '/sys/kernel/debug/tracing/instances/foo/current_tracer'
> 
> trace-cmd dies in disable_trace() calling set_plugin("nop").
> After introducing this patch, trace-cmd works fine in both old kernels and
> current kernel.
> 
> 2) # ./trace-cmd record -B foo -e sched -p nop
> 
> It also works fine after introducing this patch in both old kernels and current
> kernel.
> 
> 3) # ./trace-cmd record -B foo -e sched -p function
> 
> For old kernels, it dies because an user should not set plugin tracer.
> For current kernel, it works fine.
> 
> Note that this patch was tested for kernel 3.11.9-200 and 3.15.0-rc2+.
> 
> Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>

Applied, thanks!

-- Steve
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