Date: Tue, 15 Nov 2016 10:23:42 -0500
From: Steven Rostedt <rostedt@goodmis.org>
To: Chunyan Zhang <zhang.chunyan@linaro.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        mingo@redhat.com, Mike Leach <mike.leach@arm.com>,
        Tor Jeremiassen <tor@ti.com>, philippe.langlais@st.com,
        Nicolas GUION <nicolas.guion@st.com>,
        Felipe Balbi <felipe.balbi@linux.intel.com>,
        Lyra Zhang <zhang.lyra@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH V7 1/3] tracing: add a possibility of exporting function
 trace to other places instead of ring buffer only
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On Tue, 15 Nov 2016 16:14:29 +0800
Chunyan Zhang <zhang.chunyan@linaro.org> wrote:

>
> > Then why have a
> >
> >         if (export->write)
> >
> >
> > Is there every going to be a case where export will not have a write
> > function?  
> 
> There shouldn't be.
> 
> I can move this if statement to the register_ftrace_export() to ensure
> users won't wrongly use it, that's saying the write() of trace_export
> has been set before being registered to 'ftrace_exports_list'.
> 

Looks like it's already there:

+int register_ftrace_export(struct trace_export *export)
+{
+	if (WARN_ON_ONCE(!export->write))
+		return -1;


-- Steve