linux-kernel - Re: [PATCH] ftrace: Document ftrace command line limitations

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Message-ID: <54583A43.2000303@hurleysoftware.com>
Date:	Mon, 03 Nov 2014 21:30:27 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ftrace: Document ftrace command line limitations

On 11/03/2014 09:14 PM, Steven Rostedt wrote:
> On Mon,  3 Nov 2014 20:45:25 -0500
> Peter Hurley <peter@...leysoftware.com> wrote:
> 
>> When using the function or function_graph tracers from the command
>> line, certain command line options have limitations.
>>
>> Document that only kernel built-in functions can be filtered via
>> ftrace_filter= or ftrace_graph_filter=. Also document that tracer-
>> specific options cannot be set on the command line via trace_options.
> 
> It's not just a command line limitation. The command line behaves
> exactly like set_ftrace_filter does. That is, it only affects the
> functions that are loaded when the filter is modified. It never updates
> functions that will be loaded when modules are.
> 
> Adding this documentation makes it seem that set_ftrace_filter has the
> ability to update functions that were not loaded yet. This is not true.
> The command line filtering behaves exactly like set_ftrace_filter does.
> It only enables the functions that are loaded at the time the function
> is set. Which was at boot up, and it just happens to be only built in
> functions at that time.

Ah, ok. I'll clarify those two lines and add to the documentation in
Documentation/trace/ftrace.txt

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