linux-kernel - Re: [PATCH] tracing: remove tracing_is

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Message-ID: <20240725121745.787c5b33@gandalf.local.home>
Date: Thu, 25 Jul 2024 12:17:45 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] tracing: remove tracing_is_on export

On Thu, 25 Jul 2024 16:41:11 +0200
Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:

 This workflow is used by many developers.  
> 
> Is it documented anywhere?  I've never heard of it before, and nothing
> really describes this in Documentation/ that I can find.

It is mentioned, but I could expand on it more:

Documentation/trace/ftrace.rst:

  tracing_on:

        This sets or displays whether writing to the trace
        ring buffer is enabled. Echo 0 into this file to disable
        the tracer or 1 to enable it. Note, this only disables
        writing to the ring buffer, the tracing overhead may
        still be occurring.

        The kernel function tracing_off() can be used within the
        kernel to disable writing to the ring buffer, which will
        set this file to "0". User space can re-enable tracing by
        echoing "1" into the file.

> 
> But as you only want these to be exported to developer kernels, why not
> say that and put that behind a debugging Kconfig option or something?

Why add the burden of having to compile the core kernel to enable it? I use
this all the time.

> That way "vendor kernels" can properly disable this as they don't want
> to give this type of functionality to random 3rd-party kernel modules.

This has been exported since 2008. Has it ever been a problem in the last
16 years?

-- Steve