linux-kernel - Re: [PATCH] tracing: Export tracing_start() and tracing

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Date:   Tue, 8 Jun 2021 14:59:27 +0200
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     Christoph Hellwig <hch@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, kernel <kernel@...s.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: Export tracing_start() and tracing_stop()

On Mon, Jun 07, 2021 at 03:14:32PM +0200, Steven Rostedt wrote:
> That said though, tracing_stop() is probably not what is wanted
> (unless its for a suspend to ram thing). According to the above
> description, the author really wants to use "tracing_off()" and not
> "tracing_stop()" as tracing_off() is faster and can be turned back on
> in user-space with the "tracing_on" file in tracefs, where as,
> tracing_stop() can not be. tracing_stop() needs a tracing_start() to
> get it going again.
> 
> And tracing_off() is already EXPORT_SYMBOL_GPL() (as it is commonly
> used for debugging of modules). Again, it shouldn't have any in-kernel
> users in modules, because, like I stated above, it's similar to
> trace_printk() which should be removed before pushing to Linus.
> 
> I'll NAK this patch for a different reason. Use tracing_off() instead.

Right, thanks, that's certainly much simpler.  I'd only used
tracing_stop() before and never noticed that tracing_on can't be used to
restart tracing, probably because the kind of problems I used it for
usually resulted in the system needing a restart anyway to be usable.