linux-kernel - Re: [PATCH] tracing: Don't display trigger file for events that don't have register func

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Message-ID: <20160502224244.1b17428c@grimm.local.home>
Date:	Mon, 2 May 2016 22:42:44 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Chunyu Hu <chuhu@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: Don't display trigger file for events that
 don't have register func

On Mon,  2 May 2016 22:14:14 +0800
Chunyu Hu <chuhu@...hat.com> wrote:

> Currently register function of the event will be called
> through the 'reg'  field of event class directly without
> any check when seting up triggers.
> 
> Triggers for events that don't support register through
> debug fs (events under events/ftrace are for perf to

Actually, they were created for trace-cmd. I'm not even sure if perf
uses the ftrace event formats.


> read event format, and most of them don't have regisgter
> function except events/ftrace/function.) can't be enabled
> at all, and an oops will be hit when setting up trigger
> for those events, so just not showing them is an easy way
> to avoid the oops.
> 
> Signed-off-by: Chunyu Hu <chuhu@...hat.com>
> ---
>  kernel/trace/trace_events.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index da1eeb6..9fb99fd 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -2138,9 +2138,10 @@ event_create_dir(struct dentry *parent, struct trace_event_file *file)
>  	trace_create_file("filter", 0644, file->dir, file,
>  			  &ftrace_event_filter_fops);
>  
> -	trace_create_file("trigger", 0644, file->dir, file,
> -			  &event_trigger_fops);
> -
> +	if (call->class->reg) {
> +		trace_create_file("trigger", 0644, file->dir, file,
> +				  &event_trigger_fops);
> +	}

As you stated, reg is there for function tracing, and is not a good
value to use as a check. Use the following check instead:

	if (!(call->flags & TRACE_EVENT_FL_IGNORE_ENABLE))
		trace_create_file("trigger", 0644, file->dir, file,
				  &event_trigger_fops);

And add a comment that states that only event directories that can be
enabled should have triggers.

-- Steve



>  #ifdef CONFIG_HIST_TRIGGERS
>  	trace_create_file("hist", 0444, file->dir, file,
>  			  &event_hist_fops);