linux-kernel - Re: [RFC][PATCH] tracing: Show available event triggers when no trigger is set

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Date:	Wed, 08 Jan 2014 16:50:47 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [RFC][PATCH] tracing: Show available event triggers when no trigger is set

Hi Steve,

On Tue, 7 Jan 2014 10:35:48 -0500, Steven Rostedt wrote:
> Currently there's no way to know what triggers exist on a kernel without
> looking at the source of the kernel or randomly trying out triggers.
> Instead of creating another file in the debugfs system, simply show
> what available triggers are there when cat'ing the trigger file when
> it has no events:
>
>  [root /sys/kernel/debug/tracing]# cat events/sched/sched_switch/trigger
>  # Available triggers:
>  # disable_event enable_event stacktrace snapshot traceoff traceon
>
> This stays consistent with other debugfs files where meta data like
> this is always proceeded with a '#' at the start of the line so that
> tools can strip these out.

[SNIP]
> +	if (v == SHOW_AVAILABLE_TRIGGERS) {
> +		seq_puts(m, "# Available triggers:\n");
> +		seq_putc(m, '#');
> +		mutex_lock(&trigger_cmd_mutex);
> +		list_for_each_entry(p, &trigger_commands, list)

I guess the list_for_each_entry_reverse() will give a more intuitive
result here:

  [root /sys/kernel/debug/tracing]# cat events/sched/sched_switch/trigger
  # Available triggers:
  # traceon traceoff snapshot stacktrace enable_event disable_event

Thanks,
Namhyung


> +			seq_printf(m, " %s", p->name);
> +		seq_putc(m, '\n');
> +		mutex_unlock(&trigger_cmd_mutex);
> +		return 0;
> +	}
>  
>  	data = list_entry(v, struct event_trigger_data, list);
>  	data->ops->print(m, data->ops, data);
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