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SubjectRe: [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@redhat.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@redhat.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);

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