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SubjectRe: [RFC][PATCH 06/10] tracing: Add trigger file for trace_markers tracefs/ftrace/print
On Mon, 14 May 2018 12:13:22 +0900
Namhyung Kim <namhyung@kernel.org> wrote:

> On Fri, May 11, 2018 at 03:49:33PM -0400, Steven Rostedt wrote:
> > From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> >
> > Allow writing to the trace_markers file initiate triggers defined in
> > tracefs/ftrace/print/trigger file. This will allow of user space to trigger
> > the same type of triggers (including histograms) that the trace events use.
> >
> > Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
> > Cc: Clark Williams <williams@redhat.com>
> > Cc: Karim Yaghmour <karim.yaghmour@opersys.com>
> > Cc: Brendan Gregg <bgregg@netflix.com>
> > Suggested-by: Joel Fernandes <joelaf@google.com>
> > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> > ---
>
> [SNIP]
> > diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
> > index e3a658bac10f..de3fce14cd00 100644
> > --- a/kernel/trace/trace_entries.h
> > +++ b/kernel/trace/trace_entries.h
> > @@ -230,7 +230,7 @@ FTRACE_ENTRY(bprint, bprint_entry,
> > FILTER_OTHER
> > );
> >
> > -FTRACE_ENTRY(print, print_entry,
> > +FTRACE_ENTRY_REG(print, print_entry,
> >
> > TRACE_PRINT,
> >
> > @@ -242,7 +242,9 @@ FTRACE_ENTRY(print, print_entry,
> > F_printk("%ps: %s",
> > (void *)__entry->ip, __entry->buf),
> >
> > - FILTER_OTHER
> > + FILTER_OTHER,
> > +
> > + ftrace_event_register
>
> I wonder this is still needed since you added __find_event_file()
> which ignores the reg field. Maybe I'm missing something..

No, that's not the reason for it. The reason is due to the
event_trigger_callback() function. I'll update the changelog to specify
this.

We have something like:

# echo snapshot > events/ftrace/print/trigger

Which will do:

event_trigger_write() {
event_trigger_regex_write() {
trigger_process_regex() {
for p in trigger_commands {
p->func(); /* trigger_snapshot_cmd->func */
event_trigger_callback() {
cmd_ops->reg() /* register_trigger() */ {
trace_event_trigger_enable_disable() {
trace_event_enable_disable() {
call->class->reg();

Without this patch, we jump to NULL and BOOM!


>
> Anyway it looks whitespace damaged.
>

Thanks, I'll fix it up.

-- Steve

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