[PATCH 5/7] tracing: Add field parsing hist error for hist triggers

[Steven Rostedt]

From: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>

If the user specifies a nonexistent field for a hist trigger, the
current code correctly flags that as an error, but doesn't tell the
user what happened.

Fix this by invoking hist_err() with an appropriate message when
nonexistent fields are specified.

Before:

  # echo 'hist:keys=pid:ts0=common_timestamp.usecs' >> /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
  -su: echo: write error: Invalid argument
  # cat /sys/kernel/debug/tracing/events/sched/sched_switch/hist

After:

  # echo 'hist:keys=pid:ts0=common_timestamp.usecs' >> /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
  -su: echo: write error: Invalid argument
  # cat /sys/kernel/debug/tracing/events/sched/sched_switch/hist
  ERROR: Couldn't find field: pid
    Last command: keys=pid:ts0=common_timestamp.usecs

Link: http://lkml.kernel.org/r/fdc8746969d16906120f162b99dd71c741e0b62c.1524790601.git.tom.zanussi@xxxxxxxxxxxxxxx

Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
Reported-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
 kernel/trace/trace_events_hist.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 66c87be4ebb2..f231fa2a3dcd 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -2481,6 +2481,7 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
 	else {
 		field = trace_find_event_field(file->event_call, field_name);
 		if (!field || !field->size) {
+			hist_err("Couldn't find field: ", field_name);
 			field = ERR_PTR(-EINVAL);
 			goto out;
 		}
-- 
2.17.0