linux-kernel - Re: [PATCH v3 0/3] tracing: Add dynamic strings for synthetic events

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Date:   Fri, 2 Oct 2020 20:55:10 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Tom Zanussi <zanussi@...nel.org>
Cc:     axelrasmussen@...gle.com, mhiramat@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/3] tracing: Add dynamic strings for synthetic
 events

On Thu,  1 Oct 2020 16:46:43 -0500
Tom Zanussi <zanussi@...nel.org> wrote:

> Hi,
> 
> This is v3 of the dynamic string support for synthetic events.
> 
> No code changes since v2, just added Fixes: tag for 'tracing: Fix
> parse_synth_field() error handling' as suggested by Masami along with
> his Reviewed-by, and Axel's Tested-bys.
> 

I added the following to make it work with trace-cmd. Dynamic strings
must have __get_str() for events in the print_fmt otherwise it can't be
parsed correctly.

-- Steve

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index 4b3ec570147a..24bc6d61aa40 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -489,8 +489,13 @@ static int __set_synth_event_print_fmt(struct synth_event *event,
 	pos += snprintf(buf + pos, LEN_OR_ZERO, "\"");
 
 	for (i = 0; i < event->n_fields; i++) {
-		pos += snprintf(buf + pos, LEN_OR_ZERO,
-				", REC->%s", event->fields[i]->name);
+		if (event->fields[i]->is_dynamic &&
+		    event->fields[i]->is_dynamic)
+			pos += snprintf(buf + pos, LEN_OR_ZERO,
+				", __get_str(%s)", event->fields[i]->name);
+		else
+			pos += snprintf(buf + pos, LEN_OR_ZERO,
+					", REC->%s", event->fields[i]->name);
 	}
 
 #undef LEN_OR_ZERO