[PATCH v13 14/29] tracing: Add hist trigger support for clearing a trace

[Tom Zanussi <tom.zanussi@linux.intel.com>]

Allow users to append 'clear' to an existing trigger in order to have
the hash table cleared.

This expands the hist trigger syntax from this:
    # echo hist:keys=xxx:vals=yyy:sort=zzz.descending:pause/cont \
           [ if filter] >> event/trigger

to this:

    # echo hist:keys=xxx:vals=yyy:sort=zzz.descending:pause/cont/clear \
          [ if filter] >> event/trigger

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
---
 kernel/trace/trace.c             |  5 ++++-
 kernel/trace/trace_events_hist.c | 24 ++++++++++++++++++++++--
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b68aedb..037f6374 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3828,7 +3828,7 @@ static const char readme_msg[] =
 	"\t            [:values=<field1[,field2,...]>]\n"
 	"\t            [:sort=<field1[,field2,...]>]\n"
 	"\t            [:size=#entries]\n"
-	"\t            [:pause][:continue]\n"
+	"\t            [:pause][:continue][:clear]\n"
 	"\t            [if <filter>]\n\n"
 	"\t    When a matching event is hit, an entry is added to a hash\n"
 	"\t    table using the key(s) and value(s) named, and the value of a\n"
@@ -3848,6 +3848,9 @@ static const char readme_msg[] =
 	"\t    trigger or to start a hist trigger but not log any events\n"
 	"\t    until told to do so.  'continue' can be used to start or\n"
 	"\t    restart a paused hist trigger.\n\n"
+	"\t    The 'clear' parameter will clear the contents of a running\n"
+	"\t    hist trigger and leave its current paused/active state\n"
+	"\t    unchanged.\n\n"
 #endif
 ;
 
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index bad1506..2995849 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -89,6 +89,7 @@ struct hist_trigger_attrs {
 	char		*sort_key_str;
 	bool		pause;
 	bool		cont;
+	bool		clear;
 	unsigned int	map_bits;
 };
 
@@ -198,6 +199,8 @@ static struct hist_trigger_attrs *parse_hist_trigger_attrs(char *trigger_str)
 			attrs->sort_key_str = kstrdup(str, GFP_KERNEL);
 		else if (!strncmp(str, "pause", strlen("pause")))
 			attrs->pause = true;
+		else if (!strncmp(str, "clear", strlen("clear")))
+			attrs->clear = true;
 		else if (!strncmp(str, "continue", strlen("continue")) ||
 			 !strncmp(str, "cont", strlen("cont")))
 			attrs->cont = true;
@@ -898,6 +901,21 @@ static struct event_trigger_ops *event_hist_get_trigger_ops(char *cmd,
 	return &event_hist_trigger_ops;
 }
 
+static void hist_clear(struct event_trigger_data *data)
+{
+	struct hist_trigger_data *hist_data = data->private_data;
+	bool paused;
+
+	paused = data->paused;
+	data->paused = true;
+
+	synchronize_sched();
+
+	tracing_map_clear(hist_data->map);
+
+	data->paused = paused;
+}
+
 static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
 				 struct event_trigger_data *data,
 				 struct trace_event_file *file)
@@ -912,13 +930,15 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
 				test->paused = true;
 			else if (hist_data->attrs->cont)
 				test->paused = false;
+			else if (hist_data->attrs->clear)
+				hist_clear(test);
 			else
 				ret = -EEXIST;
 			goto out;
 		}
 	}
 
-	if (hist_data->attrs->cont) {
+	if (hist_data->attrs->cont || hist_data->attrs->clear) {
 		ret = -ENOENT;
 		goto out;
 	}
@@ -1017,7 +1037,7 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	 * triggers registered a failure too.
 	 */
 	if (!ret) {
-		if (!(attrs->pause || attrs->cont))
+		if (!(attrs->pause || attrs->cont || attrs->clear))
 			ret = -ENOENT;
 		goto out_free;
 	} else if (ret < 0)
-- 
1.9.3