[PATCH] libtracefs: Do not allow tracefs_synth_set_instance() on created synth

[PATCH] libtracefs: Do not allow tracefs_synth_set_instance() on created synth

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

If tracefs_synth_create() is called on a synthetic event descriptor, do
not let its instance change after that. Currently
tracefs_synth_set_instance() returns success when called on a created
instance, where it has no effect. Make it fail in such cases.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 src/tracefs-hist.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/tracefs-hist.c b/src/tracefs-hist.c
index 1e3df6c67d7e..ecfce7442176 100644
--- a/src/tracefs-hist.c
+++ b/src/tracefs-hist.c
@@ -748,6 +748,7 @@ struct name_hash {
  * @start_parens: Current parenthesis level for start event
  * @end_parens: Current parenthesis level for end event
  * @new_format: onmatch().trace(synth_event,..) or onmatch().synth_event(...)
+ * @created: Set if tracefs_synth_create() was called on this; cleared on destroy()
  */
 struct tracefs_synth {
 	struct tracefs_instance *instance;
@@ -778,6 +779,7 @@ struct tracefs_synth {
 	char			arg_name[16];
 	int			arg_cnt;
 	bool			new_format;
+	bool			created;
 };
 
  /*
@@ -2207,7 +2209,7 @@ tracefs_synth_get_start_hist(struct tracefs_synth *synth)
  */
 int tracefs_synth_set_instance(struct tracefs_synth *synth, struct tracefs_instance *instance)
 {
-	if (!synth)
+	if (!synth || synth->created)
 		return -1;
 	synth->instance = instance;
 	return 0;
@@ -2271,6 +2273,8 @@ int tracefs_synth_create(struct tracefs_synth *synth)
 	if (ret < 0)
 		goto remove_start_hist;
 
+	synth->created = true;
+
 	return 0;
 
  remove_start_hist:
@@ -2334,6 +2338,9 @@ int tracefs_synth_destroy(struct tracefs_synth *synth)
 
 	ret = tracefs_dynevent_destroy(synth->dyn_event, true);
 
+	if (!ret)
+		synth->created = false;
+
 	return ret ? -1 : 0;
 }
 
-- 
2.39.2