2 files changed, 102 insertions, 14 deletions

diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
index 2ce565a73dd5..d1973cb8388b 100644
--- a/tools/lib/traceevent/event-parse.c
+++ b/tools/lib/traceevent/event-parse.c
@@ -5560,6 +5560,29 @@ int pevent_register_print_function(struct pevent *pevent,
         return ret;
 }
 
+static struct event_format *pevent_search_event(struct pevent *pevent, int id,
+                                                const char *sys_name,
+                                                const char *event_name)
+{
+        struct event_format *event;
+
+        if (id >= 0) {
+                /* search by id */
+                event = pevent_find_event(pevent, id);
+                if (!event)
+                        return NULL;
+                if (event_name && (strcmp(event_name, event->name) != 0))
+                        return NULL;
+                if (sys_name && (strcmp(sys_name, event->system) != 0))
+                        return NULL;
+        } else {
+                event = pevent_find_event_by_name(pevent, sys_name, event_name);
+                if (!event)
+                        return NULL;
+        }
+        return event;
+}
+
 /**
  * pevent_register_event_handler - register a way to parse an event
  * @pevent: the handle to the pevent
@@ -5584,20 +5607,9 @@ int pevent_register_event_handler(struct pevent *pevent, int id,
         struct event_format *event;
         struct event_handler *handle;
 
-        if (id >= 0) {
-                /* search by id */
-                event = pevent_find_event(pevent, id);
-                if (!event)
-                        goto not_found;
-                if (event_name && (strcmp(event_name, event->name) != 0))
-                        goto not_found;
-                if (sys_name && (strcmp(sys_name, event->system) != 0))
-                        goto not_found;
-        } else {
-                event = pevent_find_event_by_name(pevent, sys_name, event_name);
-                if (!event)
-                        goto not_found;
-        }
+        event = pevent_search_event(pevent, id, sys_name, event_name);
+        if (event == NULL)
+                goto not_found;
 
         pr_stat("overriding event (%d) %s:%s with new print handler",
                 event->id, event->system, event->name);
@@ -5637,6 +5649,79 @@ int pevent_register_event_handler(struct pevent *pevent, int id,
         return -1;
 }
 
+static int handle_matches(struct event_handler *handler, int id,
+                          const char *sys_name, const char *event_name,
+                          pevent_event_handler_func func, void *context)
+{
+        if (id >= 0 && id != handler->id)
+                return 0;
+
+        if (event_name && (strcmp(event_name, handler->event_name) != 0))
+                return 0;
+
+        if (sys_name && (strcmp(sys_name, handler->sys_name) != 0))
+                return 0;
+
+        if (func != handler->func || context != handler->context)
+                return 0;
+
+        return 1;
+}
+
+/**
+ * pevent_unregister_event_handler - unregister an existing event handler
+ * @pevent: the handle to the pevent
+ * @id: the id of the event to unregister
+ * @sys_name: the system name the handler belongs to
+ * @event_name: the name of the event handler
+ * @func: the function to call to parse the event information
+ * @context: the data to be passed to @func
+ *
+ * This function removes existing event handler (parser).
+ *
+ * If @id is >= 0, then it is used to find the event.
+ * else @sys_name and @event_name are used.
+ *
+ * Returns 0 if handler was removed successfully, -1 if event was not found.
+ */
+int pevent_unregister_event_handler(struct pevent *pevent, int id,
+                                    const char *sys_name, const char *event_name,
+                                    pevent_event_handler_func func, void *context)
+{
+        struct event_format *event;
+        struct event_handler *handle;
+        struct event_handler **next;
+
+        event = pevent_search_event(pevent, id, sys_name, event_name);
+        if (event == NULL)
+                goto not_found;
+
+        if (event->handler == func && event->context == context) {
+                pr_stat("removing override handler for event (%d) %s:%s. Going back to default handler.",
+                        event->id, event->system, event->name);
+
+                event->handler = NULL;
+                event->context = NULL;
+                return 0;
+        }
+
+not_found:
+        for (next = &pevent->handlers; *next; next = &(*next)->next) {
+                handle = *next;
+                if (handle_matches(handle, id, sys_name, event_name,
+                                   func, context))
+                        break;
+        }
+
+        if (!(*next))
+                return -1;
+
+        *next = handle->next;
+        free_handler(handle);
+
+        return 0;
+}
+
 /**
  * pevent_alloc - create a pevent handle
  */
diff --git a/tools/lib/traceevent/event-parse.h b/tools/lib/traceevent/event-parse.h
index a3beca56cb35..c48acfbc6230 100644
--- a/tools/lib/traceevent/event-parse.h
+++ b/tools/lib/traceevent/event-parse.h
@@ -624,6 +624,9 @@ int pevent_print_func_field(struct trace_seq *s, const char *fmt,
 int pevent_register_event_handler(struct pevent *pevent, int id,
                                   const char *sys_name, const char *event_name,
                                   pevent_event_handler_func func, void *context);
+int pevent_unregister_event_handler(struct pevent *pevent, int id,
+                                    const char *sys_name, const char *event_name,
+                                    pevent_event_handler_func func, void *context);
 int pevent_register_print_function(struct pevent *pevent,
                                    pevent_func_handler func,
                                    enum pevent_func_arg_type ret_type,