tracing: Add a test for ftrace_parse_event_string()

The parsing logic is a bit complicated and about to become more so.

Add a unit test to avoid regressions.

Link: https://patch.msgid.link/20260908-tracing-cli-event-filter-v2-5-05396a3fb663@linutronix.de
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/Kconfig

@@ -151,6 +151,14 @@ config EVENT_TRACING
 	select GLOB
 	bool
 
+config EVENT_TRACING_TEST
+	tristate "Test for event tracing" if !KUNIT_ALL_TESTS
+	depends on EVENT_TRACING
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  KUnit test for the event tracing implementation.
+
 config CONTEXT_SWITCH_TRACER
 	bool
 

kernel/trace/Makefile

@@ -96,6 +96,7 @@ obj-$(CONFIG_EVENT_TRACING) += blktrace.o
 endif
 obj-$(CONFIG_EVENT_TRACING) += trace_events.o
 obj-$(CONFIG_EVENT_TRACING) += trace_export.o
+obj-$(CONFIG_EVENT_TRACING_TEST) += trace_events_test.o
 obj-$(CONFIG_FTRACE_SYSCALLS) += trace_syscalls.o
 ifeq ($(CONFIG_PERF_EVENTS),y)
 obj-$(CONFIG_EVENT_TRACING) += trace_event_perf.o

kernel/trace/trace.h

@@ -2509,3 +2509,7 @@ static inline int rv_init_interface(void)
 	})
 
 #endif /* _LINUX_KERNEL_TRACE_H */
+
+#if IS_ENABLED(CONFIG_KUNIT)
+void ftrace_parse_event_string(char *buf, char **match, char **sub, char **event, char **mod);
+#endif

kernel/trace/trace_events.c

@@ -25,6 +25,8 @@
 #include <linux/delay.h>
 #include <linux/btf.h>
 
+#include <kunit/visibility.h>
+
 #include <trace/events/sched.h>
 #include <trace/syscall.h>
 
@@ -1443,7 +1445,7 @@ static int __ftrace_set_clr_event(struct trace_array *tr, const char *match,
 	return ret;
 }
 
-static void
+VISIBLE_IF_KUNIT void
 ftrace_parse_event_string(char *buf, char **match, char **sub, char **event, char **mod)
 {
 	*event = NULL;
@@ -1485,6 +1487,7 @@ ftrace_parse_event_string(char *buf, char **match, char **sub, char **event, cha
 			*match = NULL;
 	}
 }
+EXPORT_SYMBOL_IF_KUNIT(ftrace_parse_event_string);
 
 int ftrace_set_clr_event(struct trace_array *tr, const char *arg_buf, int set)
 {

kernel/trace/trace_events_test.c

@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/module.h>
+
+#include <kunit/test.h>
+
+#include "trace.h"
+
+struct parse_event_string_test_case {
+	const char *input;
+
+	const char *match, *sub, *event, *mod;
+};
+
+static const struct parse_event_string_test_case parse_event_string_test_cases[] = {
+	{
+		"",
+		.match	= "",
+	},
+	{
+		"*:event",
+		.event	= "event",
+	},
+	{
+		":event",
+		.event	= "event",
+	},
+	{
+		"sub:*",
+		.sub	= "sub",
+	},
+	{
+		"sub:",
+		.sub	= "sub",
+	},
+	{
+		"sub:event",
+		.sub	= "sub",
+		.event	= "event",
+	},
+	{
+		"match",
+		.match	= "match",
+	},
+	{
+		":mod:module",
+		.mod	= "module",
+	},
+	{
+		"sub:event:mod:module",
+		.sub	= "sub",
+		.event	= "event",
+		.mod	= "module",
+	},
+};
+
+static void
+parse_event_string_test_desc(const struct parse_event_string_test_case *params, char *desc)
+{
+	snprintf(desc, KUNIT_PARAM_DESC_SIZE, "'%s'", params->input);
+}
+
+KUNIT_ARRAY_PARAM(parse_event_string, parse_event_string_test_cases, parse_event_string_test_desc);
+
+#define EXPECT_NULL_OR_STR_EQ(test, left, right)		\
+({								\
+	if ((left) != NULL)					\
+		KUNIT_EXPECT_STREQ(test, (left), (right));	\
+	else							\
+		KUNIT_EXPECT_NULL(test, (right));		\
+})
+
+static void parse_event_string(struct kunit *test)
+{
+	const struct parse_event_string_test_case *params = test->param_value;
+	char *input, *match, *sub, *event, *mod;
+
+	input = kunit_kstrdup(test, params->input, GFP_KERNEL);
+	if (!input)
+		kunit_skip(test, "ENOMEM");
+
+	ftrace_parse_event_string(input, &match, &sub, &event, &mod);
+
+	EXPECT_NULL_OR_STR_EQ(test, match, params->match);
+	EXPECT_NULL_OR_STR_EQ(test, sub, params->sub);
+	EXPECT_NULL_OR_STR_EQ(test, event, params->event);
+	EXPECT_NULL_OR_STR_EQ(test, mod, params->mod);
+}
+
+static struct kunit_case trace_events_test_cases[] = {
+	KUNIT_CASE_PARAM(parse_event_string, parse_event_string_gen_params),
+	{}
+};
+
+static struct kunit_suite trace_events_test_suite = {
+	.name = "trace-events",
+	.test_cases = trace_events_test_cases,
+};
+kunit_test_suite(trace_events_test_suite);
+
+MODULE_DESCRIPTION("KUnit test for the event tracing implementation");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");