kunit: Add example parameterized test with shared resource management using the Resource API

Add example_params_test_with_init() to illustrate how to manage
shared resources across a parameterized KUnit test. This example
showcases the use of the new param_init() function and its registration
to a test using the KUNIT_CASE_PARAM_WITH_INIT() macro.

Additionally, the test demonstrates how to directly pass a parameter array
to the parameterized test context via kunit_register_params_array()
and leveraging the Resource API for shared resource management.

Link: https://lore.kernel.org/r/20250826091341.1427123-6-davidgow@google.com
Reviewed-by: Rae Moar <rmoar@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Marie Zhussupova <marievic@google.com>
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: Marie Zhussupova

lib/kunit/kunit-example-test.c

@@ -277,6 +277,117 @@ static void example_slow_test(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, 1 + 1, 2);
 }
 
+/*
+ * This custom function allocates memory and sets the information we want
+ * stored in the kunit_resource->data field.
+ */
+static int example_resource_init(struct kunit_resource *res, void *context)
+{
+	int *info = kmalloc(sizeof(*info), GFP_KERNEL);
+
+	if (!info)
+		return -ENOMEM;
+	*info = *(int *)context;
+	res->data = info;
+	return 0;
+}
+
+/*
+ * This function deallocates memory for the kunit_resource->data field.
+ */
+static void example_resource_free(struct kunit_resource *res)
+{
+	kfree(res->data);
+}
+
+/*
+ * This match function is invoked by kunit_find_resource() to locate
+ * a test resource based on certain criteria.
+ */
+static bool example_resource_alloc_match(struct kunit *test,
+					 struct kunit_resource *res,
+					 void *match_data)
+{
+	return res->data && res->free == example_resource_free;
+}
+
+/*
+ * This is an example of a function that provides a description for each of the
+ * parameters in a parameterized test.
+ */
+static void example_param_array_get_desc(struct kunit *test, const void *p, char *desc)
+{
+	const struct example_param *param = p;
+
+	snprintf(desc, KUNIT_PARAM_DESC_SIZE,
+		 "example check if %d is less than or equal to 3", param->value);
+}
+
+/*
+ * This function gets passed in the parameterized test context i.e. the
+ * struct kunit belonging to the parameterized test. You can use this function
+ * to add resources you want shared across the whole parameterized test or
+ * for additional setup.
+ */
+static int example_param_init(struct kunit *test)
+{
+	int ctx = 3; /* Data to be stored. */
+	size_t arr_size = ARRAY_SIZE(example_params_array);
+
+	/*
+	 * This allocates a struct kunit_resource, sets its data field to
+	 * ctx, and adds it to the struct kunit's resources list. Note that
+	 * this is parameterized test managed. So, it doesn't need to have
+	 * a custom exit function to deallocation as it will get cleaned up at
+	 * the end of the parameterized test.
+	 */
+	void *data = kunit_alloc_resource(test, example_resource_init, example_resource_free,
+					  GFP_KERNEL, &ctx);
+
+	if (!data)
+		return -ENOMEM;
+	/*
+	 * Pass the parameter array information to the parameterized test context
+	 * struct kunit. Note that you will need to provide kunit_array_gen_params()
+	 * as the generator function to KUNIT_CASE_PARAM_WITH_INIT() when registering
+	 * a parameter array this route.
+	 */
+	kunit_register_params_array(test, example_params_array, arr_size,
+				    example_param_array_get_desc);
+	return 0;
+}
+
+/*
+ * This is an example of a test that uses shared resources available in the
+ * parameterized test context.
+ */
+static void example_params_test_with_init(struct kunit *test)
+{
+	int threshold;
+	struct kunit_resource *res;
+	const struct example_param *param = test->param_value;
+
+	/* By design, param pointer will not be NULL. */
+	KUNIT_ASSERT_NOT_NULL(test, param);
+
+	/*
+	 * Here we pass test->parent to search for shared resources in the
+	 * parameterized test context.
+	 */
+	res = kunit_find_resource(test->parent, example_resource_alloc_match, NULL);
+
+	KUNIT_ASSERT_NOT_NULL(test, res);
+
+	/* Since kunit_resource->data is a void pointer we need to typecast it. */
+	threshold = *((int *)res->data);
+
+	/* Assert that the parameter is less than or equal to a certain threshold. */
+	KUNIT_ASSERT_LE(test, param->value, threshold);
+
+	/* This decreases the reference count after calling kunit_find_resource(). */
+	kunit_put_resource(res);
+}
+
 /*
  * Here we make a list of all the test cases we want to add to the test suite
  * below.
@@ -296,6 +407,8 @@ static struct kunit_case example_test_cases[] = {
 	KUNIT_CASE(example_static_stub_using_fn_ptr_test),
 	KUNIT_CASE(example_priv_test),
 	KUNIT_CASE_PARAM(example_params_test, example_gen_params),
+	KUNIT_CASE_PARAM_WITH_INIT(example_params_test_with_init, kunit_array_gen_params,
+				   example_param_init, NULL),
 	KUNIT_CASE_SLOW(example_slow_test),
 	{}
 };