smb/client: introduce KUnit test to check search result of smb2_error_map_table

The KUnit test are executed when cifs.ko is loaded.

Just like `fs/ext4/mballoc.c` includes `fs/ext4/mballoc-test.c`.
`smb2maperror.c` also includes `smb2maperror_test.c`, allowing KUnit
tests to access any functions and variables in `smb2maperror.c`.

The maperror_test_check_search() checks whether all elements can be
correctly found in the array.

Suggested-by: David Howells <dhowells@redhat.com>
Signed-off-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: ChenXiaoSong

fs/smb/Kconfig

@@ -9,3 +9,20 @@ config SMBFS
 	tristate
 	default y if CIFS=y || SMB_SERVER=y
 	default m if CIFS=m || SMB_SERVER=m
+
+config SMB_KUNIT_TESTS
+	tristate "KUnit tests for SMB" if !KUNIT_ALL_TESTS
+	depends on SMBFS && KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  This builds the SMB KUnit tests.
+
+	  KUnit tests run during boot and output the results to the debug log
+	  in TAP format (https://testanything.org/). Only useful for kernel devs
+	  running KUnit test harness and are not for inclusion into a production
+	  build.
+
+	  For more information on KUnit and unit tests in general please refer
+	  to the KUnit documentation in Documentation/dev-tools/kunit/.
+
+	  If unsure, say N.

fs/smb/client/smb2maperror.c

@@ -114,3 +114,11 @@ int __init smb2_init_maperror(void)
 
 	return 0;
 }
+
+#define SMB_CLIENT_KUNIT_AVAILABLE \
+	((IS_MODULE(CONFIG_CIFS) && IS_ENABLED(CONFIG_KUNIT)) || \
+	 (IS_BUILTIN(CONFIG_CIFS) && IS_BUILTIN(CONFIG_KUNIT)))
+
+#if SMB_CLIENT_KUNIT_AVAILABLE && IS_ENABLED(CONFIG_SMB_KUNIT_TESTS)
+#include "smb2maperror_test.c"
+#endif /* CONFIG_SMB_KUNIT_TESTS */

fs/smb/client/smb2maperror_test.c

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: LGPL-2.1
+/*
+ *
+ *   KUnit tests of SMB2 maperror
+ *
+ *   Copyright (C) 2025 KylinSoft Co., Ltd. All rights reserved.
+ *   Author(s): ChenXiaoSong <chenxiaosong@kylinos.cn>
+ *
+ */
+
+#include <kunit/test.h>
+
+static void
+test_cmp_map(struct kunit *test, const struct status_to_posix_error *expect)
+{
+	const struct status_to_posix_error *result;
+
+	result = smb2_get_err_map(expect->smb2_status);
+	KUNIT_EXPECT_PTR_NE(test, NULL, result);
+	KUNIT_EXPECT_EQ(test, expect->smb2_status, result->smb2_status);
+	KUNIT_EXPECT_EQ(test, expect->posix_error, result->posix_error);
+	KUNIT_EXPECT_STREQ(test, expect->status_string, result->status_string);
+}
+
+static void maperror_test_check_search(struct kunit *test)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(smb2_error_map_table); i++)
+		test_cmp_map(test, &smb2_error_map_table[i]);
+}
+
+static struct kunit_case maperror_test_cases[] = {
+	KUNIT_CASE(maperror_test_check_search),
+	{}
+};
+
+static struct kunit_suite maperror_suite = {
+	.name = "smb2_maperror",
+	.test_cases = maperror_test_cases,
+};
+
+kunit_test_suite(maperror_suite);
+
+MODULE_LICENSE("GPL");