hfs: introduce KUnit tests for HFS string operations

This patch implements the initial Kunit based set of
unit tests for HFS string operations. It checks
functionality of hfs_strcmp(), hfs_hash_dentry(),
and hfs_compare_dentry() methods.

./tools/testing/kunit/kunit.py run --kunitconfig ./fs/hfs/.kunitconfig

[16:04:50] Configuring KUnit Kernel ...
Regenerating .config ...
Populating config with:
$ make ARCH=um O=.kunit olddefconfig
[16:04:51] Building KUnit Kernel ...
Populating config with:
$ make ARCH=um O=.kunit olddefconfig
Building with:
$ make all compile_commands.json scripts_gdb ARCH=um O=.kunit --jobs=22
[16:04:59] Starting KUnit Kernel (1/1)...
[16:04:59] ============================================================
Running tests with:
$ .kunit/linux kunit.enable=1 mem=1G console=tty kunit_shutdown=halt
[16:04:59] ================= hfs_string (3 subtests) ==================
[16:04:59] [PASSED] hfs_strcmp_test
[16:04:59] [PASSED] hfs_hash_dentry_test
[16:04:59] [PASSED] hfs_compare_dentry_test
[16:04:59] =================== [PASSED] hfs_string ====================
[16:04:59] ============================================================
[16:04:59] Testing complete. Ran 3 tests: passed: 3
[16:04:59] Elapsed time: 9.087s total, 1.310s configuring, 7.611s building, 0.125s running

v2
Fix linker error.

v3
Chen Linxuan suggested to use EXPORT_SYMBOL_IF_KUNIT.

Signed-off-by: Viacheslav Dubeyko <[e-mail]>
cc: John Paul Adrian Glaubitz <[e-mail]>
cc: Yangtao Li <[e-mail]>
cc: [e-mail]
cc: Chen Linxuan <[e-mail]>
Reviewed-by: Chen Linxuan <[e-mail]>
Signed-off-by: Viacheslav Dubeyko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Viacheslav Dubeyko <[e-mail]>

fs/hfs/.kunitconfig

···
+CONFIG_KUNIT=y
+CONFIG_HFS_FS=y
+CONFIG_HFS_KUNIT_TEST=y
+CONFIG_BLOCK=y
+CONFIG_BUFFER_HEAD=y
+CONFIG_NLS=y
+CONFIG_LEGACY_DIRECT_IO=y

fs/hfs/Kconfig

···
 
 	  To compile this file system support as a module, choose M here: the
 	  module will be called hfs.
+
+config HFS_KUNIT_TEST
+	tristate "KUnit tests for HFS filesystem" if !KUNIT_ALL_TESTS
+	depends on HFS_FS && KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  This builds KUnit tests for the HFS filesystem.
+
+	  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/.

fs/hfs/Makefile

···
 	    catalog.o dir.o extent.o inode.o attr.o mdb.o \
             part_tbl.o string.o super.o sysdep.o trans.o
 
+# KUnit tests
+obj-$(CONFIG_HFS_KUNIT_TEST) += string_test.o

fs/hfs/string.c

···
 #include "hfs_fs.h"
 #include <linux/dcache.h>
 
+#include <kunit/visibility.h>
+
 /*================ File-local variables ================*/
 
 /*
···
 	this->hash = end_name_hash(hash);
 	return 0;
 }
+EXPORT_SYMBOL_IF_KUNIT(hfs_hash_dentry);
 
 /*
  * Compare two strings in the HFS filename character ordering
···
 	}
 	return len1 - len2;
 }
+EXPORT_SYMBOL_IF_KUNIT(hfs_strcmp);
 
 /*
  * Test for equality of two strings in the HFS filename character ordering.
···
 	}
 	return 0;
 }
+EXPORT_SYMBOL_IF_KUNIT(hfs_compare_dentry);

fs/hfs/string_test.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit tests for HFS string operations
+ *
+ * Copyright (C) 2025 Viacheslav Dubeyko <[e-mail]>
+ */
+
+#include <kunit/test.h>
+#include <linux/dcache.h>
+#include "hfs_fs.h"
+
+/* Test hfs_strcmp function */
+static void hfs_strcmp_test(struct kunit *test)
+{
+	/* Test equal strings */
+	KUNIT_EXPECT_EQ(test, 0, hfs_strcmp("hello", 5, "hello", 5));
+	KUNIT_EXPECT_EQ(test, 0, hfs_strcmp("test", 4, "test", 4));
+	KUNIT_EXPECT_EQ(test, 0, hfs_strcmp("", 0, "", 0));
+
+	/* Test unequal strings */
+	KUNIT_EXPECT_NE(test, 0, hfs_strcmp("hello", 5, "world", 5));
+	KUNIT_EXPECT_NE(test, 0, hfs_strcmp("test", 4, "testing", 7));
+
+	/* Test different lengths */
+	KUNIT_EXPECT_LT(test, hfs_strcmp("test", 4, "testing", 7), 0);
+	KUNIT_EXPECT_GT(test, hfs_strcmp("testing", 7, "test", 4), 0);
+
+	/* Test case insensitive comparison (HFS should handle case) */
+	KUNIT_EXPECT_EQ(test, 0, hfs_strcmp("Test", 4, "TEST", 4));
+	KUNIT_EXPECT_EQ(test, 0, hfs_strcmp("hello", 5, "HELLO", 5));
+
+	/* Test with special characters */
+	KUNIT_EXPECT_EQ(test, 0, hfs_strcmp("file.txt", 8, "file.txt", 8));
+	KUNIT_EXPECT_NE(test, 0, hfs_strcmp("file.txt", 8, "file.dat", 8));
+
+	/* Test boundary cases */
+	KUNIT_EXPECT_EQ(test, 0, hfs_strcmp("a", 1, "a", 1));
+	KUNIT_EXPECT_NE(test, 0, hfs_strcmp("a", 1, "b", 1));
+}
+
+/* Test hfs_hash_dentry function */
+static void hfs_hash_dentry_test(struct kunit *test)
+{
+	struct qstr test_name1, test_name2, test_name3;
+	struct dentry dentry = {};
+	char name1[] = "testfile";
+	char name2[] = "TestFile";
+	char name3[] = "different";
+
+	/* Initialize test strings */
+	test_name1.name = name1;
+	test_name1.len = strlen(name1);
+	test_name1.hash = 0;
+
+	test_name2.name = name2;
+	test_name2.len = strlen(name2);
+	test_name2.hash = 0;
+
+	test_name3.name = name3;
+	test_name3.len = strlen(name3);
+	test_name3.hash = 0;
+
+	/* Test hashing */
+	KUNIT_EXPECT_EQ(test, 0, hfs_hash_dentry(&dentry, &test_name1));
+	KUNIT_EXPECT_EQ(test, 0, hfs_hash_dentry(&dentry, &test_name2));
+	KUNIT_EXPECT_EQ(test, 0, hfs_hash_dentry(&dentry, &test_name3));
+
+	/* Case insensitive names should hash the same */
+	KUNIT_EXPECT_EQ(test, test_name1.hash, test_name2.hash);
+
+	/* Different names should have different hashes */
+	KUNIT_EXPECT_NE(test, test_name1.hash, test_name3.hash);
+}
+
+/* Test hfs_compare_dentry function */
+static void hfs_compare_dentry_test(struct kunit *test)
+{
+	struct qstr test_name;
+	struct dentry dentry = {};
+	char name[] = "TestFile";
+
+	test_name.name = name;
+	test_name.len = strlen(name);
+
+	/* Test exact match */
+	KUNIT_EXPECT_EQ(test, 0, hfs_compare_dentry(&dentry, 8,
+						    "TestFile", &test_name));
+
+	/* Test case insensitive match */
+	KUNIT_EXPECT_EQ(test, 0, hfs_compare_dentry(&dentry, 8,
+						    "testfile", &test_name));
+	KUNIT_EXPECT_EQ(test, 0, hfs_compare_dentry(&dentry, 8,
+						    "TESTFILE", &test_name));
+
+	/* Test different names */
+	KUNIT_EXPECT_EQ(test, 1, hfs_compare_dentry(&dentry, 8,
+						    "DiffFile", &test_name));
+
+	/* Test different lengths */
+	KUNIT_EXPECT_EQ(test, 1, hfs_compare_dentry(&dentry, 7,
+						    "TestFil", &test_name));
+	KUNIT_EXPECT_EQ(test, 1, hfs_compare_dentry(&dentry, 9,
+						    "TestFiles", &test_name));
+
+	/* Test empty string */
+	test_name.name = "";
+	test_name.len = 0;
+	KUNIT_EXPECT_EQ(test, 0, hfs_compare_dentry(&dentry, 0, "", &test_name));
+
+	/* Test HFS_NAMELEN boundary */
+	test_name.name = "This_is_a_very_long_filename_that_exceeds_normal_limits";
+	test_name.len = strlen(test_name.name);
+	KUNIT_EXPECT_EQ(test, 0, hfs_compare_dentry(&dentry, HFS_NAMELEN,
+			"This_is_a_very_long_filename_th", &test_name));
+}
+
+static struct kunit_case hfs_string_test_cases[] = {
+	KUNIT_CASE(hfs_strcmp_test),
+	KUNIT_CASE(hfs_hash_dentry_test),
+	KUNIT_CASE(hfs_compare_dentry_test),
+	{}
+};
+
+static struct kunit_suite hfs_string_test_suite = {
+	.name = "hfs_string",
+	.test_cases = hfs_string_test_cases,
+};
+
+kunit_test_suite(hfs_string_test_suite);
+
+MODULE_DESCRIPTION("KUnit tests for HFS string operations");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");