fat: Add KUnit tests for checksums and timestamps

Add some basic sanity-check tests for the fat_checksum() function and
the fat_time_unix2fat() and fat_time_fat2unix() functions. These unit
tests verify these functions return correct output for a number of test
inputs.

These tests were inspired by -- and serve a similar purpose to -- the
timestamp parsing KUnit tests in ext4[1].

Note that, unlike fat_time_unix2fat, fat_time_fat2unix wasn't previously
exported, so this patch exports it as well. This is required for the
case where we're building the fat and fat_test as modules.

Fixed minor checkpatch coding style errors and typos in commit log:
Shuah Khan <skhan@linuxfoundation.org>

[1]:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/ext4/inode-test.c

Signed-off-by: David Gow <davidgow@google.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Tested-by: Daniel Latypov <dlatypov@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

fs/fat/.kunitconfig

@@ -0,0 +1,5 @@
+CONFIG_KUNIT=y
+CONFIG_FAT_FS=y
+CONFIG_MSDOS_FS=y
+CONFIG_VFAT_FS=y
+CONFIG_FAT_KUNIT_TEST=y

fs/fat/Kconfig

@@ -77,7 +77,7 @@ config VFAT_FS
 
 config FAT_DEFAULT_CODEPAGE
 	int "Default codepage for FAT"
-	depends on MSDOS_FS || VFAT_FS
+	depends on FAT_FS
 	default 437
 	help
 	  This option should be set to the codepage of your FAT filesystems.
@@ -115,3 +115,15 @@ config FAT_DEFAULT_UTF8
 	  Say Y if you use UTF-8 encoding for file names, N otherwise.
 
 	  See <file:Documentation/filesystems/vfat.rst> for more information.
+
+config FAT_KUNIT_TEST
+	tristate "Unit Tests for FAT filesystems" if !KUNIT_ALL_TESTS
+	depends on KUNIT && FAT_FS
+	default KUNIT_ALL_TESTS
+	help
+	  This builds the FAT KUnit tests
+
+	  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/fat/Makefile

@@ -10,3 +10,5 @@ obj-$(CONFIG_MSDOS_FS) += msdos.o
 fat-y := cache.o dir.o fatent.o file.o inode.o misc.o nfs.o
 vfat-y := namei_vfat.o
 msdos-y := namei_msdos.o
+
+obj-$(CONFIG_FAT_KUNIT_TEST) += fat_test.o

fs/fat/fat_test.c

@@ -0,0 +1,196 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit tests for FAT filesystems.
+ *
+ * Copyright (C) 2020 Google LLC.
+ * Author: David Gow <davidgow@google.com>
+ */
+
+#include <kunit/test.h>
+
+#include "fat.h"
+
+static void fat_checksum_test(struct kunit *test)
+{
+	/* With no extension. */
+	KUNIT_EXPECT_EQ(test, fat_checksum("VMLINUX    "), (u8)44);
+	/* With 3-letter extension. */
+	KUNIT_EXPECT_EQ(test, fat_checksum("README  TXT"), (u8)115);
+	/* With short (1-letter) extension. */
+	KUNIT_EXPECT_EQ(test, fat_checksum("ABCDEFGHA  "), (u8)98);
+}
+
+struct fat_timestamp_testcase {
+	const char *name;
+	struct timespec64 ts;
+	__le16 time;
+	__le16 date;
+	u8 cs;
+	int time_offset;
+};
+
+static struct fat_timestamp_testcase time_test_cases[] = {
+	{
+		.name = "Earliest possible UTC (1980-01-01 00:00:00)",
+		.ts = {.tv_sec = 315532800LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(0),
+		.date = cpu_to_le16(33),
+		.cs = 0,
+		.time_offset = 0,
+	},
+	{
+		.name = "Latest possible UTC (2107-12-31 23:59:58)",
+		.ts = {.tv_sec = 4354819198LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(49021),
+		.date = cpu_to_le16(65439),
+		.cs = 0,
+		.time_offset = 0,
+	},
+	{
+		.name = "Earliest possible (UTC-11) (== 1979-12-31 13:00:00 UTC)",
+		.ts = {.tv_sec = 315493200LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(0),
+		.date = cpu_to_le16(33),
+		.cs = 0,
+		.time_offset = 11 * 60,
+	},
+	{
+		.name = "Latest possible (UTC+11) (== 2108-01-01 10:59:58 UTC)",
+		.ts = {.tv_sec = 4354858798LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(49021),
+		.date = cpu_to_le16(65439),
+		.cs = 0,
+		.time_offset = -11 * 60,
+	},
+	{
+		.name = "Leap Day / Year (1996-02-29 00:00:00)",
+		.ts = {.tv_sec = 825552000LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(0),
+		.date = cpu_to_le16(8285),
+		.cs = 0,
+		.time_offset = 0,
+	},
+	{
+		.name = "Year 2000 is leap year (2000-02-29 00:00:00)",
+		.ts = {.tv_sec = 951782400LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(0),
+		.date = cpu_to_le16(10333),
+		.cs = 0,
+		.time_offset = 0,
+	},
+	{
+		.name = "Year 2100 not leap year (2100-03-01 00:00:00)",
+		.ts = {.tv_sec = 4107542400LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(0),
+		.date = cpu_to_le16(61537),
+		.cs = 0,
+		.time_offset = 0,
+	},
+	{
+		.name = "Leap year + timezone UTC+1 (== 2004-02-29 00:30:00 UTC)",
+		.ts = {.tv_sec = 1078014600LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(48064),
+		.date = cpu_to_le16(12380),
+		.cs = 0,
+		.time_offset = -60,
+	},
+	{
+		.name = "Leap year + timezone UTC-1 (== 2004-02-29 23:30:00 UTC)",
+		.ts = {.tv_sec = 1078097400LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(960),
+		.date = cpu_to_le16(12385),
+		.cs = 0,
+		.time_offset = 60,
+	},
+	{
+		.name = "VFAT odd-second resolution (1999-12-31 23:59:59)",
+		.ts = {.tv_sec = 946684799LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(49021),
+		.date = cpu_to_le16(10143),
+		.cs = 100,
+		.time_offset = 0,
+	},
+	{
+		.name = "VFAT 10ms resolution (1980-01-01 00:00:00:0010)",
+		.ts = {.tv_sec = 315532800LL, .tv_nsec = 10000000L},
+		.time = cpu_to_le16(0),
+		.date = cpu_to_le16(33),
+		.cs = 1,
+		.time_offset = 0,
+	},
+};
+
+static void time_testcase_desc(struct fat_timestamp_testcase *t,
+			       char *desc)
+{
+	strscpy(desc, t->name, KUNIT_PARAM_DESC_SIZE);
+}
+
+KUNIT_ARRAY_PARAM(fat_time, time_test_cases, time_testcase_desc);
+
+static void fat_time_fat2unix_test(struct kunit *test)
+{
+	static struct msdos_sb_info fake_sb;
+	struct timespec64 ts;
+	struct fat_timestamp_testcase *testcase =
+		(struct fat_timestamp_testcase *)test->param_value;
+
+	fake_sb.options.tz_set = 1;
+	fake_sb.options.time_offset = testcase->time_offset;
+
+	fat_time_fat2unix(&fake_sb, &ts,
+			  testcase->time,
+			  testcase->date,
+			  testcase->cs);
+	KUNIT_EXPECT_EQ_MSG(test,
+			    testcase->ts.tv_sec,
+			    ts.tv_sec,
+			    "Timestamp mismatch (seconds)\n");
+	KUNIT_EXPECT_EQ_MSG(test,
+			    testcase->ts.tv_nsec,
+			    ts.tv_nsec,
+			    "Timestamp mismatch (nanoseconds)\n");
+}
+
+static void fat_time_unix2fat_test(struct kunit *test)
+{
+	static struct msdos_sb_info fake_sb;
+	__le16 date, time;
+	u8 cs;
+	struct fat_timestamp_testcase *testcase =
+		(struct fat_timestamp_testcase *)test->param_value;
+
+	fake_sb.options.tz_set = 1;
+	fake_sb.options.time_offset = testcase->time_offset;
+
+	fat_time_unix2fat(&fake_sb, &testcase->ts,
+			  &time, &date, &cs);
+	KUNIT_EXPECT_EQ_MSG(test,
+			    le16_to_cpu(testcase->time),
+			    le16_to_cpu(time),
+			    "Time mismatch\n");
+	KUNIT_EXPECT_EQ_MSG(test,
+			    le16_to_cpu(testcase->date),
+			    le16_to_cpu(date),
+			    "Date mismatch\n");
+	KUNIT_EXPECT_EQ_MSG(test,
+			    testcase->cs,
+			    cs,
+			    "Centisecond mismatch\n");
+}
+
+static struct kunit_case fat_test_cases[] = {
+	KUNIT_CASE(fat_checksum_test),
+	KUNIT_CASE_PARAM(fat_time_fat2unix_test, fat_time_gen_params),
+	KUNIT_CASE_PARAM(fat_time_unix2fat_test, fat_time_gen_params),
+	{},
+};
+
+static struct kunit_suite fat_test_suite = {
+	.name = "fat_test",
+	.test_cases = fat_test_cases,
+};
+
+kunit_test_suites(&fat_test_suite);
+
+MODULE_LICENSE("GPL v2");

fs/fat/misc.c

@@ -230,6 +230,9 @@ void fat_time_fat2unix(struct msdos_sb_info *sbi, struct timespec64 *ts,
 	}
 }
 
+/* Export fat_time_fat2unix() for the fat_test KUnit tests. */
+EXPORT_SYMBOL_GPL(fat_time_fat2unix);
+
 /* Convert linear UNIX date to a FAT time/date pair. */
 void fat_time_unix2fat(struct msdos_sb_info *sbi, struct timespec64 *ts,
 		       __le16 *time, __le16 *date, u8 *time_cs)