[PATCH v2] fat: add KUnit tests for timestamp conversion helpers

[aviv.daum@gmail.com]

From: avivdaum <aviv.daum@gmail.com>

Extend fat_test with coverage for FAT timestamp edge cases that are not
currently exercised.

Add tests for fat_time_unix2fat() clamping at the UTC boundaries and
when time_offset pushes an otherwise valid timestamp outside the FAT
date range. Also cover the NULL time_cs path used by existing callers,
and verify fat_truncate_atime() truncation across timezone offsets.

Signed-off-by: avivdaum <aviv.daum@gmail.com>

v2:
- Compare __le16 values directly in unix2fat tests

---
 fs/fat/fat_test.c | 181 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 173 insertions(+), 8 deletions(-)

diff --git a/fs/fat/fat_test.c b/fs/fat/fat_test.c
index 1f0062659..5c97a7fcc 100644
--- a/fs/fat/fat_test.c
+++ b/fs/fat/fat_test.c
@@ -29,6 +29,22 @@ struct fat_timestamp_testcase {
 	int time_offset;
 };
 
+struct fat_unix2fat_clamp_testcase {
+	const char *name;
+	struct timespec64 ts;
+	__le16 time;
+	__le16 date;
+	u8 cs;
+	int time_offset;
+};
+
+struct fat_truncate_atime_testcase {
+	const char *name;
+	struct timespec64 ts;
+	struct timespec64 expected;
+	int time_offset;
+};
+
 static struct fat_timestamp_testcase time_test_cases[] = {
 	{
 		.name = "Earliest possible UTC (1980-01-01 00:00:00)",
@@ -120,13 +136,92 @@ static struct fat_timestamp_testcase time_test_cases[] = {
 	},
 };
 
+static struct fat_unix2fat_clamp_testcase unix2fat_clamp_test_cases[] = {
+	{
+		.name = "Clamp to earliest FAT date for 1979-12-31 23:59:59 UTC",
+		.ts = {.tv_sec = 315532799LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(0),
+		.date = cpu_to_le16(33),
+		.cs = 0,
+		.time_offset = 0,
+	},
+	{
+		.name = "Clamp after time_offset=-60 pushes 1980-01-01 00:30 UTC below 1980",
+		.ts = {.tv_sec = 315534600LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(0),
+		.date = cpu_to_le16(33),
+		.cs = 0,
+		.time_offset = -60,
+	},
+	{
+		.name = "Clamp to latest FAT date for 2108-01-01 00:00:00 UTC",
+		.ts = {.tv_sec = 4354819200LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(49021),
+		.date = cpu_to_le16(65439),
+		.cs = 199,
+		.time_offset = 0,
+	},
+	{
+		.name = "Clamp after time_offset=60 pushes 2107-12-31 23:30 UTC beyond 2107",
+		.ts = {.tv_sec = 4354817400LL, .tv_nsec = 0L},
+		.time = cpu_to_le16(49021),
+		.date = cpu_to_le16(65439),
+		.cs = 199,
+		.time_offset = 60,
+	},
+};
+
+static struct fat_truncate_atime_testcase truncate_atime_test_cases[] = {
+	{
+		.name = "UTC atime truncates to 2004-02-29 00:00:00",
+		.ts = {.tv_sec = 1078058096LL, .tv_nsec = 789000000L},
+		.expected = {.tv_sec = 1078012800LL, .tv_nsec = 0L},
+		.time_offset = 0,
+	},
+	{
+		.name = "time_offset=-60 truncates 2004-02-29 00:30 UTC to previous local midnight",
+		.ts = {.tv_sec = 1078014645LL, .tv_nsec = 123000000L},
+		.expected = {.tv_sec = 1077930000LL, .tv_nsec = 0L},
+		.time_offset = -60,
+	},
+	{
+		.name = "time_offset=60 truncates 2004-02-29 23:30 UTC to next local midnight",
+		.ts = {.tv_sec = 1078097445LL, .tv_nsec = 123000000L},
+		.expected = {.tv_sec = 1078095600LL, .tv_nsec = 0L},
+		.time_offset = 60,
+	},
+};
+
 static void time_testcase_desc(struct fat_timestamp_testcase *t,
 			       char *desc)
 {
 	strscpy(desc, t->name, KUNIT_PARAM_DESC_SIZE);
 }
 
+static void unix2fat_clamp_testcase_desc(struct fat_unix2fat_clamp_testcase *t,
+					 char *desc)
+{
+	strscpy(desc, t->name, KUNIT_PARAM_DESC_SIZE);
+}
+
+static void truncate_atime_testcase_desc(struct fat_truncate_atime_testcase *t,
+					 char *desc)
+{
+	strscpy(desc, t->name, KUNIT_PARAM_DESC_SIZE);
+}
+
 KUNIT_ARRAY_PARAM(fat_time, time_test_cases, time_testcase_desc);
+KUNIT_ARRAY_PARAM(fat_unix2fat_clamp, unix2fat_clamp_test_cases,
+		  unix2fat_clamp_testcase_desc);
+KUNIT_ARRAY_PARAM(fat_truncate_atime, truncate_atime_test_cases,
+		  truncate_atime_testcase_desc);
+
+static void fat_test_set_time_offset(struct msdos_sb_info *sbi, int time_offset)
+{
+	*sbi = (struct msdos_sb_info){};
+	sbi->options.tz_set = 1;
+	sbi->options.time_offset = time_offset;
+}
 
 static void fat_time_fat2unix_test(struct kunit *test)
 {
@@ -135,8 +230,7 @@ static void fat_time_fat2unix_test(struct kunit *test)
 	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_test_set_time_offset(&fake_sb, testcase->time_offset);
 
 	fat_time_fat2unix(&fake_sb, &ts,
 			  testcase->time,
@@ -160,18 +254,17 @@ static void fat_time_unix2fat_test(struct kunit *test)
 	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_test_set_time_offset(&fake_sb, 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),
+			    testcase->time,
+			    time,
 			    "Time mismatch\n");
 	KUNIT_EXPECT_EQ_MSG(test,
-			    le16_to_cpu(testcase->date),
-			    le16_to_cpu(date),
+			    testcase->date,
+			    date,
 			    "Date mismatch\n");
 	KUNIT_EXPECT_EQ_MSG(test,
 			    testcase->cs,
@@ -179,10 +272,82 @@ static void fat_time_unix2fat_test(struct kunit *test)
 			    "Centisecond mismatch\n");
 }
 
+static void fat_time_unix2fat_clamp_test(struct kunit *test)
+{
+	static struct msdos_sb_info fake_sb;
+	__le16 date, time;
+	u8 cs;
+	struct fat_unix2fat_clamp_testcase *testcase =
+		(struct fat_unix2fat_clamp_testcase *)test->param_value;
+
+	fat_test_set_time_offset(&fake_sb, testcase->time_offset);
+
+	fat_time_unix2fat(&fake_sb, &testcase->ts, &time, &date, &cs);
+	KUNIT_EXPECT_EQ_MSG(test,
+			    testcase->time,
+			    time,
+			    "Clamped time mismatch\n");
+	KUNIT_EXPECT_EQ_MSG(test,
+			    testcase->date,
+			    date,
+			    "Clamped date mismatch\n");
+	KUNIT_EXPECT_EQ_MSG(test,
+			    testcase->cs,
+			    cs,
+			    "Clamped centisecond mismatch\n");
+}
+
+static void fat_time_unix2fat_no_csec_test(struct kunit *test)
+{
+	static struct msdos_sb_info fake_sb;
+	struct timespec64 ts = {
+		.tv_sec = 946684799LL,
+		.tv_nsec = 0L,
+	};
+	__le16 date, time;
+
+	fat_test_set_time_offset(&fake_sb, 0);
+
+	fat_time_unix2fat(&fake_sb, &ts, &time, &date, NULL);
+	KUNIT_EXPECT_EQ_MSG(test,
+			    49021,
+			    le16_to_cpu(time),
+			    "Time mismatch without centiseconds\n");
+	KUNIT_EXPECT_EQ_MSG(test,
+			    10143,
+			    le16_to_cpu(date),
+			    "Date mismatch without centiseconds\n");
+}
+
+static void fat_truncate_atime_test(struct kunit *test)
+{
+	static struct msdos_sb_info fake_sb;
+	struct timespec64 actual;
+	struct fat_truncate_atime_testcase *testcase =
+		(struct fat_truncate_atime_testcase *)test->param_value;
+
+	fat_test_set_time_offset(&fake_sb, testcase->time_offset);
+
+	actual = fat_truncate_atime(&fake_sb, &testcase->ts);
+	KUNIT_EXPECT_EQ_MSG(test,
+			    testcase->expected.tv_sec,
+			    actual.tv_sec,
+			    "Atime truncation seconds mismatch\n");
+	KUNIT_EXPECT_EQ_MSG(test,
+			    testcase->expected.tv_nsec,
+			    actual.tv_nsec,
+			    "Atime truncation nanoseconds 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),
+	KUNIT_CASE_PARAM(fat_time_unix2fat_clamp_test,
+			 fat_unix2fat_clamp_gen_params),
+	KUNIT_CASE(fat_time_unix2fat_no_csec_test),
+	KUNIT_CASE_PARAM(fat_truncate_atime_test,
+			 fat_truncate_atime_gen_params),
 	{},
 };
 
-- 
2.34.1