Add a KUnit test for strnlen() to verify correctness across
different string lengths and memory alignments.

Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
---
 lib/tests/string_kunit.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index 88da97e50c8e..89fe52378442 100644
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -129,6 +129,35 @@ static void string_test_strlen(struct kunit *test)
 	}
 }
 
+static void string_test_strnlen(struct kunit *test)
+{
+	char *s;
+	size_t len, offset;
+	const size_t buf_size = STRING_TEST_MAX_LEN + STRING_TEST_MAX_OFFSET + 1;
+
+	s = kunit_kzalloc(test, buf_size, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, s);
+
+	memset(s, 'A', buf_size);
+	s[buf_size - 1] = '\0';
+
+	for (offset = 0; offset < STRING_TEST_MAX_OFFSET; offset++) {
+		for (len = 0; len <= STRING_TEST_MAX_LEN; len++) {
+			s[offset + len] = '\0';
+
+			if (len > 0)
+				KUNIT_EXPECT_EQ(test, strnlen(s + offset, len - 1), len - 1);
+
+			KUNIT_EXPECT_EQ(test, strnlen(s + offset, len), len);
+
+			KUNIT_EXPECT_EQ(test, strnlen(s + offset, len + 1), len);
+			KUNIT_EXPECT_EQ(test, strnlen(s + offset, len + 10), len);
+
+			s[offset + len] = 'A';
+		}
+	}
+}
+
 static void string_test_strchr(struct kunit *test)
 {
 	const char *test_string = "abcdefghijkl";
@@ -644,6 +673,7 @@ static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_memset32),
 	KUNIT_CASE(string_test_memset64),
 	KUNIT_CASE(string_test_strlen),
+	KUNIT_CASE(string_test_strnlen),
 	KUNIT_CASE(string_test_strchr),
 	KUNIT_CASE(string_test_strnchr),
 	KUNIT_CASE(string_test_strspn),
-- 
2.25.1

On Tue, Jan 13, 2026 at 04:27:40PM +0800, Feng Jiang wrote:
> Add a KUnit test for strnlen() to verify correctness across
> different string lengths and memory alignments.

...

> +	for (offset = 0; offset < STRING_TEST_MAX_OFFSET; offset++) {
> +		for (len = 0; len <= STRING_TEST_MAX_LEN; len++) {
> +			s[offset + len] = '\0';

This should be one or two characters further so you check should also check for
non-NUL terminated strings...

> +			if (len > 0)
> +				KUNIT_EXPECT_EQ(test, strnlen(s + offset, len - 1), len - 1);

...or make more tests, with len - 2 at least.

> +			KUNIT_EXPECT_EQ(test, strnlen(s + offset, len), len);

> +			KUNIT_EXPECT_EQ(test, strnlen(s + offset, len + 1), len);

I would also add + 2 test case.

> +			KUNIT_EXPECT_EQ(test, strnlen(s + offset, len + 10), len);

> +			s[offset + len] = 'A';
> +		}
> +	}
> +}

-- 
With Best Regards,
Andy Shevchenko