seq_buf: Introduce KUnit tests

Add KUnit tests for the seq_buf API to ensure its correctness and
prevent future regressions, covering the following functions:
- seq_buf_init()
- DECLARE_SEQ_BUF()
- seq_buf_clear()
- seq_buf_puts()
- seq_buf_putc()
- seq_buf_printf()
- seq_buf_get_buf()
- seq_buf_commit()

$ tools/testing/kunit/kunit.py run seq_buf
=================== seq_buf (9 subtests) ===================
[PASSED] seq_buf_init_test
[PASSED] seq_buf_declare_test
[PASSED] seq_buf_clear_test
[PASSED] seq_buf_puts_test
[PASSED] seq_buf_puts_overflow_test
[PASSED] seq_buf_putc_test
[PASSED] seq_buf_printf_test
[PASSED] seq_buf_printf_overflow_test
[PASSED] seq_buf_get_buf_commit_test
===================== [PASSED] seq_buf =====================

Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: David Gow <[e-mail]>
Signed-off-by: Kees Cook <[e-mail]>

lib/Kconfig.debug

···
 
 	  If unsure, say N.
 
+config SEQ_BUF_KUNIT_TEST
+	tristate "KUnit test for seq_buf" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  This builds unit tests for the seq_buf library.
+
+	  If unsure, say N.
+
 config STRING_KUNIT_TEST
 	tristate "KUnit test string functions at runtime" if !KUNIT_ALL_TESTS
 	depends on KUNIT

lib/tests/Makefile

···
 obj-$(CONFIG_PRINTF_KUNIT_TEST) += printf_kunit.o
 obj-$(CONFIG_RANDSTRUCT_KUNIT_TEST) += randstruct_kunit.o
 obj-$(CONFIG_SCANF_KUNIT_TEST) += scanf_kunit.o
+obj-$(CONFIG_SEQ_BUF_KUNIT_TEST) += seq_buf_kunit.o
 obj-$(CONFIG_SIPHASH_KUNIT_TEST) += siphash_kunit.o
 obj-$(CONFIG_SLUB_KUNIT_TEST) += slub_kunit.o
 obj-$(CONFIG_TEST_SORT) += test_sort.o

lib/tests/seq_buf_kunit.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit tests for the seq_buf API
+ *
+ * Copyright (C) 2025, Google LLC.
+ */
+
+#include <kunit/test.h>
+#include <linux/seq_buf.h>
+
+static void seq_buf_init_test(struct kunit *test)
+{
+	char buf[32];
+	struct seq_buf s;
+
+	seq_buf_init(&s, buf, sizeof(buf));
+
+	KUNIT_EXPECT_EQ(test, s.size, 32);
+	KUNIT_EXPECT_EQ(test, s.len, 0);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_EQ(test, seq_buf_buffer_left(&s), 32);
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 0);
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "");
+}
+
+static void seq_buf_declare_test(struct kunit *test)
+{
+	DECLARE_SEQ_BUF(s, 24);
+
+	KUNIT_EXPECT_EQ(test, s.size, 24);
+	KUNIT_EXPECT_EQ(test, s.len, 0);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_EQ(test, seq_buf_buffer_left(&s), 24);
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 0);
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "");
+}
+
+static void seq_buf_clear_test(struct kunit *test)
+{
+	DECLARE_SEQ_BUF(s, 128);
+
+	seq_buf_puts(&s, "hello");
+	KUNIT_EXPECT_EQ(test, s.len, 5);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "hello");
+
+	seq_buf_clear(&s);
+
+	KUNIT_EXPECT_EQ(test, s.len, 0);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "");
+}
+
+static void seq_buf_puts_test(struct kunit *test)
+{
+	DECLARE_SEQ_BUF(s, 16);
+
+	seq_buf_puts(&s, "hello");
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 5);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "hello");
+
+	seq_buf_puts(&s, " world");
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 11);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "hello world");
+}
+
+static void seq_buf_puts_overflow_test(struct kunit *test)
+{
+	DECLARE_SEQ_BUF(s, 10);
+
+	seq_buf_puts(&s, "123456789");
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 9);
+
+	seq_buf_puts(&s, "0");
+	KUNIT_EXPECT_TRUE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 10);
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "123456789");
+
+	seq_buf_clear(&s);
+	KUNIT_EXPECT_EQ(test, s.len, 0);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "");
+}
+
+static void seq_buf_putc_test(struct kunit *test)
+{
+	DECLARE_SEQ_BUF(s, 4);
+
+	seq_buf_putc(&s, 'a');
+	seq_buf_putc(&s, 'b');
+	seq_buf_putc(&s, 'c');
+
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 3);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "abc");
+
+	seq_buf_putc(&s, 'd');
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 4);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "abc");
+
+	seq_buf_putc(&s, 'e');
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 4);
+	KUNIT_EXPECT_TRUE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "abc");
+
+	seq_buf_clear(&s);
+	KUNIT_EXPECT_EQ(test, s.len, 0);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "");
+}
+
+static void seq_buf_printf_test(struct kunit *test)
+{
+	DECLARE_SEQ_BUF(s, 32);
+
+	seq_buf_printf(&s, "hello %s", "world");
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 11);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "hello world");
+
+	seq_buf_printf(&s, " %d", 123);
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 15);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "hello world 123");
+}
+
+static void seq_buf_printf_overflow_test(struct kunit *test)
+{
+	DECLARE_SEQ_BUF(s, 16);
+
+	seq_buf_printf(&s, "%lu", 1234567890UL);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 10);
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "1234567890");
+
+	seq_buf_printf(&s, "%s", "abcdefghij");
+	KUNIT_EXPECT_TRUE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 16);
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "1234567890abcde");
+
+	seq_buf_clear(&s);
+	KUNIT_EXPECT_EQ(test, s.len, 0);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "");
+}
+
+static void seq_buf_get_buf_commit_test(struct kunit *test)
+{
+	DECLARE_SEQ_BUF(s, 16);
+	char *buf;
+	size_t len;
+
+	len = seq_buf_get_buf(&s, &buf);
+	KUNIT_EXPECT_EQ(test, len, 16);
+	KUNIT_EXPECT_PTR_NE(test, buf, NULL);
+
+	memcpy(buf, "hello", 5);
+	seq_buf_commit(&s, 5);
+
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 5);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "hello");
+
+	len = seq_buf_get_buf(&s, &buf);
+	KUNIT_EXPECT_EQ(test, len, 11);
+	KUNIT_EXPECT_PTR_NE(test, buf, NULL);
+
+	memcpy(buf, " worlds!", 8);
+	seq_buf_commit(&s, 6);
+
+	KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 11);
+	KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s));
+	KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "hello world");
+
+	len = seq_buf_get_buf(&s, &buf);
+	KUNIT_EXPECT_EQ(test, len, 5);
+	KUNIT_EXPECT_PTR_NE(test, buf, NULL);
+
+	seq_buf_commit(&s, -1);
+	KUNIT_EXPECT_TRUE(test, seq_buf_has_overflowed(&s));
+}
+
+static struct kunit_case seq_buf_test_cases[] = {
+	KUNIT_CASE(seq_buf_init_test),
+	KUNIT_CASE(seq_buf_declare_test),
+	KUNIT_CASE(seq_buf_clear_test),
+	KUNIT_CASE(seq_buf_puts_test),
+	KUNIT_CASE(seq_buf_puts_overflow_test),
+	KUNIT_CASE(seq_buf_putc_test),
+	KUNIT_CASE(seq_buf_printf_test),
+	KUNIT_CASE(seq_buf_printf_overflow_test),
+	KUNIT_CASE(seq_buf_get_buf_commit_test),
+	{}
+};
+
+static struct kunit_suite seq_buf_test_suite = {
+	.name = "seq_buf",
+	.test_cases = seq_buf_test_cases,
+};
+
+kunit_test_suite(seq_buf_test_suite);
+
+MODULE_DESCRIPTION("Runtime test cases for seq_buf string API");
+MODULE_LICENSE("GPL");