kernel-testing

Kernel Testing

Purpose

Guide agents through testing the Linux kernel: KUnit in-kernel unit tests, the kselftest harness, syzkaller fuzzing with kcov coverage, Linux Test Project (LTP) syscall regression, and KernelCI integration for continuous testing.

When to Use

• Writing unit tests for kernel library code or driver helpers
• Adding regression tests to tools/testing/selftests/
• Fuzzing syscalls and ioctl interfaces with syzkaller
• Measuring kernel code coverage with kcov
• Running LTP for syscall compatibility validation
• Setting up CI for kernel patches

Workflow

1. KUnit — in-kernel unit tests

// test_example.c
#include <kunit/test.h>

static void example_test(struct kunit *test)
{
    KUNIT_EXPECT_EQ(test, 1 + 1, 2);
    KUNIT_ASSERT_NOT_ERR_OR_NULL(test, kmalloc(16, GFP_KERNEL));
}

static struct kunit_case example_test_cases[] = {
    KUNIT_CASE(example_test),
    {}
};

static struct kunit_suite example_suite = {
    .name = "example",
    .test_cases = example_test_cases,
};
kunit_test_suite(example_suite);

MODULE_LICENSE("GPL");

# Makefile
obj-$(CONFIG_KUNIT) += test_example.o

# Run KUnit (in-tree)
./tools/testing/kunit/kunit.py run

# Run specific test
./tools/testing/kunit/kunit.py run --filter example

# With cross-compilation
./tools/testing/kunit/kunit.py run --cross_compile aarch64-linux-gnu- \
    --arch arm64

KUnit runs in kernel context (UMH or dedicated kunit kernel). Use kunit_kmalloc for test allocations.

2. kselftest harness

# Build all selftests
cd tools/testing/selftests
make -j$(nproc)

# Run all
make run_tests

# Run specific test
./memfd/memfd_test
./mount/run_unprivileged_remount.sh

Adding a new selftest:

tools/testing/selftests/mytest/
├── Makefile
├── mytest.c
└── config        # optional kconfig requirements

# tools/testing/selftests/mytest/Makefile
CFLAGS += -Wall
TEST_GEN_FILES := mytest
TEST_PROGS := mytest

include ../lib.mk