Overview
In this article, we will discuss various frameworks and tools for testing the Linux kernel. First, we will introduce the LTP (Linux Test Project) project. Then, we'll discuss other testing tools and frameworks. Finally, we will discuss testing of new Linux drivers that we cannot test using regular kernel testing tools.
LTP
URL: https://github.com/linux-test-project/ltp
LTP is an open source collection of automation tools that we can use to create build processes, perform automated tests, and debug the Linux kernel. The LTP project is jointly developed by IBM, Cisco, RHEL and other organizations.
Build System
LTP's build system provides the structure for Linux kernel projects. Not only that, it also uses a new Makefile system that provides an enhanced build process, making the maintenance of Linux projects more manageable.
C Test Cases
We can write LTP test cases in C language or a portable POSIX compatible shell language. The test cases use the LTP test application programming interface (API), which is written entirely in C language. Additionally, we can write test cases for glibc and musl C libraries.
Autotest
URL: https://github.com/autotest/autotest
Autotest is a testing framework designed specifically for testing the Linux kernel. It provides modules for building fully automated test grids.
Autotest module includes
Client module, used to actually execute the tests within the project directory
Server module, which allows us to manage test clients on multiple remote machines
Autotest Database module, used to store the results of the test grid Scheduler
, used to execute and test the grid Related cron jobs
Command line interface using Autotest
A web frontend for visualizing test results and scheduling jobs
For rigorous testing, we can also combine LTP test cases with the Autotest scheduler, since Autotest does not provide for testing Linux The kernel's C testing API.
Kmemleak
Kmemleak is a development feature of the mainline Linux kernel. Memory allocated by the kernel sometimes cannot be freed. Therefore, it can be both a performance issue and a security hazard.
Using Kmemleak, we can check for memory leaks generated by the kernel. However, it does not fix the problem, but instead tracks possible leaks and reports them to /sys/kernel/debug/memleak. In a way, Kmemleak is very similar to garbage collectors in high-level languages such as Java and C#.
Additionally, if we are using the Linux kernel, we can also use this feature by enabling "CONFIG_DEBUG_KMEMLEAK" in the kernel configuration. In most popular distributions, this feature is disabled by default:
$ zgrep "CONFIG_DEBUG_KMEMLEAK" /proc/config.gz
# CONFIG_DEBUG_KMEMLEAK is not setThis makes sense since we don't need it in production.
Kmemcheck
Like Kmemleak, Kmemcheck is also a developed feature of the Linux kernel. However, they perform different tasks.
Kmemcheck is responsible for checking whether the kernel code accesses uninitialized structures in memory. For example, the kernel allocates a block of memory, but does not fill it up, and then attempts to access the location. This can cause serious bugs and performance issues.
It should be noted that this feature is only available on x86 systems.
Linaro LAVA
LAVA (Linaro Automation and Validation Architecture) is a continuous integration for deploying operating systems onto physical and virtual hardware to run tests. These tests include startup, bootloader, and system-level tests. It is designed specifically for ARM systems.
We can use LAVA to check the validity of the changes we have made to the kernel code. Not only that, we can also check if the kernel is optimized both in terms of speed and size. LAVA then writes these metrics to a file for further analysis.
The LAVA framework is primarily used for testing mobile operating systems since most mobile phones use ARM or some form of ARM architecture.
Debugger
A debugger is a tool that allows us to execute program code line by line. It provides us with an easy way to monitor program flow and find obscure errors. However, we should know that the step debugger does not perform unit testing.
GDB
On Linux, we have GDB (GNU Debugger) and KGDB (Kernel GDB). GDB is a universal debugger that allows us to debug code in multiple programming languages, including C. Although we cannot use GDB to debug the kernel code directly, we can set up QEMU through GDB and easily view the executing kernel code.
KGDB
KGDB is a debugger for BSD operating systems and Linux. To use KGDB we need two machines connected via serial connection or firewire. One runs the kernel and the other runs the debugger. The two machines communicate through the GDB remote protocol.
Device Driver Testing
Testing Linux device drivers can become very tedious because there is no magic bullet for testing Linux device drivers. Therefore, all testing must be done manually on physical hardware. Although we can test the driver on a virtual machine, it may not work properly due to the abstraction layer added by the virtual machine.
In order to test the driver, we need to manually load the driver after booting Linux and check for initialization errors. Afterwards, we can use the debugger and in some cases perform automated testing.
The following are supporting learning materials. For those who are doing [software testing], it should be the most comprehensive and complete preparation warehouse. This warehouse has also accompanied me through the most difficult journey. I hope it can also help you!
