Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

8 files changed, 1340 insertions, 0 deletions

diff --git a/Documentation/dev-tools/kunit/api/index.rst b/Documentation/dev-tools/kunit/api/index.rst
new file mode 100644
index 000000000..9b9bffe5d
--- /dev/null
+++ b/Documentation/dev-tools/kunit/api/index.rst
@@ -0,0 +1,16 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=============
+API Reference
+=============
+.. toctree::
+
+	test
+
+This section documents the KUnit kernel testing API. It is divided into the
+following sections:
+
+================================= ==============================================
+:doc:`test`                       documents all of the standard testing API
+                                  excluding mocking or mocking related features.
+================================= ==============================================
diff --git a/Documentation/dev-tools/kunit/api/test.rst b/Documentation/dev-tools/kunit/api/test.rst
new file mode 100644
index 000000000..aaa97f17e
--- /dev/null
+++ b/Documentation/dev-tools/kunit/api/test.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========
+Test API
+========
+
+This file documents all of the standard testing API excluding mocking or mocking
+related features.
+
+.. kernel-doc:: include/kunit/test.h
+   :internal:
diff --git a/Documentation/dev-tools/kunit/faq.rst b/Documentation/dev-tools/kunit/faq.rst
new file mode 100644
index 000000000..8d5029ad2
--- /dev/null
+++ b/Documentation/dev-tools/kunit/faq.rst
@@ -0,0 +1,103 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==========================
+Frequently Asked Questions
+==========================
+
+How is this different from Autotest, kselftest, etc?
+====================================================
+KUnit is a unit testing framework. Autotest, kselftest (and some others) are
+not.
+
+A `unit test <https://martinfowler.com/bliki/UnitTest.html>`_ is supposed to
+test a single unit of code in isolation, hence the name. A unit test should be
+the finest granularity of testing and as such should allow all possible code
+paths to be tested in the code under test; this is only possible if the code
+under test is very small and does not have any external dependencies outside of
+the test's control like hardware.
+
+There are no testing frameworks currently available for the kernel that do not
+require installing the kernel on a test machine or in a VM and all require
+tests to be written in userspace and run on the kernel under test; this is true
+for Autotest, kselftest, and some others, disqualifying any of them from being
+considered unit testing frameworks.
+
+Does KUnit support running on architectures other than UML?
+===========================================================
+
+Yes, well, mostly.
+
+For the most part, the KUnit core framework (what you use to write the tests)
+can compile to any architecture; it compiles like just another part of the
+kernel and runs when the kernel boots, or when built as a module, when the
+module is loaded.  However, there is some infrastructure,
+like the KUnit Wrapper (``tools/testing/kunit/kunit.py``) that does not support
+other architectures.
+
+In short, this means that, yes, you can run KUnit on other architectures, but
+it might require more work than using KUnit on UML.
+
+For more information, see :ref:`kunit-on-non-uml`.
+
+What is the difference between a unit test and these other kinds of tests?
+==========================================================================
+Most existing tests for the Linux kernel would be categorized as an integration
+test, or an end-to-end test.
+
+- A unit test is supposed to test a single unit of code in isolation, hence the
+  name. A unit test should be the finest granularity of testing and as such
+  should allow all possible code paths to be tested in the code under test; this
+  is only possible if the code under test is very small and does not have any
+  external dependencies outside of the test's control like hardware.
+- An integration test tests the interaction between a minimal set of components,
+  usually just two or three. For example, someone might write an integration
+  test to test the interaction between a driver and a piece of hardware, or to
+  test the interaction between the userspace libraries the kernel provides and
+  the kernel itself; however, one of these tests would probably not test the
+  entire kernel along with hardware interactions and interactions with the
+  userspace.
+- An end-to-end test usually tests the entire system from the perspective of the
+  code under test. For example, someone might write an end-to-end test for the
+  kernel by installing a production configuration of the kernel on production
+  hardware with a production userspace and then trying to exercise some behavior
+  that depends on interactions between the hardware, the kernel, and userspace.
+
+KUnit isn't working, what should I do?
+======================================
+
+Unfortunately, there are a number of things which can break, but here are some
+things to try.
+
+1. Try running ``./tools/testing/kunit/kunit.py run`` with the ``--raw_output``
+   parameter. This might show details or error messages hidden by the kunit_tool
+   parser.
+2. Instead of running ``kunit.py run``, try running ``kunit.py config``,
+   ``kunit.py build``, and ``kunit.py exec`` independently. This can help track
+   down where an issue is occurring. (If you think the parser is at fault, you
+   can run it manually against stdin or a file with ``kunit.py parse``.)
+3. Running the UML kernel directly can often reveal issues or error messages
+   kunit_tool ignores. This should be as simple as running ``./vmlinux`` after
+   building the UML kernel (e.g., by using ``kunit.py build``). Note that UML
+   has some unusual requirements (such as the host having a tmpfs filesystem
+   mounted), and has had issues in the past when built statically and the host
+   has KASLR enabled. (On older host kernels, you may need to run ``setarch
+   `uname -m` -R ./vmlinux`` to disable KASLR.)
+4. Make sure the kernel .config has ``CONFIG_KUNIT=y`` and at least one test
+   (e.g. ``CONFIG_KUNIT_EXAMPLE_TEST=y``). kunit_tool will keep its .config
+   around, so you can see what config was used after running ``kunit.py run``.
+   It also preserves any config changes you might make, so you can
+   enable/disable things with ``make ARCH=um menuconfig`` or similar, and then
+   re-run kunit_tool.
+5. Try to run ``make ARCH=um defconfig`` before running ``kunit.py run``. This
+   may help clean up any residual config items which could be causing problems.
+6. Finally, try running KUnit outside UML. KUnit and KUnit tests can be
+   built into any kernel, or can be built as a module and loaded at runtime.
+   Doing so should allow you to determine if UML is causing the issue you're
+   seeing. When tests are built-in, they will execute when the kernel boots, and
+   modules will automatically execute associated tests when loaded. Test results
+   can be collected from ``/sys/kernel/debug/kunit/<test suite>/results``, and
+   can be parsed with ``kunit.py parse``. For more details, see "KUnit on
+   non-UML architectures" in :doc:`usage`.
+
+If none of the above tricks help, you are always welcome to email any issues to
+kunit-dev@googlegroups.com.
diff --git a/Documentation/dev-tools/kunit/index.rst b/Documentation/dev-tools/kunit/index.rst
new file mode 100644
index 000000000..c234a3ab3
--- /dev/null
+++ b/Documentation/dev-tools/kunit/index.rst
@@ -0,0 +1,94 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=========================================
+KUnit - Unit Testing for the Linux Kernel
+=========================================
+
+.. toctree::
+	:maxdepth: 2
+
+	start
+	usage
+	kunit-tool
+	api/index
+	style
+	faq
+
+What is KUnit?
+==============
+
+KUnit is a lightweight unit testing and mocking framework for the Linux kernel.
+
+KUnit is heavily inspired by JUnit, Python's unittest.mock, and
+Googletest/Googlemock for C++. KUnit provides facilities for defining unit test
+cases, grouping related test cases into test suites, providing common
+infrastructure for running tests, and much more.
+
+KUnit consists of a kernel component, which provides a set of macros for easily
+writing unit tests. Tests written against KUnit will run on kernel boot if
+built-in, or when loaded if built as a module. These tests write out results to
+the kernel log in `TAP <https://testanything.org/>`_ format.
+
+To make running these tests (and reading the results) easier, KUnit offers
+:doc:`kunit_tool <kunit-tool>`, which builds a `User Mode Linux
+<http://user-mode-linux.sourceforge.net>`_ kernel, runs it, and parses the test
+results. This provides a quick way of running KUnit tests during development,
+without requiring a virtual machine or separate hardware.
+
+Get started now: :doc:`start`
+
+Why KUnit?
+==========
+
+A unit test is supposed to test a single unit of code in isolation, hence the
+name. A unit test should be the finest granularity of testing and as such should
+allow all possible code paths to be tested in the code under test; this is only
+possible if the code under test is very small and does not have any external
+dependencies outside of the test's control like hardware.
+
+KUnit provides a common framework for unit tests within the kernel.
+
+KUnit tests can be run on most architectures, and most tests are architecture
+independent. All built-in KUnit tests run on kernel startup.  Alternatively,
+KUnit and KUnit tests can be built as modules and tests will run when the test
+module is loaded.
+
+.. note::
+
+        KUnit can also run tests without needing a virtual machine or actual
+        hardware under User Mode Linux. User Mode Linux is a Linux architecture,
+        like ARM or x86, which compiles the kernel as a Linux executable. KUnit
+        can be used with UML either by building with ``ARCH=um`` (like any other
+        architecture), or by using :doc:`kunit_tool <kunit-tool>`.
+
+KUnit is fast. Excluding build time, from invocation to completion KUnit can run
+several dozen tests in only 10 to 20 seconds; this might not sound like a big
+deal to some people, but having such fast and easy to run tests fundamentally
+changes the way you go about testing and even writing code in the first place.
+Linus himself said in his `git talk at Google
+<https://gist.github.com/lorn/1272686/revisions#diff-53c65572127855f1b003db4064a94573R874>`_:
+
+	"... a lot of people seem to think that performance is about doing the
+	same thing, just doing it faster, and that is not true. That is not what
+	performance is all about. If you can do something really fast, really
+	well, people will start using it differently."
+
+In this context Linus was talking about branching and merging,
+but this point also applies to testing. If your tests are slow, unreliable, are
+difficult to write, and require a special setup or special hardware to run,
+then you wait a lot longer to write tests, and you wait a lot longer to run
+tests; this means that tests are likely to break, unlikely to test a lot of
+things, and are unlikely to be rerun once they pass. If your tests are really
+fast, you run them all the time, every time you make a change, and every time
+someone sends you some code. Why trust that someone ran all their tests
+correctly on every change when you can just run them yourself in less time than
+it takes to read their test log?
+
+How do I use it?
+================
+
+*   :doc:`start` - for new users of KUnit
+*   :doc:`usage` - for a more detailed explanation of KUnit features
+*   :doc:`api/index` - for the list of KUnit APIs used for testing
+*   :doc:`kunit-tool` - for more information on the kunit_tool helper script
+*   :doc:`faq` - for answers to some common questions about KUnit
diff --git a/Documentation/dev-tools/kunit/kunit-tool.rst b/Documentation/dev-tools/kunit/kunit-tool.rst
new file mode 100644
index 000000000..29ae2fee8
--- /dev/null
+++ b/Documentation/dev-tools/kunit/kunit-tool.rst
@@ -0,0 +1,57 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================
+kunit_tool How-To
+=================
+
+What is kunit_tool?
+===================
+
+kunit_tool is a script (``tools/testing/kunit/kunit.py``) that aids in building
+the Linux kernel as UML (`User Mode Linux
+<http://user-mode-linux.sourceforge.net/>`_), running KUnit tests, parsing
+the test results and displaying them in a user friendly manner.
+
+kunit_tool addresses the problem of being able to run tests without needing a
+virtual machine or actual hardware with User Mode Linux. User Mode Linux is a
+Linux architecture, like ARM or x86; however, unlike other architectures it
+compiles the kernel as a standalone Linux executable that can be run like any
+other program directly inside of a host operating system. To be clear, it does
+not require any virtualization support: it is just a regular program.
+
+What is a .kunitconfig?
+=======================
+
+It's just a defconfig that kunit_tool looks for in the base directory.
+kunit_tool uses it to generate a .config as you might expect. In addition, it
+verifies that the generated .config contains the CONFIG options in the
+.kunitconfig; the reason it does this is so that it is easy to be sure that a
+CONFIG that enables a test actually ends up in the .config.
+
+How do I use kunit_tool?
+========================
+
+If a kunitconfig is present at the root directory, all you have to do is:
+
+.. code-block:: bash
+
+	./tools/testing/kunit/kunit.py run
+
+However, you most likely want to use it with the following options:
+
+.. code-block:: bash
+
+	./tools/testing/kunit/kunit.py run --timeout=30 --jobs=`nproc --all`
+
+- ``--timeout`` sets a maximum amount of time to allow tests to run.
+- ``--jobs`` sets the number of threads to use to build the kernel.
+
+.. note::
+	This command will work even without a .kunitconfig file: if no
+        .kunitconfig is present, a default one will be used instead.
+
+For a list of all the flags supported by kunit_tool, you can run:
+
+.. code-block:: bash
+
+	./tools/testing/kunit/kunit.py run --help
diff --git a/Documentation/dev-tools/kunit/start.rst b/Documentation/dev-tools/kunit/start.rst
new file mode 100644
index 000000000..454f30781
--- /dev/null
+++ b/Documentation/dev-tools/kunit/start.rst
@@ -0,0 +1,237 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+Getting Started
+===============
+
+Installing dependencies
+=======================
+KUnit has the same dependencies as the Linux kernel. As long as you can build
+the kernel, you can run KUnit.
+
+Running tests with the KUnit Wrapper
+====================================
+Included with KUnit is a simple Python wrapper which runs tests under User Mode
+Linux, and formats the test results.
+
+The wrapper can be run with:
+
+.. code-block:: bash
+
+	./tools/testing/kunit/kunit.py run
+
+For more information on this wrapper (also called kunit_tool) check out the
+:doc:`kunit-tool` page.
+
+Creating a .kunitconfig
+-----------------------
+If you want to run a specific set of tests (rather than those listed in the
+KUnit defconfig), you can provide Kconfig options in the ``.kunitconfig`` file.
+This file essentially contains the regular Kernel config, with the specific
+test targets as well. The ``.kunitconfig`` should also contain any other config
+options required by the tests.
+
+A good starting point for a ``.kunitconfig`` is the KUnit defconfig:
+
+.. code-block:: bash
+
+	cd $PATH_TO_LINUX_REPO
+	cp arch/um/configs/kunit_defconfig .kunitconfig
+
+You can then add any other Kconfig options you wish, e.g.:
+
+.. code-block:: none
+
+	CONFIG_LIST_KUNIT_TEST=y
+
+:doc:`kunit_tool <kunit-tool>` will ensure that all config options set in
+``.kunitconfig`` are set in the kernel ``.config`` before running the tests.
+It'll warn you if you haven't included the dependencies of the options you're
+using.
+
+.. note::
+   Note that removing something from the ``.kunitconfig`` will not trigger a
+   rebuild of the ``.config`` file: the configuration is only updated if the
+   ``.kunitconfig`` is not a subset of ``.config``. This means that you can use
+   other tools (such as make menuconfig) to adjust other config options.
+
+
+Running the tests (KUnit Wrapper)
+---------------------------------
+
+To make sure that everything is set up correctly, simply invoke the Python
+wrapper from your kernel repo:
+
+.. code-block:: bash
+
+	./tools/testing/kunit/kunit.py run
+
+.. note::
+   You may want to run ``make mrproper`` first.
+
+If everything worked correctly, you should see the following:
+
+.. code-block:: bash
+
+	Generating .config ...
+	Building KUnit Kernel ...
+	Starting KUnit Kernel ...
+
+followed by a list of tests that are run. All of them should be passing.
+
+.. note::
+	Because it is building a lot of sources for the first time, the
+	``Building KUnit kernel`` step may take a while.
+
+Running tests without the KUnit Wrapper
+=======================================
+
+If you'd rather not use the KUnit Wrapper (if, for example, you need to
+integrate with other systems, or use an architecture other than UML), KUnit can
+be included in any kernel, and the results read out and parsed manually.
+
+.. note::
+   KUnit is not designed for use in a production system, and it's possible that
+   tests may reduce the stability or security of the system.
+
+
+
+Configuring the kernel
+----------------------
+
+In order to enable KUnit itself, you simply need to enable the ``CONFIG_KUNIT``
+Kconfig option (it's under Kernel Hacking/Kernel Testing and Coverage in
+menuconfig). From there, you can enable any KUnit tests you want: they usually
+have config options ending in ``_KUNIT_TEST``.
+
+KUnit and KUnit tests can be compiled as modules: in this case the tests in a
+module will be run when the module is loaded.
+
+
+Running the tests (w/o KUnit Wrapper)
+-------------------------------------
+
+Build and run your kernel as usual. Test output will be written to the kernel
+log in `TAP <https://testanything.org/>`_ format.
+
+.. note::
+   It's possible that there will be other lines and/or data interspersed in the
+   TAP output.
+
+
+Writing your first test
+=======================
+
+In your kernel repo let's add some code that we can test. Create a file
+``drivers/misc/example.h`` with the contents:
+
+.. code-block:: c
+
+	int misc_example_add(int left, int right);
+
+create a file ``drivers/misc/example.c``:
+
+.. code-block:: c
+
+	#include <linux/errno.h>
+
+	#include "example.h"
+
+	int misc_example_add(int left, int right)
+	{
+		return left + right;
+	}
+
+Now add the following lines to ``drivers/misc/Kconfig``:
+
+.. code-block:: kconfig
+
+	config MISC_EXAMPLE
+		bool "My example"
+
+and the following lines to ``drivers/misc/Makefile``:
+
+.. code-block:: make
+
+	obj-$(CONFIG_MISC_EXAMPLE) += example.o
+
+Now we are ready to write the test. The test will be in
+``drivers/misc/example-test.c``:
+
+.. code-block:: c
+
+	#include <kunit/test.h>
+	#include "example.h"
+
+	/* Define the test cases. */
+
+	static void misc_example_add_test_basic(struct kunit *test)
+	{
+		KUNIT_EXPECT_EQ(test, 1, misc_example_add(1, 0));
+		KUNIT_EXPECT_EQ(test, 2, misc_example_add(1, 1));
+		KUNIT_EXPECT_EQ(test, 0, misc_example_add(-1, 1));
+		KUNIT_EXPECT_EQ(test, INT_MAX, misc_example_add(0, INT_MAX));
+		KUNIT_EXPECT_EQ(test, -1, misc_example_add(INT_MAX, INT_MIN));
+	}
+
+	static void misc_example_test_failure(struct kunit *test)
+	{
+		KUNIT_FAIL(test, "This test never passes.");
+	}
+
+	static struct kunit_case misc_example_test_cases[] = {
+		KUNIT_CASE(misc_example_add_test_basic),
+		KUNIT_CASE(misc_example_test_failure),
+		{}
+	};
+
+	static struct kunit_suite misc_example_test_suite = {
+		.name = "misc-example",
+		.test_cases = misc_example_test_cases,
+	};
+	kunit_test_suite(misc_example_test_suite);
+
+Now add the following to ``drivers/misc/Kconfig``:
+
+.. code-block:: kconfig
+
+	config MISC_EXAMPLE_TEST
+		bool "Test for my example"
+		depends on MISC_EXAMPLE && KUNIT=y
+
+and the following to ``drivers/misc/Makefile``:
+
+.. code-block:: make
+
+	obj-$(CONFIG_MISC_EXAMPLE_TEST) += example-test.o
+
+Now add it to your ``.kunitconfig``:
+
+.. code-block:: none
+
+	CONFIG_MISC_EXAMPLE=y
+	CONFIG_MISC_EXAMPLE_TEST=y
+
+Now you can run the test:
+
+.. code-block:: bash
+
+	./tools/testing/kunit/kunit.py run
+
+You should see the following failure:
+
+.. code-block:: none
+
+	...
+	[16:08:57] [PASSED] misc-example:misc_example_add_test_basic
+	[16:08:57] [FAILED] misc-example:misc_example_test_failure
+	[16:08:57] EXPECTATION FAILED at drivers/misc/example-test.c:17
+	[16:08:57] 	This test never passes.
+	...
+
+Congrats! You just wrote your first KUnit test!
+
+Next Steps
+==========
+*   Check out the :doc:`usage` page for a more
+    in-depth explanation of KUnit.
diff --git a/Documentation/dev-tools/kunit/style.rst b/Documentation/dev-tools/kunit/style.rst
new file mode 100644
index 000000000..8dbcdc552
--- /dev/null
+++ b/Documentation/dev-tools/kunit/style.rst
@@ -0,0 +1,205 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===========================
+Test Style and Nomenclature
+===========================
+
+To make finding, writing, and using KUnit tests as simple as possible, it's
+strongly encouraged that they are named and written according to the guidelines
+below. While it's possible to write KUnit tests which do not follow these rules,
+they may break some tooling, may conflict with other tests, and may not be run
+automatically by testing systems.
+
+It's recommended that you only deviate from these guidelines when:
+
+1. Porting tests to KUnit which are already known with an existing name, or
+2. Writing tests which would cause serious problems if automatically run (e.g.,
+   non-deterministically producing false positives or negatives, or taking an
+   extremely long time to run).
+
+Subsystems, Suites, and Tests
+=============================
+
+In order to make tests as easy to find as possible, they're grouped into suites
+and subsystems. A test suite is a group of tests which test a related area of
+the kernel, and a subsystem is a set of test suites which test different parts
+of the same kernel subsystem or driver.
+
+Subsystems
+----------
+
+Every test suite must belong to a subsystem. A subsystem is a collection of one
+or more KUnit test suites which test the same driver or part of the kernel. A
+rule of thumb is that a test subsystem should match a single kernel module. If
+the code being tested can't be compiled as a module, in many cases the subsystem
+should correspond to a directory in the source tree or an entry in the
+MAINTAINERS file. If unsure, follow the conventions set by tests in similar
+areas.
+
+Test subsystems should be named after the code being tested, either after the
+module (wherever possible), or after the directory or files being tested. Test
+subsystems should be named to avoid ambiguity where necessary.
+
+If a test subsystem name has multiple components, they should be separated by
+underscores. *Do not* include "test" or "kunit" directly in the subsystem name
+unless you are actually testing other tests or the kunit framework itself.
+
+Example subsystems could be:
+
+``ext4``
+  Matches the module and filesystem name.
+``apparmor``
+  Matches the module name and LSM name.
+``kasan``
+  Common name for the tool, prominent part of the path ``mm/kasan``
+``snd_hda_codec_hdmi``
+  Has several components (``snd``, ``hda``, ``codec``, ``hdmi``) separated by
+  underscores. Matches the module name.
+
+Avoid names like these:
+
+``linear-ranges``
+  Names should use underscores, not dashes, to separate words. Prefer
+  ``linear_ranges``.
+``qos-kunit-test``
+  As well as using underscores, this name should not have "kunit-test" as a
+  suffix, and ``qos`` is ambiguous as a subsystem name. ``power_qos`` would be a
+  better name.
+``pc_parallel_port``
+  The corresponding module name is ``parport_pc``, so this subsystem should also
+  be named ``parport_pc``.
+
+.. note::
+        The KUnit API and tools do not explicitly know about subsystems. They're
+        simply a way of categorising test suites and naming modules which
+        provides a simple, consistent way for humans to find and run tests. This
+        may change in the future, though.
+
+Suites
+------
+
+KUnit tests are grouped into test suites, which cover a specific area of
+functionality being tested. Test suites can have shared initialisation and
+shutdown code which is run for all tests in the suite.
+Not all subsystems will need to be split into multiple test suites (e.g. simple drivers).
+
+Test suites are named after the subsystem they are part of. If a subsystem
+contains several suites, the specific area under test should be appended to the
+subsystem name, separated by an underscore.
+
+In the event that there are multiple types of test using KUnit within a
+subsystem (e.g., both unit tests and integration tests), they should be put into
+separate suites, with the type of test as the last element in the suite name.
+Unless these tests are actually present, avoid using ``_test``, ``_unittest`` or
+similar in the suite name.
+
+The full test suite name (including the subsystem name) should be specified as
+the ``.name`` member of the ``kunit_suite`` struct, and forms the base for the
+module name (see below).
+
+Example test suites could include:
+
+``ext4_inode``
+  Part of the ``ext4`` subsystem, testing the ``inode`` area.
+``kunit_try_catch``
+  Part of the ``kunit`` implementation itself, testing the ``try_catch`` area.
+``apparmor_property_entry``
+  Part of the ``apparmor`` subsystem, testing the ``property_entry`` area.
+``kasan``
+  The ``kasan`` subsystem has only one suite, so the suite name is the same as
+  the subsystem name.
+
+Avoid names like:
+
+``ext4_ext4_inode``
+  There's no reason to state the subsystem twice.
+``property_entry``
+  The suite name is ambiguous without the subsystem name.
+``kasan_integration_test``
+  Because there is only one suite in the ``kasan`` subsystem, the suite should
+  just be called ``kasan``. There's no need to redundantly add
+  ``integration_test``. Should a separate test suite with, for example, unit
+  tests be added, then that suite could be named ``kasan_unittest`` or similar.
+
+Test Cases
+----------
+
+Individual tests consist of a single function which tests a constrained
+codepath, property, or function. In the test output, individual tests' results
+will show up as subtests of the suite's results.
+
+Tests should be named after what they're testing. This is often the name of the
+function being tested, with a description of the input or codepath being tested.
+As tests are C functions, they should be named and written in accordance with
+the kernel coding style.
+
+.. note::
+        As tests are themselves functions, their names cannot conflict with
+        other C identifiers in the kernel. This may require some creative
+        naming. It's a good idea to make your test functions `static` to avoid
+        polluting the global namespace.
+
+Example test names include:
+
+``unpack_u32_with_null_name``
+  Tests the ``unpack_u32`` function when a NULL name is passed in.
+``test_list_splice``
+  Tests the ``list_splice`` macro. It has the prefix ``test_`` to avoid a
+  name conflict with the macro itself.
+
+
+Should it be necessary to refer to a test outside the context of its test suite,
+the *fully-qualified* name of a test should be the suite name followed by the
+test name, separated by a colon (i.e. ``suite:test``).
+
+Test Kconfig Entries
+====================
+
+Every test suite should be tied to a Kconfig entry.
+
+This Kconfig entry must:
+
+* be named ``CONFIG_<name>_KUNIT_TEST``: where <name> is the name of the test
+  suite.
+* be listed either alongside the config entries for the driver/subsystem being
+  tested, or be under [Kernel Hacking]→[Kernel Testing and Coverage]
+* depend on ``CONFIG_KUNIT``
+* be visible only if ``CONFIG_KUNIT_ALL_TESTS`` is not enabled.
+* have a default value of ``CONFIG_KUNIT_ALL_TESTS``.
+* have a brief description of KUnit in the help text
+
+Unless there's a specific reason not to (e.g. the test is unable to be built as
+a module), Kconfig entries for tests should be tristate.
+
+An example Kconfig entry:
+
+.. code-block:: none
+
+	config FOO_KUNIT_TEST
+		tristate "KUnit test for foo" if !KUNIT_ALL_TESTS
+		depends on KUNIT
+		default KUNIT_ALL_TESTS
+		help
+		  This builds unit tests for foo.
+
+		  For more information on KUnit and unit tests in general, please refer
+		  to the KUnit documentation in Documentation/dev-tools/kunit/.
+
+		  If unsure, say N.
+
+
+Test File and Module Names
+==========================
+
+KUnit tests can often be compiled as a module. These modules should be named
+after the test suite, followed by ``_test``. If this is likely to conflict with
+non-KUnit tests, the suffix ``_kunit`` can also be used.
+
+The easiest way of achieving this is to name the file containing the test suite
+``<suite>_test.c`` (or, as above, ``<suite>_kunit.c``). This file should be
+placed next to the code under test.
+
+If the suite name contains some or all of the name of the test's parent
+directory, it may make sense to modify the source filename to reduce redundancy.
+For example, a ``foo_firmware`` suite could be in the ``foo/firmware_test.c``
+file.
diff --git a/Documentation/dev-tools/kunit/usage.rst b/Documentation/dev-tools/kunit/usage.rst
new file mode 100644
index 000000000..9c28c518e
--- /dev/null
+++ b/Documentation/dev-tools/kunit/usage.rst
@@ -0,0 +1,617 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===========
+Using KUnit
+===========
+
+The purpose of this document is to describe what KUnit is, how it works, how it
+is intended to be used, and all the concepts and terminology that are needed to
+understand it. This guide assumes a working knowledge of the Linux kernel and
+some basic knowledge of testing.
+
+For a high level introduction to KUnit, including setting up KUnit for your
+project, see :doc:`start`.
+
+Organization of this document
+=============================
+
+This document is organized into two main sections: Testing and Isolating
+Behavior. The first covers what unit tests are and how to use KUnit to write
+them. The second covers how to use KUnit to isolate code and make it possible
+to unit test code that was otherwise un-unit-testable.
+
+Testing
+=======
+
+What is KUnit?
+--------------
+
+"K" is short for "kernel" so "KUnit" is the "(Linux) Kernel Unit Testing
+Framework." KUnit is intended first and foremost for writing unit tests; it is
+general enough that it can be used to write integration tests; however, this is
+a secondary goal. KUnit has no ambition of being the only testing framework for
+the kernel; for example, it does not intend to be an end-to-end testing
+framework.
+
+What is Unit Testing?
+---------------------
+
+A `unit test <https://martinfowler.com/bliki/UnitTest.html>`_ is a test that
+tests code at the smallest possible scope, a *unit* of code. In the C
+programming language that's a function.
+
+Unit tests should be written for all the publicly exposed functions in a
+compilation unit; so that is all the functions that are exported in either a
+*class* (defined below) or all functions which are **not** static.
+
+Writing Tests
+-------------
+
+Test Cases
+~~~~~~~~~~
+
+The fundamental unit in KUnit is the test case. A test case is a function with
+the signature ``void (*)(struct kunit *test)``. It calls a function to be tested
+and then sets *expectations* for what should happen. For example:
+
+.. code-block:: c
+
+	void example_test_success(struct kunit *test)
+	{
+	}
+
+	void example_test_failure(struct kunit *test)
+	{
+		KUNIT_FAIL(test, "This test never passes.");
+	}
+
+In the above example ``example_test_success`` always passes because it does
+nothing; no expectations are set, so all expectations pass. On the other hand
+``example_test_failure`` always fails because it calls ``KUNIT_FAIL``, which is
+a special expectation that logs a message and causes the test case to fail.
+
+Expectations
+~~~~~~~~~~~~
+An *expectation* is a way to specify that you expect a piece of code to do
+something in a test. An expectation is called like a function. A test is made
+by setting expectations about the behavior of a piece of code under test; when
+one or more of the expectations fail, the test case fails and information about
+the failure is logged. For example:
+
+.. code-block:: c
+
+	void add_test_basic(struct kunit *test)
+	{
+		KUNIT_EXPECT_EQ(test, 1, add(1, 0));
+		KUNIT_EXPECT_EQ(test, 2, add(1, 1));
+	}
+
+In the above example ``add_test_basic`` makes a number of assertions about the
+behavior of a function called ``add``; the first parameter is always of type
+``struct kunit *``, which contains information about the current test context;
+the second parameter, in this case, is what the value is expected to be; the
+last value is what the value actually is. If ``add`` passes all of these
+expectations, the test case, ``add_test_basic`` will pass; if any one of these
+expectations fails, the test case will fail.
+
+It is important to understand that a test case *fails* when any expectation is
+violated; however, the test will continue running, potentially trying other
+expectations until the test case ends or is otherwise terminated. This is as
+opposed to *assertions* which are discussed later.
+
+To learn about more expectations supported by KUnit, see :doc:`api/test`.
+
+.. note::
+   A single test case should be pretty short, pretty easy to understand,
+   focused on a single behavior.
+
+For example, if we wanted to properly test the add function above, we would
+create additional tests cases which would each test a different property that an
+add function should have like this:
+
+.. code-block:: c
+
+	void add_test_basic(struct kunit *test)
+	{
+		KUNIT_EXPECT_EQ(test, 1, add(1, 0));
+		KUNIT_EXPECT_EQ(test, 2, add(1, 1));
+	}
+
+	void add_test_negative(struct kunit *test)
+	{
+		KUNIT_EXPECT_EQ(test, 0, add(-1, 1));
+	}
+
+	void add_test_max(struct kunit *test)
+	{
+		KUNIT_EXPECT_EQ(test, INT_MAX, add(0, INT_MAX));
+		KUNIT_EXPECT_EQ(test, -1, add(INT_MAX, INT_MIN));
+	}
+
+	void add_test_overflow(struct kunit *test)
+	{
+		KUNIT_EXPECT_EQ(test, INT_MIN, add(INT_MAX, 1));
+	}
+
+Notice how it is immediately obvious what all the properties that we are testing
+for are.
+
+Assertions
+~~~~~~~~~~
+
+KUnit also has the concept of an *assertion*. An assertion is just like an
+expectation except the assertion immediately terminates the test case if it is
+not satisfied.
+
+For example:
+
+.. code-block:: c
+
+	static void mock_test_do_expect_default_return(struct kunit *test)
+	{
+		struct mock_test_context *ctx = test->priv;
+		struct mock *mock = ctx->mock;
+		int param0 = 5, param1 = -5;
+		const char *two_param_types[] = {"int", "int"};
+		const void *two_params[] = {&param0, &param1};
+		const void *ret;
+
+		ret = mock->do_expect(mock,
+				      "test_printk", test_printk,
+				      two_param_types, two_params,
+				      ARRAY_SIZE(two_params));
+		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ret);
+		KUNIT_EXPECT_EQ(test, -4, *((int *) ret));
+	}
+
+In this example, the method under test should return a pointer to a value, so
+if the pointer returned by the method is null or an errno, we don't want to
+bother continuing the test since the following expectation could crash the test
+case. `ASSERT_NOT_ERR_OR_NULL(...)` allows us to bail out of the test case if
+the appropriate conditions have not been satisfied to complete the test.
+
+Test Suites
+~~~~~~~~~~~
+
+Now obviously one unit test isn't very helpful; the power comes from having
+many test cases covering all of a unit's behaviors. Consequently it is common
+to have many *similar* tests; in order to reduce duplication in these closely
+related tests most unit testing frameworks - including KUnit - provide the
+concept of a *test suite*. A *test suite* is just a collection of test cases
+for a unit of code with a set up function that gets invoked before every test
+case and then a tear down function that gets invoked after every test case
+completes.
+
+Example:
+
+.. code-block:: c
+
+	static struct kunit_case example_test_cases[] = {
+		KUNIT_CASE(example_test_foo),
+		KUNIT_CASE(example_test_bar),
+		KUNIT_CASE(example_test_baz),
+		{}
+	};
+
+	static struct kunit_suite example_test_suite = {
+		.name = "example",
+		.init = example_test_init,
+		.exit = example_test_exit,
+		.test_cases = example_test_cases,
+	};
+	kunit_test_suite(example_test_suite);
+
+In the above example the test suite, ``example_test_suite``, would run the test
+cases ``example_test_foo``, ``example_test_bar``, and ``example_test_baz``;
+each would have ``example_test_init`` called immediately before it and would
+have ``example_test_exit`` called immediately after it.
+``kunit_test_suite(example_test_suite)`` registers the test suite with the
+KUnit test framework.
+
+.. note::
+   A test case will only be run if it is associated with a test suite.
+
+``kunit_test_suite(...)`` is a macro which tells the linker to put the specified
+test suite in a special linker section so that it can be run by KUnit either
+after late_init, or when the test module is loaded (depending on whether the
+test was built in or not).
+
+For more information on these types of things see the :doc:`api/test`.
+
+Isolating Behavior
+==================
+
+The most important aspect of unit testing that other forms of testing do not
+provide is the ability to limit the amount of code under test to a single unit.
+In practice, this is only possible by being able to control what code gets run
+when the unit under test calls a function and this is usually accomplished
+through some sort of indirection where a function is exposed as part of an API
+such that the definition of that function can be changed without affecting the
+rest of the code base. In the kernel this primarily comes from two constructs,
+classes, structs that contain function pointers that are provided by the
+implementer, and architecture-specific functions which have definitions selected
+at compile time.
+
+Classes
+-------
+
+Classes are not a construct that is built into the C programming language;
+however, it is an easily derived concept. Accordingly, pretty much every project
+that does not use a standardized object oriented library (like GNOME's GObject)
+has their own slightly different way of doing object oriented programming; the
+Linux kernel is no exception.
+
+The central concept in kernel object oriented programming is the class. In the
+kernel, a *class* is a struct that contains function pointers. This creates a
+contract between *implementers* and *users* since it forces them to use the
+same function signature without having to call the function directly. In order
+for it to truly be a class, the function pointers must specify that a pointer
+to the class, known as a *class handle*, be one of the parameters; this makes
+it possible for the member functions (also known as *methods*) to have access
+to member variables (more commonly known as *fields*) allowing the same
+implementation to have multiple *instances*.
+
+Typically a class can be *overridden* by *child classes* by embedding the
+*parent class* in the child class. Then when a method provided by the child
+class is called, the child implementation knows that the pointer passed to it is
+of a parent contained within the child; because of this, the child can compute
+the pointer to itself because the pointer to the parent is always a fixed offset
+from the pointer to the child; this offset is the offset of the parent contained
+in the child struct. For example:
+
+.. code-block:: c
+
+	struct shape {
+		int (*area)(struct shape *this);
+	};
+
+	struct rectangle {
+		struct shape parent;
+		int length;
+		int width;
+	};
+
+	int rectangle_area(struct shape *this)
+	{
+		struct rectangle *self = container_of(this, struct shape, parent);
+
+		return self->length * self->width;
+	};
+
+	void rectangle_new(struct rectangle *self, int length, int width)
+	{
+		self->parent.area = rectangle_area;
+		self->length = length;
+		self->width = width;
+	}
+
+In this example (as in most kernel code) the operation of computing the pointer
+to the child from the pointer to the parent is done by ``container_of``.
+
+Faking Classes
+~~~~~~~~~~~~~~
+
+In order to unit test a piece of code that calls a method in a class, the
+behavior of the method must be controllable, otherwise the test ceases to be a
+unit test and becomes an integration test.
+
+A fake just provides an implementation of a piece of code that is different than
+what runs in a production instance, but behaves identically from the standpoint
+of the callers; this is usually done to replace a dependency that is hard to
+deal with, or is slow.
+
+A good example for this might be implementing a fake EEPROM that just stores the
+"contents" in an internal buffer. For example, let's assume we have a class that
+represents an EEPROM:
+
+.. code-block:: c
+
+	struct eeprom {
+		ssize_t (*read)(struct eeprom *this, size_t offset, char *buffer, size_t count);
+		ssize_t (*write)(struct eeprom *this, size_t offset, const char *buffer, size_t count);
+	};
+
+And we want to test some code that buffers writes to the EEPROM:
+
+.. code-block:: c
+
+	struct eeprom_buffer {
+		ssize_t (*write)(struct eeprom_buffer *this, const char *buffer, size_t count);
+		int flush(struct eeprom_buffer *this);
+		size_t flush_count; /* Flushes when buffer exceeds flush_count. */
+	};
+
+	struct eeprom_buffer *new_eeprom_buffer(struct eeprom *eeprom);
+	void destroy_eeprom_buffer(struct eeprom *eeprom);
+
+We can easily test this code by *faking out* the underlying EEPROM:
+
+.. code-block:: c
+
+	struct fake_eeprom {
+		struct eeprom parent;
+		char contents[FAKE_EEPROM_CONTENTS_SIZE];
+	};
+
+	ssize_t fake_eeprom_read(struct eeprom *parent, size_t offset, char *buffer, size_t count)
+	{
+		struct fake_eeprom *this = container_of(parent, struct fake_eeprom, parent);
+
+		count = min(count, FAKE_EEPROM_CONTENTS_SIZE - offset);
+		memcpy(buffer, this->contents + offset, count);
+
+		return count;
+	}
+
+	ssize_t fake_eeprom_write(struct eeprom *parent, size_t offset, const char *buffer, size_t count)
+	{
+		struct fake_eeprom *this = container_of(parent, struct fake_eeprom, parent);
+
+		count = min(count, FAKE_EEPROM_CONTENTS_SIZE - offset);
+		memcpy(this->contents + offset, buffer, count);
+
+		return count;
+	}
+
+	void fake_eeprom_init(struct fake_eeprom *this)
+	{
+		this->parent.read = fake_eeprom_read;
+		this->parent.write = fake_eeprom_write;
+		memset(this->contents, 0, FAKE_EEPROM_CONTENTS_SIZE);
+	}
+
+We can now use it to test ``struct eeprom_buffer``:
+
+.. code-block:: c
+
+	struct eeprom_buffer_test {
+		struct fake_eeprom *fake_eeprom;
+		struct eeprom_buffer *eeprom_buffer;
+	};
+
+	static void eeprom_buffer_test_does_not_write_until_flush(struct kunit *test)
+	{
+		struct eeprom_buffer_test *ctx = test->priv;
+		struct eeprom_buffer *eeprom_buffer = ctx->eeprom_buffer;
+		struct fake_eeprom *fake_eeprom = ctx->fake_eeprom;
+		char buffer[] = {0xff};
+
+		eeprom_buffer->flush_count = SIZE_MAX;
+
+		eeprom_buffer->write(eeprom_buffer, buffer, 1);
+		KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0);
+
+		eeprom_buffer->write(eeprom_buffer, buffer, 1);
+		KUNIT_EXPECT_EQ(test, fake_eeprom->contents[1], 0);
+
+		eeprom_buffer->flush(eeprom_buffer);
+		KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0xff);
+		KUNIT_EXPECT_EQ(test, fake_eeprom->contents[1], 0xff);
+	}
+
+	static void eeprom_buffer_test_flushes_after_flush_count_met(struct kunit *test)
+	{
+		struct eeprom_buffer_test *ctx = test->priv;
+		struct eeprom_buffer *eeprom_buffer = ctx->eeprom_buffer;
+		struct fake_eeprom *fake_eeprom = ctx->fake_eeprom;
+		char buffer[] = {0xff};
+
+		eeprom_buffer->flush_count = 2;
+
+		eeprom_buffer->write(eeprom_buffer, buffer, 1);
+		KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0);
+
+		eeprom_buffer->write(eeprom_buffer, buffer, 1);
+		KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0xff);
+		KUNIT_EXPECT_EQ(test, fake_eeprom->contents[1], 0xff);
+	}
+
+	static void eeprom_buffer_test_flushes_increments_of_flush_count(struct kunit *test)
+	{
+		struct eeprom_buffer_test *ctx = test->priv;
+		struct eeprom_buffer *eeprom_buffer = ctx->eeprom_buffer;
+		struct fake_eeprom *fake_eeprom = ctx->fake_eeprom;
+		char buffer[] = {0xff, 0xff};
+
+		eeprom_buffer->flush_count = 2;
+
+		eeprom_buffer->write(eeprom_buffer, buffer, 1);
+		KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0);
+
+		eeprom_buffer->write(eeprom_buffer, buffer, 2);
+		KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0xff);
+		KUNIT_EXPECT_EQ(test, fake_eeprom->contents[1], 0xff);
+		/* Should have only flushed the first two bytes. */
+		KUNIT_EXPECT_EQ(test, fake_eeprom->contents[2], 0);
+	}
+
+	static int eeprom_buffer_test_init(struct kunit *test)
+	{
+		struct eeprom_buffer_test *ctx;
+
+		ctx = kunit_kzalloc(test, sizeof(*ctx), GFP_KERNEL);
+		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx);
+
+		ctx->fake_eeprom = kunit_kzalloc(test, sizeof(*ctx->fake_eeprom), GFP_KERNEL);
+		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx->fake_eeprom);
+		fake_eeprom_init(ctx->fake_eeprom);
+
+		ctx->eeprom_buffer = new_eeprom_buffer(&ctx->fake_eeprom->parent);
+		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx->eeprom_buffer);
+
+		test->priv = ctx;
+
+		return 0;
+	}
+
+	static void eeprom_buffer_test_exit(struct kunit *test)
+	{
+		struct eeprom_buffer_test *ctx = test->priv;
+
+		destroy_eeprom_buffer(ctx->eeprom_buffer);
+	}
+
+.. _kunit-on-non-uml:
+
+KUnit on non-UML architectures
+==============================
+
+By default KUnit uses UML as a way to provide dependencies for code under test.
+Under most circumstances KUnit's usage of UML should be treated as an
+implementation detail of how KUnit works under the hood. Nevertheless, there
+are instances where being able to run architecture-specific code or test
+against real hardware is desirable. For these reasons KUnit supports running on
+other architectures.
+
+Running existing KUnit tests on non-UML architectures
+-----------------------------------------------------
+
+There are some special considerations when running existing KUnit tests on
+non-UML architectures:
+
+*   Hardware may not be deterministic, so a test that always passes or fails
+    when run under UML may not always do so on real hardware.
+*   Hardware and VM environments may not be hermetic. KUnit tries its best to
+    provide a hermetic environment to run tests; however, it cannot manage state
+    that it doesn't know about outside of the kernel. Consequently, tests that
+    may be hermetic on UML may not be hermetic on other architectures.
+*   Some features and tooling may not be supported outside of UML.
+*   Hardware and VMs are slower than UML.
+
+None of these are reasons not to run your KUnit tests on real hardware; they are
+only things to be aware of when doing so.
+
+The biggest impediment will likely be that certain KUnit features and
+infrastructure may not support your target environment. For example, at this
+time the KUnit Wrapper (``tools/testing/kunit/kunit.py``) does not work outside
+of UML. Unfortunately, there is no way around this. Using UML (or even just a
+particular architecture) allows us to make a lot of assumptions that make it
+possible to do things which might otherwise be impossible.
+
+Nevertheless, all core KUnit framework features are fully supported on all
+architectures, and using them is straightforward: all you need to do is to take
+your kunitconfig, your Kconfig options for the tests you would like to run, and
+merge them into whatever config your are using for your platform. That's it!
+
+For example, let's say you have the following kunitconfig:
+
+.. code-block:: none
+
+	CONFIG_KUNIT=y
+	CONFIG_KUNIT_EXAMPLE_TEST=y
+
+If you wanted to run this test on an x86 VM, you might add the following config
+options to your ``.config``:
+
+.. code-block:: none
+
+	CONFIG_KUNIT=y
+	CONFIG_KUNIT_EXAMPLE_TEST=y
+	CONFIG_SERIAL_8250=y
+	CONFIG_SERIAL_8250_CONSOLE=y
+
+All these new options do is enable support for a common serial console needed
+for logging.
+
+Next, you could build a kernel with these tests as follows:
+
+
+.. code-block:: bash
+
+	make ARCH=x86 olddefconfig
+	make ARCH=x86
+
+Once you have built a kernel, you could run it on QEMU as follows:
+
+.. code-block:: bash
+
+	qemu-system-x86_64 -enable-kvm \
+			   -m 1024 \
+			   -kernel arch/x86_64/boot/bzImage \
+			   -append 'console=ttyS0' \
+			   --nographic
+
+Interspersed in the kernel logs you might see the following:
+
+.. code-block:: none
+
+	TAP version 14
+		# Subtest: example
+		1..1
+		# example_simple_test: initializing
+		ok 1 - example_simple_test
+	ok 1 - example
+
+Congratulations, you just ran a KUnit test on the x86 architecture!
+
+In a similar manner, kunit and kunit tests can also be built as modules,
+so if you wanted to run tests in this way you might add the following config
+options to your ``.config``:
+
+.. code-block:: none
+
+	CONFIG_KUNIT=m
+	CONFIG_KUNIT_EXAMPLE_TEST=m
+
+Once the kernel is built and installed, a simple
+
+.. code-block:: bash
+
+	modprobe example-test
+
+...will run the tests.
+
+.. note::
+   Note that you should make sure your test depends on ``KUNIT=y`` in Kconfig
+   if the test does not support module build.  Otherwise, it will trigger
+   compile errors if ``CONFIG_KUNIT`` is ``m``.
+
+Writing new tests for other architectures
+-----------------------------------------
+
+The first thing you must do is ask yourself whether it is necessary to write a
+KUnit test for a specific architecture, and then whether it is necessary to
+write that test for a particular piece of hardware. In general, writing a test
+that depends on having access to a particular piece of hardware or software (not
+included in the Linux source repo) should be avoided at all costs.
+
+Even if you only ever plan on running your KUnit test on your hardware
+configuration, other people may want to run your tests and may not have access
+to your hardware. If you write your test to run on UML, then anyone can run your
+tests without knowing anything about your particular setup, and you can still
+run your tests on your hardware setup just by compiling for your architecture.
+
+.. important::
+   Always prefer tests that run on UML to tests that only run under a particular
+   architecture, and always prefer tests that run under QEMU or another easy
+   (and monetarily free) to obtain software environment to a specific piece of
+   hardware.
+
+Nevertheless, there are still valid reasons to write an architecture or hardware
+specific test: for example, you might want to test some code that really belongs
+in ``arch/some-arch/*``. Even so, try your best to write the test so that it
+does not depend on physical hardware: if some of your test cases don't need the
+hardware, only require the hardware for tests that actually need it.
+
+Now that you have narrowed down exactly what bits are hardware specific, the
+actual procedure for writing and running the tests is pretty much the same as
+writing normal KUnit tests. One special caveat is that you have to reset
+hardware state in between test cases; if this is not possible, you may only be
+able to run one test case per invocation.
+
+.. TODO(brendanhiggins@google.com): Add an actual example of an architecture-
+   dependent KUnit test.
+
+KUnit debugfs representation
+============================
+When kunit test suites are initialized, they create an associated directory
+in ``/sys/kernel/debug/kunit/<test-suite>``.  The directory contains one file
+
+- results: "cat results" displays results of each test case and the results
+  of the entire suite for the last test run.
+
+The debugfs representation is primarily of use when kunit test suites are
+run in a native environment, either as modules or builtin.  Having a way
+to display results like this is valuable as otherwise results can be
+intermixed with other events in dmesg output.  The maximum size of each
+results file is KUNIT_LOG_SIZE bytes (defined in ``include/kunit/test.h``).