[PATCH v3] Documentation: kunit: Make the KUnit documentation less UML-specific

[David Gow]

Remove some of the outmoded "Why KUnit" rationale, and move some
UML-specific information to the kunit_tool page. Also update the Getting
Started guide to mention running tests without the kunit_tool wrapper.

Signed-off-by: David Gow <davidgow@xxxxxxxxxx>
---
Thanks: I've added a note to the "Why KUnit" section which I think
better reflects both the UML is optional, and that it can be used both
with and without kunit_tool.


Changelog:

v3:
- Added a note that KUnit can be used with UML, both with and without
  kunit_tool to replace the section moved to kunit_tool.
v2:
https://lore.kernel.org/linux-kselftest/f99a3d4d-ad65-5fd1-3407-db33f378b1fa@xxxxxxxxx/T/
- Reinstated the "Why Kunit?" section, minus the comparison with other
  testing frameworks (covered in the FAQ), and the description of UML.
- Moved the description of UML into to kunit_tool page.
- Tidied up the wording around how KUnit is built and run to make it
  work
  without the UML description.
v1:
https://lore.kernel.org/linux-kselftest/9c703dea-a9e1-94e2-c12d-3cb0a09e75ac@xxxxxxxxx/T/
- Initial patch

 Documentation/dev-tools/kunit/index.rst      | 41 ++++++----
 Documentation/dev-tools/kunit/kunit-tool.rst |  7 ++
 Documentation/dev-tools/kunit/start.rst      | 80 ++++++++++++++++----
 3 files changed, 100 insertions(+), 28 deletions(-)

diff --git a/Documentation/dev-tools/kunit/index.rst b/Documentation/dev-tools/kunit/index.rst
index d16a4d2c3a41..9e77d0c90ff4 100644
--- a/Documentation/dev-tools/kunit/index.rst
+++ b/Documentation/dev-tools/kunit/index.rst
@@ -17,14 +17,23 @@ What is KUnit?
 ==============
 
 KUnit is a lightweight unit testing and mocking framework for the Linux kernel.
-These tests are able to be run locally on a developer's workstation without a VM
-or special hardware.
 
 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 offsers
+: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?
@@ -36,22 +45,21 @@ 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.
 
-Outside of KUnit, 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 running on
-the kernel; this is true for Autotest, and kselftest, disqualifying
-any of them from being considered unit testing frameworks.
-
-KUnit 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
-to a standalone program 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.
+KUnit provides a common framework for unit tests within the kernel.
 
-Alternatively, kunit and kunit tests can be built as modules and tests will
+KUnit tests can be run on most kernel configurations, 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
@@ -75,9 +83,12 @@ 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
index 50d46394e97e..949af2da81e5 100644
--- a/Documentation/dev-tools/kunit/kunit-tool.rst
+++ b/Documentation/dev-tools/kunit/kunit-tool.rst
@@ -12,6 +12,13 @@ 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?
 ======================
 
diff --git a/Documentation/dev-tools/kunit/start.rst b/Documentation/dev-tools/kunit/start.rst
index 4e1d24db6b13..e1c5ce80ce12 100644
--- a/Documentation/dev-tools/kunit/start.rst
+++ b/Documentation/dev-tools/kunit/start.rst
@@ -9,11 +9,10 @@ Installing dependencies
 KUnit has the same dependencies as the Linux kernel. As long as you can build
 the kernel, you can run KUnit.
 
-KUnit Wrapper
-=============
-Included with KUnit is a simple Python wrapper that helps format the output to
-easily use and read KUnit output. It handles building and running the kernel, as
-well as formatting the output.
+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:
 
@@ -21,22 +20,42 @@ The wrapper can be run with:
 
 	./tools/testing/kunit/kunit.py run --defconfig
 
-For more information on this wrapper (also called kunit_tool) checkout the
+For more information on this wrapper (also called kunit_tool) check out the
 :doc:`kunit-tool` page.
 
 Creating a .kunitconfig
-=======================
-The Python script is a thin wrapper around Kbuild. As such, it needs to be
-configured with a ``.kunitconfig`` file. This file essentially contains the
-regular Kernel config, with the specific test targets as well.
-
+-----------------------
+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
 
-Verifying KUnit Works
----------------------
+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
+-----------------
 
 To make sure that everything is set up correctly, simply invoke the Python
 wrapper from your kernel repo:
@@ -62,6 +81,41 @@ followed by a list of tests that are run. All of them should be passing.
 	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
+-----------------
+
+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
 =======================
 
-- 
2.25.0.265.gbab2e86ba0-goog