[PATCH linux-kselftest/test v1] Documentation: kunit: add documentation for kunit_tool

[Brendan Higgins <brendanhiggins@google.com>]

Add documentation for the Python script used to build, run, and collect
results from the kernel known as kunit_tool. kunit_tool
(tools/testing/kunit/kunit.py) was already added in previous commits.

Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
---
 Documentation/dev-tools/kunit/index.rst      |  1 +
 Documentation/dev-tools/kunit/kunit-tool.rst | 57 ++++++++++++++++++++
 Documentation/dev-tools/kunit/start.rst      |  3 ++
 3 files changed, 61 insertions(+)
 create mode 100644 Documentation/dev-tools/kunit/kunit-tool.rst

diff --git a/Documentation/dev-tools/kunit/index.rst b/Documentation/dev-tools/kunit/index.rst
index 26ffb46bdf99d..c60d760a0eed1 100644
--- a/Documentation/dev-tools/kunit/index.rst
+++ b/Documentation/dev-tools/kunit/index.rst
@@ -9,6 +9,7 @@ KUnit - Unit Testing for the Linux Kernel
 
 	start
 	usage
+	kunit-tool
 	api/index
 	faq
 
diff --git a/Documentation/dev-tools/kunit/kunit-tool.rst b/Documentation/dev-tools/kunit/kunit-tool.rst
new file mode 100644
index 0000000000000..aa1a93649a45a
--- /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 set of scripts that aid in building the Linux kernel as UML
+(`User Mode Linux <http://user-mode-linux.sourceforge.net/old/>`_), running
+KUnit tests, parsing the test results and displaying them in a user friendly
+manner.
+
+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=8
+
+- ``--timeout`` sets a maximum amount of time to allow tests to run.
+- ``--jobs`` sets the number of threads to use to build the kernel.
+
+If you just want to use the defconfig that ships with the kernel, you can
+append the ``--defconfig`` flag as well:
+
+.. code-block:: bash
+
+	./tools/testing/kunit/kunit.py run --timeout=30 --jobs=8 --defconfig
+
+.. note::
+	This command is particularly helpful for getting started because it
+	just works. No kunitconfig needs to be present.
+
+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
index aeeddfafeea20..1535c4394cfa2 100644
--- a/Documentation/dev-tools/kunit/start.rst
+++ b/Documentation/dev-tools/kunit/start.rst
@@ -21,6 +21,9 @@ The wrapper can be run with:
 
    ./tools/testing/kunit/kunit.py run
 
+For more information on this wrapper (also called kunit_tool) checkout the
+:doc:`kunit-tool` page.
+
 Creating a kunitconfig
 ======================
 The Python script is a thin wrapper around Kbuild as such, it needs to be
-- 
2.24.0.432.g9d3f5f5b63-goog