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Subject[PATCH v6 3/7] Documentation: KUnit: Added KUnit Architecture
From
Describe the components of KUnit and how the kernel mode parts
interact with kunit_tool.

Signed-off-by: Harinder Singh <sharinder@google.com>
---
.../dev-tools/kunit/architecture.rst | 204 ++++++++++++++++++
Documentation/dev-tools/kunit/index.rst | 2 +
.../kunit/kunit_suitememorydiagram.svg | 81 +++++++
Documentation/dev-tools/kunit/start.rst | 1 +
4 files changed, 288 insertions(+)
create mode 100644 Documentation/dev-tools/kunit/architecture.rst
create mode 100644 Documentation/dev-tools/kunit/kunit_suitememorydiagram.svg

diff --git a/Documentation/dev-tools/kunit/architecture.rst b/Documentation/dev-tools/kunit/architecture.rst
new file mode 100644
index 000000000000..aa2cea821e25
--- /dev/null
+++ b/Documentation/dev-tools/kunit/architecture.rst
@@ -0,0 +1,204 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==================
+KUnit Architecture
+==================
+
+The KUnit architecture can be divided into two parts:
+
+- Kernel testing library
+- kunit_tool (Command line test harness)
+
+In-Kernel Testing Framework
+===========================
+
+The kernel testing library supports KUnit tests written in C using
+KUnit. KUnit tests are kernel code. KUnit does several things:
+
+- Organizes tests
+- Reports test results
+- Provides test utilities
+
+Test Cases
+----------
+
+The fundamental unit in KUnit is the test case. The KUnit test cases are
+grouped into KUnit suites. A KUnit test case is a function with type
+signature ``void (*)(struct kunit *test)``.
+These test case functions are wrapped in a struct called
+``struct kunit_case``. For code, see:
+
+.. kernel-doc:: include/kunit/test.h
+ :identifiers: kunit_case
+
+.. note:
+ ``generate_params`` is optional for non-parameterized tests.
+
+Each KUnit test case gets a ``struct kunit`` context
+object passed to it that tracks a running test. The KUnit assertion
+macros and other KUnit utilities use the ``struct kunit`` context
+object. As an exception, there are two fields:
+
+- ``->priv``: The setup functions can use it to store arbitrary test
+ user data.
+
+- ``->param_value``: It contains the parameter value which can be
+ retrieved in the parameterized tests.
+
+Test Suites
+-----------
+
+A KUnit suite includes a collection of test cases. The KUnit suites
+are represented by the ``struct kunit_suite``. For 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``, runs the
+test cases ``example_test_foo``, ``example_test_bar``, and
+``example_test_baz``. Before running the test, the ``example_test_init``
+is called and after running the test, ``example_test_exit`` is called.
+The ``kunit_test_suite(example_test_suite)`` registers the test suite
+with the KUnit test framework.
+
+Executor
+--------
+
+The KUnit executor can list and run built-in KUnit tests on boot.
+The Test suites are stored in a linker section
+called ``.kunit_test_suites``. For code, see:
+https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/asm-generic/vmlinux.lds.h?h=v5.15#n945.
+The linker section consists of an array of pointers to
+``struct kunit_suite``, and is populated by the ``kunit_test_suites()``
+macro. To run all tests compiled into the kernel, the KUnit executor
+iterates over the linker section array.
+
+.. kernel-figure:: kunit_suitememorydiagram.svg
+ :alt: KUnit Suite Memory
+
+ KUnit Suite Memory Diagram
+
+On the kernel boot, the KUnit executor uses the start and end addresses
+of this section to iterate over and run all tests. For code, see:
+https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/kunit/executor.c
+
+When built as a module, the ``kunit_test_suites()`` macro defines a
+``module_init()`` function, which runs all the tests in the compilation
+unit instead of utilizing the executor.
+
+In KUnit tests, some error classes do not affect other tests
+or parts of the kernel, each KUnit case executes in a separate thread
+context. For code, see:
+https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/kunit/try-catch.c?h=v5.15#n58
+
+Assertion Macros
+----------------
+
+KUnit tests verify state using expectations/assertions.
+All expectations/assertions are formatted as:
+``KUNIT_{EXPECT|ASSERT}_<op>[_MSG](kunit, property[, message])``
+
+- ``{EXPECT|ASSERT}`` determines whether the check is an assertion or an
+ expectation.
+
+ - For an expectation, if the check fails, marks the test as failed
+ and logs the failure.
+
+ - An assertion, on failure, causes the test case to terminate
+ immediately.
+
+ - Assertions call function:
+ ``void __noreturn kunit_abort(struct kunit *)``.
+
+ - ``kunit_abort`` calls function:
+ ``void __noreturn kunit_try_catch_throw(struct kunit_try_catch *try_catch)``.
+
+ - ``kunit_try_catch_throw`` calls function:
+ ``void complete_and_exit(struct completion *, long) __noreturn;``
+ and terminates the special thread context.
+
+- ``<op>`` denotes a check with options: ``TRUE`` (supplied property
+ has the boolean value “true”), ``EQ`` (two supplied properties are
+ equal), ``NOT_ERR_OR_NULL`` (supplied pointer is not null and does not
+ contain an “err” value).
+
+- ``[_MSG]`` prints a custom message on failure.
+
+Test Result Reporting
+---------------------
+KUnit prints test results in KTAP format. KTAP is based on TAP14, see:
+https://github.com/isaacs/testanything.github.io/blob/tap14/tap-version-14-specification.md.
+KTAP (yet to be standardized format) works with KUnit and Kselftest.
+The KUnit executor prints KTAP results to dmesg, and debugfs
+(if configured).
+
+Parameterized Tests
+-------------------
+
+Each KUnit parameterized test is associated with a collection of
+parameters. The test is invoked multiple times, once for each parameter
+value and the parameter is stored in the ``param_value`` field.
+The test case includes a ``KUNIT_CASE_PARAM()`` macro that accepts a
+generator function.
+The generator function is passed the previous parameter and returns the next
+parameter. It also provides a macro to generate common-case generators based on
+arrays.
+
+For code, see:
+
+.. kernel-doc:: include/kunit/test.h
+ :identifiers: KUNIT_ARRAY_PARAM
+
+
+kunit_tool (Command Line Test Harness)
+======================================
+
+kunit_tool is a Python script ``(tools/testing/kunit/kunit.py)``
+that can be used to configure, build, exec, parse and run (runs other
+commands in order) test results. You can either run KUnit tests using
+kunit_tool or can include KUnit in kernel and parse manually.
+
+- ``configure`` command generates the kernel ``.config`` from a
+ ``.kunitconfig`` file (and any architecture-specific options).
+ For some architectures, additional config options are specified in the
+ ``qemu_config`` Python script
+ (For example: ``tools/testing/kunit/qemu_configs/powerpc.py``).
+ It parses both the existing ``.config`` and the ``.kunitconfig`` files
+ and ensures that ``.config`` is a superset of ``.kunitconfig``.
+ If this is not the case, it will combine the two and run
+ ``make olddefconfig`` to regenerate the ``.config`` file. It then
+ verifies that ``.config`` is now a superset. This checks if all
+ Kconfig dependencies are correctly specified in ``.kunitconfig``.
+ ``kunit_config.py`` includes the parsing Kconfigs code. The code which
+ runs ``make olddefconfig`` is a part of ``kunit_kernel.py``. You can
+ invoke this command via: ``./tools/testing/kunit/kunit.py config`` and
+ generate a ``.config`` file.
+- ``build`` runs ``make`` on the kernel tree with required options
+ (depends on the architecture and some options, for example: build_dir)
+ and reports any errors.
+ To build a KUnit kernel from the current ``.config``, you can use the
+ ``build`` argument: ``./tools/testing/kunit/kunit.py build``.
+- ``exec`` command executes kernel results either directly (using
+ User-mode Linux configuration), or via an emulator such
+ as QEMU. It reads results from the log via standard
+ output (stdout), and passes them to ``parse`` to be parsed.
+ If you already have built a kernel with built-in KUnit tests,
+ you can run the kernel and display the test results with the ``exec``
+ argument: ``./tools/testing/kunit/kunit.py exec``.
+- ``parse`` extracts the KTAP output from a kernel log, parses
+ the test results, and prints a summary. For failed tests, any
+ diagnostic output will be included.
diff --git a/Documentation/dev-tools/kunit/index.rst b/Documentation/dev-tools/kunit/index.rst
index 55d2444b0745..50d3ef9359dd 100644
--- a/Documentation/dev-tools/kunit/index.rst
+++ b/Documentation/dev-tools/kunit/index.rst
@@ -9,6 +9,7 @@ KUnit - Linux Kernel Unit Testing
:caption: Contents:

start
+ architecture
usage
kunit-tool
api/index
@@ -96,6 +97,7 @@ How do I use it?
================

* Documentation/dev-tools/kunit/start.rst - for KUnit new users.
+* Documentation/dev-tools/kunit/architecture.rst - KUnit architecture.
* Documentation/dev-tools/kunit/usage.rst - KUnit features.
* Documentation/dev-tools/kunit/tips.rst - best practices with
examples.
diff --git a/Documentation/dev-tools/kunit/kunit_suitememorydiagram.svg b/Documentation/dev-tools/kunit/kunit_suitememorydiagram.svg
new file mode 100644
index 000000000000..cf8fddc27500
--- /dev/null
+++ b/Documentation/dev-tools/kunit/kunit_suitememorydiagram.svg
@@ -0,0 +1,81 @@
+<?xml version="1.0" encoding="UTF-8"?>
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diff --git a/Documentation/dev-tools/kunit/start.rst b/Documentation/dev-tools/kunit/start.rst
index 55f8df1abd40..5dd2c88fa2bd 100644
--- a/Documentation/dev-tools/kunit/start.rst
+++ b/Documentation/dev-tools/kunit/start.rst
@@ -240,6 +240,7 @@ Congrats! You just wrote your first KUnit test.
Next Steps
==========

+* Documentation/dev-tools/kunit/architecture.rst - KUnit architecture.
* Documentation/dev-tools/kunit/usage.rst - KUnit features.
* Documentation/dev-tools/kunit/tips.rst - best practices with
examples.
--
2.34.1.173.g76aa8bc2d0-goog
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