[PATCH v3 6/6] Documentation: Add debugfs docs with run after boot

[Rae Moar <rmoar@google.com>]

Expand the documentation on the KUnit debugfs filesystem on the
run_manual.rst page.

Add section describing how to access results using debugfs.

Add section describing how to run tests after boot using debugfs.

Signed-off-by: Rae Moar <rmoar@google.com>
---

Changes since v2:
- Add info to documentation about cleaning up data, init tests, and
  running tests concurrently

 Documentation/dev-tools/kunit/run_manual.rst | 49 ++++++++++++++++++--
 1 file changed, 45 insertions(+), 4 deletions(-)

diff --git a/Documentation/dev-tools/kunit/run_manual.rst b/Documentation/dev-tools/kunit/run_manual.rst
index e7b46421f247..aebb52ba9605 100644
--- a/Documentation/dev-tools/kunit/run_manual.rst
+++ b/Documentation/dev-tools/kunit/run_manual.rst
@@ -49,9 +49,50 @@ loaded.
 
 The results will appear in TAP format in ``dmesg``.
 
+debugfs
+=======
+
+``debugfs`` is a file system that enables user interaction with the files to
+make kernel information available to user space (See more information at
+Documentation/filesystems/debugfs.html)
+
+By default, only the root user has access to the debugfs directory.
+
+If ``CONFIG_KUNIT_DEBUGFS`` is enabled, you can use KUnit debugfs
+filesystem to perform the following actions.
+
+Retrieve Test Results
+=====================
+
+You can use debugfs to retrieve KUnit test results. The test results are
+accessible from the debugfs filesystem in the following read-only file:
+
+.. code-block :: bash
+
+	/sys/kernel/debug/kunit/<test_suite>/results
+
+The test results are available in KTAP format.
+
+Run Tests After Kernel Has Booted
+=================================
+
+You can use the debugfs filesystem to trigger built-in tests to run after
+boot. To run the test suite, you can use the following command to write to
+the ``/sys/kernel/debug/kunit/<test_suite>/run`` file:
+
+.. code-block :: bash
+
+	echo "any string" > /sys/kernel/debugfs/kunit/<test_suite>/run
+
+As a result, the test suite runs and the results are printed to the kernel
+log.
+
+However, this feature is not available with KUnit tests that use init data.
+
+Also, you cannot use this feature to run tests concurrently as there is a
+mutex lock around running KUnit tests at the same time.
+
 .. note ::
 
-	If ``CONFIG_KUNIT_DEBUGFS`` is enabled, KUnit test results will
-	be accessible from the ``debugfs`` filesystem (if mounted).
-	They will be in ``/sys/kernel/debug/kunit/<test_suite>/results``, in
-	TAP format.
+	For test authors, to use this feature, tests will need to correctly initialise
+	and/or clean up any data, so the test runs correctly a second time.
-- 
2.43.0.rc2.451.g8631bc7472-goog