kunit: tool: reconfigure when the used kunitconfig changes

Problem: currently, if you remove something from your kunitconfig,
kunit.py will not regenerate the .config file.
The same thing happens if you did --kunitconfig_add=CONFIG_KASAN=y [1]
and then ran again without it. Your new run will still have KASAN.

The reason is that kunit.py won't regenerate the .config file if it's a
superset of the kunitconfig. This speeds it up a bit for iterating.

This patch adds an additional check that forces kunit.py to regenerate
the .config file if the current kunitconfig doesn't match the previous
one.

What this means:
* deleting entries from .kunitconfig works as one would expect
* dropping  a --kunitconfig_add also triggers a rebuild
* you can still edit .config directly to turn on new options

We implement this by creating a `last_used_kunitconfig` file in the
build directory (so .kunit, by default) after we generate the .config.
When comparing the kconfigs, we compare python sets, so duplicates and
permutations don't trip us up.

The majority of this patch is adding unit tests for the existing logic
and for the new case where `last_used_kunitconfig` differs.

[1] https://lore.kernel.org/linux-kselftest/20211106013058.2621799-2-dlatypov@google.com/

Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/Documentation/dev-tools/kunit/start.rst b/Documentation/dev-tools/kunit/start.rst
index 1e00f9226f74..0a5e65540974 100644
--- a/Documentation/dev-tools/kunit/start.rst
+++ b/Documentation/dev-tools/kunit/start.rst
@@ -50,10 +50,10 @@ 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.
+   If you change the ``.kunitconfig``, kunit.py will trigger a rebuild of the
+   ``.config`` file. But you can edit the ``.config`` file directly or with
+   tools like ``make menuconfig O=.kunit``. As long as its a superset of
+   ``.kunitconfig``, kunit.py won't overwrite your changes.
 
 
 Running the tests (KUnit Wrapper)