Re: [PATCH] kunit: tool: reconfigure when the used kunitconfig changes

[David Gow <davidgow@google.com>]

On Fri, Nov 19, 2021 at 3:03 AM 'Daniel Latypov' via KUnit Development
<kunit-dev@googlegroups.com> wrote:
>
> 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>
> ---

Note that this patch has some prerequisites before it applies cleanly,
notably this series:
https://patchwork.kernel.org/project/linux-kselftest/list/?series=576317

I'm also seeing a couple of issues with this, though I haven't had a
chance to track down the cause fully, so it could just be another
missing prerequisite, or me doing something silly.

In particular:
- Removing items from .kunit/.kunitconfig still wasn't triggering a reconfig.
- Running with --arch=x86_64 was giving me a "FileNotFoundError:
[Errno 2] No such file or directory: '.kunit/last_used_kunitconfig'"
error:

davidgow@spirogrip:~/kunit-linux$ ./tools/testing/kunit/kunit.py run
--arch=x86_64
[23:00:01] Configuring KUnit Kernel ...
Regenerating .config ...
Populating config with:
$ make ARCH=x86_64 olddefconfig O=.kunit
Traceback (most recent call last):
 File "/usr/local/google/home/davidgow/kunit-linux/./tools/testing/kunit/kunit.py",
line 503, in <module>
   main(sys.argv[1:])
 File "/usr/local/google/home/davidgow/kunit-linux/./tools/testing/kunit/kunit.py",
line 420, in main
   result = run_tests(linux, request)
 File "/usr/local/google/home/davidgow/kunit-linux/./tools/testing/kunit/kunit.py",
line 216, in run_tests
   config_result = config_tests(linux, config_request)
 File "/usr/local/google/home/davidgow/kunit-linux/./tools/testing/kunit/kunit.py",
line 62, in config_tests
   success = linux.build_reconfig(request.build_dir, request.make_options)
 File "/usr/local/google/home/davidgow/kunit-linux/tools/testing/kunit/kunit_kernel.py",
line 320, in build_reconfig
   return self.build_config(build_dir, make_options)
 File "/usr/local/google/home/davidgow/kunit-linux/tools/testing/kunit/kunit_kernel.py",
line 295, in build_config
   os.remove(old_path)  # write_to_file appends to the file
FileNotFoundError: [Errno 2] No such file or directory:
'.kunit/last_used_kunitconfig'


Otherwise, while I wasn't completely convinced by this change at
first, I'm much happier with it having thought a bit more about it, so
I'm definitely on-board with the idea. My only real reservation is
that this is a change in behaviour, and some people (including me)
occasionally may rely on the old behaviour. This does make more sense
now, though, and the old behaviour wasn't useful enough to justify it,
IMHO.

Cheers,
-- David