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Date: Thu, 17 Jul 2025 15:23:00 +0200
From: Christoph Hellwig <hch@lst.de>
To: Thomas =?iso-8859-1?Q?Wei=DFschuh?= <thomas.weissschuh@linutronix.de>
Cc: Masahiro Yamada <masahiroy@kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>, Willy Tarreau <w@1wt.eu>,
	Thomas =?iso-8859-1?Q?Wei=DFschuh?= <linux@weissschuh.net>,
	Brendan Higgins <brendan.higgins@linux.dev>,
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	Shuah Khan <shuah@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
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	Christoph Hellwig <hch@lst.de>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-kselftest@vger.kernel.org, kunit-dev@googlegroups.com,
	linux-doc@vger.kernel.org, workflows@vger.kernel.org,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v5 00/15] kunit: Introduce UAPI testing framework
Message-ID: <20250717132259.GA25835@lst.de>
References: <20250717-kunit-kselftests-v5-0-442b711cde2e@linutronix.de>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Thu, Jul 17, 2025 at 10:48:02AM +0200, Thomas Weißschuh wrote:
> Currently testing of userspace and in-kernel API use two different
> frameworks.

Which is kinda expected as one has to run in the kernel to test
in-kernel kernel space APIs, and the other tests externally provided
kernel functionality.

> Therefore kunit is much easier to run against different kernel
> configurations and architectures.

Which is is normal.  unit tests are always easier to run than
integration tests.

> This series aims to combine kselftests and kunit, avoiding both their
> limitations. It works by compiling the userspace kselftests as part of
> the regular kernel build, embedding them into the kunit kernel or module
> and executing them from there.

This is really weird.  "Running userspace code is hard, so we package
it in the kernel".  I had my own fair share of problems with kselftests,
mostly because of the lack of structure and automated way to run them,
but adding them to the kernel (or a module) is overshooting the target
by far.

> If the kernel toolchain is not fit to
> produce userspace because of a missing libc, the kernel's own nolibc can
> be used instead.

Is nolibc enough to run all the selftests?  If so we should just do
it unconditionally, but linking to different libraries by availability
seems a bit problematic.

> The structured TAP output from the kselftest is integrated into the
> kunit KTAP output transparently, the kunit parser can parse the combined
> logs together.

Good idea!