linux-kernel - Re: [PATCH v2 00/17] kunit: introduce KUnit, the Linux kernel unit testing framework

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Date:   Wed, 8 May 2019 21:44:07 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        keescook@...gle.com, kieran.bingham@...asonboard.com,
        mcgrof@...nel.org, robh@...nel.org, sboyd@...nel.org,
        shuah@...nel.org, devicetree@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, kunit-dev@...glegroups.com,
        linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-um@...ts.infradead.org, Alexander.Levin@...rosoft.com,
        Tim.Bird@...y.com, amir73il@...il.com, dan.carpenter@...cle.com,
        dan.j.williams@...el.com, daniel@...ll.ch, jdike@...toit.com,
        joel@....id.au, julia.lawall@...6.fr, khilman@...libre.com,
        knut.omang@...cle.com, logang@...tatee.com, mpe@...erman.id.au,
        pmladek@...e.com, richard@....at, rientjes@...gle.com,
        rostedt@...dmis.org, wfg@...ux.intel.com
Subject: Re: [PATCH v2 00/17] kunit: introduce KUnit, the Linux kernel unit
 testing framework

On Wed, May 08, 2019 at 05:58:49PM -0700, Frank Rowand wrote:
> 
> If KUnit is added to the kernel, and a subsystem that I am submitting
> code for has chosen to use KUnit instead of kselftest, then yes, I do
> *have* to use KUnit if my submission needs to contain a test for the
> code unless I want to convince the maintainer that somehow my case
> is special and I prefer to use kselftest instead of KUnittest.

That's going to be between you and the maintainer.  Today, if you want
to submit a substantive change to xfs or ext4, you're going to be
asked to create test for that new feature using xfstests.  It doesn't
matter that xfstests isn't in the kernel --- if that's what is
required by the maintainer.

> > supposed to be a simple way to run a large number of small tests that
> > for specific small components in a system.
> 
> kselftest also supports running a subset of tests.  That subset of tests
> can also be a large number of small tests.  There is nothing inherent
> in KUnit vs kselftest in this regard, as far as I am aware.

The big difference is that kselftests are driven by a C program that
runs in userspace.  Take a look at tools/testing/selftests/filesystem/dnotify_test.c
it has a main(int argc, char *argv) function.

In contrast, KUnit are fragments of C code which run in the kernel;
not in userspace.  This allows us to test internal functions inside
complex file system (such as the block allocator in ext4) directly.
This makes it *fundamentally* different from kselftest.

Cheers,

						- Ted