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

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Date:   Fri, 10 May 2019 14:12:40 -0700
From:   Frank Rowand <frowand.list@...il.com>
To:     Theodore Ts'o <tytso@....edu>, Tim.Bird@...y.com,
        knut.omang@...cle.com, gregkh@...uxfoundation.org,
        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, 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, 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 5/9/19 2:42 PM, Theodore Ts'o wrote:
> On Thu, May 09, 2019 at 11:12:12AM -0700, Frank Rowand wrote:
>>
>>    "My understanding is that the intent of KUnit is to avoid booting a kernel on
>>    real hardware or in a virtual machine.  That seems to be a matter of semantics
>>    to me because isn't invoking a UML Linux just running the Linux kernel in
>>    a different form of virtualization?
>>
>>    So I do not understand why KUnit is an improvement over kselftest.
>>
>>    ...
>>
>>    What am I missing?"
> 
> One major difference: kselftest requires a userspace environment; it
> starts systemd, requires a root file system from which you can load
> modules, etc.  Kunit doesn't require a root file system; doesn't
> require that you start systemd; doesn't allow you to run arbitrary
> perl, python, bash, etc. scripts.  As such, it's much lighter weight
> than kselftest, and will have much less overhead before you can start
> running tests.  So it's not really the same kind of virtualization.
> 
> Does this help?
> 
> 					- Ted
> 

I'm back to reply to this subthread, after a delay, as promised.

That is the type of information that I was looking for, so
thank you for the reply.

However, the reply is incorrect.  Kselftest in-kernel tests (which
is the context here) can be configured as built in instead of as
a module, and built in a UML kernel.  The UML kernel can boot,
running the in-kernel tests before UML attempts to invoke the
init process.

No userspace environment needed.  So exactly the same overhead
as KUnit when invoked in that manner.