Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v2 00/17] kunit: introduce KUnit, the Linux kernel unit
 testing framework
To:     Theodore Ts'o <tytso@mit.edu>, Tim.Bird@sony.com,
        knut.omang@oracle.com, gregkh@linuxfoundation.org,
        brendanhiggins@google.com, keescook@google.com,
        kieran.bingham@ideasonboard.com, mcgrof@kernel.org,
        robh@kernel.org, sboyd@kernel.org, shuah@kernel.org,
        devicetree@vger.kernel.org, dri-devel@lists.freedesktop.org,
        kunit-dev@googlegroups.com, linux-doc@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kbuild@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-nvdimm@lists.01.org, linux-um@lists.infradead.org,
        Alexander.Levin@microsoft.com, amir73il@gmail.com,
        dan.carpenter@oracle.com, dan.j.williams@intel.com,
        daniel@ffwll.ch, jdike@addtoit.com, joel@jms.id.au,
        julia.lawall@lip6.fr, khilman@baylibre.com, logang@deltatee.com,
        mpe@ellerman.id.au, pmladek@suse.com, richard@nod.at,
        rientjes@google.com, rostedt@goodmis.org, wfg@linux.intel.com
References: <54940124-50df-16ec-1a32-ad794ee05da7@gmail.com>
 <20190507080119.GB28121@kroah.com>
 <a09a7e0e-9894-8c1a-34eb-fc482b1759d0@gmail.com>
 <20190509015856.GB7031@mit.edu>
 <580e092f-fa4e-eedc-9e9a-a57dd085f0a6@gmail.com>
 <20190509032017.GA29703@mit.edu>
 <7fd35df81c06f6eb319223a22e7b93f29926edb9.camel@oracle.com>
 <20190509133551.GD29703@mit.edu>
 <ECADFF3FD767C149AD96A924E7EA6EAF9770D591@USCULXMSG01.am.sony.com>
 <875c546d-9713-bb59-47e4-77a1d2c69a6d@gmail.com>
 <20190509214233.GA20877@mit.edu>
From:   Frank Rowand <frowand.list@gmail.com>
Message-ID: <80c72e64-2665-bd51-f78c-97f50f9a53ba@gmail.com>
Date:   Fri, 10 May 2019 14:12:40 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.6.1
MIME-Version: 1.0
In-Reply-To: <20190509214233.GA20877@mit.edu>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.