linux-kernel - Re: [RFC v4 00/17] kunit: introduce KUnit, the Linux kernel unit testing framework

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Date:   Fri, 22 Feb 2019 17:52:37 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.ibm.com>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Brendan Higgins <brendanhiggins@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Luis Chamberlain <mcgrof@...nel.org>, shuah@...nel.org,
        Rob Herring <robh@...nel.org>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Joel Stanley <joel@....id.au>,
        Michael Ellerman <mpe@...erman.id.au>,
        Joe Perches <joe@...ches.com>, brakmo@...com,
        Steven Rostedt <rostedt@...dmis.org>,
        "Bird\, Timothy" <Tim.Bird@...y.com>,
        Kevin Hilman <khilman@...libre.com>,
        Julia Lawall <julia.lawall@...6.fr>,
        linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        linux-um@...ts.infradead.org, Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Knut Omang <knut.omang@...cle.com>,
        devicetree <devicetree@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        Amir Goldstein <amir73il@...il.com>, dan.carpenter@...cle.com,
        wfg@...ux.intel.com
Subject: Re: [RFC v4 00/17] kunit: introduce KUnit, the Linux kernel unit testing framework


Frank Rowand <frowand.list@...il.com> writes:

> On 2/19/19 10:34 PM, Brendan Higgins wrote:
>> On Mon, Feb 18, 2019 at 12:02 PM Frank Rowand <frowand.list@...il.com> wrote:
>> <snip>
>>> I have not read through the patches in any detail.  I have read some of
>>> the code to try to understand the patches to the devicetree unit tests.
>>> So that may limit how valid my comments below are.
>>
>> No problem.
>>
>>>
>>> I found the code difficult to read in places where it should have been
>>> much simpler to read.  Structuring the code in a pseudo object oriented
>>> style meant that everywhere in a code path that I encountered a dynamic
>>> function call, I had to go find where that dynamic function call was
>>> initialized (and being the cautious person that I am, verify that
>>> no where else was the value of that dynamic function call).  With
>>> primitive vi and tags, that search would have instead just been a
>>> simple key press (or at worst a few keys) if hard coded function
>>> calls were done instead of dynamic function calls.  In the code paths
>>> that I looked at, I did not see any case of a dynamic function being
>>> anything other than the value it was originally initialized as.
>>> There may be such cases, I did not read the entire patch set.  There
>>> may also be cases envisioned in the architects mind of how this
>>> flexibility may be of future value.  Dunno.
>>
>> Yeah, a lot of it is intended to make architecture specific
>> implementations and some other future work easier. Some of it is also
>> for testing purposes. Admittedly some is for neither reason, but given
>> the heavy usage elsewhere, I figured there was no harm since it was
>> all private internal usage anyway.
>>
>
> Increasing the cost for me (and all the other potential code readers)
> to read the code is harm.

Dynamic function calls aren't necessary for arch-specific
implementations either. See for example arch_kexec_image_load() in
kernel/kexec_file.c, which uses a weak symbol that is overriden by
arch-specific code. Not everybody likes weak symbols, so another
alternative (which admitedly not everybody likes either) is to use a
macro with the name of the arch-specific function, as used by
arch_kexec_post_alloc_pages() in <linux/kexec.h> for instance.

--
Thiago Jung Bauermann
IBM Linux Technology Center