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From:   Brendan Higgins <brendanhiggins@google.com>
Date:   Wed, 27 Feb 2019 20:18:46 -0800
Message-ID: <CAFd5g450Vy73fR5mfbuZe=KUzsFD=NAbg40GbuVmJg2udp3tmQ@mail.gmail.com>
Subject: Re: [RFC v4 00/17] kunit: introduce KUnit, the Linux kernel unit
 testing framework
To:     Thiago Jung Bauermann <bauerman@linux.ibm.com>
Cc:     Frank Rowand <frowand.list@gmail.com>,
        Kees Cook <keescook@google.com>,
        Luis Chamberlain <mcgrof@kernel.org>, shuah@kernel.org,
        Rob Herring <robh@kernel.org>,
        Kieran Bingham <kieran.bingham@ideasonboard.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Joel Stanley <joel@jms.id.au>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Joe Perches <joe@perches.com>, brakmo@fb.com,
        Steven Rostedt <rostedt@goodmis.org>,
        "Bird, Timothy" <Tim.Bird@sony.com>,
        Kevin Hilman <khilman@baylibre.com>,
        Julia Lawall <julia.lawall@lip6.fr>,
        linux-kselftest@vger.kernel.org, kunit-dev@googlegroups.com,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jeff Dike <jdike@addtoit.com>,
        Richard Weinberger <richard@nod.at>,
        linux-um@lists.infradead.org, Daniel Vetter <daniel@ffwll.ch>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Dan Williams <dan.j.williams@intel.com>,
        linux-nvdimm <linux-nvdimm@lists.01.org>,
        Knut Omang <knut.omang@oracle.com>,
        devicetree <devicetree@vger.kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>,
        Amir Goldstein <amir73il@gmail.com>, dan.carpenter@oracle.com,
        wfg@linux.intel.com
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On Fri, Feb 22, 2019 at 12:53 PM Thiago Jung Bauermann
<bauerman@linux.ibm.com> wrote:
>
>
> Frank Rowand <frowand.list@gmail.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@gmail.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.

I personally have a strong preference for dynamic function calls over
weak symbols or macros, but I can change it if it really makes
anyone's eyes bleed.