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

From: Brendan Higgins
Date: Wed Feb 27 2019 - 23:19:01 EST

On Fri, Feb 22, 2019 at 12:53 PM Thiago Jung Bauermann
<bauerman@xxxxxxxxxxxxx> wrote:
> Frank Rowand <frowand.list@xxxxxxxxx> writes:
> > On 2/19/19 10:34 PM, Brendan Higgins wrote:
> >> On Mon, Feb 18, 2019 at 12:02 PM Frank Rowand <frowand.list@xxxxxxxxx> 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.