Re: [PATCH v18 00/19] kunit: introduce KUnit, the Linux kernel unit testing framework

Brendan Higgins
2019-10-07T08:20:47Z

On Sun, Oct 6, 2019 at 9:55 AM Theodore Y. Ts'o <tytso@mit.edu> wrote:
>
> On Fri, Oct 04, 2019 at 06:18:04PM -0700, Brendan Higgins wrote:
> > > Let's talk about current state. Right now kunit is in linux-next and
> > > we want to add a few more tests. We will have to coordinate the effort.
> > > Once kunit get into mainline, then the need for this coordination goes
> > > down.
> >
> > Sure, I was just thinking that getting other people to write the tests
> > would be better. Since not only is it then useful to someone else, it
> > provides the best possible exercise of KUnit.
>
> Well, one thing we *can* do is if (a) if we can create a kselftest
> branch which we know is stable and won't change, and (b) we can get
> assurances that Linus *will* accept that branch during the next merge
> window, those subsystems which want to use kself test can simply pull
> it into their tree.

Yeah, I can't think of any reason that you haven't outlined already
why that might not work, but that seems kind of like circumventing
Linus.

> We've done this before in the file system world, when there has been
> some common set of changes needed to improve, say, Direct I/O, where
> the changes are put into a standalone branch, say, in the xfs tree,
> and those file systems which need it as a building block can pull it
> into their tree, and then add the changes needed to use those changes
> into their file system git tree. These changes are generally not
> terribly controversial, and we've not had to worry about people want
> to bikeshed the changes.
>
> There is a risk with doing this of course, which is that if the branch
> *is* controversial, or gets bike-shedded for some reason, then Linus
> gets upset and any branches which depended on said branch will get
> rejected at the next merge window. Which is the requirement for (a)
> and (b) above. Presumably, the fact that people were unwilling to let
> Kunit land during this merge window might will *because* we think more
> changes might be pending?

My understanding, based on what I have been told, is that we were
simply unlucky with the timing when Linus pulled the branch in the
first week of the 5.4 merge window (Friday), such that once I fixed
the directory naming issue, the updated changes didn't spend enough
time in linux-next. And now with this issue fixed and KUnit back in
linux-next, if nothing interesting happens between now and 5.5, it
will be accepted in the 5.5 merge window. I do not think that anyone
is expecting anymore changes before merging.

Shuah, Linus, is my understanding correct?

> The other thing I suppose I can do is to let the ext4 kunit tests land
> in ext4 tree, but with the necessary #ifdef's around things like
> "#include <kunit/test.h>" so that the build won't blow up w/o kunit
> changes being in the tree that I'm building. It means I won't be able
> to run the tests without creating a test integration branch and
> merging in kunit by hand, which will super-annoying, of course. And
> if some of the bike-shedding is in Kunit's interfaces, then that
> becomes problematic as well, since any tests that are in ext4.git tree
> might change if people want to rename Kunit's publically exported
> functions (for example).

Yeah, that seems even worse. I'm sorry to have caused this frustration.

> > Hey Ted, do you know if that ext4 timestamp test can go in through
> > linux-kselftest? It seemed fairly self-contained. Or is that what you
> > were saying wouldn't work for you?
>
> Well, I was hoping that we might start creating more tests beyond just
> the ext4 timestamp tests....

Okay, that's what I thought (and what I hoped) you were saying :-)

I hope we can figure out something that will work for you. Or
otherwise that you won't mind waiting until 5.5.

Sorry