Re: [PATCH v2 linux-kselftest-test 1/3] kunit: allow kunit tests to be loaded as a module

[Brendan Higgins <brendanhiggins@google.com>]

Sorry for the delayed reply. I will be on vacation until Wednesday,
October 16th.

On Wed, Oct 9, 2019 at 9:36 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>
> On Tue, 8 Oct 2019, Brendan Higgins wrote:
>
> > On Tue, Oct 08, 2019 at 03:55:44PM +0100, Alan Maguire wrote:
[...]
> > > diff --git a/lib/kunit/string-stream.c b/lib/kunit/string-stream.c
> > > index e6d17aa..e4f3a97 100644
> > > --- a/lib/kunit/string-stream.c
> > > +++ b/lib/kunit/string-stream.c
> > > @@ -100,6 +100,7 @@ int string_stream_vadd(struct string_stream *stream,
> > >
> > >     return 0;
> > >  }
> > > +EXPORT_SYMBOL_GPL(string_stream_vadd);
> >
> > Is this actually needed by anything other than lib/kunit/test.c right
> > now? Maybe we should move the include file into the kunit/ directory to
> > hide these so no one else can use them.
> >
>
> I tried this, and it's the right answer I think but it exposes
> a problem with symbol visibility when kunit is compiled as a module.
> More on this below...
>
> > >  int string_stream_add(struct string_stream *stream, const char *fmt, ...)
> > >  {
> > > @@ -112,6 +113,7 @@ int string_stream_add(struct string_stream *stream, const char *fmt, ...)
> > >
> > >     return result;
> > >  }
> > > +EXPORT_SYMBOL_GPL(string_stream_add);
> > [...]
> > > diff --git a/lib/kunit/test.c b/lib/kunit/test.c
> > > index c83c0fa..e7896f1 100644
> > > --- a/lib/kunit/test.c
> > > +++ b/lib/kunit/test.c
> > [...]
> > > @@ -50,6 +51,7 @@ static unsigned long kunit_test_timeout(void)
> > >      * For more background on this topic, see:
> > >      * https://mike-bland.com/2011/11/01/small-medium-large.html
> > >      */
> > > +#ifndef MODULE
> >
> > Why is this block of code "ifndef MODULE"?
> >
>
> Symbol visibility is the problem again; sysctl_hung_task_timeout_secs
> isn't exported so when kunit is a module it can't find the symbol.
>
> I think I saw Kees mentioned something about symbol lookup too; in KTF
> Knut solved this by defining ktf_find_symbol(). I'd suggest we may need a
> kunit_find_symbol() with a function signature

I thought we were just talking about exposing symbols for linking
outside of a compilation unit (static vs. not static); nevertheless, I
think you are right that it is relevant here. Kees, thoughts?

> void *kunit_find_symbol(const char *modname, const char *symbol_name);
>
> ...which does a [module_]kallsyms_lookup_sym().
>
> If the above makes sense I can look at adding it as a patch (and adding
> a test of it of course!). What do you think?

So that won't work if you are trying to link against a symbol not in a
module, right? Also, it won't work against a static symbol, right?

Even so, I think it is pretty wonky to expect users to either a)
export any symbol name to be tested, or b) have to access them via
kunit_find_symbol. I think it is fine to have some tests that cannot
be compiled as modules, if there is no other user friendly way to make
this work in those cases.

Thoughts?