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From:   Brendan Higgins <brendanhiggins@google.com>
Date:   Tue, 27 Aug 2019 15:51:42 -0700
Message-ID: <CAFd5g451bou3bDu9VBNanH9tPQb5ybb-P7HFyQmF6ExM-U6Q1A@mail.gmail.com>
Subject: Re: [PATCH v1] kunit: fix failure to build without printk
To:     "Bird, Timothy" <Tim.Bird@sony.com>
Cc:     shuah <shuah@kernel.org>, kunit-dev@googlegroups.com,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>, sfr@canb.auug.org.au
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On Tue, Aug 27, 2019 at 3:38 PM <Tim.Bird@sony.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Brendan Higgins
> >
> > On Tue, Aug 27, 2019 at 3:00 PM shuah <shuah@kernel.org> wrote:
> > >
> > > On 8/27/19 3:36 PM, Brendan Higgins wrote:
> > > > On Tue, Aug 27, 2019 at 2:09 PM Brendan Higgins
> > > > <brendanhiggins@google.com> wrote:
> > > >>
> > > >> On Tue, Aug 27, 2019 at 2:03 PM Brendan Higgins
> > > >> <brendanhiggins@google.com> wrote:
> > > >>>
> > > >>> On Tue, Aug 27, 2019 at 1:21 PM shuah <shuah@kernel.org> wrote:
> > > >>>>
> > > >>>> On 8/27/19 11:49 AM, Brendan Higgins wrote:
> > > >>>>> Previously KUnit assumed that printk would always be present,
> > which is
> > > >>>>> not a valid assumption to make. Fix that by ifdefing out functions
> > which
> > > >>>>> directly depend on printk core functions similar to what dev_printk
> > > >>>>> does.
> > > >>>>>
> > > >>>>> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> > > >>>>> Link: https://lore.kernel.org/linux-kselftest/0352fae9-564f-4a97-
> > 715a-fabe016259df@kernel.org/T/#t
> > > >>>>> Cc: Stephen Rothwell <sfr@canb.auug.org.au>
> > > >>>>> Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
> > > >>>>> ---
> > > >>>>>    include/kunit/test.h |  7 +++++++
> > > >>>>>    kunit/test.c         | 41 ++++++++++++++++++++++++-----------------
> > > >>>>>    2 files changed, 31 insertions(+), 17 deletions(-)
> > > >>>>>
> > > >>>>> diff --git a/include/kunit/test.h b/include/kunit/test.h
> > > >>>>> index 8b7eb03d4971..339af5f95c4a 100644
> > > >>>>> --- a/include/kunit/test.h
> > > >>>>> +++ b/include/kunit/test.h
> > > >>>>> @@ -339,9 +339,16 @@ static inline void *kunit_kzalloc(struct kunit
> > *test, size_t size, gfp_t gfp)
> > > >>> [...]
> > > >>>> Okay after reviewing this, I am not sure why you need to do all
> > > >>>> this.
> > > >>>>
> > > >>>> Why can't you just change the root function that throws the warn:
> > > >>>>
> > > >>>>    static int kunit_vprintk_emit(int level, const char *fmt, va_list args)
> > > >>>> {
> > > >>>>           return vprintk_emit(0, level, NULL, 0, fmt, args);
> > > >>>> }
> > > >>>>
> > > >>>> You aren'r really doing anything extra here, other than calling
> > > >>>> vprintk_emit()
> > > >>>
> > > >>> Yeah, I did that a while ago. I think it was a combination of trying
> > > >>> to avoid an extra layer of adding and then removing the log level, and
> > > >>> that's what dev_printk and friends did.
> > > >>>
> > > >>> But I think you are probably right. It's a lot of maintenance overhead
> > > >>> to get rid of that. Probably best to just use what the printk people
> > > >>> have.
> > > >>>
> > > >>>> Unless I am missing something, can't you solve this problem by
> > including
> > > >>>> printk.h and let it handle the !CONFIG_PRINTK case?
> > > >>>
> > > >>> Randy, I hope you don't mind, but I am going to ask you to re-ack my
> > > >>> next revision since it basically addresses the problem in a totally
> > > >>> different way.
> > > >>
> > > >> Actually, scratch that. Checkpatch doesn't like me calling printk
> > > >> without using a KERN_<LEVEL>.
> > > >>
> > > >> Now that I am thinking back to when I wrote this. I think it also
> > > >> might not like using a dynamic KERN_<LEVEL> either (printk("%s my
> > > >> message", KERN_INFO)).
> > > >>
> > > >> I am going to have to do some more investigation.
> > > >
> > > > Alright, I am pretty sure it is safe to do printk("%smessage",
> > KERN_<LEVEL>);
> > > >
> > > > Looking at the printk implementation, it appears to do the format
> > > > before it checks the log level:
> > > >
> > > >
> > https://elixir.bootlin.com/linux/v5.2.10/source/kernel/printk/printk.c#L1907
> > > >
> > > > So I am pretty sure we can do it either with the vprintk_emit or with
> > printk.
> > >
> > > Let me see if we are on the same page first. I am asking if you can
> > > just include printk.h for vprintk_emit() define for both CONFIG_PRINTK
> > > and !CONFIG_PRINTK cases.
> >
> > Ah sorry, I misunderstood you.
> >
> > No, that doesn't work. I tried including linux/printk.h, and I get the
> > same error.
> >
> > The reason for this is that vprintk_emit() is only defined when
> > CONFIG_PRINTK=y:
> >
> > https://elixir.bootlin.com/linux/latest/ident/vprintk_emit
>
> Ugh.  That's just a bug in include/linux/printk.h
>
> There should be a stub definition for vprintk_emit() in the #else part
> of #ifdef CONFIG_PRINTK.
>
> You shouldn't be dealing with whether printk is present or not
> in the kunit code.  All the printk-related routines are supposed
> to evaporate themselves, based on the conditional in
> include/linux/printk.h
>
> That should be fixed there instead of in your code.

Alright. That makes sense.

I will submit a patch to fix it.

Sorry for not suggesting that, I just assumed that it was my mistake
in how I was using printk.

> Let me know if you'd like me to submit a patch for that.  I only hesitate
> because your patch depends on it, and IMHO it makes more sense to
> include it in your batch than separately. Otherwise there's a patch race
> condition.

Thanks for clearing up the confusion!