linux-kernel - Re: [PATCH v1] kunit: fix failure to build without printk

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Message-ID: <10b44374-829d-0daa-8fb0-4450582cb40c@kernel.org>
Date:   Tue, 27 Aug 2019 16:00:55 -0600
From:   shuah <shuah@...nel.org>
To:     Brendan Higgins <brendanhiggins@...gle.com>
Cc:     kunit-dev@...glegroups.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        shuah <shuah@...nel.org>
Subject: Re: [PATCH v1] kunit: fix failure to build without printk

On 8/27/19 3:36 PM, Brendan Higgins wrote:
> On Tue, Aug 27, 2019 at 2:09 PM Brendan Higgins
> <brendanhiggins@...gle.com> wrote:
>>
>> On Tue, Aug 27, 2019 at 2:03 PM Brendan Higgins
>> <brendanhiggins@...gle.com> wrote:
>>>
>>> On Tue, Aug 27, 2019 at 1:21 PM shuah <shuah@...nel.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@...radead.org>
>>>>> Link: https://lore.kernel.org/linux-kselftest/0352fae9-564f-4a97-715a-fabe016259df@kernel.org/T/#t
>>>>> Cc: Stephen Rothwell <sfr@...b.auug.org.au>
>>>>> Signed-off-by: Brendan Higgins <brendanhiggins@...gle.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.

I am not asking you to use printk() in place of vprintk_emit().
It is perfectly fine to use vprintk_emit()

> 
> So it appears that we have to weigh the following trade-offs:
> 
> Using vprintk_emit:
> 
> Pros:
>   - That's what dev_printk uses.

Not sure what you mean by this. I am suggesting if you can just
call vprintk_emit() and include printk.h and not have to ifdef
around all the other callers of kunit_vprintk_emit()

Yes. There is the other issue of why do you need the complexity
of having kunit_vprintk_emit() at all.

thanks,
-- Shuah