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

From: shuah
Date: Tue Aug 27 2019 - 18:55:26 EST

On 8/27/19 4:16 PM, Brendan Higgins wrote:
On Tue, Aug 27, 2019 at 3:00 PM shuah <shuah@xxxxxxxxxx> wrote:

On 8/27/19 3:36 PM, Brendan Higgins wrote:
On Tue, Aug 27, 2019 at 2:09 PM Brendan Higgins
<brendanhiggins@xxxxxxxxxx> wrote:

On Tue, Aug 27, 2019 at 2:03 PM Brendan Higgins
<brendanhiggins@xxxxxxxxxx> wrote:

On Tue, Aug 27, 2019 at 1:21 PM shuah <shuah@xxxxxxxxxx> 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

Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Signed-off-by: Brendan Higgins <brendanhiggins@xxxxxxxxxx>
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

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

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

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:

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:

This is the real problem here. printk.h defines several for

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

Okay, cool.

So it appears that we have to weigh the following trade-offs:

Using vprintk_emit:

- 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()

Oh, I was just saying that I heavily based my implementation of
kunit_printk on dev_printk. So I have a high degree of confidence that
it is okay to use it the way that I am using it.

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

Right, and the problem with the alternative, is there is no good
kernel API for logging with the log level set dynamically. printk
prefers to have it as a string prefix on the format string, but I
cannot do that because I need to add my own prefix to the format

So, I guess I should just go ahead and address the earlier comments on
this patch?

So what does your code do in the case of !CONFIG_PRINTK. From my read of
it, it returns 0 from kunit_printk_emit(0 from my read of it. What I am
saying is this is a lot of indirection instead of fixing the leaf
function which is kunit_vprintk_emit().

+#else /* CONFIG_PRINTK */
+static inline int kunit_printk_emit(int level, const char *fmt, ...)
+ return 0;
+#endif /* CONFIG_PRINTK */

Does the following work?

#if defined CONFIG_PRINTK
static int kunit_vprintk_emit(int level, const char *fmt, va_list args)
return vprintk_emit(0, level, NULL, 0, fmt, args);
static int kunit_vprintk_emit(int level, const char *fmt, va_list args)
return 0;

I think the real problem is in the printk.h with its missing define for
vprintk_emit() for !CONFIG_PRINTK case. There seem to only one call for
this in drivers/base/core.c in CONFIG_PRINTK path. Unless I am totally
missing some context for why there is no stub for vprintk_emit() for

-- Shuah