Messages in this thread | | | Subject | Re: [PATCH v1] kunit: fix failure to build without printk | From | shuah <> | Date | Tue, 27 Aug 2019 16:55:21 -0600 |
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On 8/27/19 4:16 PM, Brendan Higgins wrote: > 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: >
This is the real problem here. printk.h defines several for !CONFIG_PRINTK case.
> https://elixir.bootlin.com/linux/latest/ident/vprintk_emit > >> 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: >>> >>> 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() > > 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 > string. > > 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); } #else static int kunit_vprintk_emit(int level, const char *fmt, va_list args) { return 0; } #endif
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 !CONFIG_PRINTK case
thanks, -- Shuah
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