linux-kernel - Re: [PATCH v5 1/3] printf: convert self-test to KUnit

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Message-ID: <Z8sW1QBgPVUmEzUd@pathway.suse.cz>
Date: Fri, 7 Mar 2025 16:55:01 +0100
From: Petr Mladek <pmladek@...e.com>
To: Tamir Duberstein <tamird@...il.com>
Cc: Arpitha Raghunandan <98.arpi@...il.com>,
	David Gow <davidgow@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Shuah Khan <shuah@...nel.org>, Jonathan Corbet <corbet@....net>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Naveen N Rao <naveen@...nel.org>,
	Brendan Higgins <brendan.higgins@...ux.dev>,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v5 1/3] printf: convert self-test to KUnit

On Thu 2025-03-06 09:41:44, Tamir Duberstein wrote:
> On Thu, Mar 6, 2025 at 9:25 AM Tamir Duberstein <tamird@...il.com> wrote:
> >
> > On Thu, Mar 6, 2025 at 7:25 AM Petr Mladek <pmladek@...e.com> wrote:
> > >
> > > On Fri 2025-02-21 15:34:30, Tamir Duberstein wrote:
> > > > Convert the printf() self-test to a KUnit test.
> > > >
> > > > [...]
> > > >
> >
> > > 2. What was the motivation to remove the trailing '\n', please?
> > >
> > >    It actually makes a difference from the printk() POV. Messages without
> > >    the trailing '\n' are _not_ flushed to the console until another
> > >    message is added. The reason is that they might still be appended
> > >    by pr_cont(). And printk() emits only complete lines to the
> > >    console.
> > >
> > >    In general, messages should include the trailing '\n' unless the
> > >    code wants to append something later or the trailing '\n' is
> > >    added by another layer of the code. It does not seem to be this case.
> > >
> > >
> > > >                       bufsize, fmt, ret, elen);
> > > > -             return 1;
> > > > +             return;
> > > >       }
> > >
> > > [...]
> >
> > I noticed in my testing that the trailing \n didn't change the test
> > output, but I didn't know the details you shared about the trailing
> > \n. I'll restore them, unless we jump straight to the KUNIT macros per
> > the discussion above.

> Ah, I forgot that `tc_fail` already delegates to KUNIT_FAIL. This was
> the reason I removed the trailing newlines -- there is a mix of
> present and absent trailing newlines in KUNIT_* macros, and it's not
> clear to me what the correct thing is. For instance, the examples in
> Documentation/dev-tools/kunit/{start,usage}.rst omit the trailing newlines.

Honestly, I am not able to find how the KUNIT_FAIL() actually prints
the message. I can't find how assert_format() is defined.

Anyway, it seems that for example, kunit_warn() prints the messages
as is in kunit_log(). It does not add the trailing '\n' on its own.

Also I do not see any empty lines when I add back the trailing '\n'
to KUNIT_FAIL() message. This suggests that even KUNIT_FAIL()
prints the messages as is and does not add any extra trailing '\n'.

In my opinion, using the trailing '\n' is the right thing to do
from the printk() POV. Please, add it back.

Best Regards,
Petr