linux-kernel - Re: [PATCH] twist: allow converting pr_devel()/pr_debug() into printk(KERN

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Message-ID: <20200528121455.GD11286@linux-b0ei>
Date:   Thu, 28 May 2020 14:14:55 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] twist: allow converting pr_devel()/pr_debug() into
 printk(KERN_DEBUG)

On Thu 2020-05-28 20:33:10, Tetsuo Handa wrote:
> On 2020/05/28 19:59, Petr Mladek wrote:
> > 2. Add twist into vprintk_store(). In the current, implementation
> >    it would do:
> > 
> >   #if TWIST
> > 	return text_len;
> >   #endif
> > 
> > 	return log_output(facility, level, lflags,
> > 			  dict, dictlen, text, text_len);
> 
> This part could be possible. But
> 
> > 1. Add twist into ddebug_add_module() and enable all newly added
> >    entries by default. For example, by calling
> >    ddebug_exec_query("*:+p", const char *modname) or what is the syntax.
> > 
> >    This will cause that any pr_devel() variant will always get called.
> 
> how to handle
> 
> >>   #define no_printk(fmt, ...)                             \
> >>   ({                                                      \
> >>           if (0)                                          \
> >>                   printk(fmt, ##__VA_ARGS__);             \
> >>           0;                                              \
> >>   })
> 
> part used by e.g. pr_devel() ? Since this macro is not using dynamic debug
> interface, vprintk_store() will not be called from the beginning. Are you
> suggesting that we should convert no_printk() to use dynamic debug interface ?

OK, this is one more path that would need special handling. Two paths
are much better than 15.


> I don't know whether enabling only in linux-next makes sense. Since not all tests
> are equally done on each git tree, available only in linux-next will not be able
> to cover all callers. Just using CONFIG_TWIST_ALWAYS_EVALUATE_PRINTK_ARGUMENTS=y
> and CONFIG_DYNAMIC_DEBUG=n is the simplest.

I hope that tests done on linux-next would be enough to trigger some
bugs. If you do not see problems in linux-next then this twist
probably is not worth the effort and code complications.

Best Regards,
Petr