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

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Date:   Thu, 28 May 2020 20:33:10 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Petr Mladek <pmladek@...e.com>
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 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 ?

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.