linux-kernel - Re: [Announce] Linux-tiny project revival

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Date:	Thu, 27 Sep 2007 09:00:36 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Rob Landley <rob@...dley.net>
Cc:	linux-tiny@...enic.com, Tim Bird <tim.bird@...sony.com>,
	linux kernel <linux-kernel@...r.kernel.org>,
	CE Linux Developers List <celinux-dev@...e.celinuxforum.org>,
	Michael Opdenacker <michael@...e-electrons.com>
Subject: Re: [Announce] Linux-tiny project revival

On Thursday 20 September 2007, you wrote:
> So instead of:
>   printk(KERN_NOTICE "Fruit=%d\n", banana);
> It would now be:
>   printk(KERN_NOTICE, "Fruit=%d\n", banana);
> 
> Change the header from:
>   #define KERN_NOTICE "<5>"
> to:
>   #define KERN_NOTICE 5
> 
> Then you can change the printk guts to do something vaguely like (untested):
> #define printk(arg1, arg2, ...) actual_printk("<" #arg1 ">" arg2, __VA_ARGS__)
> 
> And so far no behavior has changed.  But now the _fun_ part is, you can add a 
> config symbol for "what is the minimum loglevel I care about?"  Set that as a 
> number from 0-9.  And then you can define the printk to do:
> 
> #define printk(level, str, ...) \
>   do { \
>     if (level < CONFIG_PRINTK_DOICARE) \
>       actual_printk("<" #level ">" str, __VA_ARGS__); \
>   } while(0);
> 

Assuming that we want to go down that road, I think you can do better with
more evil macro magic, by using something along the lines of

#define KERN_NOTICE "<5>",

#define PRINTK_CONTINUED "",

 #define printk(level, str, ...) \
   do { \
     if (sizeof(level) == 1) /* continued printk */\
	actual_printk(str, __VA_ARGS__); \
     else if ((level[1] - '0') < CONFIG_PRINTK_DOICARE) \
       actual_printk(level str, __VA_ARGS__); \
   } while(0);

Then you don't have to change every single printk in the kernel, but
only those that don't currently come with a log level. More importantly,
you can do the conversion without a flag day, by spreading (an empty)
PRINTK_CONTINUED in places that do need a printk without a log level.

	Arnd <><
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