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From: Arnd Bergmann <arnd@arndb.de>
To: Rob Landley <rob@landley.net>
Subject: Re: [Announce] Linux-tiny project revival
Date: Thu, 27 Sep 2007 09:00:36 +0200
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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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