Re: [Announce] Linux-tiny project revival

Arnd Bergmann
2007-09-27T07:12:38Z

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.