Subject: Re: [tip:core/printk] printk: introduce printk_once()

From: Thomas Renninger <[email-masked]>
Date: Thu, 5 Feb 2009 15:12:10 +0100

On Thursday 05 February 2009 14:04:20 Ingo Molnar wrote:
> 
> * Ingo Molnar <[email-masked]> wrote:
> 
> > printk_once() would be nice indeed - it's a frequent construct.
> 
> Something like the patch below?
Yes, nice.
Sorry, I can't test it right now, I really have to do something else.
I can give it a test in some hours or tomorrow.

I'd also wait a week with the WARN_ONCE cleanup until this is
in linux-next and then fix it up correctly just "once" :)

powernow-k8 printing a backtrace in linux-next in broken BIOS case
for a week or two shouldn't be an issue.

No need to answer, just tell me if this does not work out.

Thanks for your suggestions,

   Thomas
 
> 	Ingo
> 
> ---------------->
> Author:     Ingo Molnar <[email-masked]>
> AuthorDate: Thu, 5 Feb 2009 13:45:43 +0100
> Commit:     Ingo Molnar <[email-masked]>
> CommitDate: Thu, 5 Feb 2009 13:52:29 +0100
> 
> printk: introduce printk_once()
> 
> This pattern shows up frequently in the kernel:
> 
>   static int once = 1;
>   ...
> 
> 		if (once) {
> 			once = 0;
> 			printk(KERN_ERR "message\n");
> 		}
>   ...
> 
> So add a printk_once() helper macro that reduces this to a single line
> of:
> 
> 		printk_once(KERN_ERR "message\n");
> 
> It works analogously to WARN_ONCE() & friends. (We use a macro not
> an inline because vararg expansion in inlines looks awkward and the
> macro is simple enough.)
> 
> Signed-off-by: Ingo Molnar <[email-masked]>
> 
> 
> ---
>  include/linux/kernel.h |   17 +++++++++++++++++
>  1 files changed, 17 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 343df9e..3c183d9 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -242,6 +242,19 @@ extern struct ratelimit_state printk_ratelimit_state;
>  extern int printk_ratelimit(void);
>  extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,
>  				   unsigned int interval_msec);
> +
> +/*
> + * Print a one-time message (analogous to WARN_ONCE() et al):
> + */
> +#define printk_once(x...) ({			\
> +	static int __print_once = 1;		\
> +						\
> +	if (__print_once) {			\
> +		__print_once = 0;		\
> +		printk(x);			\
> +	}					\
> +})
> +
>  #else
>  static inline int vprintk(const char *s, va_list args)
>  	__attribute__ ((format (printf, 1, 0)));
> @@ -253,6 +266,10 @@ static inline int printk_ratelimit(void) { return 0; }
>  static inline bool printk_timed_ratelimit(unsigned long *caller_jiffies, \
>  					  unsigned int interval_msec)	\
>  		{ return false; }
> +
> +/* No effect, but we still get type checking even in the !PRINTK case: */
> +#define printk_once(x...) printk(x)
> +
>  #endif
>  
>  extern int printk_needs_cpu(int cpu);
> --
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