linux-kernel - Re: early_printk accessing __log

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Date:	Wed, 18 Jul 2007 23:58:24 -0400
From:	Robin Getz <rgetz@...ckfin.uclinux.org>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, "Greg Ungerer" <gerg@...pgear.com>,
	"Russell King" <rmk@....linux.org.uk>,
	Paul Mundt <lethal@...ux-sh.org>,
	"Mike Frysinger" <vapier.adi@...il.com>,
	"Tim Bird" <tim.bird@...sony.com>, bryan.wu@...log.com
Subject: Re: early_printk accessing __log_buf

On Wed 18 Jul 2007 20:26, Andrew Morton pondered:
> Robin Getz wrote:
> > [need to access _log_buf from external for early debugging code]
> > 
> > Something simple like - early_copy_log_buff(void *dest, size_t n) 
> > 
> > copies n bytes from log_buf to memory area dest. Returns number of
> > bytes that could not be copied. Can find out how many bytes are in
> > the log_buff by calling with zero size.
> 
> When I was at $EARLIER_EMPLOYER, we had code in there to copy the last
> kilobyte-odd of the log buffer into flash when the box oopsed.
> 

Hmm - I think that if you call with NULL dest, and have it advance the 
pointer, you could do the same thing with something like:

 /* see how many bytes are in the buff */
 length = early_copy_log_buff(NULL, NULL);
 /* advance the pointer, so we only copy the last 1k */
 if (length >= 1024 )
    left = early_copy_log_buff(NULL, length - 1024);
 /* copy to temp buffer, to save to flash */
 early_copy_log_buff(buff, 1024);
 save_buff_to_flash(buff);

That way - you can put this in the standard places for failure, and still have 
only one function polluting printk.c (Although if you want to use it for 
failure trapping - it's up for "normal" run time use, and doesn't go into 
__init. 

> Probably there are others, but they'll mainly be in the consumer/embedded
>  area, and those sorts of engineers don't read this mailing list much.

Adding a few more 'embedded' folks - who might have some thoughts/opinions.

-Robin

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