Re: [PATCH] printk: make line continuation not result in stray emergency errors

[Roland Hieber <r.hieber@pengutronix.de>]

On Tue, Nov 20, 2018 at 09:50:44PM +0100, Roland Hieber wrote:
> The levels of pr_emerg() and pr_cont() are both set to 0. When pr_cont()
> is used to continue a previous line, and colored console output is
> enabled, this can result in garbled log messages being printed, e.g.:
> 
>     ERROR: HABv4: -------- HAB warning Event 0 --------
>     ERROR: HABv4: event data:
>     ERROR: HABv4:  dbEMERG:  00EMERG:  24EMERG:  42EMERG:   69EMERG:  30EMERG:  e1EMERG:  1d
>     ERROR: HABv4:  00EMERG:  04EMERG:  00EMERG:  02EMERG:   40EMERG:  00EMERG:  36EMERG:  06
>     ERROR: HABv4:  55EMERG:  55EMERG:  00EMERG:  03EMERG:   00EMERG:  00EMERG:  00EMERG:  00
>     ERROR: HABv4:  00EMERG:  00EMERG:  00EMERG:  00EMERG:   00EMERG:  00EMERG:  00EMERG:  00
>     ERROR: HABv4:  00EMERG:  00EMERG:  00EMERG:  01EMERG:
>     ERROR: HABv4: Status: Operation completed with warning (0x69)
> 
> Note the additional "EMERG: " in front of each continuation, which is
> inserted by pr_cont(buf) being expanded to pr_printk(0, buf). These
> additional strings show up in deep red on the console (which is not
> supported in Git commit messages…). One might argue that this is the
> same color as the "ERROR: " prefix, but when pr_cont() is used with
> pr_notice() and pr_warning(), which are printed in blue and yellow
> respectively, at least then the change in color would lead to additional
> confusion.
> 
> The log level argument to pr_printk is defined as int, so we can solve
> this by defining the level for pr_cont() to -1, which is not used for
> any loglevel:
> 
>     ERROR: HABv4: -------- HAB warning Event 0 --------
>     ERROR: HABv4: event data:
>     ERROR: HABv4:  db 00 24 42  69 30 e1 1d
>     ERROR: HABv4:  00 04 00 02  40 00 36 06
>     ERROR: HABv4:  55 55 00 03  00 00 00 00
>     ERROR: HABv4:  00 00 00 00  00 00 00 00
>     ERROR: HABv4:  00 00 00 01
>     ERROR: HABv4: Status: Operation completed with warning (0x69)
> 
> Fixes: 0fcefdd9369050f35a88b41dcd42cc5a3c6c6b33 ("printk: Add pr_cont")
> Fixes: ea0e077ed65a003e4d7a1e023aee38cbe2d14898 ("printk: Fix pr_cont")
> Signed-off-by: Roland Hieber <r.hieber@pengutronix.de>
> ---
>  include/printk.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/printk.h b/include/printk.h
> index 4384fb85ea..858e800543 100644
> --- a/include/printk.h
> +++ b/include/printk.h
> @@ -84,21 +84,21 @@ static inline int pr_print(int level, const char *format, ...)
>  #define pr_emerg(fmt, arg...)	__pr_printk(0, pr_fmt(fmt), ##arg)
>  #define pr_alert(fmt, arg...)	__pr_printk(1, pr_fmt(fmt), ##arg)
>  #define pr_crit(fmt, arg...)	__pr_printk(2, pr_fmt(fmt), ##arg)
>  #define pr_err(fmt, arg...)	__pr_printk(3, pr_fmt(fmt), ##arg)
>  #define pr_warning(fmt, arg...)	__pr_printk(4, pr_fmt(fmt), ##arg)
>  #define pr_notice(fmt, arg...)	__pr_printk(5, pr_fmt(fmt), ##arg)
>  #define pr_info(fmt, arg...)	__pr_printk(6, pr_fmt(fmt), ##arg)
>  #define pr_debug(fmt, arg...)	__pr_printk(7, pr_fmt(fmt), ##arg)
>  #define debug(fmt, arg...)	__pr_printk(7, pr_fmt(fmt), ##arg)
>  #define pr_vdebug(fmt, arg...)	__pr_printk(8, pr_fmt(fmt), ##arg)
> -#define pr_cont(fmt, arg...)	__pr_printk(0, fmt, ##arg)
> +#define pr_cont(fmt, arg...)	__pr_printk(-1, fmt, ##arg)

Hmmm. There is a different ugly detail here: pr_cont()s are always
printed regardless of the current loglevel, also with the old
implementation. I think we could remember the last used loglevel in
pr_debug(), pr_err(), pr_info() etc. code paths and let pr_printk()
decide on that basis if pr_cont() should be printed or not, i.e. from
which loglevel the current pr_cont() is a continuation.

But for now, this is out of scope of this patch. :)

 - Roland

>  
>  #define printk_once(fmt, ...)					\
>  ({								\
>  	static bool __print_once	;			\
>  								\
>  	if (!__print_once) {					\
>  		__print_once = true;				\
>  		printk(fmt, ##__VA_ARGS__);			\
>  	}							\
>  })
> -- 
> 2.19.1
> 
> 
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-- 
Roland Hieber                     | r.hieber@pengutronix.de     |
Pengutronix e.K.                  | https://www.pengutronix.de/ |
Peiner Str. 6-8, 31137 Hildesheim | Phone: +49-5121-206917-5086 |
Amtsgericht Hildesheim, HRA 2686  | Fax:   +49-5121-206917-5555 |

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