On Tuesday, September 01, 2009 4:24 PM, Tim Bird wrote:
> Marc Andre Tanner wrote:
>> The macro filters out printk messages based on a configurable verbosity
>> level (CONFIG_PRINTK_VERBOSITY).
>>
>> Signed-off-by: Marc Andre Tanner <mat@xxxxxxxxxxxxxx>
>> ---
>> include/linux/kernel.h | 24 ++++++++++++++++++++++++
>> 1 files changed, 24 insertions(+), 0 deletions(-)
>>
>> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
>> index c2b3047..1f5d01f 100644
>> --- a/include/linux/kernel.h
>> +++ b/include/linux/kernel.h
>> @@ -242,6 +242,30 @@ asmlinkage int printk(const char * fmt, ...)
>> asmlinkage int printk_unfiltered(const char *fmt, ...)
>> __attribute__ ((format (printf, 1, 2))) __cold;
>>
>> +#if defined(CONFIG_PRINTK_VERBOSITY) && CONFIG_PRINTK_VERBOSITY > 0
>> +/*
>> + * The idea here is to wrap the actual printk function with a macro which
>> + * will filter out all messages above a certain verbosity level. Because
>> + * the if condition evaluates to a constant expression the compiler will be
>> + * able to eliminate it and the resulting kernel image will be smaller.
>> + *
>> + * The check with sizeof(void*) should make sure that we don't operate on
>> + * pointers, which the compiler wouldn't be able to optimize out, but only
>> + * on string constants.
>> + */
>> +
>> +#include <linux/stringify.h>
>> +
>> +#define printk(fmt, ...) ({ \
>> + if (sizeof(fmt) == sizeof(void *) || \
>> + (((const char *)(fmt))[0] != '<' && CONFIG_PRINTK_VERBOSITY >= 4) || \
>> + (((const char *)(fmt))[0] == '<' && \
>> + ((const char *)(fmt))[1] <= *__stringify(CONFIG_PRINTK_VERBOSITY))) \
>> + printk((fmt), ##__VA_ARGS__); \
>> +})
>> +
>> +#endif /* CONFIG_PRINTK_VERBOSITY */
>> +
>> extern struct ratelimit_state printk_ratelimit_state;
>> extern int printk_ratelimit(void);
>> extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,
>
>
>
> Some places in the kernel break the message into pieces, like so:
>
> printk(KERN_ERR, "Error: first part ");
> ...
> printk(" more info for error.\n");
Technically, shouldn't the second part of the message actually be:
printk(KERN_CONT " more info for error.\n");
Maybe some mechanism could be created to handle the continued message
if they have the KERN_CONT?
> These parts would not be handled consistently under certain
> conditions.
>
> It would be confusing to see only part of the message,
> but I don't know how often this construct is used. Maybe
> another mechanism is needed to ensure that continuation
> printk lines have the same log level as their start strings.
>
> But, overall, very slick! It's nice to see a solution that doesn't
> require changing all printks statements in the kernel.
I haven't looked over this patch series yet but does it work with the
pr_<level> macros (pr_info, pr_err, etc.)?
Regards,
Hartley
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