[RFC] Make dynamic debug infrastructure more flexible

On Thu, 2020-05-21 at 09:08 -0700, Joe Perches wrote:
> On Thu, 2020-05-21 at 16:28 +0300, Stanimir Varbanov wrote:
> > Here we introduce few debug macros with levels (low, medium and
> > high) and debug macro for firmware. Enabling the particular level
> > will be done by dynamic debug.
> 
> I'd rather make the logging level facility generic in
> dynamic debug than prefix all formats with what could
> be non-specific content.
> 
> From a long time ago:
> 
> https://groups.google.com/forum/#!msg/linux.kernel/VlWbno-ZAFw/k_fFadhNHXcJ

Hey Jason.

I believe there are 6 bits left in the unsigned int
use for the line number and flags in struct _ddebug

Assuming the use of a mechanism like

	pr_debug_level(level, fmt, ...)

would you be OK with something like this to enable a
level or bitmask test of dynamic debug logging output?

where the output is controlled by something like

echo 'file <filename> level <n> +p' > <debugfs>/dynamic_debug/control

to enable dynamic debug output only at level <n> or higher
or maybe match a bitmap of <n>

(modulo all the rest of the code necessary to use it?)
---
 include/linux/dynamic_debug.h | 2 ++
 1 file changed, 2 insertions(+)

Hi Joe, Jason,

On 5/21/20 11:06 PM, Joe Perches wrote:
> On Thu, 2020-05-21 at 09:08 -0700, Joe Perches wrote:
>> On Thu, 2020-05-21 at 16:28 +0300, Stanimir Varbanov wrote:
>>> Here we introduce few debug macros with levels (low, medium and
>>> high) and debug macro for firmware. Enabling the particular level
>>> will be done by dynamic debug.
>>
>> I'd rather make the logging level facility generic in
>> dynamic debug than prefix all formats with what could
>> be non-specific content.

I like the idea. To be honest I researched the dynamic debug for such
level debugging facility but found it will be too complex to implement.
I guess now when you catch me it will be better to add it in dyndbg ;) .

>>
>> From a long time ago:
>>
>> https://groups.google.com/forum/#!msg/linux.kernel/VlWbno-ZAFw/k_fFadhNHXcJ
> 
> Hey Jason.
> 
> I believe there are 6 bits left in the unsigned int
> use for the line number and flags in struct _ddebug
> 
> Assuming the use of a mechanism like
> 
> 	pr_debug_level(level, fmt, ...)
> 
> would you be OK with something like this to enable a
> level or bitmask test of dynamic debug logging output?
> 
> where the output is controlled by something like
> 
> echo 'file <filename> level <n> +p' > <debugfs>/dynamic_debug/control

I guess for bitmask it should be?

echo 'file <> bitmask <0xn> +p' >  $CONTROL

> 
> to enable dynamic debug output only at level <n> or higher
> or maybe match a bitmap of <n>
> 
> (modulo all the rest of the code necessary to use it?)
> ---
>  include/linux/dynamic_debug.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
> index abcd5fde30eb..616dbb2b5921 100644
> --- a/include/linux/dynamic_debug.h
> +++ b/include/linux/dynamic_debug.h
> @@ -38,6 +38,8 @@ struct _ddebug {
>  #define _DPRINTK_FLAGS_DEFAULT 0
>  #endif
>  	unsigned int flags:8;
> +	unsigned int level:5;
> +	unsigned int level_is_bitmask:1;
>  #ifdef CONFIG_JUMP_LABEL
>  	union {
>  		struct static_key_true dd_key_true;
> 
>