linux-kernel - Re: RFC: dynamic debug enhancements?

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Date:	Mon, 29 Aug 2011 12:21:53 -0600
From:	Jim Cromie <jim.cromie@...il.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Jason Baron <jbaron@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: RFC: dynamic debug enhancements?

On Tue, Aug 23, 2011 at 7:00 PM, Joe Perches <joe@...ches.com> wrote:
> On Tue, 2011-08-23 at 10:23 -0400, Jason Baron wrote:
>> On Sun, Aug 21, 2011 at 05:15:43PM -0700, Joe Perches wrote:
>> > I recently went through drivers/media and updated
>> > lots of calls to pr_<level>.
>> > A common pattern for debugging there and elsewhere
>> > treewide is the use of macros like:
>> > #define dprintk(level, fmt, ...)                    \
>> > do {                                                        \
>> >     if (level > [some_modparam_var])                \
>> >             pr_debug(fmt, ##__VA_ARGS__);           \
>> > } while (0)
>> > and
>> > #define dprintk(mask, fmt, ...)                             \
>> > do {                                                        \
>> >     if (mask & [some_modparam_var])                 \
>> >             pr_debug(fmt, ##__VA_ARGS__);           \
>> > } while (0)
>> > It might be useful to have standardized calls
>> > like pr_debug_level and pr_debug_mask instead
>> > of multiple hand-rolled variants treewide.
> []
>> looks interesting. I'm wondering how we handle module parameters though?
>> In the dynamic debug disabled case, we'd have to standardize the module
>> params names. And for the dynamic debug enabled case, I'm not sure how
>> we would honor those module params?
>
> One possibility would be to require a #define
> before use.
>
> Something like the DEBUG_VARIABLE used in
> drivers/media/ and include/media/.
>
> Maybe something like:
>
> #define DYNAMIC_DEBUG_LEVEL_VARIABLE module_var_foo
> and/or
> #define DYNAMIC_DEBUG_MASK_VARIABLE module_var_bar
>
> and
>
> $ echo 'module <foo> mask <n>' > <debugfs>/dynamic_debug/control
> and
> $ echo 'module <foo> level <n>' > <debugfs>/dynamic_debug/control
>
> could work to set the module control variable too.
>
>
>

how about just passing in condition directly ?

#define pr_dbg_if( cond, fmt, ... )                  \
do {                                                        \
    if (cond)                \
            pr_debug(fmt, ##__VA_ARGS__);           \
} while (0)

this will serve both mask and level, and could underlie both of them,
and its clear - no hidden checks against a variable named elsewhere.
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