linux-kernel - Re: [PATCH 1/7] dynamic debug v2

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Date:	Thu, 17 Jul 2008 17:20:40 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Greg KH <greg@...ah.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	joe@...ches.com, nick@...k-andrew.net, randy.dunlap@...cle.com
Subject: Re: [PATCH 1/7] dynamic debug v2 - infrastructure

On Thu, Jul 17, 2008 at 12:01:03AM -0700, Greg KH wrote:
> Return-Path: <greg@...ah.com>
> On Tue, Jul 15, 2008 at 05:31:08PM -0400, Jason Baron wrote:
> > diff --git a/include/linux/device.h b/include/linux/device.h
> > index 1a06026..fb03dbc 100644
> > --- a/include/linux/device.h
> > +++ b/include/linux/device.h
> > @@ -592,7 +592,11 @@ extern const char *dev_driver_string(struct device *dev);
> >  #define dev_info(dev, format, arg...)		\
> >  	dev_printk(KERN_INFO , dev , format , ## arg)
> >  
> > -#ifdef DEBUG
> > +#if defined(CONFIG_DYNAMIC_PRINTK_DEBUG)
> > +#define dev_dbg(dev, format, ...) do { \
> > +	dynamic_dev_dbg(dev, format, ##__VA_ARGS__); \
> > +	} while (0)
> > +#elif defined(DEBUG)
> >  #define dev_dbg(dev, format, arg...)		\
> >  	dev_printk(KERN_DEBUG , dev , format , ## arg)
> >  #else
> 
> In looking at your follow-on patches, where you add this to subsystems,
> it seems that you have to add a lot of #include <linux/dynamic_printk.h>
> lines.
> 
> And in looking at this modification to device.h, I think lots of the
> kernel should break, but you are getting it "for free" by including the
> .h file within kernel.h.
> 
> Why not also include it here in device.h?
> 

I don't believe the follow-on patches include "<linux/dynamic_printk.h>". 
However, some of them do include a subsystem specific #include. For example,
the cpufreq subsystem include, <linux/dynamic_debug_cpufreq.h>:

+++ b/include/linux/dynamic_debug_cpufreq.h
@@ -0,0 +1,8 @@
+#define DYNAMIC_DEBUG_NUM_FLAGS "3"
+#define DYNAMIC_DEBUG_FLAG_NAMES "CPUFREQ_DEBUG_CORE,CPUFREQ_DEBUG_DRIVER,CPUFREQ_DEBUG_GOVERNOR"
+#define DYNAMIC_DEBUG_TYPE "2"
+#define DYNAMIC_DEBUG_MODNAME "cpufreq_shared"
+
+#ifdef CONFIG_CPU_FREQ_DEBUG
+#define DEBUG 1
+#endif

This header file conveys that cpufreq subsystem, wants non-default options-it
has 3 debugging flags that can be set, and all modules in the subsystem are
tied together using the module name: "cpufreq_shared".  

I don't have an explicit #include of kernel.h in device.h b/c it already picked
up.

> Also, with this change, code that is already using dev_dbg() today is
> instantly converted over to this logic now, right?
> 

that is correct. any callers of dev_dbg() don't have to do anything. its really
only the more complex debugging, where there are flags or levels that need to
make adjustments to work with the new infrastructure.

thanks,

-Jason 
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