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Subject: Re: [PATCH 2/8] dynamic debug - core infrastructure
From: Joe Perches <joe@perches.com>
To: Jason Baron <jbaron@redhat.com>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, greg@kroah.com,
       nick@nick-andrew.net, randy.dunlap@oracle.com
In-Reply-To: <20080613190039.GC8813@redhat.com>
References: <20080613190039.GC8813@redhat.com>
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Date: Fri, 13 Jun 2008 15:30:18 -0700
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On Fri, 2008-06-13 at 15:00 -0400, Jason Baron wrote:
> This is the core patch that implements a new dynamic debug
> infrastructure.

Some general and specific comments.

> +int dynamic_printk_enabled[NR_CPUS];

I don't understand why you use NR_CPUS.

Also, I think the major use cases are 1 or 2 modules enabled,
no modules enabled, or all modules enabled, so the hashing of
module names is particularly not useful.

Any pr_debug or dev_dbg is in a slow path.

I think a list and a direct comparison to KBUILD_MODNAME
would be simpler and as fast as necessary.

> +         To set the level or flag value for type 'level' or 'flag': 
> +
> +               $echo "set level=<#> <module_name>" > dynamic_printk/modules
> +

I think that set level=<#> should also work for "all"

Perhaps a simpler interface would be to use
	enable <module> <level>
where <level> not specified is 0.

> +int unregister_debug_module(char *mod_name)
> +{
> +	struct debug_name *element;
> +	struct debug_name *parent = NULL;
> +	int ret = 0;
> +	int i;
> +
> +	down(&debug_list_mutex);
> +	element = find_debug_module(mod_name);
> +	if (!element) {
> +		ret = -EINVAL;
> +		goto out;
> +	}

[]

> +out:
> +	up(&debug_list_mutex);
> +	return 0;
> +}

Because the return values aren't used,
the functions might as well be declared void

You should probably add a sprinkling of "const"
to the argument lists.

+extern void dynamic_printk(char *, char *, ...);

+	dynamic_printk(KBUILD_MODNAME,                     \
+			KERN_DEBUG KBUILD_MODNAME ": " fmt,\

Instead of prefixing every fmt with KBUILD_MODNAME ": ",
why not change this to something like:

extern void dynamic_printk(const char *level, const char *module,
			   const char *fmt, ...);

and just do the printk in 2 parts?

	if (module_enabled) {
		printk("%s%s: ", level, module);
		vprintk(fmt, args);
	}

If not that, why should dynamic_printk prefix a KBUILD_MODNAME
at all?  Why not just check if the module is enabled, then
output what the code specifies?

trivial:  The dynamic versions of the dev_dbg and pr_debug macros
don't return the number of chars output, but always return 0.