linux-kernel - Re: [PATCH 03/25] Unionfs: display informational messages only if debug is on

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Date:	Wed, 26 Sep 2007 17:24:08 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	Erez Zadok <ezk@...sunysb.edu>
cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, viro@....linux.org.uk,
	hch@...radead.org
Subject: Re: [PATCH 03/25] Unionfs: display informational messages only if
 debug is on 


On Sep 26 2007 10:01, Erez Zadok wrote:
>> 
>> On Sep 25 2007 23:09, Erez Zadok wrote:
>> >--- a/fs/unionfs/commonfops.c
>> >+++ b/fs/unionfs/commonfops.c
>> >@@ -394,8 +394,8 @@ int unionfs_file_revalidate(struct file *file, bool willwrite)
>> > 	if (willwrite && IS_WRITE_FLAG(file->f_flags) &&
>> > 	    !IS_WRITE_FLAG(unionfs_lower_file(file)->f_flags) &&
>> > 	    is_robranch(dentry)) {
>> >-		printk(KERN_DEBUG "unionfs: do delay copyup of \"%s\"\n",
>> >-		       dentry->d_name.name);
>> >+		dprintk(KERN_DEBUG "unionfs: do delay copyup of \"%s\"\n",
>> >+			dentry->d_name.name);
>> 
>> Don't we have pr_debug() for that?
>
>Jan, what's the policy on people writing their own debugging printk systems.

Generally, the rule is "don't (re)invent another debug system"

>I've looked at what other file systems do, and found out that it varies a lot:

Oh that's either old code or code that has not been reviewed properly.
Fact is that I have been made aware of pr_debug() "often enough"
on netfilter-devel, and it looks like a good idea.

>I wanted something simple to allow me to not printk something that's just
>for informational/debugging purposes, but w/o having to #ifdef the printk in
>question, or define a complex debugging-level printk system.

Surprise, pr_debug() is just that all nicely wrapped up.
Want debug? Do it like this.

#ifdef CONFIG_UNIONFS_DEBUG
#	define DEBUG 1
#endif

and pr_debug() works magic.

>Now, looking at pr_debug (in linux/kernel.h), and indeed some filesystems
>(e.g., affs and configfs) use it.  But pr_debug is only active when #define
>DEBUG is on (not CONFIG_DEBUG).  I didn't see a config option that enable
>DEBUG: is there one?

No I do not think so. But when you grep for dprintk, you should also
grep for DEBUG, to be fair :p

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