From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: linux-next: manual merge of the cleancache tree with Linus'
 tree
Date: Wed, 23 Mar 2011 23:42:24 -0700
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To: Minchan Kim <minchan.kim@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>, Dan Magenheimer <dan.magenheimer@oracle.com>, linux-next@vger.kernel.org, linux-kernel@vger.kernel.org, Linus <torvalds@linux-foundation.org>

On Thu, 24 Mar 2011 14:58:06 +0900 Minchan Kim <minchan.kim@gmail.com> wrote:

> Dan, one more thing.
> 
> #define cleancache_fs_enabled_mapping(_mapping) \
>         (mapping->host->i_sb->cleancache_poolid >= 0)
> 
> One is "_mapping", another is  "mapping"

It should be implemented in C too.  This is the case for almost all
"functions" which are implemented as macros and it's rather a mystery
why we keep on typing #define!

It is not only for cleanliness and for typechecking, but also because
constructs such as

	{
		struct address_space *foo = ...;
		if (cleancache_fs_enabled_mapping(foo))
			...;
	}

will generate an unused-var warning against `foo' if CONFIG_CLEANCACHE=n. 
Implementing the function in C fixes that.  With current gcc, anyway.