linux-ext4 - Re: [PATCH 4.4 091/100] ext2: fix empty body warnings when -Wextra is used

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Date:   Sat, 25 Apr 2020 04:47:17 -0700
From:   Joe Perches <joe@...ches.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        Jan Kara <jack@...e.com>, linux-ext4@...r.kernel.org,
        Jan Kara <jack@...e.cz>, Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.4 091/100] ext2: fix empty body warnings when -Wextra
 is used

On Sat, 2020-04-25 at 04:43 -0700, Joe Perches wrote:
> On Wed, 2020-04-22 at 11:57 +0200, Greg Kroah-Hartman wrote:
> > From: Randy Dunlap <rdunlap@...radead.org>
> > 
> > [ Upstream commit 44a52022e7f15cbaab957df1c14f7a4f527ef7cf ]
> > 
> > When EXT2_ATTR_DEBUG is not defined, modify the 2 debug macros
> > to use the no_printk() macro instead of <nothing>.
> > This fixes gcc warnings when -Wextra is used:
> > 
> > ../fs/ext2/xattr.c:252:42: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body]
> > ../fs/ext2/xattr.c:258:42: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body]
> > ../fs/ext2/xattr.c:330:42: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body]
> > ../fs/ext2/xattr.c:872:45: warning: suggest braces around empty body in an ‘else’ statement [-Wempty-body]
> > 
> > I have verified that the only object code change (with gcc 7.5.0) is
> > the reversal of some instructions from 'cmp a,b' to 'cmp b,a'.
> 
> It'd be better to use the ext4 style defines:
> 
> fs/ext4/xattr.c:# define ea_idebug(inode, fmt, ...)                                     \
> fs/ext4/xattr.c-        printk(KERN_DEBUG "inode %s:%lu: " fmt "\n",                    \
> fs/ext4/xattr.c-               inode->i_sb->s_id, inode->i_ino, ##__VA_ARGS__)
> fs/ext4/xattr.c:# define ea_bdebug(bh, fmt, ...)                                        \
> fs/ext4/xattr.c-        printk(KERN_DEBUG "block %pg:%lu: " fmt "\n",                   \
> fs/ext4/xattr.c-               bh->b_bdev, (unsigned long)bh->b_blocknr, ##__VA_ARGS__)
> --
> fs/ext4/xattr.c:# define ea_idebug(inode, fmt, ...)     no_printk(fmt, ##__VA_ARGS__)
> fs/ext4/xattr.c:# define ea_bdebug(bh, fmt, ...)        no_printk(fmt, ##__VA_ARGS__)
> 
> So the output logging won't be split across multiple lines.

And beyond that, why is a -Wextra warning being fixed in -stable at all?