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 04:43:31 -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 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.

> diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c
[]
> @@ -55,6 +55,7 @@
>  
>  #include <linux/buffer_head.h>
>  #include <linux/init.h>
> +#include <linux/printk.h>
>  #include <linux/slab.h>
>  #include <linux/mbcache.h>
>  #include <linux/quotaops.h>
> @@ -85,8 +86,8 @@
>  		printk("\n"); \
>  	} while (0)
>  #else
> -# define ea_idebug(f...)
> -# define ea_bdebug(f...)
> +# define ea_idebug(inode, f...)	no_printk(f)
> +# define ea_bdebug(bh, f...)	no_printk(f)
>  #endif
>  
>  static int ext2_xattr_set2(struct inode *, struct buffer_head *,

---
 fs/ext2/xattr.c | 22 ++++++++--------------
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c
index 943cc46..7740582 100644
--- a/fs/ext2/xattr.c
+++ b/fs/ext2/xattr.c
@@ -72,21 +72,15 @@
 #define IS_LAST_ENTRY(entry) (*(__u32 *)(entry) == 0)
 
 #ifdef EXT2_XATTR_DEBUG
-# define ea_idebug(inode, f...) do { \
-		printk(KERN_DEBUG "inode %s:%ld: ", \
-			inode->i_sb->s_id, inode->i_ino); \
-		printk(f); \
-		printk("\n"); \
-	} while (0)
-# define ea_bdebug(bh, f...) do { \
-		printk(KERN_DEBUG "block %pg:%lu: ", \
-			bh->b_bdev, (unsigned long) bh->b_blocknr); \
-		printk(f); \
-		printk("\n"); \
-	} while (0)
+# define ea_idebug(inode, fmt, ...)					\
+	printk(KERN_DEBUG "inode %s:%lu: " fmt "\n",			\
+	       inode->i_sb->s_id, inode->i_ino, ##__VA_ARGS__)
+# define ea_bdebug(bh, fmt, ...)					\
+	printk(KERN_DEBUG "block %pg:%lu: " fmt "\n",			\
+	       bh->b_bdev, (unsigned long)bh->b_blocknr, ##__VA_ARGS__)
 #else
-# define ea_idebug(inode, f...)	no_printk(f)
-# define ea_bdebug(bh, f...)	no_printk(f)
+# define ea_idebug(inode, fmt, ...)	no_printk(fmt, ##__VA_ARGS__)
+# define ea_bdebug(bh, fmt, ...)	no_printk(fmt, ##__VA_ARGS__)
 #endif
 
 static int ext2_xattr_set2(struct inode *, struct buffer_head *,