[PATCH] dm block manager: use do/while(0) for empty macros

[PATCH] dm block manager: use do/while(0) for empty macros

[Arnd Bergmann]

make W=1 reports a new warning for the dm-block-manager:

drivers/md/persistent-data/dm-block-manager.c: In function ‘dm_bm_unlock’:
drivers/md/persistent-data/dm-block-manager.c:598:3: error: suggest braces around empty body in an ‘else’ statement [-Werror=empty-body]

This is completely harmless, but generally speaking it's a good idea to
address this warning as it can often detect nasty bugs, and replacing
empty macros with "do { } while (0)" is generally considered good style
to make code more robust anyway.

Fixes: f94bdb2e26b6 ("dm block manager: make block locking optional")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/md/persistent-data/dm-block-manager.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/md/persistent-data/dm-block-manager.c b/drivers/md/persistent-data/dm-block-manager.c
index b619c383d88d..a6dde7cab458 100644
--- a/drivers/md/persistent-data/dm-block-manager.c
+++ b/drivers/md/persistent-data/dm-block-manager.c
@@ -306,13 +306,13 @@ static void report_recursive_bug(dm_block_t b, int r)
 
 #else  /* !CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING */
 
-#define bl_init(x)
+#define bl_init(x) do { } while (0)
 #define bl_down_read(x) 0
 #define bl_down_read_nonblock(x) 0
-#define bl_up_read(x)
+#define bl_up_read(x) do { } while (0)
 #define bl_down_write(x) 0
-#define bl_up_write(x)
-#define report_recursive_bug(x, y)
+#define bl_up_write(x) do { } while (0)
+#define report_recursive_bug(x, y) do { } while (0)
 
 #endif /* CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING */
 
-- 
2.9.0

Re: dm block manager: use do/while(0) for empty macros

[Mike Snitzer]

On Tue, Oct 25 2016 at 11:54am -0400,
Arnd Bergmann <arnd@arndb.de> wrote:

> make W=1 reports a new warning for the dm-block-manager:
> 
> drivers/md/persistent-data/dm-block-manager.c: In function ‘dm_bm_unlock’:
> drivers/md/persistent-data/dm-block-manager.c:598:3: error: suggest braces around empty body in an ‘else’ statement [-Werror=empty-body]
> 
> This is completely harmless, but generally speaking it's a good idea to
> address this warning as it can often detect nasty bugs, and replacing
> empty macros with "do { } while (0)" is generally considered good style
> to make code more robust anyway.
> 
> Fixes: f94bdb2e26b6 ("dm block manager: make block locking optional")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Thanks Arnd, I'll fold this in.  I suspected this was the right thing to
do.  Strange that my build didn't say anything through, I used:
make C=1 CF=-D__CHECK_ENDIAN__ M=drivers/md

I'll be sure to use make W=1 in the future.

> ---
>  drivers/md/persistent-data/dm-block-manager.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/md/persistent-data/dm-block-manager.c b/drivers/md/persistent-data/dm-block-manager.c
> index b619c383d88d..a6dde7cab458 100644
> --- a/drivers/md/persistent-data/dm-block-manager.c
> +++ b/drivers/md/persistent-data/dm-block-manager.c
> @@ -306,13 +306,13 @@ static void report_recursive_bug(dm_block_t b, int r)
>  
>  #else  /* !CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING */
>  
> -#define bl_init(x)
> +#define bl_init(x) do { } while (0)
>  #define bl_down_read(x) 0
>  #define bl_down_read_nonblock(x) 0
> -#define bl_up_read(x)
> +#define bl_up_read(x) do { } while (0)
>  #define bl_down_write(x) 0
> -#define bl_up_write(x)
> -#define report_recursive_bug(x, y)
> +#define bl_up_write(x) do { } while (0)
> +#define report_recursive_bug(x, y) do { } while (0)
>  
>  #endif /* CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING */
>  
> -- 
> 2.9.0
> 
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