Re: [PATCH] btrfs: Fix backref.c selftest compilation warning

[David Sterba]

On Sat, Apr 11, 2020 at 11:49:15PM +0800, Tang Bin wrote:
> Fix missing braces compilation warning in the ARM
> compiler environment:
>     fs/btrfs/backref.c: In function âis_shared_data_backrefâ:
>     fs/btrfs/backref.c:394:9: warning: missing braces around initializer [-Wmissing-braces]
>       struct prelim_ref target = {0};
>     fs/btrfs/backref.c:394:9: warning: (near initialization for âtarget.rbnodeâ) [-Wmissing-braces]
> 
> Signed-off-by: Tang Bin <tangbin@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Shengju Zhang <zhangshengju@xxxxxxxxxxxxxxxxxxxx>
> ---
>  fs/btrfs/backref.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
> index 9c380e7..0cc0257 100644
> --- a/fs/btrfs/backref.c
> +++ b/fs/btrfs/backref.c
> @@ -391,7 +391,7 @@ static int is_shared_data_backref(struct preftrees *preftrees, u64 bytenr)
>  	struct rb_node **p = &preftrees->direct.root.rb_root.rb_node;
>  	struct rb_node *parent = NULL;
>  	struct prelim_ref *ref = NULL;
> -	struct prelim_ref target = {0};
> +	struct prelim_ref target = {};

I wonder why this initialization is a problem while there are about 20
other uses of "{0}". The warning is about the embedded rbnode, but why
does a more recent compiler not warn about that? Is this a missing fix
from the one you use?

I don't mind fixing compiler warnings as long as it bothers enough
people, eg. we have fixes reported by gcc 7 but I'm hesitant to fix
anything older without a good reason.