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

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Message-ID: <20200414151931.GU5920@twin.jikos.cz>
Date:   Tue, 14 Apr 2020 17:19:31 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Tang Bin <tangbin@...s.chinamobile.com>
Cc:     clm@...com, josef@...icpanda.com, dsterba@...e.com,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shengju Zhang <zhangshengju@...s.chinamobile.com>
Subject: Re: [PATCH] btrfs: Fix backref.c selftest compilation warning

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 ‘is_shared_data_backref’:
>     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 ‘target.rbnode’) [-Wmissing-braces]
> 
> Signed-off-by: Tang Bin <tangbin@...s.chinamobile.com>
> Signed-off-by: Shengju Zhang <zhangshengju@...s.chinamobile.com>
> ---
>  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.