Re: Prevent compiler warning on block.c

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

05.05.2021 10:59, Miroslav Rezanina wrote:
> Commit 3108a15cf (block: introduce bdrv_drop_filter()) introduced uninitialized
> variable to_cow_parent in bdrv_replace_node_common function that is used only when
> detach_subchain is true. It is used in two places. First if block properly initialize
> the variable and second block use it.
> 
> However, compiler treats this two blocks as two independent cases so it thinks first
> block can fail test and second one pass (although both use same condition). This cause
> warning that variable can be uninitialized in second block.
> 
> To prevent this warning, initialize the variable with NULL.
> 
> Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
> ---
> diff --git a/block.c b/block.c
> index 874c22c43e..3ca27bd2d9 100644
> --- a/block.c
> +++ b/block.c
> @@ -4851,7 +4851,7 @@ static int bdrv_replace_node_common(BlockDriverState *from,
>       Transaction *tran = tran_new();
>       g_autoptr(GHashTable) found = NULL;
>       g_autoptr(GSList) refresh_list = NULL;
> -    BlockDriverState *to_cow_parent;
> +    BlockDriverState *to_cow_parent = NULL;

May be

+    BlockDriverState *to_cow_parent = NULL; /* Silence compiler warning */

>       int ret;
> 
>       if (detach_subchain) {
> 

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

-- 
Best regards,
Vladimir