Re: [PATCH 11/21] block/copy-before-write: use file child instead of backing

[Max Reitz <mreitz@redhat.com>]

On 17.05.21 08:44, Vladimir Sementsov-Ogievskiy wrote:
> We are going to publish copy-before-write filter, and there no public
> backing-child-based filter in Qemu. No reason to create a precedent, so
> let's refactor copy-before-write filter instead.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   block/copy-before-write.c | 40 ++++++++++++++++++++++-----------------
>   1 file changed, 23 insertions(+), 17 deletions(-)
> 
> diff --git a/block/copy-before-write.c b/block/copy-before-write.c
> index af2bb97a30..2f06a524b8 100644
> --- a/block/copy-before-write.c
> +++ b/block/copy-before-write.c

[...]

> @@ -201,22 +195,34 @@ BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
>       state->target = bdrv_attach_child(top, target, "target", &child_of_bds,
>                                         BDRV_CHILD_DATA, errp);
>       if (!state->target) {
> +        error_prepend(errp, "Cannot attach target child: ");
>           bdrv_unref(target);
>           bdrv_unref(top);
>           return NULL;
>       }
>   
> +    bdrv_ref(source);
> +    top->file = bdrv_attach_child(top, source, "file", &child_of_bds,
> +                                  BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
> +                                  errp);
> +    if (!top->file) {
> +        error_prepend(errp, "Cannot attach file child: ");
> +        bdrv_unref(source);

Already existing in the code above, but why is the reference to @source 
dropped here?  Shouldn’t bdrv_attach_child()’s error path have done that 
already?

Max

> +        bdrv_unref(top);
> +        return NULL;
> +    }