Re: [Qemu-block] [PATCH v3 4/7] block: remove legacy I/O throttling

[Stefan Hajnoczi]

On Fri, Aug 25, 2017 at 04:23:29PM +0300, Manos Pitsidianakis wrote:
>  void blk_io_limits_disable(BlockBackend *blk)
>  {
> -    assert(blk->public.throttle_group_member.throttle_state);
> -    bdrv_drained_begin(blk_bs(blk));
> -    throttle_group_unregister_tgm(&blk->public.throttle_group_member);
> -    bdrv_drained_end(blk_bs(blk));
> +    BlockDriverState *bs, *throttle_node;
> +
> +    throttle_node = blk_get_public(blk)->throttle_node;
> +
> +    assert(throttle_node);
> +
> +    bs = throttle_node->file->bs;
> +    bdrv_drained_begin(bs);
> +
> +    /* Ref throttle_node's child bs to ensure it won't go away */
> +    bdrv_ref(bs);

Is this really necessary?  bdrv_replace_node() also takes a temporary
reference:

  bdrv_ref(to);
  bdrv_replace_child_noperm(c, to);
  bdrv_unref(from);