Re: [Qemu-block] [PATCH v2 8/9] block: Introduce BlockDriver.bdrv_drain callback

[Stefan Hajnoczi]

On Thu, Oct 29, 2015 at 10:14:25AM +0800, Fam Zheng wrote:
>  void bdrv_drain(BlockDriverState *bs)
>  {
> +    BdrvChild *child;
>      bool busy = true;
>  
> +    if (bs->drv && bs->drv->bdrv_drain) {
> +        bs->drv->bdrv_drain(bs);
> +    }
> +    QLIST_FOREACH(child, &bs->children, next) {
> +        bdrv_drain(child->bs);
> +    }
>      while (busy) {
>          /* Keep iterating */
>           bdrv_flush_io_queue(bs);

Recursing calls aio_poll() once for each BDS node and I think it's not
necessary and could be a performance problem.

Stefan

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