Re: [Qemu-devel] [PATCH v2 05/12] block: Introduce "drained begin/end" API

[Paolo Bonzini <pbonzini@redhat.com>]

On 12/10/2015 13:50, Fam Zheng wrote:
> +void bdrv_drained_begin(BlockDriverState *bs)
> +{
> +    if (bs->quiesce_counter++) {
> +        return;
> +    }
> +    aio_disable_external(bdrv_get_aio_context(bs));
> +    bdrv_drain(bs);
> +}

I think bdrv_drain should be called unconditionally, i.e. before the
"if".  This should also solve Kevin's doubt about new allocating write
request reenabling the timer: any write request from the drained section
happens normally, until you get a nested drain request and then the
callback completes the requests.

Paolo