Re: [Qemu-devel] [PULL 18/33] vhost-user-scsi: Introduce vhost-user-scsi host device

[Paolo Bonzini]

On 08/06/2017 13:05, Felipe Franciosi wrote:
>> Weird.  Doesn't QEMU wait for response to GET_VRING_BASE? I think
>> it does since we migrate the returned value.
>
> It does and that's what I said on my first message. On
> GET_VRING_BASE, a vhost-user-scsi backend application will stop
> picking up new requests and, _additionally_, quiesce the VQ (by
> waiting for any outstanding I/O to complete or cancelling them)
> before returning the last_avail_idx.

Yes, I understand now.

> Such an application therefore doesn't _necessarily_ need a drain
> call. However, we could extend vhost-user to include a message for
> draining (which can be implemented as "wait for pending I/O to
> complete" or "cancel all outstanding" depending on the
> implementation).

Ok, and I see that vhost_dev_stop also calls get_vring_base so my
worries are appeased. :)

Paolo