Re: [Qemu-block] [PATCH 2/2] virtio-blk: use aio handler for data plane

[Michael S. Tsirkin]

On Tue, Mar 29, 2016 at 03:56:18PM +0200, Paolo Bonzini wrote:
> 
> 
> On 29/03/2016 15:42, Michael S. Tsirkin wrote:
> > @@ -262,6 +274,7 @@ void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
> >  
> >      /* Stop notifications for new requests from guest */
> >      virtio_queue_aio_set_host_notifier_handler(s->vq, s->ctx, false, 
> > false);
> 
> I think that this should have been ", true, false" even before your
> patch; I'd prefer to fix it even if the problem is latent.

Makes sense - post a patch?

> The patch looks good, and it might even be an API improvement
> independent of Conny's patches.  The reentrancy _is_ hard to understand,
> and eliminating it makes the new API not just a hack.
> 
> In that case I would unify the new function with
> virtio_queue_aio_set_host_notifier_handler.  In other words
> 
> - virtio_queue_aio_set_host_notifier_handler(vq, ctx, NULL) is
> the same as
> 
>      virtio_set_queue_aio(s->vq, NULL);
>      virtio_queue_aio_set_host_notifier_handler(vq, ctx, true, false);
> 
> - virtio_queue_aio_set_host_notifier_handler(vq, ctx, fn) is the same as
> 
>      virtio_queue_aio_set_host_notifier_handler(vq, ctx, true, true);
>      virtio_set_queue_aio(vq, fn);
> 
> Thanks,
> 
> Paolo

In that case, we'll have to also change scsi to use the new API.
A bit more work, to be sure.
Does scsi have the same problem as blk?

> > +    virtio_set_queue_aio(s->vq, NULL);
> >  
> >      /* Drain and switch bs back to the QEMU main loop */
> >      blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context());