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Date: Thu, 29 Nov 2012 10:17:37 -0500 (EST)
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v4 04/11] dataplane: add virtqueue vring
	code
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, qemu-devel@nongnu.org, Blue Swirl <blauwirbel@gmail.com>, khoa@us.ibm.com, Stefan Hajnoczi <stefanha@redhat.com>, Asias He <asias@redhat.com>


> > +/* Toggle guest->host notifies */
> > +void vring_set_notification(VirtIODevice *vdev, Vring *vring, bool
> > enable)
> > +{
> > +    if (vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) {
> > +        if (enable) {
> > +            vring_avail_event(&vring->vr) = vring->vr.avail->idx;
> > +        }
> > +    } else if (enable) {
> > +        vring->vr.used->flags &= ~VRING_USED_F_NO_NOTIFY;
> > +    } else {
> > +        vring->vr.used->flags |= VRING_USED_F_NO_NOTIFY;
> > +    }
> > +}

This is similar to the (guest-side) virtqueue_disable_cb/virtqueue_enable_cb.

Perhaps having two functions will be easier to use, because from your
other code it looks like you'd benefit from a return value when
enable == true (again similar to virtqueue_enable_cb).

Paolo