# Re: \[PATCH 07/18\] virtio ring: inline function to check for events

- From: Michael S. Tsirkin \<mst@redhat.com\>
- Date: 2011-05-05 08:57:37 
- List: netdev
- Page: https://ratatoskr.run/netdev/2011/05/3711297
- Thread: https://ratatoskr.run/kvm/2011/05/3711132/t.md

```text
On Thu, May 05, 2011 at 09:34:46AM +0100, Stefan Hajnoczi wrote:
> On Wed, May 4, 2011 at 9:51 PM, Michael S. Tsirkin [ref] wrote:
> > With the new used_event and avail_event and features, both
> > host and guest need similar logic to check whether events are
> > enabled, so it helps to put the common code in the header.
> >
> > Note that Xen has similar logic for notification hold-off
> > in include/xen/interface/io/ring.h with req_event and req_prod
> > corresponding to event_idx + 1 and new_idx respectively.
> > +1 comes from the fact that req_event and req_prod in Xen start at 1,
> > while event index in virtio starts at 0.
> >
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  include/linux/virtio_ring.h |   14 ++++++++++++++
> >  1 files changed, 14 insertions(+), 0 deletions(-)
> >
> > diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
> > index f791772..2a3b0ea 100644
> > --- a/include/linux/virtio_ring.h
> > +++ b/include/linux/virtio_ring.h
> > @@ -124,6 +124,20 @@ static inline unsigned vring_size(unsigned int num, unsigned long align)
> >                + sizeof(__u16) * 3 + sizeof(struct vring_used_elem) * num;
> >  }
> >
> > +/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
> > +/* Assuming a given event_idx value from the other size, if
> 
> s/other size/other side/ ?
> 
> Stefan

Exactly. Good catch, thanks.

-- 
MST
```