linux-kernel - Re: [PATCH 07/18] virtio ring: inline function to check for events

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Date:	Thu, 5 May 2011 11:56:56 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Stefan Hajnoczi <stefanha@...il.com>
Cc:	linux-kernel@...r.kernel.org, Krishna Kumar <krkumar2@...ibm.com>,
	Carsten Otte <cotte@...ibm.com>, lguest@...ts.ozlabs.org,
	Shirley Ma <xma@...ibm.com>, kvm@...r.kernel.org,
	linux-s390@...r.kernel.org, netdev@...r.kernel.org,
	habanero@...ux.vnet.ibm.com,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	virtualization@...ts.linux-foundation.org, steved@...ibm.com,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Tom Lendacky <tahm@...ux.vnet.ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux390@...ibm.com
Subject: Re: [PATCH 07/18] virtio ring: inline function to check for events

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 <mst@...hat.com> 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@...hat.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
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