From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH 05/18] virtio: used event index interface Date: Thu, 5 May 2011 12:38:17 +0300 Message-ID: <20110505093816.GE28378@redhat.com> References: <201105041656.11009.tahm@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <201105041656.11009.tahm@linux.vnet.ibm.com> Sender: kvm-owner@vger.kernel.org List-Archive: List-Post: To: Tom Lendacky Cc: linux-kernel@vger.kernel.org, Rusty Russell , Carsten Otte , Christian Borntraeger , linux390@de.ibm.com, Martin Schwidefsky , Heiko Carstens , Shirley Ma , lguest@lists.ozlabs.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, Krishna Kumar , steved@us.ibm.com, habanero@linux.vnet.ibm.com List-ID: On Wed, May 04, 2011 at 04:56:09PM -0500, Tom Lendacky wrote: > On Wednesday, May 04, 2011 03:51:09 PM Michael S. Tsirkin wrote: > > Define a new feature bit for the guest to utilize a used_event index > > (like Xen) instead if a flag bit to enable/disable interrupts. > > > > Signed-off-by: Michael S. Tsirkin > > --- > > include/linux/virtio_ring.h | 9 +++++++++ > > 1 files changed, 9 insertions(+), 0 deletions(-) > > > > diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h > > index e4d144b..f5c1b75 100644 > > --- a/include/linux/virtio_ring.h > > +++ b/include/linux/virtio_ring.h > > @@ -29,6 +29,10 @@ > > /* We support indirect buffer descriptors */ > > #define VIRTIO_RING_F_INDIRECT_DESC 28 > > > > +/* The Guest publishes the used index for which it expects an interrupt > > + * at the end of the avail ring. Host should ignore the avail->flags > > field. */ +#define VIRTIO_RING_F_USED_EVENT_IDX 29 > > + > > /* Virtio ring descriptors: 16 bytes. These can chain together via > > "next". */ struct vring_desc { > > /* Address (guest-physical). */ > > @@ -83,6 +87,7 @@ struct vring { > > * __u16 avail_flags; > > * __u16 avail_idx; > > * __u16 available[num]; > > + * __u16 used_event_idx; > > * > > * // Padding to the next align boundary. > > * char pad[]; > > @@ -93,6 +98,10 @@ struct vring { > > * struct vring_used_elem used[num]; > > * }; > > */ > > +/* We publish the used event index at the end of the available ring. > > + * It is at the end for backwards compatibility. */ > > +#define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) > > + > > static inline void vring_init(struct vring *vr, unsigned int num, void *p, > > unsigned long align) > > { > > You should update the vring_size procedure to account for the extra field at > the end of the available ring by change the "(2 + num)" to "(3 + num)": > return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (3 + num) > > Tom In practice it gives the same result because of the alignment, but sure. Thanks! -- MST