Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753299Ab1EEJj1 (ORCPT ); Thu, 5 May 2011 05:39:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36010 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752517Ab1EEJjZ (ORCPT ); Thu, 5 May 2011 05:39:25 -0400 Date: Thu, 5 May 2011 12:38:17 +0300 From: "Michael S. Tsirkin" 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 Subject: Re: [PATCH 05/18] virtio: used event index interface 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 Content-Disposition: inline In-Reply-To: <201105041656.11009.tahm@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2336 Lines: 61 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/