Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754592AbcCDLZX (ORCPT ); Fri, 4 Mar 2016 06:25:23 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46513 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751414AbcCDLZT (ORCPT ); Fri, 4 Mar 2016 06:25:19 -0500 From: Jason Wang To: mst@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: RAPOPORT@il.ibm.com, yang.zhang.wz@gmail.com, borntraeger@de.ibm.com, Jason Wang Subject: [PATCH V4 2/3] vhost: introduce vhost_vq_avail_empty() Date: Fri, 4 Mar 2016 06:24:52 -0500 Message-Id: <1457090693-55974-3-git-send-email-jasowang@redhat.com> In-Reply-To: <1457090693-55974-1-git-send-email-jasowang@redhat.com> References: <1457090693-55974-1-git-send-email-jasowang@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Fri, 04 Mar 2016 11:25:18 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1857 Lines: 50 This patch introduces a helper which will return true if we're sure that the available ring is empty for a specific vq. When we're not sure, e.g vq access failure, return false instead. This could be used for busy polling code to exit the busy loop. Signed-off-by: Jason Wang --- drivers/vhost/vhost.c | 14 ++++++++++++++ drivers/vhost/vhost.h | 1 + 2 files changed, 15 insertions(+) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 90ac092..89301fd 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -1633,6 +1633,20 @@ void vhost_add_used_and_signal_n(struct vhost_dev *dev, } EXPORT_SYMBOL_GPL(vhost_add_used_and_signal_n); +/* return true if we're sure that avaiable ring is empty */ +bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *vq) +{ + __virtio16 avail_idx; + int r; + + r = __get_user(avail_idx, &vq->avail->idx); + if (r) + return false; + + return vhost16_to_cpu(vq, avail_idx) == vq->avail_idx; +} +EXPORT_SYMBOL_GPL(vhost_vq_avail_empty); + /* OK, now we need to know about added descriptors. */ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) { diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h index 43284ad..a7a43f0 100644 --- a/drivers/vhost/vhost.h +++ b/drivers/vhost/vhost.h @@ -159,6 +159,7 @@ void vhost_add_used_and_signal_n(struct vhost_dev *, struct vhost_virtqueue *, struct vring_used_elem *heads, unsigned count); void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *); void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *); +bool vhost_vq_avail_empty(struct vhost_dev *, struct vhost_virtqueue *); bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *); int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log, -- 1.8.3.1