From 29b9f5efd78ae0f9cc02dd169b6e80d2c404bade Mon Sep 17 00:00:00 2001
From: Jason Wang <jasowang@redhat.com>
Date: Fri, 25 Sep 2015 13:21:29 +0800
Subject: [PATCH] virtio: introduce virtqueue_discard()

This patch introduces virtqueue_discard() to discard a descriptor and
unmap the sgs. This will be used by the patch that will discard
descriptor when packet is truncated.

Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/virtio/virtio.c         |    7 +++++++
 include/hw/gvirtio/virtio.h |    2 ++
 2 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/tools/qemu-xen/hw/virtio/virtio.c b/tools/qemu-xen/hw/virtio/virtio.c
index 6f2b96c..d0bc72e 100644
--- a/tools/qemu-xen/hw/virtio/virtio.c
+++ b/tools/qemu-xen/hw/virtio/virtio.c
@@ -267,6 +267,13 @@ static void virtqueue_unmap_sg(VirtQueue *vq, const VirtQueueElement *elem,
                                   0, elem->out_sg[i].iov_len);
 }
 
+void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem,
+                       unsigned int len)
+{
+    vq->last_avail_idx--;
+    virtqueue_unmap_sg(vq, elem, len);
+}
+
 void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
                     unsigned int len, unsigned int idx)
 {
diff --git a/tools/qemu-xen/include/hw/virtio/virtio.h b/tools/qemu-xen/include/hw/virtio/virtio.h
index 6201ee8..9d09115 100644
--- a/tools/qemu-xen/include/hw/virtio/virtio.h
+++ b/tools/qemu-xen/include/hw/virtio/virtio.h
@@ -146,6 +146,8 @@ void virtio_del_queue(VirtIODevice *vdev, int n);
 void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem,
                     unsigned int len);
 void virtqueue_flush(VirtQueue *vq, unsigned int count);
+void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem,
+                       unsigned int len);
 void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
                     unsigned int len, unsigned int idx);
 
-- 
1.7.0.4