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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>

(cherry picked from commit 29b9f5efd78ae0f9cc02dd169b6e80d2c404bade)
---
 hw/virtio/virtio.c         | 7 +++++++
 include/hw/virtio/virtio.h | 2 ++
 2 files changed, 9 insertions(+)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 7d88f26..e9f72a5 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -263,6 +263,13 @@ 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/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index d95f8b6..1899654 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -136,6 +136,8 @@ 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);