[PATCH RFC v2 04/13] hw/virtio/vhost-shadow-virtqueue: used callback

[Connor Kite <connorkite@gmail.com>]

Adds a callback to shadow virtqueues in order to enable
non-default processing of used vring elements from the device.

Signed-off-by: Connor Kite <connorkite@gmail.com>
---
 hw/virtio/vhost-shadow-virtqueue.c |  9 +++++++++
 hw/virtio/vhost-shadow-virtqueue.h | 16 ++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index c8831d52be..496e7e58a3 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -675,6 +675,15 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
                 break;
             }
 
+            if (svq->ops && svq->ops->used_callback) {
+                int r = svq->ops->used_callback(svq, elem, svq->ops_opaque);
+
+                if (r < 0) {
+                    /* VQ or handler is broken. Do not set guest notifier */
+                    return;
+                }
+            }
+
             if (unlikely(i >= svq->vring.num)) {
                 qemu_log_mask(LOG_GUEST_ERROR,
                          "More than %u used buffers obtained in a %u size SVQ",
diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h
index ec16a1e838..fd68319fb7 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -56,8 +56,24 @@ typedef int (*VirtQueueAvailCallback)(VhostShadowVirtqueue *svq,
                                       VirtQueueElement *elem,
                                       void *vq_callback_opaque);
 
+/**
+ * Callback to handle a used buffer
+ *
+ * @svq: Shadow virtqueue
+ * @elem: Element placed in the queue by the device
+ * @vq_callback_opaque: Used to pass arguments to callback
+ *
+ * Returns 0 if the vq is running as expected. Returns a negative errno on
+ * failure.  The callback should not add used elements to the vq shadowed
+ * by the svq as that is done separately after the callback returns.
+ */
+typedef int (*VirtQueueUsedCallback)(VhostShadowVirtqueue *svq,
+                                      VirtQueueElement *elem,
+                                      void *vq_callback_opaque);
+
 typedef struct VhostShadowVirtqueueOps {
     VirtQueueAvailCallback avail_handler;
+    VirtQueueUsedCallback used_callback;
 } VhostShadowVirtqueueOps;
 
 /* Shadow virtqueue to relay notifications */

-- 
2.43.0