[PATCH v6 04/12] vhost: Do not depend on !NULL VirtQueueElement on vhost_svq_flush

["Eugenio Pérez" <eperezma@redhat.com>]

Since QEMU will be able to inject new elements on CVQ to restore the
state, we need not to depend on a VirtQueueElement to know if a new
element has been used by the device or not. Instead of check that, check
if there are new elements only using used idx on vhost_svq_flush.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
v6: Change less from the previous function
---
 hw/virtio/vhost-shadow-virtqueue.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 1b49bf54f2..f863b08627 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -499,17 +499,20 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
 size_t vhost_svq_poll(VhostShadowVirtqueue *svq)
 {
     int64_t start_us = g_get_monotonic_time();
+    uint32_t len;
+
     do {
-        uint32_t len;
-        VirtQueueElement *elem = vhost_svq_get_buf(svq, &len);
-        if (elem) {
-            return len;
+        if (vhost_svq_more_used(svq)) {
+            break;
         }
 
         if (unlikely(g_get_monotonic_time() - start_us > 10e6)) {
             return 0;
         }
     } while (true);
+
+    vhost_svq_get_buf(svq, &len);
+    return len;
 }
 
 /**
-- 
2.31.1