diff --git "a/\350\231\232\346\213\237\345\214\226/virtio.md" "b/\350\231\232\346\213\237\345\214\226/virtio.md"
index 4b96cb1..c22fbe5 100644
--- "a/\350\231\232\346\213\237\345\214\226/virtio.md"
+++ "b/\350\231\232\346\213\237\345\214\226/virtio.md"
@@ -33,4 +33,11 @@ avail == used && used == vq->vq_packed.used_wrap_counter;
 avail_wrap_counter ==  1 -> a 1 u 0
 avail_wrap_counter ==  0 -> a 0 u 1
 
+if (vq->used_wrap_counter) {
+    flags |= VRING_DESC_F_USED;
+    flags |= VRING_DESC_F_AVAIL;
+} else {
+    flags &= ~VRING_DESC_F_USED;
+    flags &= ~VRING_DESC_F_AVAIL;
+}