vlib: add vlib_buffer_alloc_to_ring API

Change-Id: I4e2804754b443f5f41fb25eed8334908c4a70f84
Signed-off-by: Damjan Marion <damarion@cisco.com>
diff --git a/src/vnet/devices/virtio/node.c b/src/vnet/devices/virtio/node.c
index 5ca0636..9477a1c 100644
--- a/src/vnet/devices/virtio/node.c
+++ b/src/vnet/devices/virtio/node.c
@@ -83,10 +83,9 @@
 virtio_refill_vring (vlib_main_t * vm, virtio_vring_t * vring)
 {
   const int hdr_sz = sizeof (struct virtio_net_hdr_v1);
-  u16 used, next, avail, n_slots, n_alloc;
+  u16 used, next, avail, n_slots;
   u16 sz = vring->size;
   u16 mask = sz - 1;
-  int i;
 
   used = vring->desc_in_use;
 
@@ -96,14 +95,8 @@
   n_slots = sz - used;
   next = vring->desc_next;
   avail = vring->avail->idx;
-  n_alloc = vlib_buffer_alloc (vm, &vring->buffers[next], n_slots);
-
-  if (PREDICT_FALSE (n_alloc < n_slots))
-    n_slots = n_alloc;
-
-  i = next + n_slots - sz;
-  if (PREDICT_FALSE (i > 0))
-    clib_memcpy (vring->buffers, &vring->buffers[sz], i * sizeof (u32));
+  n_slots = vlib_buffer_alloc_to_ring (vm, vring->buffers, next, vring->size,
+				       n_slots);
 
   while (n_slots)
     {