Create pos attribute

Author: Cuda-Chen

virtio-snd.c

@@ -303,6 +303,7 @@ typedef struct {
 typedef struct {
     void *addr; /* points to the guest OS buffer */
     uint32_t len;
+    uint32_t pos; /* current position in this node */
     struct list_head q;
 } vsnd_buf_queue_node_t;
 
@@ -929,6 +930,7 @@ static void __virtio_snd_frame_enqueue(void *payload,
     vsnd_buf_queue_node_t *node = malloc(sizeof(*node));
     node->addr = payload;
     node->len = n;
+    node->pos = 0;
     list_push(&node->q, &props->buf_queue_head);
 #if WRITEOUT
     fwrite(node->addr, sizeof(void), node->len, outfile);