Print the content of the first and last descriptor

Author: Cuda-Chen

virtio-snd.c

@@ -683,7 +683,7 @@ static int virtio_snd_tx_desc_handler(virtio_snd_state_t *vsnd,
     INIT_QUEUE_HEAD(&q);
 
     /* Collect the descriptors */
-    int i = 0;
+    int cnt = 0;
     while (true) {
         /* The size of the `struct virtq_desc` is 4 words */
         const uint32_t *desc = &vsnd->ram[queue->QueueDesc + desc_idx * 4];
@@ -701,12 +701,12 @@ static int virtio_snd_tx_desc_handler(virtio_snd_state_t *vsnd,
         queue_push(&node->q, &q);
         desc_idx = desc[3] >> 16; /* vq_desc[desc_cnt].next */
 
-        i++;
+        cnt++;
         sleep(1);
 
         /* Leave the loop if next-flag is not set */
         if (!(desc[3] & VIRTIO_DESC_F_NEXT)) {
-            fprintf(stderr, "index %" PRIu32 " no next flag\n", i);
+            fprintf(stderr, "index %" PRIu32 " no next flag\n", cnt);
             break;
         }
     }
@@ -733,11 +733,27 @@ static int virtio_snd_tx_desc_handler(virtio_snd_state_t *vsnd,
     *plen = vq_desc[1].len + sizeof(*response);
 #endif
     int idx = 0;
+    uint32_t stream_id;
+    uintptr_t base = vsnd->ram;
     queue_for_each_entry(node, &q, q)
     {
         uint32_t addr = node->vq_desc.addr;
         uint32_t len = node->vq_desc.len;
-        printf("node %d addr %" PRIu32 " len %" PRIu32 "\n", idx, addr, len);
+        fprintf(stderr, "idx %d addr %" PRIu32 " len %" PRIu32 "\n", idx, addr, len);
+        if (idx == 0) {  // the first descriptor
+            const virtio_snd_pcm_xfer_t *request = (virtio_snd_pcm_xfer_t *)(base + addr);
+            stream_id = request->stream_id;
+            fprintf(stderr, "stream_id %" PRIu32 "\n", stream_id);
+        } else if (idx == cnt - 1) {  // the last descriptor
+            virtio_snd_pcm_status_t *response = (virtio_snd_pcm_status_t *)(base + addr);
+            response->status = VIRTIO_SND_S_OK;
+            response->latency_bytes =
+                0;                     /* TODO: show the actual latency bytes */
+            *plen = sizeof(*response); /* TODO: set the read length of buffer of
+                                          PCM frames */
+            fprintf(stderr, "TX response\n");
+        }
+
         idx++;
     }