Fixing wrong descriptor reading precedence

Author: Cuda-Chen

virtio-snd.c

@@ -146,6 +146,7 @@ typedef struct {
     uint32_t chmaps;
 } virtio_snd_config_t;
 
+/* VirtIO sound common header */
 typedef struct {
     uint32_t code;
 } virtio_snd_hdr_t;
@@ -400,12 +401,11 @@ static int virtio_snd_desc_handler(virtio_snd_state_t *vsnd,
      * maybe wrong. */
     /* A full virtio_snd_query_info is composed of 3 descriptors, where
      * the first descriptor contains:
-     *   struct virtio_snd_hdr hdr
+     *   struct virtio_snd_hdr hdr (for request)
      * the second descriptors contains:
-     *   le32 start_id
-     *   le32 count
+     *   struct virtio_snd_hdr hdr (for response)
      * the third descriptors contains:
-     *   le32 size
+     *   (payload)
      */
     struct virtq_desc vq_desc[VSND_DESC_CNT];
 
@@ -434,10 +434,13 @@ static int virtio_snd_desc_handler(virtio_snd_state_t *vsnd,
     }
 
     /* Process the header */
+    const virtio_snd_hdr_t *request =
+        (virtio_snd_hdr_t *) ((uintptr_t) vsnd->ram + vq_desc[0].addr);
+    uint32_t type = request->code;
+    virtio_snd_hdr_t *response =
+        (virtio_snd_hdr_t *) ((uintptr_t) vsnd->ram + vq_desc[1].addr);
     const virtio_snd_query_info_t *query =
         (virtio_snd_query_info_t *) ((uintptr_t) vsnd->ram + vq_desc[0].addr);
-    uint32_t type = query->hdr.code;
-    uint32_t *status = (uint32_t *) ((uintptr_t) vsnd->ram + vq_desc[2].addr);
 
     /* Process the data */
     switch (type) {
@@ -467,14 +470,14 @@ static int virtio_snd_desc_handler(virtio_snd_state_t *vsnd,
         break;
     default:
         fprintf(stderr, "unsupported virtio-snd operation!\n");
-        *status = VIRTIO_SND_S_NOT_SUPP;
+        response->code = VIRTIO_SND_S_NOT_SUPP;
         *plen = 0;
         return -1;
     }
 
     /* Return the device status */
-    *status = VIRTIO_SND_S_OK;
-    *plen = vq_desc[1].len;
+    response->code = VIRTIO_SND_S_OK;
+    *plen = vq_desc[2].len;
 
     return 0;
 }