vhost: introduce vhost_backend_get_vq_index method

Minusing the idx with the base(dev->vq_index) for vhost-kernel, and
then adding it back for vhost-user doesn't seem right. Here introduces
a new method vhost_backend_get_vq_index() for getting the right vq
index for following vhost messages calls.

Suggested-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Tested-by: Marcel Apfelbaum <marcel@redhat.com>

hw/virtio/vhost-backend.c

@@ -42,11 +42,19 @@ static int vhost_kernel_cleanup(struct vhost_dev *dev)
     return close(fd);
 }
 
+static int vhost_kernel_get_vq_index(struct vhost_dev *dev, int idx)
+{
+    assert(idx >= dev->vq_index && idx < dev->vq_index + dev->nvqs);
+
+    return idx - dev->vq_index;
+}
+
 static const VhostOps kernel_ops = {
         .backend_type = VHOST_BACKEND_TYPE_KERNEL,
         .vhost_call = vhost_kernel_call,
         .vhost_backend_init = vhost_kernel_init,
-        .vhost_backend_cleanup = vhost_kernel_cleanup
+        .vhost_backend_cleanup = vhost_kernel_cleanup,
+        .vhost_backend_get_vq_index = vhost_kernel_get_vq_index,
 };
 
 int vhost_set_backend_type(struct vhost_dev *dev, VhostBackendType backend_type)

hw/virtio/vhost-user.c

@@ -393,9 +393,17 @@ static int vhost_user_cleanup(struct vhost_dev *dev)
     return 0;
 }
 
+static int vhost_user_get_vq_index(struct vhost_dev *dev, int idx)
+{
+    assert(idx >= dev->vq_index && idx < dev->vq_index + dev->nvqs);
+
+    return idx;
+}
+
 const VhostOps user_ops = {
         .backend_type = VHOST_BACKEND_TYPE_USER,
         .vhost_call = vhost_user_call,
         .vhost_backend_init = vhost_user_init,
-        .vhost_backend_cleanup = vhost_user_cleanup
+        .vhost_backend_cleanup = vhost_user_cleanup,
-        };
+        .vhost_backend_get_vq_index = vhost_user_get_vq_index,
+};

hw/virtio/vhost.c

@@ -719,7 +719,7 @@ static int vhost_virtqueue_start(struct vhost_dev *dev,
 {
     hwaddr s, l, a;
     int r;
-    int vhost_vq_index = idx - dev->vq_index;
+    int vhost_vq_index = dev->vhost_ops->vhost_backend_get_vq_index(dev, idx);
     struct vhost_vring_file file = {
         .index = vhost_vq_index
     };
@@ -728,7 +728,6 @@ static int vhost_virtqueue_start(struct vhost_dev *dev,
     };
     struct VirtQueue *vvq = virtio_get_queue(vdev, idx);
 
-    assert(idx >= dev->vq_index && idx < dev->vq_index + dev->nvqs);
 
     vq->num = state.num = virtio_queue_get_num(vdev, idx);
     r = dev->vhost_ops->vhost_call(dev, VHOST_SET_VRING_NUM, &state);
@@ -822,12 +821,12 @@ static void vhost_virtqueue_stop(struct vhost_dev *dev,
                                     struct vhost_virtqueue *vq,
                                     unsigned idx)
 {
-    int vhost_vq_index = idx - dev->vq_index;
+    int vhost_vq_index = dev->vhost_ops->vhost_backend_get_vq_index(dev, idx);
     struct vhost_vring_state state = {
         .index = vhost_vq_index,
     };
     int r;
-    assert(idx >= dev->vq_index && idx < dev->vq_index + dev->nvqs);
+
     r = dev->vhost_ops->vhost_call(dev, VHOST_GET_VRING_BASE, &state);
     if (r < 0) {
         fprintf(stderr, "vhost VQ %d ring restore failed: %d\n", idx, r);
@@ -1066,17 +1065,15 @@ void vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
 {
     struct VirtQueue *vvq = virtio_get_queue(vdev, n);
     int r, index = n - hdev->vq_index;
+    struct vhost_vring_file file;
 
-    assert(n >= hdev->vq_index && n < hdev->vq_index + hdev->nvqs);
-
-    struct vhost_vring_file file = {
-        .index = index
-    };
     if (mask) {
         file.fd = event_notifier_get_fd(&hdev->vqs[index].masked_notifier);
     } else {
         file.fd = event_notifier_get_fd(virtio_queue_get_guest_notifier(vvq));
     }
+
+    file.index = hdev->vhost_ops->vhost_backend_get_vq_index(hdev, n);
     r = hdev->vhost_ops->vhost_call(hdev, VHOST_SET_VRING_CALL, &file);
     assert(r >= 0);
 }

include/hw/virtio/vhost-backend.h

@@ -24,12 +24,14 @@ typedef int (*vhost_call)(struct vhost_dev *dev, unsigned long int request,
              void *arg);
 typedef int (*vhost_backend_init)(struct vhost_dev *dev, void *opaque);
 typedef int (*vhost_backend_cleanup)(struct vhost_dev *dev);
+typedef int (*vhost_backend_get_vq_index)(struct vhost_dev *dev, int idx);
 
 typedef struct VhostOps {
     VhostBackendType backend_type;
     vhost_call vhost_call;
     vhost_backend_init vhost_backend_init;
     vhost_backend_cleanup vhost_backend_cleanup;
+    vhost_backend_get_vq_index vhost_backend_get_vq_index;
 } VhostOps;
 
 extern const VhostOps user_ops;