vhost: add vhost_net_set_backend()

Not all vhost-user backends support ops->vhost_net_set_backend(). It is
a nicer to provide an assert/error than to crash trying to
call. Furthermore, it improves a bit the code by hiding vhost_ops
details.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

2 files changed, 13 insertions, 6 deletions

diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index dd41a8e..dc61dc1 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -242,8 +242,7 @@ static int vhost_net_start_one(struct vhost_net *net,
         qemu_set_fd_handler(net->backend, NULL, NULL, NULL);
         file.fd = net->backend;
         for (file.index = 0; file.index < net->dev.nvqs; ++file.index) {
-            const VhostOps *vhost_ops = net->dev.vhost_ops;
-            r = vhost_ops->vhost_net_set_backend(&net->dev, &file);
+            r = vhost_net_set_backend(&net->dev, &file);
             if (r < 0) {
                 r = -errno;
                 goto fail;
@@ -255,8 +254,7 @@ fail:
     file.fd = -1;
     if (net->nc->info->type == NET_CLIENT_DRIVER_TAP) {
         while (file.index-- > 0) {
-            const VhostOps *vhost_ops = net->dev.vhost_ops;
-            int r = vhost_ops->vhost_net_set_backend(&net->dev, &file);
+            int r = vhost_net_set_backend(&net->dev, &file);
             assert(r >= 0);
         }
     }
@@ -277,8 +275,7 @@ static void vhost_net_stop_one(struct vhost_net *net,
 
     if (net->nc->info->type == NET_CLIENT_DRIVER_TAP) {
         for (file.index = 0; file.index < net->dev.nvqs; ++file.index) {
-            const VhostOps *vhost_ops = net->dev.vhost_ops;
-            int r = vhost_ops->vhost_net_set_backend(&net->dev, &file);
+            int r = vhost_net_set_backend(&net->dev, &file);
             assert(r >= 0);
         }
     }
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 2d0d1d1..b0e8ecc 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1369,3 +1369,13 @@ void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev)
     vhost_log_put(hdev, true);
     hdev->started = false;
 }
+
+int vhost_net_set_backend(struct vhost_dev *hdev,
+                          struct vhost_vring_file *file)
+{
+    if (hdev->vhost_ops->vhost_net_set_backend) {
+        return hdev->vhost_ops->vhost_net_set_backend(hdev, file);
+    }
+
+    return -1;
+}