[PATCH 3/4] vhost_net: stop use backend_features

[Vladimir Sementsov-Ogievskiy]

We are going to drop backend_features variable as an extra one.
Call to qemu_has_vnet_hdr() is cheap.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@yandex-team.ru>
---
 hw/net/vhost_net.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index 891f235a0a6..38cbc6caa14 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -139,7 +139,8 @@ int vhost_net_set_config(struct vhost_net *net, const 
uint8_t *data,
 
 void vhost_net_ack_features(struct vhost_net *net, uint64_t features)
 {
-    net->dev.acked_features = net->dev.backend_features;
+    net->dev.acked_features = qemu_has_vnet_hdr(net->nc)
+        ? 0 : (1ULL << VHOST_NET_F_VIRTIO_NET_HDR);
     vhost_ack_features(&net->dev, vhost_net_get_feature_bits(net), features);
 }
 
@@ -338,12 +339,9 @@ struct vhost_net *vhost_net_init(VhostNetOptions *options)
         if (r < 0) {
             goto fail;
         }
-        net->dev.backend_features = qemu_has_vnet_hdr(options->net_backend)
-            ? 0 : (1ULL << VHOST_NET_F_VIRTIO_NET_HDR);
         net->backend = r;
         net->dev.protocol_features = 0;
     } else {
-        net->dev.backend_features = 0;
         net->dev.protocol_features = 0;
         net->backend = -1;
 
@@ -363,10 +361,10 @@ struct vhost_net *vhost_net_init(VhostNetOptions *options)
                                sizeof(struct virtio_net_hdr_mrg_rxbuf))) {
             net->dev.features &= ~(1ULL << VIRTIO_NET_F_MRG_RXBUF);
         }
-        if (~net->dev.features & net->dev.backend_features) {
-            fprintf(stderr, "vhost lacks feature mask 0x%" PRIx64
-                   " for backend\n",
-                   (uint64_t)(~net->dev.features & net->dev.backend_features));
+        if (!qemu_has_vnet_hdr(options->net_backend) &&
+            (~net->dev.features & (1ULL << VHOST_NET_F_VIRTIO_NET_HDR))) {
+            fprintf(stderr, "vhost lacks feature mask 0x%llx for backend\n",
+                    ~net->dev.features & (1ULL << VHOST_NET_F_VIRTIO_NET_HDR));
             goto fail;
         }
     }
-- 
2.48.1