Re: [PATCHv2 net-next 1/5] net: add a common function to compute features from lowers devices

diff --git a/net/core/dev.c b/net/core/dev.c
index 1d1650d9ecff..5c1c8b016c8e 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -12577,6 +12577,82 @@ netdev_features_t netdev_increment_features(netdev_features_t all,
 }
 EXPORT_SYMBOL(netdev_increment_features);
 
+/**
+ *	netdev_compute_features_from_lowers - compute feature from lowers
+ *	@dev: the upper device
+ *
+ *	Recompute the upper device's feature based on all lower devices.
+ */
+void netdev_compute_features_from_lowers(struct net_device *dev)
+{
+	unsigned int dst_release_flag = IFF_XMIT_DST_RELEASE | IFF_XMIT_DST_RELEASE_PERM;
+	netdev_features_t gso_partial_features = VIRTUAL_DEV_GSO_PARTIAL_FEATURES;
+#ifdef CONFIG_XFRM_OFFLOAD
+	netdev_features_t xfrm_features  = VIRTUAL_DEV_XFRM_FEATURES;
+#endif
+	netdev_features_t mpls_features  = VIRTUAL_DEV_MPLS_FEATURES;
+	netdev_features_t vlan_features = VIRTUAL_DEV_VLAN_FEATURES;
+	netdev_features_t enc_features  = VIRTUAL_DEV_ENC_FEATURES;
+	unsigned int tso_max_size = TSO_MAX_SIZE;
+	u16 tso_max_segs = TSO_MAX_SEGS;
+	struct net_device *lower_dev;
+	struct list_head *iter;
+
+	mpls_features = netdev_base_features(mpls_features);
+	vlan_features = netdev_base_features(vlan_features);
+	enc_features = netdev_base_features(enc_features);
+
+	netdev_for_each_lower_dev(dev, lower_dev, iter) {
+		gso_partial_features = netdev_increment_features(gso_partial_features,
+								 lower_dev->gso_partial_features,
+								 VIRTUAL_DEV_GSO_PARTIAL_FEATURES);
+
+		vlan_features = netdev_increment_features(vlan_features,
+							  lower_dev->vlan_features,
+							  VIRTUAL_DEV_VLAN_FEATURES);
+
+#ifdef CONFIG_XFRM_OFFLOAD
+		xfrm_features = netdev_increment_features(xfrm_features,
+							  lower_dev->hw_enc_features,
+							  VIRTUAL_DEV_XFRM_FEATURES);
+#endif
+
+		enc_features = netdev_increment_features(enc_features,
+							 lower_dev->hw_enc_features,
+							 VIRTUAL_DEV_ENC_FEATURES);
+
+		mpls_features = netdev_increment_features(mpls_features,
+							  lower_dev->mpls_features,
+							  VIRTUAL_DEV_MPLS_FEATURES);
+
+		dst_release_flag &= lower_dev->priv_flags;
+
+		tso_max_size = min(tso_max_size, lower_dev->tso_max_size);
+		tso_max_segs = min(tso_max_segs, lower_dev->tso_max_segs);
+	}
+
+	dev->gso_partial_features = gso_partial_features;
+	dev->vlan_features = vlan_features;
+#ifdef CONFIG_XFRM_OFFLOAD
+	dev->hw_enc_features |= xfrm_features;
+#endif