net: add a common function to compute features for upper devices

Some high level software drivers need to compute features from lower
devices. But each has their own implementations and may lost some
feature compute. Let's use one common function to compute features
for kinds of these devices.

The new helper uses the current bond implementation as the reference
one, as the latter already handles all the relevant aspects: netdev
features, TSO limits and dst retention.

Suggested-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://patch.msgid.link/20251017034155.61990-2-liuhangbin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 88 insertions, 0 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 9482b905c66a..378c2d010faf 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -12693,6 +12693,94 @@ netdev_features_t netdev_increment_features(netdev_features_t all,
 }
 EXPORT_SYMBOL(netdev_increment_features);
 
+/**
+ *	netdev_compute_master_upper_features - compute feature from lowers
+ *	@dev: the upper device
+ *	@update_header: whether to update upper device's header_len/headroom/tailroom
+ *
+ *	Recompute the upper device's feature based on all lower devices.
+ */
+void netdev_compute_master_upper_features(struct net_device *dev, bool update_header)
+{
+	unsigned int dst_release_flag = IFF_XMIT_DST_RELEASE | IFF_XMIT_DST_RELEASE_PERM;
+	netdev_features_t gso_partial_features = MASTER_UPPER_DEV_GSO_PARTIAL_FEATURES;
+	netdev_features_t xfrm_features = MASTER_UPPER_DEV_XFRM_FEATURES;
+	netdev_features_t mpls_features = MASTER_UPPER_DEV_MPLS_FEATURES;
+	netdev_features_t vlan_features = MASTER_UPPER_DEV_VLAN_FEATURES;
+	netdev_features_t enc_features = MASTER_UPPER_DEV_ENC_FEATURES;
+	unsigned short max_header_len = ETH_HLEN;
+	unsigned int tso_max_size = TSO_MAX_SIZE;
+	unsigned short max_headroom = 0;
+	unsigned short max_tailroom = 0;
+	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,
+								 MASTER_UPPER_DEV_GSO_PARTIAL_FEATURES);
+
+		vlan_features = netdev_increment_features(vlan_features,
+							  lower_dev->vlan_features,
+							  MASTER_UPPER_DEV_VLAN_FEATURES);
+
+		enc_features = netdev_increment_features(enc_features,
+							 lower_dev->hw_enc_features,
+							 MASTER_UPPER_DEV_ENC_FEATURES);
+
+		if (IS_ENABLED(CONFIG_XFRM_OFFLOAD))
+			xfrm_features = netdev_increment_features(xfrm_features,
+								  lower_dev->hw_enc_features,
+								  MASTER_UPPER_DEV_XFRM_FEATURES);
+
+		mpls_features = netdev_increment_features(mpls_features,
+							  lower_dev->mpls_features,
+							  MASTER_UPPER_DEV_MPLS_FEATURES);
+
+		dst_release_flag &= lower_dev->priv_flags;
+
+		if (update_header) {
+			max_header_len = max(max_header_len, lower_dev->hard_header_len);
+			max_headroom = max(max_headroom, lower_dev->needed_headroom);
+			max_tailroom = max(max_tailroom, lower_dev->needed_tailroom);
+		}
+
+		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;
+	dev->hw_enc_features = enc_features | NETIF_F_GSO_ENCAP_ALL |
+			       NETIF_F_HW_VLAN_CTAG_TX |
+			       NETIF_F_HW_VLAN_STAG_TX;
+	if (IS_ENABLED(CONFIG_XFRM_OFFLOAD))
+		dev->hw_enc_features |= xfrm_features;
+	dev->mpls_features = mpls_features;
+
+	dev->priv_flags &= ~IFF_XMIT_DST_RELEASE;
+	if ((dev->priv_flags & IFF_XMIT_DST_RELEASE_PERM) &&
+	    dst_release_flag == (IFF_XMIT_DST_RELEASE | IFF_XMIT_DST_RELEASE_PERM))
+		dev->priv_flags |= IFF_XMIT_DST_RELEASE;
+
+	if (update_header) {
+		dev->hard_header_len = max_header_len;
+		dev->needed_headroom = max_headroom;
+		dev->needed_tailroom = max_tailroom;
+	}
+
+	netif_set_tso_max_segs(dev, tso_max_segs);
+	netif_set_tso_max_size(dev, tso_max_size);
+
+	netdev_change_features(dev);
+}
+EXPORT_SYMBOL(netdev_compute_master_upper_features);
+
 static struct hlist_head * __net_init netdev_create_hash(void)
 {
 	int i;