[PATCH] bonding: inherit zero-copy flags of slaves

This change allows a bonding device to inherit the "zero-copy"
features of its slave devices.

It was inspired by a couple of previous postings on this topic:
http://marc.theaimsgroup.com/?l=bonding-devel&m=111924607327794&w=2
http://marc.theaimsgroup.com/?l=bonding-devel&m=111925242706297&w=2
and it's largely a combination of the patches that appear in those
emails.
Signed-off-by: NArthur Kepner <akepner@sgi.com>

drivers/net/bonding/bond_main.c

@@ -1604,6 +1604,44 @@ static int bond_sethwaddr(struct net_device *bond_dev, struct net_device *slave_
 	return 0;
 }
 
+#define BOND_INTERSECT_FEATURES \
+	(NETIF_F_SG|NETIF_F_IP_CSUM|NETIF_F_NO_CSUM|NETIF_F_HW_CSUM)
+
+/* 
+ * Compute the features available to the bonding device by 
+ * intersection of all of the slave devices' BOND_INTERSECT_FEATURES.
+ * Call this after attaching or detaching a slave to update the 
+ * bond's features.
+ */
+static int bond_compute_features(struct bonding *bond)
+{
+	int i;
+	struct slave *slave;
+	struct net_device *bond_dev = bond->dev;
+	int features = bond->bond_features;
+
+	bond_for_each_slave(bond, slave, i) {
+		struct net_device * slave_dev = slave->dev;
+		if (i == 0) {
+			features |= BOND_INTERSECT_FEATURES;
+		}
+		features &=
+			~(~slave_dev->features & BOND_INTERSECT_FEATURES);
+	}
+
+	/* turn off NETIF_F_SG if we need a csum and h/w can't do it */
+	if ((features & NETIF_F_SG) && 
+		!(features & (NETIF_F_IP_CSUM |
+			      NETIF_F_NO_CSUM |
+			      NETIF_F_HW_CSUM))) {
+		features &= ~NETIF_F_SG;
+	}
+
+	bond_dev->features = features;
+
+	return 0;
+}
+
 /* enslave device <slave> to bond device <master> */
 static int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
 {
@@ -1811,6 +1849,8 @@ static int bond_enslave(struct net_device *bond_dev, struct net_device *slave_de
 	new_slave->delay = 0;
 	new_slave->link_failure_count = 0;
 
+	bond_compute_features(bond);
+
 	if (bond->params.miimon && !bond->params.use_carrier) {
 		link_reporting = bond_check_dev_link(bond, slave_dev, 1);
 
@@ -2100,6 +2140,8 @@ static int bond_release(struct net_device *bond_dev, struct net_device *slave_de
 	/* release the slave from its bond */
 	bond_detach_slave(bond, slave);
 
+	bond_compute_features(bond);
+
 	if (bond->primary_slave == slave) {
 		bond->primary_slave = NULL;
 	}
@@ -2243,6 +2285,8 @@ static int bond_release_all(struct net_device *bond_dev)
 			bond_alb_deinit_slave(bond, slave);
 		}
 
+		bond_compute_features(bond);
+
 		/* now that the slave is detached, unlock and perform
 		 * all the undo steps that should not be called from
 		 * within a lock.
@@ -3588,6 +3632,7 @@ static int bond_master_netdev_event(unsigned long event, struct net_device *bond
 static int bond_slave_netdev_event(unsigned long event, struct net_device *slave_dev)
 {
 	struct net_device *bond_dev = slave_dev->master;
+	struct bonding *bond = bond_dev->priv;
 
 	switch (event) {
 	case NETDEV_UNREGISTER:
@@ -3626,6 +3671,9 @@ static int bond_slave_netdev_event(unsigned long event, struct net_device *slave
 		 * TODO: handle changing the primary's name
 		 */
 		break;
+	case NETDEV_FEAT_CHANGE:
+		bond_compute_features(bond);
+		break;
 	default:
 		break;
 	}
@@ -4526,6 +4574,11 @@ static inline void bond_set_mode_ops(struct bonding *bond, int mode)
 	}
 }
 
+static struct ethtool_ops bond_ethtool_ops = {
+	.get_tx_csum		= ethtool_op_get_tx_csum,
+	.get_sg			= ethtool_op_get_sg,
+};
+
 /*
  * Does not allocate but creates a /proc entry.
  * Allowed to fail.
@@ -4555,6 +4608,7 @@ static int __init bond_init(struct net_device *bond_dev, struct bond_params *par
 	bond_dev->stop = bond_close;
 	bond_dev->get_stats = bond_get_stats;
 	bond_dev->do_ioctl = bond_do_ioctl;
+	bond_dev->ethtool_ops = &bond_ethtool_ops;
 	bond_dev->set_multicast_list = bond_set_multicast_list;
 	bond_dev->change_mtu = bond_change_mtu;
 	bond_dev->set_mac_address = bond_set_mac_address;
@@ -4591,6 +4645,8 @@ static int __init bond_init(struct net_device *bond_dev, struct bond_params *par
 			       NETIF_F_HW_VLAN_RX |
 			       NETIF_F_HW_VLAN_FILTER);
 
+	bond->bond_features = bond_dev->features;
+
 #ifdef CONFIG_PROC_FS
 	bond_create_proc_entry(bond);
 #endif

drivers/net/bonding/bonding.h

@@ -211,6 +211,9 @@ struct bonding {
 	struct   bond_params params;
 	struct   list_head vlan_list;
 	struct   vlan_group *vlgrp;
+	/* the features the bonding device supports, independently 
+	 * of any slaves */
+	int	 bond_features; 
 };
 
 /**