[NET]: Inline net_device_stats

Network drivers which keep stats allocate their own stats structure
then write a get_stats() function to return them.  It would be nice if
this were done by default.

1) Add a new "stats" field to "struct net_device".
2) Add a new feature field to say "this driver uses the internal one"
3) Have a default "get_stats" which returns NULL if that feature not set.
4) Change callers to check result of get_stats call for NULL, not if
   ->get_stats is set.

This should not break backwards compatibility with older drivers, yet
allow modern drivers to shed some boilerplate code.

Lightly tested: works for a modified lguest network driver.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/s390/appldata/appldata_net_sum.c

@@ -108,10 +108,10 @@ static void appldata_get_net_sum_data(void *data)
 	collisions = 0;
 	read_lock(&dev_base_lock);
 	for (dev = dev_base; dev != NULL; dev = dev->next) {
-		if (dev->get_stats == NULL) {
+		stats = dev->get_stats(dev);
+		if (stats == NULL) {
 			continue;
 		}
-		stats = dev->get_stats(dev);
 		rx_packets += stats->rx_packets;
 		tx_packets += stats->tx_packets;
 		rx_bytes   += stats->rx_bytes;

drivers/net/bonding/bond_main.c

@@ -3640,9 +3640,8 @@ static struct net_device_stats *bond_get_stats(struct net_device *bond_dev)
 	read_lock_bh(&bond->lock);
 
 	bond_for_each_slave(bond, slave, i) {
-		if (slave->dev->get_stats) {
-			sstats = slave->dev->get_stats(slave->dev);
-
+		sstats = slave->dev->get_stats(slave->dev);
+		if (sstats) {
 			stats->rx_packets += sstats->rx_packets;
 			stats->rx_bytes += sstats->rx_bytes;
 			stats->rx_errors += sstats->rx_errors;

drivers/parisc/led.c

@@ -372,9 +372,9 @@ static __inline__ int led_get_net_activity(void)
 		continue;
 	    if (LOOPBACK(in_dev->ifa_list->ifa_local))
 		continue;
-	    if (!dev->get_stats) 
-		continue;
 	    stats = dev->get_stats(dev);
+	    if (!stats)
+		continue;
 	    rx_total += stats->rx_packets;
 	    tx_total += stats->tx_packets;
 	}

include/linux/netdevice.h

@@ -323,6 +323,7 @@ struct net_device
 #define NETIF_F_VLAN_CHALLENGED	1024	/* Device cannot handle VLAN packets */
 #define NETIF_F_GSO		2048	/* Enable software GSO. */
 #define NETIF_F_LLTX		4096	/* LockLess TX */
+#define NETIF_F_INTERNAL_STATS	8192	/* Use stats structure in net_device */
 
 	/* Segmentation offload features */
 #define NETIF_F_GSO_SHIFT	16
@@ -347,6 +348,7 @@ struct net_device
 
 
 	struct net_device_stats* (*get_stats)(struct net_device *dev);
+	struct net_device_stats	stats;
 
 	/* List of functions to handle Wireless Extensions (instead of ioctl).
 	 * See <net/iw_handler.h> for details. Jean II */

net/core/dev.c

@@ -817,7 +817,6 @@ static int default_rebuild_header(struct sk_buff *skb)
 	return 1;
 }
 
-
 /**
  *	dev_open	- prepare an interface for use.
  *	@dev:	device to open
@@ -2096,9 +2095,9 @@ void dev_seq_stop(struct seq_file *seq, void *v)
 
 static void dev_seq_printf_stats(struct seq_file *seq, struct net_device *dev)
 {
-	if (dev->get_stats) {
-		struct net_device_stats *stats = dev->get_stats(dev);
+	struct net_device_stats *stats = dev->get_stats(dev);
 
+	if (stats) {
 		seq_printf(seq, "%6s:%8lu %7lu %4lu %4lu %4lu %5lu %10lu %9lu "
 				"%8lu %7lu %4lu %4lu %4lu %5lu %7lu %10lu\n",
 			   dev->name, stats->rx_bytes, stats->rx_packets,
@@ -3282,6 +3281,13 @@ void netdev_run_todo(void)
 	mutex_unlock(&net_todo_run_mutex);
 }
 
+static struct net_device_stats *maybe_internal_stats(struct net_device *dev)
+{
+	if (dev->features & NETIF_F_INTERNAL_STATS)
+		return &dev->stats;
+	return NULL;
+}
+
 /**
  *	alloc_netdev - allocate network device
  *	@sizeof_priv:	size of private data to allocate space for
@@ -3317,6 +3323,7 @@ struct net_device *alloc_netdev(int sizeof_priv, const char *name,
 	if (sizeof_priv)
 		dev->priv = netdev_priv(dev);
 
+	dev->get_stats = maybe_internal_stats;
 	setup(dev);
 	strcpy(dev->name, name);
 	return dev;