net_device and netdev private struct allocation improvements.

1) Ensure alignment of both net_device and private area.
2) Introduce netdev_priv(), an inline which allows the dynamic private
   area (dev->priv) to be calculated as a constant offset from the
   base struct net_device at compile time.

drivers/net/net_init.c

@@ -73,23 +73,28 @@
 struct net_device *alloc_netdev(int sizeof_priv, const char *mask,
 				       void (*setup)(struct net_device *))
 {
+	void *p;
 	struct net_device *dev;
 	int alloc_size;
 
-	/* ensure 32-byte alignment of the private area */
-	alloc_size = sizeof (*dev) + sizeof_priv + 31;
+	/* ensure 32-byte alignment of both the device and private area */
 
-	dev = (struct net_device *) kmalloc (alloc_size, GFP_KERNEL);
-	if (dev == NULL)
-	{
-		printk(KERN_ERR "alloc_dev: Unable to allocate device memory.\n");
+	alloc_size = (sizeof(struct net_device) + 31) & ~31;
+	alloc_size += sizeof_priv + 31;
+
+	p = kmalloc (alloc_size, GFP_KERNEL);
+	if (!p) {
+		printk(KERN_ERR "alloc_dev: Unable to allocate device.\n");
 		return NULL;
 	}
 
-	memset(dev, 0, alloc_size);
+	memset(p, 0, alloc_size);
+
+	dev = (struct net_device *)(((long)p + 31) & ~31);
+	dev->padded = (char *)dev - (char *)p;
 
 	if (sizeof_priv)
-		dev->priv = (void *) (((long)(dev + 1) + 31) & ~31);
+		dev->priv = netdev_priv(dev);
 
 	setup(dev);
 	strcpy(dev->name, mask);

include/linux/netdevice.h

@@ -470,8 +470,15 @@ struct net_device
 	/* class/net/name entry */
 	struct class_device	class_dev;
 	struct net_device_stats* (*last_stats)(struct net_device *);
+	/* how much padding had been added by alloc_netdev() */
+	int padded;
 };
 
+static inline void *netdev_priv(struct net_device *dev)
+{
+	return (char *)dev + ((sizeof(struct net_device) + 31) & ~31);
+}
+
 #define SET_MODULE_OWNER(dev) do { } while (0)
 /* Set the sysfs physical device reference for the network logical device
  * if set prior to registration will cause a symlink during initialization.

net/core/dev.c

@@ -2899,7 +2899,7 @@ void free_netdev(struct net_device *dev)
 {
 	/*  Compatiablity with error handling in drivers */
 	if (dev->reg_state == NETREG_UNINITIALIZED) {
-		kfree(dev);
+		kfree((char *)dev - dev->padded);
 		return;
 	}
 

net/core/net-sysfs.c

@@ -372,7 +372,7 @@ static void netdev_release(struct class_device *cd)
 
 	BUG_ON(dev->reg_state != NETREG_RELEASED);
 
-	kfree(dev);
+	kfree((char *)dev - dev->padded);
 }
 
 static struct class net_class = {