net: macvtap driver

In order to use macvlan with qemu and other tools that require
a tap file descriptor, the macvtap driver adds a small backend
with a character device with the same interface as the tun
driver, with a minimum set of features.

Macvtap interfaces are created in the same way as macvlan
interfaces using ip link, but the netif is just used as a
handle for configuration and accounting, while the data
goes through the chardev. Each macvtap interface has its
own character device, simplifying permission management
significantly over the generic tun/tap driver.

Cc: Patrick McHardy <kaber@trash.net>
Cc: Stephen Hemminger <shemminger@linux-foundation.org>
Cc: David S. Miller" <davem@davemloft.net>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Or Gerlitz <ogerlitz@voltaire.com>
Cc: netdev@vger.kernel.org
Cc: bridge@lists.linux-foundation.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/Kconfig

@@ -90,6 +90,18 @@ config MACVLAN
 	  To compile this driver as a module, choose M here: the module
 	  will be called macvlan.
 
+config MACVTAP
+	tristate "MAC-VLAN based tap driver (EXPERIMENTAL)"
+	depends on MACVLAN
+	help
+	  This adds a specialized tap character device driver that is based
+	  on the MAC-VLAN network interface, called macvtap. A macvtap device
+	  can be added in the same way as a macvlan device, using 'type
+	  macvlan', and then be accessed through the tap user space interface.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called macvtap.
+
 config EQUALIZER
 	tristate "EQL (serial line load balancing) support"
 	---help---

drivers/net/Makefile

@@ -169,6 +169,7 @@ obj-$(CONFIG_XEN_NETDEV_FRONTEND) += xen-netfront.o
 obj-$(CONFIG_DUMMY) += dummy.o
 obj-$(CONFIG_IFB) += ifb.o
 obj-$(CONFIG_MACVLAN) += macvlan.o
+obj-$(CONFIG_MACVTAP) += macvtap.o
 obj-$(CONFIG_DE600) += de600.o
 obj-$(CONFIG_DE620) += de620.o
 obj-$(CONFIG_LANCE) += lance.o

include/linux/if_macvlan.h

@@ -34,6 +34,7 @@ struct macvlan_dev {
 	enum macvlan_mode	mode;
 	int (*receive)(struct sk_buff *skb);
 	int (*forward)(struct net_device *dev, struct sk_buff *skb);
+	struct macvtap_queue	*tap;
 };
 
 static inline void macvlan_count_rx(const struct macvlan_dev *vlan,