mac80211-next: rtnetlink wifi simulation device

This device takes over an existing network device and produces a
new one that appears like a wireless connection, returning enough canned
responses to nl80211 to satisfy a standard connection manager. If
necessary, it can also be set up one step removed from an existing
network device, such as through a vlan/80211Q or macvlan connection to
not disrupt the existing network interface.

To use it to wrap a bare ethernet connection:

ip link add link eth0 name wlan0 type virt_wifi

You may have to rename or otherwise hide the eth0 from your connection
manager, as the original network link will become unusuable and only
the wireless wrapper will be functional. This can also be combined with
vlan or macvlan links on top of eth0 to share the network between
distinct links, but that requires support outside the machine for
accepting vlan-tagged packets or packets from multiple MAC addresses.

This is being used for Google's Remote Android Virtual Device project,
which runs Android devices in virtual machines. The standard network
interfaces provided inside the virtual machines are all ethernet.
However, Android is not interested in ethernet devices and would rather
connect to a wireless interface. This patch allows the virtual machine
guest to treat one of its network connections as wireless rather than
ethernet, satisfying Android's network connection requirements.

We believe this is a generally useful driver for simulating wireless
network connections in other environments where a wireless connection is
desired by some userspace process but is not available.

This is distinct from other testing efforts such as mac80211_hwsim by
being a cfg80211 device instead of mac80211 device, allowing straight
pass-through on the data plane instead of forcing packaging of ethernet
data into mac80211 frames.
Signed-off-by: NA. Cody Schuffelen <schuffelen@google.com>
Acked-by: NAlistair Strachan <astrachan@google.com>
Acked-by: NGreg Hartman <ghartman@google.com>
Acked-by: NTristan Muntsinger <muntsinger@google.com>
[make it a tristate]
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

drivers/net/wireless/Kconfig

@@ -114,4 +114,11 @@ config USB_NET_RNDIS_WLAN
 
 	  If you choose to build a module, it'll be called rndis_wlan.
 
+config VIRT_WIFI
+	tristate "Wifi wrapper for ethernet drivers"
+	depends on CFG80211
+	---help---
+	  This option adds support for ethernet connections to appear as if they
+	  are wifi connections through a special rtnetlink device.
+
 endif # WLAN

drivers/net/wireless/Makefile

@@ -27,3 +27,5 @@ obj-$(CONFIG_PCMCIA_WL3501)	+= wl3501_cs.o
 obj-$(CONFIG_USB_NET_RNDIS_WLAN)	+= rndis_wlan.o
 
 obj-$(CONFIG_MAC80211_HWSIM)	+= mac80211_hwsim.o
+
+obj-$(CONFIG_VIRT_WIFI)	+= virt_wifi.o

drivers/net/wireless/virt_wifi.c

+// SPDX-License-Identifier: GPL-2.0
+/* drivers/net/wireless/virt_wifi.c
+ *
+ * A fake implementation of cfg80211_ops that can be tacked on to an ethernet
+ * net_device to make it appear as a wireless connection.
+ *
+ * Copyright (C) 2018 Google, Inc.
+ *
+ * Author: schuffelen@google.com
+ */
+
+#include <net/cfg80211.h>
+#include <net/rtnetlink.h>
+#include <linux/etherdevice.h>
+#include <linux/module.h>
+
+#include <net/cfg80211.h>
+#include <net/rtnetlink.h>
+#include <linux/etherdevice.h>
+#include <linux/module.h>
+
+static struct wiphy *common_wiphy;
+
+struct virt_wifi_wiphy_priv {
+	struct delayed_work scan_result;
+	struct cfg80211_scan_request *scan_request;
+	bool being_deleted;
+};
+
+static struct ieee80211_channel channel_2ghz = {
+	.band = NL80211_BAND_2GHZ,
+	.center_freq = 2432,
+	.hw_value = 2432,
+	.max_power = 20,
+};
+
+static struct ieee80211_rate bitrates_2ghz[] = {
+	{ .bitrate = 10 },
+	{ .bitrate = 20 },
+	{ .bitrate = 55 },
+	{ .bitrate = 110 },
+	{ .bitrate = 60 },
+	{ .bitrate = 120 },
+	{ .bitrate = 240 },
+};
+
+static struct ieee80211_supported_band band_2ghz = {
+	.channels = &channel_2ghz,
+	.bitrates = bitrates_2ghz,
+	.band = NL80211_BAND_2GHZ,
+	.n_channels = 1,
+	.n_bitrates = ARRAY_SIZE(bitrates_2ghz),
+	.ht_cap = {
+		.ht_supported = true,
+		.cap = IEEE80211_HT_CAP_SUP_WIDTH_20_40 |
+		       IEEE80211_HT_CAP_GRN_FLD |
+		       IEEE80211_HT_CAP_SGI_20 |
+		       IEEE80211_HT_CAP_SGI_40 |
+		       IEEE80211_HT_CAP_DSSSCCK40,
+		.ampdu_factor = 0x3,
+		.ampdu_density = 0x6,
+		.mcs = {
+			.rx_mask = {0xff, 0xff},
+			.tx_params = IEEE80211_HT_MCS_TX_DEFINED,
+		},
+	},
+};
+
+static struct ieee80211_channel channel_5ghz = {
+	.band = NL80211_BAND_5GHZ,
+	.center_freq = 5240,
+	.hw_value = 5240,
+	.max_power = 20,
+};
+
+static struct ieee80211_rate bitrates_5ghz[] = {
+	{ .bitrate = 60 },
+	{ .bitrate = 120 },
+	{ .bitrate = 240 },
+};
+
+#define RX_MCS_MAP (IEEE80211_VHT_MCS_SUPPORT_0_9 << 0 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 2 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 4 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 6 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 8 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 10 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 12 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 14)
+
+#define TX_MCS_MAP (IEEE80211_VHT_MCS_SUPPORT_0_9 << 0 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 2 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 4 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 6 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 8 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 10 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 12 | \
+		    IEEE80211_VHT_MCS_SUPPORT_0_9 << 14)
+
+static struct ieee80211_supported_band band_5ghz = {
+	.channels = &channel_5ghz,
+	.bitrates = bitrates_5ghz,
+	.band = NL80211_BAND_5GHZ,
+	.n_channels = 1,
+	.n_bitrates = ARRAY_SIZE(bitrates_5ghz),
+	.ht_cap = {
+		.ht_supported = true,
+		.cap = IEEE80211_HT_CAP_SUP_WIDTH_20_40 |
+		       IEEE80211_HT_CAP_GRN_FLD |
+		       IEEE80211_HT_CAP_SGI_20 |
+		       IEEE80211_HT_CAP_SGI_40 |
+		       IEEE80211_HT_CAP_DSSSCCK40,
+		.ampdu_factor = 0x3,
+		.ampdu_density = 0x6,
+		.mcs = {
+			.rx_mask = {0xff, 0xff},
+			.tx_params = IEEE80211_HT_MCS_TX_DEFINED,
+		},
+	},
+	.vht_cap = {
+		.vht_supported = true,
+		.cap = IEEE80211_VHT_CAP_MAX_MPDU_LENGTH_11454 |
+		       IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_160_80PLUS80MHZ |
+		       IEEE80211_VHT_CAP_RXLDPC |
+		       IEEE80211_VHT_CAP_SHORT_GI_80 |
+		       IEEE80211_VHT_CAP_SHORT_GI_160 |
+		       IEEE80211_VHT_CAP_TXSTBC |
+		       IEEE80211_VHT_CAP_RXSTBC_1 |
+		       IEEE80211_VHT_CAP_RXSTBC_2 |
+		       IEEE80211_VHT_CAP_RXSTBC_3 |
+		       IEEE80211_VHT_CAP_RXSTBC_4 |
+		       IEEE80211_VHT_CAP_MAX_A_MPDU_LENGTH_EXPONENT_MASK,
+		.vht_mcs = {
+			.rx_mcs_map = cpu_to_le16(RX_MCS_MAP),
+			.tx_mcs_map = cpu_to_le16(TX_MCS_MAP),
+		}
+	},
+};
+
+/* Assigned at module init. Guaranteed locally-administered and unicast. */
+static u8 fake_router_bssid[ETH_ALEN] __ro_after_init = {};
+
+/* Called with the rtnl lock held. */
+static int virt_wifi_scan(struct wiphy *wiphy,
+			  struct cfg80211_scan_request *request)
+{
+	struct virt_wifi_wiphy_priv *priv = wiphy_priv(wiphy);
+
+	wiphy_debug(wiphy, "scan\n");
+
+	if (priv->scan_request || priv->being_deleted)
+		return -EBUSY;
+
+	priv->scan_request = request;
+	schedule_delayed_work(&priv->scan_result, HZ * 2);
+
+	return 0;
+}
+
+/* Acquires and releases the rdev BSS lock. */
+static void virt_wifi_scan_result(struct work_struct *work)
+{
+	struct {
+		u8 tag;
+		u8 len;
+		u8 ssid[8];
+	} __packed ssid = {
+		.tag = WLAN_EID_SSID, .len = 8, .ssid = "VirtWifi",
+	};
+	struct cfg80211_bss *informed_bss;
+	struct virt_wifi_wiphy_priv *priv =
+		container_of(work, struct virt_wifi_wiphy_priv,
+			     scan_result.work);
+	struct wiphy *wiphy = priv_to_wiphy(priv);
+	struct cfg80211_scan_info scan_info = { .aborted = false };
+
+	informed_bss = cfg80211_inform_bss(wiphy, &channel_5ghz,
+					   CFG80211_BSS_FTYPE_PRESP,
+					   fake_router_bssid,
+					   ktime_get_boot_ns(),
+					   WLAN_CAPABILITY_ESS, 0,
+					   (void *)&ssid, sizeof(ssid),
+					   DBM_TO_MBM(-50), GFP_KERNEL);
+	cfg80211_put_bss(wiphy, informed_bss);
+
+	/* Schedules work which acquires and releases the rtnl lock. */
+	cfg80211_scan_done(priv->scan_request, &scan_info);
+	priv->scan_request = NULL;
+}
+
+/* May acquire and release the rdev BSS lock. */
+static void virt_wifi_cancel_scan(struct wiphy *wiphy)
+{
+	struct virt_wifi_wiphy_priv *priv = wiphy_priv(wiphy);
+
+	cancel_delayed_work_sync(&priv->scan_result);
+	/* Clean up dangling callbacks if necessary. */
+	if (priv->scan_request) {
+		struct cfg80211_scan_info scan_info = { .aborted = true };
+		/* Schedules work which acquires and releases the rtnl lock. */
+		cfg80211_scan_done(priv->scan_request, &scan_info);
+		priv->scan_request = NULL;
+	}
+}
+
+struct virt_wifi_netdev_priv {
+	struct delayed_work connect;
+	struct net_device *lowerdev;
+	struct net_device *upperdev;
+	u32 tx_packets;
+	u32 tx_failed;
+	u8 connect_requested_bss[ETH_ALEN];
+	bool is_up;
+	bool is_connected;
+	bool being_deleted;
+};
+
+/* Called with the rtnl lock held. */
+static int virt_wifi_connect(struct wiphy *wiphy, struct net_device *netdev,
+			     struct cfg80211_connect_params *sme)
+{
+	struct virt_wifi_netdev_priv *priv = netdev_priv(netdev);
+	bool could_schedule;
+
+	if (priv->being_deleted || !priv->is_up)
+		return -EBUSY;
+
+	could_schedule = schedule_delayed_work(&priv->connect, HZ * 2);
+	if (!could_schedule)
+		return -EBUSY;
+
+	if (sme->bssid)
+		ether_addr_copy(priv->connect_requested_bss, sme->bssid);
+	else
+		eth_zero_addr(priv->connect_requested_bss);
+
+	wiphy_debug(wiphy, "connect\n");
+
+	return 0;
+}
+
+/* Acquires and releases the rdev event lock. */
+static void virt_wifi_connect_complete(struct work_struct *work)
+{
+	struct virt_wifi_netdev_priv *priv =
+		container_of(work, struct virt_wifi_netdev_priv, connect.work);
+	u8 *requested_bss = priv->connect_requested_bss;
+	bool has_addr = !is_zero_ether_addr(requested_bss);
+	bool right_addr = ether_addr_equal(requested_bss, fake_router_bssid);
+	u16 status = WLAN_STATUS_SUCCESS;
+
+	if (!priv->is_up || (has_addr && !right_addr))
+		status = WLAN_STATUS_UNSPECIFIED_FAILURE;
+	else
+		priv->is_connected = true;
+
+	/* Schedules an event that acquires the rtnl lock. */
+	cfg80211_connect_result(priv->upperdev, requested_bss, NULL, 0, NULL, 0,
+				status, GFP_KERNEL);
+	netif_carrier_on(priv->upperdev);
+}
+
+/* May acquire and release the rdev event lock. */
+static void virt_wifi_cancel_connect(struct net_device *netdev)
+{
+	struct virt_wifi_netdev_priv *priv = netdev_priv(netdev);
+
+	/* If there is work pending, clean up dangling callbacks. */
+	if (cancel_delayed_work_sync(&priv->connect)) {
+		/* Schedules an event that acquires the rtnl lock. */
+		cfg80211_connect_result(priv->upperdev,
+					priv->connect_requested_bss, NULL, 0,
+					NULL, 0,
+					WLAN_STATUS_UNSPECIFIED_FAILURE,
+					GFP_KERNEL);
+	}
+}
+
+/* Called with the rtnl lock held. Acquires the rdev event lock. */
+static int virt_wifi_disconnect(struct wiphy *wiphy, struct net_device *netdev,
+				u16 reason_code)
+{
+	struct virt_wifi_netdev_priv *priv = netdev_priv(netdev);
+
+	if (priv->being_deleted)
+		return -EBUSY;
+
+	wiphy_debug(wiphy, "disconnect\n");
+	virt_wifi_cancel_connect(netdev);
+
+	cfg80211_disconnected(netdev, reason_code, NULL, 0, true, GFP_KERNEL);
+	priv->is_connected = false;
+	netif_carrier_off(netdev);
+
+	return 0;
+}
+
+/* Called with the rtnl lock held. */
+static int virt_wifi_get_station(struct wiphy *wiphy, struct net_device *dev,
+				 const u8 *mac, struct station_info *sinfo)
+{
+	struct virt_wifi_netdev_priv *priv = netdev_priv(dev);
+
+	wiphy_debug(wiphy, "get_station\n");
+
+	if (!priv->is_connected || !ether_addr_equal(mac, fake_router_bssid))
+		return -ENOENT;
+
+	sinfo->filled = BIT_ULL(NL80211_STA_INFO_TX_PACKETS) |
+		BIT_ULL(NL80211_STA_INFO_TX_FAILED) |
+		BIT_ULL(NL80211_STA_INFO_SIGNAL) |
+		BIT_ULL(NL80211_STA_INFO_TX_BITRATE);
+	sinfo->tx_packets = priv->tx_packets;
+	sinfo->tx_failed = priv->tx_failed;
+	/* For CFG80211_SIGNAL_TYPE_MBM, value is expressed in _dBm_ */
+	sinfo->signal = -50;
+	sinfo->txrate = (struct rate_info) {
+		.legacy = 10, /* units are 100kbit/s */
+	};
+	return 0;
+}
+
+/* Called with the rtnl lock held. */
+static int virt_wifi_dump_station(struct wiphy *wiphy, struct net_device *dev,
+				  int idx, u8 *mac, struct station_info *sinfo)
+{
+	struct virt_wifi_netdev_priv *priv = netdev_priv(dev);
+
+	wiphy_debug(wiphy, "dump_station\n");
+
+	if (idx != 0 || !priv->is_connected)
+		return -ENOENT;
+
+	ether_addr_copy(mac, fake_router_bssid);
+	return virt_wifi_get_station(wiphy, dev, fake_router_bssid, sinfo);
+}
+
+static const struct cfg80211_ops virt_wifi_cfg80211_ops = {
+	.scan = virt_wifi_scan,
+
+	.connect = virt_wifi_connect,
+	.disconnect = virt_wifi_disconnect,
+
+	.get_station = virt_wifi_get_station,
+	.dump_station = virt_wifi_dump_station,
+};
+
+/* Acquires and releases the rtnl lock. */
+static struct wiphy *virt_wifi_make_wiphy(void)
+{
+	struct wiphy *wiphy;
+	struct virt_wifi_wiphy_priv *priv;
+	int err;
+
+	wiphy = wiphy_new(&virt_wifi_cfg80211_ops, sizeof(*priv));
+
+	if (!wiphy)
+		return NULL;
+
+	wiphy->max_scan_ssids = 4;
+	wiphy->max_scan_ie_len = 1000;
+	wiphy->signal_type = CFG80211_SIGNAL_TYPE_MBM;
+
+	wiphy->bands[NL80211_BAND_2GHZ] = &band_2ghz;
+	wiphy->bands[NL80211_BAND_5GHZ] = &band_5ghz;
+	wiphy->bands[NL80211_BAND_60GHZ] = NULL;
+
+	wiphy->regulatory_flags = REGULATORY_WIPHY_SELF_MANAGED;
+	wiphy->interface_modes = BIT(NL80211_IFTYPE_STATION);
+
+	priv = wiphy_priv(wiphy);
+	priv->being_deleted = false;
+	priv->scan_request = NULL;
+	INIT_DELAYED_WORK(&priv->scan_result, virt_wifi_scan_result);
+
+	err = wiphy_register(wiphy);
+	if (err < 0) {
+		wiphy_free(wiphy);
+		return NULL;
+	}
+
+	return wiphy;
+}
+
+/* Acquires and releases the rtnl lock. */
+static void virt_wifi_destroy_wiphy(struct wiphy *wiphy)
+{
+	struct virt_wifi_wiphy_priv *priv;
+
+	WARN(!wiphy, "%s called with null wiphy", __func__);
+	if (!wiphy)
+		return;
+
+	priv = wiphy_priv(wiphy);
+	priv->being_deleted = true;
+	virt_wifi_cancel_scan(wiphy);
+
+	if (wiphy->registered)
+		wiphy_unregister(wiphy);
+	wiphy_free(wiphy);
+}
+
+/* Enters and exits a RCU-bh critical section. */
+static netdev_tx_t virt_wifi_start_xmit(struct sk_buff *skb,
+					struct net_device *dev)
+{
+	struct virt_wifi_netdev_priv *priv = netdev_priv(dev);
+
+	priv->tx_packets++;
+	if (!priv->is_connected) {
+		priv->tx_failed++;
+		return NET_XMIT_DROP;
+	}
+
+	skb->dev = priv->lowerdev;
+	return dev_queue_xmit(skb);
+}
+
+/* Called with rtnl lock held. */
+static int virt_wifi_net_device_open(struct net_device *dev)
+{
+	struct virt_wifi_netdev_priv *priv = netdev_priv(dev);
+
+	priv->is_up = true;
+	return 0;
+}
+
+/* Called with rtnl lock held. */
+static int virt_wifi_net_device_stop(struct net_device *dev)
+{
+	struct virt_wifi_netdev_priv *n_priv = netdev_priv(dev);
+	struct virt_wifi_wiphy_priv *w_priv;
+
+	n_priv->is_up = false;
+
+	if (!dev->ieee80211_ptr)
+		return 0;
+	w_priv = wiphy_priv(dev->ieee80211_ptr->wiphy);
+
+	virt_wifi_cancel_scan(dev->ieee80211_ptr->wiphy);
+	virt_wifi_cancel_connect(dev);
+	netif_carrier_off(dev);
+
+	return 0;
+}
+
+static const struct net_device_ops virt_wifi_ops = {
+	.ndo_start_xmit = virt_wifi_start_xmit,
+	.ndo_open = virt_wifi_net_device_open,
+	.ndo_stop = virt_wifi_net_device_stop,
+};
+
+/* Invoked as part of rtnl lock release. */
+static void virt_wifi_net_device_destructor(struct net_device *dev)
+{
+	/* Delayed past dellink to allow nl80211 to react to the device being
+	 * deleted.
+	 */
+	kfree(dev->ieee80211_ptr);
+	dev->ieee80211_ptr = NULL;
+	free_netdev(dev);
+}
+
+/* No lock interaction. */
+static void virt_wifi_setup(struct net_device *dev)
+{
+	ether_setup(dev);
+	dev->netdev_ops = &virt_wifi_ops;
+	dev->priv_destructor = virt_wifi_net_device_destructor;
+}
+
+/* Called in a RCU read critical section from netif_receive_skb */
+static rx_handler_result_t virt_wifi_rx_handler(struct sk_buff **pskb)
+{
+	struct sk_buff *skb = *pskb;
+	struct virt_wifi_netdev_priv *priv =
+		rcu_dereference(skb->dev->rx_handler_data);
+
+	if (!priv->is_connected)
+		return RX_HANDLER_PASS;
+
+	/* GFP_ATOMIC because this is a packet interrupt handler. */
+	skb = skb_share_check(skb, GFP_ATOMIC);
+	if (!skb) {
+		dev_err(&priv->upperdev->dev, "can't skb_share_check\n");
+		return RX_HANDLER_CONSUMED;
+	}
+
+	*pskb = skb;
+	skb->dev = priv->upperdev;
+	skb->pkt_type = PACKET_HOST;
+	return RX_HANDLER_ANOTHER;
+}
+
+/* Called with rtnl lock held. */
+static int virt_wifi_newlink(struct net *src_net, struct net_device *dev,
+			     struct nlattr *tb[], struct nlattr *data[],
+			     struct netlink_ext_ack *extack)
+{
+	struct virt_wifi_netdev_priv *priv = netdev_priv(dev);
+	int err;
+
+	if (!tb[IFLA_LINK])
+		return -EINVAL;
+
+	netif_carrier_off(dev);
+
+	priv->upperdev = dev;
+	priv->lowerdev = __dev_get_by_index(src_net,
+					    nla_get_u32(tb[IFLA_LINK]));
+
+	if (!priv->lowerdev)
+		return -ENODEV;
+	if (!tb[IFLA_MTU])
+		dev->mtu = priv->lowerdev->mtu;
+	else if (dev->mtu > priv->lowerdev->mtu)
+		return -EINVAL;
+
+	err = netdev_rx_handler_register(priv->lowerdev, virt_wifi_rx_handler,
+					 priv);
+	if (err) {
+		dev_err(&priv->lowerdev->dev,
+			"can't netdev_rx_handler_register: %d\n", err);
+		return err;
+	}
+
+	eth_hw_addr_inherit(dev, priv->lowerdev);
+	netif_stacked_transfer_operstate(priv->lowerdev, dev);
+
+	SET_NETDEV_DEV(dev, &priv->lowerdev->dev);
+	dev->ieee80211_ptr = kzalloc(sizeof(*dev->ieee80211_ptr), GFP_KERNEL);
+
+	if (!dev->ieee80211_ptr)
+		goto remove_handler;
+
+	dev->ieee80211_ptr->iftype = NL80211_IFTYPE_STATION;
+	dev->ieee80211_ptr->wiphy = common_wiphy;
+
+	err = register_netdevice(dev);
+	if (err) {
+		dev_err(&priv->lowerdev->dev, "can't register_netdevice: %d\n",
+			err);
+		goto free_wireless_dev;
+	}
+
+	err = netdev_upper_dev_link(priv->lowerdev, dev, extack);
+	if (err) {
+		dev_err(&priv->lowerdev->dev, "can't netdev_upper_dev_link: %d\n",
+			err);
+		goto unregister_netdev;
+	}
+
+	priv->being_deleted = false;
+	priv->is_connected = false;
+	priv->is_up = false;
+	INIT_DELAYED_WORK(&priv->connect, virt_wifi_connect_complete);
+
+	return 0;
+unregister_netdev:
+	unregister_netdevice(dev);
+free_wireless_dev:
+	kfree(dev->ieee80211_ptr);
+	dev->ieee80211_ptr = NULL;
+remove_handler:
+	netdev_rx_handler_unregister(priv->lowerdev);
+
+	return err;
+}
+
+/* Called with rtnl lock held. */
+static void virt_wifi_dellink(struct net_device *dev,
+			      struct list_head *head)
+{
+	struct virt_wifi_netdev_priv *priv = netdev_priv(dev);
+
+	if (dev->ieee80211_ptr)
+		virt_wifi_cancel_scan(dev->ieee80211_ptr->wiphy);
+
+	priv->being_deleted = true;
+	virt_wifi_cancel_connect(dev);
+	netif_carrier_off(dev);
+
+	netdev_rx_handler_unregister(priv->lowerdev);
+	netdev_upper_dev_unlink(priv->lowerdev, dev);
+
+	unregister_netdevice_queue(dev, head);
+
+	/* Deleting the wiphy is handled in the module destructor. */
+}
+
+static struct rtnl_link_ops virt_wifi_link_ops = {
+	.kind		= "virt_wifi",
+	.setup		= virt_wifi_setup,
+	.newlink	= virt_wifi_newlink,
+	.dellink	= virt_wifi_dellink,
+	.priv_size	= sizeof(struct virt_wifi_netdev_priv),
+};
+
+/* Acquires and releases the rtnl lock. */
+static int __init virt_wifi_init_module(void)
+{
+	int err;
+
+	/* Guaranteed to be locallly-administered and not multicast. */
+	eth_random_addr(fake_router_bssid);
+
+	common_wiphy = virt_wifi_make_wiphy();
+	if (!common_wiphy)
+		return -ENOMEM;
+
+	err = rtnl_link_register(&virt_wifi_link_ops);
+	if (err)
+		virt_wifi_destroy_wiphy(common_wiphy);
+
+	return err;
+}
+
+/* Acquires and releases the rtnl lock. */
+static void __exit virt_wifi_cleanup_module(void)
+{
+	/* Will delete any devices that depend on the wiphy. */
+	rtnl_link_unregister(&virt_wifi_link_ops);
+	virt_wifi_destroy_wiphy(common_wiphy);
+}
+
+module_init(virt_wifi_init_module);
+module_exit(virt_wifi_cleanup_module);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Cody Schuffelen <schuffelen@google.com>");
+MODULE_DESCRIPTION("Driver for a wireless wrapper of ethernet devices");
+MODULE_ALIAS_RTNL_LINK("virt_wifi");