drivers/net/xen-netback/xenbus.c - kernel/msm-4.9 - Gitiles

 /*
  * Xenbus code for netif backend
  *
  * Copyright (C) 2005 Rusty Russell <rusty@rustcorp.com.au>
  * Copyright (C) 2005 XenSource Ltd
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
  * (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

 #include "common.h"

 struct backend_info {
 	struct xenbus_device *dev;
 	struct xenvif *vif;
 	enum xenbus_state frontend_state;
 	struct xenbus_watch hotplug_status_watch;
 	u8 have_hotplug_status_watch:1;
 };

 static int connect_rings(struct backend_info *);
 static void connect(struct backend_info *);
 static void backend_create_xenvif(struct backend_info *be);
 static void unregister_hotplug_status_watch(struct backend_info *be);

 static int netback_remove(struct xenbus_device *dev)
 {
 	struct backend_info *be = dev_get_drvdata(&dev->dev);

 	unregister_hotplug_status_watch(be);
 	if (be->vif) {
 		kobject_uevent(&dev->dev.kobj, KOBJ_OFFLINE);
 		xenbus_rm(XBT_NIL, dev->nodename, "hotplug-status");
 		xenvif_disconnect(be->vif);
 		be->vif = NULL;
 	}
 	kfree(be);
 	dev_set_drvdata(&dev->dev, NULL);
 	return 0;
 }


 /**
  * Entry point to this code when a new device is created.  Allocate the basic
  * structures and switch to InitWait.
  */
 static int netback_probe(struct xenbus_device *dev,
 			 const struct xenbus_device_id *id)
 {
 	const char *message;
 	struct xenbus_transaction xbt;
 	int err;
 	int sg;
 	struct backend_info *be = kzalloc(sizeof(struct backend_info),
 					  GFP_KERNEL);
 	if (!be) {
 		xenbus_dev_fatal(dev, -ENOMEM,
 				 "allocating backend structure");
 		return -ENOMEM;
 	}

 	be->dev = dev;
 	dev_set_drvdata(&dev->dev, be);

 	sg = 1;

 	do {
 		err = xenbus_transaction_start(&xbt);
 		if (err) {
 			xenbus_dev_fatal(dev, err, "starting transaction");
 			goto fail;
 		}

 		err = xenbus_printf(xbt, dev->nodename, "feature-sg", "%d", sg);
 		if (err) {
 			message = "writing feature-sg";
 			goto abort_transaction;
 		}

 		err = xenbus_printf(xbt, dev->nodename, "feature-gso-tcpv4",
 				    "%d", sg);
 		if (err) {
 			message = "writing feature-gso-tcpv4";
 			goto abort_transaction;
 		}

 		/* We support rx-copy path. */
 		err = xenbus_printf(xbt, dev->nodename,
 				    "feature-rx-copy", "%d", 1);
 		if (err) {
 			message = "writing feature-rx-copy";
 			goto abort_transaction;
 		}

 		/*
 		 * We don't support rx-flip path (except old guests who don't
 		 * grok this feature flag).
 		 */
 		err = xenbus_printf(xbt, dev->nodename,
 				    "feature-rx-flip", "%d", 0);
 		if (err) {
 			message = "writing feature-rx-flip";
 			goto abort_transaction;
 		}

 		err = xenbus_transaction_end(xbt, 0);
 	} while (err == -EAGAIN);

 	if (err) {
 		xenbus_dev_fatal(dev, err, "completing transaction");
 		goto fail;
 	}

 	/*
 	 * Split event channels support, this is optional so it is not
 	 * put inside the above loop.
 	 */
 	err = xenbus_printf(XBT_NIL, dev->nodename,
 			    "feature-split-event-channels",
 			    "%u", separate_tx_rx_irq);
 	if (err)
 		pr_debug("Error writing feature-split-event-channels\n");

 	err = xenbus_switch_state(dev, XenbusStateInitWait);
 	if (err)
 		goto fail;

 	/* This kicks hotplug scripts, so do it immediately. */
 	backend_create_xenvif(be);

 	return 0;

 abort_transaction:
 	xenbus_transaction_end(xbt, 1);
 	xenbus_dev_fatal(dev, err, "%s", message);
 fail:
 	pr_debug("failed\n");
 	netback_remove(dev);
 	return err;
 }


 /*
  * Handle the creation of the hotplug script environment.  We add the script
  * and vif variables to the environment, for the benefit of the vif-* hotplug
  * scripts.
  */
 static int netback_uevent(struct xenbus_device *xdev,
 			  struct kobj_uevent_env *env)
 {
 	struct backend_info *be = dev_get_drvdata(&xdev->dev);
 	char *val;

 	val = xenbus_read(XBT_NIL, xdev->nodename, "script", NULL);
 	if (IS_ERR(val)) {
 		int err = PTR_ERR(val);
 		xenbus_dev_fatal(xdev, err, "reading script");
 		return err;
 	} else {
 		if (add_uevent_var(env, "script=%s", val)) {
 			kfree(val);
 			return -ENOMEM;
 		}
 		kfree(val);
 	}

 	if (!be || !be->vif)
 		return 0;

 	return add_uevent_var(env, "vif=%s", be->vif->dev->name);
 }


 static void backend_create_xenvif(struct backend_info *be)
 {
 	int err;
 	long handle;
 	struct xenbus_device *dev = be->dev;

 	if (be->vif != NULL)
 		return;

 	err = xenbus_scanf(XBT_NIL, dev->nodename, "handle", "%li", &handle);
 	if (err != 1) {
 		xenbus_dev_fatal(dev, err, "reading handle");
 		return;
 	}

 	be->vif = xenvif_alloc(&dev->dev, dev->otherend_id, handle);
 	if (IS_ERR(be->vif)) {
 		err = PTR_ERR(be->vif);
 		be->vif = NULL;
 		xenbus_dev_fatal(dev, err, "creating interface");
 		return;
 	}

 	kobject_uevent(&dev->dev.kobj, KOBJ_ONLINE);
 }


 static void disconnect_backend(struct xenbus_device *dev)
 {
 	struct backend_info *be = dev_get_drvdata(&dev->dev);

 	if (be->vif) {
 		xenbus_rm(XBT_NIL, dev->nodename, "hotplug-status");
 		xenvif_disconnect(be->vif);
 		be->vif = NULL;
 	}
 }

 /**
  * Callback received when the frontend's state changes.
  */
 static void frontend_changed(struct xenbus_device *dev,
 			     enum xenbus_state frontend_state)
 {
 	struct backend_info *be = dev_get_drvdata(&dev->dev);

 	pr_debug("frontend state %s\n", xenbus_strstate(frontend_state));

 	be->frontend_state = frontend_state;

 	switch (frontend_state) {
 	case XenbusStateInitialising:
 		if (dev->state == XenbusStateClosed) {
 			pr_info("%s: prepare for reconnect\n", dev->nodename);
 			xenbus_switch_state(dev, XenbusStateInitWait);
 		}
 		break;

 	case XenbusStateInitialised:
 		break;

 	case XenbusStateConnected:
 		if (dev->state == XenbusStateConnected)
 			break;
 		backend_create_xenvif(be);
 		if (be->vif)
 			connect(be);
 		break;

 	case XenbusStateClosing:
 		if (be->vif)
 			kobject_uevent(&dev->dev.kobj, KOBJ_OFFLINE);
 		disconnect_backend(dev);
 		xenbus_switch_state(dev, XenbusStateClosing);
 		break;

 	case XenbusStateClosed:
 		xenbus_switch_state(dev, XenbusStateClosed);
 		if (xenbus_dev_is_online(dev))
 			break;
 		/* fall through if not online */
 	case XenbusStateUnknown:
 		device_unregister(&dev->dev);
 		break;

 	default:
 		xenbus_dev_fatal(dev, -EINVAL, "saw state %d at frontend",
 				 frontend_state);
 		break;
 	}
 }


 static void xen_net_read_rate(struct xenbus_device *dev,
 			      unsigned long *bytes, unsigned long *usec)
 {
 	char *s, *e;
 	unsigned long b, u;
 	char *ratestr;

 	/* Default to unlimited bandwidth. */
 	*bytes = ~0UL;
 	*usec = 0;

 	ratestr = xenbus_read(XBT_NIL, dev->nodename, "rate", NULL);
 	if (IS_ERR(ratestr))
 		return;

 	s = ratestr;
 	b = simple_strtoul(s, &e, 10);
 	if ((s == e) || (*e != ','))
 		goto fail;

 	s = e + 1;
 	u = simple_strtoul(s, &e, 10);
 	if ((s == e) || (*e != '\0'))
 		goto fail;

 	*bytes = b;
 	*usec = u;

 	kfree(ratestr);
 	return;

  fail:
 	pr_warn("Failed to parse network rate limit. Traffic unlimited.\n");
 	kfree(ratestr);
 }

 static int xen_net_read_mac(struct xenbus_device *dev, u8 mac[])
 {
 	char *s, *e, *macstr;
 	int i;

 	macstr = s = xenbus_read(XBT_NIL, dev->nodename, "mac", NULL);
 	if (IS_ERR(macstr))
 		return PTR_ERR(macstr);

 	for (i = 0; i < ETH_ALEN; i++) {
 		mac[i] = simple_strtoul(s, &e, 16);
 		if ((s == e) || (*e != ((i == ETH_ALEN-1) ? '\0' : ':'))) {
 			kfree(macstr);
 			return -ENOENT;
 		}
 		s = e+1;
 	}

 	kfree(macstr);
 	return 0;
 }

 static void unregister_hotplug_status_watch(struct backend_info *be)
 {
 	if (be->have_hotplug_status_watch) {
 		unregister_xenbus_watch(&be->hotplug_status_watch);
 		kfree(be->hotplug_status_watch.node);
 	}
 	be->have_hotplug_status_watch = 0;
 }

 static void hotplug_status_changed(struct xenbus_watch *watch,
 				   const char **vec,
 				   unsigned int vec_size)
 {
 	struct backend_info *be = container_of(watch,
 					       struct backend_info,
 					       hotplug_status_watch);
 	char *str;
 	unsigned int len;

 	str = xenbus_read(XBT_NIL, be->dev->nodename, "hotplug-status", &len);
 	if (IS_ERR(str))
 		return;
 	if (len == sizeof("connected")-1 && !memcmp(str, "connected", len)) {
 		xenbus_switch_state(be->dev, XenbusStateConnected);
 		/* Not interested in this watch anymore. */
 		unregister_hotplug_status_watch(be);
 	}
 	kfree(str);
 }

 static void connect(struct backend_info *be)
 {
 	int err;
 	struct xenbus_device *dev = be->dev;

 	err = connect_rings(be);
 	if (err)
 		return;

 	err = xen_net_read_mac(dev, be->vif->fe_dev_addr);
 	if (err) {
 		xenbus_dev_fatal(dev, err, "parsing %s/mac", dev->nodename);
 		return;
 	}

 	xen_net_read_rate(dev, &be->vif->credit_bytes,
 			  &be->vif->credit_usec);
 	be->vif->remaining_credit = be->vif->credit_bytes;

 	unregister_hotplug_status_watch(be);
 	err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch,
 				   hotplug_status_changed,
 				   "%s/%s", dev->nodename, "hotplug-status");
 	if (err) {
 		/* Switch now, since we can't do a watch. */
 		xenbus_switch_state(dev, XenbusStateConnected);
 	} else {
 		be->have_hotplug_status_watch = 1;
 	}

 	netif_wake_queue(be->vif->dev);
 }


 static int connect_rings(struct backend_info *be)
 {
 	struct xenvif *vif = be->vif;
 	struct xenbus_device *dev = be->dev;
 	unsigned long tx_ring_ref, rx_ring_ref;
 	unsigned int tx_evtchn, rx_evtchn, rx_copy;
 	int err;
 	int val;

 	err = xenbus_gather(XBT_NIL, dev->otherend,
 			    "tx-ring-ref", "%lu", &tx_ring_ref,
 			    "rx-ring-ref", "%lu", &rx_ring_ref, NULL);
 	if (err) {
 		xenbus_dev_fatal(dev, err,
 				 "reading %s/ring-ref",
 				 dev->otherend);
 		return err;
 	}

 	/* Try split event channels first, then single event channel. */
 	err = xenbus_gather(XBT_NIL, dev->otherend,
 			    "event-channel-tx", "%u", &tx_evtchn,
 			    "event-channel-rx", "%u", &rx_evtchn, NULL);
 	if (err < 0) {
 		err = xenbus_scanf(XBT_NIL, dev->otherend,
 				   "event-channel", "%u", &tx_evtchn);
 		if (err < 0) {
 			xenbus_dev_fatal(dev, err,
 					 "reading %s/event-channel(-tx/rx)",
 					 dev->otherend);
 			return err;
 		}
 		rx_evtchn = tx_evtchn;
 	}

 	err = xenbus_scanf(XBT_NIL, dev->otherend, "request-rx-copy", "%u",
 			   &rx_copy);
 	if (err == -ENOENT) {
 		err = 0;
 		rx_copy = 0;
 	}
 	if (err < 0) {
 		xenbus_dev_fatal(dev, err, "reading %s/request-rx-copy",
 				 dev->otherend);
 		return err;
 	}
 	if (!rx_copy)
 		return -EOPNOTSUPP;

 	if (vif->dev->tx_queue_len != 0) {
 		if (xenbus_scanf(XBT_NIL, dev->otherend,
 				 "feature-rx-notify", "%d", &val) < 0)
 			val = 0;
 		if (val)
 			vif->can_queue = 1;
 		else
 			/* Must be non-zero for pfifo_fast to work. */
 			vif->dev->tx_queue_len = 1;
 	}

 	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-sg",
 			 "%d", &val) < 0)
 		val = 0;
 	vif->can_sg = !!val;

 	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv4",
 			 "%d", &val) < 0)
 		val = 0;
 	vif->gso = !!val;

 	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv4-prefix",
 			 "%d", &val) < 0)
 		val = 0;
 	vif->gso_prefix = !!val;

 	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-no-csum-offload",
 			 "%d", &val) < 0)
 		val = 0;
 	vif->csum = !val;

 	/* Map the shared frame, irq etc. */
 	err = xenvif_connect(vif, tx_ring_ref, rx_ring_ref,
 			     tx_evtchn, rx_evtchn);
 	if (err) {
 		xenbus_dev_fatal(dev, err,
 				 "mapping shared-frames %lu/%lu port tx %u rx %u",
 				 tx_ring_ref, rx_ring_ref,
 				 tx_evtchn, rx_evtchn);
 		return err;
 	}
 	return 0;
 }


 /* ** Driver Registration ** */


 static const struct xenbus_device_id netback_ids[] = {
 	{ "vif" },
 	{ "" }
 };


 static DEFINE_XENBUS_DRIVER(netback, ,
 	.probe = netback_probe,
 	.remove = netback_remove,
 	.uevent = netback_uevent,
 	.otherend_changed = frontend_changed,
 );

 int xenvif_xenbus_init(void)
 {
 	return xenbus_register_backend(&netback_driver);
 }

 void xenvif_xenbus_fini(void)
 {
 	return xenbus_unregister_driver(&netback_driver);
 }
	/*
	* Xenbus code for netif backend
	*
	* Copyright (C) 2005 Rusty Russell <rusty@rustcorp.com.au>
	* Copyright (C) 2005 XenSource Ltd
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
	*/

	#include "common.h"

	struct backend_info {
	struct xenbus_device *dev;
	struct xenvif *vif;
	enum xenbus_state frontend_state;
	struct xenbus_watch hotplug_status_watch;
	u8 have_hotplug_status_watch:1;
	};

	static int connect_rings(struct backend_info *);
	static void connect(struct backend_info *);
	static void backend_create_xenvif(struct backend_info *be);
	static void unregister_hotplug_status_watch(struct backend_info *be);

	static int netback_remove(struct xenbus_device *dev)
	{
	struct backend_info *be = dev_get_drvdata(&dev->dev);

	unregister_hotplug_status_watch(be);
	if (be->vif) {
	kobject_uevent(&dev->dev.kobj, KOBJ_OFFLINE);
	xenbus_rm(XBT_NIL, dev->nodename, "hotplug-status");
	xenvif_disconnect(be->vif);
	be->vif = NULL;
	}
	kfree(be);
	dev_set_drvdata(&dev->dev, NULL);
	return 0;
	}


	/**
	* Entry point to this code when a new device is created. Allocate the basic
	* structures and switch to InitWait.
	*/
	static int netback_probe(struct xenbus_device *dev,
	const struct xenbus_device_id *id)
	{
	const char *message;
	struct xenbus_transaction xbt;
	int err;
	int sg;
	struct backend_info *be = kzalloc(sizeof(struct backend_info),
	GFP_KERNEL);
	if (!be) {
	xenbus_dev_fatal(dev, -ENOMEM,
	"allocating backend structure");
	return -ENOMEM;
	}

	be->dev = dev;
	dev_set_drvdata(&dev->dev, be);

	sg = 1;

	do {
	err = xenbus_transaction_start(&xbt);
	if (err) {
	xenbus_dev_fatal(dev, err, "starting transaction");
	goto fail;
	}

	err = xenbus_printf(xbt, dev->nodename, "feature-sg", "%d", sg);
	if (err) {
	message = "writing feature-sg";
	goto abort_transaction;
	}

	err = xenbus_printf(xbt, dev->nodename, "feature-gso-tcpv4",
	"%d", sg);
	if (err) {
	message = "writing feature-gso-tcpv4";
	goto abort_transaction;
	}

	/* We support rx-copy path. */
	err = xenbus_printf(xbt, dev->nodename,
	"feature-rx-copy", "%d", 1);
	if (err) {
	message = "writing feature-rx-copy";
	goto abort_transaction;
	}

	/*
	* We don't support rx-flip path (except old guests who don't
	* grok this feature flag).
	*/
	err = xenbus_printf(xbt, dev->nodename,
	"feature-rx-flip", "%d", 0);
	if (err) {
	message = "writing feature-rx-flip";
	goto abort_transaction;
	}

	err = xenbus_transaction_end(xbt, 0);
	} while (err == -EAGAIN);

	if (err) {
	xenbus_dev_fatal(dev, err, "completing transaction");
	goto fail;
	}

	/*
	* Split event channels support, this is optional so it is not
	* put inside the above loop.
	*/
	err = xenbus_printf(XBT_NIL, dev->nodename,
	"feature-split-event-channels",
	"%u", separate_tx_rx_irq);
	if (err)
	pr_debug("Error writing feature-split-event-channels\n");

	err = xenbus_switch_state(dev, XenbusStateInitWait);
	if (err)
	goto fail;

	/* This kicks hotplug scripts, so do it immediately. */
	backend_create_xenvif(be);

	return 0;

	abort_transaction:
	xenbus_transaction_end(xbt, 1);
	xenbus_dev_fatal(dev, err, "%s", message);
	fail:
	pr_debug("failed\n");
	netback_remove(dev);
	return err;
	}


	/*
	* Handle the creation of the hotplug script environment. We add the script
	* and vif variables to the environment, for the benefit of the vif-* hotplug
	* scripts.
	*/
	static int netback_uevent(struct xenbus_device *xdev,
	struct kobj_uevent_env *env)
	{
	struct backend_info *be = dev_get_drvdata(&xdev->dev);
	char *val;

	val = xenbus_read(XBT_NIL, xdev->nodename, "script", NULL);
	if (IS_ERR(val)) {
	int err = PTR_ERR(val);
	xenbus_dev_fatal(xdev, err, "reading script");
	return err;
	} else {
	if (add_uevent_var(env, "script=%s", val)) {
	kfree(val);
	return -ENOMEM;
	}
	kfree(val);
	}

	if (!be \|\| !be->vif)
	return 0;

	return add_uevent_var(env, "vif=%s", be->vif->dev->name);
	}


	static void backend_create_xenvif(struct backend_info *be)
	{
	int err;
	long handle;
	struct xenbus_device *dev = be->dev;

	if (be->vif != NULL)
	return;

	err = xenbus_scanf(XBT_NIL, dev->nodename, "handle", "%li", &handle);
	if (err != 1) {
	xenbus_dev_fatal(dev, err, "reading handle");
	return;
	}

	be->vif = xenvif_alloc(&dev->dev, dev->otherend_id, handle);
	if (IS_ERR(be->vif)) {
	err = PTR_ERR(be->vif);
	be->vif = NULL;
	xenbus_dev_fatal(dev, err, "creating interface");
	return;
	}

	kobject_uevent(&dev->dev.kobj, KOBJ_ONLINE);
	}


	static void disconnect_backend(struct xenbus_device *dev)
	{
	struct backend_info *be = dev_get_drvdata(&dev->dev);

	if (be->vif) {
	xenbus_rm(XBT_NIL, dev->nodename, "hotplug-status");
	xenvif_disconnect(be->vif);
	be->vif = NULL;
	}
	}

	/**
	* Callback received when the frontend's state changes.
	*/
	static void frontend_changed(struct xenbus_device *dev,
	enum xenbus_state frontend_state)
	{
	struct backend_info *be = dev_get_drvdata(&dev->dev);

	pr_debug("frontend state %s\n", xenbus_strstate(frontend_state));

	be->frontend_state = frontend_state;

	switch (frontend_state) {
	case XenbusStateInitialising:
	if (dev->state == XenbusStateClosed) {
	pr_info("%s: prepare for reconnect\n", dev->nodename);
	xenbus_switch_state(dev, XenbusStateInitWait);
	}
	break;

	case XenbusStateInitialised:
	break;

	case XenbusStateConnected:
	if (dev->state == XenbusStateConnected)
	break;
	backend_create_xenvif(be);
	if (be->vif)
	connect(be);
	break;

	case XenbusStateClosing:
	if (be->vif)
	kobject_uevent(&dev->dev.kobj, KOBJ_OFFLINE);
	disconnect_backend(dev);
	xenbus_switch_state(dev, XenbusStateClosing);
	break;

	case XenbusStateClosed:
	xenbus_switch_state(dev, XenbusStateClosed);
	if (xenbus_dev_is_online(dev))
	break;
	/* fall through if not online */
	case XenbusStateUnknown:
	device_unregister(&dev->dev);
	break;

	default:
	xenbus_dev_fatal(dev, -EINVAL, "saw state %d at frontend",
	frontend_state);
	break;
	}
	}


	static void xen_net_read_rate(struct xenbus_device *dev,
	unsigned long bytes, unsigned long usec)
	{
	char s, e;
	unsigned long b, u;
	char *ratestr;

	/* Default to unlimited bandwidth. */
	*bytes = ~0UL;
	*usec = 0;

	ratestr = xenbus_read(XBT_NIL, dev->nodename, "rate", NULL);
	if (IS_ERR(ratestr))
	return;

	s = ratestr;
	b = simple_strtoul(s, &e, 10);
	if ((s == e) \|\| (*e != ','))
	goto fail;

	s = e + 1;
	u = simple_strtoul(s, &e, 10);
	if ((s == e) \|\| (*e != '\0'))
	goto fail;

	*bytes = b;
	*usec = u;

	kfree(ratestr);
	return;

	fail:
	pr_warn("Failed to parse network rate limit. Traffic unlimited.\n");
	kfree(ratestr);
	}

	static int xen_net_read_mac(struct xenbus_device *dev, u8 mac[])
	{
	char s, e, *macstr;
	int i;

	macstr = s = xenbus_read(XBT_NIL, dev->nodename, "mac", NULL);
	if (IS_ERR(macstr))
	return PTR_ERR(macstr);

	for (i = 0; i < ETH_ALEN; i++) {
	mac[i] = simple_strtoul(s, &e, 16);
	if ((s == e) \|\| (*e != ((i == ETH_ALEN-1) ? '\0' : ':'))) {
	kfree(macstr);
	return -ENOENT;
	}
	s = e+1;
	}

	kfree(macstr);
	return 0;
	}

	static void unregister_hotplug_status_watch(struct backend_info *be)
	{
	if (be->have_hotplug_status_watch) {
	unregister_xenbus_watch(&be->hotplug_status_watch);
	kfree(be->hotplug_status_watch.node);
	}
	be->have_hotplug_status_watch = 0;
	}

	static void hotplug_status_changed(struct xenbus_watch *watch,
	const char **vec,
	unsigned int vec_size)
	{
	struct backend_info *be = container_of(watch,
	struct backend_info,
	hotplug_status_watch);
	char *str;
	unsigned int len;

	str = xenbus_read(XBT_NIL, be->dev->nodename, "hotplug-status", &len);
	if (IS_ERR(str))
	return;
	if (len == sizeof("connected")-1 && !memcmp(str, "connected", len)) {
	xenbus_switch_state(be->dev, XenbusStateConnected);
	/* Not interested in this watch anymore. */
	unregister_hotplug_status_watch(be);
	}
	kfree(str);
	}

	static void connect(struct backend_info *be)
	{
	int err;
	struct xenbus_device *dev = be->dev;

	err = connect_rings(be);
	if (err)
	return;

	err = xen_net_read_mac(dev, be->vif->fe_dev_addr);
	if (err) {
	xenbus_dev_fatal(dev, err, "parsing %s/mac", dev->nodename);
	return;
	}

	xen_net_read_rate(dev, &be->vif->credit_bytes,
	&be->vif->credit_usec);
	be->vif->remaining_credit = be->vif->credit_bytes;

	unregister_hotplug_status_watch(be);
	err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch,
	hotplug_status_changed,
	"%s/%s", dev->nodename, "hotplug-status");
	if (err) {
	/* Switch now, since we can't do a watch. */
	xenbus_switch_state(dev, XenbusStateConnected);
	} else {
	be->have_hotplug_status_watch = 1;
	}

	netif_wake_queue(be->vif->dev);
	}


	static int connect_rings(struct backend_info *be)
	{
	struct xenvif *vif = be->vif;
	struct xenbus_device *dev = be->dev;
	unsigned long tx_ring_ref, rx_ring_ref;
	unsigned int tx_evtchn, rx_evtchn, rx_copy;
	int err;
	int val;

	err = xenbus_gather(XBT_NIL, dev->otherend,
	"tx-ring-ref", "%lu", &tx_ring_ref,
	"rx-ring-ref", "%lu", &rx_ring_ref, NULL);
	if (err) {
	xenbus_dev_fatal(dev, err,
	"reading %s/ring-ref",
	dev->otherend);
	return err;
	}

	/* Try split event channels first, then single event channel. */
	err = xenbus_gather(XBT_NIL, dev->otherend,
	"event-channel-tx", "%u", &tx_evtchn,
	"event-channel-rx", "%u", &rx_evtchn, NULL);
	if (err < 0) {
	err = xenbus_scanf(XBT_NIL, dev->otherend,
	"event-channel", "%u", &tx_evtchn);
	if (err < 0) {
	xenbus_dev_fatal(dev, err,
	"reading %s/event-channel(-tx/rx)",
	dev->otherend);
	return err;
	}
	rx_evtchn = tx_evtchn;
	}

	err = xenbus_scanf(XBT_NIL, dev->otherend, "request-rx-copy", "%u",
	&rx_copy);
	if (err == -ENOENT) {
	err = 0;
	rx_copy = 0;
	}
	if (err < 0) {
	xenbus_dev_fatal(dev, err, "reading %s/request-rx-copy",
	dev->otherend);
	return err;
	}
	if (!rx_copy)
	return -EOPNOTSUPP;

	if (vif->dev->tx_queue_len != 0) {
	if (xenbus_scanf(XBT_NIL, dev->otherend,
	"feature-rx-notify", "%d", &val) < 0)
	val = 0;
	if (val)
	vif->can_queue = 1;
	else
	/* Must be non-zero for pfifo_fast to work. */
	vif->dev->tx_queue_len = 1;
	}

	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-sg",
	"%d", &val) < 0)
	val = 0;
	vif->can_sg = !!val;

	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv4",
	"%d", &val) < 0)
	val = 0;
	vif->gso = !!val;

	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv4-prefix",
	"%d", &val) < 0)
	val = 0;
	vif->gso_prefix = !!val;

	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-no-csum-offload",
	"%d", &val) < 0)
	val = 0;
	vif->csum = !val;

	/* Map the shared frame, irq etc. */
	err = xenvif_connect(vif, tx_ring_ref, rx_ring_ref,
	tx_evtchn, rx_evtchn);
	if (err) {
	xenbus_dev_fatal(dev, err,
	"mapping shared-frames %lu/%lu port tx %u rx %u",
	tx_ring_ref, rx_ring_ref,
	tx_evtchn, rx_evtchn);
	return err;
	}
	return 0;
	}


	/* Driver Registration */


	static const struct xenbus_device_id netback_ids[] = {
	{ "vif" },
	{ "" }
	};


	static DEFINE_XENBUS_DRIVER(netback, ,
	.probe = netback_probe,
	.remove = netback_remove,
	.uevent = netback_uevent,
	.otherend_changed = frontend_changed,
	);

	int xenvif_xenbus_init(void)
	{
	return xenbus_register_backend(&netback_driver);
	}

	void xenvif_xenbus_fini(void)
	{
	return xenbus_unregister_driver(&netback_driver);
	}