drivers/xen/pvcalls-back.c - SHIFTPHONES/mainline/linux - Gitiles

 /*
  * (c) 2017 Stefano Stabellini <stefano@aporeto.com>
  *
  * 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.
  */

 #include <linux/inet.h>
 #include <linux/kthread.h>
 #include <linux/list.h>
 #include <linux/radix-tree.h>
 #include <linux/module.h>
 #include <linux/semaphore.h>
 #include <linux/wait.h>
 #include <net/sock.h>
 #include <net/inet_common.h>
 #include <net/inet_connection_sock.h>
 #include <net/request_sock.h>

 #include <xen/events.h>
 #include <xen/grant_table.h>
 #include <xen/xen.h>
 #include <xen/xenbus.h>
 #include <xen/interface/io/pvcalls.h>

 #define PVCALLS_VERSIONS "1"
 #define MAX_RING_ORDER XENBUS_MAX_RING_GRANT_ORDER

 struct pvcalls_back_global {
 	struct list_head frontends;
 	struct semaphore frontends_lock;
 } pvcalls_back_global;

 /*
  * Per-frontend data structure. It contains pointers to the command
  * ring, its event channel, a list of active sockets and a tree of
  * passive sockets.
  */
 struct pvcalls_fedata {
 	struct list_head list;
 	struct xenbus_device *dev;
 	struct xen_pvcalls_sring *sring;
 	struct xen_pvcalls_back_ring ring;
 	int irq;
 	struct list_head socket_mappings;
 	struct radix_tree_root socketpass_mappings;
 	struct semaphore socket_lock;
 };

 static int pvcalls_back_socket(struct xenbus_device *dev,
 		struct xen_pvcalls_request *req)
 {
 	struct pvcalls_fedata *fedata;
 	int ret;
 	struct xen_pvcalls_response *rsp;

 	fedata = dev_get_drvdata(&dev->dev);

 	if (req->u.socket.domain != AF_INET ||
 	    req->u.socket.type != SOCK_STREAM ||
 	    (req->u.socket.protocol != IPPROTO_IP &&
 	     req->u.socket.protocol != AF_INET))
 		ret = -EAFNOSUPPORT;
 	else
 		ret = 0;

 	/* leave the actual socket allocation for later */

 	rsp = RING_GET_RESPONSE(&fedata->ring, fedata->ring.rsp_prod_pvt++);
 	rsp->req_id = req->req_id;
 	rsp->cmd = req->cmd;
 	rsp->u.socket.id = req->u.socket.id;
 	rsp->ret = ret;

 	return 0;
 }

 static int pvcalls_back_connect(struct xenbus_device *dev,
 				struct xen_pvcalls_request *req)
 {
 	return 0;
 }

 static int pvcalls_back_release(struct xenbus_device *dev,
 				struct xen_pvcalls_request *req)
 {
 	return 0;
 }

 static int pvcalls_back_bind(struct xenbus_device *dev,
 			     struct xen_pvcalls_request *req)
 {
 	return 0;
 }

 static int pvcalls_back_listen(struct xenbus_device *dev,
 			       struct xen_pvcalls_request *req)
 {
 	return 0;
 }

 static int pvcalls_back_accept(struct xenbus_device *dev,
 			       struct xen_pvcalls_request *req)
 {
 	return 0;
 }

 static int pvcalls_back_poll(struct xenbus_device *dev,
 			     struct xen_pvcalls_request *req)
 {
 	return 0;
 }

 static int pvcalls_back_handle_cmd(struct xenbus_device *dev,
 				   struct xen_pvcalls_request *req)
 {
 	int ret = 0;

 	switch (req->cmd) {
 	case PVCALLS_SOCKET:
 		ret = pvcalls_back_socket(dev, req);
 		break;
 	case PVCALLS_CONNECT:
 		ret = pvcalls_back_connect(dev, req);
 		break;
 	case PVCALLS_RELEASE:
 		ret = pvcalls_back_release(dev, req);
 		break;
 	case PVCALLS_BIND:
 		ret = pvcalls_back_bind(dev, req);
 		break;
 	case PVCALLS_LISTEN:
 		ret = pvcalls_back_listen(dev, req);
 		break;
 	case PVCALLS_ACCEPT:
 		ret = pvcalls_back_accept(dev, req);
 		break;
 	case PVCALLS_POLL:
 		ret = pvcalls_back_poll(dev, req);
 		break;
 	default:
 	{
 		struct pvcalls_fedata *fedata;
 		struct xen_pvcalls_response *rsp;

 		fedata = dev_get_drvdata(&dev->dev);
 		rsp = RING_GET_RESPONSE(
 				&fedata->ring, fedata->ring.rsp_prod_pvt++);
 		rsp->req_id = req->req_id;
 		rsp->cmd = req->cmd;
 		rsp->ret = -ENOTSUPP;
 		break;
 	}
 	}
 	return ret;
 }

 static void pvcalls_back_work(struct pvcalls_fedata *fedata)
 {
 	int notify, notify_all = 0, more = 1;
 	struct xen_pvcalls_request req;
 	struct xenbus_device *dev = fedata->dev;

 	while (more) {
 		while (RING_HAS_UNCONSUMED_REQUESTS(&fedata->ring)) {
 			RING_COPY_REQUEST(&fedata->ring,
 					  fedata->ring.req_cons++,
 					  &req);

 			if (!pvcalls_back_handle_cmd(dev, &req)) {
 				RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(
 					&fedata->ring, notify);
 				notify_all += notify;
 			}
 		}

 		if (notify_all) {
 			notify_remote_via_irq(fedata->irq);
 			notify_all = 0;
 		}

 		RING_FINAL_CHECK_FOR_REQUESTS(&fedata->ring, more);
 	}
 }

 static irqreturn_t pvcalls_back_event(int irq, void *dev_id)
 {
 	struct xenbus_device *dev = dev_id;
 	struct pvcalls_fedata *fedata = NULL;

 	if (dev == NULL)
 		return IRQ_HANDLED;

 	fedata = dev_get_drvdata(&dev->dev);
 	if (fedata == NULL)
 		return IRQ_HANDLED;

 	pvcalls_back_work(fedata);
 	return IRQ_HANDLED;
 }

 static int backend_connect(struct xenbus_device *dev)
 {
 	int err, evtchn;
 	grant_ref_t ring_ref;
 	struct pvcalls_fedata *fedata = NULL;

 	fedata = kzalloc(sizeof(struct pvcalls_fedata), GFP_KERNEL);
 	if (!fedata)
 		return -ENOMEM;

 	fedata->irq = -1;
 	err = xenbus_scanf(XBT_NIL, dev->otherend, "port", "%u",
 			   &evtchn);
 	if (err != 1) {
 		err = -EINVAL;
 		xenbus_dev_fatal(dev, err, "reading %s/event-channel",
 				 dev->otherend);
 		goto error;
 	}

 	err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-ref", "%u", &ring_ref);
 	if (err != 1) {
 		err = -EINVAL;
 		xenbus_dev_fatal(dev, err, "reading %s/ring-ref",
 				 dev->otherend);
 		goto error;
 	}

 	err = bind_interdomain_evtchn_to_irq(dev->otherend_id, evtchn);
 	if (err < 0)
 		goto error;
 	fedata->irq = err;

 	err = request_threaded_irq(fedata->irq, NULL, pvcalls_back_event,
 				   IRQF_ONESHOT, "pvcalls-back", dev);
 	if (err < 0)
 		goto error;

 	err = xenbus_map_ring_valloc(dev, &ring_ref, 1,
 				     (void **)&fedata->sring);
 	if (err < 0)
 		goto error;

 	BACK_RING_INIT(&fedata->ring, fedata->sring, XEN_PAGE_SIZE * 1);
 	fedata->dev = dev;

 	INIT_LIST_HEAD(&fedata->socket_mappings);
 	INIT_RADIX_TREE(&fedata->socketpass_mappings, GFP_KERNEL);
 	sema_init(&fedata->socket_lock, 1);
 	dev_set_drvdata(&dev->dev, fedata);

 	down(&pvcalls_back_global.frontends_lock);
 	list_add_tail(&fedata->list, &pvcalls_back_global.frontends);
 	up(&pvcalls_back_global.frontends_lock);

 	return 0;

  error:
 	if (fedata->irq >= 0)
 		unbind_from_irqhandler(fedata->irq, dev);
 	if (fedata->sring != NULL)
 		xenbus_unmap_ring_vfree(dev, fedata->sring);
 	kfree(fedata);
 	return err;
 }

 static int backend_disconnect(struct xenbus_device *dev)
 {
 	return 0;
 }

 static int pvcalls_back_probe(struct xenbus_device *dev,
 			      const struct xenbus_device_id *id)
 {
 	int err, abort;
 	struct xenbus_transaction xbt;

 again:
 	abort = 1;

 	err = xenbus_transaction_start(&xbt);
 	if (err) {
 		pr_warn("%s cannot create xenstore transaction\n", __func__);
 		return err;
 	}

 	err = xenbus_printf(xbt, dev->nodename, "versions", "%s",
 			    PVCALLS_VERSIONS);
 	if (err) {
 		pr_warn("%s write out 'versions' failed\n", __func__);
 		goto abort;
 	}

 	err = xenbus_printf(xbt, dev->nodename, "max-page-order", "%u",
 			    MAX_RING_ORDER);
 	if (err) {
 		pr_warn("%s write out 'max-page-order' failed\n", __func__);
 		goto abort;
 	}

 	err = xenbus_printf(xbt, dev->nodename, "function-calls",
 			    XENBUS_FUNCTIONS_CALLS);
 	if (err) {
 		pr_warn("%s write out 'function-calls' failed\n", __func__);
 		goto abort;
 	}

 	abort = 0;
 abort:
 	err = xenbus_transaction_end(xbt, abort);
 	if (err) {
 		if (err == -EAGAIN && !abort)
 			goto again;
 		pr_warn("%s cannot complete xenstore transaction\n", __func__);
 		return err;
 	}

 	if (abort)
 		return -EFAULT;

 	xenbus_switch_state(dev, XenbusStateInitWait);

 	return 0;
 }

 static void set_backend_state(struct xenbus_device *dev,
 			      enum xenbus_state state)
 {
 	while (dev->state != state) {
 		switch (dev->state) {
 		case XenbusStateClosed:
 			switch (state) {
 			case XenbusStateInitWait:
 			case XenbusStateConnected:
 				xenbus_switch_state(dev, XenbusStateInitWait);
 				break;
 			case XenbusStateClosing:
 				xenbus_switch_state(dev, XenbusStateClosing);
 				break;
 			default:
 				__WARN();
 			}
 			break;
 		case XenbusStateInitWait:
 		case XenbusStateInitialised:
 			switch (state) {
 			case XenbusStateConnected:
 				backend_connect(dev);
 				xenbus_switch_state(dev, XenbusStateConnected);
 				break;
 			case XenbusStateClosing:
 			case XenbusStateClosed:
 				xenbus_switch_state(dev, XenbusStateClosing);
 				break;
 			default:
 				__WARN();
 			}
 			break;
 		case XenbusStateConnected:
 			switch (state) {
 			case XenbusStateInitWait:
 			case XenbusStateClosing:
 			case XenbusStateClosed:
 				down(&pvcalls_back_global.frontends_lock);
 				backend_disconnect(dev);
 				up(&pvcalls_back_global.frontends_lock);
 				xenbus_switch_state(dev, XenbusStateClosing);
 				break;
 			default:
 				__WARN();
 			}
 			break;
 		case XenbusStateClosing:
 			switch (state) {
 			case XenbusStateInitWait:
 			case XenbusStateConnected:
 			case XenbusStateClosed:
 				xenbus_switch_state(dev, XenbusStateClosed);
 				break;
 			default:
 				__WARN();
 			}
 			break;
 		default:
 			__WARN();
 		}
 	}
 }

 static void pvcalls_back_changed(struct xenbus_device *dev,
 				 enum xenbus_state frontend_state)
 {
 	switch (frontend_state) {
 	case XenbusStateInitialising:
 		set_backend_state(dev, XenbusStateInitWait);
 		break;

 	case XenbusStateInitialised:
 	case XenbusStateConnected:
 		set_backend_state(dev, XenbusStateConnected);
 		break;

 	case XenbusStateClosing:
 		set_backend_state(dev, XenbusStateClosing);
 		break;

 	case XenbusStateClosed:
 		set_backend_state(dev, XenbusStateClosed);
 		if (xenbus_dev_is_online(dev))
 			break;
 		device_unregister(&dev->dev);
 		break;
 	case XenbusStateUnknown:
 		set_backend_state(dev, XenbusStateClosed);
 		device_unregister(&dev->dev);
 		break;

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

 static int pvcalls_back_remove(struct xenbus_device *dev)
 {
 	return 0;
 }

 static int pvcalls_back_uevent(struct xenbus_device *xdev,
 			       struct kobj_uevent_env *env)
 {
 	return 0;
 }

 static const struct xenbus_device_id pvcalls_back_ids[] = {
 	{ "pvcalls" },
 	{ "" }
 };

 static struct xenbus_driver pvcalls_back_driver = {
 	.ids = pvcalls_back_ids,
 	.probe = pvcalls_back_probe,
 	.remove = pvcalls_back_remove,
 	.uevent = pvcalls_back_uevent,
 	.otherend_changed = pvcalls_back_changed,
 };

 static int __init pvcalls_back_init(void)
 {
 	int ret;

 	if (!xen_domain())
 		return -ENODEV;

 	ret = xenbus_register_backend(&pvcalls_back_driver);
 	if (ret < 0)
 		return ret;

 	sema_init(&pvcalls_back_global.frontends_lock, 1);
 	INIT_LIST_HEAD(&pvcalls_back_global.frontends);
 	return 0;
 }
 module_init(pvcalls_back_init);
	/*
	* (c) 2017 Stefano Stabellini <stefano@aporeto.com>
	*
	* 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.
	*/

	#include <linux/inet.h>
	#include <linux/kthread.h>
	#include <linux/list.h>
	#include <linux/radix-tree.h>
	#include <linux/module.h>
	#include <linux/semaphore.h>
	#include <linux/wait.h>
	#include <net/sock.h>
	#include <net/inet_common.h>
	#include <net/inet_connection_sock.h>
	#include <net/request_sock.h>

	#include <xen/events.h>
	#include <xen/grant_table.h>
	#include <xen/xen.h>
	#include <xen/xenbus.h>
	#include <xen/interface/io/pvcalls.h>

	#define PVCALLS_VERSIONS "1"
	#define MAX_RING_ORDER XENBUS_MAX_RING_GRANT_ORDER

	struct pvcalls_back_global {
	struct list_head frontends;
	struct semaphore frontends_lock;
	} pvcalls_back_global;

	/*
	* Per-frontend data structure. It contains pointers to the command
	* ring, its event channel, a list of active sockets and a tree of
	* passive sockets.
	*/
	struct pvcalls_fedata {
	struct list_head list;
	struct xenbus_device *dev;
	struct xen_pvcalls_sring *sring;
	struct xen_pvcalls_back_ring ring;
	int irq;
	struct list_head socket_mappings;
	struct radix_tree_root socketpass_mappings;
	struct semaphore socket_lock;
	};

	static int pvcalls_back_socket(struct xenbus_device *dev,
	struct xen_pvcalls_request *req)
	{
	struct pvcalls_fedata *fedata;
	int ret;
	struct xen_pvcalls_response *rsp;

	fedata = dev_get_drvdata(&dev->dev);

	if (req->u.socket.domain != AF_INET \|\|
	req->u.socket.type != SOCK_STREAM \|\|
	(req->u.socket.protocol != IPPROTO_IP &&
	req->u.socket.protocol != AF_INET))
	ret = -EAFNOSUPPORT;
	else
	ret = 0;

	/* leave the actual socket allocation for later */

	rsp = RING_GET_RESPONSE(&fedata->ring, fedata->ring.rsp_prod_pvt++);
	rsp->req_id = req->req_id;
	rsp->cmd = req->cmd;
	rsp->u.socket.id = req->u.socket.id;
	rsp->ret = ret;

	return 0;
	}

	static int pvcalls_back_connect(struct xenbus_device *dev,
	struct xen_pvcalls_request *req)
	{
	return 0;
	}

	static int pvcalls_back_release(struct xenbus_device *dev,
	struct xen_pvcalls_request *req)
	{
	return 0;
	}

	static int pvcalls_back_bind(struct xenbus_device *dev,
	struct xen_pvcalls_request *req)
	{
	return 0;
	}

	static int pvcalls_back_listen(struct xenbus_device *dev,
	struct xen_pvcalls_request *req)
	{
	return 0;
	}

	static int pvcalls_back_accept(struct xenbus_device *dev,
	struct xen_pvcalls_request *req)
	{
	return 0;
	}

	static int pvcalls_back_poll(struct xenbus_device *dev,
	struct xen_pvcalls_request *req)
	{
	return 0;
	}

	static int pvcalls_back_handle_cmd(struct xenbus_device *dev,
	struct xen_pvcalls_request *req)
	{
	int ret = 0;

	switch (req->cmd) {
	case PVCALLS_SOCKET:
	ret = pvcalls_back_socket(dev, req);
	break;
	case PVCALLS_CONNECT:
	ret = pvcalls_back_connect(dev, req);
	break;
	case PVCALLS_RELEASE:
	ret = pvcalls_back_release(dev, req);
	break;
	case PVCALLS_BIND:
	ret = pvcalls_back_bind(dev, req);
	break;
	case PVCALLS_LISTEN:
	ret = pvcalls_back_listen(dev, req);
	break;
	case PVCALLS_ACCEPT:
	ret = pvcalls_back_accept(dev, req);
	break;
	case PVCALLS_POLL:
	ret = pvcalls_back_poll(dev, req);
	break;
	default:
	{
	struct pvcalls_fedata *fedata;
	struct xen_pvcalls_response *rsp;

	fedata = dev_get_drvdata(&dev->dev);
	rsp = RING_GET_RESPONSE(
	&fedata->ring, fedata->ring.rsp_prod_pvt++);
	rsp->req_id = req->req_id;
	rsp->cmd = req->cmd;
	rsp->ret = -ENOTSUPP;
	break;
	}
	}
	return ret;
	}

	static void pvcalls_back_work(struct pvcalls_fedata *fedata)
	{
	int notify, notify_all = 0, more = 1;
	struct xen_pvcalls_request req;
	struct xenbus_device *dev = fedata->dev;

	while (more) {
	while (RING_HAS_UNCONSUMED_REQUESTS(&fedata->ring)) {
	RING_COPY_REQUEST(&fedata->ring,
	fedata->ring.req_cons++,
	&req);

	if (!pvcalls_back_handle_cmd(dev, &req)) {
	RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(
	&fedata->ring, notify);
	notify_all += notify;
	}
	}

	if (notify_all) {
	notify_remote_via_irq(fedata->irq);
	notify_all = 0;
	}

	RING_FINAL_CHECK_FOR_REQUESTS(&fedata->ring, more);
	}
	}

	static irqreturn_t pvcalls_back_event(int irq, void *dev_id)
	{
	struct xenbus_device *dev = dev_id;
	struct pvcalls_fedata *fedata = NULL;

	if (dev == NULL)
	return IRQ_HANDLED;

	fedata = dev_get_drvdata(&dev->dev);
	if (fedata == NULL)
	return IRQ_HANDLED;

	pvcalls_back_work(fedata);
	return IRQ_HANDLED;
	}

	static int backend_connect(struct xenbus_device *dev)
	{
	int err, evtchn;
	grant_ref_t ring_ref;
	struct pvcalls_fedata *fedata = NULL;

	fedata = kzalloc(sizeof(struct pvcalls_fedata), GFP_KERNEL);
	if (!fedata)
	return -ENOMEM;

	fedata->irq = -1;
	err = xenbus_scanf(XBT_NIL, dev->otherend, "port", "%u",
	&evtchn);
	if (err != 1) {
	err = -EINVAL;
	xenbus_dev_fatal(dev, err, "reading %s/event-channel",
	dev->otherend);
	goto error;
	}

	err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-ref", "%u", &ring_ref);
	if (err != 1) {
	err = -EINVAL;
	xenbus_dev_fatal(dev, err, "reading %s/ring-ref",
	dev->otherend);
	goto error;
	}

	err = bind_interdomain_evtchn_to_irq(dev->otherend_id, evtchn);
	if (err < 0)
	goto error;
	fedata->irq = err;

	err = request_threaded_irq(fedata->irq, NULL, pvcalls_back_event,
	IRQF_ONESHOT, "pvcalls-back", dev);
	if (err < 0)
	goto error;

	err = xenbus_map_ring_valloc(dev, &ring_ref, 1,
	(void **)&fedata->sring);
	if (err < 0)
	goto error;

	BACK_RING_INIT(&fedata->ring, fedata->sring, XEN_PAGE_SIZE * 1);
	fedata->dev = dev;

	INIT_LIST_HEAD(&fedata->socket_mappings);
	INIT_RADIX_TREE(&fedata->socketpass_mappings, GFP_KERNEL);
	sema_init(&fedata->socket_lock, 1);
	dev_set_drvdata(&dev->dev, fedata);

	down(&pvcalls_back_global.frontends_lock);
	list_add_tail(&fedata->list, &pvcalls_back_global.frontends);
	up(&pvcalls_back_global.frontends_lock);

	return 0;

	error:
	if (fedata->irq >= 0)
	unbind_from_irqhandler(fedata->irq, dev);
	if (fedata->sring != NULL)
	xenbus_unmap_ring_vfree(dev, fedata->sring);
	kfree(fedata);
	return err;
	}

	static int backend_disconnect(struct xenbus_device *dev)
	{
	return 0;
	}

	static int pvcalls_back_probe(struct xenbus_device *dev,
	const struct xenbus_device_id *id)
	{
	int err, abort;
	struct xenbus_transaction xbt;

	again:
	abort = 1;

	err = xenbus_transaction_start(&xbt);
	if (err) {
	pr_warn("%s cannot create xenstore transaction\n", __func__);
	return err;
	}

	err = xenbus_printf(xbt, dev->nodename, "versions", "%s",
	PVCALLS_VERSIONS);
	if (err) {
	pr_warn("%s write out 'versions' failed\n", __func__);
	goto abort;
	}

	err = xenbus_printf(xbt, dev->nodename, "max-page-order", "%u",
	MAX_RING_ORDER);
	if (err) {
	pr_warn("%s write out 'max-page-order' failed\n", __func__);
	goto abort;
	}

	err = xenbus_printf(xbt, dev->nodename, "function-calls",
	XENBUS_FUNCTIONS_CALLS);
	if (err) {
	pr_warn("%s write out 'function-calls' failed\n", __func__);
	goto abort;
	}

	abort = 0;
	abort:
	err = xenbus_transaction_end(xbt, abort);
	if (err) {
	if (err == -EAGAIN && !abort)
	goto again;
	pr_warn("%s cannot complete xenstore transaction\n", __func__);
	return err;
	}

	if (abort)
	return -EFAULT;

	xenbus_switch_state(dev, XenbusStateInitWait);

	return 0;
	}

	static void set_backend_state(struct xenbus_device *dev,
	enum xenbus_state state)
	{
	while (dev->state != state) {
	switch (dev->state) {
	case XenbusStateClosed:
	switch (state) {
	case XenbusStateInitWait:
	case XenbusStateConnected:
	xenbus_switch_state(dev, XenbusStateInitWait);
	break;
	case XenbusStateClosing:
	xenbus_switch_state(dev, XenbusStateClosing);
	break;
	default:
	__WARN();
	}
	break;
	case XenbusStateInitWait:
	case XenbusStateInitialised:
	switch (state) {
	case XenbusStateConnected:
	backend_connect(dev);
	xenbus_switch_state(dev, XenbusStateConnected);
	break;
	case XenbusStateClosing:
	case XenbusStateClosed:
	xenbus_switch_state(dev, XenbusStateClosing);
	break;
	default:
	__WARN();
	}
	break;
	case XenbusStateConnected:
	switch (state) {
	case XenbusStateInitWait:
	case XenbusStateClosing:
	case XenbusStateClosed:
	down(&pvcalls_back_global.frontends_lock);
	backend_disconnect(dev);
	up(&pvcalls_back_global.frontends_lock);
	xenbus_switch_state(dev, XenbusStateClosing);
	break;
	default:
	__WARN();
	}
	break;
	case XenbusStateClosing:
	switch (state) {
	case XenbusStateInitWait:
	case XenbusStateConnected:
	case XenbusStateClosed:
	xenbus_switch_state(dev, XenbusStateClosed);
	break;
	default:
	__WARN();
	}
	break;
	default:
	__WARN();
	}
	}
	}

	static void pvcalls_back_changed(struct xenbus_device *dev,
	enum xenbus_state frontend_state)
	{
	switch (frontend_state) {
	case XenbusStateInitialising:
	set_backend_state(dev, XenbusStateInitWait);
	break;

	case XenbusStateInitialised:
	case XenbusStateConnected:
	set_backend_state(dev, XenbusStateConnected);
	break;

	case XenbusStateClosing:
	set_backend_state(dev, XenbusStateClosing);
	break;

	case XenbusStateClosed:
	set_backend_state(dev, XenbusStateClosed);
	if (xenbus_dev_is_online(dev))
	break;
	device_unregister(&dev->dev);
	break;
	case XenbusStateUnknown:
	set_backend_state(dev, XenbusStateClosed);
	device_unregister(&dev->dev);
	break;

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

	static int pvcalls_back_remove(struct xenbus_device *dev)
	{
	return 0;
	}

	static int pvcalls_back_uevent(struct xenbus_device *xdev,
	struct kobj_uevent_env *env)
	{
	return 0;
	}

	static const struct xenbus_device_id pvcalls_back_ids[] = {
	{ "pvcalls" },
	{ "" }
	};

	static struct xenbus_driver pvcalls_back_driver = {
	.ids = pvcalls_back_ids,
	.probe = pvcalls_back_probe,
	.remove = pvcalls_back_remove,
	.uevent = pvcalls_back_uevent,
	.otherend_changed = pvcalls_back_changed,
	};

	static int __init pvcalls_back_init(void)
	{
	int ret;

	if (!xen_domain())
	return -ENODEV;

	ret = xenbus_register_backend(&pvcalls_back_driver);
	if (ret < 0)
	return ret;

	sema_init(&pvcalls_back_global.frontends_lock, 1);
	INIT_LIST_HEAD(&pvcalls_back_global.frontends);
	return 0;
	}
	module_init(pvcalls_back_init);