/*
 * (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/kthread.h>
#include <linux/list.h>
#include <linux/radix-tree.h>
#include <linux/module.h>
#include <linux/semaphore.h>
#include <linux/wait.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)
{
	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);