/*
 * (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/module.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_INVALID_ID UINT_MAX
#define PVCALLS_RING_ORDER XENBUS_MAX_RING_GRANT_ORDER
#define PVCALLS_NR_RSP_PER_RING __CONST_RING_SIZE(xen_pvcalls, XEN_PAGE_SIZE)

struct pvcalls_bedata {
	struct xen_pvcalls_front_ring ring;
	grant_ref_t ref;
	int irq;

	struct list_head socket_mappings;
	spinlock_t socket_lock;

	wait_queue_head_t inflight_req;
	struct xen_pvcalls_response rsp[PVCALLS_NR_RSP_PER_RING];
};
/* Only one front/back connection supported. */
static struct xenbus_device *pvcalls_front_dev;
static atomic_t pvcalls_refcount;

/* first increment refcount, then proceed */
#define pvcalls_enter() {               \
	atomic_inc(&pvcalls_refcount);      \
}

/* first complete other operations, then decrement refcount */
#define pvcalls_exit() {                \
	atomic_dec(&pvcalls_refcount);      \
}

struct sock_mapping {
	bool active_socket;
	struct list_head list;
	struct socket *sock;
};

static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
{
	return IRQ_HANDLED;
}

static void pvcalls_front_free_map(struct pvcalls_bedata *bedata,
				   struct sock_mapping *map)
{
}

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

static int pvcalls_front_remove(struct xenbus_device *dev)
{
	struct pvcalls_bedata *bedata;
	struct sock_mapping *map = NULL, *n;

	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
	dev_set_drvdata(&dev->dev, NULL);
	pvcalls_front_dev = NULL;
	if (bedata->irq >= 0)
		unbind_from_irqhandler(bedata->irq, dev);

	smp_mb();
	while (atomic_read(&pvcalls_refcount) > 0)
		cpu_relax();
	list_for_each_entry_safe(map, n, &bedata->socket_mappings, list) {
		if (map->active_socket) {
			/* No need to lock, refcount is 0 */
			pvcalls_front_free_map(bedata, map);
		} else {
			list_del(&map->list);
			kfree(map);
		}
	}
	if (bedata->ref >= 0)
		gnttab_end_foreign_access(bedata->ref, 0, 0);
	kfree(bedata->ring.sring);
	kfree(bedata);
	xenbus_switch_state(dev, XenbusStateClosed);
	return 0;
}

static int pvcalls_front_probe(struct xenbus_device *dev,
			  const struct xenbus_device_id *id)
{
	int ret = -ENOMEM, evtchn, i;
	unsigned int max_page_order, function_calls, len;
	char *versions;
	grant_ref_t gref_head = 0;
	struct xenbus_transaction xbt;
	struct pvcalls_bedata *bedata = NULL;
	struct xen_pvcalls_sring *sring;

	if (pvcalls_front_dev != NULL) {
		dev_err(&dev->dev, "only one PV Calls connection supported\n");
		return -EINVAL;
	}

	versions = xenbus_read(XBT_NIL, dev->otherend, "versions", &len);
	if (!len)
		return -EINVAL;
	if (strcmp(versions, "1")) {
		kfree(versions);
		return -EINVAL;
	}
	kfree(versions);
	max_page_order = xenbus_read_unsigned(dev->otherend,
					      "max-page-order", 0);
	if (max_page_order < PVCALLS_RING_ORDER)
		return -ENODEV;
	function_calls = xenbus_read_unsigned(dev->otherend,
					      "function-calls", 0);
	/* See XENBUS_FUNCTIONS_CALLS in pvcalls.h */
	if (function_calls != 1)
		return -ENODEV;
	pr_info("%s max-page-order is %u\n", __func__, max_page_order);

	bedata = kzalloc(sizeof(struct pvcalls_bedata), GFP_KERNEL);
	if (!bedata)
		return -ENOMEM;

	dev_set_drvdata(&dev->dev, bedata);
	pvcalls_front_dev = dev;
	init_waitqueue_head(&bedata->inflight_req);
	INIT_LIST_HEAD(&bedata->socket_mappings);
	spin_lock_init(&bedata->socket_lock);
	bedata->irq = -1;
	bedata->ref = -1;

	for (i = 0; i < PVCALLS_NR_RSP_PER_RING; i++)
		bedata->rsp[i].req_id = PVCALLS_INVALID_ID;

	sring = (struct xen_pvcalls_sring *) __get_free_page(GFP_KERNEL |
							     __GFP_ZERO);
	if (!sring)
		goto error;
	SHARED_RING_INIT(sring);
	FRONT_RING_INIT(&bedata->ring, sring, XEN_PAGE_SIZE);

	ret = xenbus_alloc_evtchn(dev, &evtchn);
	if (ret)
		goto error;

	bedata->irq = bind_evtchn_to_irqhandler(evtchn,
						pvcalls_front_event_handler,
						0, "pvcalls-frontend", dev);
	if (bedata->irq < 0) {
		ret = bedata->irq;
		goto error;
	}

	ret = gnttab_alloc_grant_references(1, &gref_head);
	if (ret < 0)
		goto error;
	bedata->ref = gnttab_claim_grant_reference(&gref_head);
	if (bedata->ref < 0) {
		ret = bedata->ref;
		goto error;
	}
	gnttab_grant_foreign_access_ref(bedata->ref, dev->otherend_id,
					virt_to_gfn((void *)sring), 0);

 again:
	ret = xenbus_transaction_start(&xbt);
	if (ret) {
		xenbus_dev_fatal(dev, ret, "starting transaction");
		goto error;
	}
	ret = xenbus_printf(xbt, dev->nodename, "version", "%u", 1);
	if (ret)
		goto error_xenbus;
	ret = xenbus_printf(xbt, dev->nodename, "ring-ref", "%d", bedata->ref);
	if (ret)
		goto error_xenbus;
	ret = xenbus_printf(xbt, dev->nodename, "port", "%u",
			    evtchn);
	if (ret)
		goto error_xenbus;
	ret = xenbus_transaction_end(xbt, 0);
	if (ret) {
		if (ret == -EAGAIN)
			goto again;
		xenbus_dev_fatal(dev, ret, "completing transaction");
		goto error;
	}
	xenbus_switch_state(dev, XenbusStateInitialised);

	return 0;

 error_xenbus:
	xenbus_transaction_end(xbt, 1);
	xenbus_dev_fatal(dev, ret, "writing xenstore");
 error:
	pvcalls_front_remove(dev);
	return ret;
}

static void pvcalls_front_changed(struct xenbus_device *dev,
			    enum xenbus_state backend_state)
{
	switch (backend_state) {
	case XenbusStateReconfiguring:
	case XenbusStateReconfigured:
	case XenbusStateInitialising:
	case XenbusStateInitialised:
	case XenbusStateUnknown:
		break;

	case XenbusStateInitWait:
		break;

	case XenbusStateConnected:
		xenbus_switch_state(dev, XenbusStateConnected);
		break;

	case XenbusStateClosed:
		if (dev->state == XenbusStateClosed)
			break;
		/* Missed the backend's CLOSING state -- fallthrough */
	case XenbusStateClosing:
		xenbus_frontend_closed(dev);
		break;
	}
}

static struct xenbus_driver pvcalls_front_driver = {
	.ids = pvcalls_front_ids,
	.probe = pvcalls_front_probe,
	.remove = pvcalls_front_remove,
	.otherend_changed = pvcalls_front_changed,
};

static int __init pvcalls_frontend_init(void)
{
	if (!xen_domain())
		return -ENODEV;

	pr_info("Initialising Xen pvcalls frontend driver\n");

	return xenbus_register_frontend(&pvcalls_front_driver);
}

module_init(pvcalls_frontend_init);