net/9p/trans_xen.c - kernel/common - Git at Google

 /*
  * linux/fs/9p/trans_xen
  *
  * Xen transport layer.
  *
  * Copyright (C) 2017 by Stefano Stabellini <[email protected]>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License version 2
  * as published by the Free Software Foundation; or, when distributed
  * separately from the Linux kernel or incorporated into other
  * software packages, subject to the following license:
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this source file (the "Software"), to deal in the Software without
  * restriction, including without limitation the rights to use, copy, modify,
  * merge, publish, distribute, sublicense, and/or sell copies of the Software,
  * and to permit persons to whom the Software is furnished to do so, subject to
  * the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  * IN THE SOFTWARE.
  */

 #include <xen/events.h>
 #include <xen/grant_table.h>
 #include <xen/xen.h>
 #include <xen/xenbus.h>
 #include <xen/interface/io/9pfs.h>

 #include <linux/module.h>
 #include <linux/spinlock.h>
 #include <net/9p/9p.h>
 #include <net/9p/client.h>
 #include <net/9p/transport.h>

 #define XEN_9PFS_NUM_RINGS 2
 #define XEN_9PFS_RING_ORDER 9
 #define XEN_9PFS_RING_SIZE(ring)  XEN_FLEX_RING_SIZE(ring->intf->ring_order)

 struct xen_9pfs_header {
 	uint32_t size;
 	uint8_t id;
 	uint16_t tag;

 	/* uint8_t sdata[]; */
 } __attribute__((packed));

 /* One per ring, more than one per 9pfs share */
 struct xen_9pfs_dataring {
 	struct xen_9pfs_front_priv *priv;

 	struct xen_9pfs_data_intf *intf;
 	grant_ref_t ref;
 	int evtchn;
 	int irq;
 	/* protect a ring from concurrent accesses */
 	spinlock_t lock;

 	struct xen_9pfs_data data;
 	wait_queue_head_t wq;
 	struct work_struct work;
 };

 /* One per 9pfs share */
 struct xen_9pfs_front_priv {
 	struct list_head list;
 	struct xenbus_device *dev;
 	char *tag;
 	struct p9_client *client;

 	int num_rings;
 	struct xen_9pfs_dataring *rings;
 };

 static LIST_HEAD(xen_9pfs_devs);
 static DEFINE_RWLOCK(xen_9pfs_lock);

 /* We don't currently allow canceling of requests */
 static int p9_xen_cancel(struct p9_client *client, struct p9_req_t *req)
 {
 	return 1;
 }

 static int p9_xen_create(struct p9_client *client, const char *addr, char *args)
 {
 	struct xen_9pfs_front_priv *priv;

 	if (addr == NULL)
 		return -EINVAL;

 	read_lock(&xen_9pfs_lock);
 	list_for_each_entry(priv, &xen_9pfs_devs, list) {
 		if (!strcmp(priv->tag, addr)) {
 			priv->client = client;
 			read_unlock(&xen_9pfs_lock);
 			return 0;
 		}
 	}
 	read_unlock(&xen_9pfs_lock);
 	return -EINVAL;
 }

 static void p9_xen_close(struct p9_client *client)
 {
 	struct xen_9pfs_front_priv *priv;

 	read_lock(&xen_9pfs_lock);
 	list_for_each_entry(priv, &xen_9pfs_devs, list) {
 		if (priv->client == client) {
 			priv->client = NULL;
 			read_unlock(&xen_9pfs_lock);
 			return;
 		}
 	}
 	read_unlock(&xen_9pfs_lock);
 }

 static bool p9_xen_write_todo(struct xen_9pfs_dataring *ring, RING_IDX size)
 {
 	RING_IDX cons, prod;

 	cons = ring->intf->out_cons;
 	prod = ring->intf->out_prod;
 	virt_mb();

 	return XEN_9PFS_RING_SIZE(ring) -
 		xen_9pfs_queued(prod, cons, XEN_9PFS_RING_SIZE(ring)) >= size;
 }

 static int p9_xen_request(struct p9_client *client, struct p9_req_t *p9_req)
 {
 	struct xen_9pfs_front_priv *priv;
 	RING_IDX cons, prod, masked_cons, masked_prod;
 	unsigned long flags;
 	u32 size = p9_req->tc.size;
 	struct xen_9pfs_dataring *ring;
 	int num;

 	read_lock(&xen_9pfs_lock);
 	list_for_each_entry(priv, &xen_9pfs_devs, list) {
 		if (priv->client == client)
 			break;
 	}
 	read_unlock(&xen_9pfs_lock);
 	if (list_entry_is_head(priv, &xen_9pfs_devs, list))
 		return -EINVAL;

 	num = p9_req->tc.tag % priv->num_rings;
 	ring = &priv->rings[num];

 again:
 	while (wait_event_killable(ring->wq,
 				   p9_xen_write_todo(ring, size)) != 0)
 		;

 	spin_lock_irqsave(&ring->lock, flags);
 	cons = ring->intf->out_cons;
 	prod = ring->intf->out_prod;
 	virt_mb();

 	if (XEN_9PFS_RING_SIZE(ring) -
 	    xen_9pfs_queued(prod, cons, XEN_9PFS_RING_SIZE(ring)) < size) {
 		spin_unlock_irqrestore(&ring->lock, flags);
 		goto again;
 	}

 	masked_prod = xen_9pfs_mask(prod, XEN_9PFS_RING_SIZE(ring));
 	masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE(ring));

 	xen_9pfs_write_packet(ring->data.out, p9_req->tc.sdata, size,
 			      &masked_prod, masked_cons,
 			      XEN_9PFS_RING_SIZE(ring));

 	p9_req->status = REQ_STATUS_SENT;
 	virt_wmb();			/* write ring before updating pointer */
 	prod += size;
 	ring->intf->out_prod = prod;
 	spin_unlock_irqrestore(&ring->lock, flags);
 	notify_remote_via_irq(ring->irq);
 	p9_req_put(client, p9_req);

 	return 0;
 }

 static void p9_xen_response(struct work_struct *work)
 {
 	struct xen_9pfs_front_priv *priv;
 	struct xen_9pfs_dataring *ring;
 	RING_IDX cons, prod, masked_cons, masked_prod;
 	struct xen_9pfs_header h;
 	struct p9_req_t *req;
 	int status;

 	ring = container_of(work, struct xen_9pfs_dataring, work);
 	priv = ring->priv;

 	while (1) {
 		cons = ring->intf->in_cons;
 		prod = ring->intf->in_prod;
 		virt_rmb();

 		if (xen_9pfs_queued(prod, cons, XEN_9PFS_RING_SIZE(ring)) <
 		    sizeof(h)) {
 			notify_remote_via_irq(ring->irq);
 			return;
 		}

 		masked_prod = xen_9pfs_mask(prod, XEN_9PFS_RING_SIZE(ring));
 		masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE(ring));

 		/* First, read just the header */
 		xen_9pfs_read_packet(&h, ring->data.in, sizeof(h),
 				     masked_prod, &masked_cons,
 				     XEN_9PFS_RING_SIZE(ring));

 		req = p9_tag_lookup(priv->client, h.tag);
 		if (!req || req->status != REQ_STATUS_SENT) {
 			dev_warn(&priv->dev->dev, "Wrong req tag=%x\n", h.tag);
 			cons += h.size;
 			virt_mb();
 			ring->intf->in_cons = cons;
 			continue;
 		}

 		if (h.size > req->rc.capacity) {
 			dev_warn(&priv->dev->dev,
 				 "requested packet size too big: %d for tag %d with capacity %zd\n",
 				 h.size, h.tag, req->rc.capacity);
 			req->status = REQ_STATUS_ERROR;
 			goto recv_error;
 		}

 		memcpy(&req->rc, &h, sizeof(h));
 		req->rc.offset = 0;

 		masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE(ring));
 		/* Then, read the whole packet (including the header) */
 		xen_9pfs_read_packet(req->rc.sdata, ring->data.in, h.size,
 				     masked_prod, &masked_cons,
 				     XEN_9PFS_RING_SIZE(ring));

 recv_error:
 		virt_mb();
 		cons += h.size;
 		ring->intf->in_cons = cons;

 		status = (req->status != REQ_STATUS_ERROR) ?
 			REQ_STATUS_RCVD : REQ_STATUS_ERROR;

 		p9_client_cb(priv->client, req, status);
 	}
 }

 static irqreturn_t xen_9pfs_front_event_handler(int irq, void *r)
 {
 	struct xen_9pfs_dataring *ring = r;

 	if (!ring || !ring->priv->client) {
 		/* ignore spurious interrupt */
 		return IRQ_HANDLED;
 	}

 	wake_up_interruptible(&ring->wq);
 	schedule_work(&ring->work);

 	return IRQ_HANDLED;
 }

 static struct p9_trans_module p9_xen_trans = {
 	.name = "xen",
 	.maxsize = 1 << (XEN_9PFS_RING_ORDER + XEN_PAGE_SHIFT - 2),
 	.def = 1,
 	.create = p9_xen_create,
 	.close = p9_xen_close,
 	.request = p9_xen_request,
 	.cancel = p9_xen_cancel,
 	.owner = THIS_MODULE,
 };

 static const struct xenbus_device_id xen_9pfs_front_ids[] = {
 	{ "9pfs" },
 	{ "" }
 };

 static void xen_9pfs_front_free(struct xen_9pfs_front_priv *priv)
 {
 	int i, j;

 	write_lock(&xen_9pfs_lock);
 	list_del(&priv->list);
 	write_unlock(&xen_9pfs_lock);

 	for (i = 0; i < priv->num_rings; i++) {
 		struct xen_9pfs_dataring *ring = &priv->rings[i];

 		cancel_work_sync(&ring->work);

 		if (!priv->rings[i].intf)
 			break;
 		if (priv->rings[i].irq > 0)
 			unbind_from_irqhandler(priv->rings[i].irq, priv->dev);
 		if (priv->rings[i].data.in) {
 			for (j = 0;
 			     j < (1 << priv->rings[i].intf->ring_order);
 			     j++) {
 				grant_ref_t ref;

 				ref = priv->rings[i].intf->ref[j];
 				gnttab_end_foreign_access(ref, 0, 0);
 			}
 			free_pages_exact(priv->rings[i].data.in,
 				   1UL << (priv->rings[i].intf->ring_order +
 					   XEN_PAGE_SHIFT));
 		}
 		gnttab_end_foreign_access(priv->rings[i].ref, 0, 0);
 		free_page((unsigned long)priv->rings[i].intf);
 	}
 	kfree(priv->rings);
 	kfree(priv->tag);
 	kfree(priv);
 }

 static int xen_9pfs_front_remove(struct xenbus_device *dev)
 {
 	struct xen_9pfs_front_priv *priv = dev_get_drvdata(&dev->dev);

 	dev_set_drvdata(&dev->dev, NULL);
 	xen_9pfs_front_free(priv);
 	return 0;
 }

 static int xen_9pfs_front_alloc_dataring(struct xenbus_device *dev,
 					 struct xen_9pfs_dataring *ring,
 					 unsigned int order)
 {
 	int i = 0;
 	int ret = -ENOMEM;
 	void *bytes = NULL;

 	init_waitqueue_head(&ring->wq);
 	spin_lock_init(&ring->lock);
 	INIT_WORK(&ring->work, p9_xen_response);

 	ring->intf = (struct xen_9pfs_data_intf *)get_zeroed_page(GFP_KERNEL);
 	if (!ring->intf)
 		return ret;
 	ret = gnttab_grant_foreign_access(dev->otherend_id,
 					  virt_to_gfn(ring->intf), 0);
 	if (ret < 0)
 		goto out;
 	ring->ref = ret;
 	bytes = alloc_pages_exact(1UL << (order + XEN_PAGE_SHIFT),
 				  GFP_KERNEL | __GFP_ZERO);
 	if (!bytes) {
 		ret = -ENOMEM;
 		goto out;
 	}
 	for (; i < (1 << order); i++) {
 		ret = gnttab_grant_foreign_access(
 				dev->otherend_id, virt_to_gfn(bytes) + i, 0);
 		if (ret < 0)
 			goto out;
 		ring->intf->ref[i] = ret;
 	}
 	ring->intf->ring_order = order;
 	ring->data.in = bytes;
 	ring->data.out = bytes + XEN_FLEX_RING_SIZE(order);

 	ret = xenbus_alloc_evtchn(dev, &ring->evtchn);
 	if (ret)
 		goto out;
 	ring->irq = bind_evtchn_to_irqhandler(ring->evtchn,
 					      xen_9pfs_front_event_handler,
 					      0, "xen_9pfs-frontend", ring);
 	if (ring->irq >= 0)
 		return 0;

 	xenbus_free_evtchn(dev, ring->evtchn);
 	ret = ring->irq;
 out:
 	if (bytes) {
 		for (i--; i >= 0; i--)
 			gnttab_end_foreign_access(ring->intf->ref[i], 0, 0);
 		free_pages_exact(bytes, 1UL << (order + XEN_PAGE_SHIFT));
 	}
 	gnttab_end_foreign_access(ring->ref, 0, 0);
 	free_page((unsigned long)ring->intf);
 	return ret;
 }

 static int xen_9pfs_front_init(struct xenbus_device *dev)
 {
 	int ret, i;
 	struct xenbus_transaction xbt;
 	struct xen_9pfs_front_priv *priv = dev_get_drvdata(&dev->dev);
 	char *versions, *v;
 	unsigned int max_rings, max_ring_order, len = 0;

 	versions = xenbus_read(XBT_NIL, dev->otherend, "versions", &len);
 	if (IS_ERR(versions))
 		return PTR_ERR(versions);
 	for (v = versions; *v; v++) {
 		if (simple_strtoul(v, &v, 10) == 1) {
 			v = NULL;
 			break;
 		}
 	}
 	if (v) {
 		kfree(versions);
 		return -EINVAL;
 	}
 	kfree(versions);
 	max_rings = xenbus_read_unsigned(dev->otherend, "max-rings", 0);
 	if (max_rings < XEN_9PFS_NUM_RINGS)
 		return -EINVAL;
 	max_ring_order = xenbus_read_unsigned(dev->otherend,
 					      "max-ring-page-order", 0);
 	if (max_ring_order > XEN_9PFS_RING_ORDER)
 		max_ring_order = XEN_9PFS_RING_ORDER;
 	if (p9_xen_trans.maxsize > XEN_FLEX_RING_SIZE(max_ring_order))
 		p9_xen_trans.maxsize = XEN_FLEX_RING_SIZE(max_ring_order) / 2;

 	priv->num_rings = XEN_9PFS_NUM_RINGS;
 	priv->rings = kcalloc(priv->num_rings, sizeof(*priv->rings),
 			      GFP_KERNEL);
 	if (!priv->rings) {
 		kfree(priv);
 		return -ENOMEM;
 	}

 	for (i = 0; i < priv->num_rings; i++) {
 		priv->rings[i].priv = priv;
 		ret = xen_9pfs_front_alloc_dataring(dev, &priv->rings[i],
 						    max_ring_order);
 		if (ret < 0)
 			goto error;
 	}

  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, "num-rings", "%u",
 			    priv->num_rings);
 	if (ret)
 		goto error_xenbus;
 	for (i = 0; i < priv->num_rings; i++) {
 		char str[16];

 		BUILD_BUG_ON(XEN_9PFS_NUM_RINGS > 9);
 		sprintf(str, "ring-ref%d", i);
 		ret = xenbus_printf(xbt, dev->nodename, str, "%d",
 				    priv->rings[i].ref);
 		if (ret)
 			goto error_xenbus;

 		sprintf(str, "event-channel-%d", i);
 		ret = xenbus_printf(xbt, dev->nodename, str, "%u",
 				    priv->rings[i].evtchn);
 		if (ret)
 			goto error_xenbus;
 	}
 	priv->tag = xenbus_read(xbt, dev->nodename, "tag", NULL);
 	if (IS_ERR(priv->tag)) {
 		ret = PTR_ERR(priv->tag);
 		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;
 	}

 	return 0;

  error_xenbus:
 	xenbus_transaction_end(xbt, 1);
 	xenbus_dev_fatal(dev, ret, "writing xenstore");
  error:
 	xen_9pfs_front_free(priv);
 	return ret;
 }

 static int xen_9pfs_front_probe(struct xenbus_device *dev,
 				const struct xenbus_device_id *id)
 {
 	struct xen_9pfs_front_priv *priv = NULL;

 	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
 	if (!priv)
 		return -ENOMEM;

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

 	write_lock(&xen_9pfs_lock);
 	list_add_tail(&priv->list, &xen_9pfs_devs);
 	write_unlock(&xen_9pfs_lock);

 	return 0;
 }

 static int xen_9pfs_front_resume(struct xenbus_device *dev)
 {
 	dev_warn(&dev->dev, "suspend/resume unsupported\n");
 	return 0;
 }

 static void xen_9pfs_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:
 		if (!xen_9pfs_front_init(dev))
 			xenbus_switch_state(dev, XenbusStateInitialised);
 		break;

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

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

 static struct xenbus_driver xen_9pfs_front_driver = {
 	.ids = xen_9pfs_front_ids,
 	.probe = xen_9pfs_front_probe,
 	.remove = xen_9pfs_front_remove,
 	.resume = xen_9pfs_front_resume,
 	.otherend_changed = xen_9pfs_front_changed,
 };

 static int p9_trans_xen_init(void)
 {
 	int rc;

 	if (!xen_domain())
 		return -ENODEV;

 	pr_info("Initialising Xen transport for 9pfs\n");

 	v9fs_register_trans(&p9_xen_trans);
 	rc = xenbus_register_frontend(&xen_9pfs_front_driver);
 	if (rc)
 		v9fs_unregister_trans(&p9_xen_trans);

 	return rc;
 }
 module_init(p9_trans_xen_init);

 static void p9_trans_xen_exit(void)
 {
 	v9fs_unregister_trans(&p9_xen_trans);
 	return xenbus_unregister_driver(&xen_9pfs_front_driver);
 }
 module_exit(p9_trans_xen_exit);

 MODULE_AUTHOR("Stefano Stabellini <[email protected]>");
 MODULE_DESCRIPTION("Xen Transport for 9P");
 MODULE_LICENSE("GPL");
	/*
	* linux/fs/9p/trans_xen
	*
	* Xen transport layer.
	*
	* Copyright (C) 2017 by Stefano Stabellini <[email protected]>
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License version 2
	* as published by the Free Software Foundation; or, when distributed
	* separately from the Linux kernel or incorporated into other
	* software packages, subject to the following license:
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this source file (the "Software"), to deal in the Software without
	* restriction, including without limitation the rights to use, copy, modify,
	* merge, publish, distribute, sublicense, and/or sell copies of the Software,
	* and to permit persons to whom the Software is furnished to do so, subject to
	* the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
	* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
	* IN THE SOFTWARE.
	*/

	#include <xen/events.h>
	#include <xen/grant_table.h>
	#include <xen/xen.h>
	#include <xen/xenbus.h>
	#include <xen/interface/io/9pfs.h>

	#include <linux/module.h>
	#include <linux/spinlock.h>
	#include <net/9p/9p.h>
	#include <net/9p/client.h>
	#include <net/9p/transport.h>

	#define XEN_9PFS_NUM_RINGS 2
	#define XEN_9PFS_RING_ORDER 9
	#define XEN_9PFS_RING_SIZE(ring) XEN_FLEX_RING_SIZE(ring->intf->ring_order)

	struct xen_9pfs_header {
	uint32_t size;
	uint8_t id;
	uint16_t tag;

	/* uint8_t sdata[]; */
	} __attribute__((packed));

	/* One per ring, more than one per 9pfs share */
	struct xen_9pfs_dataring {
	struct xen_9pfs_front_priv *priv;

	struct xen_9pfs_data_intf *intf;
	grant_ref_t ref;
	int evtchn;
	int irq;
	/* protect a ring from concurrent accesses */
	spinlock_t lock;

	struct xen_9pfs_data data;
	wait_queue_head_t wq;
	struct work_struct work;
	};

	/* One per 9pfs share */
	struct xen_9pfs_front_priv {
	struct list_head list;
	struct xenbus_device *dev;
	char *tag;
	struct p9_client *client;

	int num_rings;
	struct xen_9pfs_dataring *rings;
	};

	static LIST_HEAD(xen_9pfs_devs);
	static DEFINE_RWLOCK(xen_9pfs_lock);

	/* We don't currently allow canceling of requests */
	static int p9_xen_cancel(struct p9_client client, struct p9_req_t req)
	{
	return 1;
	}

	static int p9_xen_create(struct p9_client client, const char addr, char *args)
	{
	struct xen_9pfs_front_priv *priv;

	if (addr == NULL)
	return -EINVAL;

	read_lock(&xen_9pfs_lock);
	list_for_each_entry(priv, &xen_9pfs_devs, list) {
	if (!strcmp(priv->tag, addr)) {
	priv->client = client;
	read_unlock(&xen_9pfs_lock);
	return 0;
	}
	}
	read_unlock(&xen_9pfs_lock);
	return -EINVAL;
	}

	static void p9_xen_close(struct p9_client *client)
	{
	struct xen_9pfs_front_priv *priv;

	read_lock(&xen_9pfs_lock);
	list_for_each_entry(priv, &xen_9pfs_devs, list) {
	if (priv->client == client) {
	priv->client = NULL;
	read_unlock(&xen_9pfs_lock);
	return;
	}
	}
	read_unlock(&xen_9pfs_lock);
	}

	static bool p9_xen_write_todo(struct xen_9pfs_dataring *ring, RING_IDX size)
	{
	RING_IDX cons, prod;

	cons = ring->intf->out_cons;
	prod = ring->intf->out_prod;
	virt_mb();

	return XEN_9PFS_RING_SIZE(ring) -
	xen_9pfs_queued(prod, cons, XEN_9PFS_RING_SIZE(ring)) >= size;
	}

	static int p9_xen_request(struct p9_client client, struct p9_req_t p9_req)
	{
	struct xen_9pfs_front_priv *priv;
	RING_IDX cons, prod, masked_cons, masked_prod;
	unsigned long flags;
	u32 size = p9_req->tc.size;
	struct xen_9pfs_dataring *ring;
	int num;

	read_lock(&xen_9pfs_lock);
	list_for_each_entry(priv, &xen_9pfs_devs, list) {
	if (priv->client == client)
	break;
	}
	read_unlock(&xen_9pfs_lock);
	if (list_entry_is_head(priv, &xen_9pfs_devs, list))
	return -EINVAL;

	num = p9_req->tc.tag % priv->num_rings;
	ring = &priv->rings[num];

	again:
	while (wait_event_killable(ring->wq,
	p9_xen_write_todo(ring, size)) != 0)
	;

	spin_lock_irqsave(&ring->lock, flags);
	cons = ring->intf->out_cons;
	prod = ring->intf->out_prod;
	virt_mb();

	if (XEN_9PFS_RING_SIZE(ring) -
	xen_9pfs_queued(prod, cons, XEN_9PFS_RING_SIZE(ring)) < size) {
	spin_unlock_irqrestore(&ring->lock, flags);
	goto again;
	}

	masked_prod = xen_9pfs_mask(prod, XEN_9PFS_RING_SIZE(ring));
	masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE(ring));

	xen_9pfs_write_packet(ring->data.out, p9_req->tc.sdata, size,
	&masked_prod, masked_cons,
	XEN_9PFS_RING_SIZE(ring));

	p9_req->status = REQ_STATUS_SENT;
	virt_wmb(); /* write ring before updating pointer */
	prod += size;
	ring->intf->out_prod = prod;
	spin_unlock_irqrestore(&ring->lock, flags);
	notify_remote_via_irq(ring->irq);
	p9_req_put(client, p9_req);

	return 0;
	}

	static void p9_xen_response(struct work_struct *work)
	{
	struct xen_9pfs_front_priv *priv;
	struct xen_9pfs_dataring *ring;
	RING_IDX cons, prod, masked_cons, masked_prod;
	struct xen_9pfs_header h;
	struct p9_req_t *req;
	int status;

	ring = container_of(work, struct xen_9pfs_dataring, work);
	priv = ring->priv;

	while (1) {
	cons = ring->intf->in_cons;
	prod = ring->intf->in_prod;
	virt_rmb();

	if (xen_9pfs_queued(prod, cons, XEN_9PFS_RING_SIZE(ring)) <
	sizeof(h)) {
	notify_remote_via_irq(ring->irq);
	return;
	}

	masked_prod = xen_9pfs_mask(prod, XEN_9PFS_RING_SIZE(ring));
	masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE(ring));

	/* First, read just the header */
	xen_9pfs_read_packet(&h, ring->data.in, sizeof(h),
	masked_prod, &masked_cons,
	XEN_9PFS_RING_SIZE(ring));

	req = p9_tag_lookup(priv->client, h.tag);
	if (!req \|\| req->status != REQ_STATUS_SENT) {
	dev_warn(&priv->dev->dev, "Wrong req tag=%x\n", h.tag);
	cons += h.size;
	virt_mb();
	ring->intf->in_cons = cons;
	continue;
	}

	if (h.size > req->rc.capacity) {
	dev_warn(&priv->dev->dev,
	"requested packet size too big: %d for tag %d with capacity %zd\n",
	h.size, h.tag, req->rc.capacity);
	req->status = REQ_STATUS_ERROR;
	goto recv_error;
	}

	memcpy(&req->rc, &h, sizeof(h));
	req->rc.offset = 0;

	masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE(ring));
	/* Then, read the whole packet (including the header) */
	xen_9pfs_read_packet(req->rc.sdata, ring->data.in, h.size,
	masked_prod, &masked_cons,
	XEN_9PFS_RING_SIZE(ring));

	recv_error:
	virt_mb();
	cons += h.size;
	ring->intf->in_cons = cons;

	status = (req->status != REQ_STATUS_ERROR) ?
	REQ_STATUS_RCVD : REQ_STATUS_ERROR;

	p9_client_cb(priv->client, req, status);
	}
	}

	static irqreturn_t xen_9pfs_front_event_handler(int irq, void *r)
	{
	struct xen_9pfs_dataring *ring = r;

	if (!ring \|\| !ring->priv->client) {
	/* ignore spurious interrupt */
	return IRQ_HANDLED;
	}

	wake_up_interruptible(&ring->wq);
	schedule_work(&ring->work);

	return IRQ_HANDLED;
	}

	static struct p9_trans_module p9_xen_trans = {
	.name = "xen",
	.maxsize = 1 << (XEN_9PFS_RING_ORDER + XEN_PAGE_SHIFT - 2),
	.def = 1,
	.create = p9_xen_create,
	.close = p9_xen_close,
	.request = p9_xen_request,
	.cancel = p9_xen_cancel,
	.owner = THIS_MODULE,
	};

	static const struct xenbus_device_id xen_9pfs_front_ids[] = {
	{ "9pfs" },
	{ "" }
	};

	static void xen_9pfs_front_free(struct xen_9pfs_front_priv *priv)
	{
	int i, j;

	write_lock(&xen_9pfs_lock);
	list_del(&priv->list);
	write_unlock(&xen_9pfs_lock);

	for (i = 0; i < priv->num_rings; i++) {
	struct xen_9pfs_dataring *ring = &priv->rings[i];

	cancel_work_sync(&ring->work);

	if (!priv->rings[i].intf)
	break;
	if (priv->rings[i].irq > 0)
	unbind_from_irqhandler(priv->rings[i].irq, priv->dev);
	if (priv->rings[i].data.in) {
	for (j = 0;
	j < (1 << priv->rings[i].intf->ring_order);
	j++) {
	grant_ref_t ref;

	ref = priv->rings[i].intf->ref[j];
	gnttab_end_foreign_access(ref, 0, 0);
	}
	free_pages_exact(priv->rings[i].data.in,
	1UL << (priv->rings[i].intf->ring_order +
	XEN_PAGE_SHIFT));
	}
	gnttab_end_foreign_access(priv->rings[i].ref, 0, 0);
	free_page((unsigned long)priv->rings[i].intf);
	}
	kfree(priv->rings);
	kfree(priv->tag);
	kfree(priv);
	}

	static int xen_9pfs_front_remove(struct xenbus_device *dev)
	{
	struct xen_9pfs_front_priv *priv = dev_get_drvdata(&dev->dev);

	dev_set_drvdata(&dev->dev, NULL);
	xen_9pfs_front_free(priv);
	return 0;
	}

	static int xen_9pfs_front_alloc_dataring(struct xenbus_device *dev,
	struct xen_9pfs_dataring *ring,
	unsigned int order)
	{
	int i = 0;
	int ret = -ENOMEM;
	void *bytes = NULL;

	init_waitqueue_head(&ring->wq);
	spin_lock_init(&ring->lock);
	INIT_WORK(&ring->work, p9_xen_response);

	ring->intf = (struct xen_9pfs_data_intf *)get_zeroed_page(GFP_KERNEL);
	if (!ring->intf)
	return ret;
	ret = gnttab_grant_foreign_access(dev->otherend_id,
	virt_to_gfn(ring->intf), 0);
	if (ret < 0)
	goto out;
	ring->ref = ret;
	bytes = alloc_pages_exact(1UL << (order + XEN_PAGE_SHIFT),
	GFP_KERNEL \| __GFP_ZERO);
	if (!bytes) {
	ret = -ENOMEM;
	goto out;
	}
	for (; i < (1 << order); i++) {
	ret = gnttab_grant_foreign_access(
	dev->otherend_id, virt_to_gfn(bytes) + i, 0);
	if (ret < 0)
	goto out;
	ring->intf->ref[i] = ret;
	}
	ring->intf->ring_order = order;
	ring->data.in = bytes;
	ring->data.out = bytes + XEN_FLEX_RING_SIZE(order);

	ret = xenbus_alloc_evtchn(dev, &ring->evtchn);
	if (ret)
	goto out;
	ring->irq = bind_evtchn_to_irqhandler(ring->evtchn,
	xen_9pfs_front_event_handler,
	0, "xen_9pfs-frontend", ring);
	if (ring->irq >= 0)
	return 0;

	xenbus_free_evtchn(dev, ring->evtchn);
	ret = ring->irq;
	out:
	if (bytes) {
	for (i--; i >= 0; i--)
	gnttab_end_foreign_access(ring->intf->ref[i], 0, 0);
	free_pages_exact(bytes, 1UL << (order + XEN_PAGE_SHIFT));
	}
	gnttab_end_foreign_access(ring->ref, 0, 0);
	free_page((unsigned long)ring->intf);
	return ret;
	}

	static int xen_9pfs_front_init(struct xenbus_device *dev)
	{
	int ret, i;
	struct xenbus_transaction xbt;
	struct xen_9pfs_front_priv *priv = dev_get_drvdata(&dev->dev);
	char versions, v;
	unsigned int max_rings, max_ring_order, len = 0;

	versions = xenbus_read(XBT_NIL, dev->otherend, "versions", &len);
	if (IS_ERR(versions))
	return PTR_ERR(versions);
	for (v = versions; *v; v++) {
	if (simple_strtoul(v, &v, 10) == 1) {
	v = NULL;
	break;
	}
	}
	if (v) {
	kfree(versions);
	return -EINVAL;
	}
	kfree(versions);
	max_rings = xenbus_read_unsigned(dev->otherend, "max-rings", 0);
	if (max_rings < XEN_9PFS_NUM_RINGS)
	return -EINVAL;
	max_ring_order = xenbus_read_unsigned(dev->otherend,
	"max-ring-page-order", 0);
	if (max_ring_order > XEN_9PFS_RING_ORDER)
	max_ring_order = XEN_9PFS_RING_ORDER;
	if (p9_xen_trans.maxsize > XEN_FLEX_RING_SIZE(max_ring_order))
	p9_xen_trans.maxsize = XEN_FLEX_RING_SIZE(max_ring_order) / 2;

	priv->num_rings = XEN_9PFS_NUM_RINGS;
	priv->rings = kcalloc(priv->num_rings, sizeof(*priv->rings),
	GFP_KERNEL);
	if (!priv->rings) {
	kfree(priv);
	return -ENOMEM;
	}

	for (i = 0; i < priv->num_rings; i++) {
	priv->rings[i].priv = priv;
	ret = xen_9pfs_front_alloc_dataring(dev, &priv->rings[i],
	max_ring_order);
	if (ret < 0)
	goto error;
	}

	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, "num-rings", "%u",
	priv->num_rings);
	if (ret)
	goto error_xenbus;
	for (i = 0; i < priv->num_rings; i++) {
	char str[16];

	BUILD_BUG_ON(XEN_9PFS_NUM_RINGS > 9);
	sprintf(str, "ring-ref%d", i);
	ret = xenbus_printf(xbt, dev->nodename, str, "%d",
	priv->rings[i].ref);
	if (ret)
	goto error_xenbus;

	sprintf(str, "event-channel-%d", i);
	ret = xenbus_printf(xbt, dev->nodename, str, "%u",
	priv->rings[i].evtchn);
	if (ret)
	goto error_xenbus;
	}
	priv->tag = xenbus_read(xbt, dev->nodename, "tag", NULL);
	if (IS_ERR(priv->tag)) {
	ret = PTR_ERR(priv->tag);
	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;
	}

	return 0;

	error_xenbus:
	xenbus_transaction_end(xbt, 1);
	xenbus_dev_fatal(dev, ret, "writing xenstore");
	error:
	xen_9pfs_front_free(priv);
	return ret;
	}

	static int xen_9pfs_front_probe(struct xenbus_device *dev,
	const struct xenbus_device_id *id)
	{
	struct xen_9pfs_front_priv *priv = NULL;

	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv)
	return -ENOMEM;

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

	write_lock(&xen_9pfs_lock);
	list_add_tail(&priv->list, &xen_9pfs_devs);
	write_unlock(&xen_9pfs_lock);

	return 0;
	}

	static int xen_9pfs_front_resume(struct xenbus_device *dev)
	{
	dev_warn(&dev->dev, "suspend/resume unsupported\n");
	return 0;
	}

	static void xen_9pfs_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:
	if (!xen_9pfs_front_init(dev))
	xenbus_switch_state(dev, XenbusStateInitialised);
	break;

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

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

	static struct xenbus_driver xen_9pfs_front_driver = {
	.ids = xen_9pfs_front_ids,
	.probe = xen_9pfs_front_probe,
	.remove = xen_9pfs_front_remove,
	.resume = xen_9pfs_front_resume,
	.otherend_changed = xen_9pfs_front_changed,
	};

	static int p9_trans_xen_init(void)
	{
	int rc;

	if (!xen_domain())
	return -ENODEV;

	pr_info("Initialising Xen transport for 9pfs\n");

	v9fs_register_trans(&p9_xen_trans);
	rc = xenbus_register_frontend(&xen_9pfs_front_driver);
	if (rc)
	v9fs_unregister_trans(&p9_xen_trans);

	return rc;
	}
	module_init(p9_trans_xen_init);

	static void p9_trans_xen_exit(void)
	{
	v9fs_unregister_trans(&p9_xen_trans);
	return xenbus_unregister_driver(&xen_9pfs_front_driver);
	}
	module_exit(p9_trans_xen_exit);

	MODULE_AUTHOR("Stefano Stabellini <[email protected]>");
	MODULE_DESCRIPTION("Xen Transport for 9P");
	MODULE_LICENSE("GPL");