text: /*
   * linux/fs/9p/trans_xen
   *
   * Xen transport layer.
   *
   * Copyright (C) 2017 by 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 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 <linux/rwlock.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 6
  #define XEN_9PFS_RING_SIZE  XEN_FLEX_RING_SIZE(XEN_9PFS_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;
  
  	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 -
  		xen_9pfs_queued(prod, cons, XEN_9PFS_RING_SIZE) >= size;
  }
  
  static int p9_xen_request(struct p9_client *client, struct p9_req_t *p9_req)
  {
  	struct xen_9pfs_front_priv *priv = NULL;
  	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 (!priv || priv->client != client)
  		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 - xen_9pfs_queued(prod, cons,
  						 XEN_9PFS_RING_SIZE) < size) {
  		spin_unlock_irqrestore(&ring->lock, flags);
  		goto again;
  	}
  
  	masked_prod = xen_9pfs_mask(prod, XEN_9PFS_RING_SIZE);
  	masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE);
  
  	xen_9pfs_write_packet(ring->data.out, p9_req->tc->sdata, size,
  			      &masked_prod, masked_cons, XEN_9PFS_RING_SIZE);
  
  	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);
  
  	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) <
  		    sizeof(h)) {
  			notify_remote_via_irq(ring->irq);
  			return;
  		}
  
  		masked_prod = xen_9pfs_mask(prod, XEN_9PFS_RING_SIZE);
  		masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE);
  
  		/* First, read just the header */
  		xen_9pfs_read_packet(&h, ring->data.in, sizeof(h),
  				     masked_prod, &masked_cons,
  				     XEN_9PFS_RING_SIZE);
  
  		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;
  		}
  
  		memcpy(req->rc, &h, sizeof(h));
  		req->rc->offset = 0;
  
  		masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE);
  		/* 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);
  
  		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),
  	.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++) {
  		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 << XEN_9PFS_RING_ORDER); j++) {
  				grant_ref_t ref;
  
  				ref = priv->rings[i].intf->ref[j];
  				gnttab_end_foreign_access(ref, 0, 0);
  			}
  			free_pages((unsigned long)priv->rings[i].data.in,
  				   XEN_9PFS_RING_ORDER -
  				   (PAGE_SHIFT - 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)
  {
  	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 = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
  			XEN_9PFS_RING_ORDER - (PAGE_SHIFT - XEN_PAGE_SHIFT));
  	if (!bytes) {
  		ret = -ENOMEM;
  		goto out;
  	}
  	for (; i < (1 << XEN_9PFS_RING_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 = XEN_9PFS_RING_ORDER;
  	ring->data.in = bytes;
  	ring->data.out = bytes + XEN_9PFS_RING_SIZE;
  
  	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((unsigned long)bytes,
  			   XEN_9PFS_RING_ORDER -
  			   (PAGE_SHIFT - XEN_PAGE_SHIFT));
  	}
  	gnttab_end_foreign_access(ring->ref, 0, 0);
  	free_page((unsigned long)ring->intf);
  	return ret;
  }
  
  static int xen_9pfs_front_probe(struct xenbus_device *dev,
  				const struct xenbus_device_id *id)
  {
  	int ret, i;
  	struct xenbus_transaction xbt;
  	struct xen_9pfs_front_priv *priv = NULL;
  	char *versions;
  	unsigned int max_rings, max_ring_order, len = 0;
  
  	versions = xenbus_read(XBT_NIL, dev->otherend, "versions", &len);
  	if (!len)
  		return -EINVAL;
  	if (strcmp(versions, "1")) {
  		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)
  		return -EINVAL;
  
  	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
  	if (!priv)
  		return -ENOMEM;
  
  	priv->dev = dev;
  	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]);
  		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%u", i);
  		ret = xenbus_printf(xbt, dev->nodename, str, "%d",
  				    priv->rings[i].ref);
  		if (ret)
  			goto error_xenbus;
  
  		sprintf(str, "event-channel-%u", 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;
  	}
  
  	write_lock(&xen_9pfs_lock);
  	list_add_tail(&priv->list, &xen_9pfs_devs);
  	write_unlock(&xen_9pfs_lock);
  	dev_set_drvdata(&dev->dev, priv);
  	xenbus_switch_state(dev, XenbusStateInitialised);
  
  	return 0;
  
   error_xenbus:
  	xenbus_transaction_end(xbt, 1);
  	xenbus_dev_fatal(dev, ret, "writing xenstore");
   error:
  	dev_set_drvdata(&dev->dev, NULL);
  	xen_9pfs_front_free(priv);
  	return ret;
  }
  
  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:
  		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 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)
  {
  	if (!xen_domain())
  		return -ENODEV;
  
  	pr_info("Initialising Xen transport for 9pfs\n");
  
  	v9fs_register_trans(&p9_xen_trans);
  	return xenbus_register_frontend(&xen_9pfs_front_driver);
  }
  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 <stefano@aporeto.com>");
  MODULE_DESCRIPTION("Xen Transport for 9P");
  MODULE_LICENSE("GPL");
  