/*

   * The Virtio 9p transport driver

   *

   * This is a block based transport driver based on the lguest block driver
   * code.

   *

   *  Copyright (C) 2007, 2008 Eric Van Hensbergen, IBM Corporation

   *
   *  Based on virtio console driver
   *  Copyright (C) 2006, 2007 Rusty Russell, IBM Corporation
   *
   *  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.
   *
   *  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.
   *
   *  You should have received a copy of the GNU General Public License
   *  along with this program; if not, write to:
   *  Free Software Foundation
   *  51 Franklin Street, Fifth Floor
   *  Boston, MA  02111-1301  USA
   *
   */
  
  #include <linux/in.h>
  #include <linux/module.h>
  #include <linux/net.h>
  #include <linux/ipv6.h>
  #include <linux/errno.h>
  #include <linux/kernel.h>
  #include <linux/un.h>
  #include <linux/uaccess.h>
  #include <linux/inet.h>
  #include <linux/idr.h>
  #include <linux/file.h>

  #include <linux/slab.h>

  #include <net/9p/9p.h>
  #include <linux/parser.h>

  #include <net/9p/client.h>

  #include <net/9p/transport.h>
  #include <linux/scatterlist.h>

  #include <linux/swap.h>

  #include <linux/virtio.h>
  #include <linux/virtio_9p.h>

  #include "trans_common.h"

  #define VIRTQUEUE_NUM	128

  /* a single mutex to manage channel initialization and attachment */

  static DEFINE_MUTEX(virtio_9p_lock);

  static DECLARE_WAIT_QUEUE_HEAD(vp_wq);
  static atomic_t vp_pinned = ATOMIC_INIT(0);

  /**
   * struct virtio_chan - per-instance transport information
   * @initialized: whether the channel is initialized
   * @inuse: whether the channel is in use
   * @lock: protects multiple elements within this structure

   * @client: client instance

   * @vdev: virtio dev associated with this channel
   * @vq: virtio queue associated with this channel

   * @sg: scatter gather list which is used to pack a request (protected?)
   *
   * We keep all per-channel information in a structure.

   * This structure is allocated within the devices dev->mem space.
   * A pointer to the structure will get put in the transport private.

   *

   */

  struct virtio_chan {

  	bool inuse;

  	spinlock_t lock;

  	struct p9_client *client;

  	struct virtio_device *vdev;

  	struct virtqueue *vq;

  	int ring_bufs_avail;
  	wait_queue_head_t *vc_wq;

  	/* This is global limit. Since we don't have a global structure,
  	 * will be placing it in each channel.
  	 */
  	int p9_max_pages;

  	/* Scatterlist: can be too big for stack. */
  	struct scatterlist sg[VIRTQUEUE_NUM];

  	int tag_len;
  	/*
  	 * tag name to identify a mount Non-null terminated
  	 */
  	char *tag;

  	struct list_head chan_list;
  };
  
  static struct list_head virtio_chan_list;

  
  /* How many bytes left in this page. */
  static unsigned int rest_of_page(void *data)
  {
  	return PAGE_SIZE - ((unsigned long)data % PAGE_SIZE);
  }

  /**
   * p9_virtio_close - reclaim resources of a channel

   * @client: client instance

   *
   * This reclaims a channel by freeing its resources and
   * reseting its inuse flag.
   *
   */

  static void p9_virtio_close(struct p9_client *client)

  {

  	struct virtio_chan *chan = client->trans;

  	mutex_lock(&virtio_9p_lock);

  	if (chan)
  		chan->inuse = false;

  	mutex_unlock(&virtio_9p_lock);

  }

  /**
   * req_done - callback which signals activity from the server
   * @vq: virtio queue activity was received on
   *
   * This notifies us that the server has triggered some activity
   * on the virtio channel - most likely a response to request we
   * sent.  Figure out which requests now have responses and wake up
   * those threads.
   *
   * Bugs: could do with some additional sanity checking, but appears to work.
   *
   */

  static void req_done(struct virtqueue *vq)

  {

  	struct virtio_chan *chan = vq->vdev->priv;
  	struct p9_fcall *rc;
  	unsigned int len;

  	struct p9_req_t *req;

  	unsigned long flags;

  	P9_DPRINTK(P9_DEBUG_TRANS, ": request done
  ");

  	while (1) {

  		spin_lock_irqsave(&chan->lock, flags);
  		rc = virtqueue_get_buf(chan->vq, &len);

  		if (rc == NULL) {

  			spin_unlock_irqrestore(&chan->lock, flags);

  			break;
  		}
  
  		chan->ring_bufs_avail = 1;
  		spin_unlock_irqrestore(&chan->lock, flags);
  		/* Wakeup if anyone waiting for VirtIO ring space. */
  		wake_up(chan->vc_wq);
  		P9_DPRINTK(P9_DEBUG_TRANS, ": rc %p
  ", rc);
  		P9_DPRINTK(P9_DEBUG_TRANS, ": lookup tag %d
  ", rc->tag);
  		req = p9_tag_lookup(chan->client, rc->tag);
  		if (req->tc->private) {
  			struct trans_rpage_info *rp = req->tc->private;

  			int p = rp->rp_nr_pages;

  			/*Release pages */
  			p9_release_req_pages(rp);

  			atomic_sub(p, &vp_pinned);
  			wake_up(&vp_wq);

  			if (rp->rp_alloc)
  				kfree(rp);
  			req->tc->private = NULL;

  		}

  		req->status = REQ_STATUS_RCVD;
  		p9_client_cb(chan->client, req);
  	}

  }

  /**
   * pack_sg_list - pack a scatter gather list from a linear buffer
   * @sg: scatter/gather list to pack into
   * @start: which segment of the sg_list to start at
   * @limit: maximum segment to pack data to
   * @data: data to pack into scatter/gather list
   * @count: amount of data to pack into the scatter/gather list
   *
   * sg_lists have multiple segments of various sizes.  This will pack
   * arbitrary data into an existing scatter gather list, segmenting the
   * data as necessary within constraints.
   *
   */

  static int
  pack_sg_list(struct scatterlist *sg, int start, int limit, char *data,
  								int count)
  {
  	int s;
  	int index = start;
  
  	while (count) {
  		s = rest_of_page(data);
  		if (s > count)
  			s = count;
  		sg_set_buf(&sg[index++], data, s);
  		count -= s;
  		data += s;

  		BUG_ON(index > limit);

  	}

  	return index-start;

  }

  /* We don't currently allow canceling of virtio requests */
  static int p9_virtio_cancel(struct p9_client *client, struct p9_req_t *req)
  {
  	return 1;
  }

  /**

   * pack_sg_list_p - Just like pack_sg_list. Instead of taking a buffer,
   * this takes a list of pages.
   * @sg: scatter/gather list to pack into
   * @start: which segment of the sg_list to start at
   * @pdata_off: Offset into the first page
   * @**pdata: a list of pages to add into sg.
   * @count: amount of data to pack into the scatter/gather list
   */
  static int
  pack_sg_list_p(struct scatterlist *sg, int start, int limit, size_t pdata_off,
  		struct page **pdata, int count)
  {
  	int s;
  	int i = 0;
  	int index = start;
  
  	if (pdata_off) {
  		s = min((int)(PAGE_SIZE - pdata_off), count);
  		sg_set_page(&sg[index++], pdata[i++], s, pdata_off);
  		count -= s;
  	}
  
  	while (count) {
  		BUG_ON(index > limit);
  		s = min((int)PAGE_SIZE, count);
  		sg_set_page(&sg[index++], pdata[i++], s, 0);
  		count -= s;
  	}
  	return index-start;
  }
  
  /**

   * p9_virtio_request - issue a request

   * @client: client instance issuing the request
   * @req: request to be issued

   *
   */

  static int

  p9_virtio_request(struct p9_client *client, struct p9_req_t *req)

  {

  	int in, out, inp, outp;

  	struct virtio_chan *chan = client->trans;
  	char *rdata = (char *)req->rc+sizeof(struct p9_fcall);

  	unsigned long flags;

  	size_t pdata_off = 0;
  	struct trans_rpage_info *rpinfo = NULL;
  	int err, pdata_len = 0;

  	P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: virtio request
  ");

  	req->status = REQ_STATUS_SENT;

  	if (req->tc->pbuf_size && (req->tc->pubuf && P9_IS_USER_CONTEXT)) {
  		int nr_pages = p9_nr_pages(req);
  		int rpinfo_size = sizeof(struct trans_rpage_info) +
  			sizeof(struct page *) * nr_pages;

  		if (atomic_read(&vp_pinned) >= chan->p9_max_pages) {
  			err = wait_event_interruptible(vp_wq,
  				atomic_read(&vp_pinned) < chan->p9_max_pages);
  			if (err  == -ERESTARTSYS)
  				return err;
  			P9_DPRINTK(P9_DEBUG_TRANS, "9p: May gup pages now.
  ");
  		}

  		if (rpinfo_size <= (req->tc->capacity - req->tc->size)) {
  			/* We can use sdata */
  			req->tc->private = req->tc->sdata + req->tc->size;
  			rpinfo = (struct trans_rpage_info *)req->tc->private;
  			rpinfo->rp_alloc = 0;
  		} else {
  			req->tc->private = kmalloc(rpinfo_size, GFP_NOFS);
  			if (!req->tc->private) {
  				P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: "
  					"private kmalloc returned NULL");
  				return -ENOMEM;
  			}
  			rpinfo = (struct trans_rpage_info *)req->tc->private;
  			rpinfo->rp_alloc = 1;
  		}
  
  		err = p9_payload_gup(req, &pdata_off, &pdata_len, nr_pages,
  				req->tc->id == P9_TREAD ? 1 : 0);
  		if (err < 0) {
  			if (rpinfo->rp_alloc)
  				kfree(rpinfo);
  			return err;

  		} else {
  			atomic_add(rpinfo->rp_nr_pages, &vp_pinned);

  		}
  	}

  req_retry_pinned:

  	spin_lock_irqsave(&chan->lock, flags);

  
  	/* Handle out VirtIO ring buffers */

  	out = pack_sg_list(chan->sg, 0, VIRTQUEUE_NUM, req->tc->sdata,

  			req->tc->size);
  
  	if (req->tc->pbuf_size && (req->tc->id == P9_TWRITE)) {
  		/* We have additional write payload buffer to take care */
  		if (req->tc->pubuf && P9_IS_USER_CONTEXT) {
  			outp = pack_sg_list_p(chan->sg, out, VIRTQUEUE_NUM,
  					pdata_off, rpinfo->rp_data, pdata_len);
  		} else {

  			char *pbuf;
  			if (req->tc->pubuf)
  				pbuf = (__force char *) req->tc->pubuf;
  			else
  				pbuf = req->tc->pkbuf;

  			outp = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, pbuf,
  					req->tc->pbuf_size);
  		}
  		out += outp;
  	}
  
  	/* Handle in VirtIO ring buffers */
  	if (req->tc->pbuf_size &&
  		((req->tc->id == P9_TREAD) || (req->tc->id == P9_TREADDIR))) {
  		/*
  		 * Take care of additional Read payload.
  		 * 11 is the read/write header = PDU Header(7) + IO Size (4).
  		 * Arrange in such a way that server places header in the
  		 * alloced memory and payload onto the user buffer.
  		 */
  		inp = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, rdata, 11);
  		/*
  		 * Running executables in the filesystem may result in
  		 * a read request with kernel buffer as opposed to user buffer.
  		 */
  		if (req->tc->pubuf && P9_IS_USER_CONTEXT) {
  			in = pack_sg_list_p(chan->sg, out+inp, VIRTQUEUE_NUM,
  					pdata_off, rpinfo->rp_data, pdata_len);
  		} else {

  			char *pbuf;
  			if (req->tc->pubuf)
  				pbuf = (__force char *) req->tc->pubuf;
  			else
  				pbuf = req->tc->pkbuf;

  			in = pack_sg_list(chan->sg, out+inp, VIRTQUEUE_NUM,
  					pbuf, req->tc->pbuf_size);
  		}
  		in += inp;
  	} else {
  		in = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, rdata,
  				client->msize);
  	}

  	err = virtqueue_add_buf(chan->vq, chan->sg, out, in, req->tc);
  	if (err < 0) {

  		if (err == -ENOSPC) {
  			chan->ring_bufs_avail = 0;
  			spin_unlock_irqrestore(&chan->lock, flags);
  			err = wait_event_interruptible(*chan->vc_wq,
  							chan->ring_bufs_avail);
  			if (err  == -ERESTARTSYS)
  				return err;
  
  			P9_DPRINTK(P9_DEBUG_TRANS, "9p:Retry virtio request
  ");

  			goto req_retry_pinned;

  		} else {
  			spin_unlock_irqrestore(&chan->lock, flags);
  			P9_DPRINTK(P9_DEBUG_TRANS,
  					"9p debug: "
  					"virtio rpc add_buf returned failure");

  			if (rpinfo && rpinfo->rp_alloc)
  				kfree(rpinfo);

  			return -EIO;
  		}

  	}

  	virtqueue_kick(chan->vq);

  	spin_unlock_irqrestore(&chan->lock, flags);

  	P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: virtio request kicked
  ");

  	return 0;

  }

  static ssize_t p9_mount_tag_show(struct device *dev,
  				struct device_attribute *attr, char *buf)
  {
  	struct virtio_chan *chan;
  	struct virtio_device *vdev;
  
  	vdev = dev_to_virtio(dev);
  	chan = vdev->priv;
  
  	return snprintf(buf, chan->tag_len + 1, "%s", chan->tag);
  }
  
  static DEVICE_ATTR(mount_tag, 0444, p9_mount_tag_show, NULL);

  /**
   * p9_virtio_probe - probe for existence of 9P virtio channels
   * @vdev: virtio device to probe
   *

   * This probes for existing virtio channels.

   *
   */

  static int p9_virtio_probe(struct virtio_device *vdev)

  {

  	__u16 tag_len;
  	char *tag;

  	int err;
  	struct virtio_chan *chan;

  	chan = kmalloc(sizeof(struct virtio_chan), GFP_KERNEL);
  	if (!chan) {
  		printk(KERN_ERR "9p: Failed to allocate virtio 9P channel
  ");

  		err = -ENOMEM;
  		goto fail;
  	}

  	chan->vdev = vdev;

  	/* We expect one virtqueue, for requests. */

  	chan->vq = virtio_find_single_vq(vdev, req_done, "requests");

  	if (IS_ERR(chan->vq)) {
  		err = PTR_ERR(chan->vq);
  		goto out_free_vq;

  	}

  	chan->vq->vdev->priv = chan;
  	spin_lock_init(&chan->lock);

  	sg_init_table(chan->sg, VIRTQUEUE_NUM);

  	chan->inuse = false;

  	if (virtio_has_feature(vdev, VIRTIO_9P_MOUNT_TAG)) {
  		vdev->config->get(vdev,
  				offsetof(struct virtio_9p_config, tag_len),
  				&tag_len, sizeof(tag_len));
  	} else {
  		err = -EINVAL;
  		goto out_free_vq;
  	}
  	tag = kmalloc(tag_len, GFP_KERNEL);
  	if (!tag) {
  		err = -ENOMEM;
  		goto out_free_vq;
  	}
  	vdev->config->get(vdev, offsetof(struct virtio_9p_config, tag),
  			tag, tag_len);
  	chan->tag = tag;
  	chan->tag_len = tag_len;

  	err = sysfs_create_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
  	if (err) {

  		goto out_free_tag;

  	}

  	chan->vc_wq = kmalloc(sizeof(wait_queue_head_t), GFP_KERNEL);
  	if (!chan->vc_wq) {
  		err = -ENOMEM;
  		goto out_free_tag;
  	}
  	init_waitqueue_head(chan->vc_wq);
  	chan->ring_bufs_avail = 1;

  	/* Ceiling limit to avoid denial of service attacks */
  	chan->p9_max_pages = nr_free_buffer_pages()/4;

  	mutex_lock(&virtio_9p_lock);
  	list_add_tail(&chan->chan_list, &virtio_chan_list);
  	mutex_unlock(&virtio_9p_lock);

  	return 0;

  out_free_tag:
  	kfree(tag);

  out_free_vq:

  	vdev->config->del_vqs(vdev);

  	kfree(chan);

  fail:

  	return err;
  }

  
  /**
   * p9_virtio_create - allocate a new virtio channel

   * @client: client instance invoking this transport

   * @devname: string identifying the channel to connect to (unused)
   * @args: args passed from sys_mount() for per-transport options (unused)

   *
   * This sets up a transport channel for 9p communication.  Right now

   * we only match the first available channel, but eventually we couldlook up
   * alternate channels by matching devname versus a virtio_config entry.
   * We use a simple reference count mechanism to ensure that only a single

   * mount has a channel open at a time.
   *

   */

  static int
  p9_virtio_create(struct p9_client *client, const char *devname, char *args)

  {

  	struct virtio_chan *chan;

  	int ret = -ENOENT;

  	int found = 0;

  	mutex_lock(&virtio_9p_lock);

  	list_for_each_entry(chan, &virtio_chan_list, chan_list) {

  		if (!strncmp(devname, chan->tag, chan->tag_len) &&
  		    strlen(devname) == chan->tag_len) {

  			if (!chan->inuse) {
  				chan->inuse = true;

  				found = 1;

  				break;
  			}

  			ret = -EBUSY;

  		}
  	}

  	mutex_unlock(&virtio_9p_lock);

  	if (!found) {

  		printk(KERN_ERR "9p: no channels available
  ");

  		return ret;

  	}

  	client->trans = (void *)chan;

  	client->status = Connected;

  	chan->client = client;

  	return 0;

  }

  /**
   * p9_virtio_remove - clean up resources associated with a virtio device
   * @vdev: virtio device to remove
   *
   */

  static void p9_virtio_remove(struct virtio_device *vdev)
  {
  	struct virtio_chan *chan = vdev->priv;
  
  	BUG_ON(chan->inuse);

  	vdev->config->del_vqs(vdev);
  
  	mutex_lock(&virtio_9p_lock);
  	list_del(&chan->chan_list);
  	mutex_unlock(&virtio_9p_lock);

  	sysfs_remove_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);

  	kfree(chan->tag);

  	kfree(chan->vc_wq);

  	kfree(chan);

  }

  static struct virtio_device_id id_table[] = {
  	{ VIRTIO_ID_9P, VIRTIO_DEV_ANY_ID },
  	{ 0 },
  };

  static unsigned int features[] = {
  	VIRTIO_9P_MOUNT_TAG,
  };

  /* The standard "struct lguest_driver": */
  static struct virtio_driver p9_virtio_drv = {

  	.feature_table  = features,
  	.feature_table_size = ARRAY_SIZE(features),
  	.driver.name    = KBUILD_MODNAME,
  	.driver.owner	= THIS_MODULE,
  	.id_table	= id_table,
  	.probe		= p9_virtio_probe,
  	.remove		= p9_virtio_remove,

  };
  
  static struct p9_trans_module p9_virtio_trans = {
  	.name = "virtio",
  	.create = p9_virtio_create,

  	.close = p9_virtio_close,

  	.request = p9_virtio_request,
  	.cancel = p9_virtio_cancel,

  	.maxsize = PAGE_SIZE*16,

  	.pref = P9_TRANS_PREF_PAYLOAD_SEP,

  	.def = 0,

  	.owner = THIS_MODULE,

  };
  
  /* The standard init function */
  static int __init p9_virtio_init(void)
  {

  	INIT_LIST_HEAD(&virtio_chan_list);

  
  	v9fs_register_trans(&p9_virtio_trans);
  	return register_virtio_driver(&p9_virtio_drv);
  }

  static void __exit p9_virtio_cleanup(void)
  {
  	unregister_virtio_driver(&p9_virtio_drv);

  	v9fs_unregister_trans(&p9_virtio_trans);

  }

  module_init(p9_virtio_init);

  module_exit(p9_virtio_cleanup);

  
  MODULE_DEVICE_TABLE(virtio, id_table);
  MODULE_AUTHOR("Eric Van Hensbergen <ericvh@gmail.com>");
  MODULE_DESCRIPTION("Virtio 9p Transport");
  MODULE_LICENSE("GPL");