/*
   * 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
   *
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #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/highmem.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.
  	 */
  	unsigned long 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_debug(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_debug(P9_DEBUG_TRANS, ": rc %p
  ", rc);
  		p9_debug(P9_DEBUG_TRANS, ": lookup tag %d
  ", rc->tag);
  		req = p9_tag_lookup(chan->client, rc->tag);
  		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;
  		BUG_ON(index > limit);
  		/* Make sure we don't terminate early. */
  		sg_unmark_end(&sg[index]);
  		sg_set_buf(&sg[index++], data, s);
  		count -= s;
  		data += s;
  	}
  	if (index-start)
  		sg_mark_end(&sg[index - 1]);
  	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: a list of pages to add into sg.
   * @nr_pages: number of pages to pack into the scatter/gather list
   * @data: data to pack into scatter/gather list
   * @count: amount of data to pack into the scatter/gather list
   */
  static int
  pack_sg_list_p(struct scatterlist *sg, int start, int limit,
  	       struct page **pdata, int nr_pages, char *data, int count)
  {
  	int i = 0, s;
  	int data_off;
  	int index = start;
  
  	BUG_ON(nr_pages > (limit - start));
  	/*
  	 * if the first page doesn't start at
  	 * page boundary find the offset
  	 */
  	data_off = offset_in_page(data);
  	while (nr_pages) {
  		s = rest_of_page(data);
  		if (s > count)
  			s = count;
  		/* Make sure we don't terminate early. */
  		sg_unmark_end(&sg[index]);
  		sg_set_page(&sg[index++], pdata[i++], s, data_off);
  		data_off = 0;
  		data += s;
  		count -= s;
  		nr_pages--;
  	}
  
  	if (index-start)
  		sg_mark_end(&sg[index - 1]);
  	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 err;
  	int in, out, out_sgs, in_sgs;
  	unsigned long flags;
  	struct virtio_chan *chan = client->trans;
  	struct scatterlist *sgs[2];
  
  	p9_debug(P9_DEBUG_TRANS, "9p debug: virtio request
  ");
  
  	req->status = REQ_STATUS_SENT;
  req_retry:
  	spin_lock_irqsave(&chan->lock, flags);
  
  	out_sgs = in_sgs = 0;
  	/* Handle out VirtIO ring buffers */
  	out = pack_sg_list(chan->sg, 0,
  			   VIRTQUEUE_NUM, req->tc->sdata, req->tc->size);
  	if (out)
  		sgs[out_sgs++] = chan->sg;
  
  	in = pack_sg_list(chan->sg, out,
  			  VIRTQUEUE_NUM, req->rc->sdata, req->rc->capacity);
  	if (in)
  		sgs[out_sgs + in_sgs++] = chan->sg + out;
  
  	err = virtqueue_add_sgs(chan->vq, sgs, out_sgs, in_sgs, req->tc,
  				GFP_ATOMIC);
  	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_debug(P9_DEBUG_TRANS, "Retry virtio request
  ");
  			goto req_retry;
  		} else {
  			spin_unlock_irqrestore(&chan->lock, flags);
  			p9_debug(P9_DEBUG_TRANS,
  				 "virtio rpc add_sgs returned failure
  ");
  			return -EIO;
  		}
  	}
  	virtqueue_kick(chan->vq);
  	spin_unlock_irqrestore(&chan->lock, flags);
  
  	p9_debug(P9_DEBUG_TRANS, "virtio request kicked
  ");
  	return 0;
  }
  
  static int p9_get_mapped_pages(struct virtio_chan *chan,
  			       struct page **pages, char *data,
  			       int nr_pages, int write, int kern_buf)
  {
  	int err;
  	if (!kern_buf) {
  		/*
  		 * We allow only p9_max_pages pinned. We wait for the
  		 * Other zc request to finish here
  		 */
  		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;
  		}
  		err = p9_payload_gup(data, &nr_pages, pages, write);
  		if (err < 0)
  			return err;
  		atomic_add(nr_pages, &vp_pinned);
  	} else {
  		/* kernel buffer, no need to pin pages */
  		int s, index = 0;
  		int count = nr_pages;
  		while (nr_pages) {
  			s = rest_of_page(data);
  			if (is_vmalloc_addr(data))
  				pages[index++] = vmalloc_to_page(data);
  			else
  				pages[index++] = kmap_to_page(data);
  			data += s;
  			nr_pages--;
  		}
  		nr_pages = count;
  	}
  	return nr_pages;
  }
  
  /**
   * p9_virtio_zc_request - issue a zero copy request
   * @client: client instance issuing the request
   * @req: request to be issued
   * @uidata: user bffer that should be ued for zero copy read
   * @uodata: user buffer that shoud be user for zero copy write
   * @inlen: read buffer size
   * @olen: write buffer size
   * @hdrlen: reader header size, This is the size of response protocol data
   *
   */
  static int
  p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
  		     char *uidata, char *uodata, int inlen,
  		     int outlen, int in_hdr_len, int kern_buf)
  {
  	int in, out, err, out_sgs, in_sgs;
  	unsigned long flags;
  	int in_nr_pages = 0, out_nr_pages = 0;
  	struct page **in_pages = NULL, **out_pages = NULL;
  	struct virtio_chan *chan = client->trans;
  	struct scatterlist *sgs[4];
  
  	p9_debug(P9_DEBUG_TRANS, "virtio request
  ");
  
  	if (uodata) {
  		out_nr_pages = p9_nr_pages(uodata, outlen);
  		out_pages = kmalloc(sizeof(struct page *) * out_nr_pages,
  				    GFP_NOFS);
  		if (!out_pages) {
  			err = -ENOMEM;
  			goto err_out;
  		}
  		out_nr_pages = p9_get_mapped_pages(chan, out_pages, uodata,
  						   out_nr_pages, 0, kern_buf);
  		if (out_nr_pages < 0) {
  			err = out_nr_pages;
  			kfree(out_pages);
  			out_pages = NULL;
  			goto err_out;
  		}
  	}
  	if (uidata) {
  		in_nr_pages = p9_nr_pages(uidata, inlen);
  		in_pages = kmalloc(sizeof(struct page *) * in_nr_pages,
  				   GFP_NOFS);
  		if (!in_pages) {
  			err = -ENOMEM;
  			goto err_out;
  		}
  		in_nr_pages = p9_get_mapped_pages(chan, in_pages, uidata,
  						  in_nr_pages, 1, kern_buf);
  		if (in_nr_pages < 0) {
  			err = in_nr_pages;
  			kfree(in_pages);
  			in_pages = NULL;
  			goto err_out;
  		}
  	}
  	req->status = REQ_STATUS_SENT;
  req_retry_pinned:
  	spin_lock_irqsave(&chan->lock, flags);
  
  	out_sgs = in_sgs = 0;
  
  	/* out data */
  	out = pack_sg_list(chan->sg, 0,
  			   VIRTQUEUE_NUM, req->tc->sdata, req->tc->size);
  
  	if (out)
  		sgs[out_sgs++] = chan->sg;
  
  	if (out_pages) {
  		sgs[out_sgs++] = chan->sg + out;
  		out += pack_sg_list_p(chan->sg, out, VIRTQUEUE_NUM,
  				      out_pages, out_nr_pages, uodata, outlen);
  	}
  		
  	/*
  	 * Take care of in data
  	 * For example TREAD have 11.
  	 * 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.
  	 */
  	in = pack_sg_list(chan->sg, out,
  			  VIRTQUEUE_NUM, req->rc->sdata, in_hdr_len);
  	if (in)
  		sgs[out_sgs + in_sgs++] = chan->sg + out;
  
  	if (in_pages) {
  		sgs[out_sgs + in_sgs++] = chan->sg + out + in;
  		in += pack_sg_list_p(chan->sg, out + in, VIRTQUEUE_NUM,
  				     in_pages, in_nr_pages, uidata, inlen);
  	}
  
  	BUG_ON(out_sgs + in_sgs > ARRAY_SIZE(sgs));
  	err = virtqueue_add_sgs(chan->vq, sgs, out_sgs, in_sgs, req->tc,
  				GFP_ATOMIC);
  	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)
  				goto err_out;
  
  			p9_debug(P9_DEBUG_TRANS, "Retry virtio request
  ");
  			goto req_retry_pinned;
  		} else {
  			spin_unlock_irqrestore(&chan->lock, flags);
  			p9_debug(P9_DEBUG_TRANS,
  				 "virtio rpc add_sgs returned failure
  ");
  			err = -EIO;
  			goto err_out;
  		}
  	}
  	virtqueue_kick(chan->vq);
  	spin_unlock_irqrestore(&chan->lock, flags);
  	p9_debug(P9_DEBUG_TRANS, "virtio request kicked
  ");
  	err = wait_event_interruptible(*req->wq,
  				       req->status >= REQ_STATUS_RCVD);
  	/*
  	 * Non kernel buffers are pinned, unpin them
  	 */
  err_out:
  	if (!kern_buf) {
  		if (in_pages) {
  			p9_release_pages(in_pages, in_nr_pages);
  			atomic_sub(in_nr_pages, &vp_pinned);
  		}
  		if (out_pages) {
  			p9_release_pages(out_pages, out_nr_pages);
  			atomic_sub(out_nr_pages, &vp_pinned);
  		}
  		/* wakeup anybody waiting for slots to pin pages */
  		wake_up(&vp_wq);
  	}
  	kfree(in_pages);
  	kfree(out_pages);
  	return err;
  }
  
  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) {
  		pr_err("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)) {
  		virtio_cread(vdev, struct virtio_9p_config, tag_len, &tag_len);
  	} else {
  		err = -EINVAL;
  		goto out_free_vq;
  	}
  	tag = kmalloc(tag_len, GFP_KERNEL);
  	if (!tag) {
  		err = -ENOMEM;
  		goto out_free_vq;
  	}
  
  	virtio_cread_bytes(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);
  
  	/* Let udev rules use the new mount_tag attribute. */
  	kobject_uevent(&(vdev->dev.kobj), KOBJ_CHANGE);
  
  	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) {
  		pr_err("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;
  
  	if (chan->inuse)
  		p9_virtio_close(chan->client);
  	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);
  	kobject_uevent(&(vdev->dev.kobj), KOBJ_CHANGE);
  	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,
  	.zc_request = p9_virtio_zc_request,
  	.cancel = p9_virtio_cancel,
  	/*
  	 * We leave one entry for input and one entry for response
  	 * headers. We also skip one more entry to accomodate, address
  	 * that are not at page boundary, that can result in an extra
  	 * page in zero copy.
  	 */
  	.maxsize = PAGE_SIZE * (VIRTQUEUE_NUM - 3),
  	.def = 1,
  	.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");