Revision 1a512c0882bd311c5b5561840fcfbe4c25b8f319 authored by Arnd Bergmann on 24 April 2018, 21:19:51 UTC, committed by Thomas Gleixner on 27 April 2018, 15:06:29 UTC
A bugfix broke the x32 shmid64_ds and msqid64_ds data structure layout
(as seen from user space)  a few years ago: Originally, __BITS_PER_LONG
was defined as 64 on x32, so we did not have padding after the 64-bit
__kernel_time_t fields, After __BITS_PER_LONG got changed to 32,
applications would observe extra padding.

In other parts of the uapi headers we seem to have a mix of those
expecting either 32 or 64 on x32 applications, so we can't easily revert
the path that broke these two structures.

Instead, this patch decouples x32 from the other architectures and moves
it back into arch specific headers, partially reverting the even older
commit 73a2d096fdf2 ("x86: remove all now-duplicate header files").

It's not clear whether this ever made any difference, since at least
glibc carries its own (correct) copy of both of these header files,
so possibly no application has ever observed the definitions here.

Based on a suggestion from H.J. Lu, I tried out the tool from
https://github.com/hjl-tools/linux-header to find other such
bugs, which pointed out the same bug in statfs(), which also has
a separate (correct) copy in glibc.

Fixes: f4b4aae18288 ("x86/headers/uapi: Fix __BITS_PER_LONG value for x32 builds")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "H . J . Lu" <hjl.tools@gmail.com>
Cc: Jeffrey Walton <noloader@gmail.com>
Cc: stable@vger.kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lkml.kernel.org/r/20180424212013.3967461-1-arnd@arndb.de

1 parent 3db3eb2
Raw File
trans_virtio.c
/*
 * 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 - offset_in_page(data);
}

/**
 * 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;
	unsigned int len;
	struct p9_req_t *req;
	unsigned long flags;

	p9_debug(P9_DEBUG_TRANS, ": request done\n");

	while (1) {
		spin_lock_irqsave(&chan->lock, flags);
		req = virtqueue_get_buf(chan->vq, &len);
		if (req == 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);
		if (len)
			p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
	}
}

/**
 * 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
 * @offs: amount of data in the beginning of first page _not_ to pack
 * @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, size_t offs, int count)
{
	int i = 0, s;
	int data_off = offs;
	int index = start;

	BUG_ON(nr_pages > (limit - start));
	/*
	 * if the first page doesn't start at
	 * page boundary find the offset
	 */
	while (nr_pages) {
		s = PAGE_SIZE - data_off;
		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;
		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\n");

	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,
				GFP_ATOMIC);
	if (err < 0) {
		if (err == -ENOSPC) {
			chan->ring_bufs_avail = 0;
			spin_unlock_irqrestore(&chan->lock, flags);
			err = wait_event_killable(*chan->vc_wq,
						  chan->ring_bufs_avail);
			if (err  == -ERESTARTSYS)
				return err;

			p9_debug(P9_DEBUG_TRANS, "Retry virtio request\n");
			goto req_retry;
		} else {
			spin_unlock_irqrestore(&chan->lock, flags);
			p9_debug(P9_DEBUG_TRANS,
				 "virtio rpc add_sgs returned failure\n");
			return -EIO;
		}
	}
	virtqueue_kick(chan->vq);
	spin_unlock_irqrestore(&chan->lock, flags);

	p9_debug(P9_DEBUG_TRANS, "virtio request kicked\n");
	return 0;
}

static int p9_get_mapped_pages(struct virtio_chan *chan,
			       struct page ***pages,
			       struct iov_iter *data,
			       int count,
			       size_t *offs,
			       int *need_drop)
{
	int nr_pages;
	int err;

	if (!iov_iter_count(data))
		return 0;

	if (!(data->type & ITER_KVEC)) {
		int n;
		/*
		 * 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_killable(vp_wq,
			      (atomic_read(&vp_pinned) < chan->p9_max_pages));
			if (err == -ERESTARTSYS)
				return err;
		}
		n = iov_iter_get_pages_alloc(data, pages, count, offs);
		if (n < 0)
			return n;
		*need_drop = 1;
		nr_pages = DIV_ROUND_UP(n + *offs, PAGE_SIZE);
		atomic_add(nr_pages, &vp_pinned);
		return n;
	} else {
		/* kernel buffer, no need to pin pages */
		int index;
		size_t len;
		void *p;

		/* we'd already checked that it's non-empty */
		while (1) {
			len = iov_iter_single_seg_count(data);
			if (likely(len)) {
				p = data->kvec->iov_base + data->iov_offset;
				break;
			}
			iov_iter_advance(data, 0);
		}
		if (len > count)
			len = count;

		nr_pages = DIV_ROUND_UP((unsigned long)p + len, PAGE_SIZE) -
			   (unsigned long)p / PAGE_SIZE;

		*pages = kmalloc(sizeof(struct page *) * nr_pages, GFP_NOFS);
		if (!*pages)
			return -ENOMEM;

		*need_drop = 0;
		p -= (*offs = offset_in_page(p));
		for (index = 0; index < nr_pages; index++) {
			if (is_vmalloc_addr(p))
				(*pages)[index] = vmalloc_to_page(p);
			else
				(*pages)[index] = kmap_to_page(p);
			p += PAGE_SIZE;
		}
		return len;
	}
}

/**
 * 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,
		     struct iov_iter *uidata, struct iov_iter *uodata,
		     int inlen, int outlen, int in_hdr_len)
{
	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];
	size_t offs;
	int need_drop = 0;

	p9_debug(P9_DEBUG_TRANS, "virtio request\n");

	if (uodata) {
		int n = p9_get_mapped_pages(chan, &out_pages, uodata,
					    outlen, &offs, &need_drop);
		if (n < 0)
			return n;
		out_nr_pages = DIV_ROUND_UP(n + offs, PAGE_SIZE);
		if (n != outlen) {
			__le32 v = cpu_to_le32(n);
			memcpy(&req->tc->sdata[req->tc->size - 4], &v, 4);
			outlen = n;
		}
	} else if (uidata) {
		int n = p9_get_mapped_pages(chan, &in_pages, uidata,
					    inlen, &offs, &need_drop);
		if (n < 0)
			return n;
		in_nr_pages = DIV_ROUND_UP(n + offs, PAGE_SIZE);
		if (n != inlen) {
			__le32 v = cpu_to_le32(n);
			memcpy(&req->tc->sdata[req->tc->size - 4], &v, 4);
			inlen = n;
		}
	}
	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, offs, 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, offs, inlen);
	}

	BUG_ON(out_sgs + in_sgs > ARRAY_SIZE(sgs));
	err = virtqueue_add_sgs(chan->vq, sgs, out_sgs, in_sgs, req,
				GFP_ATOMIC);
	if (err < 0) {
		if (err == -ENOSPC) {
			chan->ring_bufs_avail = 0;
			spin_unlock_irqrestore(&chan->lock, flags);
			err = wait_event_killable(*chan->vc_wq,
						  chan->ring_bufs_avail);
			if (err  == -ERESTARTSYS)
				goto err_out;

			p9_debug(P9_DEBUG_TRANS, "Retry virtio request\n");
			goto req_retry_pinned;
		} else {
			spin_unlock_irqrestore(&chan->lock, flags);
			p9_debug(P9_DEBUG_TRANS,
				 "virtio rpc add_sgs returned failure\n");
			err = -EIO;
			goto err_out;
		}
	}
	virtqueue_kick(chan->vq);
	spin_unlock_irqrestore(&chan->lock, flags);
	p9_debug(P9_DEBUG_TRANS, "virtio request kicked\n");
	err = wait_event_killable(*req->wq, req->status >= REQ_STATUS_RCVD);
	/*
	 * Non kernel buffers are pinned, unpin them
	 */
err_out:
	if (need_drop) {
		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);
	}
	kvfree(in_pages);
	kvfree(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;

	memcpy(buf, chan->tag, chan->tag_len);
	buf[chan->tag_len] = 0;

	return chan->tag_len + 1;
}

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;

	if (!vdev->config->get) {
		dev_err(&vdev->dev, "%s failure: config access disabled\n",
			__func__);
		return -EINVAL;
	}

	chan = kmalloc(sizeof(struct virtio_chan), GFP_KERNEL);
	if (!chan) {
		pr_err("Failed to allocate virtio 9P channel\n");
		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;

	virtio_device_ready(vdev);

	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 for device %s\n", devname);
		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;
	unsigned long warning_time;

	mutex_lock(&virtio_9p_lock);

	/* Remove self from list so we don't get new users. */
	list_del(&chan->chan_list);
	warning_time = jiffies;

	/* Wait for existing users to close. */
	while (chan->inuse) {
		mutex_unlock(&virtio_9p_lock);
		msleep(250);
		if (time_after(jiffies, warning_time + 10 * HZ)) {
			dev_emerg(&vdev->dev,
				  "p9_virtio_remove: waiting for device in use.\n");
			warning_time = jiffies;
		}
		mutex_lock(&virtio_9p_lock);
	}

	mutex_unlock(&virtio_9p_lock);

	vdev->config->reset(vdev);
	vdev->config->del_vqs(vdev);

	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");
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