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* The Guest 9p transport driver
* This is a trivial pipe-based transport driver based on the lguest console
* code: we use lguest's DMA mechanism to send bytes out, and register a
* DMA buffer to receive bytes in. It is assumed to be present and available
* from the very beginning of boot.
* This may be have been done by just instaniating another HVC console,
* but HVC's blocksize of 16 bytes is annoying and painful to performance.
* A more efficient transport could be built based on the virtio block driver
* but it requires some changes in the 9p transport model (which are in
* progress)
* Copyright (C) 2007 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
* 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 <net/9p/9p.h>
#include <linux/parser.h>
#include <net/9p/transport.h>
#include <linux/scatterlist.h>
#include <linux/virtio.h>
#include <linux/virtio_9p.h>
/* a single mutex to manage channel initialization and attachment */
static DECLARE_MUTEX(virtio_9p_lock);
/* global which tracks highest initialized channel */
static int chan_index;
/* 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.
static struct virtio_chan {
bool initialized; /* channel is initialized */
bool inuse; /* channel is in use */
struct virtqueue *in_vq, *out_vq;
struct virtio_device *vdev;
/* This is our input buffer, and how much data is left in it. */
unsigned int in_len;
char *in, *inbuf;
wait_queue_head_t wq; /* waitq for buffer */
} channels[MAX_9P_CHAN];
/* How many bytes left in this page. */
static unsigned int rest_of_page(void *data)
return PAGE_SIZE - ((unsigned long)data % PAGE_SIZE);
static int p9_virtio_write(struct p9_trans *trans, void *buf, int count)
struct virtio_chan *chan = (struct virtio_chan *) trans->priv;
struct virtqueue *out_vq = chan->out_vq;
struct scatterlist sg[1];
unsigned int len;
P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: virtio write (%d)\n", count);
/* keep it simple - make sure we don't overflow a page */
if (rest_of_page(buf) < count)
count = rest_of_page(buf);
sg_init_one(sg, buf, count);
/* add_buf wants a token to identify this buffer: we hand it any
* non-NULL pointer, since there's only ever one buffer. */
if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) == 0) {
/* Tell Host to go! */
/* Chill out until it's done with the buffer. */
while (!out_vq->vq_ops->get_buf(out_vq, &len))
P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: virtio wrote (%d)\n", count);
/* We're expected to return the amount of data we wrote: all of it. */
return count;
/* Create a scatter-gather list representing our input buffer and put it in the
* queue. */
static void add_inbuf(struct virtio_chan *chan)
struct scatterlist sg[1];
sg_init_one(sg, chan->inbuf, PAGE_SIZE);
/* We should always be able to add one buffer to an empty queue. */
if (chan->in_vq->vq_ops->add_buf(chan->in_vq, sg, 0, 1, chan->inbuf))
static int p9_virtio_read(struct p9_trans *trans, void *buf, int count)
struct virtio_chan *chan = (struct virtio_chan *) trans->priv;
struct virtqueue *in_vq = chan->in_vq;
P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: virtio read (%d)\n", count);
/* If we don't have an input queue yet, we can't get input. */
/* No buffer? Try to get one. */
if (!chan->in_len) {
chan->in = in_vq->vq_ops->get_buf(in_vq, &chan->in_len);
if (!chan->in)
return 0;
/* You want more than we have to give? Well, try wanting less! */
if (chan->in_len < count)
count = chan->in_len;
/* Copy across to their buffer and increment offset. */
memcpy(buf, chan->in, count);
chan->in += count;
chan->in_len -= count;
/* Finished? Re-register buffer so Host will use it again. */
if (chan->in_len == 0)
P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: virtio finished read (%d)\n",
return count;
/* The poll function is used by 9p transports to determine if there
* is there is activity available on a particular channel. In our case
* we use it to wait for a callback from the input routines.
static unsigned int
p9_virtio_poll(struct p9_trans *trans, struct poll_table_struct *pt)
struct virtio_chan *chan = (struct virtio_chan *)trans->priv;
struct virtqueue *in_vq = chan->in_vq;
int ret = POLLOUT; /* we can always handle more output */
poll_wait(NULL, &chan->wq, pt);
/* No buffer? Try to get one. */
if (!chan->in_len)
chan->in = in_vq->vq_ops->get_buf(in_vq, &chan->in_len);
if (chan->in_len)
ret |= POLLIN;
return ret;
static void p9_virtio_close(struct p9_trans *trans)
struct virtio_chan *chan = trans->priv;
chan->inuse = false;
static bool p9_virtio_intr(struct virtqueue *q)
struct virtio_chan *chan = q->vdev->priv;
P9_DPRINTK(P9_DEBUG_TRANS, "9p poll_wakeup: %p\n", &chan->wq);
return true;
static int p9_virtio_probe(struct virtio_device *dev)
int err;
struct virtio_chan *chan;
int index;
index = chan_index++;
chan = &channels[index];
if (chan_index > MAX_9P_CHAN) {
printk(KERN_ERR "9p: virtio: Maximum channels exceeded\n");
chan->vdev = dev;
/* This is the scratch page we use to receive console input */
chan->inbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
if (!chan->inbuf) {
err = -ENOMEM;
goto fail;
/* Find the input queue. */
dev->priv = chan;
chan->in_vq = dev->config->find_vq(dev, p9_virtio_intr);
if (IS_ERR(chan->in_vq)) {
err = PTR_ERR(chan->in_vq);
goto free;
chan->out_vq = dev->config->find_vq(dev, NULL);
if (IS_ERR(chan->out_vq)) {
err = PTR_ERR(chan->out_vq);
goto free_in_vq;
/* Register the input buffer the first time. */
chan->inuse = false;
chan->initialized = true;
return 0;
return err;
/* 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 struct p9_trans *p9_virtio_create(const char *devname, char *args)
struct p9_trans *trans;
int index = 0;
struct virtio_chan *chan = channels;
while (index < MAX_9P_CHAN) {
if (chan->initialized && !chan->inuse) {
chan->inuse = true;
} else {
chan = &channels[index];
if (index >= MAX_9P_CHAN) {
printk(KERN_ERR "9p: virtio: couldn't find a free channel\n");
return NULL;
trans = kmalloc(sizeof(struct p9_trans), GFP_KERNEL);
if (!trans) {
printk(KERN_ERR "9p: couldn't allocate transport\n");
return ERR_PTR(-ENOMEM);
trans->write = p9_virtio_write;
trans->read = p9_virtio_read;
trans->close = p9_virtio_close;
trans->poll = p9_virtio_poll;
trans->priv = chan;
return trans;
#define VIRTIO_ID_9P 9
static struct virtio_device_id id_table[] = {
{ 0 },
/* The standard "struct lguest_driver": */
static struct virtio_driver p9_virtio_drv = { = KBUILD_MODNAME,
.driver.owner = THIS_MODULE,
.id_table = id_table,
.probe = p9_virtio_probe,
static struct p9_trans_module p9_virtio_trans = {
.name = "virtio",
.create = p9_virtio_create,
.maxsize = PAGE_SIZE,
.def = 0,
/* The standard init function */
static int __init p9_virtio_init(void)
int count;
for (count = 0; count < MAX_9P_CHAN; count++)
channels[count].initialized = false;
return register_virtio_driver(&p9_virtio_drv);
MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_AUTHOR("Eric Van Hensbergen <>");
MODULE_DESCRIPTION("Virtio 9p Transport");