9p: add virtio transport

This adds a transport to 9p for communicating between guests and a host
using a virtio based transport.

Signed-off-by: Eric Van Hensbergen <[e-mail]>

Documentation/filesystems/9p.txt

···
 
   trans=name	select an alternative transport.  Valid options are
   		currently:
- 			unix - specifying a named pipe mount point
- 			tcp  - specifying a normal TCP/IP connection
- 			fd   - used passed file descriptors for connection
+			unix 	- specifying a named pipe mount point
+			tcp	- specifying a normal TCP/IP connection
+			fd   	- used passed file descriptors for connection
                                 (see rfdno and wfdno)
+			virtio	- connect to the next virtio channel available
+				(from lguest or KVM with trans_virtio module)
 
   uname=name	user name to attempt mount as on the remote server.  The
   		server may override or ignore this value.  Certain user

include/linux/virtio_9p.h

···
+#ifndef _LINUX_VIRTIO_9P_H
+#define _LINUX_VIRTIO_9P_H
+#include <linux/virtio_config.h>
+
+/* The ID for virtio console */
+#define VIRTIO_ID_9P	9
+/* Maximum number of virtio channels per partition (1 for now) */
+#define MAX_9P_CHAN	1
+
+#endif /* _LINUX_VIRTIO_9P_H */

net/9p/Kconfig

···
 	  file descriptors.  TCP/IP is the default transport for 9p,
 	  so if you are going to use 9p, you'll likely want this.
 
+config NET_9P_VIRTIO
+	depends on NET_9P && EXPERIMENTAL && VIRTIO
+	tristate "9P Virtio Transport (Experimental)"
+	help
+	  This builds support for a transports between
+	  guest partitions and a host partition.
+
 config NET_9P_DEBUG
 	bool "Debug information"
 	depends on NET_9P

net/9p/Makefile

···
 obj-$(CONFIG_NET_9P) := 9pnet.o
 obj-$(CONFIG_NET_9P_FD) += 9pnet_fd.o
+obj-$(CONFIG_NET_9P_VIRTIO) += 9pnet_virtio.o
 
 9pnet-objs := \
 	mod.o \
···
 
 9pnet_fd-objs := \
 	trans_fd.o \
+
+9pnet_virtio-objs := \
+	trans_virtio.o \

net/9p/trans_virtio.c

···
+/*
+ * 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
+ *  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 <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! */
+		out_vq->vq_ops->kick(out_vq);
+		/* Chill out until it's done with the buffer. */
+		while (!out_vq->vq_ops->get_buf(out_vq, &len))
+			cpu_relax();
+	}
+
+	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))
+		BUG();
+	chan->in_vq->vq_ops->kick(chan->in_vq);
+}
+
+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. */
+	BUG_ON(!in_vq);
+
+	/* 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)
+		add_inbuf(chan);
+
+	P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: virtio finished read (%d)\n",
+									count);
+
+	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;
+
+	down(&virtio_9p_lock);
+	chan->inuse = false;
+	up(&virtio_9p_lock);
+
+	kfree(trans);
+}
+
+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);
+	wake_up_interruptible(&chan->wq);
+
+	return true;
+}
+
+static int p9_virtio_probe(struct virtio_device *dev)
+{
+	int err;
+	struct virtio_chan *chan;
+	int index;
+
+	down(&virtio_9p_lock);
+	index = chan_index++;
+	chan = &channels[index];
+	up(&virtio_9p_lock);
+
+	if (chan_index > MAX_9P_CHAN) {
+		printk(KERN_ERR "9p: virtio: Maximum channels exceeded\n");
+		BUG();
+	}
+
+	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;
+	}
+
+	init_waitqueue_head(&chan->wq);
+
+	/* Register the input buffer the first time. */
+	add_inbuf(chan);
+	chan->inuse = false;
+	chan->initialized = true;
+
+	return 0;
+
+free_in_vq:
+	dev->config->del_vq(chan->in_vq);
+free:
+	kfree(chan->inbuf);
+fail:
+	down(&virtio_9p_lock);
+	chan_index--;
+	up(&virtio_9p_lock);
+	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;
+
+	down(&virtio_9p_lock);
+	while (index < MAX_9P_CHAN) {
+		if (chan->initialized && !chan->inuse) {
+			chan->inuse = true;
+			break;
+		} else {
+			index++;
+			chan = &channels[index];
+		}
+	}
+	up(&virtio_9p_lock);
+
+	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[] = {
+	{ VIRTIO_ID_9P, VIRTIO_DEV_ANY_ID },
+	{ 0 },
+};
+
+/* The standard "struct lguest_driver": */
+static struct virtio_driver p9_virtio_drv = {
+	.driver.name = 	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;
+
+	v9fs_register_trans(&p9_virtio_trans);
+	return register_virtio_driver(&p9_virtio_drv);
+}
+
+module_init(p9_virtio_init);
+
+MODULE_DEVICE_TABLE(virtio, id_table);
+MODULE_AUTHOR("Eric Van Hensbergen <[e-mail]>");
+MODULE_DESCRIPTION("Virtio 9p Transport");
+MODULE_LICENSE("GPL");