Re: [Qemu-devel] [PATCH] virtio-serial: PCI device for simple host <-> guest communication

[Amit Shah <amit.shah@redhat.com>]

On (Tue) Jun 09 2009 [13:56:57], Anthony Liguori wrote:
> Richard W.M. Jones wrote:
>> On Tue, Jun 09, 2009 at 10:12:48PM +0530, Amit Shah wrote:
>> [...]
>>
>> Are you going to post the virtio driver for the Linux kernel later?
>>   
>
> Yeah, I'd like to see the Linux driver before drawing conclusions.

Pasting here a slightly older version of the patch. I'm actively working
on it; a few things might have changed but the basic idea remains the
same.

		Amit


diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 735bbe2..a023346 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -666,6 +666,12 @@ config VIRTIO_CONSOLE
 	help
 	  Virtio console for use with lguest and other hypervisors.
 
+config VIRTIO_SERIAL
+	tristate "Virtio serial"
+	select VIRTIO
+	select VIRTIO_RING
+	help
+	  Virtio serial device driver for simple guest and host communication
 
 config HVCS
 	tristate "IBM Hypervisor Virtual Console Server support"
diff --git a/drivers/char/Makefile b/drivers/char/Makefile
index 9caf5b5..e5bee21 100644
--- a/drivers/char/Makefile
+++ b/drivers/char/Makefile
@@ -53,6 +53,7 @@ obj-$(CONFIG_HVC_XEN)		+= hvc_xen.o
 obj-$(CONFIG_HVC_IUCV)		+= hvc_iucv.o
 obj-$(CONFIG_HVC_UDBG)		+= hvc_udbg.o
 obj-$(CONFIG_VIRTIO_CONSOLE)	+= virtio_console.o
+obj-$(CONFIG_VIRTIO_SERIAL)	+= virtio_serial.o
 obj-$(CONFIG_RAW_DRIVER)	+= raw.o
 obj-$(CONFIG_SGI_SNSC)		+= snsc.o snsc_event.o
 obj-$(CONFIG_MSPEC)		+= mspec.o
diff --git a/drivers/char/virtio_serial.c b/drivers/char/virtio_serial.c
new file mode 100644
index 0000000..0a5e90a
--- /dev/null
+++ b/drivers/char/virtio_serial.c
@@ -0,0 +1,531 @@
+/*
+ * VirtIO Serial driver
+ *
+ * This is paravirtualised serial guest<->host communication channel
+ * for relaying short messages and events in either direction.
+ *
+ * One PCI device can have multiple serial ports so that different
+ * applications can communicate without polluting the PCI device space
+ * in the guest.
+ *
+ * Copyright (C) 2009, Red Hat, Inc.
+ *
+ * Author(s): Amit Shah <amit.shah@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 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 the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <linux/cdev.h>
+#include <linux/err.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/poll.h>
+#include <linux/virtio.h>
+#include <linux/virtio_serial.h>
+
+struct virtio_serial_struct {
+	struct virtio_device *vdev;
+	struct virtqueue *ctrl_vq;
+	struct virtio_serial_port *ports;
+	u8 nr_devs; /* number of devices we can open */
+};
+
+struct virtio_serial_port {
+	struct virtio_serial_struct *virtserial;
+	struct virtqueue *in_vq, *out_vq;
+
+	/* The name given to this channel, if any. NOT zero-terminated */
+	char *name;
+
+	/* Each port associates with a separate char device */
+	dev_t dev;
+	struct cdev cdev;
+
+#define RECV_BUFFERS_PER_PORT 1
+	char *pages[RECV_BUFFERS_PER_PORT];
+	struct scatterlist *recv_sg;
+	unsigned int read_len;
+	char *read_buf;
+};
+
+static struct virtio_serial_struct virtserial;
+
+/* This should become per-port data */
+static DECLARE_COMPLETION(have_data);
+
+static int major = 60; /* from the experimental range */
+
+static struct virtio_serial_port *get_port_from_idx(u8 idx)
+{
+	if (idx > virtserial.nr_devs || idx < 0)
+		return NULL;
+
+	return &virtserial.ports[idx];
+}
+
+static int get_id_from_vq(struct virtqueue *vq)
+{
+	int i;
+
+	for (i = 0; i < virtserial.nr_devs; i++) {
+		if (virtserial.ports[i].in_vq == vq
+		    || virtserial.ports[i].out_vq == vq)
+			return i;
+	}
+	return -1;
+}
+
+static struct virtio_serial_port *get_port_from_vq(struct virtqueue *vq)
+{
+	int idx;
+
+	idx = get_id_from_vq(vq);
+	if (idx < 0)
+		return NULL;
+	return &virtserial.ports[idx];
+}
+
+static void receive_data(struct virtqueue *vq)
+{
+	struct virtio_serial_port *port;
+
+	port = get_port_from_vq(vq);
+
+	/* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
+	port->read_buf = vq->vq_ops->get_buf(vq, &port->read_len);
+	if (!port->read_buf)
+		return;
+
+	complete(&have_data);
+}
+
+static int receive_control_response(struct virtqueue *vq)
+{
+	int ret;
+	char *data;
+	uint8_t idx;
+	uint32_t key;
+	unsigned int len;
+	struct virtio_serial_port *port;
+
+	/* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
+	data = vq->vq_ops->get_buf(vq, &len);
+	if (!data)
+		return 0;
+
+	memcpy(&key, data, 4);
+	ret = -EINVAL;
+	switch (key) {
+	case VIRTIO_SERIAL_GET_PORT_NAME:
+		if (len < 6) {
+			/* Not enough data for this ioctl:
+			 * key (4 bytes) + idx (1 byte) + port name
+			 */
+			/* XXX: return something else? */
+			ret = -EIO;
+			break;
+		}
+		memcpy(&idx, data + 4, 1);
+
+		port = get_port_from_idx(idx);
+		if (!port) {
+			ret = -EINVAL;
+			break;
+		}
+		len -= 5;
+		if (len > VIRTIO_SERIAL_NAME_MAX_LEN)
+			len = VIRTIO_SERIAL_NAME_MAX_LEN;
+
+		/* If the port is getting renamed */
+		kfree(port->name);
+
+		port->name = kzalloc(len, GFP_KERNEL);
+		if (!port->name) {
+			ret = -ENOMEM;
+			break;
+		}
+		memcpy(port->name, data + 5, len);
+		ret = len;
+		break;
+	}
+	return ret;
+}
+
+static int request_control_info(u32 key, u8 idx)
+{
+	int ret;
+	char *vbuf, *obuf;
+	struct scatterlist sg[2];
+
+	vbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!vbuf)
+		return -ENOMEM;
+	obuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!obuf)
+		return -ENOMEM;
+
+	memcpy(vbuf, &key, 4);
+	memcpy(vbuf + 4, &idx, 1);
+
+	sg_init_table(sg, 2);
+	sg_set_buf(&sg[0], vbuf, PAGE_SIZE);
+	sg_set_buf(&sg[1], obuf, PAGE_SIZE);
+
+	if (virtserial.ctrl_vq->vq_ops->add_buf(virtserial.ctrl_vq, sg, 1, 1,
+						obuf) == 0) {
+		/* Tell Host to go! */
+		virtserial.ctrl_vq->vq_ops->kick(virtserial.ctrl_vq);
+
+		/* Chill out until it's done with the buffer. */
+		ret = receive_control_response(virtserial.ctrl_vq);
+		while (ret == 0) {
+			cpu_relax();
+			ret = receive_control_response(virtserial.ctrl_vq);
+		}
+	}
+	kfree(vbuf);
+	kfree(obuf);
+
+	return ret;
+}
+
+
+static ssize_t virtserial_read(struct file *filp, char __user *ubuf,
+			       size_t count, loff_t *offp)
+{
+	struct virtqueue *in_vq;
+	struct virtio_serial_port *port;
+	ssize_t ret;
+
+	port = filp->private_data;
+	in_vq = port->in_vq;
+
+	if (port->read_len == 0)
+		return 0;
+
+	if (count > port->read_len)
+		count = port->read_len;
+
+	ret = copy_to_user(ubuf, port->read_buf, count);
+
+	/* Return the number of bytes actually copied */
+	ret = count - ret;
+
+	port->read_buf += ret;
+	port->read_len -= ret;
+
+	if (!port->read_len) {
+		/* FIXME: Assuming only one page per port */
+		in_vq->vq_ops->add_buf(in_vq, port->recv_sg, 0, 1,
+				       port->pages[0]);
+		/* FIXME: it's a bug if add_buf didn't succeed */
+		in_vq->vq_ops->kick(in_vq);
+	}
+	return ret;
+}
+
+static ssize_t virtserial_write(struct file *filp, const char __user *ubuf,
+				size_t count, loff_t *offp)
+{
+	ssize_t ret;
+	char *vbuf;
+	unsigned int len, size;
+	struct virtqueue *out_vq;
+	struct scatterlist sg[1];
+	struct virtio_serial_port *port;
+
+	size = min(count, PAGE_SIZE);
+	vbuf = kmalloc(size, GFP_KERNEL);
+	if (!vbuf)
+		return -EFBIG;
+	ret = copy_from_user(vbuf, ubuf, size);
+
+	/* Return the number of bytes actually written */
+	ret = size - ret;
+
+	port = filp->private_data;
+	out_vq = port->out_vq;
+
+	sg_init_one(sg, vbuf, ret);
+
+	/* 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();
+	}
+	kfree(vbuf);
+
+	/* We're expected to return the amount of data we wrote */
+	return ret;
+}
+
+static long virtserial_ioctl(struct file *filp, unsigned int ioctl,
+			     unsigned long arg)
+{
+	int ret;
+	struct virtio_serial_port *port;
+	struct virtio_serial_port_name *port_name;
+
+	port = filp->private_data;
+
+	ret = -EINVAL;
+	switch (ioctl) {
+	case VIRTIO_SERIAL_IOCTL_GET_PORT_NAME:
+		port_name = (struct virtio_serial_port_name *)arg;
+
+		if (!port->name) {
+			ret = request_control_info(VIRTIO_SERIAL_GET_PORT_NAME,
+						   get_id_from_vq(port->in_vq));
+			if (ret < 0) {
+				/* Of IOCTL error return codes, only
+				 * this one comes close to what has
+				 * happened: either out of memory or
+				 * the virtio-serial backend didn't
+				 * have the associated name for the
+				 * port
+				 */
+				ret = -EFAULT;
+				break;
+			}
+		}
+		ret = copy_to_user(port_name->name,
+				   port->name, VIRTIO_SERIAL_NAME_MAX_LEN);
+		if (ret < 0) {
+			ret = -EINVAL;
+			break;
+		}
+		if (ret > 0) {
+			/* Do something? -- There is still data to be
+			 * copied to userspace
+			 */
+			ret = 0;
+		}
+		break;
+	}
+	return ret;
+}
+
+static int virtserial_release(struct inode *inode, struct file *filp)
+{
+	printk(KERN_NOTICE "%s\n", __func__);
+	return 0;
+}
+
+static int virtserial_open(struct inode *inode, struct file *filp)
+{
+	struct cdev *cdev = inode->i_cdev;
+	struct virtio_serial_port *port;
+
+	port = container_of(cdev, struct virtio_serial_port,
+			    cdev);
+
+	filp->private_data = port;
+	return 0;
+}
+
+static unsigned int virtserial_poll(struct file *filp, poll_table *wait)
+{
+	printk(KERN_NOTICE "%s\n", __func__);
+	return 0;
+}
+
+static const struct file_operations virtserial_fops = {
+	.owner = THIS_MODULE,
+	.open  = virtserial_open,
+	.read  = virtserial_read,
+	.write = virtserial_write,
+	.compat_ioctl = virtserial_ioctl,
+	.unlocked_ioctl = virtserial_ioctl,
+	.poll  = virtserial_poll,
+	.release = virtserial_release,
+};
+
+static int port_setup_recv_buffers(struct virtio_serial_port *port)
+{
+	int ret;
+	int i, nr_buffers = RECV_BUFFERS_PER_PORT;
+	struct virtqueue *vq = port->in_vq;
+
+	ret = -ENOMEM;
+	port->recv_sg = kzalloc(sizeof(struct scatterlist) * nr_buffers,
+				GFP_KERNEL);
+	if (!port->recv_sg)
+		return ret;
+
+	sg_init_table(port->recv_sg, nr_buffers);
+
+	for (i = 0; i < nr_buffers; i++) {
+		port->pages[i] = kzalloc(PAGE_SIZE, GFP_KERNEL);
+		if (!port->pages[i])
+			goto free_pages;
+
+		sg_set_buf(&port->recv_sg[i], port->pages[i], PAGE_SIZE);
+		ret = vq->vq_ops->add_buf(vq, port->recv_sg, 0, 1,
+					  port->pages[i]);
+		if (ret < 0)
+			goto free_pages;
+	}
+	vq->vq_ops->kick(vq);
+
+	return 0;
+
+free_pages:
+	for (; i >= 0; i--)
+		kfree(port->pages[i]);
+	kfree(port->recv_sg);
+
+	return ret;
+}
+
+static int virtserial_probe(struct virtio_device *vdev)
+{
+	int i, ret;
+	struct virtio_serial_port *port;
+	struct virtio_serial_config virtsercfg;
+
+	vdev->config->get(vdev, offsetof(struct virtio_serial_config, nr_ports),
+			  &virtsercfg.nr_ports, sizeof(virtsercfg.nr_ports));
+
+	virtserial.vdev = vdev;
+	virtserial.nr_devs = virtsercfg.nr_ports;
+	virtserial.ports = kzalloc(sizeof(struct virtio_serial_port)
+				   * virtserial.nr_devs, GFP_KERNEL);
+	if (!virtserial.ports) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	virtserial.ctrl_vq = vdev->config->find_vq(vdev, 0, NULL);
+	for (i = 0; i < virtserial.nr_devs; i++) {
+		port = &virtserial.ports[i];
+
+		port->in_vq = vdev->config->find_vq(vdev, (i * 2) + 1,
+						    receive_data);
+		if (IS_ERR(port->in_vq)) {
+			ret = PTR_ERR(port->in_vq);
+			goto fail;
+		}
+		port->out_vq = vdev->config->find_vq(vdev, (i * 2) + 2, NULL);
+		if (IS_ERR(port->out_vq)) {
+			ret = PTR_ERR(port->out_vq);
+			goto free_in_vq;
+		}
+		cdev_init(&port->cdev, &virtserial_fops);
+		port->dev = MKDEV(major, i);
+
+		/* XXX Do this for each port or do it once? */
+		ret = register_chrdev_region(port->dev, 1, "virtio-serial");
+		if (ret < 0) {
+			printk(KERN_ERR "%s: can't register chrdev region\n",
+			       __func__);
+			goto free_out_vq;
+		}
+		ret = cdev_add(&port->cdev, port->dev, 1);
+		if (ret < 0) {
+			printk(KERN_ERR "%s: can't add cdev\n", __func__);
+			goto free_cdev_region;
+		}
+
+		/* Finally set up some receive buffers */
+		ret = port_setup_recv_buffers(port);
+		if (ret < 0)
+			printk(KERN_NOTICE "%s: err for setup_recv_buff\n", __func__);
+	}
+	return 0;
+
+/* Rehaul this */
+free_cdev_region:
+	unregister_chrdev_region(port->dev, 1);
+free_out_vq:
+	vdev->config->del_vq(port->out_vq);
+free_in_vq:
+	vdev->config->del_vq(port->in_vq);
+fail:
+	return ret;
+}
+
+
+static void virtserial_remove(struct virtio_device *vdev)
+{
+	int i, j;
+
+	vdev->config->del_vq(virtserial.ctrl_vq);
+
+	for (i = 0; i < virtserial.nr_devs; i++) {
+		struct virtio_serial_port *port;
+
+		port = &virtserial.ports[i];
+		if (port->dev) {
+			/* FIXME: Take a long, hard look at this */
+			unregister_chrdev_region(port->dev, 1);
+			cdev_del(&port->cdev);
+
+			vdev->config->del_vq(port->out_vq);
+			vdev->config->del_vq(port->in_vq);
+
+			kfree(port->name);
+			kfree(port->recv_sg);
+			for (j = 0; j < RECV_BUFFERS_PER_PORT; j++)
+				kfree(port->pages[j]);
+		}
+	}
+}
+
+static void virtserial_apply_config(struct virtio_device *vdev)
+{
+	struct virtio_serial_config virtserconf;
+
+	vdev->config->get(vdev, offsetof(struct virtio_serial_config, nr_ports),
+			  &virtserconf.nr_ports, sizeof(virtserconf.nr_ports));
+	printk(KERN_NOTICE "%s: %u ports found\n", __func__, virtserconf.nr_ports);
+}
+
+
+static struct virtio_device_id id_table[] = {
+	{ VIRTIO_ID_SERIAL, VIRTIO_DEV_ANY_ID },
+	{ 0 },
+};
+
+static struct virtio_driver virtio_serial = {
+  //	.feature_table = features,
+  //	.feature_table_size = ARRAY_SIZE(features),
+	.driver.name =	KBUILD_MODNAME,
+	.driver.owner =	THIS_MODULE,
+	.id_table =	id_table,
+	.probe =	virtserial_probe,
+	.remove =	virtserial_remove,
+	.config_changed = virtserial_apply_config,
+};
+
+static int __init init(void)
+{
+	return register_virtio_driver(&virtio_serial);
+}
+
+static void __exit fini(void)
+{
+	unregister_virtio_driver(&virtio_serial);
+}
+module_init(init);
+module_exit(fini);
+
+MODULE_DEVICE_TABLE(virtio, id_table);
+MODULE_DESCRIPTION("Virtio serial driver");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/virtio_serial.h b/include/linux/virtio_serial.h
new file mode 100644
index 0000000..5528b11
--- /dev/null
+++ b/include/linux/virtio_serial.h
@@ -0,0 +1,34 @@
+#ifndef _LINUX_VIRTIO_SERIAL_H
+#define _LINUX_VIRTIO_SERIAL_H
+#include <linux/types.h>
+#include <linux/virtio_config.h>
+
+/* Guest kernel - Host interface */
+
+/* The ID for virtio serial */
+#define VIRTIO_ID_SERIAL	7
+
+struct virtio_serial_config {
+	__u8 nr_ports;
+	__u16 status;
+} __attribute__((packed));
+
+
+#define VIRTIO_SERIAL_NAME_MAX_LEN 30
+
+/* Some defines for the control channel key */
+#define VIRTIO_SERIAL_GET_PORT_NAME 1
+
+/* Guest kernel - Guest userspace interface */
+
+/* IOCTL-related */
+#define VIRTIO_SERIAL_IO 0xAF
+
+struct virtio_serial_port_name {
+	char name[VIRTIO_SERIAL_NAME_MAX_LEN];
+};
+
+#define VIRTIO_SERIAL_IOCTL_GET_PORT_NAME	_IOWR(VIRTIO_SERIAL_IO, 0x00, \
+			    struct virtio_serial_port_name)
+
+#endif /* _LINUX_VIRTIO_SERIAL_H */