virtio: console: Add file operations to ports for open/read/write/poll

Allow guest userspace applications to open, read from, write to, poll
the ports via the char dev interface.

When a port gets opened, a notification is sent to the host via a
control message indicating a connection has been established. Similarly,
on closing of the port, a notification is sent indicating disconnection.
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/char/virtio_console.c

@@ -19,11 +19,15 @@
 #include <linux/cdev.h>
 #include <linux/device.h>
 #include <linux/err.h>
+#include <linux/fs.h>
 #include <linux/init.h>
 #include <linux/list.h>
+#include <linux/poll.h>
+#include <linux/sched.h>
 #include <linux/spinlock.h>
 #include <linux/virtio.h>
 #include <linux/virtio_console.h>
+#include <linux/wait.h>
 #include <linux/workqueue.h>
 #include "hvc_console.h"
 
@@ -163,8 +167,14 @@ struct port {
 	struct cdev cdev;
 	struct device *dev;
 
+	/* A waitqueue for poll() or blocking read operations */
+	wait_queue_head_t waitqueue;
+
 	/* The 'id' to identify the port with the Host */
 	u32 id;
+
+	/* Is the host device open */
+	bool host_connected;
 };
 
 /* This is the very early arch-specified put chars function. */
@@ -417,6 +427,146 @@ static ssize_t fill_readbuf(struct port *port, char *out_buf, size_t out_count,
 	return out_count;
 }
 
+/* The condition that must be true for polling to end */
+static bool wait_is_over(struct port *port)
+{
+	return port_has_data(port) || !port->host_connected;
+}
+
+static ssize_t port_fops_read(struct file *filp, char __user *ubuf,
+			      size_t count, loff_t *offp)
+{
+	struct port *port;
+	ssize_t ret;
+
+	port = filp->private_data;
+
+	if (!port_has_data(port)) {
+		/*
+		 * If nothing's connected on the host just return 0 in
+		 * case of list_empty; this tells the userspace app
+		 * that there's no connection
+		 */
+		if (!port->host_connected)
+			return 0;
+		if (filp->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+
+		ret = wait_event_interruptible(port->waitqueue,
+					       wait_is_over(port));
+		if (ret < 0)
+			return ret;
+	}
+	/*
+	 * We could've received a disconnection message while we were
+	 * waiting for more data.
+	 *
+	 * This check is not clubbed in the if() statement above as we
+	 * might receive some data as well as the host could get
+	 * disconnected after we got woken up from our wait.  So we
+	 * really want to give off whatever data we have and only then
+	 * check for host_connected.
+	 */
+	if (!port_has_data(port) && !port->host_connected)
+		return 0;
+
+	return fill_readbuf(port, ubuf, count, true);
+}
+
+static ssize_t port_fops_write(struct file *filp, const char __user *ubuf,
+			       size_t count, loff_t *offp)
+{
+	struct port *port;
+	char *buf;
+	ssize_t ret;
+
+	port = filp->private_data;
+
+	count = min((size_t)(32 * 1024), count);
+
+	buf = kmalloc(count, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	ret = copy_from_user(buf, ubuf, count);
+	if (ret) {
+		ret = -EFAULT;
+		goto free_buf;
+	}
+
+	ret = send_buf(port, buf, count);
+free_buf:
+	kfree(buf);
+	return ret;
+}
+
+static unsigned int port_fops_poll(struct file *filp, poll_table *wait)
+{
+	struct port *port;
+	unsigned int ret;
+
+	port = filp->private_data;
+	poll_wait(filp, &port->waitqueue, wait);
+
+	ret = 0;
+	if (port->inbuf)
+		ret |= POLLIN | POLLRDNORM;
+	if (port->host_connected)
+		ret |= POLLOUT;
+	if (!port->host_connected)
+		ret |= POLLHUP;
+
+	return ret;
+}
+
+static int port_fops_release(struct inode *inode, struct file *filp)
+{
+	struct port *port;
+
+	port = filp->private_data;
+
+	/* Notify host of port being closed */
+	send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 0);
+
+	return 0;
+}
+
+static int port_fops_open(struct inode *inode, struct file *filp)
+{
+	struct cdev *cdev = inode->i_cdev;
+	struct port *port;
+
+	port = container_of(cdev, struct port, cdev);
+	filp->private_data = port;
+
+	/*
+	 * Don't allow opening of console port devices -- that's done
+	 * via /dev/hvc
+	 */
+	if (is_console_port(port))
+		return -ENXIO;
+
+	/* Notify host of port being opened */
+	send_control_msg(filp->private_data, VIRTIO_CONSOLE_PORT_OPEN, 1);
+
+	return 0;
+}
+
+/*
+ * The file operations that we support: programs in the guest can open
+ * a console device, read from it, write to it, poll for data and
+ * close it.  The devices are at
+ *   /dev/vport<device number>p<port number>
+ */
+static const struct file_operations port_fops = {
+	.owner = THIS_MODULE,
+	.open  = port_fops_open,
+	.read  = port_fops_read,
+	.write = port_fops_write,
+	.poll  = port_fops_poll,
+	.release = port_fops_release,
+};
+
 /*
  * The put_chars() callback is pretty straightforward.
  *
@@ -560,6 +710,9 @@ int init_port_console(struct port *port)
 	list_add_tail(&port->cons.list, &pdrvdata.consoles);
 	spin_unlock_irq(&pdrvdata_lock);
 
+	/* Notify host of port being opened */
+	send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 1);
+
 	return 0;
 }
 
@@ -599,6 +752,10 @@ static void handle_control_message(struct ports_device *portdev,
 		port->cons.hvc->irq_requested = 1;
 		resize_console(port);
 		break;
+	case VIRTIO_CONSOLE_PORT_OPEN:
+		port->host_connected = cpkt->value;
+		wake_up_interruptible(&port->waitqueue);
+		break;
 	}
 }
 
@@ -645,6 +802,8 @@ static void in_intr(struct virtqueue *vq)
 
 	spin_unlock_irqrestore(&port->inbuf_lock, flags);
 
+	wake_up_interruptible(&port->waitqueue);
+
 	if (is_console_port(port) && hvc_poll(port->cons.hvc))
 		hvc_kick();
 }
@@ -697,10 +856,12 @@ static int add_port(struct ports_device *portdev, u32 id)
 	port->inbuf = NULL;
 	port->cons.hvc = NULL;
 
+	port->host_connected = false;
+
 	port->in_vq = portdev->in_vqs[port->id];
 	port->out_vq = portdev->out_vqs[port->id];
 
-	cdev_init(&port->cdev, NULL);
+	cdev_init(&port->cdev, &port_fops);
 
 	devt = MKDEV(portdev->chr_major, id);
 	err = cdev_add(&port->cdev, devt, 1);
@@ -721,6 +882,7 @@ static int add_port(struct ports_device *portdev, u32 id)
 	}
 
 	spin_lock_init(&port->inbuf_lock);
+	init_waitqueue_head(&port->waitqueue);
 
 	inbuf = alloc_buf(PAGE_SIZE);
 	if (!inbuf) {

include/linux/virtio_console.h

@@ -39,6 +39,7 @@ struct virtio_console_control {
 #define VIRTIO_CONSOLE_PORT_READY	0
 #define VIRTIO_CONSOLE_CONSOLE_PORT	1
 #define VIRTIO_CONSOLE_RESIZE		2
+#define VIRTIO_CONSOLE_PORT_OPEN	3
 
 #ifdef __KERNEL__
 int __init virtio_cons_early_init(int (*put_chars)(u32, const char *, int));