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>

1 files changed, 163 insertions, 1 deletions

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 64ef476d6557..ece1546fbb20 100644
--- a/drivers/char/virtio_console.c
+++ b/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) {