virtio: console: Ensure only one process can have a port open at a time

Add a guest_connected field that ensures only one process
can have a port open at a time.

This also ensures we don't have a race when we later add support for
dropping buffers when closing the char dev and buffer caching is turned
off for the particular port.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index ece1546fbb20d379441d1608ed6c9d792954f522..5e3503a313120d715522d3ddbf06e1d8c37deadd 100644 (file)
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -175,6 +175,9 @@ struct port {
 
        /* Is the host device open */
        bool host_connected;
+
+       /* We should allow only one process to open a port */
+       bool guest_connected;
 };
 
 /* This is the very early arch-specified put chars function. */
@@ -528,6 +531,8 @@ static int port_fops_release(struct inode *inode, struct file *filp)
        /* Notify host of port being closed */
        send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 0);
 
+       port->guest_connected = false;
+
        return 0;
 }
 
@@ -546,6 +551,16 @@ static int port_fops_open(struct inode *inode, struct file *filp)
        if (is_console_port(port))
                return -ENXIO;
 
+       /* Allow only one process to open a particular port at a time */
+       spin_lock_irq(&port->inbuf_lock);
+       if (port->guest_connected) {
+               spin_unlock_irq(&port->inbuf_lock);
+               return -EMFILE;
+       }
+
+       port->guest_connected = true;
+       spin_unlock_irq(&port->inbuf_lock);
+
        /* Notify host of port being opened */
        send_control_msg(filp->private_data, VIRTIO_CONSOLE_PORT_OPEN, 1);
 
@@ -709,6 +724,7 @@ int init_port_console(struct port *port)
        pdrvdata.next_vtermno++;
        list_add_tail(&port->cons.list, &pdrvdata.consoles);
        spin_unlock_irq(&pdrvdata_lock);
+       port->guest_connected = true;
 
        /* Notify host of port being opened */
        send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 1);
@@ -856,7 +872,7 @@ static int add_port(struct ports_device *portdev, u32 id)
        port->inbuf = NULL;
        port->cons.hvc = NULL;
 
-       port->host_connected = false;
+       port->host_connected = port->guest_connected = false;
 
        port->in_vq = portdev->in_vqs[port->id];
        port->out_vq = portdev->out_vqs[port->id];