virtio: console: Add ability to hot-unplug ports

Remove port data; deregister from the hvc core if it's a console port.

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

2 files changed, 64 insertions, 2 deletions

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 7c53f58c87ba..9f20fda9c56f 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -783,6 +783,36 @@ static struct attribute_group port_attribute_group = {
         .attrs = port_sysfs_entries,
 };
 
+/* Remove all port-specific data. */
+static int remove_port(struct port *port)
+{
+        spin_lock_irq(&port->portdev->ports_lock);
+        list_del(&port->list);
+        spin_unlock_irq(&port->portdev->ports_lock);
+
+        if (is_console_port(port)) {
+                spin_lock_irq(&pdrvdata_lock);
+                list_del(&port->cons.list);
+                spin_unlock_irq(&pdrvdata_lock);
+                hvc_remove(port->cons.hvc);
+        }
+        if (port->guest_connected)
+                send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 0);
+
+        while (port->in_vq->vq_ops->detach_unused_buf(port->in_vq))
+                ;
+
+        sysfs_remove_group(&port->dev->kobj, &port_attribute_group);
+        device_destroy(pdrvdata.class, port->dev->devt);
+        cdev_del(&port->cdev);
+
+        discard_port_data(port);
+        kfree(port->name);
+
+        kfree(port);
+        return 0;
+}
+
 /* Any private messages that the Host and Guest want to share */
 static void handle_control_message(struct ports_device *portdev,
                                    struct port_buffer *buf)
@@ -854,6 +884,32 @@ static void handle_control_message(struct ports_device *portdev,
                                 err);
 
                 break;
+        case VIRTIO_CONSOLE_PORT_REMOVE:
+                /*
+                 * Hot unplug the port.  We don't decrement nr_ports
+                 * since we don't want to deal with extra complexities
+                 * of using the lowest-available port id: We can just
+                 * pick up the nr_ports number as the id and not have
+                 * userspace send it to us.  This helps us in two
+                 * ways:
+                 *
+                 * - We don't need to have a 'port_id' field in the
+                 *   config space when a port is hot-added.  This is a
+                 *   good thing as we might queue up multiple hotplug
+                 *   requests issued in our workqueue.
+                 *
+                 * - Another way to deal with this would have been to
+                 *   use a bitmap of the active ports and select the
+                 *   lowest non-active port from that map.  That
+                 *   bloats the already tight config space and we
+                 *   would end up artificially limiting the
+                 *   max. number of ports to sizeof(bitmap).  Right
+                 *   now we can support 2^32 ports (as the port id is
+                 *   stored in a u32 type).
+                 *
+                 */
+                remove_port(port);
+                break;
         }
 }
 
@@ -1078,12 +1134,17 @@ static void config_work_handler(struct work_struct *work)
                 /*
                  * Port 0 got hot-added.  Since we already did all the
                  * other initialisation for it, just tell the Host
-                 * that the port is ready.
+                 * that the port is ready if we find the port.  In
+                 * case the port was hot-removed earlier, we call
+                 * add_port to add the port.
                  */
                 struct port *port;
 
                 port = find_port_by_id(portdev, 0);
-                send_control_msg(port, VIRTIO_CONSOLE_PORT_READY, 1);
+                if (!port)
+                        add_port(portdev, 0);
+                else
+                        send_control_msg(port, VIRTIO_CONSOLE_PORT_READY, 1);
                 return;
         }
         if (virtconconf.nr_ports > portdev->config.max_nr_ports) {
diff --git a/include/linux/virtio_console.h b/include/linux/virtio_console.h
index 1ebf007812a8..ae4f039515b4 100644
--- a/include/linux/virtio_console.h
+++ b/include/linux/virtio_console.h
@@ -41,6 +41,7 @@ struct virtio_console_control {
 #define VIRTIO_CONSOLE_RESIZE           2
 #define VIRTIO_CONSOLE_PORT_OPEN        3
 #define VIRTIO_CONSOLE_PORT_NAME        4
+#define VIRTIO_CONSOLE_PORT_REMOVE      5
 
 #ifdef __KERNEL__
 int __init virtio_cons_early_init(int (*put_chars)(u32, const char *, int));