virtio_console: support console resizing

this patch uses the new hvc callback hvc_resize to set the window size
which allows to change the tty size of hvc_console via a hvc_resize
function.

I have added a new feature bit VIRTIO_CONSOLE_F_SIZE. The driver will
change the window size on tty open and via the config_changed callback
of the transport. Currently lguest and kvm_s390 have not implemented this
callback, but the callback can be implemented at a later point in time.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/char/hvc_console.c

@@ -695,6 +695,7 @@ void hvc_resize(struct hvc_struct *hp, struct winsize ws)
 	hp->ws = ws;
 	schedule_work(&hp->tty_resize);
 }
+EXPORT_SYMBOL_GPL(hvc_resize);
 
 /*
  * This kthread is either polling or interrupt driven.  This is determined by

drivers/char/virtio_console.c

@@ -137,13 +137,34 @@ int __init virtio_cons_early_init(int (*put_chars)(u32, const char *, int))
 	return hvc_instantiate(0, 0, &virtio_cons);
 }
 
+/*
+ * virtio console configuration. This supports:
+ * - console resize
+ */
+static void virtcons_apply_config(struct virtio_device *dev)
+{
+	struct winsize ws;
+
+	if (virtio_has_feature(dev, VIRTIO_CONSOLE_F_SIZE)) {
+		dev->config->get(dev,
+				 offsetof(struct virtio_console_config, cols),
+				 &ws.ws_col, sizeof(u16));
+		dev->config->get(dev,
+				 offsetof(struct virtio_console_config, rows),
+				 &ws.ws_row, sizeof(u16));
+		hvc_resize(hvc, ws);
+	}
+}
+
 /*
  * we support only one console, the hvc struct is a global var
- * There is no need to do anything
+ * We set the configuration at this point, since we now have a tty
  */
 static int notifier_add_vio(struct hvc_struct *hp, int data)
 {
 	hp->irq_requested = 1;
+	virtcons_apply_config(vdev);
+
 	return 0;
 }
 
@@ -234,11 +255,18 @@ static struct virtio_device_id id_table[] = {
 	{ 0 },
 };
 
+static unsigned int features[] = {
+	VIRTIO_CONSOLE_F_SIZE,
+};
+
 static struct virtio_driver virtio_console = {
+	.feature_table = features,
+	.feature_table_size = ARRAY_SIZE(features),
 	.driver.name =	KBUILD_MODNAME,
 	.driver.owner =	THIS_MODULE,
 	.id_table =	id_table,
 	.probe =	virtcons_probe,
+	.config_changed = virtcons_apply_config,
 };
 
 static int __init init(void)

include/linux/virtio_console.h

@@ -7,6 +7,17 @@
 /* The ID for virtio console */
 #define VIRTIO_ID_CONSOLE	3
 
+/* Feature bits */
+#define VIRTIO_CONSOLE_F_SIZE	0	/* Does host provide console size? */
+
+struct virtio_console_config {
+	/* colums of the screens */
+	__u16 cols;
+	/* rows of the screens */
+	__u16 rows;
+} __attribute__((packed));
+
+
 #ifdef __KERNEL__
 int __init virtio_cons_early_init(int (*put_chars)(u32, const char *, int));
 #endif /* __KERNEL__ */