[PATCH 1/2][PVFB][TOOLS] PVFB frontend can send bogus screen updates

[Markus Armbruster <armbru@redhat.com>]

The PVFB frontend can get confused and send a screen update to the
backend when the screen is actually clean.  Such an update asks for
the impossible rectangle (x1, x2, y1, y2) = (INT_MAX, 0, INT_MAX, 0).
Fix by setting the dirty flag in the obvious place: when the dirty
rectangle is grown.

Signed-off-by: Markus Armbruster <armbru@redhat.com>

diff -r cf8b6cafa2f0 drivers/xen/fbfront/xenfb.c
--- a/drivers/xen/fbfront/xenfb.c	Thu Nov 08 18:26:08 2007 +0000
+++ b/drivers/xen/fbfront/xenfb.c	Tue Nov 13 17:32:48 2007 +0100
@@ -201,6 +201,11 @@ static void xenfb_update_screen(struct x
 
 	mutex_unlock(&info->mm_lock);
 
+	if (x2 < x1 || y2 < y1) {
+		printk("xenfb_update_screen bogus rect %d %d %d %d\n",
+		       x1, x2, y1, y2);
+		WARN_ON(1);
+	}
 	xenfb_do_update(info, x1, y1, x2 - x1, y2 - y1);
 }
 
@@ -252,7 +257,6 @@ static void xenfb_timer(unsigned long da
 static void xenfb_timer(unsigned long data)
 {
 	struct xenfb_info *info = (struct xenfb_info *)data;
-	info->dirty = 1;
 	wake_up(&info->wq);
 }
 
@@ -272,6 +276,7 @@ static void __xenfb_refresh(struct xenfb
 		info->x1 = x1;
 	if (info->x2 < x2)
 		info->x2 = x2;
+	info->dirty = 1;
 
 	if (timer_pending(&info->refresh))
 		return;