Re: [Xen-devel] [PATCH,RFC] linux Potential clean up of console transition

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

While I dislike the overwriting too, I don't think this is the solution. I never
found time to locate where the orig_{x,y} members of struct screen_info
are (supposed to be) used, but I think that this would be a better way to
solve the problem. This is in particular because your approach pushes off
Xen messages that someone else might find useful in case of an early crash.

Jan

>>> Bill Burns <bburns@xxxxxxxxxx> 04.12.08 23:22 >>>

When using a video monitor for the console there is
an issue with the transition between Hypervisor
output and dom0 output (this is at least true in
3.1.2/2.6.18 vintage systems).

What happens is that the screen is full of the (XEN)
messages and then the dom0 kernel starts off at the top
of the screen and over prints until the screen starts
to scroll. It's not all that noticeable since the
output tends to be blow right past the issue.

But when the "quiet" boot arg is used for the dom0
kernel it can be user space output that collides and
that can pose a problem. Like when a prompt for
an encrypted file system cannot be read due to the
mess on the screen.

Below is a crude little loop that could be used to
avoid the issue by outputting newlines to push
the beginning of dom0's output to the bottom of
the screen. Other suggestions are welcome. Note
is uses KERN_ERR since "quiet" blocks output
at the default printk level.

 Bill


--- drivers/xen/console/console.c.orig  2008-10-21 15:26:25.000000000 -0400
+++ drivers/xen/console/console.c       2008-12-04 17:23:12.000000000 -0500
@@ -192,6 +192,8 @@ static struct console kcons_info = {

 static int __init xen_console_init(void)
 {
+        int i;
+
        if (!is_running_on_xen())
                goto out;

@@ -230,6 +232,10 @@ static int __init xen_console_init(void)

        register_console(&kcons_info);

+        if (screen_info.orig_video_mode == 3) {
+                for (i = 0; i < screen_info.orig_video_lines; i++)
+                        printk(KERN_ERR "\n");
+        }
  out:
        return 0;
 }


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