From: Bill Burns <bburns@redhat.com>
Date: Thu, 4 Dec 2008 06:26:05 -0500
Subject: [xen] console: make LUKS passphrase readable
Message-id: 4937BE4D.3020309@redhat.com
O-Subject: Re: [RHEL5.3 PATCH 1/1 v3] Make LUKS passphrase readable on Xen
Bugzilla: 466240
RH-Acked-by: Markus Armbruster <armbru@redhat.com>
RH-Acked-by: Don Dutile <ddutile@redhat.com>

Same patch actually, just added a patch description as requested
during review. So please use this one with the description.

 Bill

#
Fix readability of user mode prompts by not overprinting
them on top of the Xen hypervisor startup messages.

After the Xen hypervisor has left it's output on the screen and dom0
starts up, printing from the dom0 begins again at the top of
the video screen. There is no "clear" operation first, so the
output is all mixed in with the previous HV output until there
are enough lines output to cause scrolling. Once the new output
reaches the bottom of the screen, scrolling starts and things
are clean from then on. This happens with or without the kernel
quiet boot arg.

So without the quiet arg the initial N lines look ugly but
you almost never see them as the kernel output comes
so fast that you never really see the Xen HV messages.

With quiet, there are only a couple kernel printk's of
severity level high enough to get printed. So the screen
sits there with the Xen messages much longer. When
the user space output starts it has the same issue
with the first N lines intermixed with the Xen HV output.
Trouble is, that if you are using encryption there is
a prompt there that is hard to see and reply too.

diff --git a/drivers/xen/console/console.c b/drivers/xen/console/console.c
index d16096d..0e7d088 100644
--- a/drivers/xen/console/console.c
+++ b/drivers/xen/console/console.c
@@ -189,6 +189,8 @@ static struct console kcons_info = {
 
 static int __init xen_console_init(void)
 {
+        int i;
+
 	if (!is_running_on_xen())
 		goto out;
 
@@ -235,6 +237,17 @@ static int __init xen_console_init(void)
 
 	register_console(&kcons_info);
 
+        /*
+         * If loglevel is low assume "quiet" arg and clear
+         * the screen to remove Hypervisor messages
+         * so that user startup prompts/messages
+         * can be seen clearly. Fixes BZ 466240.
+         */
+        if ((console_loglevel <  default_console_loglevel) &&
+            (screen_info.orig_video_mode == 3)) {
+                for (i = 0; i < screen_info.orig_video_lines; i++)
+                        printk(KERN_ERR "\n");
+        }
  out:
 	return 0;
 }