From f76317d9dc35dbc576820ba6c2a6a8e41f5338b5 Mon Sep 17 00:00:00 2001
From: Michael Chang <[email protected]>
Date: Thu, 19 May 2022 13:08:12 +0800
Subject: [PATCH] Fix infinite boot loop on headless system in qemu

After finishing headless virtual machine installation via serial
console, the reboot fails in grub with infinte boot loop and also
keyboard input for serial console is unresponsive.

The cause of infinte loop boils down to legacy vga driver in grub
crashes when '-dispaly none' is used as qemu's display type described in
the manual as:

"Do not display video output. The guest will still see an emulated
graphics card, but its output will not be displayed tothe QEMU  user.
This option differs from the -nographic option in that it only affects
what is done with video output; -nographic also changes the destination
of the serial and parallel port data."

Given there's no sensible way found to skip the emulated device from the
legacy vga module, we ended up removing it from all_video dependency so
it wouldn't be loaded by default. In any case, the vbe module remain
loaded and should fulfill the requirement of most hardwares even twenty
years old or more.

The unresponsive serial input is also fixed by ensuring that console
input is loaded via appended so that they won't fail altogether with
errors by other console device if specifying on the same list.

Signed-off-by: Michael Chang <[email protected]>
---
 grub-core/genmoddep.awk  |  3 +++
 util/grub.d/00_header.in | 10 +++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

--- a/grub-core/genmoddep.awk
+++ b/grub-core/genmoddep.awk
@@ -98,6 +98,9 @@
   }
   modlist = ""
   while (getline <"video.lst") {
+      if ($1 == "vga") {
+          continue;
+      }
       modlist = modlist " " $1;
   }
   printf "all_video:%s\n", modlist;
--- a/util/grub.d/00_header.in
+++ b/util/grub.d/00_header.in
@@ -287,7 +287,15 @@
   ;;
   x*)
     cat << EOF
-terminal_output ${GRUB_TERMINAL_OUTPUT}
+
+for i in ${GRUB_TERMINAL_OUTPUT}; do
+  if [ x\${use_append} = xtrue ]; then
+     terminal_output --append \$i
+  elif terminal_output \$i; then
+     use_append=true;
+  fi
+done
+
 EOF
   ;;
 esac