examples: aarch64-virt-base: fix display support

Fix display support. Switch to disabled by default if no display backend
is set. $GUEST_DISPLAY configures QEMU -display <backend> if configured
(variable not empty). Empty variable will use -nographic.

This also uses -nodefaults regardless of the setting of the display to
replicate the same setup in x86_64 example.
From documentation [1]:
  Don’t create default devices. Normally, QEMU sets the default devices
  like serial port, parallel port, virtual console, monitor device, VGA
  adapter, floppy and CD-ROM drive and others. The -nodefaults option will
  disable all those default devices.

[1] Manual for -nodefaults.
https://www.qemu.org/docs/master/system/qemu-manpage.html
https://www.qemu.org/docs/master/system/invocation.html

This has been tested only on macOS with cocoa as $GUEST_DISPLAY.

qemu-system-aarch -display help
Available display backend types:
none
curses
cocoa
dbus

Display backend types in Debian arm64 machines are:
qemu-system-aarch -display help
Available display backend types:
none
gtk
sdl
egl-headless
curses
spice-app
dbus

Signed-off-by: Daniel Gomez <[email protected]>

examples/vm/aarch64-virt-base.conf

@@ -4,7 +4,7 @@
 #
 # Configuration variables
 #
-#   GUEST_DISPLAY            Set to '1' to enable graphical output
+#   GUEST_DISPLAY            Display option (QEMU -display parameter).
 #   GUEST_VIOMMU             Set to '1' to add a virtual IOMMU to the machine
 #   GUEST_CPU                CPU model (QEMU -cpu paramater, default: 'host')
 #   GUEST_SMP                SMP configuration (QEMU -smp parameter, default: '4')
@@ -23,7 +23,7 @@ fi
 QEMU_SYSTEM_BINARY=${QEMU_SYSTEM_AARCH64}
 : "${GUEST_BOOT_BASE:="img/debian-11-genericcloud-arm64.qcow2"}"
 
-: "${GUEST_DISPLAY:="1"}"
+: "${GUEST_DISPLAY:=""}"
 : "${GUEST_CPU:="host"}"
 : "${GUEST_MEMORY:="2G"}"
 : "${GUEST_ACCEL:="kvm"}"
@@ -35,11 +35,17 @@ QEMU_SYSTEM_BINARY=${QEMU_SYSTEM_AARCH64}
 : "${GUEST_KERNEL_CONSOLE:="ttyAMA0"}"
 
 _setup_aarch64_virt_base() {
-  QEMU_PARAMS+=("-nographic")
+  QEMU_PARAMS+=("-nodefaults")
 
-  if [[ $GUEST_DISPLAY -eq 0 ]]; then
-    #QEMU_PARAMS+=("-display" "none")
+  if [[ -z $GUEST_DISPLAY ]]; then
     QEMU_PARAMS+=("-nographic")
+  else
+    QEMU_PARAMS+=("-device" "virtio-gpu-pci")
+    QEMU_PARAMS+=("-display" "$GUEST_DISPLAY")
+    QEMU_PARAMS+=("-device" "virtio-keyboard-pci")
+    QEMU_PARAMS+=("-device" "virtio-mouse-pci")
+    QEMU_PARAMS+=("-device" "qemu-xhci")
+    QEMU_PARAMS+=("-device" "usb-tablet")
   fi
 
   QEMU_PARAMS+=("-machine" "virt,accel=$GUEST_ACCEL,kernel-irqchip=split")