menu on scsi and dasd bootmaps tested successfully.
There is one thing that we might want to fix (can be an addon patch since this
is a non-customer
scenario (no libvirt)).
If you start QEMU manually without a bootindex, the -boot menu=on is ignored
if no drive has a bootindex.
For example:
-drive file=/dev/dasda,if=none,id=d1 -device
virtio-blk-ccw,drive=d1,bootindex=1 -boot menu=on
does work
-drive file=/dev/dasda -boot menu=on
does not
instead it prints:
qemu-system-s390x: boot menu is not supported for this device type.
and the boots up the default entry.
That should indeed be a separate patch, as it would move logic currently
in the BIOS up to QEMU (find the first defined virtio disk and select it
as boot disk).
In fact it's more complicated than that, because it would have to
properly account for -boot order=[acdn] and produce the respective IPLB.
While it makes sense, I wouldn't rush that in but rather change the
error message to indicate that -device bootindex is needed to activate
the menu, at least for the time being.
[...]