ref: e6fa5a21f97c13caea47c0a434d5672ab45da2d6
dir: /sys/src/boot/qemu/boot.txt/
mw.b 0x40010000 0x0 0x10000
load ${devtype} ${devnum}:${bootpart} 0x40010000 ${prefix}plan9.ini
load ${devtype} ${devnum}:${bootpart} 0x40100000 ${prefix}9qemu.u && bootm 0x40100000