#!/bin/sh

# creates an overlay qemu image using another image as base
# also prepares a script to boot the image
# depends: qemu
#
# configure the br0 interface as global bridge:
# https://wiki.archlinux.org/index.php/Bridge_with_netctl
#
# /etc/qemu-ifup:
# sudo ifconfig $1 0.0.0.0 promisc up
# sudo brctl addif br0 $1
# sleep 2
#
# /etc/qemu-ifdown:
# sudo brctl delif br0 $1
#
# on the console set the vnc password:
# change vnc password xxx

USAGE() {
    echo "Usage: $(basename $0) base [n [mem]]" 1>&2
    exit 1
}

BASE=$(test -n "$1" && echo "$1")
N=$(test -n "$2" && echo "$2" || echo 1)
MEM=$(test -n "$3" && echo "$3" || echo 128M)

test -f "$BASE" ||
    { echo "File $BASE does not exist" 1>&2 && USAGE; }
test "$N" -ge 0 && test "$N" -le 99 ||
    { echo "Provide a number in 0--99 for n" 1>&2 && USAGE; }

NN=$(printf "%02d" $N)
IMAGE=vm${NN}.img
INITSH=vm${NN}.sh
MACADDR="52:54:ff:12:34:$NN"

test -f "$IMAGE" &&
    { echo "File $IMAGE exists" 1>&2 && USAGE; }
test -f "$INITSH" &&
    { echo "File $INITSH exists" 1>&2 && USAGE; }

MKBOOT() {
cat << EOF > $INITSH
#!/bin/sh

qemu-system-x86_64 \\
    -enable-kvm \\
    -m $MEM \\
    -hda $IMAGE \\
    -net nic,macaddr=$MACADDR -net tap \\
    -vnc :$N,password -monitor stdio
EOF
}

qemu-img create -f qcow2 -b $BASE $IMAGE
MKBOOT
chmod +x $INITSH