#!/bin/bash -eu
#
# (Virtualized) Linux init process.
#
# Perform necessary setup, change into the directory passed via the
# "working_dir=" kernel parameter and then run the command passed via the
# "command=" kernel parameter. When finished, signal the exit code of the
# command back to Qemu and exit.

exit_qemu() {
    RV=$?
    set +e

    # Convert return code into a 4-byte binary value and write it to the configured
    # port of the Qemu isa-debug-exit device to shut down the virtual machine with
    # that exit code.
    printf '00000000: %02x 00 00 00' ${RV} | xxd -r | dd of=/dev/port seek=${exit_port} bs=1 count=4 status=none

    # Fallthrough: reboot in case the above command didn't exit Qemu. When used in
    # conjunction with Qemu's --no-reboot parameter, this is safer (with respect to
    # stuck CI runs) than halting the VM.
    echo 1 > /proc/sys/kernel/sysrq
    echo b > /proc/sysrq-trigger
}

trap "exit_qemu" ERR EXIT

mount -t proc none /proc
echo 0 > /proc/sys/kernel/printk

ip link set up dev lo
ip route add default dev lo

cd ${working_dir}
${command}