#! /usr/bin/env bash

# Start a QEMU/KVM virtual machine.
#
# --cpu <num>
#   CPU hardware threads to allocate to the VM, 1 by default.
#
# --ram <num>
#   RAM to allocate to the VM, 2G by default (can be specified with G,
#   M suffixes).
#
# --tap <tap>
#   Existing tap interface to use instead of creating a new one.
#
# --mac <addr>
#   MAC address to use for the machine.
#
# --monitor <path>
#   Monitor UNIX socket path, /tmp/machine-<tap>-mon.sock if unspecified.
#
# --console <path>
#   Console UNIX socket path, /tmp/machine-<tap>-con.sock if unspecified.
#
# --stdio
#   Connect both console and monitor to stdio (multiplexed).
#
# --stdio-monior
#   Connect only monitor to stdio.
#
usage="usage: $0 [<options>] <machine-img> [<extra-qemu-options>]"

owd="$(pwd)"
trap "{ cd '$owd'; exit 1; }" ERR
set -o errtrace # Trap in functions.

function info () { echo "$*" 1>&2; }
function error () { info "$*"; exit 1; }

qemu=(qemu-system-x86_64 -enable-kvm)

# The bridge is only used if we are cretaing the tap.
#
br=br0

cpu=1
ram=2G
tap=
mac="de:ad:be:ef:b8:da"
mon=
con=
stdio=
stdio_monitor=

while [ "$#" -gt 0 ]; do
  case "$1" in
    --cpu)
      shift
      cpu="$1"
      shift
      ;;
    --ram)
      shift
      ram="$1"
      shift
      ;;
    --tap)
      shift
      tap="$1"
      shift
      ;;
    --mac)
      shift
      mac="$1"
      shift
      ;;
    --monitor)
      shift
      mon="$1"
      shift
      ;;
    --console)
      shift
      con="$1"
      shift
      ;;
    --stdio)
      stdio=true
      stdio_monitor=
      shift
      ;;
    --stdio-monitor)
      stdio=
      stdio_monitor=true
      shift
      ;;
    *)
      break
      ;;
  esac
done

img="$1"
shift

if [ -z "$img" ]; then
  error "missing machine image"
fi

if [ ! -f "$img" ]; then
  error "machine image '$img' does not exist"
fi

# Open the reading file descriptor and lock the machine image. Fail if unable
# to lock.
#
# Note that the file descriptor is automatically closed on the script exit and
# the lock is released.
#
exec {lfd}<"$img"

if ! flock -n "$lfd"; then
  error "machine is already running"
fi

del_tap=
if [ -z "$tap" ]; then
  tap=tap9
  sudo ip tuntap delete "$tap" mode tap || true
  sudo ip tuntap add "$tap" mode tap user "$(whoami)"
  sudo ip link set "$tap" up
  #sleep 0.5s
  sudo ip link set "$tap" master "$br"
  del_tap=true
fi

if [ -z "$mon" ]; then
  mon="/tmp/machine-$tap-mon.sock"
fi

if [ -z "$con" ]; then
  con="/tmp/machine-$tap-con.sock"
fi

ops=(\
  -m "$ram" \
  -cpu host -smp "$cpu,sockets=1,cores=$cpu,threads=1" \
  \
  -netdev "tap,id=net0,ifname=$tap,script=no" \
  -device "virtio-net-pci,netdev=net0,mac=$mac" \
  \
  -drive  "if=none,id=disk0,file=$img,format=raw" \
  -device "virtio-blk-pci,scsi=off,drive=disk0" \
  \
  -nographic \
)

# Console/monitor options.
#
if [ "$stdio" ]; then
  # Multiplex the monitor and serial console onto stdio. In particular, this
  # makes sure Ctrl-c is passed to the guest (rather than termination the QEMU
  # process). To switch between monitor and console, Ctrl-a,c (to terminate
  # QEMU, type quit in the monitor).
  #
  ops+=(-serial mon:stdio)
else
  # Monitor.
  #
  if [ "$stdio_monitor" ]; then
    ops+=(-chardev stdio,id=mon)
  else
    ops+=(-chardev "socket,id=mon,path=$mon,server,nowait")
  fi

  ops+=(-mon chardev=mon,mode=readline)

  # Console.
  #
  ops+=(-chardev "socket,id=con,path=$con,server,nowait" \
        -serial chardev:con)
fi

"${qemu[@]}" "${ops[@]}" -boot c "$@"

if [ "$del_tap" ]; then
  sudo ip tuntap delete "$tap" mode tap
fi